U.S. Department of Transportation Publication No. FHWA NHI-05-039 

Federal Highway Administration December 2005 

 

NHI Course No. 132078_______________________________ 

Micropile Design and Construction 

 

Reference Manual 

ROAD SURFACE

FINISHED GRADE

SLIDE PLANE

CONCRETE CAP

CASE 1

NON RETICULATED

MICROPILE STRUCTURE

NEW BRIDGE STRUCTURE

BRIDGE ABUTMENT

NEW MICROPILE

FOUNDATION SUPPORT

(TYP)

SURCHARGE

FINAL GRADE

CONCRETE CAP

CASE 2 RETICULATED

MICROPILE WALL

ORIGINAL

GRADE

SECTION A – A

EXISTING

FOOTING & PILES

EXISTING DRIVEN

PIPE PILES (TYP)

NEW FOOTING

EXTENSION

EXISTING BRIDGE

PIER W/PILE

SUPPORTED

FOOTING

NEW MICROPILES

A

NEW MICROPILES

FOUNDATION SUPPORT

SLOPE STABILIZATION

SEISMIC RETROFIT OF BRIDGES

EARTH RETENTION

WALL FACING

 National Highway Institute
NOTICE 

The contents of this report reflect the views of the authors, who are responsible for 

the facts and the accuracy of the data presented herein. The contents do not 

necessarily reflect policy of the Department of Transportation. This report does not 

constitute a standard, specification, or regulation. The United States Government 

does not endorse products or manufacturers. Trade or manufacturer's names 

appear herein only because they are considered essential to the objective of this 

document. 
Technical Report Documentation Page

1. REPORT NO. 

FHWA-NHI-05-039

2. GOVERNMENT 

ACCESSION NO. 

3. RECIPIENT'S CATALOG NO. 

5. REPORT DATE 

 December 2005

4. TITLE AND SUBTITLE 

Micropile Design and Construction 

(Reference Manual for NHI Course 132078) 6. PERFORMING ORGANIZATION CODE 

7. AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NO. 

Paul J. Sabatinia

 P.E., Ph.D.; Burak Tanyua

Ph.D.; Tom Armourb P.E.; Paul Groneckb

P.E.; and James Keeleyb

 P.E.

a

 GeoSyntec Consultants, Chicago, IL 

b

 DBM Contractors Inc. Federal Way, WA

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. WORK UNIT NO. 

Ryan R. Berg & Associates, Inc. 

2190 Leyland Alcove 

Woodbury, MN 55125

IN COOPERATION AND ASSOCIATION WITH: 

ADSC – The International Association of 

Foundation Drilling 

14180 Dallas Parkway, Suite 510 

Dallas, TX 75254

11. CONTRACT OR GRANT NO. 

DTFH61-03-T-63043

12. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF REPORT & PERIOD COVERED 

National Highway Institute 

Federal Highway Administration 

U.S. Department of Transportation 

Washington, D.C.

14. SPONSORING AGENCY CODE 

15. SUPPLEMENTARY NOTES 

FHWA COTR – Larry Jones 

FHWA Technical Consultants: Jerry A. DiMaggio, P.E. and Barry Siel, P.E. 

This manual is an updated and revised version of FHWA SA-97-070 prepared by DBM Contractors 

Inc. and authored by T. Armour, P. Groneck, J. Keeley and S. Sharma; June 2000.

16. ABSTRACT The use of micropiles has grown significantly since their conception in the 

1950s, and in particular since the mid-1980s. Micropiles have been used mainly as foundation 

support elements to resist static and seismic loads, and to a lesser extent, as in-situ 

reinforcements to provide stabilization of slopes and excavations. Many of these applications 

are for transportation structures. This manual is intended to be a “practitioner-oriented” 

document containing sufficient information on the geotechnical and structural design of 

micropiles for foundation support and for slope stabilization. Information is also provided on 

inspection and load testing procedures, cost data, and contracting methods to facilitate the safe 

and cost-effective use of micropiles on transportation projects. Two detailed design examples 

and a generic commentary guideline specification for micropiles is included in the manual.

17. KEY WORDS Micropiles, structural 

foundation, load testing, slope stabilization 

18. DISTRIBUTION STATEMENT 

No restrictions.

19. SECURITY CLASSIF. 

Unclassified

20. SECURITY CLASSIF. 

Unclassified

21. NO. OF PAGES 

436 

22. PRICE
SI CONVERSION FACTORS

APPROXIMATE CONVERSIONS FROM SI UNITS 

Symbol When You 

Know Multiply By To Find Symbol

 LENGTH 

mm 

m 

m 

km

millimeters 

meters 

meters 

kilometers

0.039 

3.28 

1.09 

0.621

inches 

feet 

yards 

miles

in 

ft 

yd 

mi

 AREA 

mm2

m2 

m2

ha 

km2

square millimeters 

square meters 

square meters 

hectares 

square kilometers

0.0016 

10.764 

1.195 

2.47 

0.386

square inches 

square feet 

square yards 

acres 

square miles

in2

ft2

yd2

ac 

mi2

 VOLUME 

ml 

l 

m3

m3

millimeters 

liters 

cubic meters 

cubic meters

0.034 

0.264 

35.71 

1.307

fluid ounces 

gallons 

cubic feet 

cubic yards

fl oz 

gal 

ft3

yd3

 MASS 

g 

kg 

tonnes

grams 

kilograms 

tonnes

0.035 

2.202 

1.103 

ounces 

pounds 

tons

oz 

lb 

tons

 TEMPERATURE 

EC Celsius 1.8 C + 32 Fahrenheit EF

 WEIGHT DENSITY 

kN/m3 kilonewton / cubic 

meter 6.36 poundforce / cubic foot pcf

 FORCE and PRESSURE or STRESS 

N 

kN 

kPa 

kPa 

newtons 

kilonewtons 

kilopascals 

kilopascals 

0.225 

225 

0.145 

20.9 

poundforce 

poundforce 

poundforce / square inch 

poundforce / square foot 

lbf 

lbf 

psi 

psf 
FHWA NHI-05-039 

Micropile Design & Construction i - iii December 2005 

TABLE OF CONTENTS 

CHAPTER 1 INTRODUCTION 

1.1 PURPOSE AND SCOPE OF MANUAL........................................................................ 1 – 1 

1.2 MICROPILE DEFINITION AND DESCRIPTION ....................................................... 1 – 4 

1.3 HISTORICAL BACKGROUND.................................................................................... 1 – 5 

1.4 REFERENCES................................................................................................................ 1 – 8 

CHAPTER 2 MICROPILE CLASSIFICATION SYSTEM 

2.1 INTRODUCTION .......................................................................................................... 2 – 1 

2.2 DESIGN APPLICATION CLASSIFICATION ............................................................. 2 – 1 

2.3 CONSTRUCTION TYPE CLASSIFICATION.............................................................. 2 – 6 

2.4 REFERENCES................................................................................................................ 2 – 8 

CHAPTER 3 MICROPILE APPLICATIONS IN TRANSPORTATION PROJECTS 

3.1 INTRODUCTION........................................................................................................... 3 – 1 

3.2 FEASIBILITY OF MICROPILES.................................................................................. 3 – 1 

3.2.1 Overview............................................................................................................ 3 – 1 

3.2.2 Physical Considerations.....................................................................................3 – 3 

3.2.3 Subsurface Conditions ....................................................................................... 3 – 4 

3.2.4 Environmental Conditions .................................................................................3 – 4 

3.2.5 Existing Structure Adaptation............................................................................ 3 – 6 

3.2.6 Micropile Limitations ........................................................................................3 – 6 

3.2.7 Economics of Micropiles ...................................................................................3 – 6 

3.3 STRUCTURAL SUPPORT ............................................................................................ 3 – 7 

3.3.1 Overview............................................................................................................ 3 – 7 

3.3.2 New Foundations ............................................................................................... 3 – 7 

3.3.3 Underpinning of Existing Foundations..............................................................3 – 9 

3.3.4 Seismic Retrofit ............................................................................................... 3 – 12 

3.4 IN-SITU REINFORCEMENT...................................................................................... 3 – 14 

3.5 REFERENCES.............................................................................................................. 3 – 20 

CHAPTER 4 CONSTRUCTION TECHNIQUES AND MATERIALS 

4.1 INTRODUCTION........................................................................................................... 4 – 1 

4.2 DRILLING ...................................................................................................................... 4 – 1 

4.2.1 Overview............................................................................................................ 4 – 1 

4.2.2 Drill Rigs............................................................................................................4 – 3 

4.2.3 Drilling Techniques ........................................................................................... 4 – 6 

4.2.4 Overburden Drilling Techniques ....................................................................... 4 – 9 

4.2.5 Open-Hole Drilling Techniques....................................................................... 4 – 13 

4.3 GROUTING .................................................................................................................. 4 – 14 

4.3.1 General............................................................................................................. 4 – 14 

4.3.2 Grout Equipment .............................................................................................4 – 16 

4.3.3 Grout Mixing ...................................................................................................4 – 19 

4.3.4 Grout Placement Techniques ...........................................................................4 – 19 
FHWA NHI-05-039 

Micropile Design & Construction i-iv December 2005

4.3.4.1 Gravity Fill Techniques (Type A Micropiles)................................. 4 – 19 

4.3.4.2 Pressure Grouting Through the Casing (Type B Micropiles) ......... 4 – 20 

4.3.4.3 Postgrouting (Type C and D Micropiles) ........................................ 4 – 21 

4.3.5 Top-Off (Secondary) Grouting ........................................................................ 4 – 26 

4.4 REINFORCING STEEL ............................................................................................... 4 – 26 

4.4.1 General............................................................................................................. 4 – 26 

4.4.2 Placement of Reinforcement............................................................................4 – 26 

4.4.3 Reinforcement Types.......................................................................................4 – 26 

4.5 REFERENCES.............................................................................................................. 4 – 35 

CHAPTER 5 DESIGN OF MICROPILES FOR STRUCTURE FOUNDATIONS 

5.1 INTRODUCTION........................................................................................................... 5 – 1 

5.2 STEP 1: EVALUATE FEASIBILITY OF MICROPILES ............................................ 5 – 3 

5.3 STEP 2: REVIEW AVAILABLE INFORMATION & GEOTECHNICAL DATA ..... 5 – 5 

5.4 STEP 3: DEVELOP APPLICABLE LOADING COMBINATIONS ........................... 5 – 7 

5.5 STEP 4: PRELIMINARY DESIGN OF MICROPILES................................................ 5 – 8 

5.5.1 Selection of Micropile Spacing..........................................................................5 – 8 

5.5.2 Selection of Micropile Length ...........................................................................5 – 8 

5.5.3 Selection of Micropile Cross Section ................................................................5 – 9 

5.5.4 Selection of Micropile Type ............................................................................5 – 10 

5.6 STEP 5: STRUCTURAL DESIGN OF MICROPILE CASED LENGTH.................. 5 – 10 

5.7 STEP 6: STRUCTURAL DESIGN OF MICROPILE UNCASED LENGTH ............ 5 – 17 

5.8 STEP 7: REVISE MICROPILE DESIGN ................................................................... 5 – 18 

5.9 STEP 8: EVALUATE GEOTECHNICAL CAPACITY OF MICROPILE................. 5 – 18 

5.9.1 Establish Stratum for Bond Zone.....................................................................5 – 18 

5.9.2 Select Ultimate Bond Stress and Calculate Bond Length................................5 – 19 

5.9.3 Evaluate Micropile Group Compression Capacity ..........................................5 – 22 

5.9.4 Evaluate Micropile Group Uplift Capacity......................................................5 – 27 

5.10 STEP 9. ESTIMATE MICROPILE GROUP SETTLEMENT .................................. 5 – 29 

5.10.1 General........................................................................................................... 5 – 29 

5.10.2 Micropile Group Settlement ..........................................................................5 – 29 

5.10.3 Micropile Elastic Movement.......................................................................... 5 – 36 

5.11 STEP 10. DESIGN MICROPILE CONNECTION AT PILE CAP........................... 5 – 38 

5.12 STEP 11. DEVELOP LOAD TESTING PROGRAM............................................... 5 – 44 

5.13 STEP 12. PREPARE DRAWINGS AND SPECIFICATIONS ................................. 5 – 45 

5.14 CORROSION PROTECTION.................................................................................... 5 – 45 

5.14.1 Background.................................................................................................... 5 – 45 

5.14.2 Evaluation of Soil Corrosion Potential ..........................................................5 – 46 

5.14.3 Corrosion Protection Systems........................................................................5 – 46 

5.14.3.1 Methods for Corrosion Protection of Reinforcing Steel ...............5 – 46 

5.14.3.2 Methods for Corrosion Protection of Steel Casing .......................5 – 48 

5.14.3.3 Corrosion Protection Requirements for Micropiles ......................5 – 50 

 5.15 PLUNGE LENGTH..................................................................................................... 5 – 51

 5.16 END BEARING MICROPILE.................................................................................... 5 – 52 

 5.17 DOWNDRAG.............................................................................................................. 5 – 53 

5.18 DESIGN OF MICROPILES FOR LATERAL LOADING ........................................ 5 – 54 

5.18.1 General........................................................................................................... 5 – 54 
FHWA NHI-05-039 

Micropile Design & Construction i - v December 2005 

5.18.2 Analysis Steps for Single Laterally Loaded Micropile..................................5 – 54 

5.18.3 Evaluation of Micropile Lateral Load Capacity at Threaded Casing Joints..5 – 60 

5.19 LATERAL RESISTANCE OF MICROPILE GROUPS ............................................ 5 – 61 

5.19.1 General........................................................................................................... 5 – 61 

5.19.2 Step By Step Design Procedure for Laterally Loaded Pile Groups...............5 – 62 

5.19.3 Soil-Structure Interaction Analyses for Micropile Groups............................ 5 – 66 

5.19.4 Battered Micropiles........................................................................................ 5 – 66 

5.20 BUCKLING CONSIDERATIONS FOR MICROPILES ........................................... 5 – 67 

5.21.1 General........................................................................................................... 5 – 67 

5.21.2 Micropile Surrounded by Very Weak or Liquefiable Soil.............................5 – 67 

5.20.3 Micropiles Installed Through Voids ..............................................................5 – 72 

5.21 SEISMIC CONSIDERATIONS.................................................................................. 5 – 73 

5.21.1 General........................................................................................................... 5 – 73 

5.21.2 Use of Battered Micropiles in Highly Seismic Regions ................................5 – 75 

5.21.3 Load Sharing with Existing Foundations.......................................................5 – 76 

5.21.4 Pile Uplift Capacity........................................................................................ 5 – 77 

5.21.5 Liquefaction ...................................................................................................5 – 77 

5.22 REFERENCES............................................................................................................ 5 – 79 

CHAPTER 6 DESIGN OF MICROPILES FOR SOIL SLOPE STABILIZATION

6.1 INTRODUCTION........................................................................................................... 6 – 1 

6.2 STEP 1: IDENTIFY PROJECT SPECIFIC CONSTRAINTS AND EVALUATE 

MICROPILE FEASIBILITY....................................................................................... 6 – 3 

6.3 STEP 2: IDENTIFY PERFORMANCE REQUIREMENTS......................................... 6 – 6 

6.4 STEP 3: REVIEW AVAILABLE INFORMATION & GEOTECHNICAL DATA ..... 6 – 7 

6.5 STEP 4: EVALUATE FACTOR OF SAFETY OF EXISTING SLOPE ...................... 6 – 9 

6.6 DESIGN CONCEPTS FOR MICROPILES USED FOR SLOPE STABILIZATION 6 – 11 

6.6.1 Overview.......................................................................................................... 6 – 11

6.6.2 Evaluating the Additional Force Required to Obtain Target Factor of Safety 6 – 12 

6.6.2.1 Micropile Location Within Slope Cross Section ..............................6 – 12 

6.6.2.2 Methods to Model Resisting Force from a Micropile.......................6 – 16 

6.6.2.3 Evaluating Slope Stability Away From Micropile............................6 – 19 

6.6.3 Load Transfer in Micropiles ............................................................................ 6 – 21 

6.6.4 Bending Momemt and Shear Capacity of Single Vertical Micropile............. 6 – 25 

6.6.4.1 Evaluation of Bending Moment Capacity of Single Vertical 

Micropile .............................................................................................6 – 25 

6.6.4.2 Evaluation of Shear Capacity of Single Vertical Micropile .............6 – 25 

6.6.5 Shear Capacity of Battered Micropile Group .................................................. 6 – 30 

6.6.6 Spacing Required to Provide Required Force to Stabilize the Slope.............. 6 – 33 

6.6.7 Potential for Soil Flow Between Micropiles....................................................6 – 35 

6.7 DESIGN EXAMPLES FOR SLOPE STABILIZATION WITH MICROPILES......... 6 – 37 

6.7.1 STEP 4: Evaluate Factor of Safety of Existing Slope..................................... 6 – 39 

6.7.2 STEP 5: Evaluate Additional Force Required to Obtain Target Factor of 

Safety ............................................................................................................. 6 – 41 

6.7.3 STEP 6: Select Micropile Cross Section ........................................................6 – 43 

6.7.4 STEP 7: Estimate Length of Micropile...........................................................6 – 44 

6.7.5 STEP 8: Evaluate Bending Capacity of Single Vertical Micropile .............. 6 – 45 
FHWA NHI-05-039 

Micropile Design & Construction i-vi December 2005

6.7.6 STEP 9: Evaluate Shear Capacity of Single Vertical Micropile ................... 6 – 47 

6.7.7 STEP 10: Evaluate Shear Capacity of Battered Micropile Group.................. 6 – 51 

6.7.8 STEP 11: Calculate Spacing Required to Provide Force to Stabilize the 

Slope................................................................................................................ 6 – 52 

6.7.9 STEP 12: Check Potential Soil Flow between Micropiles .............................6 – 53 

6.7.10 STEP 13: Perform Structural Design of Concrete Cap Beam ......................6 – 54 

6.8 SHEAR CAPACITY OF MICROPILES FOR ANALYSIS ....................................... 6 – 58 

6.9 CASE HISTORIES ....................................................................................................... 6 – 59 

6.9.1 Stabilization of Blue Trail Landslide Using Micropiles, Wyoming................6 – 59 

6.9.2 Stabilization of Sum-271 Landslide Using Micropiles, Ohio ........................ 6 – 62 

6.9.3 Stabilization of Littleville Landslide using Micropiles, Alabama ................... 6 – 66 

6.10 REFERENCES............................................................................................................ 6 – 67 

CHAPTER 7 PILE LOAD TESTING 

7.1 INTRODUCTION............................................................................................................ 7 – 1 

7.2 OVERVIEW OF MICROPILE LOAD TESTING .......................................................... 7 – 1 

7.3 LOAD TESTING EQUIPMENT ..................................................................................... 7 – 3 

 7.3.1 General............................................................................................................... 7 – 3 

7.3.2 Load Testing Equipment.................................................................................... 7 – 3 

7.4 MICROPILE LOAD TESTING PROCEDURES.......................................................... 7 – 11 

 7.4.1 Verification Tests............................................................................................. 7 – 11 

7.4.1.1 General ............................................................................................ 7 – 11 

7.4.1.2 Procedures for Verification Test .....................................................7 – 11 

7.4.1.3 Recording of Verification Test Data ...............................................7 – 12 

 7.4.2 Proof Testing.................................................................................................... 7 – 15 

7.4.2.1 General ............................................................................................ 7 – 15 

7.4.2.2 Proof Test Procedures and Recording and Analysis of Proof Test 

Data ............................................................................................ 7 – 15 

 7.4.3 Micropile Acceptance Criteria.........................................................................7 – 15

7.4.3.1 Acceptance of Verification Test......................................................7 – 15 

7.4.3.2 Acceptance of Proof Test ................................................................ 7 – 18 

7.4.3.3 Consequences of Failure ................................................................. 7 – 18 

7.5 MICROPILE LOAD TEST REPORT ........................................................................... 7 – 19 

7.6 EVALUATION OF PROJECT LOAD TESTING REQUIREMENTS ........................ 7 – 20 

 7.6.1 Introduction...................................................................................................... 7 – 20 

 7.6.2 Load Testing Program for Verification Tests ..................................................7 – 20 

7.6.3 Load Testing Program for Proof Tests.............................................................7 – 21 

7.6.4 Test Load Magnitude ....................................................................................... 7 – 22 

7.6.5 Method of Load Application............................................................................ 7 – 23 

7.7 OTHER LOAD TESTING TECHNIQUES................................................................... 7 – 23 

 7.7.1 General............................................................................................................. 7 – 23 

 7.7.2 Dynamic Load Testing.....................................................................................7 – 24 

7.7.3 Statnamic Load Testing ...................................................................................7 – 26 

7.8 REFERENCES.............................................................................................................. 7 – 28 

CHAPTER 8 CONSTRUCTION INSPECTION/QUALITY CONTROL 

8.1 INTRODUCTION........................................................................................................... 8 – 1 
FHWA NHI-05-039 

Micropile Design & Construction i - vii December 2005 

8.2 INSPECTION ROLES UNDER CERTAIN CONTRACT APPROACHES ................. 8 – 1 

8.3 PRE-PROJECT PREPARATION................................................................................... 8 – 2 

8.4 INSPECTION OF MICROPILE MATERIALS ............................................................. 8 – 5 

8.4.1 General............................................................................................................... 8 – 5 

8.4.2 Storing and Handling of Cement ....................................................................... 8 – 5 

8.4.3 Storing and Handling of Reinforcing Steel........................................................ 8 – 6 

8.5 INSPECTION OF CONSTRUCTION ACTIVITIES..................................................... 8 – 8 

8.5.1 Inspection of Drilling Activities ........................................................................ 8 – 8 

8.5.2 Inspection of Reinforcement Installation Activities .......................................... 8 – 9 

8.5.3 Inspection of Grouting Activities..................................................................... 8 – 10 

8.6 REQUIRED PROJECT DOCUMENTATION............................................................. 8 – 12 

8.6.1 Micropile Load Testing.................................................................................... 8 – 12 

8.6.2 Production Micropiles......................................................................................8 – 13 

8.6.3 Grouting Records for Production Micropiles .................................................. 8 – 13 

8.7 REFERENCES.............................................................................................................. 8 – 18 

CHAPTER 9 CONTRACTING METHODS 

9.1 INTRODUCTION........................................................................................................... 9 – 1 

9.2 CONTRACTOR QUALIFICATION.............................................................................. 9 – 1 

9.3 METHOD CONTRACTING APPROACH.................................................................... 9 – 2 

9.3.1 Standard Design.................................................................................................9 – 4 

9.3.2 Alternate Micropile Design................................................................................9 – 5 

9.3.3 Cost Reduction Incentive Proposal (Value Engineering) .................................. 9 – 5 

9.4 PERFORMANCE SPECIFICATIONS........................................................................... 9 – 6 

9.5 DESIGN/BUILD APPROACH....................................................................................... 9 – 7 

9.5.1 General............................................................................................................... 9 – 7 

9.3.2 Postbid Design ................................................................................................... 9 – 7 

9.5.3 Prebid Design..................................................................................................... 9 – 8 

9.6 CONTRACT PLANS...................................................................................................... 9 – 9 

CHAPTER 10 COST ESTIMATING 

10.1 INTRODUCTION....................................................................................................... 10 – 1

10.2 FACTORS THAT INFLUENCE MICROPILE COSTS ............................................ 10 – 1 

10.2.1 Overview........................................................................................................ 10 – 1 

10.2.2 Micropile Material Costs ............................................................................... 10 – 1 

10.2.3 Equipment Cost..............................................................................................10 – 3 

10.2.4 Labor Cost...................................................................................................... 10 – 4 

10.2.5 Load Testing Costs ........................................................................................ 10 – 4 

10.3 MICROPILE COST ANALYSIS ............................................................................... 10 – 5 

10.3.1 Overview........................................................................................................ 10 – 5 

10.3.2 Effects of Project-Specific Constraints on Cost............................................. 10 – 6 

10.3.3 Micropile Cost Estimate Examples................................................................10 – 6 

 10.3.3.1 Sample Problem No. 1 (Bridge Abutment Support)..........................10 – 6 

 10.3.3.2 Sample Problem No. 2 (Seismic Retrofit) .........................................10 – 8 

10.4 MEASUREMENT AND PAYMENT FOR MICROPILES.......................................10 – 8 
FHWA NHI-05-039 

Micropile Design & Construction i-viii December 2005

 

GLOSSARY OF TERMS 

APPENDIX A – DESIGN CONCEPT OF CASE 2 MICROPILE NETWORKS FOR 

 SLOPE STABILIZATION 

APPENDIX B – LPILE ANALYSIS RESULTS FOR SLOPE STABILIZATION 

 PROBLEM 

APPENDIX C – MICROPILE GUIDE CONSTRUCTION SPECIFICATION 

APPENDIX D – SAMPLE PROBLEM NO.1, 

 BRIDGE FOUNDATION ABUTMENT SUPPORT 

APPENDIX E – SAMPLE PROBLEM NO. 2, LATERALLY LOADED MICROPILE 

 
FHWA NHI-05-039 

Micropile Design & Construction i - ix December 2005 

LIST OF TABLES 

Table 2-1. Details of Micropile Classification Based on Type of Grouting ........................ 2 – 9 

Table 3-1. Relationship Between Micropile Application, Design Behavior, 

and Construction Type ............................................................................... 3 – 3 

Table 4-1. Overburden Drilling Methods ......................................................................... 4 – 10 

Table 4-2. Dimensions, Yield, and Ultimate Strengths for Standard Reinforcing Bars ... 4 – 27 

Table 4-3. Dimensions and Yield Strength for DSI Threadbar ........................................ 4 – 29 

Table 4-4. Dimensions and Yield Strength of Common Hollow Injection Bars ............... 4 – 31 

Table 4-5. Dimensions and Yield Strength of Common Micropile Pipe Types & Sizes.... 4 – 33 

Table 5-1. Design Steps for Micropiles Used for Structural Foundations........................... 5 – 2 

Table 5-2. Guidelines for Minimum Number of Investigation Points and Depth of 

Investigation. ................................................................................................. 5 – 6 

Table 5-3. Summary of Typical 

bond (Grout-to-Ground Bond) Values for 

Micropile Design......................................................................................... 5 – 21 

Table 5-4. Efficiency Factors for Micropile Groups in Cohesive Soils............................ 5 – 23 

Table 5-5. Criteria for Assessing Ground Corrosion Potential ........................................... 5 – 46 

Table 5-6. Corrosion Protection Requirements for Micropiles........................................... 5 – 50 

Table 5-7 Values of ε50 for Intact Clays.............................................................................. 5 – 55 

Table 5-8 Values of ε50 for Stiff Clays................................................................................ 5 – 56 

Table 5-9 Soil –modulus Parameter (k) for Sands. ............................................................. 5 – 56 

Table 5-10 Soil –modulus Parameter (k) for Clays............................................................. 5 – 56 

Table 5-11 Guidance on Level of Fixity for Micropile-Footing Connections.................... 5 – 58 

Table 5-12 Elastic Constants of Various Soils Based on Soil Type ................................... 5 – 69 

Table 5-13 Elastic Constants of Various Soils Based on SPT N Value.............................. 5 – 70 

Table 6-1. Design Steps for Micropiles for Slope Stabilization .......................................... 6 – 3 

Table 6-2. Mult Values for Design Example....................................................................... 6 – 47 

Table 6-3. Hult(Ψds) for Various Batter Angles .................................................................... 6 – 52

Table 6-4. Comparison of Actual Loads to Design Loads for 

 Blue Trail Landslide Project. ........................................................................ 6 – 62 

Table 7-1. Verification Test Load Schedule ....................................................................... 7 – 13 

Table 7-2. Proof Test Load Schedule.................................................................................. 7 – 16 

Table 7-3. Recommendations on Minimum Number of Test Micropiles for 

 Proof Testing ............................................................................................ 7 – 22 

Table 8-1. Example Micropile Installation Log ............................................................... 8 – 14 

Table 8-2. Example Completed Micropile Installation Log ............................................ 8 – 15 
FHWA NHI-05-039 

Micropile Design & Construction i-x December 2005

Table 10-1. Typical Breakdown of Micropile Unit Costs................................................... 10 – 2 

Table 10-2. Material Costs of Steel Casings used for Micropiles....................................... 10 – 2 

Table 10-3. Material Costs of Steel Reinforcing Bars used for Micropiles........................ 10 – 3 

Table 10-4. Effects of Project-Specific Factors on Micropile Cost .................................... 10 – 5 

Table 10-5. Sample Problem No. 1 – Cost Analysis (Bridge Abutment Support) ........... 10 – 7 

Table 10-6. Sample Problem No. 2 – Cost Analysis (Seismic Retrofit) ........................... 10 – 9 

Table 10-7. Micropile Measurement and Payment Units ............................................... 10 – 10 
FHWA NHI-05-039 

Micropile Design & Construction i - xi December 2005 

LIST OF FIGURES 

Figure 1 - 1. Micropile Construction Sequence using Casing ............................................... 1 – 4 

Figure 1 - 2. Classical Arrangement of Root Piles for Underpinning....................................1 – 6 

Figure 1 - 3. Typical Network of Reticulated Micropiles......................................................1 – 7 

Figure 2 – 1. CASE 1 Micropiles........................................................................................... 2 – 2 

Figure 2 – 2. CASE 2 Micropiles – Reticulated Pile Network .............................................. 2 – 3 

Figure 2 – 3. CASE 1 Micropile Arrangements.....................................................................2 – 4 

Figure 2 – 4. CASE 2 Micropile Arrangements.....................................................................2 – 5 

Figure 2 – 5. Micropile Classification Based on Type of Grouting.......................................2 – 7 

Figure 3 – 1. Classification of Micropile Applications.......................................................... 3 – 2 

Figure 3 – 2. Low Headroom Micropile Installation ............................................................ 3 – 4 

Figure 3 – 3. Protection of an Existing Diaphragm Wall with a Secant Micropile 

Screen using Anti-acid Mortar .................................................................... 3 – 5 

Figure 3 - 4. Micropiles Used Under New Abutments for Bridge Over Mahoning Creek, 

Armstrong County, Pennsylvania ...................................................... 3 – 8 

Figure 3 – 5. Micropiles for Foundation Support of Transportation Applications .............3 – 10 

Figure 3 - 6. Underpinning of West Emerson Street Viaduct, Seattle, Washington ..........3 – 11 

Figure 3 – 7. Underpinning Arrangement for Pocomoke River Bridge, Maryland.............3 – 12 

Figure 3 - 8. Seismic Retrofit of I-110, North Connector, Los Angeles, California ..........3 – 13 

Figure 3 – 9. Typical Configurations for Inclined Micropile Walls .................................... 3 – 15 

Figure 3 – 10. State Road 4023 Micropile Slope Stabilization, Armstrong County, 

Pennsylvania.............................................................................................. 3 – 16 

Figure 3 – 11. Cross Section Showing Steep Canyon Slope and Temporary Micropile 

Shoring ...................................................................................................... 3 – 17 

Figure 3 – 12. Wall 600 Permanent Earth Retention, Portland, Oregon..............................3 – 18 

Figure 3 – 13. Photo of Slope Stabilization at FH-7 Project in Mendocino National Forest, 

California................................................................................................... 3 – 18 

Figure 3 – 14. Schematic of Slope Stabilization at FH-7 Project in Mendocino National 

Forest, California.......................................................................................3 – 19 

Figure 4 – 1. Typical Micropile Construction Sequence Using Casing................................. 4 – 2 

Figure 4 - 2. Large Track-mounted Rotary Hydraulic Drill Rig...........................................4 – 3 

Figure 4 - 3. Small Track-mounted Rotary Hydraulic Drill Rig...........................................4 – 4 

Figure 4 - 4. Small Frame-mounted Rotary Hydraulic Drill Rig..........................................4 – 5 

Figure 4 - 5. Casing with Heavy Duty Casing Crown .......................................................... 4 – 7 

Figure 4 - 6. Drill Rigs Equipped (a) with Tricone Roller Bit and (b) for Double Head 

Drilling ............................................................................................... 4 – 7 

Figure 4 - 7. Rotary Percussive Drilling (a) Drive Head and (b) Drive Head and Shoe ......4 – 8 

Figure 4 - 8. Rotary Duplex Drilling (a) Drills Rods and (b) Various Casing Shoes...........4 – 8 

Figure 4 - 9. Overburden Drilling Methods ........................................................................... 4 – 9 

Figure 4 - 10. Effect of Water Content on Grout Compressive Strength and Flow 

Properties................................................................................................... 4 – 14 
FHWA NHI-05-039 

Micropile Design & Construction i-xii December 2005

Figure 4 - 11. Various Types of Colloidal Mixers............................................................... 4 – 17 

Figure 4 - 12. Various Types of Paddle Mixers...................................................................4 – 18 

Figure 4 - 13. Principle of the Tube à Manchette Method of Postgrouting Injection ......... 4 – 23 

Figure 4 - 14. Use of Reinforcement Tube as a Tube á Manchette Postgrouting System ...4 – 24 

Figure 4 - 15. Circulating Loop Arrangement for Pressure Grouting..................................4 – 25 

Figure 4 - 16. Multiple Bar Reinforcement with Bar Centralizer/Spacer............................ 4 – 28 

Figure 4 - 17. Details of Continuously Threaded Dywidag Bar .......................................... 4 – 29 

Figure 4 - 18. Details of Composite High-capacity Type 1B Micropiles............................ 4 – 34 

Figure 5 - 1. Detail of a Composite Reinforced Micropile ...................................................5 – 3 

Figure 5 - 2. Example Micropile Detail ..............................................................................5 – 12 

Figure 5 - 3. Block Failure Mode for Micropile Group in Cohesive Soil with Cap in 

Contact with Ground ................................................................................. 5 – 24

Figure 5 - 4. End-bearing Resistance of Piles in Layered Soils..........................................5 – 26

Figure 5 - 5. Model to Calculate Micropile Group Uplift Capacity in Cohesive Soils ......5 – 27 

Figure 5 - 6. Model to Calculate Micropile Group Uplift Capacity in Cohesionless Soils 5 – 28

Figure 5 - 7. Equivalent Footing Concept for Uniform Soil................................................5 – 30

Figure 5 - 8. Equivalent Footing Concept for Firm Soil Underlying Soft Soil Layer .........5 – 31 

Figure 5 - 9. Bearing Capacity Index versus Corrected SPT Blowcount ............................ 5 – 35 

Figure 5 - 10. Pile to Footing Connection Detail.................................................................5 – 39 

Figure 5 - 11. Pile to Footing Connection Detail.................................................................5 – 40 

Figure 5 - 12. Pile to Footing Connection Detail.................................................................5 – 41 

Figure 5 - 13. Pile to Footing Connection Detail.................................................................5 – 42 

Figure 5 - 14. Pile to New Footing Connection Detail used for Moderate Loads. ..............5 – 43 

Figure 5 - 15. Pile to New Footing Connection Detail used for High Loads.......................5 – 43 

Figure 5 - 16. Pile to Existing Footing Connection Detail...................................................5 – 44

Figure 5 - 17. GEWI Piles with (a) Grout Protection only; and (b) Double Corrosion 

Protection................................................................................................... 5 – 49 

Figure 5 - 18. Detail of Load Transfer through the Casing Plunge Length. ........................ 5 – 52 

Figure 5 - 19. LPILE Analysis Result for Bending Moment.............................................. 5 – 59 

Figure 5 - 20. LPILE Analysis Result for Lateral Micropile Deflection .............................5 – 59 

Figure 5 - 21. Illustration of P-Multiplier Concept for Lateral Group Analysis..................5 – 64 

Figure 5 - 22. Load-Deflection & Bending Moment-Deflection for Pile Group Analysis..5 – 65 

Figure 5 - 23. Limiting Lateral Modulus for Various Micropile Materials .........................5 – 70 

Figure 5 - 24. Micropile Installed Through Voids in Karstic Terrain; (a) Actual 

Configuration, (b) Model Used for Estimation of Structural Capacity.....5 – 72 

Figure 5 - 25. Three-dimensional soil pile interaction.........................................................5 – 74 

Figure 5 - 26. Plan View of Micropile Foundation.............................................................. 5 – 75 

Figure 5 - 27. Lateral Response of Micropile Foundations to Different Flexural 

Reinforcement Ratios ................................................................................ 5 – 76 

Figure 6 - 1. Micropile System in Approach 1 .....................................................................6 – 1 

Figure 6 - 2. Micropile System in Approach 2 .....................................................................6 – 2 

Figure 6 - 3. Concentrated Movements Recorded from Inclinometer at the Slip Surface....6 – 6 

Figure 6 - 4. Residual Friction Angle for Clayey Soils ......................................................6 – 10 

Figure 6 - 5. Example Slope Geometry...............................................................................6 – 13 
FHWA NHI-05-039 

Micropile Design & Construction i - xiii December 2005 

Figure 6 - 6. Relationship between Force Required for FS = 1.3 and Location of the 

Micropile ...................................................................................................6 – 14 

Figure 6 - 7. Effect of Micropile Placed Too Far Upslope (FSmin < 1.3)............................ 6 – 15 

Figure 6 - 8. Effect of Micropile Placed Too Far Downslope (FSmin < 1.3).......................6 – 15 

Figure 6 - 9. Micropiles with Battered Upslope Leg and Battered Downslope Leg........... 6 – 17 

Figure 6 - 10. Single Vertical Micropile Model for Design Analyses................................6 – 17 

Figure 6 - 11. Relationship Between Hreq and Cohesive Strength for Micropile Analysis 

Model ........................................................................................................6 – 18 

Figure 6 - 12. Slope Stability Analysis Search Limits Away From Micropile Location....6 – 19 

Figure 6 - 13. Potential Instability Resulting from Future Excavation...............................6 – 20 

Figure 6 - 14. Example Resultant Axial Force and Bending Moment Diagrams for (a) 

Downslope and (b) Upslope Micropile ..................................................... 6 – 22 

Figure 6 - 15. (a) Micropile Resistance Length Not Sufficient to Prevent Pullout and (b) 

Micropile Resistance Length Sufficient to Prevent Pullout ......................6 – 24 

Figure 6 - 16. An Example Distribution of P-Y Curves with Depth Obtained from Laterally 

Loaded Pile Analysis.................................................................................6 – 27 

Figure 6 - 17. Utilizing P-Y Curves Obtained from Laterally Loaded Pile Analysis in (a) Up 

Analysis and (b) Down Analysis...............................................................6 – 28

Figure 6 - 18. Example of Calculated Bending Moment Diagrams for Up and Down 

Analyses. ................................................................................................... 6 – 29

Figure 6 - 19 Forces Acting on (a) Vertical and (b) Inclined Micropile Along the Slip 

Surface....................................................................................................... 6 – 31 

Figure 6 - 20 Relationship between Adjusted Capacity of Individual Micropiles and 

Inclination Angle.......................................................................................6 – 32 

Figure 6 - 21 Definition of Inclination Angle When (a) Slip Surface is Horizontal and (b) 

Slip Surface is not Horizontal. .................................................................. 6 – 34 

Figure 6 - 22 Spacing between Micropiles. .........................................................................6 – 35 

Figure 6 - 23 Plastically Deforming Soil between Two Adjacent Micropiles.....................6 – 36 

Figure 6 - 24 Slope Geometry and Subsurface Information for the Design Example .........6 – 38 

Figure 6 - 25 FSmin Determined from Trial Shear Strength Parameters. .............................6 – 40 

Figure 6 - 26 FSmin of the Slope Based on Modified Shear Strength Parameters................6 – 41 

Figure 6 - 27 Slope Stability Analysis to Determine Additional Force to Obtain Target 

Factor of Safety. ........................................................................................ 6 – 42 

Figure 6 - 28 Stability of the (a) Upslope Away from the Micropile and (b) Downslope 

Away from the Micropile..........................................................................6 – 43 

Figure 6 - 29 Micropile Cross-Section for the Design Example..........................................6 – 44 

Figure 6 - 30 Single Vertical Micropile Modeled in LPILE................................................ 6 – 46 

Figure 6 - 31 Depths Chosen for p-y Curves for Entire Length of the Micropile ...............6 – 48 

Figure 6 - 32 Process to Evaluate Shear Resistance (Q) of Single Vertical Micropile Using 

Up and Down Laterally Loaded Pile Analyses .........................................6 – 49 

Figure 6 - 33 Modeling Soil Layers with Previously Determined p-y Curves ....................6 – 50 

Figure 6 - 34 Interpolation of Hult for Battered Downslope Micropile Leg.........................6 – 53 

Figure 6 - 35 Spreadsheet Calculations Based on Eq. 6-12 to Obtain Hult-soil/pile for the 

Example Problem ......................................................................................6 – 55 

Figure 6 - 36 Equations Used in Each Cell in Figure 6-35..................................................6 – 56 

Figure 6 - 37 Graphical Solution for Hult-soil/pile Based on Figure 6-36 ................................6 – 57 

Figure 6 - 38 Extent of Blue Trail Landslide.......................................................................6 – 60 
FHWA NHI-05-039 

Micropile Design & Construction i-xiv December 2005

Figure 6 - 39 Conceptual Design Drawing of the MSE and NRM Walls for Blue Trail 

Landslide Project.......................................................................................6 – 60 

Figure 6 - 40 Typical Section of Micropile and Ground Anchor Wall for Blue Trail 

Landslide Project.......................................................................................6 – 61 

Figure 6 - 41 Typical Section of Micropile and Ground Anchor Wall at SUM-271...........6 – 63 

Figure 6 - 42 Comparison of Axial Loads for the SUM-271 Project ..................................6 – 64 

Figure 6 - 43 Comparison of Bending Moments for the SUM-271 Project ........................6 – 65 

Figure 6 - 44 Typical Section of Micropile and Anchor Wall at Littleville, Alabama........6 – 66 

Figure 7 - 1. Schematic of Compression Load Test Arrangement........................................7 – 4 

Figure 7 - 2. Schematic of Tension Load Test Arrangement................................................7 – 4 

Figure 7 - 3. Schematic of Lateral Load Test Arrangement .................................................7 – 5 

Figure 7 - 4. Compression Load Test Set-Up .......................................................................7 – 5 

Figure 7 - 5. Tension Load Test Setup.................................................................................. 7 – 6 

Figure 7 - 6. Photograph of Lateral Load Test Set-Up .........................................................7 – 7 

Figure 7 - 7. Typical Pressure Gauge Calibration Curve......................................................7 – 7 

Figure 7 - 8. Strain Gauge Locations on Micropiles for SUM-271 Project........................7 – 10 

Figure 7 - 9. Load Displacement Curve of Verification Tests............................................7 – 14 

Figure 7 - 10. Plotting Elastic and Residual Movement of Verification Test Data. ............7 – 14

Figure 7 - 11. Plotting of Proof Test Data............................................................................ 7 – 17 

Figure 7 - 12. Dynamic Test Set-Up for Micropile..............................................................7 – 25 

Figure 7 - 13. Statnamic Test Set-Up...................................................................................7 – 27 

Figure 8 - 1. QA Inspector Responsibilities for a Typical Micropile Project.......................8 – 4 

Figure 8 - 2. Cement Storage ................................................................................................ 8 – 6 

Figure 8 - 3. Storage of Reinforcing Steel ............................................................................8 – 7 

Figure 8 - 4. Double Corrosion Protected (Encapsulated) Reinforcing Steel ......................8 – 8 

Figure 8 - 5. Reinforcement Centralizers............................................................................8 – 10 

Figure 8 - 6. Drill Rig Pressure Gauge................................................................................8 – 11 

Figure 8 - 7. Grout Cubes for Compressive Strength Testing ............................................ 8 – 16 

Figure 8 - 8. Baroid Mud Balance Test...............................................................................8 – 17 
FHWA NHI-05-039 Chapter 1 - Introduction 

Micropile Design & Construction 1-1 December 2005 

CHAPTER 1 

INTRODUCTION 

1.1 PURPOSE AND SCOPE OF MANUAL 

The use of micropiles has grown significantly since their conception in the 1950s, and in 

particular since the mid-1980s. Micropiles have been used mainly as foundation support 

elements to resist static and seismic loads, and to a lesser extent, as in-situ reinforcements to 

provide stabilization of slopes and excavations. Many of these applications are for 

transportation structures. 

In 1993, the Federal Highway Administration (FHWA) sponsored a project to review the 

state-of-the-practice of micropiles. The research group for this project included contractors, 

consultants, academics, and owners. The document produced from this project, entitled 

Drilled and Grouted Micropiles – State-of-the-Practice Review (FHWA, 1997) provided a 

comprehensive international review and detailed analysis of available research and 

development results, laboratory and field testing data, design methods, construction 

methodologies, site observations, and monitored case studies. As part of this study, the 

limitations and uncertainties in the state-of-the-practice were evaluated, and further research 

needs were assessed. One of the highlighted needs was a manual of design and construction 

guidelines intended for use by practicing highway agency geotechnical and structural 

engineers. 

In response to this need, the FHWA sponsored the development of the manual Micropile 

Design and Construction Guidelines, Implementation Manual (FHWA, 2000). Funding and 

development of the manual was a cooperative effort between FHWA, U.S. micropile 

specialty contractors, and several state DOTs. The manual is intended to be a “practitioneroriented” document containing sufficient information on micropile design, construction 

specifications, inspection and testing procedures, cost data, and contracting methods to 

facilitate the safe and cost-effective use of micropiles on transportation projects. 

This manual is a revision to the 2001 Implementation Manual. The major revisions to the 

manual include: 

Chapter 3:

• Existing case history information has been updated and additional case histories have 

been added which specifically address the evaluation of micropile feasibility for 

specific projects. 
FHWA NHI-05-039 Chapter 1 - Introduction 

Micropile Design & Construction 1-2 December 2005 

Chapter 4:

• A description of sonic drilling techniques has been added. 

Chapter 5:

• Information on corrosion protection has been updated to reflect current FHWA 

practice regarding assessment of ground conditions and to include recommendations 

for levels of corrosion protection provided in the Deep Foundations Institute (DFI) 

“Guide to Drafting a Specification for High Capacity Drilled and Grouted Micropiles 

for Structural Support” (DFI, 2003). 

• A design flowchart for micropiles used for structural support is provided. This 

flowchart addresses all appropriate structural and geotechnical strength and service 

limit states. 

• Guideline information on recommended subsurface investigation (i.e., depth and 

spacing of geotechncial borings) has been added. 

• The factor of safety for grout-ground bond has been reduced from 2.5 to 2.0 to 

reflect current practice. A discussion on the rationale for this modification is 

presented. 

• Specific information on geotechnical strength limit states including vertical capacity 

(compression and uplift) and downdrag is provided for micropiles. 

• Evaluation of combined axial compression and bending, and methods to evaluate 

potential micropile buckling have been added. Detailed information on lateral 

loading of micropiles and methods to evaluate the structural capacity at a threaded 

connection are included. 

• Structural design considerations for battered micropiles are included. 

• Information on micropile group settlement and group lateral movement is included. 

• A section on seismic considerations in the design of micropiles for seismic retrofit 

applications has been added. Relevant information from the FOREVER (2003) 

research project and design information from the current Japanese manual on seismic 

design of micropiles (Japanese Public Works Research Institute, 2002) is included. 
FHWA NHI-05-039 Chapter 1 - Introduction 

Micropile Design & Construction 1-3 December 2005 

Chapter 6:

• Detailed information on the feasibility of micropiles for slope stabilization projects is 

provided including guidance on the assessment of geotechnical parameters required 

for analyses. Specific information on the limitations of the design method is 

provided. 

• Three detailed case histories on the use micropiles for slope stabilization have been 

added. 

• The design method for micropiles used to stabilize slopes has been modified to 

include a step-by-step design approach with information concerning: (1) effect of 

micropile location on slope stability; (2) effect of passive resistance in front of 

micropile structure; (3) axial load transfer in a micropile used for slope stabilization; 

and (4) step-by-step approach to the iterative design involving the analysis of the 

portions of the micropiles above a potential slip surface and below a potential slip 

surface. 

Chapter 7:

• Guidance on the evaluations to be performed to develop a micropile load testing 

program for verification and proof testing are provided. 

• Information is presented on the use of pile driver analyzing (PDA) techniques and 

Statnamic testing as a potential tool for micropile construction quality assurance. 

Chapter 8:

• A micropile inspector responsibilities summary checklist and an updated micropile 

installation log are provided. 

Chapter 10:

• Information on cost estimating is updated and includes specific information on major 

cost elements for micropiles including steel materials and labor costs. Information 

on load testing costs is also provided. Specific recommendations regarding typical 

measurement and payment items for a micropile project is provided. 
FHWA NHI-05-039 Chapter 1 - Introduction 

Micropile Design & Construction 1-4 December 2005 

1.2 MICROPILE DEFINITION AND DESCRIPTION 

A micropile is a small-diameter (typically less than 300 mm (12 in.)), drilled and grouted 

non-displacement pile that is typically reinforced. A micropile is constructed by drilling a 

borehole, placing steel reinforcement, and grouting the hole as illustrated in Figure 1-1. 

Micropiles can withstand relatively significant axial loads and moderate lateral loads, and 

may be considered a substitute for conventional driven piles or drilled shafts or as one 

component in a composite soil/pile mass, depending upon the design concept employed. 

Micropiles are installed by methods that cause minimal disturbance to adjacent structures, 

soil, and the environment. They can be installed where access is restrictive and in all soil 

types and ground conditions. Micropiles can be installed at any angle below the horizontal 

using the same type of equipment used for the installation of ground anchors and for grouting 

projects. 

BEGIN DRILLING

&/OR INSTALLATION

OF TEMPORARY

CASING

COMPLETE

DRILLING TO

DEPTH

REMOVE INNER

DRILL BIT &

ROD (IF USED)

PLACE

REINFORCEMENT &

GROUT (BY TREMIE)

REMOVE

TEMPORARY

CASING, INJECT

FURTHER GROUT

UNDER

PRESSURE AS

APPLICABLE

COMPLETE PILE

(CASING MAY BE

LEFT IN PLACE

THROUGH THE

COMPRESSIBLE

STRATUM)

ADDITIONAL GROUT

COMPRESSIBLE

STRATUM

BEARING

STRATUM

Figure 1-1. Micropile Construction Sequence. 
FHWA NHI-05-039 Chapter 1 - Introduction 

Micropile Design & Construction 1-5 December 2005 

Since the installation procedure causes minimal vibration and noise and can be used in 

conditions of low headroom, micropiles are often used to underpin existing structures. 

Specialized drilling equipment is often required to install the micropiles from within existing 

basement or other limited headroom facilities. 

Most of the applied load on conventional cast-in-place drilled or non-displacement piles is 

structurally resisted by the reinforced concrete; increased structural capacity is achieved by 

increased cross-sectional and surface areas. Micropile structural capacities, by comparison, 

rely on high-capacity steel elements to resist most or the entire applied load. These steel 

elements may occupy as much as one-half of the drillhole cross section. The special drilling 

and grouting methods used in micropile installation allow for high grout/ground bond values 

along the grout/ground interface. The grout transfers the load through friction from the 

reinforcement to the ground in the micropile bond zone in a manner similar to that of ground 

anchors. Due to the small pile diameter, any end-bearing contribution in micropiles is 

generally neglected. The grout/ground bond strength achieved is influenced primarily by the 

ground type and grouting method used, i.e., pressure grouting or gravity feed. The role of the 

drilling method is also influential, although less well quantified. 

1.3 HISTORICAL BACKGROUND 

Micropiles were conceived in Italy in the early 1950s, in response to the demand for 

innovative techniques for underpinning historic buildings and monuments that had sustained 

damage with time, and especially during World War II. A reliable underpinning system was 

required to support structural loads with minimal movement and for installation in accessrestrictive environments with minimal disturbance to the existing structure. An Italian 

specialty contractor called Fondedile, for whom Dr. Fernando Lizzi was the technical 

director, developed the palo radice, or root pile, for underpinning applications. The palo 

radice is a small-diameter, drilled, cast-in-place, lightly reinforced, grouted pile. The classic 

arrangement of pali radice for underpinning is shown in Figure 1-2. 

Although steel was in short supply in postwar Europe, labor was inexpensive, abundant, and 

often of high mechanical ability. Such conditions encouraged the development of these 

lightly reinforced, cast-in-place root pile elements, largely designed and installed by specialty 

contractors on a design-build basis. Load testing on these new root piles measured capacities 

in excess of 400 kN (90 kips), although the design capacity based on contemporary 

conventional bored pile design methodologies suggested capacities of less than 100 kN (23 

kips). Direct full-scale load tests were performed at relatively little cost, fostering the 
FHWA NHI-05-039 Chapter 1 - Introduction 

Micropile Design & Construction 1-6 December 2005 

acquisition and publication of a wealth of testing information. No grout/ground bond failures 

were recorded during these early tests. 

The use of root piles grew in Italy throughout the 1950s. Fondedile introduced the 

technology in the United Kingdom in 1962 for the underpinning of several historic structures, 

and by 1965, it was being used in Germany on underground urban transportation projects. 

For proprietary reasons, the term “micropile” replaced “root pile” at that time. 

Initially, the majority of micropile applications were structural underpinning in urban 

environments. Starting in 1957, additional engineering demands resulted in the introduction 

of systems of reticoli di pali radice (reticulated root piles). Such systems comprise multiple 

vertical and inclined micropiles interlocked in a three-dimensional network, creating a 

laterally confined soil/pile composite structure (Figure 1-3). Reticulated micropile networks 

were used for slope stabilization, reinforcement of quay walls, protection of buried 

structures, and other soil and structure support and ground reinforcement applications. 

A A

MICROPILE (TYP)

HORIZONTAL

CROSS- SECTION A-A

VERTICAL

CROSS- SECTION

Figure 1-2. Arrangement of Root Piles (pali radice) for Underpinning. 
FHWA NHI-05-039 Chapter 1 - Introduction 

Micropile Design & Construction 1-7 December 2005 

BIG CRACK IN THE SOFT

LIMESTONE FORMATION

RC BEAMS

SOFT LIMESTONE

CLAY

RETICULATED

PALI RADICE RETICULATED PALI RADICE

FOR THE COLUMN

REINFORCEMENT

EXISTING MASONRY

REINFORCED BY

RETICULATED PALI

RADICE

TYPICAL COLUMN

PLAN VIEW

Figure 1-3. Typical Network of Reticulated (reticolo di pali radice) Micropiles. 
FHWA NHI-05-039 Chapter 1 - Introduction 

Micropile Design & Construction 1-8 December 2005 

Other proprietary micropiles were developed in Switzerland and Germany, and the 

technologies were quickly exported overseas by branches or licensees of the originating 

contractors. Portions of Asia soon became a major market. 

Fondedile introduced the use of micropiles in North America in 1973 through a number of 

underpinning applications in the New York and Boston areas. The micropile technology did 

not grow rapidly in the United States, however, until the mid-1980s. At that time an 

abundance of successful published case histories, consistent influence by specialty 

contractors, and the growing needs of consultants and owners working in old urban 

environments overcame the skepticism and concerns of the traditional East Coast piling 

market (Bruce, 1988). 

1.4 REFERENCES

Bruce, D. A. (1988), “Developments in Geotechnical Construction Processes for Urban 

Engineering”, Civil Engineering Practice, Vol. 3, No. 1, Spring, pp. 49-97. 

Deep Foundations Institute (DFI) (2003), “Guide to Drafting a Specification for High 

Capacity Drilled and Grouted Micropiles for Structural Support.” 

FHWA (1997), “Drilled and Grouted Micropiles, State-of-Practice Review”, Bruce, D. A. 

and Juran, I., Reports No. FHWA-RD-96-016, 017, 018, and 019. 

FHWA (2000), “Micropile Design and Construction Guidelines Implementation Manual”, 

Armour, T., Groneck, P., Keeley, J., and Sharma, S., Report No. FHWA-SA-97-070. 

Japanese Public Works Research Institute (2002), “Design and Execution Manual for Seismic 

Retrofitting of Existing Pile Foundations with High Capacity Micropiles”, Foundation 

Engineering Research Team, Structures Research Group. 

FOREVER (2003), “Synthesis of the Results of the National Project on Micropiles”, 

International Center for Ground Improvement, Polytechnic University, Juran, I., Jahir 

Hasan, Weinstein, G. M, and Sourisseau, L. 
FHWA NHI-05-039 Chapter 2 – Micropile Classification System 

Micropile Design & Construction 2-1 December 2005

CHAPTER 2 

MICROPILE CLASSIFICATION SYSTEM 

2.1 INTRODUCTION 

In 1997, the FHWA published a 4-volume report summarizing the state-of-the-practice for 

micopiles (FHWA-RD-96-016, –017, -018, and –019; 1997). In that report, a micropile 

classification system was developed. This system is based on two criteria: (1) philosophy of 

behavior (design); and (2) method of grouting (construction). The philosophy of behavior 

dictates the method employed in designing the micropile. The method of grouting defines 

the grout/ground bond strength (or side resistance), which generally controls micropile 

capacity. The classification system consists of a two-part designation: a number, which 

denotes the micropile behavior (design), and a letter, which designates the method of 

grouting (construction). 

2.2 DESIGN APPLICATION CLASSIFICATION 

The design of an individual micropile or a group of micropiles differs greatly from that of a 

network of closely-spaced reticulated micropiles. This difference led to the definition of 

CASE 1 micropile elements, which are loaded directly and where the micropile 

reinforcement resists the majority of the applied load (Figure 2-1). CASE 2 micropile 

elements circumscribe and internally reinforce the soil to theoretically make a reinforced soil 

composite that resists applied loads (Figure 2-2). This is referred to as a reticulated micropile 

network. 

CASE 1 micropiles can be used as an alternative to more conventional types of piles since 

they are used to transfer structural loads to a deeper, more competent or stable stratum. Such 

directly loaded piles, whether for axial (compression or tension) or lateral loading conditions, 

are referred to as CASE 1 elements. The load is primarily resisted structurally by the steel 

reinforcement and geotechnically by side resistance developed over a “bond zone” of the 

individual micropiles. At least 90 percent of all international applications to date, and 

virtually all of the projects in North America have involved CASE 1 micropiles. Such 

micropiles are designed to act individually, although, they may be installed in groups. 

Typical arrangements of CASE 1 micropiles are illustrated in Figure 2-3. 
FHWA NHI-05-039 Chapter 2 – Micropile Classification System 

Micropile Design & Construction 2-2 December 2005

MICROPILES

DRILLED

SHAFT MICROPILES

DRILLED

SHAFT

VERTICAL LATERAL

COMPRESSIBLE

STRATUM

BEARING

STRATUM

EXTENT OF

SOIL-PILE

INTERACTION

MICROPILES

DRILLED

SHAFT

MOVING SOIL

STABLE SOIL

EXTENT OF

SOIL-PILE

INTERACTION

TO SUSTAIN AXIAL LOADS TO SUSTAIN LATERAL LOADS

Figure 2-1. CASE 1 Micropiles. 
FHWA NHI-05-039 Chapter 2 – Micropile Classification System 

Micropile Design & Construction 2-3 December 2005

TO SUPPORT VERTICAL LOAD

AND LATERAL LOADS (IF NEEDED)

COMPOSITE

BLOCK

TO LOWER CENTER OF

GRAVITY OF SOIL-STRUCTURE

UNIT TO IMPROVE STABILITY

COMPOSITE

BLOCK

CAP BEAM

PALI RADICE (ROOT PILE)

RETICULATED STRUCTURE

BLOCK CENTER

OF GRAVITY

STRUCTURE CENTER

OF GRAVITY

RESULTANT CENTER

OF GRAVITY

Figure 2-2. CASE 2 Micropiles – Reticulated Micropile Network. 

The remaining micropile applications involve networks of reticulated micropiles as 

components of a reinforced soil mass which is used to provide stabilization and support. 

These micropiles are referred to as CASE 2 elements. Structural loads are applied to the 

entire reinforced soil mass, as compared to individual micropiles (as for CASE 1 micropiles). 

CASE 2 micropiles are lightly reinforced because they are not individually loaded. A 

conceptual application of a network of reticulated micropiles is illustrated in Figure 2-4. 
FHWA NHI-05-039 Chapter 2 – Micropile Classification System 

Micropile Design & Construction 2-4 December 2005

FOUNDATION SUPPORT

SLOPE STABILIZATION

NEW BRIDGE STRUCTURE

BRIDGE ABUTMENT

NEW MICROPILE

FOUNDATIONS

SUPPORT (TYP)

REINFORCED

CONCRETE CAP

ROAD

SURFACE

FINISHED GRADE

CASE 1 NON RETICULATED

MICROPILE STRUCTURE (TYP)

APPROXIMATE

FAILURE PLANE

2H:1V

Figure 2-3. CASE 1 Micropile Arrangements. 
FHWA NHI-05-039 Chapter 2 – Micropile Classification System 

Micropile Design & Construction 2-5 December 2005

CONCRETE

CAP

SURCHARGE

ORIGINAL GRADE

FINAL GRADE

WALL FACING

CASE 2

RETICULATED

MICROPILE WALL

EARTH RETENTION

Figure 2-4. CASE 2 Micropile Arrangements. 

This philosophy of behavior (design) of an individual CASE 1 micropile is the same as that 

of a group of CASE 1 micropiles. A group of CASE 1 elements is defined as a closely 

spaced (typically parallel) arrangement of micropiles, each of which will be loaded directly. 

Design methodologies for individual CASE 1 elements and groups of CASE 1 elements are 

discussed in Chapters 5 and 6. The behavior and design approach of a group of CASE 1 

elements should not be confused with those of a reticulated network (i.e., CASE 2 

micropiles), although their geometries may appear to be similar. 

Very few CASE 2 micropile applications have been constructed in the U.S. Given the 

current general trend of using high capacity micropiles, the use of CASE 2 micropiles on 
FHWA NHI-05-039 Chapter 2 – Micropile Classification System 

Micropile Design & Construction 2-6 December 2005

future U.S. projects appears to be quite limited. Also, the use of CASE 2 micropiles, 

especially for public sector projects, will likely be disallowed until such time that an 

appropriate database of performance data becomes available for these micropiles to allow for 

a technically sound and safe design procedure to be developed. 

2.3 CONSTRUCTION TYPE CLASSIFICATION 

The method of grouting is typically the most sensitive construction process influencing 

grout/ground bond capacity. Grout/ground bond capacity varies directly with the grouting 

method. The second part of the micropile classification consists of a letter designation (A 

through D) based primarily on the method of placement and pressure under which grouting is 

performed during construction. The use of drill casing and reinforcement define subclassifications. The classification is shown schematically in Figure 2-5 and is described 

subsequently. 

• Type A: For Type A micropiles, grout is placed under gravity head only. 

Sand-cement mortars or neat cement grouts can be used. The micropile 

excavation may be underreamed to increase tensile capacity, although this 

technique is not common or used with any other micropile type. 

• Type B: Type B indicates that neat cement grout is placed into the hole under 

pressure as the temporary drill casing is withdrawn. Injection pressures 

typically range from 0.5 to 1 MPa (72 to 145 psi) to avoid hydrofracturing the 

surrounding ground or causing excessive grout takes, and to maintain a seal 

around the casing during its withdrawal, where possible. 

• Type C: Type C indicates a two-step process of grouting including: (1) neat 

cement grout is placed under gravity head as with Type A; and (2) prior to 

hardening of the primary grout (after approximately 15 to 25 minutes), similar 

grout is injected one time via a sleeved grout pipe without the use of a packer 

(at the bond zone interface) at a pressure of at least 1 MPa (145 psi). This pile 

type appears to be used only in France, and is referred to as IGU (Injection 

Globale et Unitaire). 
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Micropile Design & Construction 2-7 December 2005

TYPE A

(GRAVITY)

TYPE B

(PRESSURE THROUGH

CASING)

TYPE C

(SINGLE GLOBAL

POSTGROUT)

TYPE D

(MULTIPLE REPEATABLE

POSTGROUT)

PRESSURE GAGE

PACKER

Figure 2-5. Micropile Classification System Based on Type of Grouting. 

• Type D: Type D indicates a two-step process of grouting similar to Type C. 

With this method, neat cement grout is placed under gravity head (as with 

Types A and C) and may be pressurized (as for Type B). After hardening of 

the initially placed grout, additional grout is injected via a sleeved grout pipe 

at a pressure of 2 to 8 MPa (290 to 1,160 psi). A packer may be used inside 

the sleeved pipe so that specific horizons can be treated several times, if 

required. This pile type is used commonly worldwide, and is referred to in 

France as the IRS (Injection Répétitive et Sélective). 
FHWA NHI-05-039 Chapter 2 – Micropile Classification System 

Micropile Design & Construction 2-8 December 2005

Table 2-1 provides additional information on Type A, B, C, and D micropiles. Subclassifications (e.g., A1, A2, and A3) are included in Table 2-1 to indicate the type of drill 

casing and reinforcement used for each method of grouting. These sub-classifications also 

represent the type of reinforcement required by design (e.g. reinforcing bar, casing, none). 

Therefore, the combined micropile classification system is based on design application (i.e., 

Case 1 or Case 2), micropile type (i.e., Type A, B, C, or D) and grouting method (i.e., 1, 2, or 

3). It is emphasized that Table 2-1 is intended to present a classification system based on the 

type of micropile construction. It is not intended to be used in contract specifications. 

2.4 REFERENCES

FHWA (1997), “Drilled and Grouted Micropiles, State-of-Practice Review”, Bruce, D. A. 

and Juran, I., Reports No. FHWA-RD-96-016, 017, 018, and 019. 

Pearlman, S. L., and Wolosick, J. R. (1992), “Pin Piles for Bridge Foundations,” 

Proceedings, 9th Annual International Bridge Conference, Pittsburgh, Pennsylvania, 

June 15-17. 
FHWA NHI-05-039 Chapter 2 – Micropile Classification System 

Micropile Design & Construction 2-9 December 2005

Table 2-1. Details of Micropile Classification Based on Type of Grouting 

(after Pearlman and Wolosick, 1992).

Micropile Type and 

Grouting Method

Subtype Drill Casing Reinforcement Grout

A1 

Temporary or 

unlined (open hole 

or auger) 

None, single bar, cage, tube or 

structural section 

A2 Permanent, full 

length 

Drill casing itself Type A

Gravity grout only 

A3 

Permanent, upper 

shaft only 

Drill casing in upper shaft, 

bar(s) or tube in lower shaft 

(may extend full length) 

Sand/cement mortar or neat 

cement grout tremied to base of 

hole (or casing), no excess 

pressure applied 

B1 

Temporary or 

unlined (open hole 

or auger) 

Monobar(s) or tube (cages 

rare due to lower structural 

capacity) 

B2 Permanent, partial 

length 

Drill casing itself 

Type B

Pressure - grouted 

through the casing or 

auger during 

withdrawal 

B3 

Permanent, upper 

shaft only 

Drill casing in upper shaft, 

bar(s) or tube in lower shaft 

(may extend full length) 

Neat cement grout is first 

tremied into drill casing/auger. 

Excess pressure (up to 1 MPa 

(145 psi) typically) is applied to 

additional grout injected during 

withdrawal of casing/auger 

C1 

Temporary or 

unlined (open hole 

or auger) 

Single bars or tube (cages rare 

due to lower structural 

capacity) 

C2 Not conducted – 

Type C

Primary grout placed 

under gravity head, 

then one phase of 

secondary “global” 

pressure grouting C3 

Not conducted – 

Neat cement grout is first 

tremied into hole (or 

casing/auger). Between 15 to 

25 minutes later, similar grout 

injected through tube (or 

reinforcing pipe) from head, 

once pressure is greater than 1 

MPa (145 psi) 

D1 

Temporary or 

unlined (open hole 

or auger) 

Single bars or tube (cages rare 

due to lower structural 

capacity) 

D2 

Possible only if 

regrout tube placed 

full-length outside 

casing 

Drill casing itself 

Type D

Primary grout placed 

under gravity head 

(Type A) or under 

pressure (Type B). 

Then one or more 

phases of secondary 

“global” pressure 

grouting D3 

Permanent, upper 

shaft only 

Drill casing in upper shaft, 

bar(s) or tube in lower shaft 

(may extend full length) 

Neat cement grout is first 

tremied (Type A) and/or 

pressurized (Type B) into hole 

or casing/auger. Several hours 

later, similar grout injected 

through sleeved pipe (or 

sleeved reinforcement) via 

packers, as many times as 

necessary to achieve bond 
FHWA NHI-05-039 Chapter 2 – Micropile Classification System 

Micropile Design & Construction 2-10 December 2005
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-1 December 2005

CHAPTER 3 

MICROPILE APPLICATIONS IN TRANSPORTATION 

PROJECTS 

3.1 INTRODUCTION 

Micropiles are currently used in two general application areas: (1) structural support; and (2) 

in-situ reinforcement (Figure 3-1). Structural support includes new foundations, 

underpinning of existing foundations, seismic retrofitting applications and foundation support 

for earth retaining structures. In-situ reinforcement is used for slope stabilization and earth 

retention; ground strengthening; settlement reduction; and structural stability. Table 3-1 

summarizes the typical design behavior and micropile construction type for each application. 

Selection factors influencing the choice of micropiles for a project application are described 

herein. Example micropile applications for structural support and in-situ reinforcement for 

transportation projects and other civil engineering projects are described. 

3.2 FEASIBILITY OF MICROPILES

3.2.1 Overview 

Micropiles have specific advantages compared to more conventional support systems. In 

general, micropiles may be feasible under the following project-specific constraints: 

• project has restricted access or is located in a remote area; 

• required support system needs to be in close pile proximity to existing structures; 

• ground and drilling conditions are difficult (e.g., karstic areas, uncontrolled fills, 

boulders); 

• pile driving would result in soil liquefaction; 

• vibration or noise needs to be minimized; 

• hazardous or contaminated spoil material will be generated during construction; and 

• adaptation of support system to existing structure is required. 

Limitations and cost information for micropiles are also presented in this section. 
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Micropile Design & Construction 3-2 December 2005

Figure 3-1. Classification of Micropile Applications. 

Review of Applications

Slope 

Stabilization 

and 

Earth Retention 

Ground 

Strengthening

Settlement

Reduction

Structural

Stability

Structural Support 

In-situ Reinforcement

Earth 

Retaining 

Structure 

Foundations 

Foundations

for 

New 

Structures

Seismic 

Retrofitting

Underpinning

of 

Existing 

Foundations

Scour 

Protection 

Repair/ 

Replacement

of Existing 

Foundations

Upgrading 

of 

Foundation

Capacity 

Arresting/

Prevention

of 

Movement
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-3 December 2005

Table 3-1. Relationship Between Micropile Application, Design Behavior and 

Construction Type (modified after FHWA, 1997). 

STRUCTURAL 

SUPPORT IN-SITU EARTH REINFORCEMENT

Application 

Underpinning of Existing 

Foundations, 

New Foundations, and 

Seismic Retrofitting 

Slope 

Stabilization and 

Earth Retention 

Ground 

Strengthening 

Settlement 

Reduction 

Structural 

Stability 

Design 

Behavior CASE 1 CASE 1 and 

CASE 2 

CASE 2 with 

minor CASE 1 CASE 2 CASE 2 

Construction 

Type 

Type A (bond zones in rock 

or stiff clays) 

Type B, C, and D in soil 

Type A and 

Type B in soil 

Types A and B 

in soil 

Type A 

in soil 

Type A 

in soil 

Frequency 

of Use 

Probably 95 percent of total 

world applications 0 to 5 percent 

3.2.2 Physical Considerations 

The drilling and grouting equipment used for micropile installation is relatively small and 

can be mobilized in restrictive areas that would prohibit the entry of conventional pile 

installation equipment. Figure 3-2 shows micropiles being installed in low headroom 

conditions, illustrating the maneuverability of the equipment. 

Micropiles can be installed in close proximity to existing walls or foundations, provided that 

there is space above for the drill-head and safe work zone or the micropiles are battered to 

provide this space. Micropile installation is not as affected by overhead power lines or other 

obstructions as are conventional pile installation systems. The equipment can be mobilized 

up steep slopes and in remote locations. Also, drilling and grouting procedures associated 

with micropile installations do not cause damage to adjacent existing structures or affect 

adjacent ground conditions when proper drilling and grouting procedures are utilized. 
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Micropile Design & Construction 3-4 December 2005

Figure 3-2. Low Headroom Micropile Installation. 

3.2.3 Subsurface Conditions 

Micropiles can be installed in areas of particularly difficult, variable, or unpredictable 

geologic conditions such as ground with cobbles and boulders, fills with buried utilities and 

miscellaneous debris, and irregular lenses of competent and weak materials. Soft clays, 

running sands, and high groundwater not conducive to conventional drilled shaft systems 

cause minimal impacts to micropile installations. Micropiles are commonly used in karstic 

limestone formations. 

3.2.4 Environmental Conditions 

Micropiles can be installed in hazardous and contaminated soils. Because of their small 

diameter, drilling results in less spoil than would be produced by conventional drilled piles. 

Also, the flush effluent can be controlled easily at the ground surface through 

containerization or the use of lined surface pits. These factors greatly reduce the potential for 

surface contamination and handling costs. 

Grout mixes can be designed to withstand chemically aggressive groundwater and soils. 

Special admixtures can be included in the grout mix design to reduce and avoid deterioration 

from acidic and corrosive environments. For example, a micropile “screen” was constructed 

from the installation of overlapping (secant) micropiles adjacent to an existing concrete 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-5 December 2005

diaphragm wall of an underground parking garage in Barcelona, Spain (Bachy, 1992). The 

existing wall was physically deteriorating due to extremely aggressive ground water (i.e., 

presence of chlorides and sulfates and pH values as low as 1.7) originating from an adjacent 

metallurgical plant (Figure 3-3). No trace of acid was detected in samples of the diaphragm 

wall collected after construction of the micropile screen. 

Micropiles can be installed in environmentally sensitive areas, including areas with fragile 

natural settings. The installation equipment is not as large or as heavy as conventional pile 

driving or shaft drilling equipment and can be used in swampy areas or other areas of wet or 

soft surface soils with minimal impacts to the environment. Portable drilling equipment is 

frequently used in areas of restricted access. 

STREET

CAR PARK

DIAPHRAGM WALL

PLANT

ACID

PH < 2

MICROPILE

SCREEN

BARRIER

SILTY CLAY

TYPICAL PLAN VIEW

2m

Figure 3-3. Protection of an Existing Diaphragm Wall with a Secant Micropile Screen using 

Anti-acid Mortar (after Bachy, 1992). 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-6 December 2005

Micropile installations cause less noise and vibration than conventional piling techniques, 

especially driven piles. The vibration from pile driving is imparted to the soil and can be 

transferred through the soil to adjacent structures. The use of micropiles in old urban 

environments and industrial/manufacturing areas can prevent this potential damage to 

adjacent sensitive structures and equipment. 

Micropiles can be installed in areas where there is a contaminated aquifer overlying a bearing 

strata. Unlike driven piles that may produce a vertical conduit for contaminate migration, 

micropiles can be installed in a manner preventing contamination of lower aquifers. 

3.2.5 Existing Structure Adaptation 

Micropiles can be added to an existing pile cap, thereby eliminating the need for an increased 

footing size. With this approach, the additional compression, tension and moment resistance 

associated with increased structural loads can be resisted effectively. Oftentimes adjacent 

utilities and/or structures restrict the possibility of enlarging the existing pile caps, thus 

eliminating more traditional piling systems. With this approach, design analyses need to 

consider the relative stiffness of the micropiles and the existing piles to estimate individual 

loads. 

3.2.6 Micropile Limitations 

Vertical micropiles may be limited in lateral capacity and cost effectiveness. The ability of 

micropiles to be installed on an incline, however, significantly enhances their lateral 

capacity. Because of their high slenderness ratio (length/diameter), micropiles may not be 

acceptable for conventional seismic retrofitting applications in areas where liquefaction may 

occur due to concerns of buckling resulting from loss of lateral support. 

The use of micropiles for slope stabilization continues to increase. However, it is 

recommended that performance data be collected on such projects as experience and detailed 

design procedures continue to evolve. 

3.2.7 Economics of Micropiles 

The lineal cost of micropiles usually exceeds that of conventional piling systems, especially 

driven piles. A detailed discussion on micropile costs is provided in Chapter 10. 

Cost effectiveness of micropiles depends on many factors. It is important to assess the cost 

of using micropiles based on the physical, environmental, and subsurface factors previously 

described. For example, for an open site with soft, clean, uniform soils and unrestricted 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-7 December 2005

access, micropiles will likely not be a competitive solution. However, for the delicate 

underpinning of an existing bridge pier in a heavily trafficked old industrial or residential 

area, micropiles can provide the most cost-effective solution. 

Care should be taken to clearly define the true final cost of a solution based on micropiles. 

Cost analysis should be based on all related costs for the entire project and not just the unit 

cost of the piling system. As with other pile systems, it would be beneficial to consider 

micropile costs in terms of $/kN of axial capacity when evaluating deep foundation 

alternatives. Micropile costs are associated with: 

• right-of-way acquisition; 

• right-of-way agreements; 

• utility realignment; 

• excavation, shoring and backfill requirements; 

• footing construction; 

• hazardous material handling; 

• dewatering; 

• erosion control; 

• access restrictions; 

• ground improvement; and 

• owner and neighbor disruption. 

3.3 STRUCTURAL SUPPORT 

3.3.1 Overview

Micropile applications for structural support include foundations for new structures, 

underpinning of existing structures, scour protection, and seismic retrofitting of existing 

structures. Many of these applications have been used for transportation projects. In this 

section, case histories involving these applications are provided. 

3.3.2 New Foundations

Micropiles are applicable in new bridge construction in areas that require deep foundation 

alternatives or in difficult ground (cobbles/boulders obstructions) where installation of 

conventional piles or drilled shafts is very difficult and/or expensive. 
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Micropile Design & Construction 3-8 December 2005

For the I-78 dual highway bridge which crosses the Delaware River between Pennsylvania 

and New Jersey (Bruce, 1988b), all of the original bridge piers were founded either on driven 

piles or spread footings on rock, with the exception of Pier E-6. At the Pier E-6 location, 

bedrock was encountered below the anticipated depth and was found to be karstic. 

Micropiles and drilled shafts were proposed as alternative foundations for the project. 

Micropiles were chosen as an alternative because of their lower cost and faster installation in 

deep karstic regions. However, because micropiles were a fairly new technology in 1988, 

micropile load testing was performed during the design phase to evaluate the feasibility of 

micropiles for this application. Load test results indicated that micropiles were feasible and 

micropiles were therefore used for Pier E-6. 

The replacement of a two-span bridge over the Mahoning Creek in Armstrong County, 

Pennsylvania (Pearlman and Wolosick, 1992) required a support system to be built for new 

abutments (see Figure 3-4). The original stone abutment foundations were constructed in 

cofferdams and founded on erodible soils overlying competent sandstone. The alternatives 

for the project were anchored caisson walls, ground anchors, and micropiles. Micropiles 

were the least expensive alternative for the project. Also, micropiles could be conveniently 

drilled through the existing stone footings and founded in the underlying sandstone. 

Figure 3–4. Micropiles Used Under New Abutments for Bridge Over Mahoning Creek, 

Armstrong County, PA (after Pearlman and Wolosick, 1992). 
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Micropile Design & Construction 3-9 December 2005

The use of micropiles allows new bridge foundations to be constructed in areas of existing 

overhead restrictions, while maintaining traffic flow. A major improvement project was 

undertaken to replace the deck of the Brooklyn-Queens Expressway in the Borough of 

Brooklyn, New York (Bruce and Gemme, 1992). As a part of this project, a new center lane 

and several new entry/exit ramps were required. Micropiles were the only alternative for the 

new viaduct and the ramp construction because of low headroom restrictions and stringent 

vibration restrictions during construction. Due to low headroom conditions, micropile casing 

were left full length in the ground. Also, traffic flow was maintained during construction. 

Although the site comprised variable fluvioglacial deposits, this did not affect the rapid 

installation of the micropiles. 

Other micropile applications used for structural support include buildings, earth retaining 

structures, and soundwalls. Figure 3-5 shows typical arrangements of micropiles for support 

of common transportation-related structures. 

3.3.3 Underpinning of Existing Foundations 

Micropiles were originally developed for underpinning existing structures. The underpinning 

of existing structures may be performed for many purposes, including: 

• arresting and preventing structural movement; 

• for upgrading load-bearing capacity of existing structures; 

• repair and replacement of deteriorating or inadequate foundations; 

• to provide scour protection for erosion-sensitive foundations; 

• raising previously settled foundations; and 

• providing a means to transfer loads to deeper strata. 

Micropiles can be installed through and bonded within existing structures providing direct 

connection with competent underlying strata without the need for new pile caps, while at the 

same time reinforcing the structure internally. 

Construction can be executed without reducing the existing foundation capacity. The West 

Emerson Street Viaduct project in Seattle, Washington (Figure 3-6) required additional 

foundation support to be built at the existing bents. The additional foundation support had to 

be designed for both tension and compression loads. The conditions at the site included tight 

access and low headroom. Low headroom caissons and micropiles were the alternatives for 

the project. Micropiles were chosen to be added on five existing bents because of their 

considerable low cost compared to low headroom caissons. 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-10 December 2005

NEW BRIDGE STRUCTURE

BRIDGE

ABUTMENT

MICROPILE

FOUNDATION

SUPPORT (TYP)

COLUMN (TYP)

MICROPILES

SOFT GROUND TUNNEL

ROADWAY

MICROPILE (TYP)

ROADWAY

MICROPILE (TYP)

SOUNDWALL

A) BRIDGE FOUNDATION SUPPORT B) MICROPILE FOUNDATION SUPPORT

FOR SOFT GROUND TUNNELING

BENEATH EXISTING STRUCTURES

 C) FOUNDATION SUPPORT FOR CAST

IN PLACE REINFORCED CONCRETE

RETAINING WALS

 D) FOUNDATION SUPPORT FOR

HIGHWAY SOUNDWALLS

Figure 3-5. Micropiles for Foundation Support of Transportation Applications. 

Structural movements can be caused by a variety of factors, including compressible ground 

beneath the existing foundation, dewatering activities, groundwater elevation fluctuations, 

deterioration of existing foundations, and adjacent deep excavations and tunneling activities. 

Micropiles can mitigate this structural movement by being installed to deeper, more 

competent bearing strata, thus providing improved structural support. Increased load-bearing 

capacity of an existing foundation may be required for several reasons. 

Additional vertical, lateral, or vibratory loads may be applied to the foundation due to 

expansion of the existing structure, increased magnitude of applied loads, or the addition of 

vibrating machinery. 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-11 December 2005

Figure 3-6. Underpinning of West Emerson Street Viaduct, Seattle, Washington. 

The 75-year-old Pocomoke River Bridge in Maryland was rehabilitated when the capacity of 

the original wooden piles of the pier foundations was compromised by exposure to river 

scour (Bruce et al., 1990). Any alternative foundations system would need to be constructed 

in the middle of the river. The improved foundation system for the bridge was required to be 

preloaded before connecting to the existing structure to prevent additional settlement of the 

sensitive structure. Micropiles and caissons were considered for this project, and micropiles 

were selected for the project and installed through the existing foundation. The underpinning 

arrangement for the Pocomoke Bridge using micropiles is shown in Figure 3-7. 

Another underpinning example is the expansion of the Exton Square Mall in Chester County, 

Pennsylvania (Cadden et al., 2001). The mall site is underlain by dolomitic limestone, which 

is defined by Pennsylvania Department of Environmental Resources as a hazardous rock due 

to its susceptibility to solutioning and sinkhole development. Deep foundations had to be 

used in order to support column loads up to 4,450 kN (1,000 kips). The alternatives 

evaluated for the project included drilled shafts, driven piles, and micropiles. Project 

constraints included performing the work while most of the stores remained open and 

performing all the interior work at night when the mall was closed. Micropiles were chosen 

as an alternative because they were judged to be best suited to the tight access, low 

headroom, logistical restrictions, irregular rock mass quality, and high individual pile 

working loads. Driven piles were not feasible because they would likely become damaged 

during installation. 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-12 December 2005

MICROPILE (TYP)

WEST ABUTMENT

(DRIVEN TIMBER PILES)

EAST ABUTMENT

(DRIVEN TIMBER PILES)

BASCULE

PIER 3

BASCULE

PIER 4

30.4 m 32 m 30.4 m

Figure 3-7. Underpining Arrangement for Pocomoke River Bridge, Maryland (after Bruce et 

al., 1990). 

3.3.4 Seismic Retrofit 

Micropiles are being used increasingly for seismic retrofitting of existing highway structures, 

especially in California. Micropiles exhibit near equal tension and compression capacities, 

therefore optimizing the additional foundation support elements used (Bruce and Chu, 1995). 

Micropiles may be economically feasible for bridge foundation retrofits having one or more 

of the following constraints: 

• restrictions on footing enlargements; 

• vibration and noise restrictions; 

• low headroom clearances; 

• difficult access; 

• high axial load demands in both tension and compression; 

• difficult drilling/driving conditions; and 

• hazardous soil sites. 

Micropiles were used as part of a seismic retrofit project for California Department of 

Transportation’s earthquake retrofit project at I-110 in Los Angeles (Pearlman et al., 1993). 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-13 December 2005

Micropiles were used at the north connector over-crossing (Figure 3-8). Initially drilled 

shafts were chosen for the project; however, difficult drilling conditions, including buried 

concrete obstructions and water-bearing flowing sand layers, low overhead conditions, and 

limited right-of-way access prohibited the use of drilled shafts. Micropiles were chosen for 

the project due to their lower cost and ability to be installed under difficult access conditions. 

Micropiles for this project were designed for tension and compression and were connected to 

the existing structure. 

Figure 3-8. Seismic Retrofit of I-110, North Connector, Los Angeles, California. 

Micropiles were used to upgrade existing foundations for a highway bridge along Route 57 

near Cairo, Illinois. The seismicity for this area of southern Illinois is controlled by the New 

Madrid Seismic Source Zone. Micropiles were designed to withstand lateral and vertical 

forces from the design earthquake. The site soils consist of approximately 7.5 m (25 ft) of 

silty clay overlying sands. The existing pier and abutment foundations include short, vertical 

and batter timber piles deriving resistance from the sandy soils. The installation of a total of 

240 micropiles occurred under low headroom conditions (under the bridge deck) and 

required excavation around the existing pier foundations. Ten micropiles were installed just 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-14 December 2005

outside the perimeter of each foundation. Reinforcing steel was doweled into the existing 

footing and a new pile cap was poured. 

Micropiles have also been used for earthquake retrofit of major bridges in the San Francisco 

Bay area and New York City. 

3.4 IN-SITU REINFORCEMENT 

Micropiles are used in two different ways to stabilize slopes. Lizzi (1982) suggests that 

micropiles be used as reticulated network systems (CASE 2), which creates a stable, 

reinforced-soil, “gravity-retaining wall”. In CASE 2 systems the reinforced soil gravity mass 

supplies the essential resisting force, and the micropiles, encompassed by the soil, supply 

additional resistance to the tensile and shear forces acting on the “wall”. Alternately, 

Pearlman and Wolosick (1992) and Palmerton (1984) suggest that groups of individual 

inclined micropiles could be used to stabilize the slope because they serve to connect the 

moving zone (above the failure surface) to the stable zone (below the failure surface). These 

micropiles provide reinforcement to resist the shearing forces that develop along the failure 

surface. Typical configurations of inclined micropile groups for slope stabilization and earth 

retention are shown in Figure 3-9. 

For rocky, stiff, or dense materials, the shear resistance of the micropiles across the failure 

surface, i.e., individual capacity; is critical (CASE 1). For loose materials, the micropiles and 

soil are mutually reinforcing and creating a gravity wall, so the individual micropile 

capacities are not as significant (CASE 2). 

Micropiles were used to stabilize a portion of State Road 4023 in Armstrong County, 

Pennsylvania (Bruce, 1988a). A 75-m (250-ft) long section of this road and railroad tracks 

located upslope were experiencing damage from slope movements towards an adjacent river. 

Rock anchors and tangent drilled shafts extending into rock were the proposed techniques for 

in-situ reinforcement. However, alternative bidding was allowed in the project. During 

bidding, inclined micropile groups were proposed as an alternative to proposed techniques 

and were accepted due to significant cost savings. The resultant savings was approximately 

$1 million compared to the lowest bid for the anchored drilled shaft wall design. The wall 

included four rows of micropiles extending across the failure plane and into competent rock 

(Figure 3-10). 

Micropiles were used to provide temporary excavation support for a project involving 

improvements to State Highway 82 near Aspen, Colorado (Macklin et al., 2004). In this 
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Micropile Design & Construction 3-15 December 2005

mountainous region, construction is hampered by difficult site access and slope instability 

risks. This site consists of loose to very dense silty to gravelly sand with cobbles and 

boulders, which were deposited as debris flow, sheet wash, and colluvium over dense alluvial 

sandy gravel with cobbles. Originally, temporary shoring using combinations of soil nails 

and tiebacks was considered for the project. However, in an effort to improve the 

construction schedule and phasing, micropiles were selected as an alternative temporary 

shoring system. The micropile shoring implemented on this project was essentially a hybrid 

between a soldier beam and lagging system and a soil nail stabilization system (Figure 3-11). 

Phasing of the project required constructing a number of bridges in a specific sequence. The 

micropile shoring system allowed the contractor to transition access road grades where 

convenient, depending upon the excavation and access requirements for any phase of the 

work. 

STEEL REINFORCING BAR

(28 mm TO 63 mm TYP)

GROUT

125mm - 230mm 125mm - 230mm

(c) PILE SECTIONS

STEEL PIPE (100 mm

TO 175 mm O.D. TYP)

(a) ROADWAY SLOPE (b) SLOPE ABOVE HIGHWAY

Figure 3-9. Typical Configurations for Inclined Micropile Walls. 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-16 December 2005

0.3m (MIN)

1.37m (MIN)

2H:1V

VARIES 150mm TO 1200mm

0.91m

CONCRETE CAP

153mm MUD SLAB

EXISTING GRADE

15m±

TOP OF

ROCK

ROW 1

(26E)

ROW 2

(16E) ROW 3

(9E)

ROW 4

(VERT)

140mm DIA

115mm DIA

Figure 3-10. State Road 4023 Micropile Slope Stabilization, Armstrong County, 

Pennsylvania (after Bruce, 1988a). 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-17 December 2005

The Portland Westside Light-Rail Project in Portland, Oregon is an example of the use of 

micropiles to provide permanent earth retention (Ueblacker, 1996). Wall 600 extends from 

the east portal of the Westside Light-Rail cut and cover tunnel approximately 183 m (600 ft) 

to just beneath the Vista Avenue Bridge. Cut heights along the retaining wall ranged from 4 

to 9.5 m (13 to 30 ft). The original design included a counterfort concrete retaining wall 

supported on a driven pile foundation. The micropile wall was accepted as a contractorproposed value engineering alternate, largely because it was an alternate solution that could 

be constructed within the available right-of-way. Micropiles were installed vertically and 

inclined (Figure 3-12). Shotcrete was used for a temporary facing with the permanent facing 

comprising an architecturally treated cast-in-place concrete. 

An early example of slope stabilization using reticulated micropiles was for Forest Highway 

7 in Mendocino National Forest, California (Palmerton, 1984). This project was one of the 

two reticulated micropiles built in U.S. at the time. The site could have been stabilized using 

either cantilever or anchored walls; however, there was an interest in this relatively new 

technology and micropiles were therefore selected as part of a demonstration project. The 

two-lane road of Forest Highway 7 was constructed across a landslide where slide movement 

had occurred as a result of excessive rainfall (Figure 3-13). A 94-m (305-ft) long section of 

the road was stabilized using reticulated micropiles (Figure 3-14). 

Feasibility evaluation for micropiles is discussed further in Chapter 5 for structural support 

applications and Chapter 6 for slope stabilization applications. 

Figure 3-11. Cross Section Showing Steep Canyon Slope and Temporary Micropile Shoring 

(after Macklin et al., 2004). 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-18 December 2005

GEOCOMPOSITE DRAIN

TRACK BALLAST

ORIGINAL COUNTERFORT

WALL ENVELOPE

MICROPILES

GRADE BEAM

75mm DIA 

WATER MAINS

EXISTING GRADE

STRUCTURAL

FILL

100mm MIN TEMP. 

SHOTCRETE FACING

305mm CIP PERMANENT

WALL FACING

Figure 3-12. Wall 600 Permanent Earth Retention, Portland, Oregon (after Ueblacker, 

1996). 

Figure 3-13. Photo of Slope Stabilization at FH-7 Project in Mendocino National Forest, 

California. 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-19 December 2005

PILE BATTER V:H

A,AN,B,BN

C

D, DN

E, EN

G, GN

F, FN

VERT.

10 : 3.4

10 : 2.6

10 : 1.3

10 : 1

10 : 1.4

ASSUMED

FAILURE

PLANE

PILE CAP

GAGE DEPTH 1.22m

5.50m

3.05m

7.93m

11.89m

10.37m

13.11m

127mm – DIAMETER

REINFORCED PILE

A D EFG C G B NFN EN DN BNAN

DOWNHILL

UPSTATION

Figure 3-14. Schematic of Slope Stabilization at FH-7 Project in Mendocino National Forest, 

California. 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-20 December 2005

3.5 REFERENCES 

Bachy (1992), “Interception of Pollution by Impervious Barrier;” Sancho de Avila Car Park, 

Barcelona, Spain, Promotional literature, Paris, France. 

Bruce, D. A. (1988a), “Developments in Geotechnical Construction Processes for Urban 

Engineering”, Civil Engineering Practice, Vol. 3, No. 1, Spring, pp. 49-97. 

Bruce, D. A., (1988b), “Aspects of Minipiling Practice in the United States,” Ground 

Engineering, Vol. 21, No. 8, pp. 20-33. 

Bruce, D. A., Pearlman, S. L., and Clark, J. H. (1990), “Foundation Rehabilitation of the 

Pocomoke River Bridge, Maryland, Using High Capacity Preloaded Pinpiles,” 

Proceedings, 7th Annual International Bridge Conference, Pittsburgh, Pennsylvania, 

June 18-20, Paper IBC-90-42, 9 pages. 

Bruce, D. A. and Gemme, R., (1992) “Current Practice in Structural Underpinning Using 

Pinpiles,” Proceedings, New York Met Section, ASCE Seminar, New York, April 21-22, 

46 pages. 

Bruce, D. A., and Chu, E. K. (1995), “Micropiles for Seismic Retrofit, Proceedings,” 

National Seismic Conference on Bridges and Highways, Sponsored by FHWA and 

Caltrans, San Diego, California, December 10-13, 17 pages. 

Cadden, A. W., Bruce, D. A., and Ciampitti, L. M. (2001), “Micropiles in Karst: A Case 

History of Difficulties and Success”, Foundations and Ground Improvement, 

Proceedings of a Specialty Conference, ASCE, June 9-13, Geotechnical Special 

Publication, No. 113, pp. 204-215. 

FHWA (1997), Drilled and Grouted Micropiles, State-of-Practice Review. Federal Highway 

Administration Publication, Report No. FHWA-RD-96-016/019, July 1997, Four 

Volumes. 

Lizzi, F. (1982), “The Pali Radice (Root Piles),” Symposium on Soil and Rock Improvement 

Techniques including Geotextiles, Reinforced Earth and Modern Piling Methods, 

Bangkok, December, Paper D1. 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-21 December 2005

Macklin, P. R., Berger, D., Zietlow, W., Herring, W., and Cullen, J. (2004), “Case History: 

Micropile Use for Temporary Excavation Support”, Geotechnical Special Publication 

“Drilled Shafts, Micropiling, Deep Mixing, Remedial Methods, and Specialty 

Foundation Systems”, ASCE Publication, No.: 124, pp: 653-661. 

Palmerton, J.B. (1984), “Stabilization of Moving Land Masses By Cast-In-Place Piles,” 

USACOE Waterways Experiment Station, Final Report GL-84-4. 

Pearlman, S. L., and Wolosick, J. R. (1992), “Pin Piles for Bridge Foundations,” 

Proceedings, 9th Annual International Bridge Conference, Pittsburgh, Pennsylvania, 

June 15-17. 

Pearlman, S.L., Campbell, B.D., and Withiam, J.L. (1992), “Slope Stabilization Using InSitu 

Earth Reinforcements” ASCE Specialty Conference on Stability and Performance of 

Slopes and Embankments – II, Berkeley, California. 

Pearlman, S.L., Wolosick, J.R., and Gronek, P.B. (1993), “Pin Piles for Seismic 

Rehabilitation of Bridges,” Proceedings 9th International Bridge Conference, Pittsburg, 

Pennsylvania. 

Ueblacker, G. (1996), “Portland Westside Lightrail Corridor Project Micropile Retaining 

Wall,” Foundation Drilling, November, pp. 8-12. 
FHWA NHI-05-039 Chapter 3 – Micropile Transportation Applications 

Micropile Design & Construction 3-22 December 2005
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-1 December 2005

CHAPTER 4 

CONSTRUCTION TECHNIQUES AND MATERIALS 

4.1 INTRODUCTION 

The purpose of this chapter is to familiarize design engineers and construction personnel with 

the different techniques and materials utilized in the construction of micropiles. Specifically, 

information is provided on: (1) types of drill rigs used for micropile drilling; (2) various 

techniques used for overburden and open hole drilling; (3) grout types with methods of 

mixing and placing; and (4) types of micropile reinforcement. The construction of a 

micropile involves a succession of processes, the most significant of which are drilling, 

placing the reinforcement, and grouting. There are a large number of drilling systems 

available for both overburden and rock and many are used for micropile construction. 

The typical construction sequence for simple Type A and B micropiles (Figure 4-1) includes 

drilling the pile shaft to the required tip elevation, placing the steel reinforcement, placing the 

initial grout by tremie, and placing additional grout under pressure (for Type B). In general, 

the drilling and grouting equipment and techniques used for the micropile construction are 

similar to those used for the installation of soil nails, ground anchors, and grout holes. 

4.2 DRILLING 

4.2.1 Overview 

Most drilling methods selected by the specialty contractor for a micropile project are likely to 

be acceptable on a particular project, provided they can form a stable hole of the required 

dimensions and within the stated tolerances, and without detriment to their surroundings. It 

is important not to exclude a particular drilling method because it does not suit a 

predetermined concept of how the project should be executed. It is equally important that the 

drilling contractor be knowledgeable of the project ground conditions, and the effects of the 

drilling method chosen. Drilling within a congested urban site in close proximity of older 

buildings or deteriorating foundations has very different constraints than drilling for new 

foundations on an open field site. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-2 December 2005

BEGIN DRILLING

&/OR INSTALLATION

OF TEMPORARY

CASING

COMPLETE

DRILLING TO

DEPTH

REMOVE INNER

DRILL BIT &

ROD (IF USED)

PLACE

REINFORCEMENT &

GROUT (BY TREMIE)

REMOVE

TEMPORARY

CASING, INJECT

FURTHER GROUT

UNDER

PRESSURE AS

APPLICABLE

COMPLETE PILE

(CASING MAY BE

LEFT IN PLACE

THROUGH THE

COMPRESSIBLE

STRATUM)

ADDITIONAL GROUT

COMPRESSIBLE

STRATUM

BEARING

STRATUM

Figure 4-1. Typical Micropile Construction Sequence Using Casing. 

The act of drilling and forming the pile excavation may disturb the surrounding ground for a 

certain time and over a certain distance. The drilling method selected by the contractor 

should avoid causing an unacceptable level of disturbance to the site and its facilities, while 

providing for installation of a micropile that supports the required capacities in the most costeffective manner. Vigorous water flushing can increase drilling rates and increase the 

removal of the fine components of mixed soils, enlarging the effective diameter in the bond 

zone and aiding in grout penetration and micropile capacity. Conversely, the use of higher 

flush flow rates and pressures should be approached with caution, with consideration to the 

risks of creating voids and surface settlement, and the risks of hydrofracturing the ground 

which could result in ground heave. 

Drilling, installation of the reinforcement, and grouting of a particular micropile should be 

completed in a series of continuous processes and executed as expeditiously as possible. 

Longer durations between completion of drilling and placing of the reinforcement and grout 

can be detrimental to the integrity of the surrounding soil. Some materials, such as 

overconsolidated clays and clay shales, can deteriorate, relax, or soften as a result of 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-3 December 2005

exposure, resulting in a loss of interfacial bond capacity. In these cases, installation of a 

micropile bond zone should be completed within one day to avoid a pile hole remaining open 

overnight. 

Other site-specific conditions may affect selection of the drilling method and flush type. The 

use of water flush may require the supply, handling, and disposal of large quantities of water. 

In areas where the water supply may be scarce, a series of ponds or tanks for settlement and 

recirculation of the water may be necessary. Requirements for cleanliness or lack of space 

for water handling and disposal may dictate the use of air flush or augers for hole drilling. 

The presence of hazardous materials in the ground and the need for careful control and 

disposal of the soil cuttings may also necessitate the use of augers for micropile installation. 

4.2.2 Drill Rigs 

Drill rigs typically used for micropile installation are hydraulic rotary (electric or diesel) 

power units. They can be track mounted allowing for maneuverability on difficult and 

sloped terrain. The size of the track-mounted drills can vary greatly, as seen in Figure 4-2 

and 4-3, with the larger drill allowing use of long sections of drill rods and casing in areas 

without overhead restrictions and the smaller drill allowing work in lower overhead and 

harder-to-reach locations. The drill mast can be mounted on a frame allowing work in 

limited-access and low-overhead areas, such as building basements. 

Figure 4-2. Large Track-Mounted Rotary Hydraulic Drill Rig. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-4 December 2005

(a) 

(b) 

Figure 4-3. Low Headroom Track-Mounted Rotary Hydraulic Drill Rig (a) not Mounted and 

(b) Mounted for Drilling. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-5 December 2005

A frame-mounted drill such as the one shown in Figure 4-4 can be connected with long hoses 

to a separate hydraulic rotary power unit. This allows placement of the power unit outside 

the area of work, thus reducing space requirements, noise in the work area, and problems 

with exhaust removal. The drill frame can be moved and supported with a fork lift or moved 

by hand with winches and supported by bolting to a concrete floor, and/or bridge footing or 

bracing from a ceiling or bridge soffit. 

The rotary head that turns the drill string (casing, augers, or rods) can be extremely powerful 

on even the smallest of rigs, allowing successful installation in the most difficult ground 

conditions. Shortening of the drill mast and the use of short jointed sections of drill string 

and micropile reinforcement allows pile installation with less than 3 m (10 ft) of overhead 

clearance. For a vertical micropile, the micropile centerline can be located within 

approximately 375 mm (15 in.) of the face of an adjacent wall. This distance may need to 

increase for micropiles larger than approximately 175 mm (7 in.) in diameter. 

Figure 4-4. Small Frame-Mounted Rotary Hydraulic Drill Rig. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-6 December 2005

4.2.3 Drilling Techniques 

The drilling method is selected with the objective of causing minimal disturbance or 

upheaval to the ground and structure while being the most efficient, economic, and reliable 

means of penetration. Micropiles must often be drilled through an overlying weak material 

to reach a more competent bearing stratum. Therefore, construction typically requires the use 

of overburden drilling techniques to penetrate and support weak and unconsolidated soils and 

fills. In addition, unless the bearing stratum is a self-supporting material, such as rock or a 

cohesive soil, the drill hole may need temporary support for its full length, e.g. through the 

use of temporary casing (Figure 4-5) or suitable drilling fluid. If self-supporting material is 

present for the full depth of the micropile, the drillhole can possibly be formed by open hole 

techniques, i.e., without the need for temporary hole support by drill casing or hollow stem 

auger. 

Alternative drilling methods are required to penetrate through an existing structure (Figure 4-

6). Concrete coring techniques may be used to provide an oversized hole in existing slabs 

and footings to allow the subsequent drill casing to pass through. In some cases, 

conventional rock drilling methods involving rotary percussive techniques can be used to 

penetrate existing lightly-reinforced footings and structures. Rotary percussive (Figure 4-7) 

or rotary duplex (Figure 4-8) techniques may be used to first penetrate an initial obstruction 

layer, such as concrete rubble, with more conventional single-tube advancement drilling used 

for completion of the micropile shaft in the soil layers below. 
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Micropile Design & Construction 4-7 December 2005

Figure 4-5. Casing with Heavy Duty Casing Crown. 

 (a) (b) 

Figure 4-6. Drill Rigs Equipped (a) with Tricone Roller Bit and (b) for Double Head 

Drilling. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-8 December 2005

 (a) (b) 

Figure 4-7. Rotary Percussive Drilling (a) Drive Head and (b) Drive Bit and Shoe. 

 (a) (b) 

Figure 4-8. Rotary Duplex Drilling (a) Drill Rods and (b) Various Casing Shoes. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-9 December 2005

Water is the most common medium for cleansing and flushing the hole during drilling, 

followed by air, drill slurries, and foam. Caution should be exercised while using air flush to 

avoid injection of the air into the surrounding ground, causing fracturing and heaving. The 

use of bentonite slurries to stabilize and flush holes will impair grout-to-ground bond 

capacity by creating a skin of clay at the interface; however, this is not an uncommon choice 

in Italian and French practice with Type D piles. Polymer drilling muds have been used 

successfully in micropile construction in all types of ground. This slurry type reduces 

concern for impairment of the bond capacity, and allows for easier cleanup and disposal 

versus bentonite slurry. 

4.2.4 Overburden Drilling Techniques 

There is a large number of proprietary overburden drilling systems sold by drilling 

equipment suppliers worldwide. In addition, specialty contractors often develop their own 

variations in response to local conditions and demands. The result is large selection of 

systems and methods. However, seven generic methods have been identified which are 

common for piles with diameters less than 300 mm (12 in) to depths less than 60 m (200 ft). 

The following is a brief discussion of these seven methods. These seven methods are also 

summarized in Table 4-1, and simply represented in Figure 4-9. 

Figure 4-9. Overburden Drilling Methods (modified after Bruce, 1989).
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-10 December 2005

Table 4-1. Overburden Drilling Methods (after Bruce, 1989). 

Drilling Method Principle Common Diameters 

and Depths Notes 

Single-tube 

advancement 

a) Drive drilling Casing with “lost point” 

percussed without flush 

50-100 mm to 30 m 

(2-4 in. to 100 ft) 

Obstructions or very dense 

soil problematic. 1 

b) External flush Casing, with shoe, rotated 

with strong water flush. 

100-250 mm to 60 m 

(4-10 in. to 200 ft) 

Needs high torque head and 

powerful flush pump. 

2 Rotary duplex 

Simultaneous rotation and 

advancement of casing plus 

internal rod, carrying flush. 

Rod may have down-thehole hammer. 

100-220 mm to 70 m 

(4-8.75 in. to 230 ft) 

Used only in very sensitive 

soil/site conditions. Needs 

positive flush return. Needs 

high torques. (Internal 

flushing only) 

3 Rotary percussive 

concentric duplex 

As 2, except casing and rods 

percussed as well as rotated. 

89-175 mm to 40 m 

(3.5-7 in. to 130 ft) 

Useful in obstructed/rocky 

conditions. Needs powerful 

top rotary percussive 

hammer. 

4 Rotary percussive 

eccentric duplex 

As 2, except eccentric bit on 

rod cuts oversized hole to 

ease casing advance. 

89-200 mm to 60 m 

(3.5-8 in. to 200 ft) 

Expensive and difficult 

system used for difficult 

overburden. Rod can be 

percussive at top, or may 

have down-the-hole hammer 

above bit. 

5 “Double head” 

duplex 

As 2 or 3, except casing and 

rods may rotate in opposite 

directions. 

100-150 mm to 60 m 

(4-6 in. to 200 ft) 

Powerful, new system for 

fast, straight drilling in very 

difficult ground. Need 

significant hydraulic power. 

Casing can be percussed by 

top hammer. Rod may be 

percussed by top hammer or 

may have down-the-hole 

hammer above bit. 

6 Hollow-stem auger 

Auger rotated to depth to 

permit subsequent 

introduction of grout and/or 

reinforcement through stem. 

100-400 mm to 30 m 

(4-16 in. to 100 ft) 

Obstructions problematic; 

care must be exercised in 

cohesionless soils. Prevents 

application of higher grout 

pressures. 

7 Sonic 

Casing is excited by a 

variable frequency, variable 

amplitude, sonic head 

100 to 300 mm to 100 

m 

(4-12 in. to 330 ft) 

No or minimal flush needed. 

Full length sample of soil 

recovered for each hole. 

Note: Drive drilling, being purely a percussive method, is not described in the text as it has no application in 

micropile construction. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-11 December 2005

• Single-Tube Advancement-External Flush (Wash Boring): The toe of the drill 

casing is fitted with an open crown or bit and the casing is advanced into the ground 

by rotation of the drill head. Water flush is pumped continuously through the casing, 

which washes debris out and away from the crown. The water-borne debris typically 

escapes to the surface around the outside of the casing, but may be lost into especially 

loose and permeable strata. Care must be exercised below sensitive structures in 

order that uncontrolled washing does not damage the structure by causing cavitation. 

Air flush is not normally used with this system due to the danger of accidentally over 

pressurizing the ground in an uncontrolled manner which can cause ground 

disturbance. Conversely, experience has shown that polymer drill flush additives can 

be very advantageous in certain ground conditions, in place of water alone (Bruce, 

1992). These do not appear to detrimentally affect grout-to-soil bond development as 

may be the case with bentonite slurries. 

• Rotary Duplex: The drill rod with a suitable drill bit is placed inside the drill casing. 

It is attached to the same rotary head as the casing, allowing simultaneous rotation 

and advancement of the combined drill and casing string. The flushing fluid, usually 

water or polymer flush, is pumped through the head down through the central drill 

rod to exit from the flushing ports of the drill bit. The flush-borne debris from the 

drilling then rises to the surface along the annulus between the drill rod and the 

casing. At the surface, the flush exits through ports in the drill head. Air flush must 

be used with caution because blockages within the annulus can allow high air 

pressures to develop at the drill bit and cause ground disturbance. 

• Rotary Percussive Duplex (Concentric): Rotary percussive duplex systems are a 

development of rotary duplex methods, whereby the drill rods and casings are 

simultaneously percussed, rotated, and advanced. The percussion is provided by a 

top-drive rotary percussive drill head. This method requires a drill head of substantial 

rotary and percussive energy. 

• Rotary Percussive Duplex (Eccentric or Lost Crown): Originally sold as the 

Overburden Drilling Eccentric (ODEX) System, this method involves the use of 

rotary percussive drilling combined with an eccentric underreaming bit. The 

eccentric bit undercuts the drill casing, which is then pushed into the oversized drill 

hole with much less rotational energy or thrust than is required with the concentric 

method. The drill casing does not require an expensive cutting shoe and suffers less 

wear and abrasion. The larger diameter options, of more than 127 mm (5 in.) in 

diameter, often involve the use of a down-the-hole hammer acting on a drive shoe at 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-12 December 2005

the toe of the casing so that the casing is effectively pulled into the borehole as 

opposed to being pushed by a top hammer. 

• Double Head Duplex: With the double head duplex method, the rods and casings 

are rotated by separate drill heads mounted one above the other on the same carriage. 

These heads provide high torque (and so enhanced soil- and obstruction-cutting 

potential), but at the penalty of low rotational speed. However, the heads are geared 

such that the lower one (rotating the outer casing), and the upper one (rotating the 

inner drill string) turn in opposite directions. The resulting aggressive cutting and 

shearing action at the bit permits high penetration rates, while the counter-rotation 

also minimizes blockage of the casing/rod annulus by debris carried in the exiting 

drill flush. In addition, the inner rods may operate by either purely rotary techniques 

or rotary percussion using top-drive or down-the-hole hammers. The counter-rotation 

feature promotes exceptional hole straightness and penetrability, even in the most 

difficult ground conditions. 

• Hollow-Stem Auger: Hollow-stem augers are continuous flight auger systems with 

a central hollow core similar to those commonly used in auger-cast piling or for 

subsurface investigation. These are installed by purely rotary heads. When drilling 

down, the hollow core is closed off by a cap on the drill bit. When the hole has been 

drilled to depth, the cap is knocked off or blown off by grout pressure, permitting the 

pile to be formed as the auger is withdrawn. Such augers may be used for drilling 

cohesive materials, very soft rocks, and are commonly used in sands. If used in sands 

with minimal cohesion or adhesion, there is a danger of loosening or cavitating the 

soil, especially in inclined holes. Post grouting is essential (Type D). 

Various forms of cutting shoes or drill bits can be attached to the lead auger, but 

heavy obstructions, such as old foundations and cobble and boulder soil conditions, 

are difficult to penetrate economically with this system. In addition, great care must 

be exercised when using augers as uncontrolled penetration rates or excessive “hole 

cleaning” may lead to excessive spoil removal, thereby risking soil loosening or 

cavitation in certain circumstances. 

• Sonic: Sonic drilling is a dual cased drilling system that employs high frequency 

mechanical vibration to take continuous core samples of overburden and most 

bedrock formations, and to advance casing into the ground. Other names for sonic 

drilling include rotosonic, rotasonic, sonicore, vibratory or resonant sonic drilling. 

The entire drill string is vibrated at a frequency of between 50 and 150 hertz and 

evenly distributes the energy and wear at the drill bit face. The rig uses a specially 
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Micropile Design & Construction 4-13 December 2005

designed hydraulically powered drill head or oscillator that is attached directly to the 

core barrel, drill pipe or outer casing. The vibrations are sent down through the drill 

steel to the face of the drill bit creating displacement, fracturing or shearing action 

depending on the material being drilled. 

4.2.5 Open Hole Drilling Techniques 

When a micropile can be formed in stable and free-standing conditions, the advancement of 

casing may be suspended and the hole continued to final depth by open-hole drilling 

techniques. There is a balance in cost between the time lost in changing to a less-expensive 

open-hole system and continuing with a more expensive overburden drilling system for the 

full hole depth. Open-hole drilling techniques may be classified as follows: 

• Rotary Percussive Drilling: Particularly for rocks of high compressive strength, 

rotary percussive techniques using either top-drive or down-the-hole hammers are 

utilized. For the small hole diameters used for micropiles, down-the-hole techniques 

are the most economical and common. Air, air/water mist, or foam is used as the 

flush. 

Top-drive systems can also use air, water, or other flushing systems, but have limited 

diameter and depth capacities, are relatively noisy, and may cause damage to the 

structure or foundation through excessive vibration. 

• Solid Core Continuous Flight Auger: In stiff to hard clays without boulders and in 

some weak rocks, drilling may be conducted with a continuous flight auger. Such 

drilling techniques are rapid, quiet, and do not require the introduction of a flushing 

medium to remove the spoil. There may be the risk of lateral decompression or wall 

remolding/interface smear, either of which may adversely affect grout-to-ground 

bond. Such augers may be used in conditions where the careful collection and 

disposal of drill spoils are particularly important. 

• Underreaming: Various devices have been developed to enlarge or underream open 

holes in cohesive soils or soft sediments, especially when the micropiles are to act in 

tension. These tools can be mechanically or hydraulically activated and will cut or 

abrade single or multiple underreams or “bells.” However, this is a time-consuming 

process, and it is rarely possible or convenient to verify its effectiveness. In addition, 

the cleaning of the underreams is often difficult; water is the best cleaning medium, 

but may cause softening of the ground. For all these reasons, it is rare to find 

underreaming used in typical micropile practice. 
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Micropile Design & Construction 4-14 December 2005

4.3 GROUTING 

4.3.1 General 

As described in Chapter 2, the grouting operations have a major impact on micropile 

capacity. Details of each type of grouting operation vary somewhat throughout the world, 

depending on the origins of the practice and the quality of the local resources. However, as 

general observations, it may be noted that: 

• Grouts are designed to provide high strength and stability (i.e., bleed), but must also 

be pumpable. As shown in Figure 4-10, this implies typical water/cement (w/c) ratios 

in the range of 0.40 to 0.50 by weight for micropile grout. In Figure 4-10, bleed 

capacity is defined as amount of free water that develops at final set. For example, 

for a w/c ratio of 1.0, 100 liters of grout would develop 20 liters of free water. 

• Grouts are produced with potable water, to reduce the danger of reinforcement 

corrosion. 

1 N/mm2 = 145 psi 

1 dyne/cm2

 = 1.45 × 10-5 psi 

Figure 4-10. Effect of Water Content on Grout Compressive Strength and Flow Properties 

(after Littlejohn and Bruce, 1977). 
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Micropile Design & Construction 4-15 December 2005

• Type I/II cement conforming to ASTM C150/AASHTO M85 is most commonly 

used, supplied either in bagged or bulk form depending on site condition, job size, 

local availability, and cost. 

• Neat cement-water grout mixes are most commonly used, although sand is a common 

additive in certain countries (e.g., Italy, Britain). Bentonite (which reduces grout 

strength) is used in primary mixes only with extreme caution, while additives are 

allowed only for cases where improved pumpability is required as for pumping over 

long distances and/or in hot conditions (e.g., high-range water reducers). 

• Design compressive strengths of 28 to 35 MPa (4,000 to 5,000 psi) can be attained 

with properly produced neat cement grouts. 

• If admixtures and/or additives are used, it is essential that they are chemically 

compatible. This is best achieved by using only one chemical supplier, and not by 

“mixing and matching”. 

The placed grout is required to serve a number of purposes, as described below. 

• It transfers the imposed loads between the reinforcement and the surrounding ground. 

• It may form part of the load-bearing cross section of the micropile. 

• It serves to protect the steel reinforcement from corrosion. 

• Its effects may extend beyond the confines of the drill hole by permeation, 

densification, and/or fissuring. 

The grout, therefore, needs to have adequate properties of fluidity, strength, stability, and 

durability. The need for grout fluidity can mistakenly lead to an increase in water content 

which has a negative impact on the other three properties. Of all the factors that influence 

grout fluidity and set properties, the water/cement ratio is the most important. Again, Figure 

4-10 illustrates why this ratio is limited to a range of 0.40 to 0.50, although even then, 

additives may be necessary to ensure adequate pumpability for ratios less than 0.40. 

It is essential to the integrity of the micropile that upon completion of the grouting operation, 

there is no significant loss of grout from any part of the micropile that will be relied upon for 

load bearing or corrosion protection. This condition can be achieved by grouting to refusal 

during micropile formation, i.e. continue grouting until no more grout take occurs. Problems 

with grout loss may necessitate the use of a filler such as sand for plugging the permeable 

layer, or may require pre-grouting the hole and redrilling and regrouting after set of the initial 

grout. Loss of grout is judged simply by observing the level of grout which remains in the 

hole after the grout has stiffened. For general guidance, a grout take over twice the “neat” 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-16 December 2005

hole volume is indicative of voided or very permeable conditions warranting special 

attention. 

For a Type B micropile, it may not always be possible to attain the desired pressures during 

grouting; the soil seal around the casing may not always be adequate to contain the 

pressurized grout. This may occur after partial pressure grouting of the bond length. If this 

occurs, the grout should be pumped until the level reaches the top of pile, at which time 

grouting is discontinued. Maintaining grout pressures at a reasonable level (0.70 MPa (100 

psi) or less) will help prevent this from occurring. If the bond lengths of the test micropiles 

(that verified the geotechnical capacity) are grouted full length with the desired pressure, 

questions may be raised as to the adequacy of micropiles that are grouted under partial 

pressure. One benefit of conducting micropile tests to typically 150 to 200 percent of the 

design load or greater is that it helps to determine if the micropiles have excess geotechnical 

capacity. Production proof tests (described in Chapter 7) may be conducted on the suspect 

micropiles. 

Because the grout is such a vital component of the micropile, close attention must be paid to 

the control and quality of the product. A grout quality control plan, which at a minimum 

should include cube or cylinder compression testing and grout density (water /cement ratio) 

testing, is discussed in Chapter 8. 

Comprehensive guides to cement grout mix design, performance, and equipment are 

provided in Littlejohn (1982), Gourlay and Carson (1982), and Houlsby (1990). Similar 

issues relating solely to the similar demands of prestressed ground anchors are summarized 

by Littlejohn and Bruce (1977).

4.3.2 Grout Equipment 

In general, any plant suitable for the mixing and pumping of fluid cementitious grouts may 

be used for the grouting of micropiles. The best quality grouts, in terms of both fluid and set 

properties, are produced by high-speed, high-shear colloidal mixers (see Figure 4-11) as 

opposed to low-speed, low-energy mixers, such as those that depend on paddles (Figure 4-

12). High speed mixers are faster and produce a homogeneous grout mix (see Section 4.3.3). 

Mixing equipment can be driven by air, diesel, or electricity, and is available in a wide range 

of capacities and sizes from many manufacturers. 

For grout placement, lower pressure injection (up to 2 MPa (290 psi)) and up to 200 

liters/min (52 gal/min)) is usually completed using constant pressure, rotary-screw type 

pumps (e.g., Moyno pumps), while higher pressure grouting, such as for Type C or D 
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Micropile Design & Construction 4-17 December 2005

micropiles, usually requires a fluctuating pressure piston or ram pump, which can deliver up 

to 8 MPa (1,160 psi) at up to 50 liters/min (13 gal/min). 

VORTEX DRUM HANY MIXER

THE ORIGINAL CHEMGROUT

COLLOIDAL MIXER

SKETCH OF LATER CHEMGROUT MIXER

CEMIX MIXERS

Left: MODEL 175 Right: MODEL 200

DOUBLE-ROTOR CONCRETE MIXER

DISCHARGE

VALVE

ROTOR ROTOR

ROTOR ROTOR

ROTOR

VORTEX DRUM DISCHARGE

VALVE

CONCRETE MIXER HANDY MIXER

ORIGINAL CHEMGROUT

COLLOIDAL MIXER

MODIFIED CHEMGROUT MIXER

CEMIX MIXER

Left MODEL 176 Right MODEL 200

DOUBLE-ROTOR COLCRETE MIXER

VORTEX DRUM HANY MIXER

THE ORIGINAL CHEMGROUT

COLLOIDAL MIXER

SKETCH OF LATER CHEMGROUT MIXER

CEMIX MIXERS

Left: MODEL 175 Right: MODEL 200

DOUBLE-ROTOR CONCRETE MIXER

DISCHARGE

VALVE

ROTOR ROTOR

ROTOR ROTOR

ROTOR

VORTEX DRUM DISCHARGE

VALVE

CONCRETE MIXER HANDY MIXER

ORIGINAL CHEMGROUT

COLLOIDAL MIXER

MODIFIED CHEMGROUT MIXER

CEMIX MIXER

Left MODEL 176 Right MODEL 200

DOUBLE-ROTOR COLCRETE MIXER

Figure 4-11. Various Types of High Speed, High Shear “Colloidal” Mixers. 
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Micropile Design & Construction 4-18 December 2005

END VIEW ELEVATION ELEVATION

MOTOR

A A

PADDLES

SECTION AA HORIZONTAL PADDLE MIXER

CHEMGROUT PADDLE MIXER

PROPELLER

FIXED IN

DRUM

PORTABLE

PROPELLER

VERTICAL PADDLE MIXER

MOVABLE

PROPELLER

END VIEW ELEVATION ELEVATION

MOTOR

A A

PADDLES

SECTION AA HORIZONTAL PADDLE MIXER

CHEMGROUT PADDLE MIXER

PROPELLER

FIXED IN

DRUM

PORTABLE

PROPELLER

VERTICAL PADDLE MIXER

MOVABLE

PROPELLER

Figure 4-12. Various Types of Paddle Mixers. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-19 December 2005

4.3.3 Grout Mixing 

During mixing, a measured volume of water is usually added to the mixer first, followed by 

cement and then aggregate or filler (if applicable). It is generally recommended that grout be 

mixed for a minimum of two minutes and that thereafter the grout is kept in continuous slow 

agitation in a holding tank prior to being pumped to the micropile. Only in cases where 

exceptionally large grout takes are anticipated should ready-mix grout be considered. The 

grout should be injected within a certain maximum time after mixing. This “safe 

workability” time should be determined on the basis of on-site tests, but is typically not in 

excess of one hour. There is no question that high speed high shear mixers produce higher 

quality, more consistent grout more quickly than do paddle mixers. Bearing in mind the 

relatively large cement particle surface area to be “wetted” (measured in “football fields” per 

single 43 kg bag), and that this must be accomplished with less than 20 liters of water, the 

intimate blending generated by the high speed mixer is essential for efficient hydration. 

Water is typically batched into the mixer by means of a calibrated tank or flow meter. 

Cement is typically batched by weight, either in bags or by bulk from a silo. Sand or fillers 

are also batched by weight from premeasured bags or more commonly, by using a gage box 

that has previously been checked and weighed. For bulk material, some method must be 

provided for controlling the quantities of components (volume or weight measurement) 

added to the mix. Admixtures are usually provided ready-proportioned to a single bag of 

cement, or the dosage can be adjusted by the mixer operator. 

4.3.4 Grout Placement Techniques 

4.3.4.1 Gravity Fill Techniques (Type A Micropiles)

For Type A micropiles, the hole is drilled to depth and it is then filled with grout and the 

reinforcement is placed. Grout should always be introduced into the drill hole through a 

tremie pipe exiting at the bottom of the hole. Grout is pumped into the bottom of the hole 

until grout of similar quality to that being injected is freely flowing from the mouth of the 

borehole. No excess pressure is applied. This type and phase of grouting is referred to as the 

primary treatment. 

The grout usually comprises a neat cement mix with w/c ratio between 0.45 and 0.50 by 

weight. Additionally, sanded mixes of up to 1:1 or 2:1 sand:cement ratio have been used in 

European practice, but they are becoming less common due to a growing trend towards the 

use of higher grouting pressures involving neat cement grouts. Gravity fill techniques tend 

now to be used only when the pile is founded in rock, or when low-capacity piles are being 

installed in stiff or hard cohesive soils, and pressure grouting is unnecessary (Bruce and 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-20 December 2005

Gemme, 1992). For sanded mixes, the w/c ratio is often extended to 0.60, assuming the 

resultant mix remains stable (i.e., bleed less than 5 percent and sand does not segregate) 

(Barley and Woodward, 1992). In the U.S., sanded mixes are only used for pregrouting, e.g., 

in karst terrains, for economic reasons. 

4.3.4.2 Pressure Grouting Through the Casing (Type B Micropiles)

For Type B micropiles, additional grout is injected under pressure after the primary grout has 

been tremied, and as the temporary casing is being withdrawn. The aim is to enhance the 

grout-to-ground bond characteristics. This operation can be limited to the load transfer 

length within the design-bearing stratum, or may be extended to the full length of the pile 

where appropriate. 

Pressure grouting is usually conducted by attaching a pressure cap to the top of the drill 

casing (this is often the drilling head itself) and injecting additional grout into the casing 

under controlled pressure. In the past, pressurization of the grout was achieved by applying 

compressed air through the grout line, since contemporary drill head details and grout pump 

technology could not accommodate the relatively viscous, sand-cement mortars. This 

method has now been rendered obsolete by the developments in pump capabilities, combined 

with the trend to use stable, neat cement grouts without sand. 

Grout pressures are measured as close to the point of injection as possible, to account for line 

losses between pump and hole. Commonly, a pressure gauge is mounted on the drill rig and 

monitored by the driller as a guide for rate of casing withdrawal during the pressurization 

phase. Alternatively, if a grouting cap is used and the casing is being extracted by means 

other than the drill rig (e.g., by hydraulic jacks), it is common to find a pressure gauge 

mounted on the cap itself. Practitioners acknowledge that there will be line losses in the 

system, but typically record the pressure indicated on the pressure gauge without the 

correction, reasoning that such losses are compensated by the extra pressure exerted by the 

grout column due to its weight in the borehole. The recommended method is to install a 

pressure gauge on the drill rig or on the line just at the cap. 

American practice is to inject additional grout at a typical average pressure between 0.5 to 1 

MPa (72 to 145 psi), with the aim of reinstating in-situ lateral soil pressures that may have 

been reduced by the drilling process and achieving permeation into coarser grained granular 

soils or fractured rocks. The maximum applied injection pressures (typically 20 kPa per 

meter (18 psi per ft) of depth in loose soils and 40 kPa per meter (36 psi per ft) of depth in 

dense soils) are dictated by the following factors: 

• need to avoid ground heave or uncontrolled loss of grout; 
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Micropile Design & Construction 4-21 December 2005

• nature of the drilling system (permissible pressures are lower for augers due to 

leakage at joints and around the flights); 

• ability of the ground to form a “seal” around the casing during its extraction and 

pressure grouting; 

• need to avoid “seizing” the casing by flash setting of the grout due to excessive 

pressure, preventing proper completion of the pile; 

• required grout-to-ground bond capacity; and 

• total micropile depth. 

The injection of grout under pressure is aimed at improving grout-to-ground skin friction, 

thus enhancing the load-carrying capacity of the micropile. Extensive experience with 

ground anchors has confirmed the effect of pressure grouting on ultimate load-holding 

capacity. 

When pressure grouting in granular soils, a certain amount of permeation and displacement 

(i.e., slight redensification or compaction occurs to “repair” the soil locally loosened during 

drilling) of loosened soils takes place. Additionally, a phenomenon known as pressure 

filtration occurs, wherein the applied grout pressure forces some of the integral mixing water 

out of the cement suspension and into the surrounding soil. This process leaves behind a 

grout of lower water content than was injected and is thus quicker setting and of higher 

strength. It also causes the formation of cake-like cement paste along the grout/soil interface 

that improves bond. In cohesive soils, some lateral displacement, compaction, or localized 

improvement of the soil can occur around the bond zone, although the improvement is 

generally less than for cohesionless soils. 

Pressure grouting also appears to cause a recompaction or redensification of the soil around 

the borehole and increases the effective diameter of the pile in the bond zone. These 

mechanisms effectively enhance grout/soil contact, leading to higher skin friction values and 

improved load/displacement performance. Such pressure grouting may also mechanically 

improve the soil between piles. 

4.3.4.3 Postgrouting (Type C and D Micropiles)

It may not be possible to exert sufficiently high grout pressures during the casing removal 

stage due to potential ground hydrofracture or leakage around the casing. In addition, some 

micropile construction methods may not use or need a temporary drill casing, and so pressure 

grouting of the Type B method is not feasible. These circumstances have led to the 

development of post-grouting techniques, whereby additional grout can be injected via 

special grout tubes some time after the placing of the primary grout (Figure 4-13). Such 

grouts are always neat cement-water mixes (for the ease of pumpability through the rubber 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-22 December 2005

valves) and may therefore have higher w/c ratios than the primary grout, being in the range 

of 0.50 to 0.75 by weight. It is reasoned that excess water from these mixes is expelled by 

pressure filtration during passage into the soil, and so the actual placed grout has a lower 

water content (and therefore higher strength). 

As described in the following paragraphs, high postgrouting pressures are typically applied, 

locally, for quite restricted periods; it may only take a few minutes to inject a sleeve. 

However, higher grout-to-ground bond capacity may, in fact, be more efficiently achieved in 

Type B micropiles, where grouting pressures are lower but are exerted over a larger area and 

a much longer period. 

Postgrouting techniques Type C and Type D micropiles are described below. 

• Type C: Neat cement grout is placed in the hole as done for Type A micropiles. 

Between 15 and 25 minutes later, and before hardening of this primary grout, similar 

grout is injected once from the head of the hole without a packer, via a 38- to 50-mm 

(1.5- to 2-in.) diameter preplaced sleeved grout pipe through the reinforcement at a 

pressure of at least 1 MPa (145 psi) (Figure 4-14). 

Type D: Neat cement grout is placed in the hole as done for Type A micropiles. 

When this primary grout has hardened, similar grout is injected via a preplaced 

sleeved grout pipe. Several phases of such injection are possible at selected horizons 

and it is typical to record pressures of 2 to 8 MPa (290 to 1,160 psi), especially at the 

beginning of each sleeve treatment when the surrounding primary grout must be 

ruptured for the first time. There is usually an interval of at least 24 hours before 

successive phases. Three or four phases of injection are not uncommon, contributing 

additional grout volumes of as much as 250 percent of the primary volume. 
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Micropile Design & Construction 4-23 December 2005

REINFORCING

STEEL

BOND ZONE

(SOIL / GROUT

INTERFACE)

CEMENT GROUT

(FIRST PHASE)

CLOSED RUBBER

SLEEVE

SLEEVED PIPE

DOUBLE

PACKER (TYP)

POST GROUT

(SECOND PHASE)

OPEN RUBBER

SLEEVE

Figure 4-13. Principle of the Tube á Manchette Method of Postgrouting Injection. 

The postgrout tube can be a separate 25- or 38-mm (1- or 1.5-in.) diameter sleeved plastic 

pipe (tube à manchette) placed together with the steel reinforcement (Figure 4-13), or it can 

be the reinforcement tube itself, suitably sleeved (Figure 4-14). In each of these cases, a 

double packer may be used to grout through the tubes from the bottom sleeve upwards. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-24 December 2005

DRILL HOLE

DIAMETER

STEEL TUBE

DOUBLE PACKER

NON RETURN VALVE

(MANCHETTE)

ANNULUS GROUT

(GROUT PRESSURE)

1st PHASE PRESSURE GROUT

2nd PHASE PRESSURE GROUT

Figure 4-14. Use of Reinforcement Tube as a Tube á Manchette Postgrouting System. 

Alternatively, pressure grouting can be conducted from the surface via a circulating-loop 

arrangement. By this method, grout is pumped around the system and the pressure is 

increased steadily by closing the pressurization value on the outlet side. At the critical 

“break out” pressure, dictated by the lateral resistance provided by the adjacent grout, the 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-25 December 2005

grout begins to flow out of the tube through one or more sleeves and enters the ground at that 

horizon. When using the loop method, it is assumed that with each successive phase of 

injection that a different sleeve opens ultimately resulting in treatment over the entire sleeved 

length (a feature guaranteed by the tube à manchette method using double packers) (Figure 4-

15). 

Figure 4-15. Circulating Loop Arrangement for Pressure Grouting (DSI, 1992). 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-26 December 2005

Where micropile structural capacity depends on the compressive strength of the grout, the 

use of low-strength bentonite primary grouts to reduce “break out” pressures should be 

avoided. 

4.3.5 Top-Off (Secondary) Grouting 

Due to slow grout seepage, bleed, or shrinkage, it is common to find that the grout level 

drops slightly prior to stiffening and hardening. In ground anchorage practice, this is simply 

rectified by topping off the hole with the lowest water-content grout practical, at some later 

phase. However, in micropile practice where a permanent casing for reinforcement of the 

upper micropile length is not used, such a cold joint should be avoided since the grout 

column should be continuous for load holding and corrosion protection reasons. Topping off 

is therefore best conducted during the stiffening phase to ensure integrity. Where particularly 

high interfacial bond stresses must be resisted between the micropile and an existing 

structure, the use of a high-strength non-shrink grout may be considered. 

4.4 REINFORCING STEEL 

4.4.1 General 

The amount of steel reinforcement placed in a micropile is determined by the loading it 

supports and the stiffness required to limit elastic displacements. Reinforcement may consist 

of a single reinforcing bar, a group of reinforcing bars, a steel pipe casing or rolled structural 

steel. In American practice, the use of a single reinforcing bar and/or a high-strength steel 

casing is commonly used. 

4.4.2 Placement of Reinforcement 

Reinforcement may be placed either prior to grouting, or placed into the grout-filled borehole 

before the temporary support (if used) is withdrawn. It must be clean of deleterious 

substances such as surface soil and mud that may contaminate the grout or coat the 

reinforcement, impairing bond development. Suitable centralizers should be firmly fixed to 

maintain the specified grout cover. Pile cages and reinforcement groups, if used, must be 

sufficiently robust to withstand the installation and grouting process and the rotation and 

withdrawal of the temporary casing. 

4.4.3 Reinforcement Types 

A description of the various types of reinforcement is provided in this section. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-27 December 2005

• Concrete Reinforcing Steel Bars (rebar): Standard reinforcing steel (Table 4-2), 

conforming to ASTM A615/AASHTO M31and ASTM A706, with yield strengths of 

420 and 520 MPa (60 and 75 ksi), is typically used. Bar sizes range in diameter from 

25 mm to 63 mm (1 to 2.5 in.). A single bar is typically used, but bar groups have 

been used. For a bar group, the individual bars can be separated by the use of spacers 

or tied to the helical reinforcement, to provide area for grout to flow between the bars 

and ensure adequate bonding between the bars and grout (Figure 4-16). Alternatively, 

bars can be bundled as long as adequate development length for the bundle is 

provided. 

Table 4-2. Dimensions, Yield, and Ultimate Strengths for Standard Reinforcing Bars. 

Steel Grade Rebar Size, mm (in) Area, mm2 (in.2) Yield Strength, kN (kip) 

19 (#6) 284 (0.44) 117 (26) 

Grade 420 22 (#7) 387 (0.60) 160 (36) (1) 

25 (#8) 510 (0.79) 211 (47) 

19 (#6) 284 (0.44) 147 (33) 

22 (#7) 387 (0.60) 200 (45) 

25 (#8) 510 (0.79) 264 (59) 

29 (#9) 645 (1.0) 334 (75 

32 (#10) 819 (1.27) 424 (95) 

36 (#11) 1006 (1.56) 520 (117) 

43 (#14) 1452 (2.25) 751 (169) 

Grade 520(2)

57 (#18) 2581 (4.0) 1335 (3000) 

Grade 550(3) 63 (2.5 in) 3168 (4.91) 1747 (393) 

Notes: (1)Grade 420 steel has yield stress of fy= 420 MPa (60 ksi) and tensile strength of fu = 620 

MPa (92 ksi) 

(2)Grade 520 steel has yield stress of fy= 520 MPa (75 ksi) and tensile strength of fu = 690 

MPa (102 ksi) 

(3)Grade 550 steel has yield stress of fy = 550 MPa (80 ksi) and tensile strength of fu = 700 

MPa (104 ksi) 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-28 December 2005

245 mm OD x 12 mm WALL

THICKNESS STEEL CASING

75 mm REINFORCING

BAR (TYP)

BAR CENTRALIZER

280 mm DIAMETER NEAT CEMENT GROUT

DRILLED HOLE

PILE

CL

120E

Figure 4-16. Multiple Bar Reinforcement with Bar Centralizer/Spacer. 

For low overhead conditions where placement of full-length bars is not feasible, mechanical 

couplers can be used. Field adjustment of individual bar lengths can be difficult if the 

coupler type requires shop fabrication. 

• Continuous-Thread Steel Bars: Steel reinforcing bars may be fabricated with a 

continuous full-length thread, such as the Dywidag Systems International (DSI) 

Threadbar or the Williams All-Thread Bar. 

The DSI Threadbar system, which is also referred to as a GEWI Threadbar (Figure 4-

17 and Table 4-3), is a common choice throughout the world for micropile 

reinforcement. The bar has a coarse pitch, continuous ribbed thread rolled on during 

production. It is available in diameters ranging from 19 mm to 63 mm (3/4 to 2-1/2 

in.) in steel conforming to ASTM A615/AASHTO M 31, with yield strengths of 420, 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-29 December 2005

520, and 550 MPa (60, 75, and 80 ksi). The size range of 32 mm to 63 mm (1-1/4 to 

2-1/2 in.) is most commonly used. Higher strength bars of steel conforming to ASTM 

A722/AASHTO M 275 with an ultimate strength of 1,035 MPa (150 ksi) are also 

available, in diameters of 26, 32, and 36 mm (1, 1-1/8, and 1-3/8 in.). 

Figure 4-17. Details of DSI Threadbar (DSI, 1993). 

Table 4-3. Dimensions and Yield Strength for DSI Threadbar. 

Steel 

Grade 

Bar 

Diameter 

mm (in) 

Area 

mm2

 (in2) 

Yield 

Strength 

kN (kip) 

Diameter 

over 

Threads 

mm (in.) 

Bar Weight 

kg/m (lbs/lf) 

32 (#10) 819 (1.27) 424 (95) 36.3 (1.43) 6.41 (4.30) 

36 (#11) 1006 (1.56) 520 (117) 40.9 (1.61) 7.91 (5.31) 

43 (#14) 1452 (2.25) 751 (169) 47.2 (1.86) 11.39 (7.65) 

520(1)

57 (#18) 2581 (4.0) 1335 (300) 63.5 (2.5) 20.24 (13.6) 

550(2) 63 (2.5in) 3168 (4.91) 1747 (393) 69.1 (2.72) 24.86 (16.7) 

Notes: (1)Grade 500 steel has yield stress of fy= 520 MPa (75 ksi) and tensile strength of fu = 690 

MPa (100 ksi). 

(2)Grade 550 steel has yield stress of fy= 552 MPa (80 ksi) and tensile strength of fu = 700 

MPa (102 ksi). 

The Williams All-Thread Bar is available in diameters ranging from 20 to 89 mm (0.8 

to 3.5 in.) in steel conforming to ASTM A615/AASHTO M 31 and from 26 to 65 mm 

(1 to 2.5 in.) in steel conforming to ASTM A722/AASHTO M 275, with an ultimate 

strength of 1,035 MPa (150 ksi). The bar has a finer thread than used on the Dywidag 

bar. 

The thread on the bars not only ensures grout-to-steel bond, but also allows the bar to 

be cut at any point and joined with a coupler to restore full tension/compression 

capacity. The continuous thread also simplifies pile-to-structure connections where 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-30 December 2005

the bar is connected to an anchor plate. A hex nut is used to connect the plate, with 

the continuous thread allowing easy adjustment of the plate location. 

• Continuous-Thread Hollow-Core Steel Bars: Steel reinforcing bars that have a 

hollow core and a continuous full-length thread include the Dwyidag, Ischebeck 

Titan, MAI International, and Chance IBO Injection Boring Rods. Typical sizes of 

hollow-core steel bars are shown in Table 4-4. It should be noted that additional sizes 

are available. Hollow-core steel bars offer the advantages of continuous thread, and 

the hollow core allows the bar to be used to drill the micropile hole. A drill bit is 

mounted on the tip of the bar, and the bar is drilled in with grout flush pumped to the 

bit through the hollow core of the bar. Alternately, an air or water flush can be used, 

with the grout placed through the bar after drilling to the final depth. 

The continuous thread allows the bar to be cut to length and coupled, and allows the 

use of a hex nut for the pile top connection. The main drawback of this type of 

reinforcement is the higher cost. 

• Steel Pipe Casing: With the trend towards micropiles that can support higher loads 

at low displacements and for the requirement to sustain lateral loads, steel-pipe 

reinforcement has become more common. Pipe reinforcement can provide significant 

steel area for support of high loading and contribution to the micropile stiffness, while 

providing high shear and reasonable bending capacity to resist the lateral loads. 

Pipe reinforcement is placed by either using the drill casing as permanent 

reinforcement, or by placing a smaller diameter permanent pipe inside the drill 

casing. Use of the drill casing for full-length reinforcement is typical only for 

micropiles founded in rock, where extraction of the casing for pressure grouting is not 

necessary. The length of the pipe sections used is dictated by the length of the drill 

mast and by the available overhead clearance. Casing sections are typically joined by 

a threaded connection, which is machined into the pipe. The reduced area of the 

threaded joint should be considered in the structural design of the pile, particularly for 

the capacity in tension and bending. Methods exist for reinforcement of the threaded 

joints that can provide a strength equivalent to the full casing section. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-31 December 2005

Table 4-4. Dimensions and Yield Strength of Common Hollow Injection Bars. 

Diameter 

Rod Size Yield 

kN (kip) 

Ultimate 

Capacity 

kN (kip) 

Inner 

mm (in.) 

Outer 

mm (in.) 

Weight 

kg/m (lb/ft) 

MAI 

R25N 150 (33.7) 200 (45) 14 (.55) 25 (1.0) 2.6 (1.74) 

MAI 

R32N 230 (51.7) 280 (63) 18.5 (.73) 32 (1.25) 3.4 (2.28) 

MAI 

R38N 400 (90) 500 (112.4) 19 (.75) 38 (1.5) 6.0 (4.0) 

MAI 

R51N 630 (141.6) 800 (179.8) 33 (1.3) 51 (2.0) 8.4 (5.64) 

IBOTITAN 

30/16 

180 (40.5) 220 (49.5) 16 (.63) 30 (1.18) 2.7 (1.8) 

IBOTITAN 

32/20 

244 (54.9) 291 (64.5) 20 (.79) 32 (1.26) 3.2 (2.15) 

IBOTITAN 

40/16 

525 (118) 660 (148.4) 16 (.63) 40 (1.57) 7.0 (4.63) 

TITAN 

73/53 970 (218.1) 1,160 (260.8) 53 (2.09) 73 (2.87) 12.3 (8.3) 

TITAN 

103/78 1,800 (404.6) 2,282 (513) 78 (3.07) 103 (4.05) 24.9 (16.7) 

Pipe in the sizes typically used for micropile construction are available in steel 

conforming to ASTM A53, A519, A252 and A106 with typical yield strengths of 241 

MPa (36 ksi). Availability of the desired pipe size may determine the grade of steel 

used. The main drawback of using these pipe grades is the relatively low yield 

strength and very high unit cost per linear meter. 

American Petroleum Institute (API) 5CT or 5L (N-80) casing may be used. The high 

yield strength of 552 MPa (80 ksi) greatly aids in the ability of the micropile to 

support high loads, and improves the strength of threaded joints machined into the 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-32 December 2005

pipe wall. The pipe is also readily available in the form of mill secondary material at 

a reasonable unit cost. The overwhelming majority of higher capacity micropiles 

installed to date in the United States have used the N-80 casing. The casing should be 

specified to meet the tensile requirements of ASTM A252, Grade 3 with a minimum 

elongation of 15 percent, except the minimum specified yield strength should be 

consistent with that used for design. A minimum of two representative coupon 

samples or mill certificates (if available) for each truckload of casing delivered to 

project should be submitted. 

Due to the high strength and typical chemical composition of the API N-80 casing, 

weldability of the casing sections requires special welding procedures. Welding 

should be performed in accordance with American Welding Society (AWS) D1.1 

“Structural Welding Code – Steel” or alternate methods or materials can be described 

on an AWS weld procedure form and that method should be approved by a welding 

specialist. Prior to welding the N-80 casing, welding procedures must be submitted 

to the owner for approval. Special welding procedures are not required for minor 

welds which do not carry structural loads. 

Pipe dimensions and yield strengths, for various grades of steel, are presented in 

Table 4-5. 

• Composite Reinforcement: For micropiles with partial length permanent drill 

casing (Type 1C, 2C and 4C), the use of a steel bar for reinforcement of the bottom 

portion of the pile is common, resulting in a composite reinforced pile (example 

shown in Figure 4-18). The reinforcing bar may be extended to the top of the 

micropile for support of tension loading. The use of varying reinforcement adds 

complexity to the pile structural analysis, with particular attention needed for the 

location and capacity of reinforcement transition. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-33 December 2005

Table 4-5. Dimensions and Yield Strength of Common Micropile Pipe Types and Sizes. 

API N-80 Pipe – Common Sizes

Casing OD 

Wall(1), mm (in.) 139.7 (5.500) 139.7 (5.500) 177.8 (7.000) 177.8 (7) 244.5 (9.625) 

Wall Thickness(1), 

mm (in.) 9.17 (0.361) 10.5 (0.415) 12.6 (0.498) 18.5 (0.73) 12.0 (0.472) 

Area(2), mm

2 

(in.2) 3760 (5.83) 4280 (6.63) 6560 (10.2) 9280 (14.4) 8760 (13.6) 

Yield Strength(3), 

kN (kip) 2,070 (466) 2,360 (530) 3,620 (814) 5,120 (1,151) 4,830 (1,086) 

ASTM A519, A106 Pipe – Common Sizes(5)

Casing OD 

Wall(1), mm (in.) 139.7 (5.50) 168.3 (6.625) 203.2 (8.00) 273.1 (10.75) - 

Wall Thickness(1), 

mm (in.) 12.7 (0.50) 12.7 (0.50) 12.7 (0.50) 16 (0.625) - 

Area(2), mm

2 

(in.2

) 5,067 (7.85) 6,208 (9.62) 7,600 (11.8) 12,850 (19.9) - 

Yield Strength(3), 

kN (kip) 1,270 (286) 1,540 (346) 1,890 (425) 3,190 (717) - 

Notes: (1)Casing outside diameter (OD) and wall thickness (t) are nominal dimensions. 

 (2)Steel area is calculated as As = (π/4) × (OD2

 - ID2). 

 (3)Nominal yield stress for API N-80 steel is Fy = 552 MPa (80 ksi). 

 (4)Nominal yield stress for ASTM A519 & A106 steel is Fy = 241 MPa (36 ksi). 

 (5)Other pipe sizes are manufactured but may not be readily available. Check for availability 

through suppliers. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-34 December 2005

TOP OF FOOTING #16 REINFORCING BAR

BAR COUPLER

176 or 211 DIA CASING

GROUT

8 EA 19 X 19

SHEAR RINGS

NOTE: ALL DIMENSIONS IN MILLIMETERS

CASED UPPER

MICROPILE

BOND LENGTH

MAX TEST LOAD – 4,500 kN

CASING: 176 or 211 mm DIA

WALL: 13 mm

BOTTOM OF

FOOTING

TOP OF DENSE

SOILS

13mm WALL

Note: 1 mm = 0.040 in and 1 kN = 0.224 kips 

Figure 4-18. Details of Example Composite High-Capacity Type 1B Micropiles. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-35 December 2005

4.5 REFERENCES 

Barley, A. D., and Woodward, M. A. (1992), “High Loading of Long Slender Minipiles,” 

Proceedings, ICE Conference on Piling European Practice and Worldwide Trends, 

Thomas Telford, London, pp. 131-136. 

Bruce, D. A. (1989), “Aspects of Minipiling Practice in the United States,” Ground 

Engineering, Vol. 22, No. 1, pp. 35-39. 

Bruce, D. A. (1992), “Recent Progress in American Pin Pile Technology,” Proceedings, 

ASCE Conference, Grouting, Soil Improvement, and Geosynthetics, New Orleans, 

Louisiana, Feb. 25-28, pp. 765-777. 

Bruce, D. A. and Gemme, R. (1992), “Current Practice in Structural Underpinning Using 

Pinpiles,” Proceedings, New York Met Section, ASCE Seminar, New York, April 21-22, 

46 pages. 

CCTG (1992), Technical Rules for the Design and Calculation of the Foundations of the 

Civil Engineering Works, Publication 62, Title V, September. 

DSI (2004), DSI Product Literature. 

Federal Highway Administration (1997), “Drilled and Grouted Micropiles: State of Practice 

Review, Volumes I, II, III, and IV.” Principal Investigators D.A. Bruce, I. Juran., 

Publication Nos. FHWA-RD-96-016. –017, -018, and –019, July. 

Gourlay and Carson, C. (1982), “The State of Grouting in the 1980’s” Grouting in 

Geotechnical Engineering, ASCE Conference, New Orleans, LA, February 10-12, pp. 

346-358. 

Houlsby, A. C. (1990), Construction and Design of Cement Grouting, John Wiley & Sons, 

442 p. 

Littlejohn, G. S. (1982), “Design of Cement Based Grouts,” Grouting in Geotechnical 

Engineering, ASCE Conference, New Orleans, LA, February 10-12, pp. 35-48. 

Littlejohn, G. S., and Bruce, D. A. (1977), Rock Anchors State-of-the-Art, Foundation 

Publications Ltd., Brentwood, Essex, England, 50 pages. 
FHWA NHI-05-039 Chapter 4 – Construction Techniques & Materials 

Micropile Design & Construction 4-36 December 2005
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-1 December 2005 

CHAPTER 5 

DESIGN OF MICROPILES FOR STRUCTURE FOUNDATIONS 

5.1 INTRODUCTION 

A typical micropile cross section used for structural foundation support is shown on Figure 5-

1. This micropile consists of an upper length reinforced with a permanent steel casing with a 

center steel reinforcing bar and a lower grouted bond length reinforced with the center 

reinforcing bar. 

The geotechnical load capacity of a micropile is sensitive to the process used during 

micropile construction, especially the techniques used for drilling the micropile shaft, 

flushing the drill cuttings, and grouting the micropile. Therefore, verification of the shaft 

resistance developed at the grout – ground interface assumed in design via micropile load 

testing is essential to confirm structure safety; load testing should therefore be considered a 

part of the design. 

The basic philosophy of micropile design differs little from that for a drilled shaft. The 

system must be capable of sustaining the anticipated loading conditions with the micropile 

components operating at safe stress levels, and with resulting displacements being within 

tolerable (or allowable) limits. For conventional drilled shafts, where the large cross 

sectional area results in high structural capacity and stiffness, the design is normally 

governed by the geotechnical load capacity, i.e., side and base resistance. Because 

micropiles have a relatively small cross sectional area, the design is usually controlled by 

structural considerations. Moreover, the high grout to ground capacities that can be 

developed using pressure grouting techniques will typically result in high geotechnical load 

capacities. 

The purpose of this chapter is to present a step-by-step generalized method for the design of 

micropiles used for structural foundations. The major steps and substeps in this design 

method are outlined in Table 5-1. Detailed information for each of these steps is presented in 

this chapter and a complete design is shown in Sample Problem No. 1. 
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Micropile Design & Construction 5-2 December 2005 

Table 5-1. Design Steps for Micropiles used for Structural Foundations.

1. Identify project requirements and evaluate micropile feasibility 

2. Review available information and perform subsurface exploration and laboratory testing 

program 

3. Develop all loading combinations 

4. Preliminary design of micropiles 

• spacing 

• length 

• cross section 

5. Evaluate allowable structural capacity of cased length 

6. Evaluate allowable structural capacity of uncased length 

7. Compare design loads to structural capacity from Steps 5 and 6 and modify structural 

section, if necessary 

8. Evaluate geotechnical capacity of micropile 

• evaluate suitable ground stratum for bond zone 

• select bond stress and calculate bond length required to resist design load 

• evaluate micropile group capacity for compression and tension (i.e., uplift) 

9. Estimate micropile group settlement 

10. Design micropile to footing connection at pile cap 

11. Develop load testing program 

12. Prepare Drawings and Specifications 

Other Design Considerations 

1. Corrosion Protection** 

2. Plunge Length 

3. End Bearing Micropiles 

4. Downdrag 

5. Lateral Loads on Single Vertical Micropiles 

6. Lateral Loads on Micropile Groups 

7. Buckling 

8. Seismic 

** Corrosion protection is a critical component of all micropile designs. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-3 December 2005 

TOP OF FOOTING

CL

MICROPILE

REINFORCING BAR

BOTTOM OF FOOTING

STEEL CASING

GROUT

CENTRALIZER

CASING PLUNGE

LENGTH

PRESSURE

 GROUTED

 MICROPILE

 BOND LENGTH

CASED UPPER

MICROPILE

 LENGTH

TOP OF DENSE

SOIL / ROCK

PILE CAP ANCHORAGE

GROUTED BOND ZONE

DIAMETER (DIA BOND)

Figure 5-1. Detail of a Composite Reinforced Micropile. 

5.2 STEP 1: EVALUATE PROJECT REQUIREMENTS AND MICROPILE 

FEASIBILITY 

It is essential to systematically consider various foundation types and to select the optimum 

alternative based on the superstructure requirements, the subsurface conditions, and 

foundation cost. Foundation types may include shallow foundations consisting of spread 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-4 December 2005 

footing or mat foundations with or without ground improvement; or deep foundations 

consisting of driven piles, drilled shafts, or micropiles. 

The feasibility of using spread footings for foundation support should be considered in any 

foundation selection process. Spread footings are generally more economical than deep 

foundations; spread footings in conjunction with ground improvement techniques should also 

be considered. Deep foundations should not be used indiscriminately for all subsurface 

conditions and for all structures. Feasibility evaluations considering shallow foundations, 

driven piles, and drilled shafts is provided in FHWA NHI-05-042 (2005). 

Where deep foundations have been judged to be the most appropriate foundation alternative 

(as compared to shallow foundations), micropiles should be compared to driven piles and 

drilled shafts. On some projects, construction of driven piles and/or drilled shafts may be 

feasible though subsurface conditions or other project constraints will increase cost. Cost 

effectiveness of micropiles should be investigated for such projects. Bidding of alternative 

foundation systems may provide the most cost-effective option. 

In assessing micropile feasibility for a specific project, micropiles will most often be 

compared to drilled shafts and/or driven piles. In many cases, either driven piles or drilled 

shafts will be more cost-effective than micropiles, therefore the cost-effective use of 

micropiles will be limited to projects with specific technical constraints that make the 

construction of drilled shafts or driven piles difficult to impossible. In general, micropiles 

may be cost-effective at project locations where: 

• subsurface conditions would make the installation of driven piles or drilled shafts 

difficult (and expensive) such as ground containing significant amounts of boulders, 

cobbles, or other large debris; 

• difficult access or limited overhead clearance is available for constructing deep 

foundations (e.g., working inside existing structures or underneath bridge decks); 

• subsurface voids may exist (e.g., potentially collapsible ground, karstic formations, 

underground mines, etc.); 

• vibration limits would preclude the use of conventional deep foundation installation 

equipment; or 

• underpinning or retrofitting of existing foundations requires strict control of 

vibrations or settlements. 

It is noted, however, that micropile capacities continue to increase as additional experience 

with this technology is obtained. Currently, micropiles in rock have been tested to ultimate 

loads as high as 4,500 kN (1,000 kips). For high capacity micropiles, the cost per unit of 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-5 December 2005 

capacity may be comparable to that for driven piles. A process to evaluate micropile project 

costs is described in Chapter 10. The user of this manual is also specifically referred to 

FHWA NHI-05-042 (2005) for information on developing cost per unit capacity for driven 

piles. 

5.3 STEP 2: REVIEW AVAILABLE INFORMATION AND GEOTECHNICAL 

DATA 

The subsurface exploration, laboratory testing, and evaluation of geotechnical design 

parameters for the design of micropiles used for structural foundation support is similar to 

that for either driven piles (see FHWA NHI-05-042 (2005) or drilled shafts (see FHWA-HI99-025, 1999). Specific elements that should precede the actual exploration program include 

a search and review of published and unpublished information at and near the site, a visual 

site inspection, and design of the subsurface exploration program. For guidance regarding 

the planning and conduct of subsurface exploration programs, refer to AASHTO Manual on 

Subsurface Investigations (1988), FHWA NHI-01-031 Manual on Subsurface Investigations 

(2001), and Geotechnical Engineering Circular 5 (GEC 5), Evaluation of Soil and Rock 

Properties (2002). 

As a minimum, the information gathering and subsurface exploration and laboratory testing 

program should obtain information to analyze foundation stability and settlement with 

respect to: 

• regional and local geology; 

• discussion of site history which may include information on mining, previous 

excavations, problems with previous construction, construction methods used for 

adjacent utilities or basements or foundations, possible occurrence of potentially 

contaminated materials, etc.; 

• logs of soil borings that includes description and classification of the soil strata 

encountered, unit weights, moisture contents, standard penetration tests (SPT) or cone 

penetrometer test (CPT) values, and description of groundwater conditions; 

• if rock is encountered, logs with rock classifications, penetration rates, degree of 

weathering and fracturing, recovery and RQD measurements, and driller’s 

observations should be provided; 

• laboratory testing results including Atterberg limits information (for silty or clayey 

soils) and grain size analyses; 

• a subsurface soil profile along the alignment of the structure developed from the soil 

boring information presenting soil type, ground water elevations, and SPT values as a 

minimum; 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-6 December 2005 

• estimated soil and/or rock shear strength and compressibility parameters; 

• determination and discussion of the presence of hazardous, contaminated, and/or 

corrosive conditions, if applicable; indicators of corrosive conditions include low soil 

resistivity, the presence of lead, sulfates, and chlorides, and observations of corrosion 

of existing site features; and 

• project-specific considerations including, for example, liquefiable soil layers, 

expansive or dispersive soil deposits, underground voids from solution weathering or 

mining activity, etc. 

Some minimum guidelines for boring spacing and depth are provided in Table 5-2. This 

table should be used only as a first step in estimating the number of borings for a particular 

design, as actual boring spacing and depth will depend upon the project type, geologic 

environment, and variability encountered during the field investigation. 

Table 5-2. Guidelines for Minimum Number of Investigation Points and Depth of 

Investigation (Modified after FHWA-IF-02-034, 2002). 

Application 

Minimum Number of 

Investigation Points and 

Location of Investigation Points 

Minimum Depth of Investigation 

Deep 

Foundations 

(Micropiles for 

Structural 

Support) 

For substructure (e.g., bridge 

piers or abutments) widths less 

than or equal to 30 m (100 ft), a 

minimum of one investigation 

point per substructure. For 

substructure widths greater than 

30 m (100 ft), a minimum of 

two investigation points per 

substructure. Additional 

investigation points should be 

provided if erratic subsurface 

conditions are encountered. 

In soil, depth of investigation should extend below the 

anticipated micropile tip elevation a minimum of 6 m (20 ft), 

or a minimum of two times the maximum micropile group 

dimension, whichever is deeper. All borings should extend 

through unsuitable strata such as unconsolidated fill, peat, 

highly organic materials, soft fine-grained soils, and loose 

coarse-grained soils to reach hard or dense materials. 

For micropiles bearing on rock, a minimum of 3 m (10 ft) of 

rock core shall be obtained at each investigation point location 

to verify that the boring has not terminated on a boulder. 

For micropiles supported on or extending into rock, a 

minimum of 3 m (10 ft) of rock core, or a length of rock core 

equal to at least three times the micropile diameter for isolated 

micropiles or two times the maximum micropile group 

dimension, whichever is greater, shall be extended below the 

anticipated micropile tip elevation to determine the physical 

characteristics of rock within the zone of foundation 

influence. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-7 December 2005 

In areas underlain by heterogeneous soil deposits and/or rock formations, it will likely be 

necessary to exceed the minimum guidelines provided in Table 5-2 to evaluate variations in 

soil and/or rock types and to assess consistency across the site area. For situations where 

micropiles will be installed in karstic formations, it may be necessary to advance a boring at 

the location of each micropile. Where battered micropiles may be used, the location of the 

micropile bond length will be offset from the footing location. Borings should be located so 

that information on bond zone soils is obtained. 

In general, all geotechnical data interpretations should be provided. The basic character and 

extent of the soil strata determined from the geotechnical investigation can be verified during 

pile installation by monitoring and logging of the penetration rates, drilling action, flush 

return, and soil cuttings. 

5.4 STEP 3: DEVELOP APPLICABLE LOADING COMBINATIONS

For state DOT projects, reference will typically be made to AASHTO Standard Specification 

for Highway Bridges (when using allowable stress design (ASD) or load factor design 

(LFD)) or to AASHTO LRFD Bridge Design Specifications (when using load and resistance 

factor design) for loadings, load combinations, and load terminology. Under any of these 

design approaches, various individual loads will be added together to develop a series of load 

combinations to be checked as part of the design. The required loads for consideration in 

design (e.g., maximum compression load, maximum tension load, and maximum transverse 

and longitudinal overturning moments) will usually be provided by the structural engineer as 

part of a design criteria package. Other loading cases that may be considered include lateral 

loads, seismic loads, and loads due to downdrag. 

For most applications, it is sufficiently accurate to assume that the foundation cap is perfectly 

rigid, i.e., the cap is free to rotate about all axes but will not bend. With this, the so-called 

“rigid cap” method can be used to distribute axial forces resulting from overturning moments 

to individual foundation elements. However, for large pile groups, relatively thin pile caps, 

and/or widely spaced foundation elements, a more sophisticated soil-structure interaction 

analysis may be required. Moreover, since micropiles are often used with pre-existing 

foundation elements, the potential differences in the stiffness of the elements may require 

that such sophisticated analyses be used. Additional discussion on available soil-structure 

interaction analysis methods is provided in Section 5.19.3. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-8 December 2005 

5.5 STEP 4: PRELIMINARY DESIGN OF MICROPILES 

5.5.1 Selection of Micropile Spacing

In all cases, the center-to-center spacing between individual micropiles should be at least 760 

mm (30 in.) or 3 micropile diameters, whichever is greater. This spacing criterion was 

originally developed for driven piles and it allows for potential deviations in drilling over 

significant depths and reduces group effects between adjacent micropiles 

The spacing of micropiles for structural foundation support will also depend on the specific 

application. For example, the spacing of micropiles used to improve (or retrofit) an existing 

foundation (or footing) will be based on the condition of the existing footing, access to the 

existing footing, and the magnitude of the loads that need to be resisted by the micropiles. 

Where relatively small design loads are involved (e.g. less than 450 kN (100 kips)), it may be 

feasible to drill and install micropiles through the existing foundation and still develop 

sufficient load transfer between the micropiles and the existing foundation to provide 

adequate capacity. Where larger loads are required or where the existing foundation has 

deteriorated, a new footing may need to be constructed around the existing footing and 

positively connected to the existing footing using steel dowels or other devices to provide the 

required capacity. 

Micropile spacing and layout can either be selected by the Owner and included in the Plans 

or the Specifications may allow for the Contractor to select the number of micropiles and 

layout. The latter provides the Contractor with the flexibility to consider whether fewer 

higher capacity micropiles may be used as compared to a baseline configuration with a 

greater number of lower capacity micropiles. 

5.5.2 Selection of Micropile Length

The total length of an individual micropile will be selected such that the required 

geotechnical capacity is developed by skin friction (or side resistance) between the grout and 

the ground over a suitable length in an appropriate stratum. The evaluation of this suitable 

length is described in Section 5.9. 

The total length will also be controlled by required penetration depths to resist downdrag and 

uplift forces and to provide additional lateral resistance where scour is a consideration or 

where other sources of lateral load need to be considered in the design. 

The maximum length of a micropile that can be achieved using common track-drilling 

equipment is greater than 90 m (300 ft). Typically, however, micropiles of such lengths 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-9 December 2005 

would be very expensive and a practical limit for most projects may be on the order of 30 m 

(100 ft). 

5.5.3 Selection of Micropile Cross Section

To carry required axial loads, it is not uncommon for up to one half of the cross sectional 

area of the micropile to comprise steel casing and/or steel reinforcing rod (s). The use of 

common casing sizes is preferred to avoid delays associated with material availability. 

Currently, the most common casing sizes in the U.S. are 141 mm (5-1/2 in.), 178 mm (7 in.), 

and 245 mm (9-5/8 in.) with a nominal yield stress of 552 MPa (80 ksi), with the 178 mm 

casing being the most common. These sizes refer to the outside diameter of the casing. 

Tables 4-2, 4-3, 4-4, and 4-5 provide material properties for common micropile 

reinforcement. 

In general, it is preferable to install fewer higher capacity micropiles as compared to a larger 

number of lower capacity micropiles to resist a given set of foundation loads. With this 

approach, less total drilling is required thus reducing overall costs. Also, it is more efficient 

to resist lateral loads, minimize lateral deflections, and/or achieve relatively high axial load 

capacities using steel casing as compared to steel reinforcing bars alone. For example, a 178 

mm (7-in.) diameter steel casing has about 2.5 times as much steel area as a 2.25-in. diameter 

reinforcing bar. Therefore, for allowable axial loads greater than approximately 900 kN (200 

kips), it is likely that steel casing would be required as compared to a micropile only 

reinforced with steel reinforcing bars. 

The bond between the cement grout and the reinforcing steel bar allows the composite action 

of the micropile, and is the mechanism for transfer of the pile load from the reinforcing steel 

to the ground. Typical ultimate bond values range from 1.0 to 1.75 MPa (145 to 254 psi) for 

smooth bars and pipe, and 2.0 to 3.5 MPa (290 to 508 psi) for deformed bars (ACI 318). 

Flaky rust on bars lowers the bond strength, but wiping off the loosest rust produces a 

rougher surface which develops a bond equal to or greater than the unrusted bar. The loose 

powdery rust appearing on bars after short exposures does not have a significant effect on 

grout-reinforcing bar bond. 

In the majority of cases, grout-to-steel bond does not govern the pile design. In general, the 

allowable load of a micropile is controlled by the structural strength of the micropile cross 

section. The procedure to calculate allowable loads in a micropile based on structural 

considerations is provided as part of Design Step 5 and 6. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-10 December 2005 

5.5.4 Selection of Micropile Type

A description of the various micropile types (Type A, B, C, and D) is provided in Chapter 4 

of this manual. The selection of the micropile type should be left to the discretion of the 

Contractor. As part of the request for bid, however, the Owner should require that the 

Contractor provide information on their proposed methods of drilling and grouting. Based on 

previous project experience, the Owner may wish to disallow certain drilling techniques 

based on project-specific constraints. For example, the need to limit surface ground 

movements for a project involving sandy ground may preclude the use of certain drilling 

techniques known to increase the potential for soil caving. The Owner should provide 

specific performance criteria (e.g., movements of structures) as part of the bid package so 

that the Contractor can select an appropriate industry-accepted drilling and grouting 

procedure. 

5.6 STEP 5: STRUCTURAL DESIGN OF MICROPILE CASED LENGTH 

1) Evaluate Allowable Compression Load for Cased Length 

The allowable compression load for the cased length of a micropile is given as: 

[ ( )] c allowable c grout Agrout Fy steel Abar Aca g P f sin

'

− = 0.4 − × +0.47 − + (Eq. 5-1) 

where 

Pc-allowable = allowable compression load; 

f'c = unconfined compressive strength of grout (typically a 28-day strength); 

Agrout = area of grout in micropile cross section (inside casing only, discount 

 grout outside the casing); 

Fy-steel = yield stress of steel; 

Abar = cross sectional area of steel reinforcing bar (if used); and 

Acasing = cross sectional area of steel casing. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-11 December 2005 

Strain Compatibility between Grout, Casing, and Reinforcing Rod

Strain compatibility under compression loads is considered for the steel components 

and grout by limiting allowable compressive stresses to the minimum allowable for 

any individual component (i.e., steel casing, steel reinforcement, or grout). 

Therefore, the maximum yield stress of steel to be used in Eq. 5-1 is the minimum 

of: (1) yield stress of casing; (2) yield stress of steel reinforcing rod; and (3) 

maximum stress based on considerations of grout failure. Additional explanation for 

the maximum stress based on grout failure is provided below. 

According to Section 8.16.2.3 of AASHTO (2002), “the maximum usable strain at 

the extreme concrete compression fiber is equal to 0.003”. Therefore, if the grout is 

limited to a compression strain of 0.003, the steel components must also be limited to 

this value. The stress in the steel at this strain level is equal to the Young’s modulus 

of steel, E, multiplied by strain (i.e., 0.003). For a typical E for steel of 200,000 MPa 

(29,000 ksi), the allowable steel yield stress is then 200,000 MPa × 0.003 = 600 

MPa (87 ksi). Therefore, the maximum stress based on considerations of grout 

failure is 600 MPa (87 ksi). 

For example, for a micropile with a casing yield strength of 241 MPa (36 ksi), a 

reinforcing rod yield strength of 520 MPa (75 ksi), and a grout failure controlled 

maximum stress of 600 MPa (87 ksi), a value of 241 MPa (36 ksi) would be used for 

the term Fy-steel in Eq. 5-1. 

An example of the evaluation of Pc-allowable is described for the micropile shown in 

Figure 5-2. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-12 December 2005 

Figure 5-2 Example Micropile Detail. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-13 December 2005 

Effect of Coupled Sections on Compression Capacity

As previously discussed in Chapter 3, steel reinforcing bars and casing are installed 

in coupled sections. For installation of micropiles in very low overhead clearance 

conditions, the length of individual casing sections may be 1 meter or shorter. 

Reinforcing bar couplers can typically provide a minimum axial capacity of 125 

percent of the intact reinforcing bar yield strength, therefore the strength properties 

of an intact reinforcing bar can be used. 

A common method for coupling individual casing lengths for micropiles is to 

machine a thread into the wall of the casing at the section ends. If the joint is 

properly designed and if the casing is filled with grout (as is commonly done), the 

joint can provide compressive capacity approximately equivalent to the strength of 

the full intact casing section. The grout provides support, preventing the male half of 

the joint from deforming inward. 

From a practical standpoint, the strength of coupled sections of reinforcing bars 

and/or casing sections is confirmed via proof testing and verification testing. 

Allowance for Corrosion

For evaluation of the allowable compression capacity of the cased length, the outside 

diameter of the steel casing is reduced to account for assumed losses in section 

resulting from corrosion over the design life. The specific losses depend on the 

agressivity of the ground in which the micropile is constructed. It is noted here, that 

the cross sectional area of the reinforcing bar is not reduced (for purposes of 

( )2 2 2

sin

2

2 2 2

sin

2 2

sin

5.5 . 6.63 . 17.13 . 4 ( ) 4

(5.5 . 4.67 . ) 6.63 . 4

2 5.5 . 2(0.415 .) 4.67

( ) 4

A D A in in in

A in in in

ID OD t in in in

A OD ID

grout drillhole ca g

ca g

w

ca g

= − = − =

= − =

= − = − =

= −

π π

π

π

( )

F ( ) ksi ksi ksi

F F grout crushing strength

y ca g

y ca g y ca g

min 80 ,87 80

min ,

sin

sin sin

= =

=

−

− −

P ksi in ksi in kips c allowable 0.4(4 )(17.13 . ) 0.47(80 )(6.63 . ) 276 2 2 ∴ − = + =

[ ] c allowable c grout Agrout Fy ca g Aca g P f sin sin

' 0.4 0.47 − = − × + −
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-14 December 2005 

calculating allowable compression capacity). Typical reinforcement coatings (e.g., 

epoxy-coating) and minimum specified grout cover thickness are selected to provide 

sufficient protection against corrosion. 

Detailed information on corrosion protection for micropiles including recommended 

losses due to corrosion for micropiles loaded in compression is provided in Section 

5.14. 

Buckling of Cased Length of Micropile

In some cases, the cased length of the micropile may be formed within, for example, 

very weak ground or in a karstic zone. In such cases, the allowable compression 

load calculated above may need to be reduced to account for bucking over this length 

of the micropile. Section 5.20 provides information on project conditions which may 

require that buckling be considered and structural calculations for evaluating the 

allowable compression load of the cased length accounting for micropile buckling. 

2) Evaluate Allowable Tension Load for Cased Length

For projects in which the micropiles will be subject to tensile loads, the allowable 

tension load Pt-allowable for the cased length of a micropile can be calculated as: 

( ) Pt allowable 55Fy steel Abar Aca sin g − =0. − × + (Eq. 5-2) 

where Fy-steel is the minimum yield stress of the bar and casing. 

Allowance for Corrosion

For aggressive ground conditions (as defined in Section 5.14), it may be 

conservatively assumed that the steel casing is not effective in carrying tensile loads, 

i.e., assume Acasing = 0 in Eq. 5-2. In this case, the central reinforcing steel should be 

designed to carry the entire tension design load. Detailed information on corrosion 

protection for micropiles loaded in tension is provided in Section 5.14. 

Effect of Coupled Sections on Tensile Capacity

Unlike compressive stresses, tension stresses have a greater impact on the integrity 

of the casing at the joint location primarily because of the reduced thickness of the 

casing over the length of the threaded area. Currently, no specific testing standard 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-15 December 2005 

exists for evaluating the tension capacity of a threaded casing joint appropriate for 

micropile applications. 

If tension loads greater than 25 percent of the allowable tension load on the intact 

casing are proposed to be resisted by a casing with flush joint threaded connections, 

the Owner should require the contractor to provide data demonstrating the adequacy 

of the proposed joint detail. Since a common testing method does not exist, testing 

procedures and test data will need to be reviewed by a qualified engineer. As 

projects involving micropiles subject to relatively large tensile forces become more 

commonplace, a means to evaluate allowable tensile stresses for threaded joints will 

become necessary, especially since many casing providers in the U.S. have a slightly 

different proprietary threading detail. 

3) Evaluate Combined Axial Compression and Bending of Cased Length

The application of lateral loads or overturning moments (from the superstructure) at 

the ground surface create bending stresses in the micropile. These bending stresses 

cause additional compressive stresses (above those from vertical compression loads 

alone) in the micropile. Allowable stresses in the cased length of the micropile are 

evaluated using a combined stress evaluation. 

As for other deep foundation elements subject to lateral loads and/or overturning 

moments, the bending moments in the pile can be evaluated using a laterally loaded 

pile analysis program such as LPILE (Reese et al., 2005). With these analyses, the 

maximum bending moment in the pile, Mmax, is calculated and used in the combined 

stress evaluation. 

The details of performing laterally loaded micropile analyses are provided in Section 

5.18. Herein, it is assumed that Mmax has been evaluated and the structural capacity 

of the cased length can be evaluated. 

The combined stress evaluation is based on the method described in Section 10.36 of 

AASHTO (2002) for structural steel sections. The design check for combined 

stresses (appropriate for micropiles) is 

1.0

1 '

≤















 −

+

b

e

a

b

a

a

F

F

f

f

F

f (Eq. 5-3) 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-16 December 2005 

where 

• fa is the axial stress = Pc/Acasing; 

• fb is the bending stress = Mmax/S where S is the elastic section modulus of 

the steel casing; 

• Fa is the allowable axial stress that would be permitted if axial force alone 

existed = 0.47 Fy-casing (see AASHTO Table 10.32.1.A); 

• Fb = is the allowable bending stress that would be permitted if bending 

moment alone existed = 0.55 Fy-casing (see AASHTO Table 10.32.1.A) ; and 

• F′e is the Euler buckling stress. 

The contribution of a central reinforcing bar to bending strength is small compared to 

that of the casing, hence its effects on bending strength are ignored in Eq. 5-3. In Eq. 

5-3, it is conservatively assumed that the maximum axial compression load, Pc, is 

carried by the steel casing only and the yield stress of the steel casing is used. 

Section properties required for the analysis are calculated as: 

( ) 4

2 2

sin Aca g = OD − ID π (Eq. 5-4a) 

( ) / 2

sin

OD

I

S ca g = (Eq. 5-4b) 

( ) 4 4

sin 64

Ica g = OD − ID π (Eq. 5-4c) 

The Euler buckling stress is calculated as: 

( )2

2

'

FS Kl r

E Fe

π = (Eq. 5-5) 

where 

• E = elastic modulus of the steel casing (typically assumed to be 200,000 

MPa (29,000 ksi)); 

• FS is a factor of safety equal to 2.12; 

• K = effective length factor (assumed equal to 1.0); 

• L = unsupported length of the micropile; and 

• r = radius of gyration of the steel casing = (Icasing/Acasing)

1/2. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-17 December 2005 

The effective length factor, K, depends on the rotational restraint at the ends of the 

micropile and the means available to resist lateral movements. This value is 

typically assumed equal to 1.0 for micropile designs. 

The assumption that the entire axial load is carried by the steel casing is 

conservative. Richards and Rothbauer (2004) proposed a combined stress check that 

can account for the contribution of the grout inside the casing to compression 

capacity. This method assumes that buckling potential is negligible. The Richards 

and Rothbauer combined stress check can be written as: 

1.0 max + ≤

c−allowable allowable

c

M

M

P

P (Eq. 5-6) 

where 

• Pc = maximum axial compression load; 

• Pc-allowable is determined from Eq. 5-1; 

• Mmax = maximum bending moment in the micropile; and 

• Mallowable = Fb (=0.55 Fy-casing) × S. 

More advanced methods which consider composite action between the steel casing 

and the grout inside the casing in carrying these axial loads could be used, but are 

beyond the scope of this manual. 

5.7 STEP 6: STRUCTURAL DESIGN OF MICROPILE UNCASED LENGTH 

The allowable compression load for the uncased length of a micropile is given as: 

( ) c allowable c Agrout Fy bar Abar P − = 0.4 f × +0.47 − × ' (Eq. 5-7) 

For the uncased portion of the pile, the reinforcing bar yield stress used in the 

calculations in compression is assumed to not exceed 600 MPa (87 ksi) (i.e., to 

prevent grout crushing at an assumed strain of 0.003 unless data is provided 

demonstrating that the confined grout can sustain higher strain levels without 

crushing). 

The allowable tension load for the uncased length of a micropile is given as: 

Pt −allowable = 55Fy−bar × Abar 0 (Eq. 5-8) .
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-18 December 2005 

In Eq. 5-8, the actual yield stress of the bar is used. 

It is noted that a combined stress evaluation (see Step 5 Part 3) is not performed for 

the uncased length since micropiles are designed so that bending stresses are 

negligible within the uncased portion of the micropile. In other words, the steel 

casing will be placed to a sufficient depth so that bending moments below that depth 

are negligible. 

5.8 STEP 7: REVISE MICROPILE DESIGN 

Based on the calculations performed in Steps 5 and 6, the micropile cross section 

should be modified if the allowable compression or tension load (for either the cased 

or uncased length) is not sufficient to carry the compression or tension design loads 

provided as part of Step 3. Possible modifications include using more micropiles, 

increasing the size of the drill hole, using a larger diameter reinforcing bar, replacing 

a single reinforcing bar with two bars, and/or increasing the steel area of the casing. 

5.9 STEP 8. EVALUATE GEOTECHNICAL CAPACITY OF MICROPILE 

5.9.1 Establish Stratum for Bond Zone 

The maximum compression and tension loads applied at the top of the micropile 

must be resisted through grout to ground bond over a specific length of the 

micropile. This length is referred to as the bond zone or bond length. This length 

can be formed in most soil and rock strata with the major differences being in the 

grout to ground bond strength that can be developed in a given ground type. The 

objective for design is to evaluate the length of this bond zone required to resist the 

applied tension and compression loads with a prescribed factor of safety (discussed 

subsequently). 

As part of this design step, all borings should be reviewed to identify strata 

appropriate for the micropile bond zone and to identify significant variations in 

subsurface conditions. Like ground anchors, certain soil deposits are not generally 

suitable as the location for the micropile bond zone, including (1) organic soils; (2) 

cohesive soils with an average liquidity index greater than 0.2; (3) cohesive soils 

with an average liquid limit greater than 50; and (4) cohesive soils with an average 

plastic index greater than 20. Micropiles installed in these deposits may be 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-19 December 2005 

susceptible to excessive creep deformations at testing and working loads. If used, 

however, for the bond zone, comprehensive testing is recommended and higher 

factors of safety for geotechnical capacity should be used, as discussed subsequently. 

5.9.2 Select Ultimate Bond Stress and Calculate Bond Length 

The allowable geotechnical bond capacity, PG-allowable, is calculated as: 

b b

bond

G allowable D L

FS

P − = ×π × ×

α

 (Eq. 5-9) 

where: 

αbond = grout to ground ultimate bond strength; 

FS = factor of safety applied to the ultimate bond strength; 

Db = diameter of the drill hole; and 

Lb = bond length 

In most cases, Eq. 5-9 will be used to calculate the estimated bond length to resist the 

maximum compression load and/or maximum tension (i.e., uplift) load based on load 

information provided as part of Step 3. To this end, Eq. 5-9 can be rearranged as: 

bond b

G allowable

b D

P FS

L

× ×

× = −

α π

 (Eq. 5-10) 

where, for Eq. 5-10, PG-allowable is equal to the maximum compression or tension load 

for design. 

Table 5-3 provides guidance for estimating the values for grout-to-ground ultimate 

bond strengths. The table includes ranges for the four methods of grouting (Type A, 

Type B, Type C, and Type D) in a variety of ground conditions. 

For most micropile projects, the contract documents will provide a minimum bond 

length. This bond length will be based on the evaluation provided in Eq. 5-10. 

Unless the design engineer has previous experience in similar ground, values no 

greater than average values (i.e., middle of range reported) for αbond from Table 5-3 

should be used. The design engineer may wish to consider lower bound values 

where granular materials are loose or for medium to high plasticity cohesive 

materials. Although the specific type of micropile (i.e., Type A, B, C, or D) will be 

selected by the Contractor, the design engineer should assume a Type A micropile 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-20 December 2005 

will be constructed for microple bond zones in rock and a Type B micropile will be 

constructed for bond zones in soil. 

Ranges of values provided in Table 5-3 and additional information on estimating 

grout-to-ground bond capacities is available in the following publications: 

• “GEC No. 4, Ground Anchors and Anchored Structures”, FHWA Report No. 

FHWA-IF-99-015, (1999).

• “Post-Tensioning Institute (PTI) Recommendations for Prestressed Rock and 

Soil Anchors”, (2004). 

• “Construction, Carrying Behavior, and Creep Characteristics of Ground 

Anchors,” H. Ostermayer, Conference on Diaphragm Walls and Anchorages, 

Institute of Civil Engineers, London, (1975). 

• “Ground Control and Improvement” by P.P. Xanthakos, L.W. Abramson, 

and D.A. Bruce, (1994). 

• “Drilled and Grouted Micropiles State-of-the-Practice Review”, FHWA 

Report Nos. RD-96-016/017/018/019; Volumes I – IV, (1997). 

• “Tiebacks”, FHWA Report No. FHWA/RD-82/047, (1982). 

• “Permanent Ground Anchors”, FHWA Report No. FHWA-DP-68-1R, 

(1988). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-21 December 2005 

Table 5-3. Summary of Typical αbond (Grout-to-Ground Bond) Values 

for Micropile Design. 

Grout-to-Ground Bond Ultimate Strengths, kPa (psi) 

Soil / Rock Description 

Type A Type B Type C Type D 

Silt & Clay (some sand) 

 (soft, medium plastic) 

35-70 

(5-10) 

35-95 

(5-14) 

50-120 

(5-17.5) 

50-145 

(5-21) 

Silt & Clay (some sand) 

 (stiff, dense to very dense) 

50-120 

(5-17.5) 

70-190 

(10-27.5) 

95-190 

(14-27.5) 

95-190 

(14-27.5) 

Sand (some silt) 

(fine, loose-medium dense) 

70-145 

(10-21) 

70-190 

(10-27.5) 

95-190 

(14-27.5) 

95- 240 

(14-35) 

Sand (some silt, gravel) 

(fine-coarse, med.-very dense) 

95-215 

(14-31) 

120-360 

(17.5-52) 

145-360 

(21-52) 

145-385 

(21-56) 

Gravel (some sand) 

(medium-very dense) 

95-265 

(14-38.5) 

120-360 

(17.5-52) 

145-360 

(21-52) 

145-385 

(21-56) 

Glacial Till (silt, sand, gravel) 

 (medium-very dense, cemented) 

95-190 

(14-27.5) 

95-310 

(14-45) 

120-310 

(17.5-45) 

120-335 

(17.5-48.5) 

Soft Shales (fresh-moderate 

fracturing, little to no weathering) 

205-550 

(30-80) N/A N/A N/A 

Slates and Hard Shales (freshmoderate fracturing, little to no 

weathering) 

515-1,380 

(75-200) N/A N/A N/A 

Limestone (fresh-moderate 

fracturing, little to no weathering) 

1,035-2,070 

(150-300) N/A N/A N/A 

Sandstone (fresh-moderate 

fracturing, little to no weathering) 

520-1,725 

(75.5-250) N/A N/A N/A 

Granite and Basalt (freshmoderate fracturing, little to no 

weathering) 

1,380-4,200 

(200-609) N/A N/A N/A 

Type A: Gravity grout only 

 Type B: Pressure grouted through the casing during casing withdrawal 

 Type C: Primary grout placed under gravity head, then one phase of secondary “global” pressure grouting 

 Type D: Primary grout placed under gravity head, then one or more phases of secondary “global” pressure 

grouting 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-22 December 2005 

For all highway projects, some amount of site-specific load testing of micropiles 

must be performed and the scope of this load testing is used to define the factor of 

safety applied to the ultimate bond strength for design. Herein, a factor of safety of 

2.0 is recommended provided the following load testing is performed: 

• At least one ultimate or verification test is conducted prior to beginning 

production micropile installation, and then one or more additional ultimate 

or verification tests must be conducted in each significantly different 

ground type encountered as construction proceeds. A larger number of 

ultimate, or verification, tests may be specified for larger projects. 

• During installation of production micropiles, proof testing must be 

conducted on a specified number of the total production piles installed. In 

general, proof tests may be performed on 5 percent of production 

micropiles. Specific proof testing requirements are discussed in Chapter 

7. 

For projects in which the micropile bond zone is formed in potentially creeping soils, 

high plasticity soils, weak rock, or any other ground type considered to be marginal 

or for which previous experience in similar ground is limited, a factor of safety value 

of 2.5 should be used to estimate the bond length and as the basis for the maximum 

load in an ultimate or verification load test. For micropiles installed in soils 

susceptible to creep, load testing will include measuring micropile deformations 

during an extended period of time at one or more test loads. The measured 

movement is compared to a maximum allowable creep movement (see Chapter 7 for 

details on sustained load (creep) testing). 

5.9.3 Evaluate Micropile Group Compression Capacity 

Micropile Groups in Cohesive Soils 

The efficiency of a micropile group installed in cohesive soils is a function of the 

center-to-center spacing of the micropiles, s, and contact condition between the 

bottom of the micropile footing cap and the soil near the ground surface (see Table 

5-4). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-23 December 2005 

Table 5-4. Efficiency Factors for Micropile Groups in Cohesive Soils. 

Case Efficiency Factor, η

If cap is in firm contact with the ground 1.0 

If cap is not in firm contact with the ground 

and the ground is stiff (i.e., undrained shear 

strength of the soil is greater than 95 kPa (1 

ton per square ft (tsf)) 

1.0 

If the cap is not in firm contact with the 

ground and the ground is relatively soft 

(i.e., undrained shear strength of the soil is 

less than 95 kPa (1 tsf)) or is disturbed 

• s = 2.5 Db

• s = 3.0 Db

• s = 6.0 Db

• 3.0 Db < s < 6.0 Db 

0.65 

0.70 

1.0 

Interpolate between 0.70 and 1.0 

At small micropiles spacings, however, the potential for the micropile group to fail 

as a “block” should be evaluated. For a micropile group of width Bg and length Lg

and depth D (as shown in Figure 5-3), the ultimate capacity of the micropile group, 

Qg, is given by: 

( ) g g g u g g c u Q = 2 (Eq. 5-11) B +2L D×s + B L ×N s

where u s is the average undrained shear strength along the depth of penetration of 

the micropiles and su is the undrained shear strength at the base of the micropile 

group. For this analysis, it is assumed that the pile cap provides no resistance. 

The bearing capacity factor used in Eq. 5-11 is calculated according to the following: 

2.5 0.2 1

0.2

5 1 ≤ 















+ 













 = +

g g g

g

c B

D for B

D

L

B

N (Eq. 5-12) 

2.5

0.2

7.5 1 > 













 = +

g g

g

c L

D for L

B

N (Eq. 5- 13) 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-24 December 2005 

Figure 5-3. Block Failure Model for Micropile Group in Cohesive Soil with Cap in Contact 

with Ground. 

Qg

Cap

Bg

Lg

Cohesive soil

with c=su and 

φ=0 

Block 

shear 

surface 

D
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-25 December 2005 

The group capacity to be used for design is evaluated using the following steps: 

Step 1: Calculate ultimate group capacity as: 

Qg = (α bond ×π ×Db ×Lb )×no. (Eq. 5-14) of micropilesin group×η

where η is obtained from Table 5-4. 

Step 2: Calculate ultimate group capacity according to Eq. 5-14 and use lower value 

(i.e., from Step 1 and Step 2) for design. 

Step 3: Use a FS value of 2.0 to calculate an allowable group capacity. 

Micropile Groups in Cohesionless Soils 

As long as the center-to-center spacing of micropiles in a group is greater than three 

times the diameter of the grouted body (i.e., s > 3Db), the capacity of a micropile 

group in cohesionless soils may be calculated as the sum of the resistance of all the 

individual micropiles in the group, i.e., use Eq. 5-14 with η=1.0. For example, for 

pressure grouted micropiles installed in cohesionless soils with a typical grouted 

diameter of 200 mm and typical minimum center-to-center spacing in the range of 

750 to 1,000 mm, it is therefore unnecessary to consider a reduction in micropile 

capacity as a result of group effects. 

For the case of micropiles installed in strong soil (which may be cohesionless soil) 

over weak or compressible soil, an alternate method to evaluate micropile group 

capacity is used, as described below. 

Micropile Groups in Strong Soil Overlying a Weak or Compressible Soil 

If a micropile group is embedded in a strong soil deposit overlying a weaker soil 

deposit, then the potential for a “punching” shear failure of the micropile group into 

the weaker soil stratum should be considered during design. 

The method proposed herein to evaluate the potential for punching shear failure of 

micropile groups is the same as that which has been developed to address this same 

issue for drilled shaft groups (see FHWA-IF-99-025, 1999). This approach requires 

that the capacity of the block of micropiles meet the following condition to assure 

safety against punching shear failure: 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-26 December 2005 

[ ] 1 1 10 q q q B

H

q q B L

Q

o

g

p o

g g

g = ≤ + − ≤ (Eq. 5-15) 

 where: 

• Qg, Bg, and Lg are as defined on Figure 5-3; 

• qo is the ultimate unit base resistance at the depth of the top of the lower (i.e., 

weaker) layer using the shear strength parameters of the lower layer; 

• q1 is the ultimate unit base resistance at the depth of the top of the upper (i.e., 

stronger) layer using the shear strength parameters of the upper layer; 

• qp is the ultimate unit base resistance at the depth of the micropile tips; and 

• H is the distance from the tip elevation of the micropiles to the elevation of 

the top of the weaker lower soil layer. 

If the piles are battered, the values for Bg and Lg should be based on the plan area of 

the pile group at the base of the piles. Satisfaction of the condition prescribed in Eq. 

5-15 should preclude the potential for a punching shear failure of the micropile group 

(see Figure 5-4). 

 

Figure 5-4. End-bearing Resistance of Piles in Layered Soils (after Meyerhof, 1976). 

D

H 

qo

qp

q1

Pile toe 10Bg

Weak Soil

Strong 

Weak Soil
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-27 December 2005 

5.9.4 Evaluate Micropile Group Uplift Capacity 

The design of micropile groups subject to uplift forces follows the method described 

in FHWA NHI-05-042 (2005) for uplift capacity for driven piles in cohesionless 

soils and for driven piles in cohesive soils. 

Micropile Groups in Cohesive Soils 

For micropile groups in cohesive soil, the group uplift capacity may be calculated 

based upon the undrained shear strength of the block of soil enclosed by the group 

plus the effective weight of the pile cap and pile-soil block as shown on Figure 5-5. 

This may be expressed as: 

( ) ug u Wg Q =2 (Eq. 5-16) Z × X +Y × s +

where u s is the average undrained soil shear strength over the depth of micropile 

embedment along the group perimeter and Wg is the effective weight of the pile/soil 

block including the pile cap. In using Eq. 5-16, a factor of safety of 2.0 should be 

used to estimate the allowable group uplift capacity. 

Figure 5-5. Model to Calculate Micropile Group Uplift Capacity in Cohesive Soils. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-28 December 2005 

Micropile Groups in Cohesionless Soils 

The uplift capacity of a micropile group in cohesionless soil may be conservatively 

taken as the effective weight of a block of soil extending upward from the base of the 

micropiles at a slope of 1H:4V as shown on Figure 5-6. In this evaluation, the 

weight of the micropiles within the block is (conservatively) considered equal to the 

weight of the soil. Using Figure 5-6, the group uplift capacity is given by: 

( ) × γ 



 



 Qug = × Abase + Atop + Abase × Atop × D

3

1 (Eq. 5-17) 

where Abase = Bg × Lg and Atop = (Bg+D/2) × (Lg+D/2) and γ is the effective unit 

weight of the soil. In Eq. 5-17, the term in brackets is simply the volume of the 

enclosed soil. A FS = 1.0 is acceptable for this analysis since the shear strength that 

would be mobilized within the soil is conservatively neglected; this implies that the 

allowable micropile group capacity would be equal to the calculated group uplift 

capacity based on Eq. 5-17. 

The allowable group uplift capacity (based on either Eq. 5-16 or 5-17) should be 

compared to the allowable uplift capacity of a single micropile multiplied by the 

number of micropiles in the group and the design should be based on the lesser group 

capacity. 

Figure 5-6. Model to Calculate Micropile Group Uplift Capacity in Cohesionless Soils. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-29 December 2005 

5.10 STEP 9. ESTIMATE MICROPILE GROUP SETTLEMENT 

5.10.1 General 

In general, methods used for estimating settlements of driven pile groups are 

applicable for micropile groups. The major components of settlement that need to be 

assessed include: (1) settlements of the ground in which the micropiles are 

constructed; and (2) elastic compression/tension of an individual micropile. These 

settlements are added together to evaluate the total settlement of the micropile group 

subject to the design load and are then compared to the allowable settlement. 

The specific value for allowable settlement will depend on the structure being 

supported, but for typical highway bridge projects, the maximum vertical movement 

will depend primarily on anticipated differential settlements between bridge piers for 

single span or continuous span bridges. 

5.10.2 Micropile Group Settlement 

Micropiles in a group can undergo vertical displacement as a result of consolidation 

of soil layers below the bottom of the micropile group. Where a single pile will 

transfer its load to the soil in the immediate vicinity of the pile, a pile group can 

distribute its load to the soil layer below the group. Consideration should be made 

for this group displacement when the soil below the group is cohesive in nature and 

subject to consolidation. The method presented herein for evaluating micropile 

group settlements is similar to that for driven piles (see FHWA-NHI-05-042, 2005). 

For purposes of calculating settlements of micropile groups in soil (for which loads 

are primarily transferred through side resistance), loads are assumed to act on an 

equivalent footing located at two-thirds of the depth of embedment of the micropiles 

into the layer that provides support (i.e., two-thirds of the depth of the micropile 

bond zone). This concept is illustrated in Figure 5-7 for a uniform soil profile and 

Figure 5-8 for a micropile bond zone formed in firm or strong layer that is overlain 

by an upper soft or weak layer (which is common for many micropile applications). 

Where a clayey layer may exist just below the tips of the micropiles, the equivalent 

footing is assumed to exist at the depth corresponding to 8/9 of the length of the 

bond zone. The reader is referred to FHWA-NHI-05-042 (FHWA, 2005) for 

additional information on the equivalent footing concept. For a pile group consisting 

of only vertical piles, the equivalent footing has a plan area that corresponds to the 

perimeter dimensions of the pile group. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-30 December 2005 

Figure 5-7. Equivalent Footing Concept for Uniform Soil (after FHWA-NHI-05-042, 2005). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-31 December 2005 

SOFT OR

WEAK LAYER

LAYER WHERE

BOND ZONE IS

FORMED

Figure 5-8. Equivalent Footing Concept for Firm Soil Underlying Soft Soil Layer. 

The pile group load over this plan area is then the bearing pressure transferred to the 

soil through the equivalent footing. The load is assumed to spread within the 

frustum of a pyramid of side slopes at 1H:2V and to cause uniform additional 

vertical pressure at lower levels. The pressure at any level is equal to the load 

carried by the group divided by the plan area of the base of the frustum at that level. 

Settlements are calculated based on the pressure increase in the underlying layers. 

This method is conservative because compression settlements from the layer defined 

from just below the top of the equivalent footing to the bottom of the micropiles do 

not take into account the increased stiffness of the profile at this location resulting 

from the micropiles. 
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Micropile Design & Construction 5-32 December 2005 

Where clayey soils may consolidate as a result of micropile group loading, nominally 

undisturbed tube samples should be collected from potential consolidating layers and 

consolidation tests should be performed to assess compressibility parameters and 

stress history information for the consolidating layer. The reader is referred to GEC 

No. 5 for specific information on consolidation testing and parameter evaluation. 

For micropile group settlements in cohesionless layers, SPT data is used to estimate 

compression parameters. 

Step By Step Procedure for Micropile Group Settlement In Cohesive Soils 

Step 1: Determine the new load imposed on soil by the pile group. 

a. Determine the location of the equivalent footing using Figure 5-7 or 5-8. 

b. Determine the dimensions of the equivalent footing. For pile groups 

consisting only of vertical piles, the equivalent footing has the same 

dimensions as the length and width of the pile group from Figure 5-7. For 

pile groups that include batter piles, the plan area of the footing should be 

calculated from the dimensions of the pile group at depth 2/3 D, including 

the plan area increase due to the pile batter. 

c. Determine the pressure distribution to soil layers below the equivalent 

footing up to the depth at which the pressure increase from the equivalent 

footing is less than 10% of existing effective overburden pressure at that 

depth. The depth at which the pressure increase is less than 10% will 

provide the total thickness of cohesive soil layer or layers to be used in 

performing settlement computations. Note that the group design load 

should be used in determining the pressure distribution for settlement 

computations, and not the ultimate group load. 

d. Divide the cohesive soil layers in the affected pressure increase zone into 

several thinner layers of 1.5 to 3 meter (5 to 10 ft) thickness. The 

thickness of each layer is the thickness H for the settlement computation 

for that layer. 

e. Determine the existing effective overburden pressure, po, at midpoint of 

each layer. 
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Micropile Design & Construction 5-33 December 2005 

f. Determine the imposed pressure increase, ∆p, at midpoint of each affected 

soil layer based on the appropriate pressure distribution. 

Step 2: Determine consolidation test parameters. 

Step 3: Compute settlements. 

Using an appropriate settlement equation, compute the settlement of each 

affected soil layer. Sum the settlements of all layers to obtain the total 

estimated soil settlement from the pile group. 

Step By Step Procedure for Micropile Group Settlement In Cohesionless Soils 

Pile groups supported in and underlain by cohesionless soils will produce only 

immediate settlements implying that the settlements will occur immediately as the 

pile group is loaded. A procedure to calculate pile group settlements in cohesionless 

soils is provided below. 

Step 1: Determine the new load imposed on soil by the pile group. 

a. Determine the location of the equivalent footing using Figure 5-7 or 5-8. 

b. Determine the dimensions of the equivalent footing. 

c. Determine the pressure distribution to soil layers below the equivalent 

footing up to the depth at which the pressure increase from the equivalent 

footing is less than 10% of existing effective overburden pressure at that 

depth. 

d. Divide the soil layers in the affected pressure increase zone into several 

thinner layers of 1.5 to 3 meter (5 to 10 ft) thickness. The thickness of 

each layer is the thickness H for the settlement computation for that layer. 

e. Determine the existing effective overburden pressure, po, at midpoint of 

each layer. 

f. Determine the imposed pressure increase, ∆p, at midpoint of each affected 

soil layer based on the appropriate pressure distribution. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-34 December 2005 

Step 2: Determine bearing capacity index for each cohesionless layer. 

Determine the average corrected (for overburden pressure and hammer 

efficiency) SPT N160 value for each cohesionless layer. Use N160 in Figure 5-9 

to obtain the bearing capacity index, C′ for each layer. 

Step 3: Compute settlements. 

Compute the settlement of each affected soil layer under the applied load 

using the following formula: 















 +∆ ∆ =

o

o

o p

p p

C

H H log 1

' (Eq. 5-18) 

Sum the settlements of all layers to obtain the total estimated soil settlement 

from the pile group. If a layered soil profile is within the compressible zone 

being considered, the two methods previously described for cohesive and 

cohesionless soils can be used separately for the appropriate layers and then 

settlements form each layer added to obtain the total settlement from the pile 

group. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-35 December 2005 

(Note: The “Inorganic SILT” curve should generally not be applied to soils that exhibit plasticity) 

Figure 5-9. Bearing Capacity Index versus Corrected SPT Blowcount (modified after 

Hough, 1959). 

Corrected SPT N-value, N160
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-36 December 2005 

5.10.3 Micropile Elastic Movement 

The calculation of the elastic compression and/or elastic tension of a single micropile 

subject to the design compression and/or tension load are presented herein. This 

elastic compression value is added to the total settlement of the group resulting from 

consolidation (as discussed in Section 5.10.2) to obtain the total estimated pile group 

settlement. 

Elastic displacement of a micropile is a function of the imposed load, the pile 

stiffness, and the load transfer characteristics of the pile to the surrounding soil via 

grout-to-ground bond. The elastic compression displacement, ∆elastic, of a micropile 

can be written in its most general form as: 

AE

PL ∆elastic = (Eq. 5-19) 

where P is the design load applied at the ground surface (kN), L is the length of the 

pile (m), A is the area of the section (m2

) and E is the elastic modulus of the section 

(kPa). Because the stiffness of the micropile may change over its length and because 

axial load is transferred to the ground, the elastic displacement may be calculated as 

the sum of elastic displacements of “n” pile segments as follows: 

∑=

∆ =

n

i i i

i i

elastic A E

PL

1

 (Eq. 5-20) 

where Li, Ai, and Ei are the length, average cross section area, and average modulus, 

respectively, for each of the pile segments. The term Pi is the average axial load at 

the pile segment. The load at the top pile segment would be the total imposed load 

to that individual pile, and would reduce in magnitude down to the mobilized end 

bearing load at the pile tip in accordance with the load transfer response from the 

micropile to the ground. Determination of a stiffness value, i.e., AE, for a micropile 

is complex due to the: 

• contribution of the grout to the pile’s stiffness due to the pile acting in 

compression; and 

• varying reinforcement (type and length) used in some micropiles, with 

casing (and perhaps bar) reinforcement in the upper portion of the pile and 

bar reinforcement in the lower portion. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-37 December 2005 

For estimates of displacement caused by compression loads, the stiffness of the 

composite section at a given point in the pile can be evaluated using the formula: 

 [ ] [ ] EApile = Agrout ×Egrout + Asteel ×Esteel (Eq. 5-21) 

For estimates of displacement caused by tension loads, the stiffness of the composite 

section can be evaluated using the formula: 

 [ ] EApile = Asteel ×Esteel (Eq. 5-22) 

The value for Egrout can be quite variable, but for design calculations may be 

estimated as Egrout (MPa) = 4732 × (f′

c (MPa))1/2 (Egrout (ksi) = 57 × (f′c (psi))1/2). 

A conservative approach to calculate elastic displacement is to assume that no load is 

transferred to the ground over the length of the micropile from the top of the 

micropile to the top of the bond zone; this implies that the elastic compression of this 

length of the micropile can be calculated according to Eq. 5-19 with P equal to the 

design load and L equal to the length of the micropile above the bond zone. If there 

are changes in the micropile cross section over that length (e.g., section with just 

reinforcing bar and section with reinforcing bar and casing), then Equation 5-20 is 

used with pile segment lengths defined based on changes in cross section. 

In the bond zone, the cross section of the micropile will usually be constant. 

Therefore, since it is assumed that the design load is carried uniformly over the 

length of the bond zone in side resistance; the elastic displacement along this length 

of the micropile can be calculated using Eq. 5-19 with P equal to the design load and 

L equal to one-half the length of the bond zone. 

For micropiles bonded in rock or for end-bearing micropiles on rock, the full length 

of the micropile above the top of rock should be assumed for the elastic length. It is 

noted that the assumption of the lengths over which elastic movements occur can be 

confirmed via load testing in which loads are incrementally cycled (similar to a 

ground anchor performance test) to allow for measurement of the elastic movement. 

An example calculation of elastic compression and tension displacement for a 

micropile is provided in Sample Problem No. 1. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-38 December 2005 

5.11 STEP 10. DESIGN MICROPILE CONNECTION AT PILE CAP 

Unless a single micropile is used to support a load, a pile cap (footing) is necessary 

to spread the structure loads and any overturning moments to all the micropiles in the 

group. Reinforced concrete pile caps are designed in accordance with the AASHTO 

Standard Specifications for Highway Bridges and individual DOTs may have 

minimum requirements for pile caps (e.g., minimum concrete cover, minimum 

embedment of pile top into cap). The structural design of reinforced concrete pile 

caps is not addressed in this manual. 

The connection between the top of the micropiles and the reinforced concrete pile 

cap can vary depending on the required capacity of the connection, the type of 

micropile reinforcement, and the details of the pile cap. Seven examples of the pileto-footing connections are shown in Figures 5-10 through 5-16. Figures 5-10 

through 5-13 show typical connections for piles that can have both tension and 

compression loads depending on load case. Figures 5-14 through 5-16 show simple 

connections for piles that are only in compression. 

Figure 5-10 shows a composite reinforced micropile connected to a new (or 

extended) footing. The footing tension and compression load is transferred to the 

pile through the top bearing plate. The stiffener plates provide bending strength to 

the plate, plus provide additional weld length for transferring the load from the 

bearing plate to the pile casing. The stiffener plates can be eliminated if the support 

of the top plate and additional weld length are not required. Additional 

considerations for this connection detail include the following: 

• The portion of the tension load carried by the reinforcing bar can be 

transferred to the top plate through the nut, reducing the plate-to-casing weld 

requirement. 

• The bond between the pile casing and the footing concrete can be utilized, 

reducing the load capacity required for the top plate and top plate to casing 

weld. 

• A portion of the compression load can be transferred from the top plate to 

the casing through bearing, reducing the weld capacity requirement. This 

requires a higher level of quality for the fabrication of the bearing surface 

between the casing and the plate. 

Sample Problem No. 1 includes the design of a pile connection similar to that shown 

in Figure 5-10. The additional considerations listed above are not included in the 

sample problem calculations. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-39 December 2005 

EXISTING FOOTING

EXTENDED FOOTING

REINFORCING

BAR W/NUT

BEARING PLATE

AS REQUIRED

STIFFNER

PLATE (TYP)

BOTTOM OF

FOOTING ELEV. STEEL CASING

TYP

Figure 5-10. Pile to Footing Connection Detail (compression and tension loads). 

Figure 5-11 shows a composite reinforced micropile connected to an existing 

footing. The pile is installed through an oversized hole cored through the existing 

footing or slab. After the pile is installed, the annulus between the core hole and the 

micropile is cleaned (usually via pressure washing) and filled with non-shrink 

cement grout. Steel rings are welded to the top section of the casing prior to pile 

installation. These rings transfer the pile load from the casing to the non-shrink 

grout. Adequate spacing must be used between the rings to avoid combining bearing 

stresses in the concrete and grout. The total capacity of the connection is controlled 

by the sum of the bearing strength of the rings, the capacity of the load transfer 

across the interface between the non-shrink grout and the existing concrete, and the 

shear capacity of the existing concrete. 

Grooves may be chipped into sides of the core hole (typical dimension = 20 mm 

deep and 32 mm wide (3/4 in. deep and 1 1⁄4 in. wide)) to increase the load carrying 

capacity of the grout to existing concrete. Also, vertical reinforcing bars may be 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-40 December 2005 

drilled and epoxied into the existing concrete around the exterior of the connection to 

increase the punching shear capacity. 

For thick existing footings, the shear rings and grooves in Figure 5-11 may be 

eliminated. Load tests on the connections are appropriate to verify the casing to 

grout bond and grout to existing concrete bond for the proposed materials and 

methods. If this connection is proposed for a project, the Contractor should be 

required to perform a load test, provide load test data from previous projects, or 

provide in-house testing to quantify that the proposed connection will be able to 

support the design load. 

Figure 5-12 shows a composite reinforced micropile connected to a new footing. 

The footing compression load is transferred to the pile through bearing on the pile 

top and reinforcing bar plate and the tension load is transferred through bearing on 

the reinforcing bar plate. A portion of the load transferred from the footing to the 

pile may be attributed to the bond between the pile casing and the footing concrete. 

REINFORCING

BAR W/NUT

BEARING PLATE

AS REQUIRED

TYP

TOP OF EXISTING

FOOTING

STEEL CASING

STEEL SHEAR RING (TYP)

NON – SHRINK GROUT

CHIPPED GROOVE

BOTTOM OF

FOOTING ELEV.

OVERSIZED CORE HOLE

(DIAMETER AS PER

CONTRACT PLANS)

Figure 5-11. Pile to Footing Connection (compression and tension loads). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-41 December 2005 

NEW FOOTING

BEARING PLATE

AS REQUIRED

STEEL CASING

BOTTOM OF

FOOTING ELEV.

FULL HEX NUT

1⁄2 HEX NUT

REINFORCING BAR

BEARING PLATE

(OPTIONAL)

Figure 5-12. Pile to Footing Connection (compression and tension loads). 

Figure 5-13 shows a bar-reinforced micropile cast into a new footing. The 

compression and tension load is transferred to the pile through bearing on the bar 

plate, and through bond between the footing concrete and the reinforcing bar. 

Competency of the construction joint between the pile grout and footing concrete is 

an important quality consideration for this pile type. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-42 December 2005 

NEW FOOTING

BEARING PLATE

AS REQUIRED

BOTTOM OF

FOOTING ELEV.

FULL HEX NUT

1⁄2 HEX NUT

REINFORCING BAR

NEW FOOTING

BEARING PLATE

AS REQUIRED

BOTTOM OF

FOOTING ELEV.

FULL HEX NUT

1⁄2 HEX NUT

REINFORCING BAR

Figure 5-13. Pile to Footing Connection (compression and tension loads). 

Figure 5-14 shows a typical compression connection for a moderately loaded 

micropile where concrete bearing stress on the pile top is within AASHTO limits 

(see AASHTO Section 8.15.2.1.3). Figure 5-15 shows a typical compression 

connection for a heavily loaded micropile where a bearing plate welded to the casing 

is required for concrete bearing stress on the pile top to be within AASHTO limits. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-43 December 2005 

NEW FOOTING

STEEL CASING

BOTTOM OF

FOOTING ELEV.

150 mm

Figure 5-14. Pile to New Footing Connection Detail used for Moderate Loads (compression 

loads). 

NEW FOOTING

STEEL CASING

BOTTOM OF

FOOTING ELEV.

BEARING PLATE

Figure 5-15. Pile to New Footing Connection Detail used for High Loads (compression 

loads). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-44 December 2005 

Figure 5-16 shows a compression connection for a pile through an existing footing. 

The bond of the non-shrink grout to the footing is a function of the proposed 

methods (cored hole, down-the-hole hammered hole, etc.) and materials (non-shrink 

grout, existing concrete, etc.). Connection load tests are appropriate to verify the 

design. 

STEEL CASING

BOTTOM OF

FOOTING ELEV.

EXISTING

FOOTING

NON-SHRINK

GROUT

Figure 5-16. Pile to Existing Footing Connection Detail (compression loads). 

5.12 STEP 11. DEVELOP LOAD TESTING PROGRAM 

Section 7.6 of this Manual provides specific information on the evaluations to be 

performed as part of the development of a load testing program. Of primary 

importance is that the scope of the load testing program be consistent with the 

selected factor of safety for the grout/ground bond strength used for geotechnical 

capacity evaluations. In Section 5.9.2, the minimum requirements for verification 

and proof testing were described which are consistent with a factor of safety of 2.0. 

For load testing, maximum test loads should not exceed 80 percent of the ultimate 

structural capacity of the micropile. The ultimate structural capacity is given by: 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-45 December 2005 

[ ] ult compression c grout grout y ca g ca g y bar Abar P − = f − × A + f − sin × A sin + f − × ' 0.85 (Eq. 5-23) 

[ ] ult tension y ca g ca g y bar Abar P − = f − sin × A sin + f − × (Eq. 5-24) 

For some designs, the verification test pile(s) may require larger pile casing and 

reinforcing bar than the production micropiles. The resulting stiffer micropile can 

adequately confirm the grout-ground bond strength for production micropiles, but 

will likely not provide representative structural displacement behavior. The 

deflections measured for proof-tested micropiles will need to be relied upon to 

provide best estimate of structural deflections. 

5.13 STEP 12. PREPARE DRAWINGS AND SPECIFICATIONS 

When the design has been finalized, drawings and specifications are prepared and the 

procedures that will be used to verify micropile capacity (e.g. load testing) should be 

defined. At the time of the bid, all of the quality control procedures to be used for 

the project should also be defined and included in the specifications. Example 

typical drawings and specifications is provided in Sample Problem No. 1. 

5.14 CORROSION PROTECTION 

5.14.1 Background

Protecting the metallic components of a micropile against the detrimental effects of corrosion 

is necessary to assure adequate long-term durability of the micropile. The degree and extent 

of corrosion protection is a function of loading condition, the expected service life of the 

micropile, the aggressiveness of the ground, the perceived importance of the structure, and 

consequences of failure. In all cases, it is the responsibility of the Project Designer to select 

the corrosion protection for each micropile. 

The variables which indicate a high corrosion potential include: 

• low resistivity of ground; 

• high concentration of chlorides or sulfides in ground or groundwater; 

• too low or too high hydrogen potential (pH) of ground or groundwater; 

• high saturation conditions; and 

• stray currents. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-46 December 2005 

The factors above collectively define ground corrosion potential (or aggressivity of the 

ground). In addition to corrosion of metallic components, potential degradation of the 

cement grout as a result of sulfate, chloride, and/or acid attack should also be considered. 

Information on cement degradation as it applies to pile design is provided in FHWA-NHI-05-

042. 

5.14.2 Evaluation of Soil Corrosion Potential

Tests listed in Table 5-5 are used to classify the corrosion potential of the ground. 

Table 5-5. Criteria for Assessing Ground Corrosion Potential (Elias et al., 2001). 

Test Units Strong Corrosion 

Potential/Aggressive 

AASHTO 

Test 

Method 

pH – < 5, >10 T 289 

Resistivity ohm-cm <3,000 T 288 

Sulfates ppm(1) >200 T 290 

Chlorides ppm >100 T 291 

 Note: (1) ppm = parts per million. 

In general, the ground is classified with a strong corrosion potential or aggressive if any one 

of the conditions listed in the third column of Table 5-5 exceeds the limits listed during 

the service life of the micropile. In addition, buried structures immediately adjacent to the 

project exhibiting corrosion or direct chemical attack might be an indication of strong 

corrosion potential. If tests are not performed, then the ground should be assumed to be 

aggressive. Classification of ground aggressivity should consider the possibility of changes 

during the service life of the structure which may cause the ground to become aggressive 

(e.g., near mining operations, chemical plants, or chemical storage areas). 

5.14.3 Corrosion Protection Systems

5.14.3.1 Methods for Corrosion Protection of Reinforcing Steel 

Corrosion protection can be provided by physical and chemical protection, or a combination 

thereof. Physical protection involves placing a continuous barrier between the reinforcing 

bar, pipe casing, other metallic parts, and the corrosion sources. Chemical protection 

consists of the use of a sacrificial material or a dielectric material, which will preclude the 

flow of electric current. Some of the corrosion protection systems currently in use utilize a 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-47 December 2005 

combination of these mechanisms. The most common systems used to provide corrosion 

protection for micropiles are described below. 

Grout Protection 

This method of corrosion protection is used as a protective measure for the steel reinforcing 

bar and involves fully covering the reinforcing bar with neat cement grout. Centralizers are 

applied along the length of the bar (Figure 5-17(a)) to ensure adequate cover of grout 

between the bar and the side of the borehole. After the bar is centered in the drillhole, neat 

grout is injected and fills up the annular space around the steel bar. The grout provides an 

alkaline environment that reduces corrosion potential. 

Epoxy Coating 

Corrosion protection with epoxy consists of coating the reinforcing rod with a fusion-bonded 

epoxy that is applied by the manufacturer prior to shipment to the construction site. The 

minimum required thickness of epoxy coatings is typically 12 mils (0.3 mm). Thicker 

coatings may reduce steel to grout bond. The epoxy coating provides physical and chemical 

protection, as epoxy is a dielectric material. In transporting and handling bars, the epoxy 

coating may be damaged before bar installation. Therefore, it is not uncommon to spray 

epoxy coating in the field on chipped or nicked surfaces. Applicable standards for epoxy 

coating and allowable extent of damage (i.e., number of discontinuities in epoxy coating per 

unit length of bar) are found in ASTM A775/AASHTO M282. Patching materials should be 

approved by the epoxy coating manufacturer and should be inert in cement grout. 

Galvanized Coating 

A common method of providing corrosion protection is galvanization, which consists of 

applying a zinc coating on the steel surface. The process is performed by hot-dipping bars 

and other metallic pieces with zinc. The protection provided by galvanized coating is both 

physical and chemical, as this process forms a protective layer of zinc oxide. Galvanization 

shall meet the requirements of ASTM A153. Galvanization should not be used on high 

strength bars. 

Encapsulation 

For maximum corrosion protection, a polyvinyl chloride (PVC) or high-density polyethylene 

(HDPE) (minimum 1-mm (0.04-in.) thick for PVC and 1.5-mm (0.06-in.) thick for HDPE) 

sheathing may be installed around the reinforcing bar similar to what is done for ground 

anchors in permanent applications. The sheathing is corrugated to transfer load to the 

surrounding grout. Grout-filled corrugated sheaths comprise double corrosion protection. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-48 December 2005 

This system may be used with DSI threadbar and GEWI Bar (Figure 5-17(b)) and others. 

The encapsulation shall meet the requirements for encapsulation of soil and rock ground 

anchors as provided in PTI (2004). 

5.14.3.2 Methods for Corrosion Protection of Steel Casing 

Grout that may fill the annulus outside the steel casing is not considered to be sufficient to 

provide a quantifiable level of corrosion protection. Corrosion resistant coatings on 

permanent drill casing is impractical due to the abrasive action of the soil on the outer surface 

of the casing which would likely result in damage to the coating. Corrosion protection for 

steel casing subject to compressive loads in aggressive environments is typically considered 

by including a sacrificial steel thickness in the design. Casing should not be used to carry 

tension loads in aggressive ground environments. 
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Micropile Design & Construction 5-49 December 2005 

TORQUED

ANCHOR

PLATE

CONCRETE

STRUCTURE

UPPER PILE

STRENGTHENING

ELASTIC

SPACER

TORQUED

ANCHOR

HEAD

ADDITIONAL

REINFORCEMENT

(COMPRESSION)

ADDITIONAL

REINFORCEMENT

(TENSION)

CEMENT

GROUT

(a)

GEWI – PILE with

Standard Corrosion Protection

(b)

GEWI – PILE with

Double Corrosion Protection

CORRUGATED

SHEATH

GEWI – BAR

OUTER

CEMENT

GROUT

INNER

CEMENT

GROUT

GEWI – BAR

Figure 5-17. GEWI Piles with (a) Grout Protection only; and (b) Double Corrosion 

Protection (Courtesy of DSI). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-50 December 2005 

5.14.3.3 Corrosion Protection Requirements for Micropiles 

Corrosion protection recommendations for micropiles are provided in Table 5-6. 

Table 5-6. Corrosion Protection Recommendations for Micropiles (after DFI, 2004).

Corrosion Protection 

Loading Tension1 Compression 

Ground Aggressive2 Non aggressive Aggressive2 Non-aggressive 

Casing a. Do not rely on 

casing for load 

capacity 

a. None required if 

tension load on 

casing is less than 

20% of casing 

thread strength 

OR 

b. Do not rely on 

casing for load 

capacity 

a. Min.1.6 mm 

(0.063 in.) 

corrosion loss on 

outside 

The Specifier may 

use different 

corrosion loss per 

site-specific 

corrosion studies. 

a. None 

The Specifier may 

use different 

corrosion loss per 

site-specific 

corrosion studies. 

Core steel 

(reinforcing 

bar)l

a. epoxy coating3

OR 

b. galvanization3

OR 

c. encapsulation 

in plastic 

sheath3

AND 

Grout cover4

a. bare steel5

OR 

b. epoxy coating3

OR 

c. galvanization3

OR 

d. encapsulation in 

plastic sheath3 

AND 

Grout cover4

a. Grout cover4 

AND 

The Specifier may 

desire to add other 

options listed for 

tension. 

a. Grout cover4

NOTES:

1. Permanent tension or temporary tension (e.g., wind, seismic, impact) on critical 

structures. For temporary tension on normal structures, corrosion protection for 

compression may be used. The recommendations for corrosion protection for micropiles 

subject to tension loadings should also be used for that length of the micropile subject to 

tension as a result of lateral loads and/or overturning moments at the ground surface. 

2. Corrosion protection must extend 5 m (15 ft) below corrosive material 

3. Core steel corrosion protection must extend a minimum of 1.5 m (5 ft) into casing 

4. Minimum 1 inch in soil and 0.5 inch in rock. If protective coatings (epoxy, 

galvanization, or encapsulation) are provided in compression, minimum cover may be 

0.25 inches in soil or rock. 

5. Not recommended for permanent or cyclic tension loads. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-51 December 2005 

Corrosion protection requirements (via sacrificial steel section losses) prescribed in Table 5-6 

for casings subject to compressive loads in an aggressive ground environment include a 

minimum section loss of 1.6 mm (0.063 in.). This value is prescribed in AASHTO Section 

4.5.7.4 for cross section reductions for concrete-filled pipe piles. Guidance on sacrificial 

thickness for structural steel elements in CCTG (1992) indicate that, for a design life of 75 

years, a steel section loss range of 2 mm (0.0787 in.) to 5 mm (0.196 mm) is appropriate for 

non-protected steel in moderately to strongly corrosive environments, respectively, where no 

specific site corrosivity studies for the steel elements have been performed. Higher section 

losses are provided for a design life greater than 75 years. 

These information sources provide a relatively wide range of corrosion losses. It is strongly 

recommended that site-specific corrosivity studies be performed where micropiles will be 

used in aggressive ground (as defined in Table 5-5). 

5.15 PLUNGE LENGTH 

The micropile detail shown in Figure 5-1 depicts a casing plunge length. With this detail 

(primarily used for micropiles with bond zones formed in soil), it is assumed that a portion of 

the micropile design load is transferred to the surrounding ground (over the plunge length) by 

the cased portion of the pile, thus reducing the load that must be supported by the uncased 

portion of the micropile (see Figure 5-18). This can allow a lesser amount of steel 

reinforcing through the uncased length to meet the structural strength requirements. The 

reduction in load applied to the uncased length is termed the transfer load, Ptransfer. 

The allowable axial load transferred through the plunge length, Ptransfer-allowable may be 

calculated as: 

 D (Plunge Length) FS

P b

bond

transfer− allowable = ×π × ×

α

 (Eq. 5-25) 

The value for this load is based on the unit grout-to-ground bond, αbond (from Table 5-3) 

acting uniformly over the casing plunge length. It must be recognized that reliably achieving 

this load transfer depends on the casing installation method, the specific soil type and 

grouting method to obtain sufficient grout coverage between the casing and the surrounding 

ground. 
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Micropile Design & Construction 5-52 December 2005 

For these reasons, micropile designs which incorporate a plunge length and a corresponding 

reduction in axial load reaching the uncased portion should be confirmed by the site-specific 

load testing information wherein axial load transfer over the plunge length is measured or can 

be computed based on verification load testing. Alternatively, Ptransfer may be conservatively 

neglected. 

PILE BOND

LENGTH

CASING PLUNGE

LENGTH

LOAD IN PILE

PPILE (kN)

1

TRANSFER LOAD:

PTRANSFER =

LOAD CARRIED BY PILE @ DEPTH 1 = PPILE

LOAD CARRIED BY PILE @ DEPTH 2 = PPILE – PTRANSFER

2

Db

αbond × 3.14 × Db × Casing Plunge Length

PILE BOND

LENGTH

CASING PLUNGE

LENGTH

LOAD IN PILE

PPILE (kN)

1

TRANSFER LOAD:

PTRANSFER =

LOAD CARRIED BY PILE @ DEPTH 1 = PPILE

LOAD CARRIED BY PILE @ DEPTH 2 = PPILE – PTRANSFER

2

Db

αbond × 3.14 × Db × Casing Plunge Length

Figure 5-18. Detail of Load Transfer Through the Casing Plunge Length. 

5.16 END BEARING MICROPILES 

Due to the relatively small cross sectional area of micropiles, load carrying capacity resulting 

from end bearing is generally considered to be negligible for micropiles in soil or weak rock. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-53 December 2005 

Micropiles founded on high quality sound rock, however, may develop their capacity 

primarily through end bearing and secondarily by side resistance. In this case, care must be 

taken to ensure that the micropile is not terminated on a boulder or on rock with voids or very 

soft material below. Where end bearing micropiles are being considered, the subsurface 

investigation should be sufficiently detailed to allow for a determination of the quality of the 

rock (see Table 5-2). 

The design for end bearing micropiles may be done similar to end bearing drilled shafts, or 

may be based on previous load test experience of similar micropiles. Typically, a nominal 

length rock socket may be used (on the order of 0.6 m (2 ft)) to assure that the micropile is, in 

fact, founded on high quality rock. The capacity of end bearing micropiles on competent 

rock will likely be controlled by the structural capacity of the micropile since very high end 

bearing capacities can be achieved for micropiles on rock. 

5.17 DOWNDRAG 

Micropiles may be subjected to additional axial compression loading due to downdrag forces 

when the soils in contact with the cased portion of the micropile (i.e., above the bond zone) 

move downward relative to the micropile and tend to “drag” the micropile downward. The 

resulting downward force will add to the load applied to the micropile by the structure at the 

ground surface. The user of this manual is referred to the NHI/FHWA reference manuals for 

design of driven piles and for drilled shafts (FHWA-NHI-05-042 and FHWA-IF-99-025, 

respectively) for background information on downdrag and methods to compute downdrag 

forces. 

The potential for downdrag exists when the surface soils can settle and where the foundation 

element passes through those settling soils into a stratum of relatively rigid geomaterial. 

Possible development of downdrag loads on micropiles should be considered where: (1) the 

site is underlain by compressible silts, clays, or peats; (2) fill has recently been placed on the 

earlier; and (3) the groundwater is substantially lowered. 

If analyses or computations indicate that the surface soils are moving downward more than 

the micropile, a conservative solution can be obtained if it is assumed that the downdrag 

force will develop along the micropile from the ground surface to the top of the bond zone. 

To compute the downdrag force from the upper weak material, grout-to-ground bond stress 

values based on Table 5-3 should be used with consideration for the grouting technique used 

over the length of the micropile formed in the relatively weak materials. The maximum load 

along the micropile would occur at the top of the bond zone and would be the sum of the 

downdrag force and the load applied at the top of the micropile. The structural capacity of 

the micropile would be checked based on this total load. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-54 December 2005 

The use of micropiles for a foundation system on sites where downdrag forces are of concern 

offers several benefits. The small surface area of a micropile will result in relatively small 

downdrag forces transmitted from the settling soil to the micropile. Further isolation of the 

micropile from the moving soils can be accomplished by installation of an additional 

oversized outer casing through the settling soils. Battered micropiles should not be used in 

soil conditions where large soil settlements are expected because of the additional bending 

forces imposed on the piles. 

5.18 DESIGN OF MICROPILES FOR LATERAL LOADING 

5.18.1 General 

It is specifically noted that the analysis of a single vertical micropile for lateral loading 

and/or overturning moments is equivalent to that for a driven pile or drilled shaft. The user 

of this manual is referred to the NHI/FHWA reference manuals for design of driven piles and 

for drilled shafts (FHWA-NHI-05-042 and FHWA-IF-99-025, respectively) for specific 

modeling details related to lateral loading analysis. Herein, the overall design procedure for 

a laterally loaded micropile is provided (within the context of a p-y analysis) and specific 

issues that must be addressed for the design of a micropile subject to lateral load are 

discussed. 

5.18.2 Analysis Steps for Single Laterally Loaded Micropile 

Step 1: Determine basic pile input parameters for the micropile including: (1) pile 

length; (2) modulus of elasticity for grout, reinforcing bar, and steel casing; (3) 

distance from pile head to ground surface; and (4) slope of ground surface. 

Step 2: Divide the micropile into segments with uniform cross sectional properties. 

For each segment, provide the pile diameter, moment of inertia, and area of pile. 

A micropile subject to lateral loads and/or overturning moments will include a cased length 

in the upper portion of the micropile. A center steel reinforcing bar may be used along the 

entire length of the micropile, however the steel bar provides negligible resistance to lateral 

loads. Lateral loads and overturning moments applied at the ground surface will usually be 

carried by the portion of the micropile from the ground surface down to a depth on the order 

of 20 micropile diameters; below that depth bending moments will usually be negligible. 

The length of the micropile to be analyzed should be such that calculated bending moments, 

shear forces, and lateral pile movement are negligible at the bottom of the micropile. This 

length can be used to select the minimum micropile cased length. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-55 December 2005 

Step 3: Delineate the soil/rock profile into layers over the maximum anticipated 

penetration depth of the trial micropile. 

Step 4: Determine the required soil input parameters for each layer. For cohesive 

soil layers, the effective unit weight of the soil and the undrained shear strength is 

required for analysis while for cohesionless soils, the effective unit weight and 

drained friction angle is required. 

The user inputs two additional parameters: (1) ε50 which is the axial strain corresponding to a 

shear stress equal to 1⁄2 of the shear strength of the material (this parameter is used for clays 

only); and (2) slope of the soil resistance versus lateral deflection curve, k. These values are 

typically selected based on soil type using Tables 5-7 through 5-10. 

It is noted that user-defined p-y curves can be used for analysis where these curves are based 

on micropile lateral load test results (which include pile lateral movement measurements at 

the ground line and at various depths along the length of the micropile) from previous 

projects in similar ground or preproduction test piles. Actual foundation lateral 

displacements will likely be less than those measured in a load test since most load test 

setups do not incorporate the beneficial effects of pile cap stiffness and embedment below the 

ground surface which will likely be part of the actual foundation structure. 

Most engineers, however, simply use the p-y curves contained within programs such as 

LPILE. These p-y curves have not been developed specifically for relatively small diameter 

micropiles but can provide reasonably accurate results. Moreover, good subsurface and shear 

strength characterization of the ground in the upper 5 m (15 ft) of the subsurface profile is 

critical to developing p-y curves for analysis (Richards and Rothbauer, 2004). If overly 

conservative assumptions regarding soil shear strength near the ground surface are used, it is 

likely that ground line lateral movements will be significantly overpredicted. Site specific 

strength data should be obtained. 

Table 5-7. Values of ε50 for intact clays (after Reese et al., 2005). 

Consistency of clay ε50

Soft 0.020 

Medium 0.010 

Stiff 0.005 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-56 December 2005 

Table 5-8. Values of ε50 for stiff clays (after Reese et al. 2005). 

Undrained shear strength 

(kPa) (psi) 

ε50

50 – 100 7.3 – 14.5 0.007 

100 -200 14.5 – 29.0 0.005 

300 -400 43.5 – 58.1 0.004 

Table 5-9. Soil-modulus parameter (k) for sands (after Reese et al., 2005). 

Loose Medium Dense 

Relative Density (kPa/m) (lb/in3

) (kPa/m) (lb/in3) (kPa/m) (lb/in3) 

Submerged Sand 5,430 20 16,300 60 33,900 125 

Sand Above WT 6,790 25 24,430 90 61,000 225 

Table 5-10. Soil-modulus parameter (k) for clays (after Reese et al., 2005). 

Undrained Shear 

Strength Clay Static Cyclic 

Consistency (kPa) (psi) (kPa/m) (lb/in3

) (kPa/m ) (lb/in3) 

Soft 12 – 24 1.74 – 

3.47 8,140 30 - - 

Medium 24 – 48 3.47 – 

6.94 27,150 100 - - 

Stiff 48 – 96 6.94 – 

13.9 136,000 500 54,300 200 

Very Stiff 96 – 192 13.9 – 

27.8 271,000 1,000 108,500 400 

Hard 192 - 383 27.8 – 

55.6 543,000 2,000 217,000 800 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-57 December 2005 

Step 5: Determine the critical loading combinations and boundary conditions to be 

analyzed. 

For each loading combination, determine the axial load, lateral load, and overturning moment 

at the ground line to be analyzed. An important input to the analysis is the assumed 

boundary condition at the ground line. In general, the assumption of full fixity at the pile 

head will result in large calculated negative bending moments at the top of the pile and small 

lateral deflections at the ground line. Conversely, the assumption of a pinned pile head 

connection will result in the largest calculated bending moment below the ground surface and 

relatively large calculated movements at the ground surface. The use of vertical micropiles 

to carry lateral loads is a relatively new application and little data exists to define the 

appropriate level of fixity for a given micropile-footing connection to be assumed for design 

analyses. 

Typical practice is to evaluate the maximum bending moment from an analysis assuming 

pinned head conditions (i.e., 0% fixity) and the maximum bending moment from an analysis 

assuming fixed head conditions (i.e., 100% fixity). The structural capacity of the micropile is 

then checked for the larger of the two calculated bending moments. 

Calculated ground line deflections are also affected by the assumed level of fixity for the 

micropile-footing connection. For assessing ground line deflections, a representative level of 

fixity should be assumed. In other words, the approach used to evaluate structural capacity is 

based on the “worst-case” bending moment from two analyses. This approach should not be 

used to assess deformations, but instead the level of fixity assumed to evaluate ground line 

deflections should be consistent with the actual micropile-footing connection. If a certain 

level of fixity is assumed in design, this level of fixity must be at least achieved by the actual 

(i.e., as-built) micropile-footing connection. To this end, Table 5-11 provides preliminary 

guidance for selecting a level of fixity for a given micropile-footing connection. The level of 

fixity (i.e., 0, 50, or 100 percent) can then be used in a lateral pile analysis to compute the 

lateral ground line deflection. 

For a given micropile-footing connection, greater fixity than that reported in Table 5-11 may 

be able to be achieved. The user of this manual should assess fixity on a project-specific 

basis. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-58 December 2005 

Table 5-11. Guidance on Level of Fixity for Micropile-Footing Connections.

0 % Fixity (Pinned Head 

Condition) 50 % Fixity(1) 100 % Fixity (Fixed 

Head Condition)(1)

Casing embedment of 300 mm 

(12 in.) or less or 

Reinforcing bar embedment with 

or without bearing plate or 

Any detail where top of 

micropile embedment is at or 

below the level of the bottom 

reinforcement of the footing 

Casing embedment of 

450 mm (18 in.) or 

Shear connection 

between casing and 

existing footing with 

minimum casing 

embedment of 450 mm 

(18 in.) 

Casing embedment of 

600 mm (24 in.) or 

more 

(1) Guidance provided assumes that footing itself is restrained. For example, if only one 

row of piles in direction of loading then 0% fixity should be assumed 

Example LPILE analysis results are provided in Figure 5-19 and 5-20. The 50% fixity 

condition can be modeled in LPILE as follows: 

• Perform LPILE analysis for case of 100% fixity (i.e., assume slope of zero for top of 

micropile) and compute negative bending moment at ground line, Mneg (100%); 

• Perform second LPILE analysis with an assumed moment boundary condition equal 

to 50 percent of Mneg (100%); this analysis is used to obtain the ground line deflection. 

Example LPILE analysis results and structural evaluation of the cased length using the 

combined stress (i.e., combined axial and bending) check (Eqs. 5-4 and 5-6) are provided in 

Sample Problem No. 2. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-59 December 2005 

0

1

2

3

4

5

6

-40 -20 0 20 40 60

Bending Moment (kN-m)

Depth (m)

Fixed Head

50% Fixity

Free Head

Figure 5-19. LPILE Analysis Result for Bending Moment. 

0

1

2

3

4

5

6

-5 0 5 10 15 20

Deflection (mm)

Depth (m)

Fixed Head

50% Fixity

Free Head

Figure 5-20. LPILE Analysis Result for Lateral Micropile Deflection. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-60 December 2005 

Step 6: Determine structural capacity of the micropile for the critical case axial and 

lateral load. 

The structural capacity of the micropile should be verified for combined stresses due to axial 

load and bending moment using Eq. 5-3 or Eq. 5-6. As previously mentioned, it may be 

conservatively assumed that the maximum bending moment is carried completely by the steel 

casing with no load being carried by the grout inside the casing. For this evaluation, it is 

assumed that the structural capacity of the micropile is not impacted by potential weaknesses 

at the threaded casing connection. The capacity of the connection and its effect on lateral 

load capacity is discussed in Section 5.5.3 and Section 5.18.3. 

If the condition prescribed in Eq. 5-3 or Eq. 5-6 is not met, additional lateral loading capacity 

can be achieved by: 

• installing an oversized casing in the top portion of the micropile where bending 

moments are high; 

• constructing a larger micropile diameter at the top (which will tend to increase lateral 

soil resistance); 

• embedding the pile cap deeper below the ground surface to develop more passive 

resistance which will result in reduced groundline deflections and bending moments 

(for a given lateral load); or 

• battering some of the micropiles. 

These options would need to be evaluated on a project-specific basis. For example, 

embedding the pile cap deeper may not be a viable option if the foundation layout has 

already been finalized for the project. That is, specific options may be outside the control of 

the micropile contractor. 

Step 7: Determine pile acceptability based on deflection under the design load and 

modify the pile section properties, as needed, to meet lateral capacity and maximum 

groundline deflection criteria. 

5.18.3 Evaluation of Micropile Lateral Load Capacity at Threaded Casing Joints 

A conservative approach is provided herein to evaluate the bending moment capacity at a 

threaded casing joint. The method assumes that the wall thickness, tw, of the casing at the 

location of a threaded joint is equal to 50 percent of the intact casing wall thickness; therefore 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-61 December 2005 

the section modulus at the joint location is reduced. The outside diameter of the casing at the 

joint is then equal to OD – 2 (tw/2) = OD – tw. The reduced section modulus of the threaded 

joint, Sjoint is calculated as: 

( )

( ) / 2

( ) 64

( )/ 2

4 4

int

int

w

w

w

jo

jo OD t

OD t ID

OD t

I

S −

× − −

= − =

π

 (Eq. 5-26) 

Eq. 5-3 is used to evaluate the maximum bending moment at a joint location, Mmax (joint), as 

follows: 

b

e

a

a

a

jo jo F

F

f

F

f M S 















× − 













 = × − ' max ( int) int 1 1 (Eq. 5-27) 

The use of this method is demonstrated and discussed in Sample Problem No. 2. 

5.19 LATERAL RESISTANCE OF MICROPILE GROUPS 

5.19.1 General 

Similar to other types of piles, micropile behavior in a group configuration is influenced by 

spacing between individual elements. The deflection of a pile group under a lateral load may 

be 2 to 3 times larger than the deflection of a single pile loaded to the same intensity. 

Holloway et al. (1981) and Brown et al. (1988) reported that piles in trailing rows of pile 

groups have significantly less resistance to a lateral load than piles in the lead row, and 

therefore exhibit greater deflections. This is due to the pile-soil-pile interaction that takes 

place in a pile group. The pile-soil-pile interaction results in the lateral capacity of a pile 

group being less than the sum of the lateral capacities of the individual piles comprising the 

group. Hence, laterally loaded pile groups have a group efficiency of less than 1. Based on 

experiments conducted as part of the FOREVER National Project (FOREVER, 2003) on 

horizontally loaded micropile groups, the following conclusions were drawn: 

• For in-line micropiles, group effects are negligible for micropile spacing between 6 to 

7 diameters; and 

• For micropiles arranged in a row perpendicular to the direction of loading, group 

effects are negligible for micropile spacing just greater than 3 diameters. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-62 December 2005 

The lateral capacity of an individual pile in a pile group is a function of its position in the 

group and the center to center pile spacing. Piles in trailing rows of pile groups have less 

resistance to a lateral load than pile sin the lead row, and therefore exhibit greater deflections. 

This is due to the pile-soil-pile interaction that takes place in a pile group. Brown et al. 

(1998) proposed a p-multiplier, Pm, be used to modify the p-y curve of an individual pile 

based upon the piles row position to account for this pile-soil-pile interaction. An illustration 

of the p-multiplier concept is presented in Figure 5-21. For piles in a given row, the same Pm

value is applied to all p-y curves along the length of the pile. In a lateral load test of a 3 by 3 

pile group in very dense sand with a center to center pile spacing of 3b, Brown found the 

leading row of piles had a Pm of 0.8 times that of an individual pile. The Pm values for the 

middle and back row of the group were 0.4 and 0.3, respectively. 

A summary of additional laterally loaded driven pile group studies is provided in FHWANHI-05-042 (2005). Also, preliminary results from the FOREVER project indicate that Pm

multipliers for micropiles may be slightly higher than those recommended herein, however, 

only limited data from centrifuge testing is available at this time. 

Brown and Bollman (1993) proposed a p-multiplier procedure for the design of laterally 

loaded pile groups. This approach, outlined in the step by step procedure that follows, may 

be used for the design of laterally loaded micropile groups. 

5.19.2 Step By Step Design Procedure For Laterally Loaded Pile Groups 

Step 1: Develop p-y curves for single pile (see guidance for single pile previously 

provided) 

Step 2: Perform LPILE analyses 

a. Perform LPILE analyses using the Pm values for each row position to 

develop load-deflection and load-moment data. 

b. Based on current data, it is suggested that Pm values of 0.8 be used for the 

lead row, 0.4 for the second row, and 0.3 for the third and subsequent 

rows. These recommendations are considered reasonable for center to 

center pile spacing of three pile diameters and pile deflections at the 

ground surface ranging from 10 to 15 percent of the micropile diameter. 

For larger center to center spacings or smaller deflections (as would be 

anticipated for typical micropile groups), these Pm values should be 

conservative. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-63 December 2005 

c. Determine shear load (at the ground line) versus deflection behavior for 

piles in each row. Plot load versus pile head deflection results similar to 

as shown in Figure 5-22(a). This plot can be developed for each row by 

selecting a set of shear loads and using LPILE to evaluate the deflection 

for each shear load. 

Step 3: Estimate group deflection under lateral load 

a. Average the load for a given deflection from all piles in the group to 

determine the average group response to a lateral load as shown in Figure 

5-22(a). 

b. Divide the lateral load to be resisted by the pile group by the number of 

piles in the group to determine the average lateral load to be resisted by 

each pile. Enter load-deflection graph similar to Figure 5-22(a) with the 

average load per pile to estimate group deflection using the group average 

load deflection curve. 

Step 4: Evaluate pile structural acceptability 

a. Plot the maximum bending moment determined from LPILE analyses 

versus deflection for each row of piles as illustrated in Figure 5-22(b). 

b. Use the estimated group deflection under the lateral load per pile to 

determine the maximum bending moment for an individual pile in each 

row. Evaluate structural capacity according to Eq. 5-3 or Eq. 5-6 where 

the Mmax used in these equations is the maximum bending moment 

corresponding to the estimated group deflection. 

Step 5: Perform refined pile group evaluation that considers superstructuresubstructure interaction. 

A detailed example demonstrating this procedure for a driven pile group can be found in 

Appendix F.8 of FHWA-NHI-05-042 (2005). The steps are the same as would be used for a 

micropile group. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-64 December 2005 

Figure 5-21. Illustration of P-Multiplier Concept for Lateral Group Analysis (after FHWANHI-05-042, 2005). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-65 December 2005 

Figure 5-22. Load-Deflection and Bending Moment-Deflection for Pile Group Analysis 

(after FHWA-NHI-05-042, 2005). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-66 December 2005 

5.19.3 Soil-Structure Interaction Analyses for Micropile Groups 

The methods described above uses analyses of single micropiles as a means to evaluate 

lateral load response of micropile groups. Micropiles are often used in combination with 

existing deep foundation elements. Because of this, estimates on the amount of load that will 

be shared by each individual foundation element need to be made. In some cases, this may 

be a statically indeterminate problem (i.e., loads need to be carried by, for example, more 

than 2 piles in a given cross section) requiring that the stiffness of the foundation elements 

(both existing and new micropiles) and the pile cap be considered in the analysis. 

The computer program FB-Pier (2001) was developed with FHWA support as the primary 

design tool for analysis of pile groups under axial and lateral loads. This program is a 

nonlinear, finite element analysis, soil-structure interaction program. FB-Pier uses a pmultiplier approach in the evaluation of laterally loaded pile groups under axial, lateral, and 

combined axial and lateral loads. Additional information on FB-Pier program capabilities 

can be found at http://bsi-web.ce.ufl.edu. The computer program GROUP (2003) can also be 

used to model pile groups (see www.ensoftinc.com). 

5.19.4 Battered Micropiles 

The lateral load-carrying capacity of individual vertical micropiles is limited compared to 

more conventional drilled shafts and driven piles. As for other deep foundation systems, 

micropiles can be battered as a means to provide additional resistance to lateral loading. 

Note that since micropile drilling equipment is designed to drill both vertically and 

subvertically, there is not a significant increase in cost (on a per unit length basis) or quality 

of finished pile for battered micropiles as compared to vertical micropiles. 

The calculation of lateral capacity of a single battered micropile is demonstrated in Sample 

Problem No. 1. The total lateral capacity of the battered micropiles is the sum of the lateral 

capacities of each battered micropile. This lateral capacity is compared to the lateral load 

applied to the foundation from the superstructure. If this sum is less than the lateral load 

applied to the foundation, the remaining load is carried by the micropiles in bending (i.e., this 

remaining load is used in a lateral load (i.e., LPILE analysis) for the structure). 

Micropile groups with vertical and battered piles should be analyzed using the soil-structure 

interaction programs described in Section 5.19.3. Pile groups that contain battered piles are 

relatively stiff and will undergo less lateral movement for a given load than for a system with 

the same number of vertical piles. However, this increased system stiffness also results in 

greater bending moments in the pile cap which is a concern, especially for highly seismic 
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Micropile Design & Construction 5-67 December 2005 

regions. Moreover, battered micropiles should not be used where the potential for ground 

settlement around the battered micropile is a possibility. These settlements will induce 

additional bending moments in the micropiles and some loss of support. Additional 

discussion on batter piles for seismic regions is discussed in Section 5.21. 

5.20 BUCKLING CONSIDERATIONS FOR MICROPILES 

5.21.1 General 

Because micropiles are frequently installed to or into relatively sound rock or dense/hard soil, 

their capacity is frequently dictated by the structural strength of the element, rather than by 

the side resistance developed between the micropile grout and surrounding ground. The 

potential for buckling is reduced by the lateral restraint provided by the surrounding ground, 

however where soft or weak soils (e.g., very soft sedimentary deposits), voids (e.g., karstic 

formations), or liquefiable soils overly the bearing strata, buckling may potentially control 

the load-carrying capacity of a micropile and should be considered in design. For this 

reason, it is critical that the subsurface investigation identify these critical zones and, also, 

the depth of these zones should be recorded during the micropile installation process. 

Herein, design analyses are presented to address micropile buckling. A more detailed 

coverage of micropile buckling is provided in Cadden and Gomez (2002). 

5.21.2 Micropile Surrounded by Very Weak Or Liquefiable Soil 

It is not possible to specifically define “very weak soil” or liquefiable soils by means of a 

readily available parameter such as SPT N value for purposes of evaluating buckling 

potential. Rather, a simple analysis is presented which uses a soil modulus parameter to 

evaluate whether buckling of the micropile is possible. The analysis involves comparing the 

critical buckling load for an axially loaded micropile, Pcr, to the maximum axial stress (i.e., 

capacity) of the micropile. For simplicity, only the contribution of the steel casing to resist 

buckling is considered, i.e., the potential benefits of grout within the casing and outside the 

casing are not considered as part of this analysis. Eq. 5-28 is used to estimate the critical 

buckling load: 

 

2

2

2

2

π

π E l

l

E I P s

cr = + (Eq. 5-28) 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-68 December 2005 

where: 

E = modulus of elasticity of the steel casing (e.g., 200,000 MPa (29,000 ksi)); 

I = moment of inertia of the micropile (previously defined for a steel casing in Eq. 5- 4); 

l = “unsupported” length of the micropile assumed to be the thickness of the relatively weak 

or potentially liquefiable soil; and 

Es = lateral reaction modulus of the soil surrounding the micropile over the “unsupported” 

length. 

Using Eq. 5-28, the limiting lateral reaction soil modulus for buckling, Es

LIMIT can be 

evaluated as: 





































 





=

2 2

4

1

y

LIMIT

s

F

E

A

I

E (Eq. 5-29) 

The first of the two terms inside the brackets in Eq. 5-29 represents the geometric properties 

of the pile, while the second term represents its material properties. The combination of these 

two terms is referred to as the pile factor and is given in units of [stress-1]. 

Using Eq. 5-29, if the Es

LIMIT value is less than the measured or assumed soil modulus, Es, 

then the geotechnical and structural strength of the micropile will control the micropile 

capacity and buckling does not need to be considered further. If the Es

LIMIT value is greater 

than Es, buckling should be evaluated further. Tables 5-12 and 5-13 provide ranges of Es

values for various soil types. 

Figure 5-23 provides a summary chart of limiting lateral reaction modulus values for various 

micropile materials. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-69 December 2005 

Table 5-12. Elastic Constants of Various Soils Based on Soil Type 

(modified after AASHTO, 2002). 

Soil Type Range of Equivalent Elastic Modulus, 

kPa (ksf) 

Clay 

Soft sensitive 

Medium stiff 

Very stiff 

2,400 - 14,400 (50 - 300) 

14,400 - 48,000 (300 – 1,000) 

48,000 - 96,000 (1,000 – 2,000) 

Loess 14,400 - 57,500 (300 – 1,200) 

Silt 1,900 - 19,000 (40 – 400) 

Fine sand 

Loose 

Medium dense 

Dense 

7,600 - 11,500 (160 – 240) 

11,500 - 19,000 (240 – 400) 

19,000 - 29,000 (400 – 600) 

Sand 

Loose 

Medium dense 

Dense 

9,600 - 29,000 (200 – 600) 

29,000 - 96,000 (600 – 1,000) 

96,000 - 76,000 (1,000 – 1,600) 

Gravel 

Loose 

Medium dense 

Dense 

29,000 - 76,000 (600 – 1,600) 

76,000 - 96,000 (1,600 – 2,000) 

96,000 - 192,000 (2,000 – 4,000) 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-70 December 2005 

Table 5-13. Elastic Constants of Various Soils Based on SPT N Value 

(modified after AASHTO, 2002).

Soil Type Equivalent Elastic Modulus, 

kPa (ksf) 

Silts, sandy silts, slightly 

cohesive mixtures 400 (N1)60 (8 (N1)60) 

Clean fine to medium sands 

and slightly silty sands 700 (N1)60 (14 (N1)60) 

Coarse sands and sands with 

little gravel 1,000 (N1)60 (20 (N1)60) 

Sandy gravels 1,200 (N1)60 (24 (N1)60) 

97

105

159

71

27

23

19

17

610610610610610610

295

253

310

343

165

350

0

100

200

300

400

500

600

700

5.5"x0.36" 80 ksi casing

7"x0.5" 80 ksi casing

7"x0.73" 80 ksi casing 

9.625"x0.47" 80 ksi casing

5 1⁄2 -inch casing

6 5⁄8–inch casing

8-inch casing

10 3⁄4 -inch casing

#10 Bar#11 Bar#14 Bar#18 Bar#20 Bar#28 Bar

30/1632/2040/2052/2673/53

103/51

Limiting Es (psi)

Figure 5-23. Limiting Lateral Modulus Values for Various Micropile Materials (after 

Cadden and Gomez, 2002). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-71 December 2005 

If the analysis presented above indicates the potential for buckling (i.e., Es

LIMIT > Es), the 

allowable compression load for the cased section subject to buckling should be calculated. 

Eq. 5-1 can be modified to account for buckling as: 

[ ] ( )

y steel

a

c allowable c grout grout y steel bar ca g F

F P f A F A A

−

− = − × + − + ×

0.47

0.4 0.47 sin

' (Eq. 5-30) 

In Eq. 5-30, the allowable stress, Fa is calculated based on the following: 

 













































< ≤ = × − −

2

2

2

0 , 1

c

y steel t

c a

t C

r

Kl

FS

F

C F

r

Kl if (Eq. 5-31) 

[ ]2

2

,

t

steel

c a

t FS Kl r

E C F

r

Kl if π

> = (Eq. 5-32) 

where 

y steel

steel

c F

E C

−

=

2 2π 

 K = effective length factor (assumed equal to 1.0 and previously defined in 

Section 5.6); 

 l = unsupported length of the micropile; 

 rt = radius of gyration of the steel section only = (I/A)1/2; 

 FS = factor of safety = 2.12 (see Table 10.32.1.A in AASHTO (2002)) and 

 Fy-steel = the casing yield stress. 

For this analysis, the unsupported length of the micropile, l, is assumed to be the thickness of 

the weak soil surrounding the micropile and the effective length factor is conservatively 

assumed to be 1.0. Also, this analysis can be used to consider scour in which the depth of 

scour is assumed to be the unsupported length of the micropile. 

Where combined axial and bending stresses are present and where buckling should be 

checked (based on the evaluations presented in this section), Eq. 5-3 should be used. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-72 December 2005 

5.20.3 Micropiles Installed through Voids 

Figure 5-24 illustrates the case of a micropile installed through a void such as for a micropile 

installed in karst terrain. The micropile is subject to a centered load P applied at the top, and 

penetrates consistent ground throughout its entire length, except at the void location. 

The structural capacity of such a micropile should be checked using Eq. 5-30. Depending on 

the procedure followed for micropile installation, the portion of the pile through the void may 

be analyzed as a doubly pinned, pinned-fixed, or fixed-fixed column and k selected 

accordingly. The model in Figure 5-24 assumes that the pile has been grouted only along the 

bond length, and that an annular gap around the casing exists throughout its unbonded length. 

Under these conditions, the micropile can be conservatively assumed to be pinned on both 

ends such that k = 1.0. 

Figure 5-24. Micropile Installed Through Voids in Karstic Terrain; (a) Actual Configuration, 

(b) Model Used for Estimation of Structural Capacity (after Cadden and Gomez, 2002). 

P 

M 

P

(a) (b)

voi
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-73 December 2005 

In cases where the pile extends through hard rock above the void, consideration should be 

given to the effect this may have on the ability of lateral loads or moments to transfer to the 

portion of the pile within the void. If the pile is fixed in a rock layer above a void, then there 

will not be any lateral load that is transferred to portion of micropile over the length of the 

void; only vertical load is transferred over that length. The calculated allowable load 

assuming lateral load is transferred over the length of the void is therefore conservative for 

this case. 

Micropiles may be susceptible to buckling-induced failure at the casing joints. To consider 

the effect of joints, Eq. 5-29 is used to evaluate the critical or limiting lateral soil reaction 

using a reduced value for the moment of inertia. This value for I is calculated as for Ijoint in 

Eq. 5-26. It is noted that this method is conservative since it assumes that the micropile 

stiffness is equivalent to that of the joint over the entire length of the unsupported micropile. 

More detailed structural analyses could be carried out that only use the reduced casing 

stiffness over the length of the joint, however, these are relatively complex and beyond the 

scope of this report. As a practical consideration, however, micropiles installed through karst 

must be designed for buckling, considering the presence of the casing joints, or should 

include installation of continuous internal reinforcement along portions of micropile 

traversing voids or very soft or loose soil. 

5.21 SEISMIC CONSIDERATIONS 

5.21.1 General 

Micropiles have been used for seismic retrofit projects in which existing deep foundations 

have been shown to have insufficient capacity to resist seismic forces consistent with the 

design earthquake. As discussed in Chapter 3, seismic retrofit projects typically involve 

adding micropiles to an existing foundation to provide additional capacity required to 

withstand seismic effects (i.e., overturning, uplift, lateral forces). Current guidance for 

seismic design of bridge foundations is provided in Division I-A of AASHTO (2002) and the 

recommendations provided here apply generally to micropiles subject to seismic effects. 

Additional information on seismic design of micropiles is found in JPWRI (2002) 

As shown in Figure 5-25, the seismic response of a pile foundation involves the distribution 

of a set of superstructure loads into the surrounding soil mass through the pile members. The 

general case involves consideration of three components of translational forces (an axial and 

two lateral shear forces) and three components of rotational moments (a torsional moment 

about the pile axis and two rotational moments about two orthogonal horizontal axes) along 

the pile member. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-74 December 2005 

 

Figure 5-25. Three-dimensional Soil Pile Interaction (after Bryant and Matlock, 1977). 

The evaluation of the dynamic response of a pile foundation can be performed using either a 

pseudo-static analysis or a dynamic response analysis. A realistic approach to dynamic 

analysis of pile foundations should account for the nonlinear behavior of near-surface soils 

and the layered nature of typical soil profiles. In view of these constraints, current design 

practice usually models the soil support characteristics along the pile by discrete nonlinear 

springs. The pile is modeled as a beam-column supported by one set of lateral springs (using 

p-y curves as previously discussed) and another set of axial springs. The curves for the axial 

load transfer characteristics of the pile are referred to as t-z curves. Torsional resistance 

against rotation of individual piles is usually ignored or assumed to be negligible for highway 

bridges, as most deep highway foundations are supported by pile groups and torsional loads 

on pile groups become resolved as lateral loads on the individual piles. 

For evaluating the vertical response of piles subject to dynamic loading, t-z curves are 

generally calculated over the entire length of the pile. Procedures for evaluating t-z curves 

are provided by Lam and Martin (1986, 1997) and Kraft et al. (1981a, b). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-75 December 2005 

5.21.2 Use of Battered Micropiles in Highly Seismic Regions 

Vertical micropiles in groups do little to resist horizontal seismic deformations due to their 

relatively low stiffness (FOREVER, 2003). Under seismic loading, however, battered 

micropiles will have a reduced positive bending moment (as compared to vertical 

micropiles), but significantly higher negative bending moments at the pile head. In current 

U.S. practice, the concern over excessive bending moments being mobilized during the 

design seismic event has resulted in some owner agencies disallowing the use of battered 

piles for seismic retrofit projects. 

Trinh et al. (2004) performed finite element analyses to investigate the effects of combined 

axial compression and lateral displacements on battered micropiles. The micropile 

foundation consisted of a square column supported on a 4572 mm by 4572 mm (180 in. by 

180 in.) 915-mm (36-in.) high pile cap. Twelve, 178-mm (7-in.) diameter micropiles 

arranged in the configuration shown in Figure 5-26 were used to support the pile cap. 

Micropiles were battered inward at 15 degrees and outward at 25 degrees from the vertical. 

2

3 4

5

6

7

8

10 9

11

12

X

1 Y

60" Square Column

180" Square Pile Cap

V 0

2

3 4

5

6

7

8

9

10

11

12

X

1 Y

OUT

IN

IN

IN

IN

IN

IN

OUT

OUT

OUT

OUT

OUT

Column

Pile Cap

0

(a) Pile spacing (b) Pile inclination 

Figure 5-26. Plan View of the Micropile Foundation (after Trinh et al., 2004). 

They concluded that with an adequate amount of flexural reinforcement in the pile cap, the 

failure mode of the micropile foundation will primarily involve yielding of the micropiles or 

pullout of the micropile itself with little (if any) yielding of the micropile-footing connection. 

Figure 5-27 shows the effect of increasing steel reinforcement in the cap. This figure 

indicates that a fully ductile response of the foundation can be achieved with a flexural 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-76 December 2005 

reinforcement ratio, ρs (equal to area of flexural steel reinforcement to cross section area) of 

about 0.5 percent. Ductility implies that the foundation does not undergo significant loss of 

lateral support at large lateral displacements and/or where the ratio of ultimate deformation to 

deformation at yield is relatively large. If the micropile-footing connection were to incur 

higher than expected loading, the connection is expected to perform in a highly ductile 

manner and the potential failure mechanism would be either pullout of the micropile or 

yielding of the micropile. 

5.21.3 Load Sharing with Existing Foundations 

Applications in which micropiles are used to seismically retrofit an existing deep foundation 

requires that load sharing between existing foundation elements and the micropiles be 

evaluated. Where additional foundation elements are required to support additional 

compression and uplift forces (e.g., rocking motions), vertical micropiles are used. 

Figure 5-27. Lateral Response of Micropile Foundation for Different Flexural 

Reinforcement Ratio (after Trinh et al., 2004). 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-77 December 2005 

For the retrofit design of an old or deteriorated foundation or for a foundation in which the 

original structural design details and specifications are uncertain, design seismic loads should 

be assumed to be carried by the micropiles only. Load sharing between existing and new 

foundations should only be considered if sufficient information on the existing foundation 

system (i.e., as-built drawings, load test results, design calculations) is available. Where this 

is considered, soil-structure interaction analyses will need to be performed. 

5.21.4 Pile Uplift Capacity

Individual piles in pile groups will be subjected to significant uplift resulting from seismic 

loading. The overturning moment applied by the seismic lateral force to the pile cap is 

typically resisted by axial resistance in the piles with the outermost piles in the group being 

subjected to relatively large cyclic axial loads. 

Section 6.4.2(B) of AASHTO (2002) Division I-A suggests that some separation between the 

bottom of the pile cap and the foundation soil is allowed, provided that the foundation soil is 

not susceptible to loss of strength (e.g., liquefaction) under the imposed cyclic loading. For 

pile groups, up to one-half the bearing area of the pile cap is allowed. In Section 6.4.2(C), 

AASHTO recommends that the ultimate capacity of the piles be used in designing the 

foundation for uplift forces resulting from seismic forces (i.e., FS = 1.0 on geotechnical uplift 

capacity). It is noted that all other permanent loads are included in this assessment. 

Structural requirements including embedment length of the pile in the pile cap and the 

detailing of the connections need to be considered, as discussed below. 

As part of the Trinh et al (2004) study, battered micropiles on the outboard side of the pile 

cap were shown to develop large tensile forces and relatively severe cracking even though 

the foundation was subject to large vertical compression forces. They concluded that a 

prudent design approach would include increasing the amount of vertical shear reinforcement 

(i.e., placing steel reinforcement at closer spacing) in the cap near the piles that are furthest 

from the column (i.e., the outboard piles) to mitigate cracking of the cap concrete. 

5.21.5 Liquefaction 

In many earthquakes where liquefaction occurs, the soil may not liquefy until the end of the 

earthquake. Therefore, piles in liquefied ground may still be able to rely on the vertical and 

lateral support of the soil in the potentially liquefied zone during the earthquake. However, 

due to uncertainties as to exactly when liquefaction will occur, it is common practice to 

assign a reduced vertical and lateral resistance to potentially liquefiable soil surrounding a 

pile if the pile is expected to function as a load carrying member during and after an 

earthquake. Results presented by Ishihara and Cubrinovski (1998) suggest that the lateral 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-78 December 2005 

resistance of a pile in liquefied ground is approximately 0.1 to 1.0 percent of the lateral 

resistance in non-liquefied ground. Therefore, if a pile foundation in potentially liquefiable 

soil is expected to carry lateral loads after the surrounding soil liquefies, batter piles may be 

required to provide adequate lateral support. This reduction in lateral support is particularly 

important for relatively flexible micropiles. 

Studies reported in the FOREVER (2003) project showed that vertical micropiles were not 

effective in reducing liquefaction. Batter micropiles, however, were shown to limit 

seismically-induced soil movements (and pore pressure buildup) resulting in no liquefaction 

in the zone affected by the piles, whereas the free-field soil did undergo liquefaction. If 

batter piles are used, the pile cap connections should be designed to sustain moment loads 

induced by lateral movements and the batter piles should be designed to sustain lateral loads 

due to soil settlement. 

 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-79 December 2005 

5.22 REFERENCES 

AASHTO (1988), “Manual on Subsurface Investigations”, American Association of State 

Highway and Transportation Officials Publication, Washington, D.C. 

AASHTO (2002), “Standard Specifications for Highway Bridges”, Association of State 

Highway and Transportation Officials Publication, Washington, D.C. ISBN: 156051-

171-0. 

Brown, D. A., Morrison, C., and Reese, L. C. (1988), “Lateral Load Behavior of Pile Group 

in Sand”, ASCE Journal of Geotechnical Engineering, Vol. 114, No. 11, pp. 1261-1276. 

Brown, D. A. and Bollman, H. T. (1993), “Pile-Supported Bridge Foundations Designed For 

Impact Loading”, Appended Document to the Proceedings of Design of Highway Bridges 

for Extreme Events, Crystal City, Virginia, pp. 265-281. 

Bruce, D. A. and Gemme, R., (1992) “Current Practice in Structural Underpinning Using 

Pinpiles,” Proceedings, New York Met Section, ASCE Seminar, New York, April 21-22, 

46 pages. 

Bryant, L.M. and Matlock, H. (1977), "Three Dimensional Analysis of Framed Structures with 

Nonlinear Pile Foundations," Proc. 9th Annual Offshore Technology Conference, Houston, 

Texas, Paper No. 2955. 

Cadden, A. and Gomez, J. (2002), “Buckling of Micropiles – A Review of Historic Research 

and Recent Experiences”, Schnabel Engineering Associates Report, West Chester, PA. 

Cheney, R. S. (1988), “Permanent Ground Anchors”, Federal Highway Administration 

Report, Report No. FHWA-DP-68-1R, Washington, D.C. 

CCTG (1992). “Technical Rules for the Design and Calculation of the Foundations of Civil 

Engineering Works,” Publication 62, Title V. 

DFI (2004), “Guide to Drafting a Specification for Micropiles”, Deep Foundations Institute, 

The International Association of Foundation Drilling, 60 pages, New Jersey. 

Elias, V., Christopher, B.R., and Berg, R.R. (2001), “Mechanically Stabilized Earth Walls 

and Reinforced Soil Slopes: Design and Construction Guidelines”, Federal Highway 

Administration, Report No. FHWA-NHI-00-043, Washington, D.C. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-80 December 2005 

Eurocode EC8 (1994), “Structures in Seismic Regions, Part 5, Foundations, Retaining 

Structures, and Geotechnical Aspects.” 

FB-PIER (2001), “A Program for the Geotechnical and Structural Aspects of Foundation and 

Pier Design”, Federal Highway Administration and University of Florida, Bridge 

Software Institute (BSI), Manual No. of the Program FHWA-IF-01-010, Distribution of 

software at http://bsi-web.ce.ufl.edu. 

FHWA/NHI (2001), “Manual on Subsurface Investigations”, Federal Highway 

Administration, Manual No. FHWA NHI-01-031, Mayne, P. W., Christopher, B. R., and 

DeJong, J., July. 

Federal Highway Administration (2005), “Design and Construction of Driven Pile 

Foundations”, Hannigan, P. J., Goble, G. G., Thendean, G., Likins, G. E., and Rausche, 

F., Publication No. FHWA-NHI-05-042, United States Department of Transportation, 

December. 

Federal Highway Administration (1997), “Drilled and Grouted Micropiles, State-of-Practice 

Review”, Bruce, D. A. and Juran, I., Report No. FHWA-RD-96-016/019, United States 

Department of Transportation, July, Four Volumes. 

Federal Highway Administration (1999), “Drilled Shafts: Construction Procedures and 

Design Methods”, O’Neil, M. W. and Reese, L. C., Publication No. FHWA-HI-99-025, 

United States Department of Transportation, August. 

FOREVER (2003), “Synthesis of the Results of the National Project on Micropiles”, 

International Center for Ground Improvement, Polytechnic University, Juran, I, Jahir 

Hasan, Weinstein, G. M, and Sourisseau, L. 

GROUP (2003), “A Program for the Analysis of Piles in a Group”, Ensoft Engineering 

Software, Distribution of software http://www.ensoftinc.com/. 

GEC No. 4 (1999), “Ground Anchors and Anchored Systems”, Geotechnical Engineering 

Circular 4, Federal Highway Administration Publication, Sabatini, P. J., Pass, D. G., and 

Bachus, R. C., Publication Number: FHWA-IF-99-015.

GEC No. 5 (2002), “Evaluation of Soil and Rock Properties”, Geotechnical Engineering 

Circular 5, Federal Highway Administration Publication, Sabatini, P. J., Bachus, R. C., 

Mayne, P. W., Schneider, J. A., and Zettler, T. E., Publication Number: FHWA-IF-02-

034. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-81 December 2005 

Holloway, D. M., Moriwaki, Y. Stevens, J. B., and Perez, J-Y. (1981), “Response of a Pile 

Group to Combined Axial and Lateral Loading”, Proceedings of the 10th International 

Conference on Soil Mechanics and Foundation Engineering, Boulimia Publishers, 

Stockholm, Vol. 2, pp. 731-734. 

Hough, B.K. (1959), “Compressibility as the Basis for Soil Bearing Value,” ASCE Journal 

of Soil Mechanics and Foundation Engineering, Vol. 85, No. SM4, pp. 11-39. 

Ishihara, K. and Cubrinovski, M. (1998), “Soil-Pile Interaction in Liquefied Deposits 

undergoing Lateral Spreading,” Proc. 11th Danube-European Conference on Soil 

Mechanics and Geotechnical Engineering, Porec, Croatia, pp. 51-64. 

Japanese Public Works Research Institute (JPWRI) (2002), “Design and Execution Manual for 

Seismic Retrofitting of Existing Pile Foundations with High Capacity Micropiles”, 

Foundation Engineering Research Team, Structures Research Group. 

Kraft, L.M., Jr, Focht, J., Jr. and Amerasinghe, S.F. (1981a), “Friction Capacity of Piles 

Driven into Clay,” Journal of Geotechnical Engineering Division, ASCE, Vol. 107, No. 

GT11, pp. 1521-1541. 

Kraft, L.M., Jr, Ray, R. and Kagawa, T. (1981b), “Theoretical t-z Curves,” Journal of 

Geotechnical Engineering Division, ASCE, Vol. 107, No. GT11, pp. 1543-1561. 

Lam, I.P. and Martin, G.R. (1986), "Seismic Design of Highway Bridge Foundations - Vol. II. 

Design Procedures and Guidelines," Report No. FHWA/RD-86-102, U.S. Department of 

Transportation, Federal Highway Administration, McLean, Virginia, 167 p. 

Lam, I.P. and Martin, G.R. (1997), "Current Developments in Seismic Design of Bridge 

Foundations," Proc. Transportation Research Board 76th Annual Meeting, Session No. 236, 

Washington, District of Columbia, 21 p. 

Meyerhoff, G.G. (1976), “Bearing Capacity and Settlement of Piled Foundations”, 

Proceedings of the American Society of Civil Engineers, GT#3, pp. 197-228. 

Ostermayer, H. (1975), “Construction, Carrying Behavior, and Creep Characteristics of 

Ground Anchors”, Conference on Diaphragm Walls and Anchorages, Institute of Civil 

Engineers, London. 

PTI (2004) “Recommendations for Prestressed Rock and Soil Anchors”, Post-Tensioning 

Institute Publication. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-82 December 2005 

Reese, L. C., Wang, S. T., Isenhower, W. M., Arréllaga, J. A., and Hendrix, J., (2005), “A 

Program for Analysis of Single Piles Under lateral Load”, Version 5.0.18, Ensoft Inc., 

Austin, TX. 

Richards, T.D. and Rothbauer, M.J. (2004), “Lateral Loads on Pin Piles (Micropiles),” 

Geotechnical Special Publication “Drilled Shafts, Micropiling, Deep Mixing, Remedial 

Methods, and Specialty Foundation Systems”, ASCE Publication, No.: 124, pp.158-174. 

Trinh, R.S., Jain, V., Kunnath, S.K., and Chai, Y.H. (2004), “Finite Element Modeling of 

Inclined Micropile Foundation under Combined Axial Compression and Lateral 

Displacement”, Final Summary Report submitted to SALUT. 

Weatherby, D. E. (1982), “Tiebacks”, Federal Highway Administration Report, Report No. 

FHWA/RD-82/047, McLean, VA. 

Xanthakos, P.P., Abramson, L. W., and Bruce, D.A., (1994) “Ground Control and 

Improvement”, John Wiley & Sons, Inc., New York, NY. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-79 December 2005 

5.22 REFERENCES 

AASHTO (1988), “Manual on Subsurface Investigations”, American Association of State 

Highway and Transportation Officials Publication, Washington, D.C. 

AASHTO (2002), “Standard Specifications for Highway Bridges”, Association of State 

Highway and Transportation Officials Publication, Washington, D.C. ISBN: 156051-

171-0. 

Brown, D. A., Morrison, C., and Reese, L. C. (1988), “Lateral Load Behavior of Pile Group 

in Sand”, ASCE Journal of Geotechnical Engineering, Vol. 114, No. 11, pp. 1261-1276. 

Brown, D. A. and Bollman, H. T. (1993), “Pile-Supported Bridge Foundations Designed For 

Impact Loading”, Appended Document to the Proceedings of Design of Highway Bridges 

for Extreme Events, Crystal City, Virginia, pp. 265-281. 

Bruce, D. A. and Gemme, R., (1992) “Current Practice in Structural Underpinning Using 

Pinpiles,” Proceedings, New York Met Section, ASCE Seminar, New York, April 21-22, 

46 pages. 

Bryant, L.M. and Matlock, H. (1977), "Three Dimensional Analysis of Framed Structures with 

Nonlinear Pile Foundations," Proc. 9th Annual Offshore Technology Conference, Houston, 

Texas, Paper No. 2955. 

Cadden, A. and Gomez, J. (2002), “Buckling of Micropiles – A Review of Historic Research 

and Recent Experiences”, Schnabel Engineering Associates Report, West Chester, PA. 

Cheney, R. S. (1988), “Permanent Ground Anchors”, Federal Highway Administration 

Report, Report No. FHWA-DP-68-1R, Washington, D.C. 

CCTG (1992). “Technical Rules for the Design and Calculation of the Foundations of Civil 

Engineering Works,” Publication 62, Title V. 

DFI (2004), “Guide to Drafting a Specification for Micropiles”, Deep Foundations Institute, 

The International Association of Foundation Drilling, 60 pages, New Jersey. 

Elias, V., Christopher, B.R., and Berg, R.R. (2001), “Mechanically Stabilized Earth Walls 

and Reinforced Soil Slopes: Design and Construction Guidelines”, Federal Highway 

Administration, Report No. FHWA-NHI-00-043, Washington, D.C. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-80 December 2005 

Eurocode EC8 (1994), “Structures in Seismic Regions, Part 5, Foundations, Retaining 

Structures, and Geotechnical Aspects.” 

FB-PIER (2001), “A Program for the Geotechnical and Structural Aspects of Foundation and 

Pier Design”, Federal Highway Administration and University of Florida, Bridge 

Software Institute (BSI), Manual No. of the Program FHWA-IF-01-010, Distribution of 

software at http://bsi-web.ce.ufl.edu. 

FHWA/NHI (2001), “Manual on Subsurface Investigations”, Federal Highway 

Administration, Manual No. FHWA NHI-01-031, Mayne, P. W., Christopher, B. R., and 

DeJong, J., July. 

Federal Highway Administration (2005), “Design and Construction of Driven Pile 

Foundations”, Hannigan, P. J., Goble, G. G., Thendean, G., Likins, G. E., and Rausche, 

F., Publication No. FHWA-NHI-05-042, United States Department of Transportation, 

December. 

Federal Highway Administration (1997), “Drilled and Grouted Micropiles, State-of-Practice 

Review”, Bruce, D. A. and Juran, I., Report No. FHWA-RD-96-016/019, United States 

Department of Transportation, July, Four Volumes. 

Federal Highway Administration (1999), “Drilled Shafts: Construction Procedures and 

Design Methods”, O’Neil, M. W. and Reese, L. C., Publication No. FHWA-HI-99-025, 

United States Department of Transportation, August. 

FOREVER (2003), “Synthesis of the Results of the National Project on Micropiles”, 

International Center for Ground Improvement, Polytechnic University, Juran, I, Jahir 

Hasan, Weinstein, G. M, and Sourisseau, L. 

GROUP (2003), “A Program for the Analysis of Piles in a Group”, Ensoft Engineering 

Software, Distribution of software http://www.ensoftinc.com/. 

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Circular 4, Federal Highway Administration Publication, Sabatini, P. J., Pass, D. G., and 

Bachus, R. C., Publication Number: FHWA-IF-99-015.

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Circular 5, Federal Highway Administration Publication, Sabatini, P. J., Bachus, R. C., 

Mayne, P. W., Schneider, J. A., and Zettler, T. E., Publication Number: FHWA-IF-02-

034. 
FHWA NHI-05-039 Chapter 5 – Design for Structure Foundations 

Micropile Design & Construction 5-81 December 2005 

Holloway, D. M., Moriwaki, Y. Stevens, J. B., and Perez, J-Y. (1981), “Response of a Pile 

Group to Combined Axial and Lateral Loading”, Proceedings of the 10th International 

Conference on Soil Mechanics and Foundation Engineering, Boulimia Publishers, 

Stockholm, Vol. 2, pp. 731-734. 

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of Soil Mechanics and Foundation Engineering, Vol. 85, No. SM4, pp. 11-39. 

Ishihara, K. and Cubrinovski, M. (1998), “Soil-Pile Interaction in Liquefied Deposits 

undergoing Lateral Spreading,” Proc. 11th Danube-European Conference on Soil 

Mechanics and Geotechnical Engineering, Porec, Croatia, pp. 51-64. 

Japanese Public Works Research Institute (JPWRI) (2002), “Design and Execution Manual for 

Seismic Retrofitting of Existing Pile Foundations with High Capacity Micropiles”, 

Foundation Engineering Research Team, Structures Research Group. 

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Driven into Clay,” Journal of Geotechnical Engineering Division, ASCE, Vol. 107, No. 

GT11, pp. 1521-1541. 

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Geotechnical Engineering Division, ASCE, Vol. 107, No. GT11, pp. 1543-1561. 

Lam, I.P. and Martin, G.R. (1986), "Seismic Design of Highway Bridge Foundations - Vol. II. 

Design Procedures and Guidelines," Report No. FHWA/RD-86-102, U.S. Department of 

Transportation, Federal Highway Administration, McLean, Virginia, 167 p. 

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Foundations," Proc. Transportation Research Board 76th Annual Meeting, Session No. 236, 

Washington, District of Columbia, 21 p. 

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Proceedings of the American Society of Civil Engineers, GT#3, pp. 197-228. 

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Ground Anchors”, Conference on Diaphragm Walls and Anchorages, Institute of Civil 

Engineers, London. 

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Institute Publication. 
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Micropile Design & Construction 5-82 December 2005 

Reese, L. C., Wang, S. T., Isenhower, W. M., Arréllaga, J. A., and Hendrix, J., (2005), “A 

Program for Analysis of Single Piles Under lateral Load”, Version 5.0.18, Ensoft Inc., 

Austin, TX. 

Richards, T.D. and Rothbauer, M.J. (2004), “Lateral Loads on Pin Piles (Micropiles),” 

Geotechnical Special Publication “Drilled Shafts, Micropiling, Deep Mixing, Remedial 

Methods, and Specialty Foundation Systems”, ASCE Publication, No.: 124, pp.158-174. 

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Inclined Micropile Foundation under Combined Axial Compression and Lateral 

Displacement”, Final Summary Report submitted to SALUT. 

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Improvement”, John Wiley & Sons, Inc., New York, NY. 
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Micropile Design & Construction 6-1 December 2005

CHAPTER 6 

DESIGN OF MICROPILES FOR SOIL SLOPE STABILIZATION 

6.1 INTRODUCTION

In addition to structural foundation support, micropiles are also used for structural slope 

stabilization. In this application, micropiles are designed to provide the required restraining 

forces to stabilize a slope using one of two approaches: 

Approach 1: Battered micropiles are installed through the unstable slope to a specific 

depth below the potential slip surface. In this approach, micropiles are affixed at the 

ground surface to a concrete cap beam (see Figure 6-1). With this method, the 

individual micropiles provide resisting forces through the mobilization of axial, shear, 

and bending resistance. The spacing of the micropiles along the slope length is 

evaluated by considering the number of micropiles necessary (per lineal meter) to 

provide the minimum required stabilizing force. The minimum required stabilizing 

force is typically that force required to increase the stability of the slope to a 

prescribed minimum factor of safety. 

Figure 6-1. Micropile System in Approach 1. 

CONCRETE CAP

ROAD

SURFACE

APPROXIMATE 

FAILURE PLANE

MICROPILE STRUCTURE (TYP)

ROAD

SURFACE

APPROXIMATE 

FAILURE PLANE

MICROPILE STRUCTURE (TYP)

REINFORCED
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Micropile Design & Construction 6-2 December 2005

Approach 2: Micropiles are installed similarly as for Approach 1, except many more 

micropiles are used (see Figure 6-2). In this case, micropiles are placed sufficiently 

close to each other to create a coherent structure of micropiles and soil. This structure 

is assumed to behave much like a gravity retaining wall in that the required 

restraining force necessary to stabilize a slope is achieved by sliding resistance 

developed along the bottom of the micropile group. For this reason, individual 

micropiles are subject to relatively small loads. The group enscribes and internally 

reinforces the soil mass so it acts as a unit. 

MICROPILE STRUCTURES

CAP BEAM

ROADWAY

COMPOSITE

BLOCK

Figure 6-2. Micropile System in Approach 2. 

In this chapter, a step-by-step design method for micropiles based on Approach 1 is 

presented (see Table 6-1). Also, Section 6.9 presents three case histories wherein Approach 

1 was used. 

A step-by-step design method for micropile groups based on Approach 2, however, cannot be 

developed at this time since limited data is available to confirm a specific design method and 

since the Approach 2 micropile system has limited applicability in current US practice. 

Design concepts for micropile groups using Approach 2 are provided in Appendix A. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-3 December 2005

Table 6-1. Design Steps for Micropiles for Soil Slope Stabilization.

1. Identify project specific constraints and evaluate feasibility 

2. Identify performance requirements 

3. Review available information and geotechnical data 

4. Evaluate factor of safety of existing slope 

5. Determine additional force required to obtain target factor of safety 

• choose a location for the single vertical micropile within the existing slope 

• model restraining force (micropile) and perform slope stability analysis 

• evaluate the stability of the slope away from micropile 

6. Select micropile cross section 

7. Estimate length of micropile 

8. Evaluate bending moment capacity of single vertical micropile 

9. Evaluate shear capacity of single vertical micropile 

10. Evaluate shear capacity of battered micropile group 

• select batter angle for upslope and downslope micropile 

• determine maximum shear capacity of a single battered micropile 

• determine maximum shear capacity of battered micropile group 

11. Calculate spacing required to provide required force to stabilize the slope 

12. Check potential for soil flow between micropiles 

13. Perform structural design of concrete cap beam 

6.2 STEP 1: IDENTIFY PROJECT SPECIFIC CONSTRAINTS AND 

EVALUATE MICROPILE FEASIBILITY 

Slope stabilization projects in which micoropiles may be feasible are usually located in 

remote areas or where difficult site access is a concern. Other project constraints common to 

slope stabilization include: 

(1) space restrictions that may include limited ROW, availability of on-site storage for 

construction materials, limited access for construction equipment, and restrictions on 

traffic disruption; 

(2) interference with above-ground utilities and nearby structures; 

(3) performing work on an unstable slope (i.e., need to perform any cut/fill operations in 

a controlled manner, potential for excess seepage in and around the work area, soil 

and/or rock fall hazards, etc.); 

(4) environmental concerns that may include local policies concerning construction 

noise, vibration, transportation of material to the site, and protection of animals and 

plants; 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-4 December 2005

(5) landscape aesthetics such as sensitivity to scars created by access road cuts or 

excavations; 

(6) disposal of rock or soil that is excavated as part of the slope stabilization method; and 

(7) cost of project. 

In assessing the use of micropiles as a means to stabilize a slope, micropiles will most often 

be compared to other structural slope stabilization measures such as ground anchors, soil nail 

walls, or driven pile or drilled shafts. 

The use of micropiles has come into favor for slope stabilization projects because micropile 

construction is relatively simple and requires a small work area, and micropiles can be 

readily installed in areas with limited equipment access, such as for landslides located in 

hilly, steep, or mountainous areas. However, the implementation of these systems still 

requires a specialty geotechnical contractor. The other advantages offered by micropiles 

include, reduced excavation compared to earth retaining systems (i.e., the system is 

constructed from the top-down, no excavation is required to construct a wall or install anchor 

supports); improved aesthetics in that the system is completely buried so that there is no 

visual evidence of an active structural stabilization system; and micropiles can be installed in 

virtually any ground type. This latter advantage is important for landslide stabilization since, 

in many cases, an upper competent layer is underlain by soft, wet soil material (comprising 

the location where landslide movements are occurring) resting on rock. The upper layer may 

comprise colluvium or talus materials which are known to contain a wide range of soil and 

rock particle sizes through which installation of driven piles or drilled shafts would be 

difficult and costly. 

The cost-effective use of micropiles will be based on the required forces necessary to 

stabilize a slope. For example, projects which involve a relatively long landslide (i.e., large 

failure surface length) or where the depth to the potential slip surface is large, may not be 

well-suited for micropiles because of the very large restraining forces required to stabilize the 

slope. It is noted, however, that micropiles can be designed to withstand relatively large 

loads by battering the micropiles to mobilize axial restraint forces. In some cases, even with 

battered micropiles, the required loads to be resisted are so large that additional restraint, 

usually from ground anchors, is required. 

For first-order comparisons, micropiles for slope stabilization range in cost from $4,000 to 

$11,000 per lineal meter of slope ($1,200 to $3,400 per lineal ft of slope). The higher end of 

the range being for projects involving relatively long micropiles (e.g., in excess of 15 m (50 

ft) to reach the top of the slide surface) and where access and other project-specific 

constraints result in relatively low micropile installation production rates (e.g., less than 90 m 

(300 ft) per day) and the need for large amounts of rock drilling. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-5 December 2005

Previous designs and contractor experience indicates that micropiles for slope stabilization 

will likely only be cost-effective if unbalanced slope forces can be resisted through the 

placement of a micropile structure at approximately the mid-height of the slope. Design 

calculations for locating the position of micropiles on a slope is described in this chapter. If a 

slope stabilization measure would be required to minimize, for example, future downward 

movements of a roadway near the top of the unstable slope, then a single micropile structure 

would likely not be sufficient to stabilize the slope since it is possible that the slope would be 

unstable in front of the micropile structure. In some cases, however, multiple micropile 

structures could be used but may not be cost effective. 

The design method described herein for micropiles is based on the assumption that the 

portion of the micropiles below the potential slip surface “tie” the slope mass above the 

potential slip surface to the more competent ground below the potential slip surface. In this 

sense, the micropiles serve as dowels. Also, the design assumes that concentrated 

deformations occur at the location of the potential slip surface. With this assumption, 

maximum bending moments and shears in the micropiles occur near the location of the 

potential slip surface. Design engineers considering the use of micropiles for a slope 

stabilization project must review available instrumentation data on slope movements. The 

design method presented herein requires that movements are occurring at a well-defined 

critical potential slip surface. As an example, Figure 6-3 shows concentrated lateral soil 

movements at approximately a depth of 8 m (25 ft). These data are from a landslide in 

Summit County, Ohio. Where slope movements are less localized, or where more than one 

potential slip surface may exist (i.e., where a single, well-defined slip surface has not been 

observed (via instrumentation) or expected (via review of subsurface information)), other 

slope stabilization measures such as anchored walls should be considered. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-6 December 2005

Figure 6-3. Concentrated Movements Recorded from Inclinometer at the Slip Surface (after 

Liang, 2000). 

6.3 STEP 2: IDENTIFY PERFORMANCE REQUIREMENTS 

The primary performance requirement for a slope stabilization project is for the stabilized 

slope to meet or exceed a target slope stability factor of safety with respect to static and 

seismic slope stability. Typical static factors of safety range from 1.3 to 1.5 depending on, 

for example, whether other structures are supported by the slope and whether only limited 

geotechnical data is available. For seismic slope stability analyses (based on pseudo-static 

analysis), a target value of 1.1 is typically used. 

Other performance (and/or design) requirements will include: 

• prescribed level of corrosion protection for the micropiles; 

• permissible variation in groundwater levels during construction; 

• maximum loads that can be carried (as part of load testing); and 

• allowable stresses for steel and concrete. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-7 December 2005

It is noted that design of earth slopes (and stabilization of slopes) is not codified in, for 

example, AASHTO (2002). Design criteria for slopes are typically developed on a projectspecific basis. 

6.4 STEP 3: REVIEW AVAILABLE INFORMATION AND GEOTECHNICAL

 DATA 

The existing slope conditions should be assessed by review of available information and 

collection of geotechnical data through a focused subsurface exploration and laboratory 

testing program. For guidance regarding the planning and execution of subsurface 

exploration programs for slopes, refer to the Manual on Subsurface Investigations (Mayne et 

al., 2001) and Geotechnical Engineering Circular (GEC) No. 5 “Evaluation of Soil and Rock 

Properties” (Sabatini et al., 2002). 

The information gathering, subsurface exploration and laboratory testing program should be 

developed with the goal of obtaining the following information: 

Topography of the area. Topographic information for the area of interest is used to develop 

analysis cross sections for slope stability analysis. If relatively recent topographic maps are 

not available for the site or if it is known that site topography has been modified since the last 

ground survey was performed, a ground surface survey of the area should be performed since 

accurate information on slope geometry is critical for analysis. 

Lateral extent of the landslide or potential landslide area. This information can be obtained 

through observations from a site inspection and through review of aerial photographs (if 

available). The lateral extent of the area to be stabilized needs to be known to enable 

potential slip surfaces with the lowest factor of safety to be identified. Usually, multiple 

parallel cross sections are analyzed using 2-dimensional limit equilibrium methods to 

determine the slip surface with the minimum slope stability factor of safety. This cross 

section is used to perform design analyses of the slope. 

Subsurface profile and groundwater conditions. The subsurface profile at the location of the 

critical cross section is developed based on information from historical borings and from 

borings advanced as part of the slope stabilization project. This exercise is carried out 

similarly as for other geotechnical features where the development of a subsurface profile is 

required. Specifically, for slopes stabilized with micropiles, borings should be advanced into 

the competent materials below the potential slip surface which will serve as the resistance 

zone for the micropile. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-8 December 2005

Groundwater conditions within the slope may be determined from the logs of soil borings, 

piezometer data, and observation wells. This information is used to model pore pressure 

conditions within the slope. It is specifically noted that the cause of slope movements is 

oftentimes related to large precipitation events which cause groundwater levels and pore 

pressures to increase in a slope mass. Where the conditions of the slope at the time of 

instability are required for analyses (e.g., where back analysis to obtain strength properties is 

required), it is necessary to develop pore pressure conditions at the time of the slope 

instability. 

The assessment of design groundwater levels (or design pore pressures) should consider the 

effect that the micropile structure will have on long-term groundwater levels within the slope. 

Typically, however, the spacing between micropiles is sufficiently large such that the 

possibility of pore pressure buildup (resulting from a potential hydraulic cutoff effect from 

the micropile structure) is relatively insignificant. Where project conditions require close 

micropile spacing and/or where the potential for significant groundwater recharge to the 

slope area is possible, the Owner should require that seepage analyses be performed that 

consider the effects of micropile spacing, micropile installation methods (e.g., effect of 

possible grout travel), precipitation events, and hydraulic conductivity of the slope material. 

Subsurface drainage systems may be required and/or the proposed micropile system may be 

designed to resist long-term seepage pressures. 

The importance of an accurate assessment of pore pressure conditions within a slope cannot 

be overemphasized. 

Soil and rock parameters for analysis. Material parameters for soil and rock are required for 

slope stability analyses and for the evaluation of the structural capacity of micropiles (using 

p-y analyses discussed subsequently). Material parameters required include soil and rock 

unit weights and shear strength parameters. 

Depending on the soil type and access to sampling locations in the slope area, soil and rock 

sampling may be difficult and obtaining nominally undisturbed soil samples for strength 

testing may be impossible. In these situations, it is prudent to collect as much index type 

data as possible (i.e., Atterberg limits, grain size analysis, and moisture content) to establish 

differences between soil and rock stratum. Based on these data, strength properties would be 

determined from engineering correlations. Common engineering correlations for soil and 

rock properties that may be used for micropile slope stabilization assessment are provided in 

GEC No. 5 (Sabatini et al., 2002). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-9 December 2005

The use of these and other correlations for geotechnical parameters should be considered 

primarily for use in preliminary design evaluations and not as a substitute for a 

comprehensive site investigation, sample collection, and laboratory testing program. 

Critical slip surface. Information on the location of the critical slip surface may be obtained 

from several sources during initial data review. In some cases, especially if the slope has 

been subject to previous movements, inclinometer data may be available which can be used 

to locate the critical slip surface. Also, boring logs and other stratigraphic information can be 

used to locate a potential slip surface. Oftentimes the critical slip surface will be located at 

the interface just above a competent soil or rock surface where water may be perched. This 

area becomes saturated and soft and slope movements may be concentrated at this location. 

For micropile design, in addition to the requisite slope stability analyses, the location of the 

critical slip surface is required for laterally loaded pile analyses. As previously introduced, 

the location of the critical potential slip surface (as determined from slope stability analysis 

and/or field observations) is used as the location where maximum lateral micropile 

movement is assumed to occur. 

Site Seismicity. As for any other slope, destabilizing forces resulting from seismicallyinduced ground accelerations need to be considered. This evaluation for slopes is typically 

performed using a pseudo-static slope stability analysis (see Kavazanjian et al. 1997). 

6.5 STEP 4: EVALUATE FACTOR OF SAFETY OF EXISTING SLOPE 

Using the information from Step 3, slope stability analysis methods are used to evaluate the 

slope stability factor of safety for the slope that is to be stabilized. Presumably, this slope is 

at a slope stability factor of safety of approximately 1.0 (if the slope has undergone 

significant movements) or may be at a slightly higher factor of safety. From this evaluation, 

the minimum factor of safety (FSmin) is evaluated. As a result of the analysis, the location of 

the critical potential slip surface is evaluated. 

Analyses are typically performed for the static and seismic case and the results are compared 

to the target minimum factor of safety (previously discussed). In performing these analyses, 

estimates of shear strength, subsurface stratigraphy, and pore pressures within the slope mass 

are developed. A special case includes one in which the slope is known to have failed or 

have undergone significant downslope movement. By definition, this slope is at a FS = 1.0 at 

the time of the failure. Micropiles for slope stabilization have been used most commonly 

with applications involving slope failures (i.e., landslides). The technique used to adjust 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-10 December 2005

shear strength parameters for this case is termed “back-analyses”. Back-analysis techniques 

involve the following steps: 

i. Estimate analysis parameters. If the slope has moved sufficiently, the residual drained 

friction angle may be used (e.g., c′ = 0, φ′ = φ′r) to model the soil material where these 

movements have occurred. Figure 6-4 may be used to evaluate φ′r. The use of 

Atterberg limits data and clay content can be used to assess residual (or largedisplacement) drained friction angle for clayey landslide material (see Figure 6-4). For 

example, based on Figure 6-4, for a landslide material with clay content between 25 

and 45 percent and with liquid limit of 60, the residual friction angle is 18 degrees. 

(1kPa = 0.145 psi) 

Note: φ’r = Residual friction angle and CF = Percent clay-particles < 0.002 mm (0.00008 in) 

Figure 6-4. Residual Friction Angle for Clayey Soils (after Stark and Eid, 1994). 

The shear strength parameters estimated are considered as trial strengths (φtrial and ctrial) 

in the back-analysis. Representative shear strength parameters for other soil and rock 

materials (i.e., those above and below soils near the critical potential slip surface) are 

evaluated based on available information and are usually not adjusted as part of the 

back analysis. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-11 December 2005

ii. Perform slope stability analysis. Limit equilibrium slope stability analysis is performed 

to obtain the factor of safety that corresponds to trial strengths. Slope stability analyses 

are performed for several analysis cross sections. The best available information for 

pore pressure values, shear strength, stratigraphy, and topography at the time of the 

failure is used in the analyses. Also, the location of the failure surface needs to be 

known with some level of certainty so that analysis results can be compared to actual 

conditions. 

iii. Adjustment of parameters until FS =1.00. If the previous slope stability analyses do not 

yield FS=1.00, shear strength parameters should be modified and analyses performed. 

This process is continued until shear strength parameters result in a corresponding FS = 

1.00 result. It is important to note that shear strength represents only one of the 

unknowns in the analysis. Pore pressures and location of the critical failure surface (at 

the time of failure) need to be understood and hence their potential uncertainty should 

also be considered when varying parameters. A back analysis that produces FS = 1.00, 

but includes a calculated critical failure surface that is not consistent with that observed 

in the field should not be relied upon. All relevant parameters need to be consistent 

with observed results. 

For the case where the existing slope may have a factor of safety greater than 1.0, but where 

the factor of safety is less than a target value, shear strengths and groundwater elevations 

should be evaluated as described in Design Step 3. In these cases, the location of the critical 

slip surface needs to be estimated based on available data. Slope stability analyses to 

evaluate FSmin should be performed considering circular and planar slip surfaces. Subsurface 

stratigraphy information should be used to evaluate the reasonableness of the calculated 

potential slip surface. 

6.6 DESIGN CONCEPTS FOR MICROPILES USED FOR SLOPE 

STABILIZATION 

6.6.1 Overview 

At this stage in the design process, an existing slope has been shown to be either unstable or 

marginally stable with a calculated slope stability factor of safety less than a target value. 

The remaining steps of the design process comprise designing a micropile system to improve 

or otherwise stabilize the slope. 

The steps specific to the geotechnical and structural design of micropiles used for slopes is 

outside the typical design practice for most geotechnical engineers. For this reason, this 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-12 December 2005

section provides background information on load transfer mechanisms and analysis methods 

used for Design Steps 5 through 13. The complete design of a micropile stabilized slope is 

demonstrated in Section 6.7. 

6.6.2 Evaluating the Additional Force Required to Obtain Target Factor of Safety 

Micropiles used for slopes are designed to prevent downward movement of the slope mass 

above the potential slip surface. The micropiles must be capable of providing the force 

required to stabilize the slope. This force is the force required to increase the factor of safety 

of the slope from an existing value to a target value. 

Slope stability analysis programs are used to determine this additional force (Hreq). The slope 

stability analyses are performed in three stages: (1) a location is chosen for the micropiles; 

(2) the micropiles are modeled explicitly in the slope stability analysis to determine the 

required restraining force; and (3) the stability of the slope away from the micropile is 

evaluated by performing additional slope stability analysis. 

6.6.2.1 Micropile Location Within Slope Cross Section

The magnitude of Hreq will vary depending on the location of the micropile within the slope. 

This affect is demonstrated using the example slope geometry provided in Figure 6-5. 

Several analyses were performed in which the location of a single micropile was adjusted 

within the cross section. At each location, the shear force provided by the micropile was 

increased until a target factor of safety (FSmin) of 1.3 was achieved for the slope. The results 

of the analyses are shown in Figure 6-6 and these results indicate that, for this example, if the 

micropile is placed at or near the toe of the slope or at or near the crest of the slope, the use 

of a micropile structure at these locations would be ineffective. In other words, regardless of 

the magnitude of force that the micropiles could develop, the target factor of safety (i.e., 

FSmin = 1.3) could never be achieved (see Figures 6-7 and 6-8 for the most critical slip 

surface). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-13 December 2005

Toe of the 

Slope

Crest of the 

Slope

Distance (m) Distance (m)

Figure 6-5. Example Slope Geometry. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-14 December 2005

700690680670660650640630620610600

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60

DISTANCE (m)

FORCE REQUIRED FOR FS = 1.3 (kN/m) FS < 1.3

FS < 1.3

Toe of the Slope

Crest of the Slope

Note: 1 m = 3.28 ft and 1 kN/m = 68.53 lb/ft 

Figure 6-6. Relationship between Force Required For FS = 1.3 and Location of the Micropile. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-15 December 2005

Figure 6-7. Effect of Micropile Placed Too Far Upslope (FSmin < 1.3). 

Figure 6-8. Effect of Micropile Placed Too Far Downslope (FSmin < 1.3). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-16 December 2005

The results of the above example indicate that the maximum benefits from micropiles 

correspond to a micropile structure placed in the vicinity of the middle of the slope. 

6.6.2.2 Methods to Model Resisting Force from a Micropile

While it is recognized that micropile structures for slope stabilization will typically include a 

battered upslope “leg” and a battered downslope “leg” connected at the ground surface via a 

concrete beam (Figure 6-9), the micropile structure is modeled considering a single vertical 

micropile from the ground surface (at the design cap beam location) to a sufficient depth into 

a competent layer (see Figure 6-10). In subsequent design steps, the shear capacity, 

inclination, and the number of micropiles required to resist Hreq is evaluated. 

Slope stability input files generated in Design Step 4 are typically modified in one of two 

ways to model the effects of a single vertical micropile, as described below. 

• Approach 1: The shear resistance provided by the single vertical micropile, Hreq, can 

be modeled as a relatively large cohesive shear strength assigned to the soil layer 

where the micropile crosses the potential slip surface. By selecting a width of say 0.5 

m, the slope stability analysis program will develop a single slice with a width of 0.5 

m having the relatively large cohesive shear strength. The relationship between Hreq

and cohesive strength is shown in Figure 6-11 for this approach. It should be noted 

Hreq is oriented at the same angle as the bottom of the slice. Repeat the slope stability 

analyses and change the cohesive strength until a factor of safety equal to the target 

value is obtained. 

• Approach 2: Some slope stability software packages enable the user to directly input 

a micropile restraining force at any given location. With this approach, it is not 

necessary to indirectly obtain the restraining force via the introduction of a thin soil 

layer with a relatively large cohesive strength. Repeat the slope stability analyses and 

change the value for the restraining force until a factor of safety equal to the target 

value is obtained. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-17 December 2005

Micropile cap beam

Battered downslope “leg”

Battered upslope “leg”

Figure 6-9. Micropiles with Battered Uplsope Leg and Battered Downslope Leg (modified 

after Hasenkamp, 1999). 

Existing Slope Surface

Slip Surface

Direction of Slope Movement

Unstable Slope Mass

Cap Beam

Vertical 

Micropile

Micropile Resistance Length

Competent Soil or Bedrock

Existing Slope Surface

Slip Surface

Direction of Slope Movement

Unstable Slope Mass

Cap Beam

Vertical 

Micropile

Micropile Resistance Length

Competent Soil or Bedrock

Figure 6-10. Single Vertical Micropile Model for Design Analyses. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-18 December 2005

w

L

α

c 

Hreq = c × L

cosα

1 Hreq = c × w ×

Figure 6-11. Relationship Between Hreq and Cohesive Strength for Micropile Analysis 

Model. 

c = Cohesive strength 

w = Width of the slice 

L = Length of the slice 

α = Angle of the slice base 

Hreq = Required shear force 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-19 December 2005

6.6.2.3 Evaluating Slope Stability Away From Micropile

Results of the previous slope stability analysis provide the location and the required 

restraining force for the slope to achieve the target factor of safety. However, it is possible 

that slip surfaces away from the micropile may have factor of safety values less than the 

target value and therefore, additional slope stability analyses should be performed. For these 

analyses, the presence of the micropile is ignored by setting the search limits for potential 

slip surfaces located entirely upslope of the micropile and for potential slip surface located 

entirely downslope of the micropile (see Figure 6-12). 

Search limits set 

downslope of micropile

Search limits set 

upslope of micropile

Micropile structure

Figure 6-12. Slope Stability Analysis Search Limits Away From Micropile Location. 

Specific practical issues are associated with the evaluation of downslope stability (as for 

Figure 6-13). If, for example, a roadway is located at the toe of the slope, then it is possible 

that future roadway widening would require excavation at the toe of the slope. Excavation 

near the toe of the slope may also be associated with certain long-term slope maintenance 

activities. For many earth retaining structures used to stabilize slopes, the resistance 

provided by soil in front of the wall (i.e., passive soil resistance) is conservatively neglected 

because of the possibility that this material would be removed at a later date. This design 

assumption can be adequately addressed with many earth retaining systems. For micropiles, 

it is explicitly noted that the assumption of zero passive soil resistance in front of the 

micropile is not considered using the design method presented herein. If slope material in 

front of the micropile were to move away from the structure as a result of instability or if soil 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-20 December 2005

were removed as part of a maintenance activity, it is likely that the micropile structure would 

experience excessive deflection or structural failure of the downslope micropiles due to the 

loss of lateral support. 

Competent Soil or Bedrock

Stabilized 

Soil Mass

Cap 

Beam

Limits of 

Future Excavation

Critical Slip Surface

Competent Soil or Bedrock

Stabilized 

Soil Mass

Cap 

Beam

Limits of 

Future Excavation

Critical Slip Surface

Figure 6-13. Potential Instability Resulting from Future Excavation. 

There are two approaches to address these issues: 

• As part of the design submittal, the Owner can require calculations to be performed 

which establish the maximum amount of excavation that could be performed in front 

of the micropiles. This critical geometry would show the greatest length of 

excavation into the slope such that a minimum factor of safety is maintained and so 

that the soil in front of the micropile structure remains stable thus providing the 

required lateral support to the front row of micropiles. Furthermore, it is 

recommended herein that this design check be performed and the information be 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-21 December 2005

provided to the Owner, regardless of whether such a check is specifically requested in 

the Contract Documents. 

• Where micropile structures are used, the Owner may fence off the area and post signs 

alerting that excavation should not be performed in the area. 

6.6.3 Load Transfer in Micropiles 

Micropiles resist unstable slope forces through a combination of axial resistance developed at 

the grout-to-ground interface both above and below the potential slip surface and structural 

(i.e., shear and bending) resistance. As mentioned earlier, the maximum lateral micropile 

movement is assumed to occur near the elevation of the critical potential slip surface. This is 

a reasonable assumption for micropiles since micropiles are relatively flexible. An example 

showing the resultant axial force and bending moment diagrams for an upslope leg and 

downslope leg of micropiles used for a slope stabilization project in Littleville, Alabama 

(Brown and Chancellor, 1997) is presented in Figure 6-14. 

The capacity of individual micropiles used for slope stabilization can be increased 

significantly by designing the micropiles to be inclined or “battered” relative to the critical 

potential slip surface. If the micropile is battered, slope movements will result in the 

tendency for the micropile to be “pulled” away from the slip surface resulting in axial tension 

forces or to be “pushed” towards the slip surface resulting in axial compression forces. 

These forces are mobilized as side resistance at the grout-to-ground interface. For micropile 

structures without ground anchors used to stabilize landslides, the upslope leg will typically 

be in tension and the downslope leg will typically be in compression. 

The maximum axial force in a micropile will occur near the location of the critical potential 

slip surface. In this sense, the development of axial resistance is similar to that for soil nails. 

For the micropiles to develop the required axial resistance for design, the micropile must be 

embedded sufficiently into the ground below the critical slip surface to prevent micropile 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-22 December 2005

(a) 

(b) 

Note: 1 kip = 4.448 kN and 1 ft = 0.3048 m 

Figure 6-14. Example Resultant Axial Force and Bending Moment Diagrams for (a) Downslope and (b) Upslope Micropile (after 

Brown and Chancellor, 1997).
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-23 December 2005

failure through pullout (if the micropile is loaded in tension) or failure as a result of 

insufficient bearing capacity (if the micropile is loaded in compression). In other words, the 

side resistance capacity of the micropile below the potential slip surface must be sufficient to 

resist axial forces developed above the potential slip surface (see Figure 6-15). 

The axial force required to be resisted by the micropile below the potential slip surface is 

assumed to be equal to the ultimate side resistance of the micropile that could develop above 

the failure surface with a factor of safety. The ultimate side resistance of the micropile above 

the failure surface, Pult, can be calculated as: 

 d Pult =αbond-above × Labove ×π × (Eq. 6-1) 

where αbond-above is the grout-to-ground ultimate bond strength above the critical slip surface, 

Labove is the length of the micropile from the slip surface to the bottom of the cap beam, and d 

is the diameter of the micropile. The value for αbond-above is estimated using Table 5-3. 

In addition to axial resistance, micropiles develop flexural resistance. The design objective 

therefore, is to select a micropile system with sufficient structural capacity to resist the 

unbalanced slope force (i.e., Hreq) without structural failure of the micropile in combined 

axial loading and bending. 

Therefore, the required length of the micropile below the slip surface, Lbelow, is calculated as: 

 FS

d

P

L

bond-below

ult

below ×

× × =

α π

 (Eq. 6-2) 

where Pult is calculated using Eq. 6-1, αbond-below is the grout-to-ground ultimate bond strength 

below the critical slip surface and is estimated using Table 5-3. A FS = 2.0 should be used in 

Eq. 6-2. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-24 December 2005

Figure 6-15. (a) Micropile Resistance Length Not Sufficient to Prevent Pullout and (b) 

Micropile Resistance Length Sufficient to Prevent Pullout. 

Currently, load testing of micropiles for slope stabilization projects is not commonplace; 

therefore required micropile side resistance has relied exclusively on contractor experience in 

similar ground. This document, however, recommends that load testing be performed. Load 

testing requirements for slope stabilization projects is provided in Chapter 7. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-25 December 2005

6.6.4 Bending Moment and Shear Capacity of Single Vertical Micropile 

6.6.4.1 Evaluation of Bending Moment Capacity of Single Vertical Micropile

The shear resistance of a micropile corresponds to the maximum shear force that can be 

applied to the micropile that results in a maximum bending moment within the micropile (at 

any location) to be just equal to the ultimate bending moment of the micropile. 

To evaluate the shear resistance of a single micropile, the ultimate bending moment (Mult) of 

the single micropile is checked. The ultimate bending moment of a single vertical micropile 

can be conveniently evaluated using the computer program LPILE (2005) or other soilstructure interaction programs used for the analysis of laterally loaded piles and shafts. 

Because micropiles are battered, they develop axial resistance through side friction between 

the grout and the ground. Since the bending moment capacity of a micropile (or any other 

structural section) varies depending on the applied axial load, the bending moment capacity 

of a single micropile is checked for two limiting axial load conditions: (1) axial load equal to 

zero, P = 0; and (2) axial load equal to the ultimate side resistance of the micropile, P = Pult 

(where Pult is calculated using Eq. 6-1). 

In these analyses, the shear capacity corresponding to the ultimate bending moment in the 

micropile is used. The rationale for this is described in Section 6.8. 

As previously discussed, axial loads in micropiles may be in tension or compression. In 

general, the uphill micropile will be in tension and the downhill micropile will be in 

compression. However, where ground anchors are incorporated into the micropile structure, 

the direction of the axial load for individual micropiles may change depending on ground 

anchor stressing and lock-off loads. For this reason, Mult should be evaluated for the P = Pult

case considering that this axial load is applied in compression and in tension. The design 

would then be based on the case that provides the lower Mult; and therefore the lower value 

for available micropile shear resistance. 

6.6.4.2 Evaluation of Shear Capacity of Single Vertical Micropile

The maximum shear force that the micropile can carry corresponds to that shear force applied 

at the elevation of the slip surface that results in a calculated maximum bending moment in 

the micropile that is equal to Mult. This maximum bending moment is affected by the 

stiffness (i.e., p-y response) of the ground above and below the potential slip surface and the 

flexural rigidity of the micropile. This evaluation can be performed using laterally loaded 

pile analyses for single elements such as that provided in LPILE. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-26 December 2005

The shear force capacity of a single vertical micropile is determined by analyzing separately 

the portion of the micropile above the potential slip surface (termed the “up” analysis) and 

the portion of the micropile below the potential slip surface (termed the “down” analysis). 

This requires, for the up analysis, adjustment of the location of previously determined p-y 

curves relative to the top of the pile in the analysis. Figure 6-16 shows p-y curves for the 

entire length of the micropile and Figure 6-17 shows how they are adjusted for the up and 

down analyses. 

The iterative process to determine the maximum shear capacity requires performing up and 

down analyses as a set. Both analyses are performed for minimum axial resistance 

conditions (i.e., P = 0) first and then for maximum axial resistance conditions (i.e., P = Pult). 

The boundary shear forces and bending moments applied at the slip surface location, 

although applied as boundary conditions in the analyses, are actually internal forces and 

bending moments within the micropile. Because of this, specific criteria need to be satisfied 

when comparing the up and down analyses results to evaluate the correctness of the analyses. 

These are described below: 

• The same value for axial load is used for both the up and down analyses. 

• The input shear force magnitude and direction applied at the slip surface location is 

the same for the up and down analyses. 

• The input bending moment applied as a boundary condition should be equal in 

magnitude and opposite in sign for the up and down analyses. 

• The calculated slope of the micropile head at the slip surface should be the same for 

the up and down analyses. 

• The head of the micropile is modeled as free. 

Figure 6-18 shows calculated bending moment diagrams for a micropile using the up and 

down analyses. These analyses show the iterative process wherein the analysis is complete 

for the case where Mmax = Mult and the pile head slope from the up and down analysis is 

equivalent. For Analysis 1, a bending moment at the slip surface location of 40 kN-m is 

assumed. With this, it is seen that the calculated slopes of the micropile from the up and 

down analysis are not the same. This implies a discontinuity in slope at the slip surface 

location, which is not possible. For the next iteration, a bending moment of 87 kN-m is 

assumed. Inspection of the table in Figure 6-18 indicates that for this slip surface location 

bending moment, the pile head slope from the up and down analysis are equivalent; it is also 

seen that the maximum calculated bending moment of 161 kN-m occurs below the slip 

surface and is approximately equal to the ultimate bending moment based on the structural 

capacity of the micropile section assumed. Thus, the analysis is complete. This procedure 

is demonstrated in the Design Example provided in Section 6.7.6.
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-27 December 2005

Slip 

Surface

Top of the Micropile

Bottom of 

the Micropile

Ground 

Surface

y

p

y

p

y

p

y

p

y

p

p-y (d1)

p-y (d5)

p-y (d4)

p-y (d3)

p-y (d2)

Labove

Lbelow

Cap Beam

d1

d2

d3

d4

d5

Figure 6-16. An Example Distribution of p-y Curves with Depth Obtained from Laterally 

Loaded Pile Analysis. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-28 December 2005

y

p

y

p

p

p-y (d3)

p-y (d1)

p-y (d2)

Micropile above 

the slip surface

d3

y

d2

d1

Labove

Micropile below 

the slip surface

d4

L d5

below

y

p

y

p p-y (d5)

p-y (d4)

Figure 6-17. Utilizing p-y Curves Obtained From Laterally Loaded Pile Analysis in: (a) Up 

Analysis and (b) Down Analysis. 

(a) 

(b) 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-29 December 2005

0 Slip Surface Location

1

2

3

4

5

-200 -150 -100 -50 0 50 100 150 200

Bending Moment (kN.m)

Distance From Slip Surface (m) 

Analysis 1

Analysis 2

UP ANALYSIS

M 

-3

-2

-1

0

-200 -150 -100 -50 M 0 50 100 150 200

Slip Surface Location

Mult = 161.3 kN.m

DOWN ANALYSIS

0 Slip Surface Location

1

2

3

4

5

-200 -150 -100 -50 0 50 100 150 200

Bending Moment (kN.m)

Distance From Slip Surface (m) 

Analysis 1

Analysis 2

UP ANALYSIS

M 

-3

-2

-1

0

-200 -150 -100 -50 M 0 50 100 150 200

Slip Surface Location

Mult = 161.3 kN.m

DOWN ANALYSIS

Analysis No. M (kN.m) Mmax (kN.m) Pile Head 

Slope (Up) 

Pile Head 

Slope (Down) 

1 40 162.98 - 0.064 - 0.025 

2 87 161.00 -0.037 -0.037 

 Note: M: Applied bending moment. 1 kN.m = 0.737 k.ft 

Figure 6-18. Example of Calculated Bending Moment Diagrams for Up and Down Analyses. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-30 December 2005

6.6.5 Shear Capacity of Battered Micropile Group 

The maximum lateral force (Hult) that an inclined (or battered) single micropile can resist at 

the location of the critical slip surface is evaluated in this step. For the analysis, the effects of 

a non-horizontal slip surface are also addressed. The value for Hult which will be compared 

to the required force to provide the target factor of safety, i.e., Hreq, is the sum of the 

individual Hult values from each battered micropile in the cross section. 

The assumed forces acting on a micropile are shown in Figure 6-19 for the case of a vertical 

micropile (where axial resistance is assumed to be zero, i.e., P=0) and for an inclined 

micropile (where axial resistance is assumed to be equal to the ultimate axial resistance 

provided by the ground above the slip surface, i.e., P=Pult). The inclination angle (ψ) may be 

defined as the angle between the slip surface and the vertical axis of the pile. 

Summing the shear (Q) and axial (P) forces shown in Figure 6-19b in the x and y direction 

results in the following: 

 Q = H cosψ - V sin ψ (Eq. 6-3) 

 sin P = V cosψ + H ψ (Eq. 6-4) 

These equations can be solved simultaneously to provide the lateral pile load (along the slip 

surface): 

 H = Q cosψ + P sinψ (Eq. 6-5) 

This lateral pile load, H, is coincident with the orientation of Hreq (see Figure 6-11). Since 

the purpose of this analysis is to evaluate the ultimate capacity of the micropile, 

corresponding ultimate values for P and Q in Eq. 6-5 are selected. The minimum axial 

resistance of a single micropile is zero and the maximum axial resistance is assumed to equal 

Pult. Because Eq. 6-5 is a function of the inclination of the micropile relative to the slip 

surface, it is necessary to select a range of inclination angles for which the analyses 

corresponding to P=0 is valid and for which the analyses corresponding to P=Pult is valid. 

According to Poulos and Davis (1980), Pult may be assumed to develop in a pile that is 

inclined at approximately 30 degrees. Therefore, Q and P in Eq. 6-5 are defined as: 

For ψ = 0o → P = 0 and Q = QP=0; therefore Hult = QP=0 (Eq. 6-6) 

For ψ ≥ 30o → P = Pult and Q = QP=Pult; therefore Hult = QP=Pult cosψ + Pult sin ψ (Eq. 6-7) 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-31 December 2005

Although axial resistance of micropiles should be mobilized even at very small inclination 

angles, it is conservative to assume that axial resistance is not mobilized until a nominal 

amount of inclination is achieved. Moreover, relying on axial resistance at small inclination 

angles implies a level of certainty in the angle of the slip surface (i.e., slope of the failure 

surface) which can probably not be achieved practically through subsurface investigation 

techniques; the accurate assessment of the failure surface angle may be difficult to achieve. 

Figure 6-19. Forces Acting On (a) Vertical and (b) Inclined Micropile Along The Slip 

Surface. 

(a) 

Slip surface

P = 0

QP=0

y-axis

x-axis

Slip surface

H

V

QP=Pult

P = Pult

ψ

y-axis

x-axis

(b) 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-32 December 2005

Therefore, for the design procedure presented herein, the following recommendations are 

provided for inclination angles between 0 and 30 degrees: 

For 0 < ψ ≤ 10ο → Hult = QP=0 (Eq. 6-8) 

For 10 < ψ < 30ο → Hult is interpolated (see Figure 6-20) (Eq. 6-9) 

0

100

200

300

400

500

600

700

0 10 20 30 40 50 60 70

Inclination Angle, ψ (Degrees)

Capacity of Individual Battered Micropiles, Hult (kN)

P = 0 and 

Q = QP=0

P = Pult and Q = QP=Pult Interpolated

Note: 1 kN = 0.2248 k 

Figure 6-20. Relationship Between Adjusted Capacity of Individual Micropiles and 

Inclination Angle. 

The relationship between adjusted capacity of the individual micropiles and inclination angle 

based on the above definitions is provided in Figure 6-20 for a specific single micropile 

design. Once the inclination angles for design are selected, Eqs. 6-7, 6-8, and 6-9 can be 

used directly to evaluate the shear capacity of each micropile in a cross section, i.e., the 

development of a figure such as Figure 6-20 is not necessary. This analysis is shown as part 

of a detailed design example in Section 6.7.7. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-33 December 2005

The inclination angle ψ is defined as the angle between the axis perpendicular to the slip 

surface and the micropile axis or as the angle between the axis perpendicular to the micropile 

axis and the slip surface (Figure 6-21). Solutions for positive and negative inclination angles 

are identical for Eqs. 6-3 and 6-4 (Poulos and Davis, 1980). Therefore, ψ should be written 

as positive in Eq. 6-5 regardless of its sign. 

Using Eq. 6-5, the capacity of the upslope micropile and the downslope micropile can be 

evaluated using the criteria presented concerning appropriate values for Q and P and 

depending on the micropile inclination angle,ψ. The inclination angle should be assessed at 

the location where each of the two micropiles crosses the slip surface. The combined 

capacity of the upslope and downslope micropile is determined as: 

 ult-pair ult ( ) ult ( ) us ds H = H Ψ + H Ψ (Eq. 6-10) 

where ψus is the inclination angle for the upslope micropile and ψds is the inclination angle 

for the downslope micropile. 

6.6.6 Spacing Required to Provide Required Force to Stabilize the Slope 

Figure 6-22 shows a detail of a typical micropile layout at the cap beam location. The 

magnitude of resisting force provided by the micropiles on a per unit length of cap beam 

basis must be at least equal to Hreq (calculated from slope stability analysis in Design Step 5). 

Also, the distance between individual micropiles along the cap beam (Soffset) must be large 

enough to permit ease of construction of the micropile elements. 

The shear capacity of the battered upslope micropile (Hult(Ψus)) and battered downslope 

micropile (Hult(Ψds)) are evaluated using Eq. 6-5 and the combined capacity of the upslope and 

downslope micropile (Hult-pair) is calculated using Eq. 6-10. From this, Smax (see Figure 6-22) 

may be evaluated as: 

 

req

ult-pair

max H

H

S = (Eq. 6-11) 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-34 December 2005

ψ

Slip surface

Axis 

perpendicular to 

slip surface

ψ

Slip surface

Axis perpendicular 

to pile axis

Micropile Micropile

(a) 

ψ

Slip surface

Axis 

perpendicular to 

slip surface

Micropile

ψ

Slip surface

Axis 

perpendicular to 

pile axis

Micropile

(b) 

Figure 6-21. Definition of Inclination Angle When (a) Slip Surface is Horizontal and (b) Slip 

Surface is not Horizontal. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-35 December 2005

 Notes: Soffset is the spacing between two micropiles 

Smax is the spacing between two upslope or downslope micropiles 

Figure 6-22. Spacing Between Micropiles. 

6.6.7 Potential for Soil Flow Between Micropiles 

If micropiles are spaced too far apart and/or if the soil above the slip surface is very weak, 

there is a potential for soil material to move in-between adjacent micropiles (Figure 6-23). 

This failure mechanism has been termed plastic flow. Ito and Matsui (1975) developed a 

theory to evaluate plastic flow between piles. The lateral force per unit thickness of soil 

acting on the micropile, q is calculated as (Hassiotis et al., 1997): 

Soffset

Soffset

Soffset

Smax

Smax

Micropile at 

upslope leg 

Pile cap 

Micropile at 

downslope leg 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-36 December 2005

{ } { }2 (A B)- D

N

-(1/2) γz N 2 F - 2 D 1 B-(2 E)-1 F - c D

N tan

1

q A c  + × × 

 



 × × × × 



















= × × × × +

φ φ φ φ

 (Eq. 6-12) 

where: 

 c = cohesion of the soil φ = friction angle of soil 

γ = unit weight of soil z = depth from ground surface 

 D1 = Smax (Eq. 6-11) D2 = opening between micropiles (Figure 6-23) 

N tan [ ] ( )( ) / 4 / 2 2

φ = π + φ





 



 +















 = ×

 tan N -1 (1/2) N

2

1

1 D

D A D

φ φ φ





 



 



 



 × + − = 8 4

N tan tan

D

D D B exp

2

1 2 π φ

φ φ

E Nφ tanφ (1/2) = ; and 

( )

E N -1

(2 tan ) 2 N N

F

(1/2) -(1/2)

φ

φ φ φ

+

× + + =

Micropile

D1 = Smax

Soil moving-in

between micropiles

D2 = D1 - b

b = micropile diameter

Micropile

D1 = Smax

Soil moving-in

between micropiles

D2 = D1 - b

b = micropile diameter

Figure 6-23. Plastically Deforming Soil between Two Adjacent Micropiles. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-37 December 2005

The ultimate horizontal force acting on the micropile due to soil movement between adjacent 

micropiles, Hult-soil/pile is the value for q integrated over the length of the micropile from the 

slip surface to the cap beam. An example spreadsheet showing this procedure is presented is 

presented in Section 6.7.9. 

To evaluate the spacing between micropiles, the calculated Hult-soil/pile is compared to the 

average resistance provided by the upslope and downslope pair (Hult-pair/2) as shown below: 

• If the plastic flow conditions are satisfied, then Smax previously calculated using Eq. 6-

11 does not need to be reduced. 

• If Hult-soil/pile < Hult-pair/2, then plastic flow conditions govern and Smax should be 

reduced. The plastic flow analysis should be repeated based on the new pile spacing 

corresponding to the reduced Smax. The final design spacing should be selected as the 

spacing that satisfies Hult-soil/pile ≥ Hult-pair/2. 

6.7 DESIGN EXAMPLE FOR SLOPE STABILIZATION WITH MICROPILES 

This section provides a complete design example for micropiles used for slope stabilization. 

The problem comprises stabilizing an embankment that exhibits creep movements 

particularly during rainy periods. The cross section of the embankment and subsurface 

information is shown in Figure 6-24. 

The roadway surcharge for design is 12 kPa. Right-of-way limitations preclude the use of a 

berm to stabilize the embankment. For this example, it is assumed that micropiles have been 

determined to be the best solution to meet the project constraints. 

Subsurface conditions are illustrated on Figure 6-24. The slope consists of silty clay 

overlying calcareous siltstone. Based on laboratory test results, the unit weight of the silty 

clay is estimated to be 21.2 kN/m3

 (134.9 pcf) and calcareous siltstone is estimated to be 23.0 

kN/m3

 (146.4 pcf). Based on the Atterberg limits results, the silty clay has a liquid limit of 

60 and hydrometer results indicate that the silty clay has up to 30 percent clay size material. 

Shear strength test results for the bedrock indicate a friction angle of 23 degrees with a 

cohesion intercept of 480 kPa (69.65 psi). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-38 December 2005

2010

0

30

10 20 0 30 50 60 40

Y DIRECTION (METERS)

X DIRECTION (METERS)

2m 12 kPa

BEDROCK

CALCAREOUS SILTSTONE

APPROXIMATE TOP OF ROCK

LIMITS OF 

RIGHT OF WAY

APPROXIMATE EXISTING GROUND SURFACE

CRITICAL SLIP SURFACE

N(BLOWS/0.3m)

2015454010

60/0.2

N(BLOWS/0.3m)

6

381646462625

60/0.1

N(BLOWS/0.3m) 26

301111353822

60/0.160/0.160/0.3

HARD RED AND BROWN

SILTY CLAY

FILL

RED STIFF TO HARD

RED SILTY CLAY

WITH BOULDERS

2010

0

30

10 20 0 30 50 60 40

Y DIRECTION (METERS)

X DIRECTION (METERS)

2m 12 kPa

BEDROCK

CALCAREOUS SILTSTONE

APPROXIMATE TOP OF ROCK

LIMITS OF 

RIGHT OF WAY

APPROXIMATE EXISTING GROUND SURFACE

CRITICAL SLIP SURFACE

N(BLOWS/0.3m)

2015454010

60/0.2

N(BLOWS/0.3m)

6

381646462625

60/0.1

N(BLOWS/0.3m) 26

301111353822

60/0.160/0.160/0.3

HARD RED AND BROWN

SILTY CLAY

FILL

RED STIFF TO HARD

RED SILTY CLAY

WITH BOULDERS

Figure 6-24. Slope Geometry and Subsurface Information for the Design Example. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-39 December 2005

The critical slip surface location was identified via observations from surficial features (i.e., 

scarp location at embankment crest and heaving near toe) and from preliminary slope 

stability analyses. 

6.7.1 STEP 4: Evaluate Factor of Safety of Existing Slope 

Perform slope stability analysis to compute the minimum factor of safety of the slope (FSmin). 

Computer programs such as XSTABL, SLIDE, or others can be used to perform the analyses. 

When performing slope stability analyses, methods such as Simplified Janbu, Simplified 

Bishop, or Spencer are used. 

Because this slope had previously undergone movements, it was assumed that the existing 

factor of safety of the slope is 1.0. A back-analysis is performed to estimate the shear 

strength parameters of the silty clay that correspond to FS = 1.0. Back-analysis is performed 

following the steps presented below: 

i. Estimate shear strength parameters. Because the slope has moved sufficiently, the 

residual drained friction angle can be used (e.g., φ′ = φ′r) to model the soil material 

where these movements have occurred. For the back-analysis, the shear strength 

parameters estimated at this stage are considered as trial strengths (φtrial and ctrial). 

Using Figure 6-4, with LL=60 and a clay fraction of 30 percent, results in φ'r equal to 

18o

 (i.e., φtrial = 18o). The cohesion of the same soil layer was assumed to be 25 kPa 

(3.63 psi) (i.e., ctrial = 25 kPa) based on previous experience with these materials. 

Slope stability analyses were performed using the computer program SLIDE and 

Spencer’s limit equilibrium method. The FS of the slope based on trial strengths (i.e., 

φtrial = 18o

 and ctrial = 25 kPa) is 1.67 (Figure 6-25). 

The trial shear strength parameters were modified using Eqs. 6-13 and 6-14: 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-40 December 2005

Bedrock

Silty Clay

Figure 6-25. FSmin Determined from Trial Shear Strength Parameters. 

 ( ) { ( )}

FS

tan trial modified tan

trial

1 φ φ − = (Eq. 6-13) 

 ( ) ( )

FStrial

trial modified c

c = (Eq. 6-14) 

Based on the above, φ’ (modified) is found to be 11o

 and c’ (modified) is 15 kPa (2.18 

psi). 

The back-analysis method presented above should be used with caution. As mentioned 

before, the calculated critical failure surface needs to be compared against the observed 

critical failure surface in the field. Also, the use of a nonzero effective stress cohesion 

intercept should be used with caution as deformations tend to reduce this cohesion. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-41 December 2005

A slope stability analysis was performed using the modified shear strength parameters of the 

slope material and the computed FS = 1.0, (Figure 6-26) and the critical slip surface 

generated by the program is found to be reasonably consistent with the actual slip surface in 

the field. 

Figure 6-26. FSmin of the Slope Based on Modified Shear Strength Parameters. 

6.7.2 STEP 5: Evaluate Additional Force Required To Obtain Target Factor of 

Safety 

A target factor of safety (FStarget) of 1.3 is selected for this slope and the micropile was 

modeled using Approach 2 (see Section 6.6.2.2) using the computer program SLIDE (2004). 

Several slope stability analyses were performed in which the micropile was located at 

approximately a midslope location. For these analyses, the shear strength assigned to the 

micropile was varied until the target factor of safety for the slope was achieved (see Figure 6-
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-42 December 2005

27). The additional force required from the micropile (Hreq) is 650 kN/m (44.54 k/ft) of slope 

length. 

Additional slope stability analyses were performed to confirm that slip surfaces upslope and 

downslope from the micropile location have an acceptable factor of safety. The results of 

these analyses are presented in Figure 6-28. From the analyses, the minimum factor of safety 

for upslope slip surfaces (FSup) is 1.30 and the minimum factor of safety for downslope slip 

surface (FSdown) is 1.35. These values are greater than FStarget, and therefore the location for 

the micropile is deemed appropriate. 

Modeled Micropile

Figure 6-27. Slope Stability Analysis to Determine Additional Force to Obtain Target Factor 

of Safety. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-43 December 2005

(a) (b) 

Figure 6-28. Stability of the (a) Upslope Away from the Micropile and (b) Downslope Away 

from the Micropile. 

If the factor of safety of the slope entirely downslope or entirely upslope of the micropile was 

less than FStarget then the location of the micropile would need to be changed or an additional 

micropile would be required. 

6.7.3 STEP 6: Select Micropile Cross Section 

In this example, the micropile cross section is selected as shown in Figure 6-29. A Type A 

micropile is used. The ground is considered nonagressive and no reduction in steel casing 

thickness is required. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-44 December 2005

API-N80 Casing

O.D.casing = 177.8 mm 

Wall Thickness = 11.50 mm

Fy = 552,000 kPa

Grout (fc’ = 27.6 MPa)

0.229 m (MIN.) Drill Hole 

API-N80 Casing

O.D.casing = 177.8 mm 

Wall Thickness = 11.50 mm

Fy = 552,000 kPa

Grout (fc’ = 27.6 MPa)

0.229 m (MIN.) Drill Hole 

Note: 1 mm = 0.04 in, 1 m = 3.281 ft, 1 MPa = 1,000 kPa = 145.1 psi 

Figure 6-29. Micropile Cross-Section for the Design Example. 

6.7.4 STEP 7: Estimate Length Of Micropile 

Estimate total length (Ltotal) of the micropile as: 

 Ltotal = Labove + Lbelow (Eq. 6-15) 

Labove is the length of micropile between the ground surface and the critical slip surface. 

Lbelow is the length of the micropile below the critical slip surface. 

In the design example, Labove is approximately 10 m (3.28 ft). This depth can be 

approximated from Figure 6-24 based on the selected micropile location shown in Figure 6-

27. To calculate Lbelow, Pult is calculated using Eq. 6-1: 

P L d 66 kPa 10 m 0.229 m 475 kN (107 k) ult =α bond-above × above ×π × = × ×π × =
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-45 December 2005

The value for αbond-above is within the range for Type A micropiles in relatively stiff silts and 

clays (see Table 5-3). 

Lbelow is calculated as: 

2.0 2.6 m (8.5 ft) 515 kPa 0.229 m

475 kN FS P L

bond-below

ult

below × = × ×

× = × × = α π d π

where αbond-below is estimated from Table 5-3 for hard shale. The bedrock at the site consists 

of siltstone, which is by definition closer to shale than sandstone or limestone. The FS for 

ultimate side resistance was selected to be 2.0. 

The estimated length to resist uplift or compression forces is calculated to be 2.6 m. 

Preliminary LPILE analyses showed that this length of micropile below the slip surface was 

not sufficient to provide fixity of the micropile. To promote fixity of the micropile below the 

critical slip surface (with respect to lateral loading considerations), the length of the 

micropile below the critical slip surface was increased from 2.6 m (8.5 ft) to 4.5 m (15 ft) 

based on further analysis. 

6.7.5 STEP 8: Evaluate Bending Capacity Of Single Vertical Micropile 

The ultimate bending moment, Mult, for a single vertical micropile with the cross section 

shown in Figure 6-29 is evaluated in this step using LPILE. The single vertical micropile 

model is shown in Figure 6-30. In addition to the cross section geometry, the following 

material properties must be specified for the analysis: (1) grout compressive strength; (2) 

yield strength of the steel casing; and (3) modulus of elasticity of the steel. 

The soil parameters for the LPILE analysis are shown in Figure 6-30. For this lateral loading 

condition, the profile at the location of the micropile was modeled using p-y curves for stiff 

clays. The undrained strength, Su, was conservatively estimated for the fill and residual soil 

layer based on measured SPT N values. Modeling the bedrock as a stiff clay is also 

conservative. More accurate parameter values could have been evaluated by more 

sophisticated testing methods. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-46 December 2005

Soil Type φ (deg) Su (kN/m2) γ’ (kN/m3

) ε50

Fill 0 120 21.2 0.0050 

Residual Soil 0 168 11.4 0.0040 

Bedrock 0 480 13.2 0.0025 

1 kPa = 0.1451 psi and 1 kN/m3 = 6.366 psf). 

Figure 6-30. Single Vertical Micropile Modeled in LPILE. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-47 December 2005

In the analysis, Mult is calculated for P = 0 and for P = Pult = 475 kN (107 k). The value for 

Mult was calculated using the option within LPILE to account for nonlinear flexural rigidity 

of the micropile. That is, the bending stiffness of the micropile reduces with increasing 

strain. The value for Mult is assumed to correspond to the bending moment in the micropile 

for which the compressive strain in the grout inside the casing is 0.003. The results of the 

Mult evaluation are shown in Table 6-2. 

Table 6-2. Mult Values for Design Example. 

P Mult

(kN) (k) (kN.m) (k.ft) 

0 0 161.3 119.0 

475 107 147.7 108.9 

6.7.6 STEP 9: Evaluate Shear Capacity of Single Vertical Micropile 

The maximum shear capacity of a single vertical micropile (Q) is determined iteratively by 

performing laterally loaded pile analyses. For the design example, p-y curves may be 

generated within LPILE in the same analyses as were performed for the calculation of Mult. 

The p-y curves are generated for various depths along the micropile and specifically for 

depths just below and above the depth of the transition between individual soil or rock layers 

(Figure 6-30). The depths chosen for this example are shown in Figure 6-31. 

After obtaining the p-y curves, the maximum shear capacity of a single vertical micropile can 

be calculated using: (1) Mult from P = 0 case; and (2) Mult from P = Pult case using up and 

down analyses. 

The iterative design process for up and down analyses is summarized in Figure 6-32. 

Perform a set of up and down analyses for P = 0 axial load case first and then perform the 

same analyses for P = Pult following the process described below: 

1. Set up the up and down analyses by inputting micropile cross section, micropile 

material properties, soil or rock parameters for each layer and p-y curves (adjust 

the location of p-y curves relative to slip surface as shown on Figure 6-17). 

2. Input a trial estimate of the shear force Q (magnitude and signs are same for up 

analysis and down analysis) and input a trial estimate of the internal bending 

moment (M) (magnitude is same but M is negative for the up analysis and 

positive for the down analysis). It should be noted that the selection of trial 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-48 December 2005

estimates for Q and M are arbitrary. If the initial estimate of Q is less than the 

value of Q which ultimately corresponds to Mult, the solution will converge. If the 

initial estimate of Q is greater than the value of Q which ultimately corresponds to 

Mult, the solution will not converge. This will be evidenced by pile head slopes 

from the up and down analysis which diverge from each other with each iteration. 

3. Perform laterally loaded pile analyses for up and down analyses and compare the 

slopes computed at the micropile head from both analyses. If the slopes at the 

micropile head are not equal then change the magnitude of the initially estimated 

M (i.e., in Step 1) and re-run both analyses again. When slopes at the pile head 

are equal from both analyses, note the calculated maximum bending moment 

(Mmax) from each analysis. 

4. Compare Mmax (greater of Mmax values from up and down analyses) with 

previously calculated bending moment capacity (Mult) for the corresponding axial 

load. 

5. If Mmax is approximately equal to Mult then Q is determined and analysis for this 

axial load case is completed. If Mmax is not equal to Mult, change the magnitude 

of the initially estimated Q (i.e., in Step 5) and re-run both analyses again. 

6. Repeat steps 1 through 4 for the P = Pult case. In step 3 use Mult calculated for the 

P = Pult case. 

Note: 1 m = 3.281 ft. 

Figure 6-31. Depths Chosen for p-y Curves for Entire Length of the Micropile. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-49 December 2005

Compare pile 

head slopes from 

up and down 

analyses

Compare pile 

head slopes from 

up and down 

analyses

If pile head slopes from both 

analyses are equal

Compare Mmax(1) with Mult

If pile head slopes from both 

analyses are equal

Compare Mmax

(1) with Mult

If pile head slopes from both 

analyses are not equal

Change M and re-run 

up and down analyses 

If pile head slopes from both 

analyses are not equal

Change M and re-run 

up and down analyses 

If Mmax equals Mult

Q is obtained.

(Analysis is complete)

If Mmax equals Mult

Q is obtained.

(Analysis is complete)

If Mmax is not equal to Mult

Change Q in both analyses and 

re-run up and down analyses

If Mmax is not equal to Mult

Change Q in both analyses and 

re-run up and down analyses

Laterally Loaded Pile Analyses

To 

Evaluate Shear Capacity of Micropiles

Laterally Loaded Pile Analyses

To 

Evaluate Shear Capacity of Micropiles

Input for “up analysis”

p-y curves

Estimated + Q

Estimated – M

P = 0 or P = Pult

Input for “up analysis”

p-y curves

Estimated + Q

Estimated – M

P = 0 or P = Pult

Input for “down analysis”

p-y curves

Estimated + Q

Estimated + M

P = 0 or P = Pult

Input for “down analysis”

p-y curves

Estimated + Q

Estimated + M

P = 0 or P = Pult

Output from “up analysis”

Slope at the pile head

Mmax (up)

Output from “up analysis”

Slope at the pile head

Mmax (up)

Output from “down analysis”

Slope at the pile head

Mmax (down)

Output from “down analysis”

Slope at the pile head

Mmax (down)

Note: (1) Mmax = the greater of Mmax (up) and Mmax (down)

Compare pile 

head slopes from 

up and down 

analyses

Compare pile 

head slopes from 

up and down 

analyses

If pile head slopes from both 

analyses are equal

Compare Mmax(1) with Mult

If pile head slopes from both 

analyses are equal

Compare Mmax

(1) with Mult

If pile head slopes from both 

analyses are not equal

Change M and re-run 

up and down analyses 

If pile head slopes from both 

analyses are not equal

Change M and re-run 

up and down analyses 

If Mmax equals Mult

Q is obtained.

(Analysis is complete)

If Mmax equals Mult

Q is obtained.

(Analysis is complete)

If Mmax is not equal to Mult

Change Q in both analyses and 

re-run up and down analyses

If Mmax is not equal to Mult

Change Q in both analyses and 

re-run up and down analyses

Laterally Loaded Pile Analyses

To 

Evaluate Shear Capacity of Micropiles

Laterally Loaded Pile Analyses

To 

Evaluate Shear Capacity of Micropiles

Input for “up analysis”

p-y curves

Estimated + Q

Estimated – M

P = 0 or P = Pult

Input for “up analysis”

p-y curves

Estimated + Q

Estimated – M

P = 0 or P = Pult

Input for “down analysis”

p-y curves

Estimated + Q

Estimated + M

P = 0 or P = Pult

Input for “down analysis”

p-y curves

Estimated + Q

Estimated + M

P = 0 or P = Pult

Output from “up analysis”

Slope at the pile head

Mmax (up)

Output from “up analysis”

Slope at the pile head

Mmax (up)

Output from “down analysis”

Slope at the pile head

Mmax (down)

Output from “down analysis”

Slope at the pile head

Mmax (down)

Note: (1) Mmax = the greater of Mmax (up) and Mmax (down)

Figure 6-32. Process to Evaluate Shear Resistance (Q) of Single Vertical Micropile Using 

Up and Down Laterally Loaded Pile Analyses. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-50 December 2005

The laterally loaded pile analysis output for P = 0 and P = Pult are presented in Appendix B. 

The up analysis is performed for the pile length of 10 m (32.8 ft) and the down analysis for 

the pile length of 4.5 m (15 ft). The soil/rock layers in up and down analyses are modeled by 

adjusting the previously determined p-y curves. For each soil layer depth, p-y curves are 

inputted in the model. An example is shown in Figure 6-33 for the up analysis. The p-y 

values in the “external p-y curve” dialog box in Figure 6-33 are the previously determined py values at a depth of 10 m. Using the adjustment shown in Figure 6-17a, they are assigned 

to a depth of 0 m for the up analysis. 

Figure 6-33. Modeling Soil Layers with Previously Determined p-y Curves. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-51 December 2005

For the P = 0 case, the shear capacity of the micropile (QP=0) is calculated as 365 kN (82 k) 

and the maximum bending moment (Mmax) is calculated as 161.3 kN.m (119.0 k.ft). The Mult

for this axial load case was previously calculated as 161.3 kN.m (119.0 k.ft) (see Table 6-2). 

For the P = Pult case, the shear capacity of the micropile (QP=Pult) is calculated as 330 kN 

(74.2 k) and the maximum bending moment is calculated as 147.7 kN.m (108.9 k.ft). The 

Mult for this axial load case was previously calculated as 147.7 kN.m (108.9 k.ft) (see Table 

6-2). 

For both axial load conditions, Mmax is approximately equal to Mult and the up/down analyses 

are considered to be complete. Therefore, both QP=0 and QP=Pult can be used in the 

subsequent design steps to evaluate the shear capacity of battered micropiles. 

6.7.7 STEP 10: Evaluate Shear Capacity of Battered Micropile Group 

For this step, the maximum lateral force that the battered micropile group or pair (i.e., 

upslope micropile leg and downslope micropile leg as shown in Figure 6-9) (Hult-pair) can 

resist at the location of the critical slip surface is evaluated (see Section 6.6.5). 

In this design example, the batter angle for the upslope micropile leg is selected as 3o

 and the 

batter angle for the downslope micropile leg is selected as 21o

. The Hult for each leg is 

calculated as shown below: 

For ψus = 3o

, Hult (ψus) = QP=0 = 365 kN (82 k) 

For ψds = 21o

, Hult (ψds) has to be interpolated. Hult (ψds) calculated for various batter angles 

are shown in Table 6-3 and interpolation for ψds =21o

 is shown in Figure 6-

34. Hult (ψus) is evaluated as 450 kN (101 k). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-52 December 2005

Table 6-3. Hult (ψds) for Various Batter Angles. 

Hult(ψds) ψds (degree) (kN) (k) Equations 

0 365 82 

10 365 82 

6-8 

30 523 117.6 

40 558 125.4 

6-7 

Therefore, according to Eq. 6-10: 

Hult-pair = Hult () () ψus + Hult ψds = 365 + 450 = 815 kN (183.2 k) 

This is the calculated maximum lateral force that the micropile pair can resist at the location 

of the critical slip surface. 

6.7.8 STEP 11: Calculate Spacing Required to Provide Force to Stabilize the Slope 

The definition of spacing between two upslope micropiles and two downslope micropiles is 

presented in Figure 6-22 and is calculated using Eq. 6-11 as: 

req

ult-pair

max H

H

S =

In the design example, Hreq is calculated as 650 kN/m (44.5 k/ft) and Hult-pair is calculated as 

815 kN (183.2 k), therefore Smax is: 

1.25 m

650 kN/m

815 kN Smax = =
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-53 December 2005

0

100

200

300

400

500

600

700

0 10 20 30 40

Inclination Angle, ψ (Degrees)

Capacity of Individual Battered Micropiles, Hult (kN)

P = 0 and Q = QP=0 P = Pult and Q = QP=Pult

Interpolated

For ψds = 21o

Hult(ψds) = 450 kN 

Note: 1 kN = 0.2248 k 

Figure 6-34. Interpolation of Hult for Battered Downslope Micropile Leg. 

6.7.9 STEP 12: Check Potential Soil Flow between Micropiles 

In this Design Step, the ultimate horizontal pile force (Hult-soil/pile) from a plastic flow analysis 

is compared to the average resistance provided by the upslope and downslope micropile pair 

(Hult-pair/2). This comparison is performed to check that Smax is adequate to prevent plastic 

soil flow above the critical slip surface between micropiles. 

For the design example, Eq. 6-12 was developed in a spreadsheet format (Figure 6-35). The 

formulas used for each cell in the spread sheet are presented in Figure 6-36. The Hult-soil/pile

column in Figure 6-35 is the summation of soil resistance against plastic flow from the 

ground surface to the depth of slip surface. This is also shown graphically in Figure 6-37. In 

the design example the depth of the critical slip surface is 10 m. Therefore, Hult-soil/pile is 

calculated for 10 m to be 753 kN (169.3 k). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-54 December 2005

For this design, Hult-soil/pile = 753 kN (169.3 k) ≥ Hult-pair/2 = 407.5 kN (91.6 k). Therefore, 

plastic flow conditions are satisfied and the calculated Smax from Design Step 11 does not 

need to be reduced. 

6.7.10 STEP 13: Perform Structural Design of Concrete Cap Beam 

The steel-reinforced CIP concrete cap beam spans and anchors the micropile array at the 

ground surface. The concrete cap beam is typically 2-m wide and 1-m deep, but, in general, 

the cap beam should have sufficient height and width to allow for at least two to three 

micropile diameters embedment into the cap beam to promote fixity of the upslope and 

downslope micropile. The structural design of the concrete cap beam follows typical 

methods for reinforced concrete (see Section 8 of AASHTO (2002)). Specific considerations 

involved in the design of a concrete cap beam include: 

• Where ground anchors are used, the cap beam provides a reaction for the ground 

anchors to be installed and subsequently stressed and locked-off. The cap beam 

needs to be designed for these forces. 

• Where ground anchors are not incorporated, axial loads transferred towards the 

ground surface should be small (particularly if the slide plane is relatively deep). 

Although these forces are postulated to be small, the provision of fixity of the 

micropile group at the cap beam will cause load transfer to the cap beam. Also, 

where the depth of the slide plane is relatively shallow, it is likely that bending 

moments in the cap beam may be on the order of bending moments calculated at the 

slide plane. For this case, soil-structure interaction analyses should be performed to 

evaluate bending moments for structural design of the cap beam. 

• In some cases, relatively significant deflections of the cap beam may need to be 

considered in the structural design. That is, ground anchor stressing, non-uniform 

depth to competent material, and/or compression of soil material within the unstable 

soil mass may result in differential settlements of the length of the cap beam. The 

resulting bending stresses and torsional stresses from such movements should be 

considered in the structural design of the cap beam. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-55 December 2005

Note:

Deifinitions of the parameters used in this spread sheet can be found in Equations 6-11 and 6-12 and Figure 6-23

Input Parameters

Smax from Design Step 11 = 1.25 m

c = 168 kPa

γ = 21.2 kN/m3

φ = 0.01 degrees (Note: for φ = 0 conditions input very small value for φ)

b = 0.1778 m

Calculations

D2 = 1.07 m Nφ = 1.00E+00 (dim)

π = 3.1415927 A = 1.25E+00

tan φ = 1.75E-04 B = 1.00E+00

φ/4 = 4.36E-05 E = 1.75E-04

π/8 = 3.93E-01 F = 5.73E+03

tan(φ/4+π/8) = 4.14E-01

Nφ tan φ = 1.75E-04

z (m) Total Resistance (kPa) Hult-soil/pile (kN/m)

0 51 51

1 55 105

2 59 162

3 63 222

4 66 287

5 70 355

6 74 427

7 78 503

8 82 583

9 85 666

10 89 753

11 93 844

12 97 939

13 100 1037

14 104 1140

15 108 1246

20 127 1832

Figure 6-35. Spreadsheet Calculations Based on Eq. 6-12 to Obtain Hult-soil/pile 

for the Example Problem.
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-56 December 2005

123456789

10111213141516171819202122232425262728293031323334353637383940

A B

Input Parameters

Smax from Design Step 11 = 1.25

c = 168

γ = 21.2

φ = 0.01

b = 0.1778

Calculations

D2 = =$B$4-$B$9

π = =PI()

tan φ = =TAN(RADIANS($B$8))

φ/4 = =RADIANS(B$8/4)

π/8 = =$B$15/8

tan(φ/4+π/8) = =TAN($B$17+$B$18)

Nφ tan φ = =$B$22*$B$16

Nφ = =TAN(($B$15/4)+(RADIANS($B$8/2)))^2

A = =($B$4)*($B$4/$B$14)^(($B$22^0.5*$B$16+$B$22-1))

B = =EXP((($B$4-$B$14)/$B$14)*$B$20*$B$19)

E = =($B$22^0.5)*$B$16

F = =((2*$B$16)+(2*($B$22^0.5))+($B$22^-0.5))/($B$25+$B$22-1)

z (m) Total Resistance (kPa)

0 =(($B$23*$B$6*((1/($B$22*$B$16))*($B$24-(2*$B$25)-1)+$B$26)))-$B$6*($B$4*$B$26-2*$B$14*$B$22^-0.5)+((($B$7*A29)/$B$22)*($B$23*$B$24-$B$14))

5 =(($B$23*$B$6*((1/($B$22*$B$16))*($B$24-(2*$B$25)-1)+$B$26)))-$B$6*($B$4*$B$26-2*$B$14*$B$22^-0.5)+((($B$7*A30)/$B$22)*($B$23*$B$24-$B$14))10 =(($B$23*$B$6*((1/($B$22*$B$16))*($B$24-(2*$B$25)-1)+$B$26)))-$B$6*($B$4*$B$26-2*$B$14*$B$22^-0.5)+((($B$7*A31)/$B$22)*($B$23*$B$24-$B$14))15 =(($B$23*$B$6*((1/($B$22*$B$16))*($B$24-(2*$B$25)-1)+$B$26)))-$B$6*($B$4*$B$26-2*$B$14*$B$22^-0.5)+((($B$7*A32)/$B$22)*($B$23*$B$24-$B$14))20 =(($B$23*$B$6*((1/($B$22*$B$16))*($B$24-(2*$B$25)-1)+$B$26)))-$B$6*($B$4*$B$26-2*$B$14*$B$22^-0.5)+((($B$7*A33)/$B$22)*($B$23*$B$24-$B$14))

z (m) Hult-soil/pile (kN/m)

0 =B295 =B36+0.5*(A30-A29)*(B30+B29)10 =B37+0.5*(A31-A30)*(B31+B30)15 =B38+0.5*(A32-A31)*(B32+B31)20 =B39+0.5*(A33-A32)*(B33+B32)

Figure 6-36. Equations Used in Each Cell in Figure 6-35. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-57 December 2005

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 5 10 15 20 25

Depth (m)

Hult-soil/pile (kN/m)

Figure 6-37. Graphical Solution for Hult-soil/pile Based on Figure 6-36. 

Summary of the Design Example

• Type A gravity-grouted micropiles comprising API-N80 casing with OD.casing = 177.8 

mm embedded 4.5 m (15 ft) into bedrock are used. 

• The upslope micropile leg is battered at 3 degrees and the downslope micropile leg is 

battered at 21 degrees. Individual micropiles in each pair should be constructed as 

close to each other as possible with just large enough space to permit ease of 

construction. 

• The spacing between two upslope micropiles and two downslope micropiles should 

be no more than 1.25 m. 

• All of the micropiles should be connected at the ground surface via a concrete beam. 

• For verification load testing, micropiles with a 4.5-m (15-ft) long bond length in rock 

(below the slip surface) should be tested to 950 kN (213 kips) (i.e., 2.0 × the 

calculated axial resistance for the micropile above the slip surface). For proof load 

testing, micropiles should be tested to 760 kN (171 kN) (i.e., 1.6 × the calculated 

axial resistance for the micropile above the slip surface). Load testing requirements 

are presented in Chapter 7. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-58 December 2005

6.8 SHEAR CAPACITY OF MICROPILES FOR ANALYSIS 

As previously noted, the shear load that an individual micropile provides is assumed to 

correspond to the maximum shear force in the micropile when the micropile has reached its 

ultimate bending capacity. The rationale for this is explained below. 

A slope that has failed (i.e., some movement has been observed and may have stopped or 

continuous or intermittent movements being measured) implies that its slope stability factor 

of safety is equal to 1.0. Since the design of the micropile-stabilized slope is predicated on 

good knowledge of the position of the failure surface and the pore pressures in the slope at 

the time of failure, then the loads and soil resistances are reasonably well-known, and, in 

fact, are equal in magnitude to each other (i.e., the FS = 1.0 condition requires this). 

The analysis now requires that the slope be stabilized to a target factor of safety (e.g., FS = 

1.3). Using the shear strengths obtained from the back-analysis of a failed slope, a shear 

force (provided by the micropile) is added until the target factor of safety for the slope is 

calculated. It is recommended that this shear force be added to the resisting forces (or 

moments) in the limit equilibrium calculations (as compared to treating it as a negative 

driving force or moment). 

In an allowable stress design format, the service loads on the micropile are equal to zero 

since the slope is “stable” at a FS of 1.0. In a retaining wall, for example, the service loads 

on the wall for the FS = 1.0 condition are not zero and may be associated with full active 

earth pressure conditions. 

To increase the factor of safety of the slope, micropiles are added. In the design, it is 

assumed that, if the ultimate shear capacity of the micropiles was mobilized at a limit (i.e., 

failure) state, the factor of safety of the slope would be at 1.3. This approach is exactly 

consistent with reinforced slope design. In that case, the design strength of the reinforcement 

corresponds to its strength at a specific design life, Tal and then slope stability analyses are 

performed to verify a target factor of safety for the slope. As for the micropile analysis 

described herein, no reductions to some allowable stress (or strength) are used. Whereas, the 

reinforced slope soil reinforcement strength is reduced to account for creep, durability, and 

construction damage, the strength of the micropile may be reduced to account for potential 

steel loss due to corrosion. 

A design engineer may incorporate additional conservatism in a project if warranted. For 

example, additional conservatism may be prudent if the failure slip surface and/or residual 

soil shear strength are not well understood for a particular slide or if the soil within the 

failure slip surface has the potential for continued long-term creep movements. Additional 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-59 December 2005

conservatism may be incorporated through selection of soil properties, phreatic surface 

assumptions, value of target slope stability factor of safety, maximum micropile shear force, 

or a combination of these. Note that a probabilistic analysis can be performed to examine 

slope stability factor of safety values for ranges of material parameters (see Duncan et al., 

1999), and that this can provide a better understanding of the effect of material parameters. 

6.9 CASE HISTORIES 

6.9.1 Stabilization of Blue Trail Landslide Using Micropiles, Wyoming 

The Blue Trail Landslide project is located on U.S. Highway 26/89 between Alpine Junction 

and Hoback Junction, Wyoming. This section of roadway is next to the canyon of the Snake 

River (Figure 6-38). This highway was constructed between 1955 and 1960 and had 

experienced episodes of movement resulting from movement of the landslide. Throughout 

the years, various remedial design alternatives were reviewed to mitigate slope movements 

and to stabilize the slide to a desired factor of safety of 1.3. Alternatives considered included 

regrading the slope and constructing a toe berm, constructing a bridge over the entire slide 

area, and installing drilled shafts near the toe of the landslide to provide structural restraint 

(Hasenkamp, 1999). These alternatives were rejected for implementation because they were 

not cost effective. Ultimately, micropiles were selected for implementation since they were 

less expensive that other alternatives and could be constructed in highly variable ground and 

under restricted access conditions. Other advantages included the ability to maintain traffic 

during construction and minimal environmental impacts. 

The design of the micropiles was performed using the design approach described in this 

chapter. Originally, two micropile walls (i.e., two sets of upslope and downslope micropiles) 

and a mechanically stabilized earth (MSE) wall were designed to stabilize the slope (Figure 

6-39). The first wall was located 3 m below the roadway (i.e., upper wall) and the second 

one was located approximately between the road and the toe of the slide (i.e., lower wall). At 

a later time, a third wall was added along the western edge of the project at about 12 m (39 

ft) below the roadway to increase the factor of safety of the slope at that location. The 

original design included a single ground anchor at each wall location. During the early 

stages of construction, it became necessary to significantly increase the restraining force 

provided by the lower wall. This was the result of a significant increase in the seismic 

coefficient that was required by a reviewing agency. This was accomplished by significantly 

increasing the capacity of the ground anchors in the lower wall. Micropiles were battered 30 

degrees from the vertical and ranged in length from 19 to 34 m (62 to 112 ft). Ground 

anchors were installed at 30 degrees from the horizontal (see Figure 6-40). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-60 December 2005

Figure 6-38. Extent of Blue Trail Landslide (after Hasenkamp, 1999). 

Figure 6-39. Conceptual Design Drawing of the MSE and NRM Walls for Blue Trail 

Landslide Project (after Hasenkamp, 1999). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-61 December 2005

Figure 6-40. Typical Section of Micropile and Ground Anchor Wall for Blue Trail Landslide 

Project (after Hasenkamp, 1999). 

The Blue Trail landslide was the first project in Wyoming in which micropiles and ground 

anchors were used to create a permanent landslide stabilization system. A comprehensive 

instrumentation and monitoring program was developed to assess the field performance of 

the walls. Instrumentation consisted of slope inclinometers, survey monuments, tilt plates, 

strain gauges attached to micropile steel casings, load cells attached to four ground anchors, 

and piezometers. Information collected included: (1) wall and slope movement; (2) load 

transfer to the micropiles and ground anchors; and (3) pore water pressures in the slide 

material (Hasenkamp, 1999). 

The construction sequence followed installation of micropile walls and then ground anchors. 

In each case, the lower wall was built first, upper wall was built second, and middle wall was 

built last. A total of 478 micropiles and 40 ground anchors were installed to stabilize the 

slope. Instrumentation data indicated that this stabilization approach was effective in 

significantly reducing slope movements. Measured axial loads in the micropiles were less 

than those assumed in the design (Table 6-4). Measured maximum bending moments ranged 

from approximately 8 to 80 percent (average 30 percent) of the ultimate bending moment 

capacity for the steel pipe of the micropiles (Table 6-4). These results indicate that wall 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-62 December 2005

performance was acceptable. The direction of axial load and bending moments in the 

micropiles of the lower wall was opposite to that assumed in the design. This resulted from 

the significant lock-off loads within the lower wall ground anchors. Micropiles in the upper 

wall showed compression for both the upslope and downslope directions. This is most likely 

the result of surcharge load associated with placement of the MSE wall and roadway over the 

upper insert wall. 

Table 6-4. Comparison of Actual Loads to Design Loads for Blue Trail Landslide 

Project (after Hasenkamp, 1999). 

Wall Micropile 

Number 

Micropile 

Orientation L (m) PDesign

(kN)(1)

PMeasured

(kN)(1)

Mult-Design 

(kN-m) 

Mult-Measured 

(kN-m) 

62 Upslope 23.8 635 -686 35.2 15.4 

63 Downslope 33.5 -894 -566 35.2 3.3 

123 Downslope 27.7 -739 153 35.2 4.0 

Upper 

124 Upslope 23.8 635 -302 35.2 14.6 

326 Downslope 19.2 -717 214 35.2 8.5 

327 Upslope 19.5 728 -594 35.2 2.9 

402 Downslope 19.5 -728 398 35.2 3.2 

Lower 

403 Upslope 19.5 728 -450 35.2 3.8 

Notes: (1) Negative values indicate compression. 

 L: Length of the micropile. 

 PDesign and PMeasured: Design axial load and axial load measured in the field, respectively. 

Mult-Design and Mult-Measured: Ultimate bending moment of micropile section and bending moment 

measured in the field, respectively. 

6.9.2 Stabilization of Sum-271 Landslide Using Micropiles, Ohio 

The SUM-271 project is located on Interstate 271 northbound in Richfield Township, 

Summit County, Ohio. The site consists of approximately 21 m (70 ft) of valley fill 

overlying relatively thin and weak layers of normally consolidated fine grained lacustrine 

soils with strong overconsolidated lacustrine soils beneath. Over the years, slope movements 

resulted in pavement settlement and cracking. Two alternatives were considered for 

stabilization. One alternative consisted of regrading the slope and constructing toe buttress 

berms and the other alternative included using micropiles (Liang, 2000). The Ohio 

Department of Transportation (ODOT) selected the micropile option. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-63 December 2005

The design of the micropiles was performed using the design approach presented in this 

chapter. Because micropiles were not able to completely develop the resisting forces 

required, ground anchors were added to the design. The wall consisted of 154 type A 

micropiles that were spaced 1.2- to 1.8-m (4- to 6-ft) apart and battered 30 degrees from the 

vertical and 41 ground anchors that were spaced 3.5 m (12 ft) apart and battered 30 degrees 

from the horizontal (Figure 6-41). 

Figure 6-41. Typical Section of Micropile and Ground Anchor Wall at SUM-271 (after 

Liang, 2000). 

A comprehensive instrumentation and monitoring program for the wall was developed for 

this project. Inclinometers were installed in the slope to monitor slope movement and strain 

gauges were attached to the micropiles to allow for measurements of axial loads and bending 

moments in the micropiles throughout construction. High capacity load cells were used to 

monitor ground anchor loads. Inclinometer data indicated that the installation of the NRM 

wall and ground anchors was effective in arresting the slope movement. 

As part of this project, detailed finite element analyses were performed to model the wall 

behavior (Liang, 2000). These analyses simulated relevant stages of construction including 

earthwork, pile cap construction, drilling, and installation of micropiles and stressing of the 

ground anchors. Finite element analysis results were compared to field instrumentation 

monitoring data to validate the capability of the FEM modeling technique and to provide 

supplemental information. Based on the finite element analysis results and field 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-64 December 2005

measurements of wall performance, the following observations and conclusions were 

developed: 

1. The maximum axial force in each micropile occurred at the location near the slip 

surface of the slope (i.e., approximately 30 ft below the ground surface) (Figure 6-

42). The direction and magnitude of the axial forces in the micropiles were consistent 

with loading conditions resulting from the various stages of construction. For 

example, the upslope micropile was initially in tension (following installation). 

When the ground anchor was tensioned, a portion near the top of the upslope 

micropile remained in tension, while the remaining portion of the wall was in 

compression. The axial forces in the downslope micropile were initially in 

compression but after the ground anchor tensioning, the compressive forces were 

reduced. However, no tension was developed in the downslope micropile. 

Figure 6-42. Comparison of Axial Loads for the SUM-271 Project (after Liang, 2000). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-65 December 2005

2. The bending moments were near zero at the location where the maximum axial forces 

occurred (Figure 6-43). The change in bending moments throughout the construction 

stages were small and were primarily due to small stiffness of the micropiles. The 

magnitude of the maximum bending moments was reasonably predicted by the finite 

element analyses. 

Figure 6-43. Comparison of Bending Moments for the SUM-271 Project (after Liang, 2000). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-66 December 2005

6.9.3 Stabilization of Littleville Landslide using Micropiles, Alabama 

The Littleville landslide is located on a section of US Route 43, Alabama. The area of the 

landslide is a fill composed of sandstone and shale cut from adjacent hillsides. The 

underlying stratum is shale with some weathering along the top surface, which is believed to 

be the failure surface. A highway was constructed at the site in the 1950s. Soon after 

construction of the original roadway was finished, stability problems arose and the road 

surface dropped due to slides in the fill material. Initially the holes were filled and the road 

was repaved. In the 1970s, the roadway was widened and the slope was flattened. However, 

ensuing rainy periods brought on the onset of more slope failures. The creep of the slope 

continued until a micropile wall with additional stabilization provided by ground anchors was 

built in 1997 to stabilize the slope (Brown and Chancellor, 1997). 

The design of micropile wall was performed following the same approach as is described in 

this chapter. A typical cross section of the slide and the reinforcement installed at the site are 

provided in Figure 6-44. The micropiles included 114-mm (4.5 in.) diameter steel casing 

with a wall thickness of 8 mm. Micropile design lengths were 7 m (23 ft) and were battered 

30 degrees from vertical. A total of 432 micropiles and 44 ground anchors were installed for 

the project. 

Figure 6-44. Typical Section of Micropile and Anchor Wall at Littleville, Alabama (after 

Brown and Chancellor, 1997). 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-67 December 2005

Instrumentation data was collected for a period of two years. Data collected included 

inclinometer measurements of slope movement, pore water pressures, and stresses developed 

in the micropiles and anchors. Piezometers have shown relatively stable water levels over 

the two years with a fluctuation of approximately two or three feet. 

Inclinometer data indicated that slope movement had effectively ceased as a result of the 

slope stabilization measure. Analysis of the strain gauge data indicated that this was 

accomplished without approaching potential failure conditions in the micropiles. The axial 

forces mobilized in the micropiles were found to be below the estimated ultimate axial load 

by a factor of approximately two, and the factor of safety was calculated to be approximately 

1.3 as originally estimated. In addition, it was found that the upslope battered micropiles 

were in tension in the vicinity of the slide plane and the downslope battered piles were in 

compression. The strain gauges also indicated higher bending moments developed in the 

micropiles in the vicinity of the slide surface. Measured maximum bending moments ranged 

from approximately 5 to 9 percent of the ultimate bending moment capacity of the 

micropiles. Loads in the ground anchors were observed to decrease slightly over time and 

this was attributed to small movements that have occurred in the uphill direction. 

6.10 REFERENCES 

Brown, D.A. and Chancellor, K. (1997), “Instrumentation, Monitoring and Analysis of the 

Performance of a Type-A INSERT Wall, Littleville, Alabama”, Highway Research 

Center, Auburn, University Alabama. 

Duncan, M.J., Navin, M. and Patterson, K., Manual for Geotechnical Engineering 

Calculations, Virginia Tech Center for Geotechnical Practice and Research, December, 

1999. 

Hasenkamp, R. N., (1999), “Evaluation of a Micropile Reinforced Earth Retaining Structure, 

Blue Trail Landslide, Wyoming”, Master Thesis, Department of Civil and Agricultural 

Engineering, University of Wyoming. 

Hassiotis, S., Chameau, J. L., and Gunaratne, M., (1997), “Design Method for Stabilization 

of Slopes with Piles”, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 

123, No. 4, 314-323 pp. 

Ito, T., and Matsui, T., (1975), “Methods to Estimate Lateral Force Acting on Stabilizing 

Piles”, Soil and Foundations, Vol. 15, No. 4. 
FHWA NHI-05-039 Chapter 6 – Slope Stabilization 

Micropile Design & Construction 6-68 December 2005

Kavazanjian, E. Jr., Matasovic, N., Hadj-Hamou, T., Sabatini, P. J. (1997), Design Guidance: 

Geotechnical Earthquake Engineering for Highways, Geotechnical Engineering 

Circular, No.3, Federal Highway Administration Publication, U.S. Department of 

Transportation, FHWA-SA-97-077. 

Liang, R.Y. (2000), “Instrumentation and Monitoring of Reticulated Micropile Slope 

Stabilization at SUM-271 Project,” submitted to the Federal Highway Administration, 

September 2000. 

Mayne, P. W., Christopher, B. R., and DeJong, J. (2001), Manual on Subsurface 

Investigations, National Highway Institute, Publication Number NHI-01-031, Federal 

Highway Administration, Washington, D.C.

O’Neil, M. W. and Reese, L. C. (1999), “Drilled Shafts: Construction and Procedures and 

Design Methods”, Federal Highway Administration Publication, Publication Number: 

FHWA-IF-99-025. 

Poulos, H. G. and Davis, E. H., (1980), Pile Foundation Analysis and Design, John Wiley 

and Sons, 397 pages. 

Reese, L. C., Wang, S. T., Isenhower, W. M., Arréllaga, J. A., and Hendrix, J., (2005), “A 

Program for Analysis of Single Piles Under lateral Load”, Version 5.0.18, Ensoft Inc., 

Austin, TX. 

Sabatini, P. J., Bachus, R. C., Mayne, P. W., Schneider, J. A., and Zettler, T. E. (2002). 

“Evaluation of Soil and Rock Properties”, Geotechnical Engineering Circular, No. 5, 

Federal Highway Administration, U.S. Department of Transportation, FHWA-IF-02-

034. 

SLIDE (2004), “Slope Stability Analyses Program”, Rocscience Inc., Ontario, Canada. 

Stark and Eid, (1994) “Drained Residual Strength of Cohesive Soils”, Journal of 

Geotechnical Engineering, Vol. 120, No. 5. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-1 December 2005

CHAPTER 7 

MICROPILE LOAD TESTING 

7.1 INTRODUCTION 

On micropile foundation support projects and slope stabilization projects, “verification” load 

testing is performed on pre-production micropiles. The purpose of the pre-production testing 

is to verify design assumptions concerning bond zone strength and the adequacy of the 

contractor’s installation methods. This testing is usually performed as the first order of work 

under the construction contract. Production micropiles are approved only after the design 

assumptions and the adequacy of the contractor’s installation method have been verified. On 

large projects, additional load testing may be performed during the design stage under a 

separate contract. 

The ability of the micropile to safely carry the design load in service is obtained through 

“proof” load testing on selected production micropiles. This proof testing provides a quality 

assurance means to confirm micropile installation procedures. 

Micropiles are tested individually using the same conventional static load testing procedures 

as are used for driven piles and drilled shafts. These tests include incremental loading (which 

may be applied in compression, tension, or laterally and which may be cycled (i.e., 

load/unload)) until the micropile reaches the selected maximum test load, structural 

displacement limit, or ground creep (i.e., movement under constant load) threshold. 

In this chapter, descriptions of “verification” and “proof” tests for micropiles are provided 

with information on typical testing equipment, schedule for load increments, and analysis of 

load-deformation data as a means to judge micropile acceptance for payment purposes.

7.2 OVERVIEW OF MICROPILE LOAD TESTING 

Micropiles are load tested in the field to verify that the required design loads can be carried 

without excessive movement and with an adequate factor of safety for the life of the 

structure. Load testing is also used to verify the adequacy of the contractor’s drilling, 

installation and grouting operations prior to (verification testing) and during (proof testing) 

construction of production micropiles. Therefore, the ground conditions, as well as the 

method, equipment, and operator used for installing production piles must be similar to those 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-2 December 2005

used for installing the test micropiles. If ground and/or installation procedures change from 

that used from the verification load testing program, additional testing should be required. If 

test results indicate faulty construction practice, or grout-to-ground load capacities less than 

required, the contractor may be required to modify the micropile installation methods. In the 

event that the required design grout-to-ground bond capacities are still not achievable, 

redesign may be necessary. 

Load testing criteria will be included in the construction specifications and will typically 

include ultimate and/or verification tests. These tests usually require loading to a maximum 

test load that includes the factor of safety assigned to the design grout-to-ground bond (i.e., 

the verification test) and/or that which results in failure defined as the inability to maintain 

constant test load without excessive micropile movement (i.e., the ultimate test). The 

ultimate tests, taken to failure, are usually only specified as part of a research project or on 

very large projects where a design phase test program can be justified. The design phase test 

program will allow the micropile design to be optimized. On typical projects, one or two 

verification tests are commonly conducted prior to beginning production pile installation, and 

then one or more additional such tests may be conducted in each significantly different 

ground type encountered as construction proceeds. A larger number of verification tests may 

be specified for larger projects. The minimum required number of verification load tests to 

be performed for a project is provided in Section 7.6.2. Since ultimate and verification tests 

are typically carried to relatively high loads, in many cases these micropiles will not be used 

as part of the final structure, i.e., they are “sacrificial” micropiles.

During installation of production micropiles, “proof” testing is conducted on a specified 

number of the total production piles installed. Proof tests are performed on production piles 

that will be incorporated into the structure provided the maximum test loads are less than 

those required to cause geotechnical or structural failure and which do not result in damage 

to the micropile. Recommendations on minimum number of proof tests to be performed for 

various applications are provided in Section 7.6.3. 

Creep tests are performed as part of verification and proof tests. Creep testing procedures are 

similar to the creep test used for ground anchors and soil nails. Creep is primarily of concern 

in organic soils and cohesive (clayey) soils with a liquid limit greater than 50 and a plasticity 

index greater than 20. The creep test consists of measuring the movement of the micropile at 

constant load over a specified period of time. This test is used to assess whether pile design 

loads can be safely carried throughout the project service life. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-3 December 2005

7.3 LOAD TESTING EQUIPMENT 

7.3.1 General 

The equipment and load testing methods used for micropiles are the same as those used for 

conventional load testing of driven piles and drilled shafts as codified in ASTM D 1143 for 

compression loading, ASTM D 3689 for tension loading, and ASTM D 3966 for lateral 

loading. Typical load test setups for compression, tension, and lateral load applications are 

shown in Figures 7-1, 7-2, and 7-3, respectively. Typical load testing equipment includes: 

(1) hydraulic jack and pump; (2) reaction and reference beams; (3) pressure gauges and load 

cells; (4) dial gauges; and (5) wire with mirror and scale. 

7.3.2 Load Testing Equipment 

The most common and convenient system includes a hydraulic jack and reaction 

arrangement. For compression testing, the load is applied by hydraulically jacking against a 

beam that is anchored by piles, micropiles, ground anchors (Figure 7-4), or by jacking 

against a weighted platform. For tension tests, loads are applied by centering the hydraulic 

jack on top of a test beam and jacking against a reaction frame connected to the micropile to 

be tested (Figure 7-5). The test beam may be supported by cribbing. For lateral load tests, 

lateral loads are applied by a hydraulic jack against a reaction system or by a hydraulic jack 

acting between two piles (Figure 7-6). With the latter method, two micropile lateral load 

tests can be performed simultaneously. 

The standard device used to monitor load is a pressure gauge attached to the jack pump. The 

readings on the jack pressure gauge are used to determine the absolute value of applied load. 

Calibration of pressure gauges should be performed within 45 working days of the date when 

they are submitted for approval for the project. Calibration certifications and graphs for 

pressure gauges and load cells must be provided by the contractor before use. An example of 

a typical pressure gauge calibration curve is given in Figure 7-7. A second certified pressure 

gauge, which is called master gage, should be kept on-site to be used for periodic check of 

jack pressure gauges. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-4 December 2005

STIFFENER PLATE REACTION BEAM

BOLTS 4 EACH AS

REQ. ON A PROJECT

BY PROJECT BASIS

EXTENSION CASING 

W / END PLATES &

STIFFENERS (TYP)

REACTION MICROPILE TOP

PLATE W / STIFFENERS

REACTION

MICROPILE

(TYP)

LOAD CELL

HYDRAULIC

JACK

TEST PILE WITH TOP

PLATE & STIFFENERS

DIAL GAUGES MOUNTED

ON AN INDEPENDENT

REFERENCE FRAME

(PER ASTM D1143)

2.13 m (TYP) 2.13 m (TYP)

TYP

TYP

NO SCALE

Note: 2.13 m = 7 ft 

Figure 7-1. Schematic of Compression Load Test Arrangement (ASTM D1143). 

STIFFENER PLATE REACTION BEAM

EXTENSION CASING 

W / END PLATES &

STIFFENERS (TYP) AS

REQUIRED ON A PROJECT

BT PROJECT BASIS

REACTION MICROPILE TOP

PLATE W / STIFFENERS

REACTION

MICROPILE

(TYP)

LOAD CELL

HYDRAULIC

JACK

TEST PILE WITH TOP

PLATE & STIFFENERS

DIAL GAUGES MOUNTED

ON AN INDEPENDENT

REFERENCE FRAME

(PER ASTM D3689)

2.13 m (TYP) 2.13 m (TYP)

TYP

TYP

NO SCALE

TRANSITION BEAM

 W/ STIFFENER

 PLATES

TRANSITION BEAM

 W/ STIFFENER PLATES

THREAD BAR

THREAD BAR

BEARING PLATE

THREAD BAR

4 EACH

THREAD BARS

Note: 2.13 m = 7 ft 

Figure 7-2. Schematic of Tension Load Test Arrangement (ASTM D3689). 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-5 December 2005

MICROPILE

(TYPICAL)

STEEL JACK

CHAIR

HYDRAULIC

JACK

REFERENCE

BEAM

DIAL GAUGE

NO SCALE

DIAL GAUGE

Figure 7-3. Schematic of Lateral Load Test Arrangement. 

Figure 7-4. Compression Load Test Set-Up. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-6 December 2005

Figure 7-5. Tension Load Test Set-Up. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-7 December 2005

Figure 7-6. Photograph of Lateral Load Test Set-Up (Note: Two micropiles are tested 

simultaneously). 

0 70 14 28 42 56

0

0.890

1.335

1.780

2.225

0.445

PRESSURE MPa

Reference Gauge: RGH 

Note: 1 MN = 224.8 k and 1 MPa = 145.1 psi 

Figure 7-7. Typical Pressure Gauge Calibration Curve. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-8 December 2005

Calibrated load cells should be used to verify that load remains constant during portions of an 

ultimate (and/or verification) load test in which the load is held for a specified period of time. 

When load cells are used, care should be taken to ensure that the cell is properly aligned with 

the axis of the micropile and jack. Load cells are used mainly to detect small changes in load 

and allow load adjustment and maintenance of constant holding load. As an example, 

assuming that the load cell reads “440" once the creep test load is reached, it is important that 

the “440" reading on the load cell be maintained through jack pressure adjustments for the 

duration of the test. This provides assurance that a constant load was indeed maintained 

throughout the creep test. It is specifically noted that load cells are not required for proof 

tests (except for extended creep testing, if needed to judge acceptability of proof-tested 

micropile). 

Vertical and/or lateral movement of the micropile head is typically measured using a dial 

gauge and/or LVDT fixed to the reference beams. Dial gauges should be capable of 

measuring and being read to the nearest 0.025 mm (0.001 in). For an axial load test, the 

gauges are mounted on an independent reference beam whose supports are located at a 

distance of five times the diameter of the test micropile. The minimum allowable distance 

between the gauges and the test micropile is 2.13 m (7 ft) as shown in Figures 7-1 and 7-2. 

The readings from three gauges are averaged to compensate for possible rotation of the pile 

head. The gauges are placed around the pile at an equal distance from the pile center. 

Micropile top displacement may be determined using a mirror with a scale mounted on the 

pile, and a wire mounted on a separate reference strung in front of the scale. The scale is 

read by adjusting the line of sight until the wire lines up with its reflection. This method 

should only be used as a backup to the dial gauge system, but it is less sensitive. 

Although not usually required, axial displacement in micropiles can be measured at discrete 

elevations in a micropile using telltales. Telltales consist of metal or fiberglass rods that are 

anchored into the micropile grout. The rod tip is embedded into the grout at the point of 

interest, with the remainder sheathed to allow free movement of the micropile. Movement at 

the top of the rod is measured with a dial gauge or electronic measuring device. Multiple 

telltales can be installed to measure movement at several points. Care must be taken to avoid 

damage to the telltales during micropile installation, such as the rods becoming damaged 

during drill string rotation, or the sheath becoming partially filled with grout. 

Strain gauges may be mounted on the reinforcing steel, allowing measurement of the level of 

strain in the reinforcement at various levels in the pile. Care must also be taken to avoid 

damage to the gauges and connecting wires during installation. If used, vibrating-wire-type 

strain gauges are recommended. From these strain measurements, axial load distribution 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-9 December 2005

with depth can be determined. Measurements from strain gauge pairs located diametrically 

opposite each other on a micropile steel casing are used to evaluate micropile bending 

moments with depth (see Figure 7-8 as an example). 

For lateral load testing, it is recommended to install an inclinometer in the micropile to obtain 

micropile lateral movement data with depth. This can be accomplished by installing the 

inclinometer to a depth of 10 to 20 micropile diameters. Specific termination depth should 

be based on lateral pile analyses performed during design. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-10 December 2005

Note: 1 in = 25.4 mm and 1 ft = 0.30 m 

Figure 7-8. Strain Gauge Locations on Micropiles for SUM-271 Project (after Liang, 2000). 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-11 December 2005

7.4 MICROPILE LOAD TESTING PROCEDURES 

7.4.1 Verification Tests 

7.4.1.1 General

For verification tests, loads can be applied in compression, tension, or laterally. The 

maximum test load for a compression or tension test are typically defined by the grout-toground bond factor of safety used in design. For micropiles, the maximum verification test 

load will usually be 2.0 to 2.5 times the design axial (compression or tension) load. For 

lateral load tests, tests are performed to 2.0 times the design lateral load. Acceptance criteria 

based on load test results is provided in Section 7.4.3. 

7.4.1.2 Procedures for Verification Test

Micropile verification testing is conducted by incrementally loading and unloading the 

micropile and measuring the movement of the micropile head at each load increment. The 

micropile-head movement reading is recorded just after the load has been applied and a 

second reading after the load has been maintained for a sufficient amount of time to ensure 

that pile-head movement has stabilized. 

The load schedule for a verification test is shown in the first three columns of Table 7-1 and 

is consistent with the loading schedule codified in DFI (2004). The first step in a verification 

test comprises applying a nominal load to the micropile head. This load, termed the 

alignment load (AL), is typically no more than ten percent of the design load and its purpose 

is to ensure that the stressing and testing equipment are properly aligned. The displacement 

measuring equipment is zeroed upon stabilization of the AL as shown on the loaddisplacement curve in Figure 7-9. During the first load cycle, the load is raised to 15 percent 

of the design load and the incremental movement is recorded. The load is then reduced back 

to the alignment load. This procedure is repeated, using load increments as shown on Table 

7-1, until the maximum testing load, referred to as the test load, is achieved. At the test load, 

a constant load is held for ten minutes prior to reducing the load. The load is assumed to 

remain reasonably constant if the deviation from the test pressure does not exceed 0.35 MPa 

(50 psi). During this ten minute load hold period, movements are measured and recorded at 

1, 2, 3, 4, 5, 6, and 10 minutes. The purpose of this load hold is to measure time-dependent 

(i.e., creep) movements of the micropile. This portion of the verification test is referred to as 

creep test. If the total movement between 1 and 10 minutes exceeds the specified maximum 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-12 December 2005

creep movement, the test load is maintained for an additional 50 minutes and total movement 

is recorded at 20, 30, 40, 50 and 60 minutes. 

7.4.1.3 Recording of Verification Test Data

The magnitude of each load is determined from the jack pressure gauge and the load cell 

measurement. The load-deformation data obtained for each load increment in a verification 

test are plotted as shown in Figure 7-10. The total movement (δt) is recorded at each load 

increment and for the alignment load. This total movement consists of elastic movement and 

residual movement. The residual movement for a given increment of load is the movement 

that corresponds to the net “irrecoverable” movement that occurs upon application of a load 

increment and the subsequent reduction of the load to the alignment load (see Figure 7-9 for 

definition of δr4). Residual movement (δr) includes elongation of the micropile and 

movement of the entire micropile through the ground. Elastic movement is simply the 

arithmetic difference between the total movement measured at the maximum load for a cycle 

and the movement measured at the alignment load (see Table 7-1). Although not used for 

micropile acceptance, residual movement is an indicator of the stress-strain behavior of the 

ground-to-grout bond in the micropile bond zone. Residual movement data should be 

collected and used for future testing or future design projects (in similar ground and load 

conditions) to estimate movements of the micropile within the bond zone. 

During the creep test portion of the verification test, the movement measured at specified 

times (i.e., 1, 2, 3, 4, 5, 6, and 10 minutes) is recorded. The time at which the total 

movement is measured for the test load (i.e., time at which 1.30 DL is applied as shown in 

Figure 7-9) represents the start time for the creep test. The movement from one to ten 

minutes after this starting time is recorded and compared to the acceptance criterion for 

creep. If the creep acceptability criterion is not satisfied, the test load is held on the 

micropile for an additional 50 minutes. The total amount of movement between 6 and 60 

minutes is recorded and compared to specified criteria. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-13 December 2005

Table 7-1. Verification Test Load Schedule (after DFI, 2004). 

Step Loading Applied 

Load 

Hold 

Time 

(min) 

Record and 

Plot Total 

Movement 

(δti)

Record and 

Plot Residual 

Movement 

(δri)

Calculate Elastic 

Movement 

(δei)

1 Apply AL 2.5 

2 Cycle 1 0.15DL 2.5 δ1

 0.30DL 2.5 δ1

 0.45DL 2.5 δt1

 AL 1 δr1 δt1- δr1= δe1

3 Cycle 2 0.15DL 1 δ2

 0.45DL 1 δ2

 0.60DL 2.5 δ2

 0.75DL 2.5 δ2

 0.90DL 2.5 δ2

 1.00DL 2.5 δt2

 AL 1 δr2 δt2- δr2= δe2

4 Cycle 3 0.15DL 1 δ3

 1.00DL 1 δ3

 1.15DL 2.5 δ3

 1.30DL δt3, zero reading for 

creep test

5 Hold load for at least 10 minutes while recording movement at specified times. If the total 

movement measured during the load hold exceeds the specified maximum value then the load 

hold should be extended to a total of 60 minutes. 

6 Cycle 3 cont’d. 1.45DL 2.5 δ3

 AL 1 δr3 δt3- δr3= δe3

7 Cycle 4 0.15DL 1 δ4

 1.45DL 1 δ4

 1.60DL 1 δ4

 1.75DL 2.5 δ4

 1.90DL 2.5 δ4

 2.00DL 10 δ4

 . 1.50DL 5 δ4

 1.00DL 5 δ4

 0.50DL 5 δ4

 AL 5 δr4 δt4- δr4= δe4

8 Remove the load and compare results to acceptance criteria. 

Notes: AL = Alignment Load, DL = Design Load, δi = total movement at a load other than maximum for 

cycle, i = number identifying a specific load cycle. Total movement is typically recorded from several dial 

gauges and the average movement is recorded. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-14 December 2005

0

1

2

3

4

5

6

0102030405060708090100110120130140150160170180190200210220230240250

Percent of design load

100

145

200

1

4

3

2

δr4

δe4

Movement

δt4

AL

45

130

Figure 7-9. Load Displacement Curve of Verification Tests. 

Percent of

 design load

4

3

2

1

4

3

2

1

Elastic

Movement

100

145200

45

0

AL

δe

Residual

Movement

δr

Figure 7-10. Plotting Elastic and Residual Movement of Verification Test Data. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-15 December 2005

7.4.2 Proof Tests 

7.4.2.1 General

Proof tests are conducted during construction on a percentage of the total production 

micropiles installed. Proof tests are intended to verify that the contractor’s construction 

procedure has remained constant and that the micropiles have not been drilled and grouted in 

a soil zone not tested by the verification testing. Micropiles are proof tested to a load 

typically equal to 160 percent of the design load. During proof testing, loads can be applied 

in compression, tension, or laterally. 

7.4.2.2 Proof Test Procedures and Recording and Analysis of Proof Test Data

The loading schedule for the proof test that is codified in DFI (2004) is outlined in Table 7-2. 

The results of an example proof test are plotted in Figure 7-11. The residual movements and 

elastic movements should be calculated for the test load from the unload cycle. This 

calculation is the same as that previously described for verification tests. 

During the creep test portion of the proof test, the movement measured at specified times 

(i.e., 1, 2, 3, 4, 5, 6, and 10 minutes) is recorded. The time at which 1.3 DL is applied 

represents the start time for the creep test. As mentioned earlier, the creep movement at any 

time is the difference between the total movement and the movement measured at one 

minute. The creep rate is defined as the slope of the curve per log cycle of time. The 

movement from one to ten minutes after this starting time is recorded and compared to the 

acceptance criteria with respect to creep. 

7.4.3 Micropile Acceptance Criteria 

7.4.3.1 Acceptance of Verification Test

There are three primary acceptance criteria that must be met for a verification-tested 

micropile, as described below. 

Rate of Pile Head Movement at the Test Load 

The acceptance criteria for verification tested micropiles include assessing whether failure 

has occurred at the test load (e.g., at 2.0 times the design load). Typically, at this load level, 

a plunging type failure will not be achieved, thus failure may be defined in terms of the rate 

of micropile head movement expressed as movement per unit of load. Herein, acceptance of 

a verification load-tested micropile requires that the slope of the load versus micropile head 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-16 December 2005

settlement curve be less than or equal to 0.15 mm/kN (0.025 in/kip) at 2.0 times the design 

load (DFI, 2004). Restated, the failure load is defined as the load where the slope of the load 

versus micropile head settlement curve first exceeds 0.15 mm/kN (0.025 in/kip). It is 

specifically noted that driven piles and drilled shafts use the Davisson criteria to define 

maximum (or failure) load during a load test. This criterion is difficult to use for a micropile 

because of the change in axial stiffness over the length of the micropile (i.e., different 

stiffness for cased and uncased lengths). At this time, the use of the Davisson criterion for 

micropiles has not been evaluated. 

Table 7-2. Proof Test Load Schedule (after DFI, 2004). 

Step Loading Applied 

Load 

Hold 

Time 

(min) 

Record and 

Plot Total 

Movement 

(δti)

Record and 

Plot Residual 

Movement 

(δri)

Calculate Elastic 

Movement 

(δei)

1 Apply AL 2.5 

2 Load Cycle 0.15DL 2.5 δ

 0.30DL 2.5 δ

 0.45DL 2.5 δ

 0.60DL 2.5 δ

 0.75DL 2.5 δ

 0.90DL 2.5 δ

 1.00DL 2.5 δ

 1.15DL 2.5 δ

 1.30DL δt, zero reading for 

creep test

3 Hold load for at least 10 minutes while recording movement at specified times. If the total 

movement measured during the load hold exceeds the specified maximum value then the load 

hold should be extended to a total of 60 minutes.

4 1.45DL 2.5 δ

 1.60DL 2.5 δ

5 Unload Cycle 1.30DL 4 δ

 1.00DL 4 δ

 0.75DL 4 δ

 0.50DL 4 δ

 0.25DL 4 δ

 AL 4 δr δt- δr = δe

6 Remove the load and compare results to acceptance criteria 

Notes: AL = Alignment Load, DL = Design Load, δ = total movement at a load. Total movement is typically 

recorded from several dial gauges and the average movement is recorded. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-17 December 2005

Creep Test

δe

δr

δt

Creep Test

δe

δr

δt

Note: 1 mm = 0.04 in and 1 kN = 0.225 kips 

Figure 7-11. Plotting of Proof Test Data. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-18 December 2005

Total Pile Head Movement at the Design Load 

For this criterion, a maximum micropile head movement is prescribed for a single micropile 

corresponding to the design load. This criterion is used for micropiles tested in compression, 

tension, or laterally. The value selected by the design engineer is based on considerations of 

movements of the superstructure being supported by the micropile foundation and should be 

developed based on project-specific requirements. 

Total Pile Head Movement under Sustained Load (Creep) 

The measured total movement for the required load hold at the 1.3 DL should not exceed 1 

mm (0.04 in.) between 1 and 10 minutes. If the movements are less than the 1 mm for this 

period, the micropile is considered acceptable with respect to creep. For verification load 

tests in which the measured total movement exceeds the criteria described above, the load is 

held for an additional 50-minute period of time. If the measured total movement over this 

additional time period does not exceed 2 mm (0.08 in.) between 6 and 60 minutes, then the 

micropile is considered acceptable with respect to creep. 

7.4.3.2 Acceptance of Proof Test

The previously described acceptance criteria for verification tests for total pile head 

movement at the design load and for total pile head movement under sustained load is used 

for a proof tested micropile. For a proof tested micropile, the creep test is performed at the 

maximum test load which is typically 1.3 DL. The evaluation of acceptable creep 

movements is the same as for verification-tested micropiles. It is noted that the creep criteria 

very rarely governs the acceptance of load tested micropiles. 

7.4.3.3 Consequences of Failure

In the event a micropile fails to meet the specified acceptance criteria during verification load 

testing of pre-production micropiles, the contractor can modify the design of the micropile 

and/or the construction procedure in order to provide the required capacity. These 

modifications may include installing replacement micropiles, modifying the installation 

procedures, increasing the micropile bond length, regrouting via pre-placed re-grout tubes, or 

changing the micropile type. Any modification that requires changes to the structure shall 

have prior review and acceptance by the Owner. The cost of the changes should be incurred 

by the contractor. 

If failure occurs during proof load testing of production piles, the contractor shall be directed 

to proof test another nearby micropile. For failed micropiles and further construction of 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-19 December 2005

other micropiles, the contractor shall modify the design, the construction procedure, or both. 

These modifications may include installing replacement micropiles, incorporating micropiles 

of reduced load capacities, modifying installation methods, increasing the bond length, or 

changing the micropile type. Any modification that requires changes to the structure shall 

have prior review and acceptance by the Owner and should be at the contractor’s expense. 

7.5 MICROPILE LOAD TEST REPORT 

For each load test, a report must be written and submitted to the Owner, typically within 24 

to 48 hours of the load test completion. The contents of this report should at least include the 

following: 

• brief project description; 

• description of site and subsurface conditions including information on the ground 

conditions at the location of the load test and a comparison to actual conditions 

encountered; 

• key personnel including the drill rig operator, the superintendent, the grout plant 

operator, and any other personnel involved in the installation and testing of the 

micropile; 

• micropile installation data including information such as length of the micropile 

(cased and uncased), number of bags of cement used to construct the micropile, size 

and type of casing and reinforcement, geology encountered (e.g. soil material, rock 

material, and water levels) during installation, and actual drilling and grouting 

records; 

• results of load test including filled-out data sheets and data presentation figures; 

• statement of load test requirements and acceptance criteria; 

• comparison of load test requirements and acceptance criteria; 

• summary statement on the load test results; 

• hydraulic jack pressure gauge and load cell calibration report; and 

• material certification, including grout compressive strength testing (e.g., 3 day test 

results may only be available) and steel mill certifications. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-20 December 2005

7.6 EVALUATION OF PROJECT LOAD TESTING REQUIREMENTS 

7.6.1 Introduction 

During the design phase of the project, consideration should be given to the scope of the 

micropile load testing program. The factors to be considered when determining the project 

testing requirements include the following: 

• total number of production micropiles; 

• magnitude and type of design loading (i.e., compression, tension, and/or lateral); 

• sensitivity and importance of the supported structure; 

• variance in ground subsurface conditions across the project site; 

• types of subsurface conditions; 

• site access and headroom/installation constraints; and 

• contractor experience. 

The project specification should include requirements for the following components of a load 

test program. These requirements are discussed in detail below, and include: 

• number and location of pre-production verification load tests; 

• number of production pile proof load tests; 

• magnitude of the test loads; 

• method of load application (single vs. multiple cycles, order of testing); 

• duration for which the test loads are applied; and 

• acceptance criteria for maximum total displacement and maximum creep 

displacement at a specified load. 

7.6.2 Load Testing Program for Verification Tests 

At least one pre-production verification micropile load test is required on all projects and the 

test is performed to at least 2.0 times the design load in accordance with Table 7-1. This 

micropile may be a sacrificial (non-production) pile or a production pile. Loading beyond 

the required minimum capacities may be conducted in an attempt to determine the ultimate 

capacity of the micropile. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-21 December 2005

The development of a verification load testing program should include the following steps 

and evaluations: 

• A site map should be developed depicting all proposed structures for the project 

(e.g., pile cap) and locations of all geotechnical borings. In general, load testing 

should be performed in close proximity to a boring to allow for correlation of load 

test results to soil stratigraphy. 

• The critical load combinations for each substructure unit should be reviewed to 

identify the types of load testing to be performed. In highly seismic regions, tension 

and/or lateral load testing may be required. In some cases, tension tests may be used 

as a substitute for compression testing, however, if compression loading is critical, at 

least one of the verification tests should be a compression test (where remaining tests 

may be substituted with tension tests). 

• All subsurface information for the project site should be reviewed to identify strata 

where the micropile bond zone will be formed. This evaluation is performed for 

each structure location. This evaluation should include an assessment of the overall 

variability of the subsurface. Micropiles are often used in mixed ground conditions 

so it is essential to identify all soil/rock micropile support horizons which may be 

relatively weak or compressible compared to other strata. 

• Based on the above evaluations, the total number of verification tests can be selected 

so that at least one verification load test is performed in each significantly different 

micropile support soil/rock stratum. The selection of testing locations must also 

consider access conditions and construction schedule. In cases where access to a 

proposed testing location is difficult, the engineer should consider if appropriate load 

testing information can be obtained at areas where greater access can be provided. 

7.6.3 Load Testing Program for Proof Tests 

Proof tests are performed primarily to confirm the contractor’s construction procedures 

throughout the project. The Owner should provide the same information for proof testing as 

was previously discussed for verification testing. Although these tests will be performed 

during construction, the Owner should provide the Contractor with the number of micropiles 

to be proof tested as early as possible during construction. The specifications, however, 

should provide the Owner with the ability to request additional proof tests and to relocate 

them, if required, based on unacceptable results or varying ground conditions. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-22 December 2005

Proof testing may consist of compression and/or tension tests. Typically, tension tests are 

less expensive because the ground may be used for reaction to the test-load rather than 

adjacent piles or reaction tie-down anchors. Therefore, if the critical load condition is in 

tension, or if results of the production tension testing can be correlated to the pre-production 

tension and compression testing results then proof tests may consists of only tension tests. 

A common requirement for proof testing is to test 5 percent of the production micropiles. 

This practice is similar to that used for driven piles associated with bridge foundations; 

however this “rule of thumb” percentage may not be appropriate for all applications. The 

following recommendations (Table 7-3) should be used in evaluating minimum proof testing 

requirements for a project. 

Table 7-3. Recommendations on Minimum Number of Test Micropiles 

for Proof Testing. 

Application Proof Test Frequency 

Underpinning Applications 1 micropile proof test per substructure unit 

Seismic Retrofit 1 micropile proof test per substructure unit 

Structural Support of New 

Construction 

1 micropile proof test per substructure unit, but not less 

than 5 percent of total production micropiles 

Slope Stabilization 2 percent of total production micropiles to a test load of 

2.0 times Pult (Pult is defined in Eq. 6-1 in Chapter 6) 

7.6.4 Test Load Magnitude 

The test load magnitude is typically controlled by the geotechnical factor of safety desired. 

This geotechnical factor of safety is usually greater than factors of safety applied for ultimate 

structural capacity considerations. Therefore, excess structural capacity may be required for 

the micropile to support the test loads based on geotechnical capacities. 

For magnitude of test loading (for structural support applications), this manual recommends: 

 Verification load testing to . . . . . . 2.0 × Design Load 

 Proof load testing to . . . . . . . . . . . 1.6 × Design Load. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-23 December 2005

The geotechnical capacity of a micropile can have an effect on the ultimate structural 

capacity, thus requiring that the same factor of safety be used for both geotechnical and 

structural considerations. Whether or not the reinforcement can be varied for the test piles 

should be considered carefully, and should be addressed in the project specifications. This 

issue has been reviewed in Chapter 5. 

7.6.5 Method of Load Application 

If the micropiles are designed for tension and compression loads, then both loading 

conditions should be tested. If the same micropile is to be tested in both tension and 

compression, it is suggested that the tension test be conducted first. This will allow the pile 

to be reseated during compression testing in the event some net upward residual movement 

occurs during the tension test. Because proof tests will be performed on random micropiles, 

the Contractor shall assure that all micropiles can be used for load testing. 

It is usually not necessary to conduct the load test on an inclined micropile, even if the 

project includes them. Installing the micropile on an incline has little, if any, effect on 

difficulty of construction and resulting capacity, particularly for micropiles installed by the 

cased hole method. However, testing an inclined micropile can be difficult and increase the 

testing costs, particularly for compression testing. 

For micropile load tests for slope stabilization, tension tests may be used. 

7.7 OTHER LOAD TESTING TECHNIQUES 

7.7.1 General 

In current practice, micropile proof testing is performed using the same load testing 

equipment and procedures as for verification testing. While proof testing is less expensive 

than verification testing because of reduced maximum test load magnitudes and reduced time 

to complete the test, the test set-up (which comprises a significant portion of the load test 

cost) is the same. For driven piles, for example, “proof” tests typically include the use of 

dynamic testing using a pile driver analyzer (PDA). PDA results can be correlated to projectspecific load testing results and, therefore, is used as a quality control measure on driven pile 

projects. PDA testing is rapid and inexpensive compared to full-scale load static load testing 

and therefore provides a means to evaluate (approximately) the static capacity of a relatively 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-24 December 2005

large number of production piles at a relatively low cost. Similarly, Statnamic testing may 

also be used as a quality control and assurance measure when used in concert with full scale 

static load tests. 

In this section, information on the use of PDA and Statnamic testing for micropiles is 

presented. At this time, neither of these methods are used on a regular basis for micropiles, 

however, they may be used increasingly as more experience is gained with these methods for 

micropile applications. 

7.7.2 Dynamic Load Testing 

Although not commonplace in current practice, the use of PDA for micropile proof testing 

could provide the same advantages as for driven piles. Since micropiles are not driven, a pile 

hammer needs to be mobilized to the site to perform the testing. Details on the use of the 

PDA and data interpretation using CAPWAP analysis methods are provided in FHWA-HI97-014 (1996). Currently, there is not sufficient field experience using PDA on micropiles to 

develop general procedures and recommendations for their use on micropile projects, 

however, one case history is reviewed herein. 

On a recent project in Northern Virginia, Gomez et al. (2004) used PDA to evaluate the static 

capacity of micropiles installed through karstic limestone to competent rock (Figure 7-12). 

Static load testing on two of three test micropiles indicated that test loads (equal to two times 

the design load) could not be achieved. It was concluded that the causes for the failure of the 

two micropiles were contamination of the contact between the grout and the rock in the bond 

zone and the difficulties encountered in cleaning the bond zone by flushing with water. 

Because of these observations, the capacity of the production micropiles that had already 

been installed needed to be evaluated. PDA testing was performed on 22 production 

micropiles of varying lengths. Because of the relatively small cross sectional area of the 

micropiles, there was concerns over potential structural damage that could result from the 

hammer striking required for the dynamic testing. In PDA testing, sufficient energy must be 

imparted to the pile to cause sufficient movement to enable estimates of capacity to be made. 

For this project, a procedure to gradually increase hammer energy was used and a cushioning 

system was fabricated in the field to prevent structural damage to the micropile. Capacities 

based on PDA results were consistent with those measured from the three static load tests. 

The authors concluded that dynamic testing (using PDA) could provide reasonably accurate 

estimates of capacity for the rest of the production micropiles tested. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-25 December 2005

Figure 7-12. Dynamic Test Set-Up for Micropile (after Gomez et al., 2004). 

As stated, specific cost advantages may be realized in using PDA as compared to static 

compression load testing for micropile proof tests. The volume of PDA tests in one day 

makes the PDA more cost effective. However, there are specific disadvantages associated 

with PDA testing of micropiles that need to be considered: 

• The creep test, which is a part of proof testing program and which is currently used 

as a means to confirm acceptability of a micropile, cannot be performed with 

dynamic test equipment. 

• Tension and lateral loading tests cannot be performed with dynamic test equipment. 

• Perhaps even more for micropiles than other pile systems, the potential for structural 

damage to the micropile needs to be considered especially as a result of potential 

eccentric loading by the pile hammer. 

• Data interpretation must be performed by an engineer with detailed knowledge of the 

testing method and its limitations (as should be required with any load testing). 

• Where tension tests are sufficient to evaluate micropile bond zone capacities, it is 

unlikely that PDA testing will be more cost-effective than conventional tension tests 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-26 December 2005

(unless test load magnitudes are very high thus requiring substantial reaction beams 

for a static load test). 

7.7.3 Statnamic Load Testing 

The Statnamic test method was developed by Bermingham and Jane (1989) and is used to 

evaluate capacity of foundations including drilled shafts, driven piles, augered cast-in-place 

piles, micropiles, stone columns, and shallow foundations. The use of this method to 

evaluate micropile capacity is increasing and several projects have been completed (although 

test data has not been published to date). Equipment, testing methods, and information on 

data interpretation are provided in Mullins et. al. (2001) for Statnamic load testing. 

The Statnamic test method uses solid fuel burned within a pressure chamber to rapidly 

accelerate upward the reaction mass positioned on the pile head. As the gas chamber 

increases, an upward force is exerted on the reaction mass, while an equal and opposite force 

pushes downward on the pile. Loading increases to a maximum and then unloads by a 

venting of the gas pressure. The magnitude and duration of the applied load and the loading 

rate are controlled by the selection of piston and cylinder size, the fuel mass, fuel type, the 

reaction mass, and the gas venting technique. 

The work area for the test set-up must be typically between 3 to 4 m (10 to 13 ft) in diameter 

and must be leveled (Figure 7-13). The set-up also requires at least 8.5 m (28 ft) of 

headroom clearance. 

The advantages of Statnamic testing for micropile load testing include: 

• Statnamic testing does not require any reaction piles or reaction system. It takes less 

time to prepare the test set-up as compared to static load testing. 

• Depending on the magnitude of load, site location, and labor costs, the cost of 

statnamic test could be on the order of one quarter to one half the cost of an 

equivalent capacity static load test. 

• Statnamic test is readily adaptable to lateral load testing, batter micropiles and axial 

load testing on land or over water. 

• Because the load duration is long enough to preclude stress wave formation, the 

analysis is simpler than for dynamic testing techniques. 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-27 December 2005

Figure 7-13. Statnamic Test Set-Up (courtesy of Applied Foundation Testing (AFT), Inc.). 

The disadvantages of Statnamic testing for micropiles include: 

• The creep test, which is a part of proof testing program and which is currently used 

as a means to confirm acceptability of a micropile, cannot be performed with 

Statnamic test equipment. 

• Tension tests have not been performed with the Statnamic device yet. 

• For tight access conditions, unless the engineer allows the location of the test pile to 

be relocated to an area with better access, Statnamic testing may not be suitable. 

• Data interpretation must be performed by an engineer with detailed knowledge of the 

testing method and current analysis methods (as should be required with any load 

test method). 
FHWA NHI-05-039 Chapter 7 – Load Testing 

Micropile Design & Construction 7-28 December 2005

7.8 REFERENCES 

ASTM D1143, “Standard Test Method for Piles Under Static Axial Compressive Load”, 

American Society for Testing and Materials, pp. 104-114, New York. 

ASTM D3689, “Standard Test Method for Individual Piles Under Static Axial Tensile Load”, 

American Society for Testing and Materials, pp. 416-426, New York. 

ASTM D3966, “Standard Test Method for Piles Under Lateral Loads”, American Society for 

Testing and Materials, pp. 440-454, New York. 

Bermingham, P. and James, M. (1989), “An Innovative Approach to Load Testing of High 

Capacity Piles”, Proceedings of the International Conference on Piling and Deep 

Foundations, V. 1, J. B. Burland and J. M. Mitchell, pp. 409-413. 

DFI (2004), “Guide to Drafting a Specification for Micropiles”, Deep Foundations Institute, 

The International Association of Foundation Drilling, 60 pages, New Jersey.. 

Gomez, J, Cadden, A., and Christopher, W. (2004), “Micropile Foundations on Karst: Static 

and Dynamic Testing Variability”, Proceedings of Fifth International Conference on 

Case Histories in Geotechnical Engineering, April 13-17, New York. 

Mullins, G., Lewis, C. L., and Justason, M. D. (2001), “Advancements in Statnamic Data 

Regression Techniques”, Deep Foundations 2002: An International Perspective on 

Theory, Design, Construction, and Performance, ASCE Geo Institute, GSP No.116, V. 

II, pp. 915-930. 
FHWA NHI-05-039 Chapter 8 – Construction Monitoring & Inspection 

Micropile Design & Construction 8-1 December 2005

CHAPTER 8 

MICROPILE CONSTRUCTION MONITORING 

AND INSPECTION 

8.1 INTRODUCTION 

The purpose of this chapter is to provide guidance regarding construction monitoring and 

inspection (i.e., construction quality assurance (QA) and construction quality control (QC) 

inspection) for micropiles. Inspection is the primary mechanism to assure that micropiles are 

constructed in accordance with the project plans and specifications. Short-term and longterm monitoring may be conducted to assess the performance of the micropiles. Construction 

monitoring activities can be carried out by the owner agency, the contractor, or a 

combination of both, depending on the contracting approach (i.e., method, performance, or 

design-build (see Chapter 9)), while performance monitoring is usually conducted by the 

owner agency. Inspection and monitoring of micropile systems which are constructed using 

performance specifications are described in this chapter. 

Quality assurance activities, if properly conducted, play a vital role in the production of highquality micropiles because conformance to project plans and specifications should result in 

micropiles that will perform adequately for the intended service life. These activities may 

involve evaluation of the following: (1) conformance of system components to material 

specifications; (2) conformance of construction methods to execution specifications; and (3) 

conformance to short-term performance specifications. 

Short-term (during construction) micropile monitoring is usually limited to monitoring 

measurements during load testing (i.e., verification, proof, and creep tests). In some cases, 

short-term monitoring may include, for example, monitoring, ground surface settlements or 

movements of nearby foundations (particularly where micropiles are used for underpinning 

applications). Long-term monitoring may be performed for micropiles used for slope 

stabilization as experience with this application of micropiles is limited to date, and this 

monitoring may include a continuation of measurements from short-term monitoring. 

8.2 INSPECTION ROLES UNDER CERTAIN CONTRACT APPROACHES 

For micropiles contracted using the method approach, QA activities are carried out by the 

owner agency based on comprehensive material and procedural requirements of ownerprovided plans and specifications. The contractor responsibility is to follow the project plans 
FHWA NHI-05-039 Chapter 8 – Construction Monitoring & Inspection 

Micropile Design & Construction 8-2 December 2005

and specifications and provide quality assurance. The owner’s inspection is conducted to 

assure strict compliance with each component of the specification. 

For the performance contracting approach, the contractor carries out QC activities. The 

owner agency will carry out a limited number of QA activities as required by project 

specifications, primarily to verify that requirements are met for materials, equipment, 

construction tolerances, and sequencing. The contractor selects the equipment and 

construction procedures used and is responsible for satisfying specified performance criteria. 

For the design-build approach, the performance of all required inspection activities are 

carried out by the contractor or are the responsibility of the contractor in accordance with the 

QA plan approved by the owner. Random quality assurance tests are done by the owner 

agency or through an independent third party inspection firm. 

8.3 PRE-PROJECT PREPARATION 

Prior to construction, the QA inspector must have an understanding of the project and 

specification requirements, particularly as related to inspection responsibilities, site and 

subsurface conditions, and material and construction requirements. Inspection 

responsibilities should be defined at a preconstruction meeting with the general contractor 

and all subcontractors (e.g., micropile installation contractor) involved in the project. The 

inspector must understand the intended function of the micropiles and other individual 

system components. Sources of information should include geotechnical reports, contract 

plans, and specifications. The inspector should contact the project engineer at the start of the 

project to discuss critical design aspects and potentially difficult site and subsurface 

conditions. 

Prior to the commencement of any construction, the micropile contractor’s work plan should 

be submitted to the engineer for review and approval. Work shall not proceed until the work 

plan has been approved. The contractor’s work plan should describe, at a minimum, the 

following elements of the work: 

1. Contractor and employee qualifications 

2. Contractor’s understanding of ground conditions with a discussion on anticipated 

difficulties related to these ground conditions 

3. Performance criteria and tolerances 

4. Location and orientation of each micropile 

5. Size and configuration (i.e., description of micropile cross section) of each micropile 
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Micropile Design & Construction 8-3 December 2005

6. Capacity requirements for each micropile 

7. Drilling equipment, including manufacturer and model numbers, flushing media, and 

a discussion of the precautions to be implemented to minimize drilling deviations 

8. List of all equipment to be used for the project with equipment loads on structure or 

adjacent ground during construction 

9. General installation plan, including proposed sequence of installation, phasing, and 

scheduling 

10. Grout design mix, along with batching, mixing, and injection techniques 

11. Reinforcement, including sizing, configuration, and corrosion protection 

12. Postgrouting methods (if anticipated to be used), procedure, and equipment 

13. Documentation of and protection methods for existing utilities and other sensitive 

elements that may be affected by the micropile work and proposed measures to 

minimize impacts of the micropile work on these elements 

14. Plan to accommodate low headroom or nearby obstructions 

15. Load testing information including identification of micropiles to be tested, type of 

testing to be performed (e.g., compression, tension, lateral), maximum anticipated test 

load for each micropile to be tested, allowable deformations under test loads, and 

details of the testing procedures for each type of test to be performed (i.e., 

compression, tension, or lateral) including sketches showing typical layout for load 

tests (e.g., location of reaction piles, position of dial gauges, etc.) 

16. Calibration information for load cells, pressure gauges, dial gauges, and any other 

testing or monitoring devices 

17. Details of connection to existing structures 

18. Remedial action plan describing measures to be implemented in the event of 

excessive movement of existing structures, release of spills to environmentally 

sensitive areas, and other potential hazards that could reasonably be anticipated at the 

start of the project 

19. Spoil handling procedures. 

Most importantly, protection of the existing environment, including underground utilities, 

must be considered. The existing site conditions should be examined by the micropile 

contractor with the inspector. The contractor is responsible for furnishing equipment suitable 

for the specific site conditions. 

Figure 8-1 provides a summary of QA inspector responsibilities for a typical micropile 

project. 
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Micropile Design & Construction 8-4 December 2005

Figure 8-1. QA Inspector Responsibilities for a Typical Micropile Project. 

REINFORCEMENT 

• Verify hole cleanliness • Observe dry cement for indications of hydration • Verify water/cement ratio and grout mix design • Verify that all grouting equipment (pumps, gauges, 

hoses, etc.) are in good working order 

• Record grout volumes and grout pressures for each 

micropile 

• Observe quality of grout at ground surface (i.e., when 

hole is full of grout) 

• Collect grout samples / perform required conformance 

testing 

POST INSTALLATION 

• Verify bar size, length, and condition just prior to 

insertion into the drillhole 

• Verify size and condition of bar couplers • Verify installation (i.e., bar should be easily pushed to 

bottom of hole without interference) 

• Verify location of centralizers (if required) • Verify pay quantities • Record load test data • Report unacceptable load test results to Engineer • Complete required forms (micropile installation logs, 

grout records, etc.) 

CONTRACTOR SET UP 

• Review Drawings, Specifications, and Micropile Work 

Plan 

• Review Contractor schedule • Inform Contractor of conformance testing 

requirements and frequency 

• Discuss anticipated ground conditions and potential 

problems with Contractor 

• Check overall condition of Contractor equipment • Verify that drill hole locations are consistent with 

Drawings 

• Review Contractor material storage area DRILLING 

• Prepare soil/excavation logs for each hole (confirm 

length of bond zone) 

• Confirm stability of each hole and record specific 

methods used to maintain hole stability 

• Verify final depth of hole • If temporary casing is used, record casing type and 

length 

• Record observations made during drilling • Check tolerances (e.g., alignment of hole, angle of 

drilling machine) 

GROUTING
FHWA NHI-05-039 Chapter 8 – Construction Monitoring & Inspection 

Micropile Design & Construction 8-5 December 2005

8.4 INSPECTION OF MICROPILE MATERIALS 

8.4.1 General 

Specifications describe minimum requirements for micropile materials. These minimum 

requirements may be defined explicitly or by reference to standard specifications such as 

those set forth by AASHTO and ASTM. Because the materials used to construct a micropile 

are common civil engineering materials, prequalified products are not commonly required, 

however, certain proprietary features may be involved in, for example, the micropile to 

footing connection. Recommendations for the storage and handling of selected materials are 

commonly included in specifications. 

Conformance to a specification requirement is commonly assessed in one of the following 

ways: (1) reviewing manufacturer or supplier certification submitted by the contractor; (2) 

reviewing of product literature and visual inspection; or (3) conformance testing. All 

materials and prefabricated elements delivered to the site must be visually examined prior to 

installation to verify required geometry and dimensions and to identify any defects in 

workmanship, contamination, or damage by handling. All nonconforming materials are 

unacceptable, unless appropriate corrections are made in accordance with specifications or by 

written approval of the project engineer. 

8.4.2 Storing and Handling of Cement 

Cement is typically supplied either in bagged (43 kg/sack) or bulk (1320 kg/bulk bag) form, 

depending on site conditions, job size, local availability, and cost. Cement should not be 

stored directly on the ground or anywhere where it may be subject to significant moisture 

absorption. An example of appropriate cement storage is provided in Figure 8-2. The 

contractor should avoid stacking the bags too high to prevent over compaction of the cement. 

Cement should be visually examined for lumps or other indications of hydration or 

contamination by foreign matter immediately prior to its use. The water used for grout 

mixing must be potable, and not contain impurities harmful to the steel or the grout. The 

contractor should also handle admixtures with care following manufacturer’s 

recommendations. Approved admixtures that have exceeded the manufacturer’s 

recommended shelf life should not be used. 
FHWA NHI-05-039 Chapter 8 – Construction Monitoring & Inspection 

Micropile Design & Construction 8-6 December 2005

Figure 8-2. Cement Storage. 

8.4.3 Storing and Handling of Reinforcing Steel

Steel reinforcement should be stored above the ground surface and be protected against 

mechanical damage and exposure to weather. Reinforcing bars should be lifted using fiber 

ropes or webbing and should be supported at several locations to prevent excessive bending. 

The micropile contractor should use care in unloading and storing all reinforcing steel 

material. The storage area should be away from construction traffic and in a protected 

location. When reinforcing steel material is delivered to the job site, it should be visually 

checked for size and any signs of corrosion. Reinforcing steel elements should be 

accompanied by mill certificates. Mill secondary pipe materials, for which mill certificates 

will not be available, require verification of steel quality through tensile and chemical testing 

of steel samples. For Buy America Contracts, United States manufacturing of materials must 

be verified. All steel reinforcing materials shall conform to the proper standards as identified 

in the project specifications. 

Properly stored steel reinforcing materials (see Figure 8-3) prevent corrosion or 

contamination by dirt, oils, and/or organics. Wood spacers placed between the ground and 
FHWA NHI-05-039 Chapter 8 – Construction Monitoring & Inspection 

Micropile Design & Construction 8-7 December 2005

the steel materials will prevent slight rusting that can occur if steel is exposed to the ground. 

A light coating of surface rust on the steel is normal and indicates that oil and grease are not 

present. Deep flaky corrosion or deep pitting of the steel is cause for rejection. All steel 

materials should be inspected just prior to their use. 

Double corrosion-protected and/or epoxy-coated steel bars should be delivered to the job site 

pre-manufactured (Figure 8-4). Extra care in handling and storage shall be given to these 

materials. Epoxy-coated bars shall be properly wrapped with padded bands and placed on 

wooden or padded supports. Pre-manufactured corrosion-protected steel bars must be 

stacked with care to prevent any damage to the corrugated tube and/or epoxy coating. Any 

repairs to epoxy coatings shall be performed in accordance with manufacturer’s 

recommendations. 

Mechanical couplers, hex nuts, centralizers, and spacers are typically delivered to the job site 

in boxes. Mill certificates will be provided for the steel couplers and hex nuts. Storage of 

these materials shall follow the same procedures as other materials. 

Figure 8-3. Storage of Reinforcing Steel. 
FHWA NHI-05-039 Chapter 8 – Construction Monitoring & Inspection 

Micropile Design & Construction 8-8 December 2005

Figure 8-4. Double Corrosion Protected (Encapsulated) Reinforcing Steel. 

8.5 INSPECTION OF CONSTRUCTION ACTIVITIES

8.5.1 Inspection of Drilling Activities

The contractor’s drilling operation should not cause unacceptable loss of ground. Signs of 

unacceptable loss of ground include the inability to withdraw the drill casing from the hole, 

large quantity of soil removal with little or no casing advancement, and subsidence of the 

ground above drilling location. The QA inspector should document this information and 

other observations of the drilling procedures in their daily reports. 

When temporary casing is to be removed during the grouting process, it should be removed 

in a manner that does not cause the pile reinforcement to become disturbed, damaged, or 

allowed to loss contact with the in-situ soil. The casing should also be kept full of grout 

during the removal operation to minimize the potential for drillhole collapse. The contractor 

is responsible for implementing all measures required to maintain an open drillhole during 

construction. Fluid levels in the drillhole must always be kept above the ground water level 

to minimize potential ground losses into the drillhole from potentially unstable soils. 
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Micropile Design & Construction 8-9 December 2005

The drilling, installation of reinforcement, and grouting of each micropile should be 

completed by the contractor in a series of continuous processes as expeditiously as possible. 

Some materials, such as consolidated clays and weak rock, can deteriorate and soften when 

exposed to air or water. Under these conditions, drilling of the pile bond zone, reinforcement 

installation, and grouting of the bond zone should be completed in one day. Unless micropile 

construction is continuous, the contractor should temporarily plug or cover the drillhole at the 

ground surface to prevent debris from falling into the borehole and for safety of the personnel 

working on the site. It is also recommended that casing material be placed (temporary or 

permanent project) a minimum of 0.3 m (1 ft) above the ground surface elevation to avoid 

drill spoils and flushing water from other operations flowing down and contaminating the 

completed hole. 

The micropile contractor shall provide for proper disposal and containment of the drilling 

spoils from the site in accordance with the approved work plan. The drill water should be 

controlled at all times to prevent erosion and to prevent accumulation of standing water 

which may freeze or otherwise create sloppy working conditions. 

Micropile inclination and position may need to deviate from that specified in the contract 

documents. Any deviation outside the tolerances provided in the Specifications, however, 

should be viewed as a design change and the contractor must notify the engineer of his 

intended change before implementing this change. In general, any deviations from the 

Drawings and Specifications should be recorded by the QA inspector and this information 

provided to the engineer. 

8.5.2 Inspection of Reinforcement Installation Activities

Reinforcement may be placed either prior to drillhole grouting, or placed into the grout-filled 

borehole before temporary casing (if used) is withdrawn. In any case, the inspector shall 

record the total pile length and bond zone length for each installed micropile. The 

reinforcement shall be capable of being inserted to its prescribed length in the hole without 

force. Inability to achieve this penetration in uncased holes usually means caving of soil into 

the hole has occurred, and withdrawal of the reinforcement and redrilling is necessary. 

Driving the reinforcement to full length or cutting off the reinforcement shall not be allowed.

Care should be exercised so as not to damage corrosion protection measures or centralizers 

during reinforcement installation. Neither epoxy-coated, double corrosion-protected, or 

uncoated steel reinforcements should be dragged across abrasive surfaces or through the 

surface soil. All splices and couplings should be checked for proper seating. The 

reinforcement must be clean of deleterious substances such as surface soil, oil, and mud, 
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Micropile Design & Construction 8-10 December 2005

which may contaminate the grout or coat the reinforcement. Centralizers and spacers shall 

be checked to ensure placement at specified intervals, typically 2.5 to 3 m (8 to 10 ft) (Figure 

8-5). Attachment of the centralizers to the reinforcement should also be checked to ensure 

that the reinforcement remains centered in the borehole. Typically centralizers are attached 

with tie-wire or duct tape. If tremie grout tubes are placed after the reinforcement has been 

positioned, care should be exercised so that the tremie tube does not interfere with the 

centralizers. 

8.5.3 Inspection of Grouting Activities 

Before any grouting begins, the condition of the grouting equipment should be checked by 

the contractor and the grout-mix design should be verified. Care in execution of the grouting 

process can greatly impact the quality of the completed micropile and its load carrying 

capacity. 

Prior to grouting, the inspector should verify the diameters of micropiles drilled without 

casings. Ideally, the contractor should grout the micropiles immediately after drilling the 

bond zone. However, if this is not possible, grouting should be performed before 

degradation of the drill hole. 

Figure 8-5. Reinforcement Centralizers. 
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Micropile Design & Construction 8-11 December 2005

The primary grouting operation involves injecting cement grout at the lowest point of the 

borehole so the hole will fill evenly without air voids. A tremie tube is typically tied to the 

reinforcing steel before insertion in the borehole. After placement of the reinforcement steel 

and tremie tube, the grout is pumped to the bottom of the pile until grout of suitable quality 

(of the same consistency as that being injected) returns to the top of the pile. The tremie tube 

is then removed from the micropile hole or left in the hole and filled with grout. 

The Contractor should perform grouting in one continuous operation. Care should be taken 

to maintain a positive head at the grout holding tank to avoid drawing air into the injected 

grout. Pressure grouting may be applied to the primary grout during casing withdrawal. 

Care must be taken with such pressures to avoid distress to the ground or adjacent structures. 

The pressure grouting process should be discontinued if grout is observed escaping at the 

ground surface. 

Grout pressures are measured as close to the point of injection as possible to account for line 

losses between the pump and the borehole. Typically, a pressure gauge is mounted on the 

drill rig and monitored by the drill rig operator as a guide during pressure grouting and casing 

withdrawal (Figure 8-6). 

Figure 8-6. Drill Rig Pressure Gauge. 
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Micropile Design & Construction 8-12 December 2005

For micropiles installed with a hollow-stem auger, the grout should be pumped under 

continuous pressure with a grout head maintained above the tip of the auger during auger 

withdrawl. The auger should be withdrawn in a controlled manner to minimize the potential 

for “necking” of the borehole to occur. 

If post grouting is performed, it is very important to monitor grout pressures and volumes 

throughout the injection of each sleeve. This will help prevent dangerous or needless over 

injection and progressively verify the effectiveness of the treatment. Post grouting pressures 

have been documented in excess of 6.5 MPa (943 psi). Typical range during injection is 2 to 

4 MPa (290 to 580 psi). 

Grouting records are of vital importance on every project and are described in Section 8.6.3. 

8.6 REQUIRED PROJECT DOCUMENTATION 

8.6.1 Micropile Load Testing 

During micropile load testing, the inspector must verify that the: (1) test pile installation 

method used is the same as will be used for the installation of the production piles; (2) pile 

load test setup is in accordance with the approved working drawings; and (3) pile is load 

tested in accordance with the project specifications. During load testing, the following 

general guidelines should be observed: 

• at no time should the micropile be loaded such that the axial stresses within the 

micropile exceed maximum allowable stresses provided in the Specifications; 

• at no time should the applied load be reduced below the alignment load; and 

• test measurements should be plotted as the test proceeds in order to identify unusual 

behavior. 

The QA inspector should check the following: 

• testing apparatus alignment; 

• use of properly calibrated jacks and gauges; 

• dial gauge arm alignment and travel length; 

• dial gauge point of contact; 

• application of the proper loads and sequencing and duration of each load; and 

• potential interference points due to pile deflection. 
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Micropile Design & Construction 8-13 December 2005

8.6.2 Production Micropiles 

Comprehensive records of the micropile installation are required to establish the basis of 

payment and to identify potentially significant deviations from the Contract Documents. 

Table 8-1 shows an example micropile installation log to be used by the micropile contractor 

and the inspector. A completed micropile installation log is provided in Table 8-2 as an 

example. 

8.6.3 Grouting Records for Production Micropiles 

Because the grout is such a vital component of the micropile, close attention should be paid 

to the quality and control of the grout. Grout production and consumption records must be 

kept daily. It is important that the actual pressure and volume of grout pumped for each 

micropile be recorded by the contractor and the inspector. 

Unconfined compressive strength of grout is determined according to AASHTO T106/ASTM 

C-109. Compressive strength is typically checked through a set of three each, 50-mm (2 in) 

grout cubes (Figure 8-7). Tests are typically performed at 3, 7, and 28 days after grouting. 

Seven-day tests are considered the most crucial, as the grout will typically attain the required 

design strength within this time period. Anticipated strength will depend upon project need, 

but compressive cube strengths can be very high, as much as 24 MPa (3,500 psi) after only 

24 hours of set time. The unconfined compressive strength is largely dependent on project 

needs, but a 28-day strength requirement between 25 and 40 MPa (3,600 and 5,800 ksi) is 

considered common for micropiles. The inspector needs to verify that the grout cube break 

strengths comply with the project specifications. Grout samples should be taken directly 

from the grout plant. It is recommended that one set of three grout cubes be taken for every 

10 micropiles installed, or every day for each grout plant in operation, whichever occurs 

more frequently. 
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Micropile Design & Construction 8-14 December 2005

Table 8-1. Example Micropile Installation Log. 

Project Name: Pile Designation #

Contract No.: Design Load Compress = Tension =

 DESIGN AS-BUILT Installation Date 

Pile Inclination Time @

Casing Dia./Wall Thickness Start of Drilling 

Reinforcement Size/Length Start of Grouting 

Casing Length below B.O.F. Pile Completion 

Cased Bond Length (Plunge) Total Duration 

Bond Length Below Casing ABBREVIATIONS 

Total Pile Length below B.O.F. B.O.F. = Bottom of Footing

Casing Length above B.O.F. 

PILE DRILLING

Drill Method Drill Rig #

Drill Bit Type and Size Drill Operator 

Time Depth from B.O.F Soil / Rock Description Flush Return 

Description

Comments

 

PILE GROUTING

Grout Plant #, Operator Cement Type

Tremie Grout Quantity (bags) Admixtures

Pressure Grout Quantity (bags) w/c Ratio

Grouting after plunge (bags) Grout Ratio (bags/m bond)

Total Grout Quantity (bags)

Depth from B.O.F Pressure Range 

Max/Average Comments

 
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Micropile Design & Construction 8-15 December 2005

Table 8-2. Example Completed Micropile Installation Log. 

Project Name: Keeley Palace Pile Designation #: Pile 1 

Contract No.: 0064 Design Load Compress = Tension =

 DESIGN AS-BUILT Installation Date 12-25-96 

Pile Inclination 0 degrees Time @ 8:00 am – 9:20 am 

Casing Dia./Wall Thickness 177/13 (mm) Start of Drilling 8:00 am 

Reinforcement Size/Length 57( mm)/15.5 (m) Start of Grouting 9:00 am 

Casing Length below B.O.F. 8 m Pile Completion 9:20 am 

Cased Bond Length (Plunge) 2 m Total Duration 1:20 

Bond Length Below Casing 6 m ABBREVIATIONS 

Total Pile Length below B.O.F. 16.5 m B.O.F. = Bottom of Footing 

Casing Length above B.O.F. 0.5 m 

PILE DRILLING

Drill Method Cased Rotary Drill Rig # 10-1 

Drill Bit Type and Size Casing Teeth – 175 mm Drill Operator Kilian 

Time Depth from B.O.F Soil / Rock Description Flush Return 

Description

Comments

0 – 5 m Gravel and Cobbles Brown, full return 

5 – 10 m Sand Gravel w/Cobbles Brown, full return 

10 – 15 m Cobbles w/Gravel Gray, full return Occasional Sand Seams 

 

PILE GROUTING

Grout Plant #, Operator 8-1, Holder Cement Type I / II

Tremie Grout Quantity (bags) 12 Admixtures None 

Pressure Grout Quantity (bags) 13 w/c Ratio 0.45 

Grouting after plunge (bags) 2 Grout Ratio (bags/m bond)

Total Grout Quantity (bags) 27 

Depth from B.O.F Pressure Range 

Max/Average (MPa) Comments

15 – 10 m 0.55 / 0.45 Grouted first 3 m under pressure, pulled remainder under static head 

10 – 5 m 0.55 / 0.47 Grouted first 3 m under pressure, pulled remainder under static head 

Plunge, 5 – 6.5 m 1.2 After plunging casing, pumped additional 2 bags at max pressure = 1.2 MPa 

 
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Micropile Design & Construction 8-16 December 2005

Figure 8-7. Grout Cubes for Compressive Strength Testing. 

Specific gravity measurements of grout are frequently checked to determine the water 

content of the grout because the water content of the grout is the prime control over grout 

properties. Neat cement grout density can be determined per the American Petroleum 

Institute (API) Recommended Practice (RP) 13B-1 by the Baroid Mud Balance Test (Figure 

8-8). The test is extremely quick and inexpensive and should be performed at least once per 

micropile. By monitoring the water/cement ratio during grouting, the inspector can ensure 

that the grout is being prepared according to the specified project mix design. A common 

specific gravity for grout is between 1.8 and 1.9, which corresponds to a water/cement ratio 

of 0.45. 

Tests that permit quality assessment prior to installation are more valuable since they permit 

immediate reaction in case of anomalies. Compressive strength values; however may only be 

established 48 hours after the sampling at the earliest. Pre-construction testing of the grout 

should be performed prior to production drilling to verify acceptability of grout mix design 

such as prior to and/or during micropile verification load testing. 
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Micropile Design & Construction 8-17 December 2005

Figure 8-8. Baroid Mud Balance Test. 
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Micropile Design & Construction 8-18 December 2005

8.7 REFERENCES 

ASTM C109, “Standard Test Method for Compressive Strength of Hydraulic Cement 

Mortars Using 2 in (50 mm) Cube Specimens”, American Society for Testing and 

Materials, New York. 

AASHTO T106, “Standard Test Method for Compressive Strength of Hydraulic Cement 

Mortars Using 2 in (50 mm) Cube Specimens”, American Association of State 

Highway Transportation Officials, Washington, DC. 
FHWA NHI-05-039 Chapter 9 – Contracting Methods 

Micropile Design & Construction 9-1 December 2005

CHAPTER 9 

CONTRACTING METHODS 

9.1 INTRODUCTION 

The purpose of this chapter is to describe contracting approaches that are commonly used in 

developing contract documents for projects involving micropiles. Two types of contracting 

methods are used to develop contract drawings and specifications for micropiles. Some 

agencies prefer one approach to the other or a mix of approaches for micropiles based on the 

criticality and complexity of a particular project, experience of the owner and their 

engineering consultants, and the availability of specialty contractors. The selection of a 

contracting method may also depend on the experience of the agency with micropile 

technology. Both contracting approaches are valid if properly implemented and each has 

advantages and disadvantages. These contracting methods include: 

Method (or Procedural) Approach. All details of design, construction materials, and 

methods are specified in the contract documents. A variant to this method allows the 

contractor to select micropile drilling and grouting methods required to achieve specified pile 

capacities. 

Performance or End-Result Approach. Lines and grades with specific design criteria and 

methods and performance requirements are provided in the contract documents. With this 

approach, a project-specific review and detailed plan submittal occurs in conjunction with the 

submittal of working drawings. 

Because specialty contractors often introduce innovative, cost-competitive solutions, it is 

recommended that the contract documents for micropile projects be structured to allow 

specialty contractors to make use of the latest available construction techniques. Thus, 

contract documents that are performance-based, with respect to drilling and grouting 

methods, are recommended. The performance approach and the variant of the method 

approach allow this flexibility. 

9.2 CONTRACTOR QUALIFICATION 

The procedures for micropile construction need to be followed closely to provide a high 

quality product. Selecting an experienced and qualified contractor to install micropiles is 
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Micropile Design & Construction 9-2 December 2005

critical to obtain a satisfactory installation. The likelihood of success further increases when 

comprehensive construction quality assurance procedures are developed and enforced by the 

owner. Agencies or owners with no previous micropile experience should seek a qualified 

third-party quality assurance provider. 

Contract documents for micropile projects should clearly define: (1) the contractor prequalification requirements; (2) submittal procedures for this qualification information; and 

(3) the means by which the owner will enforce these requirements. Such pre-qualification 

requirements are commonly being used by many transportation agencies for other specialty 

construction techniques, such as permanent ground anchors, soil nail walls, drilled shaft 

foundations, and shotcreting. However, where formal pre-qualification may not be allowed, 

agencies should request that bidders demonstrate that they meet specific micropile 

experience requirements. 

The recommended minimum qualifications for each micropile contractor are provided below. 

1. The contractor firm and its proposed employees for the project should provide 

evidence of previous successful experience in the design and installation of 

micropiles. Owner references in the design and installation of micropiles of similar 

scope to those proposed for the application project should be provided. 

Documentation shall include at least five successful projects performed in the last five 

years. 

2. The contractor firm shall assign an engineer to supervise the work who has at least 

three years of experience in micropile design and construction of at least 3 

successfully completed projects over the past 5 years. 

3. The contractor firm must have previous drilling experience in similar ground to 

anticipated project conditions. The contractor firm must submit at least three 

successful load test reports from different projects of similar scope to project. 

4. Project superintendents and drill operators responsible for installation of micropile 

system must have micropile installation experience on at least 3 successfully 

completed projects over the past 5 years. 

9.3 METHOD CONTRACTING APPROACH

The method contracting approach includes the development of a detailed set of plans and 

specifications to be provided in the bidding documents. The advantage of this approach is 

that complete design details and specifications are developed and reviewed by experienced 
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Micropile Design & Construction 9-3 December 2005

representatives. This approach further empowers agency engineers to examine options that 

may be available during design but requires engineering staff trained in micropile design and 

construction methods. The staff then also becomes a valuable asset during construction, 

when questions and/or design modifications are required. 

Under this contracting procedure, the agency is fully responsible for the design and 

performance of the micropile, as long as the contractor has installed each component (e.g., 

pile casing, grout, steel reinforcement) in strict accordance with the contract documents. The 

agency assumes all risks and is responsible for directing the work if changes to the design are 

required based on actual field conditions. The use of a method specification is recommended 

only for agencies that have developed sufficient in-house expertise and consider micropile 

design and construction control as a conventional or standard method for foundation system 

or slope stabilization. 

The use of a variant to this method, in which the contractor is responsible for developing the 

required pile capacity by varying the drilling and grouting methods, drill hole diameter, and 

length of piles from specified minimums, has several advantages. It empowers contractors to 

maximize the use of their experience and specialized equipment and allows the agency to 

share the major risk, (i.e., pile capacity for a specified length), with the contractor. The 

owner typically establishes the following: 

• scope of work; 

• micropile design loadings and spacing; 

• footing details; 

• corrosion protection; 

• micropile testing procedures and requirements; 

• instrumentation requirements (if any); 

• special design considerations (e.g., scour and liquefaction potential); and 

• performance criteria. 

The micropile contractor specifies the following: 

• micropile construction process; 

• micropile type; 
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Micropile Design & Construction 9-4 December 2005

• micropile design; and 

• pile top to footing connection design. 

This division of work allows the qualified specialty contractors to provide an economical 

micropile design, while satisfying the design requirements. This method also allows 

responsibility for the work to be shared between the owner and the micropile contractor. 

While this is slightly more restrictive than the contractor design/build specification method, it 

is still flexible enough to allow for some innovation and cost savings. Various types of 

owner-controlled design specifications are described subsequently. 

9.3.1 Standard Design

The contract documents for the Standard Design Type are prepared to allow for various 

qualified micropile designs. The owner’s engineer provides the micropile design loadings, 

footing design, and pile layout for foundation support. In addition, the owner provides the 

following: 

• geotechnical reports and data; 

• micropile design parameters (foundation support projects only) including maximum 

pile sizes, axial pile loads, lateral pile loads, displacement requirements, and ductility 

requirements; 

• existing utility plans; 

• site limitations, including: (1) access limitations; (2) right of way; (3) scour potential; 

(4) liquefaction potential; (5) noise requirements; (6) vibration requirements; and (7) 

potential for hazardous and/or contaminated materials; 

• contractor working drawing/design submittal and review requirements including time 

frame and information on penalties; 

• material specifications; 

• testing requirements; 

• instrumentation requirements (if any); 

• micropile acceptance criteria; and 

• method of measurement and payment. 
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Micropile Design & Construction 9-5 December 2005

It is recommended that micropile measurement and payment be performed on a unit-permicropile basis separately for: (1) furnished and installed production piles; (2) verification 

testing; and (3) proof testing, except for piles founded in rock, for which an add/deduct 

footage price may be included. 

During the bidding process, micropile contractors prepare a preliminary design and a firm 

cost proposal based on the owner’s plans and specifications. If the project is to be 

subcontracted, general contractors will receive bids from each specialty subcontractor and 

includes the best offer in their proposal. The name of the recommended micropile 

subcontractor is included in the general contractor’s bid, which is then submitted. Once the 

contract has been awarded, the selected specialty contractor prepares working drawings and 

design calculations and submits them to the engineer for review and approval. After 

acceptance of the design, construction begins. 

9.3.2 Alternate Micropile Design

For the Alternate Microple Design method, the owner provides a base design in the contract 

documents utilizing a more traditional foundation support system. The contract documents 

allow alternate micropile designs to be submitted by the listed specialty contractors on a onefor-one pile replacement of the owner-designed pile system. The information described 

under Standard Design Type is also required. Alternatively, this approach can be used to 

allow micropile contractors to submit designs which include fewer higher capacity 

micropiles than the conventional pile footing design requires, and allows the owner’s 

engineer to maintain control of the footing design. 

The information necessary in the contract documents is similar to that previously mentioned, 

except the owner provides two to three alternative pile footing designs on the plans with the 

associated pile design and load criteria. 

9.3.3 Cost Reduction Incentive Proposal (Value Engineering)

The Cost Reduction Incentive Proposal is another long-established form of alternate proposal 

used in the United States. When Cost Reduction Incentive Proposals are permitted, it is 

important that the owner specify any additional restrictions that may apply, such as right-of-
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Micropile Design & Construction 9-6 December 2005

way restrictions. Foundation support elements are usually the first order of work, so review 

and approval of the Cost Reduction Incentive Proposal needs to be performed in a timely 

manner. 

9.4 PERFORMANCE SPECIFICATIONS

This approach is often called “line and grade” or “conceptual plans”. Under this approach, 

the agency: (1) prepares drawings defining the geometric requirements for the structure and 

material specifications for the components; (2) defines performance requirements including 

factors of safety; and (3) indicates the range of acceptable construction and design methods. 

This approach, when coupled with sound specifications and pre-qualification of contractors, 

offers several benefits. Design of the structure is performed by trained and experienced staff 

and can utilize contractors’ proprietary equipment and methods along with material 

components successfully and routinely used in the past. Also, the performance specification 

approach lessens engineering costs and manpower requirements for the agency and transfers 

some of the project design costs to construction. The disadvantage is that agency engineers 

must have adequate expertise to perform a design review, approve construction 

modifications, and engage a consultant with demonstrated proficiency in micropile 

technology. It is noted that the limitations previously described under the method approach 

for pre-qualification of contractors for certain public agencies also apply to pre-qualification 

with the performance contracting approach. 

Bid quantities are obtained from specified pay limits denoted on the drawings and can be bid 

on a lump sum or unit-price basis. The basis for detailed designs to be submitted after 

contract award is detailed as a special provision, as would construction control and 

monitoring requirements. The special provision should clearly identify the required 

submittals, schedule for submittals, and schedule for review and approval of these submittals. 

Items to be contained in the special provision are calculations and shop drawing submittals. 

In the design/build method, the owner’s engineer typically provides the following 

information: 

• scope of work; 

• total structure loads; 

• footing details; 

• corrosion protection; 
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Micropile Design & Construction 9-7 December 2005

• micropile testing procedures and requirements; 

• instrumentation requirements (if any); 

• special design considerations (e.g., scour and liquefaction potential); and 

• performance criteria. 

The micropile contractor specifies the following: 

• micropile construction process; 

• micropile type and quantity; 

• micropile design; 

• revisions to footing details to accomodate micropile design; and 

• pile top to footing connection design. 

Based upon specified limitations and requirements, a design/build proposal is submitted, 

either before the bid advertisement (pre-bid), or after contract award (post-bid). 

Measurement and payment is typically made on a lump-sum basis. 

9.5 DESIGN/BUILD APPROACH 

9.5.1 General 

In design/build construction, the specialty contractor becomes an important part of the 

project team and is involved in all foundation and ground-support aspects of the project. The 

micropile contractor is responsible for the adequacy of the design and construction and the 

owner is responsible for the accuracy of the information upon which the design is based. The 

two recommended types of contractor design/build specifications follow. 

9.5.2 Postbid Design

The contract documents for the postbid design/build method are prepared to allow for various 

contractor-designed alternatives. The owner’s engineer provides design and detailing of 

ancillary structures, and the performance criteria and objectives necessary for the micropile 

system design and installation. This information includes, as a minimum, the following: 
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Micropile Design & Construction 9-8 December 2005

• geotechnical reports and data; 

• structure loadings (axial, lateral and moment); 

• existing utility drawings; 

• design criteria and parameters; 

• site limitations (e.g., right of way); 

• design and details of ancillary structures; 

• contractor working drawing/design submittal and review requirements; and 

• micropile acceptance criteria. 

During the bidding process, the micropile contractors prepare a preliminary design and a firm 

cost proposal based on the owner’s plans and specifications. For subcontracted items, 

general contractors will receive bids from each specialty subcontractor and include the best 

cost proposals in their bids. The name of the recommended micropile subcontractors are 

included in the general contractor’s bid, which is then submitted. Once the contract has been 

awarded, the selected specialty contractor prepares their detailed design calculations and 

working drawing and submits them to the engineer for review and approval. After 

acceptance of the design, construction begins. 

9.5.3 Prebid Design

The contract documents for the prebid design/build method are also prepared to allow for 

contractor-designed micropiling alternatives. The major difference in this method is the 

timing of the design and the bidding. Performance criteria and necessary project design 

information are usually made available 60 to 90 days prior to the contract advertisement date. 

Micropile contractors prepare and submit final design calculations and working drawings for 

the owner’s review and approval. Once the designs (typically two to three total) are 

approved, a list of specialty contractors with approved designs are included in the contract 

documents. Often the specialty contractors’ proprietary working drawings are included in 

the contract bid documents. These drawings illustrate the proposed construction and assist 

the general contractors in understanding and coordinating their other project tasks with the 

proposed micropile construction. General contractors then receive bids from each 

subcontractor, bidding only on their own proprietary design, and include the best cost 

proposal in their bid. The name of the recommended micropile subcontractor is included in 
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Micropile Design & Construction 9-9 December 2005

the general contractor’s bid, which is then submitted. Once the contract is awarded, the 

selected general contractor and specialty micropile contractor can begin work immediately. 

9.6 CONTRACT PLANS 

For all of the specification methods mentioned, the contract plans must include sufficient 

information to allow the contractor to develop a bid proposal that meets the owner’s 

objectives. The quality of the subsurface information, existing utility plan, and micropile 

design criteria are very important for a successful project. Inadequate subsurface information 

and conservative pile design criteria may create expensive contractor contingencies, higher 

pile prices and increase claim potential. 

Sample contract plans and guide construction specifications utilizing owner controlled design 

methods is provided in Appendix C-1 and utilizing contractor design/build methods is 

provided in Appendix C-2. 
FHWA NHI-05-039 Chapter 9 – Contracting Methods 

Micropile Design & Construction 9-10 December 2005
FHWA NHI-05-039 Chapter 10 – Cost Estimating 

Micropile Design & Construction 10-1 December 2005

CHAPTER 10 

COST ESTIMATING 

10.1 INTRODUCTION 

The purpose of this chapter is to present an approach that may be used to develop a cost 

estimate for any micropile project. The cost estimate method described is similar to that 

commonly used in engineering to develop a conceptual cost estimate. That is, sufficient 

detail is used to identify the cost components which may have the largest effect on total 

project cost, however specific bid quantities and potential bidding contractors is not 

necessarily known. 

The method requires that a baseline cost for micropiles be known. Over the past ten years, 

numerous micropile projects have been completed in the United States and typical micropile 

costs have decreased during this time period mostly due to experience gained by specialty 

micropile contractors and advances in micropile installation equipment. In 2004, a 

reasonable “average” price for micropiles is on the order of $300 per linear meter of 

micropile. This value is considered to be appropriate for any region of the U.S. and for any 

type of micropile project. The cost estimate method presented herein is used to adjust this 

baseline average price to account for project-specific technical and non-technical constraints. 

Prior to describing the cost estimating method for micropiles, a discussion on the key factors 

which affect micropile costs is presented. 

10.2 FACTORS THAT INFLUENCE MICROPILE COSTS 

10.2.1 Overview

Table 10-1 provides a breakdown of the typical ranges of costs for materials, labor, and 

equipment for micropiles. Also listed as a separate component is load testing costs. In many 

cases, load testing costs may be paid for as a separate pay item. 

10.2.2 Micropile Material Costs 

The principal material components of micropiles include threaded steel casings, cement 

grout, steel reinforcing bars, and centralizers. Because of higher load capacities that continue 

to be achieved by micropiles, it is clear that costs for structural steel within the micropile 

cross section represent a significant cost component. 
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Micropile Design & Construction 10-2 December 2005

Table 10-1. Typical Breakdown of Micropile Unit Costs. 

Unit Cost Breakdown Percent 

Material 25 – 40 

Equipment 20 – 30 

Labor 25 – 60 

Load Testing <5 

Threaded Steel Casing 

The most commonly used casings for micropile applications in the United States have 

outside diameters of 140 mm (5.5 in.), 175 mm (7 in.), and 241 mm (9-5/8 in.). The cost of 

each casing type (without threads) is provided in Table 10-2. These costs are subject to 

relatively large fluctuations in the prevailing cost of steel and the costs provided are 

considered to be representative for 2004. In some cases, contractors may have access to 

previously used casings which would likely reduce steel material costs. 

Table 10-2. Material Costs of Steel Casings Used for Micropiles. 

Casing Outside Diameter Casing Wall Thickness Cost of casing ($)

(mm) (in) (mm) (in) per meter per foot 

139.7 5.500 10.5 0.415 15 – 25 5 – 8 

177.8 7.000 12.6 0.498 35 – 45 11 – 14 

244.5 9.625 13.8 0.545 50 – 60 15 – 18 

Note: Representative early 2004 costs. 

Because of low headroom conditions or difficult access, micropile casings are oftentimes 

installed in relatively short sections, thereby requiring a means to connect individual casing 

sections. Joints for casing are typically flush threaded joints. Threading costs wherein both 

ends are threaded (i.e., male and female threads) will typically cost in the range of $50 to $70 

(2004) per casing. Therefore, where short casing lengths are required, threading costs can be 

relatively significant and the Owner should carefully assess the specific requirements for 

casing section lengths for a project. For example, where the cost of a 1-m-long 140-mm-
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Micropile Design & Construction 10-3 December 2005

casing may be on the order of $20, threading costs for each 1-m section may be on the order 

of $60, or 3 times the casing cost. Alternatively, the threading cost of a 4-m-long 140-mmcasing would be less than the cost of the casing itself. 

Steel Reinforcing Rods 

The most commonly used reinforcement bars for micropile applications in the United States 

have outside diameter of 57 mm (2-1/4 in.) and 64 mm (2-1/2 in.). The 2004 material costs 

for these reinforcement bars are provided in Table 10-3. Centralizer material costs are 

relatively insignificant. 

Table 10-3. Material Costs of Steel Reinforcing Bars Used for Micropiles. 

Outside Diameter Cost of reinforcing bar ($)

Bar Size #

(mm) (in) per meter per foot 

18 57 2.25 20 – 26 6 – 8 

20 64 2.5 26 – 32 8 – 10 

Note: Representative early 2004 costs 

10.2.3 Equipment Cost 

Overall equipment costs for micropile projects have decreased in recent years mostly due to 

the greater availability of drilling and grouting equipment. While it is difficult to assign 

specific costs for equipment, since they represent fixed costs for a contractor on a given 

project, the Owner should recognize that drilling equipment costs will be linked to ground 

conditions and the relative ease of drilling. Drilling costs for micropiles in excessively hard 

or bouldery ground to relatively great depths (e.g., greater than say 30 m (100 ft)) will be 

significant. Usually smaller drilling equipment may be less costly than larger equipment; 

however, for very tight access conditions with low headroom (e.g., less than say 3 m (10 ft)) 

and difficult drilling conditions, specialized equipment will be required. Depending on the 

specialty contractor, the use of this equipment may represent a significant cost. 
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Micropile Design & Construction 10-4 December 2005

10.2.4 Labor Cost 

A typical micropile crew consists of four individuals including a project superintendent, 

drilling operator, and two laborers. The effect of labor on micropile unit costs are directly 

linked to the ease of installation and daily micropile installation rates. 

For projects involving relatively easy drilling and low to moderate capacity micropiles, a 

typical crew may install up to 6 to 20, 15-m (50-ft) long (maximum) micropiles per day. For 

such a project, labor may comprise 25 to 30 percent of the total project cost. However, in 

tight access areas and difficult drilling conditions the labor cost may increase to 30 to 45 

percent of the total cost due to extra time and effort required. In extra labor-intensive 

projects and where prevailing labor costs are high (e.g., major urban areas), labor cost may 

comprise up to 60 percent of the micropile costs. 

10.2.5 Load Testing Costs

Load testing costs depend on the access conditions of the site, the type of testing (i.e., 

compression, tension, and/or lateral load testing), the number of tests, testing protocol (i.e., 

“quick” load or standard load tests), and the required load capacity. 

The engineer will typically select the number and type of load tests, however, compression 

load tests will always be more expensive than a comparable (i.e., similar maximum testing 

load) tension test. The primary reason for this is that reaction piles or anchors need to be 

constructed for the compression test. The cost range for verification load tests range from 

$10,000 to $25,000 per test with the lower end of the range being representative for tension 

tests and the upper end being representative for compression tests. Proof tests (which are 

commonly carried to significantly lower loads than verification tests and which are 

performed in less time) range in cost from $6,000 to $10,000. These costs are considered 

representative for typical projects. 

Where very difficult access limits equipment access, load testing costs can be significantly 

higher. For example, high load capacity load tests in an easy access area may be on the order 

of $25,000 per test whereas for difficult access areas and where relatively high load 

capacities need to be verified (e.g., greater than 200 tons), load tests could be greater than 

$50,000 per test. 
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Micropile Design & Construction 10-5 December 2005

10.3 MICROPILE COST ANALYSIS 

10.3.1 Overview

An Owner considering the use of micropiles for a project may use the previously provided 

average cost of $300 per linear meter with the modifications provided in Table 10-4 to 

develop a preliminary cost estimate for their specific project. Table 10-4 has been developed 

based on micropile contractor input and reflects the relative effect of project-specific factors 

on micropile construction costs. The use of this table is described subsequently using two 

example projects and additional discussion on the specific factors provided in this table is 

also provided. 

Table 10-4. Effects of Project-Specific Factors on Micropile Cost. 

Cost Factor Influence Range Cost Influence 

Physical and access conditions Very easy to very difficult 0% to +100% 

Geology/ground conditions Very easy to very difficult 0% to +50% 

Pile capacity Very low to very high(1) -30% to +30% 

Pile lengths Very short to very long(2) -25% to +25% 

Pile quantities Very high to very low(3) -50% to +100% 

Testing requirements Very low to very high(4) -10% to +10% 

Mobilization/demobilization One to multiple 0% to +10% 

Continuous drilling operations Continuous to not continuous(5) 0% to +25% 

Union agreements Nonunion to very strong -15% to +30% 

Overhead and profit Very low to very high -10% to +100% 

Notes: (1)Moderate pile capacity = 1,000 kN (225 kips). 

 (2)Average pile length = 15 m (50 ft). 

 (3)Average pile quantity = 50. 

 (4)Average is one verification test and proof testing 5% of all piles. 

 (5)Not continuous drilling operation implies significant down time periods during drilling operations. 
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Micropile Design & Construction 10-6 December 2005

10.3.2 Effects of Project-Specific Constraints on Cost

The first two factors in Table 10-4 concerning access and ground conditions are shown to 

have a large effect on micropile cost. Effects related to difficult access and difficult ground 

conditions (e.g., drilling in excessively hard ground), however, would likely have a similar 

cost implication for driven piles and drilled shafts as well. 

Pile capacity affects cost since higher capacity micropiles will require longer bond zone 

lengths which may comprise longer rock sockets than would be required for more moderately 

loaded micropiles. Also, greater structural requirements (i.e., increased steel area) are 

associated with higher capacity micropiles. 

The length of a pile effects costs in several ways, for example: 

• the longer the pile length, the more individual sections of steel casing will be 

required; 

• beyond certain lengths, drilling costs may increase because of the need for more 

robust equipment to reach greater depths; and 

• greater need may exist for hole stabilization at significant depths. 

Table 10-4 indicates that the most significant relative cost reduction is associated with pile 

quantities. Large pile projects will enable the contractor to define project backlog and longterm personnel requirements. 

The last entry in Table 10-4 (i.e., overhead and profit) relates to perceived contractor risk for 

a particular project. While this factor may be difficult for an Owner to assess as part of a 

preliminary cost estimate, should other factors in Table 10-4 generally result in increases 

above the average cost, it is reasonable to assume that a contractor may view the project as 

containing relatively significant risk, especially where ground conditions are expected to 

result in difficult drilling and low productivity. 

10.3.3 Micropile Cost Estimate Examples

The use of Table 10-4 is demonstrated in two sample problems provided below. 

10.3.3.1 Sample Problem No. 1 (Bridge Abutment Support)

Given: Single-span bridge located in mountainous terrain approximately 125 km 

northwest of Denver, Colorado. Each abutment is to be supported on 12 CASE 

1, Type B micropiles with ultimate capacities of 1,190 kN (270 kips) in 

compression, and 490 kN (110 kips) in tension, and approximately 12 m (40 ft) 
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Micropile Design & Construction 10-7 December 2005

in length. Testing requirements are one verification pile load test (compression 

only) on a sacrificial pile and two proof tests. Access to each work bench must 

be established. Drilling of bond zone is expected to be very difficult, due to 

cobbles and boulders. Drilling will be continuous at each location with an 

additional set-up of Abutment 2. 

Solution: Evaluate each influence factor as shown in Table 10-5 below and multiply by 

cost of micropile per meter price. 

Based on Table 10-5 the cost is adjusted as: 

$555 / linear meter of micropile 100

85 Average cost ($) $300 x 1 =



 



 = +

The length of each micropile is 12 m (40 ft), therefore the unit price would be; 

Average cost ($) = $555 x 12 m = $6,660 / each 

Table 10-5. Sample Problem No. 1 – Cost Analysis 

(Bridge Abutment Support).

Cost Factor Influence Cost Influence (%)

Physical and access conditions Easy access 10 

Geology/ground conditions Difficult drilling 30 

Pile capacity Moderate pile capacity 0 

Pile lengths Average pile lengths 0 

Pile quantities Low pile quantities 25 

Testing requirements Average # of testing 10 

Mobilization/demobilization One mobilization 0 

Continuous drilling operations Two setups 5 

Union agreements Standard union agreements 0 

Overhead and profit High-risk project 5 

Total: 85%
FHWA NHI-05-039 Chapter 10 – Cost Estimating 

Micropile Design & Construction 10-8 December 2005

10.3.3.2 Sample Problem No. 2 (Seismic Retrofit) 

Given: Seismic retrofit of a 200-m (650-ft) long concrete viaduct located in San 

Francisco, California. A total of 30 footings need retrofitting with 12 Type B 

micropiles per footing (resulting in a total of 360 micropiles for the project). 

Ultimate capacities are 2,500 kN (560 kips) in compression and 1,500 kN (340 

kips) in tension. Subsurface profile includes approximately 10 to 12 meters (330 

to 40 ft) of medium dense silty sands over weathered to moderately weathered 

serpentine bedrock. Micropiles average approximately 20 meters (66 ft) in 

length. Testing requirements include 1 verification pile load test (compression 

only) on a sacrificial pile and 30 proof tests. Access to each pile location is 

good, and overhead clearance varies between 5 to 12 meters (16 to 40 ft) for each 

footing. Drilling is assumed to be continuous allowing setups between each 

footing. 

Solution: Evaluate each influence factor as shown in Table 10-6 below and multiply by 

cost of micropile per meter price. 

Based on Table 10-6 the cost could be adjusted as: 

$330 / linear meter of micropile 100

10 Average cost ($) $300 x 1 =



 



 = +

The length of each micropile is 20 m, therefore the unit price would be; 

Average cost ($) = $330 x 20 = $ 6,600 / each 

10.4 MEASUREMENT AND PAYMENT FOR MICROPILES 

Table 10-7 provides a summary of typical pay items for a micropile project. It is recognized 

that design-build projects may use lump sum units for most of the pay items. With respect to 

payment for the micropile itself, alternative pricing may include payment per unit length of 

micropile or payment per pile with an add or deduct if actual pile lengths vary from a 

predetermined pile length used for the bid. 
FHWA NHI-05-039 Chapter 10 – Cost Estimating 

Micropile Design & Construction 10-9 December 2005

Table 10-6. Sample Problem No. 2 – Cost Analysis (Seismic Retrofit). 

Cost Factor Influence Cost Influence (%)

Physical and access conditions Easy access 10 

Geology/ground conditions Easy drilling 10 

Pile capacity High pile capacities 10 

Pile lengths Moderate pile lengths 0 

Pile quantities Large pile quantity -30 

Testing requirements Relatively extensive 5 

Mobilization/demobilization One mobilization 0 

Continuous drilling operations Continuous drilling 0 

Union agreements Strong union 10 

Overhead and profit Lower risk project -5 

Total 10%

Additional pay items will be required for projects involving difficult ground in which 

specific problems may be anticipated during the bid period. For example, where micropiles 

are to be installed in karstic regions, a pay item should be developed for grout volume above 

some minimum volume. However, specifications should require that where grout volumes 

are no greater than two times the theoretical volume of the drillhole, that there is no 

additional compensation for grouting, i.e., the per pile cost for a micropile shall include grout 

volumes up to two times the theoretical grout volume. Also, if obstructions are anticipated, 

the specifications should include a pay item for removal of obstructions. Payment for 

obstruction removal may be performed on a time and material basis. Where this approach is 

used, it is important to use a contractor with previous experience in similar ground conditions 

and to provide full-time construction inspection during obstruction removal. Whenever a 

time and material basis may be used for payment on a project, the Owner should request 

detailed information on labor and material charges as part of the contractor’s bid. 
FHWA NHI-05-039 Chapter 10 – Cost Estimating 

Micropile Design & Construction 10-10 December 2005

Table 10-7. Micropile Measurement and Payment Units. 

Description Unit 

Mobilization/Demobilization Lump sum 

Conduct Preproduction Test Pile Program Lump sum 

Verification Load Test Per each 

Proof Load Test Per each 

Furnish and install micropile (foundation support) Per each 

Furnish and install micropile (slope stabilization) Per lineal meter of 

cap beam 
FHWA NHI-05-039 Glossary 

Micropile Design & Construction Glossary-1 December 2005 

GLOSSARY OF TERMS 

Admixture: Substance added to the grout to control bleed and/or shrinkage, improve 

flowability, reduce water content, or retard setting time. 

Alignment Load (AL): A minimum load applied to micropile during testing to keep the 

testing equipment correctly positioned. 

Bond Length or Bond Zone: The length of the micropile that is bonded to the ground and 

used to transfer the applied axial loads to the surrounding soil or rock. 

Bond-breaker: A sleeve placed over the steel reinforcement to prevent load transfer. 

CASE 1 Micropile: A pile designed to accept vertical or lateral load directly, and transfer it 

to an appropriate bearing stratum. Usually includes significant steel reinforcement. 

CASE 2 Micropile: One of a network of low-capacity piles used to delineate and internally 

reinforce a volume of soil. 

Casing: Steel tube introduced during the drilling process in overburden soil to temporarily 

stabilize the drill hole. This is usually withdrawn as the pile is grouted, although in 

certain types of micropiles, some casing is permanently left in place to reinforce the 

unbonded length or provide additional capacity. 

Centralizer: A device to support and position the reinforcing steel in the drill hole and/or 

casing so that a minimum grout cover is provided. 

Coarse-grained Soils: Soils with more than 50 percent of the material by weight, larger than 

the No. 200 (0.075 mm) sieve size. 

Cohesive Soils: Fine-grain soils that exhibit plasticity. Atterberg limits are commonly used 

to determine plasticity and better define a soil as cohesive or noncohesive. 

Contractor: The person/firm responsible for performing the micropile work. 

Corrosion-inhibiting Compound: Material used to protect against corrosion and/or 

lubricate the reinforcing steel. 

Coupler: A device by which the pile load capacity can be transmitted from one partial length 

of reinforcement to another. 
FHWA NHI-05-039 Glossary 

Micropile Design & Construction Glossary-2 December 2005

Creep Movement: The movement that occurs during the creep test of a micropile under a 

constant load. 

Design Load (DL): The maximum load expected to be applied to the micropile during its 

service life. 

Duplex Drilling: An overburden drilling system involving the simultaneous advancement of 

(inner) drill rod and (outer) drill casing. Flush from the inner drill rod exits the hole 

via the annulus between rod and casing. 

Elastic Movement: The recoverable movement measured during a micropile test. 

Encapsulation: A grout filled corrugated or deformed tube protecting the reinforcing steel 

against corrosion. 

Fine-grained Soils: Soils with at least 50 percent of the material, by weight, smaller than the 

No. 200 (0.075 mm) sieve size. 

Free (unbonded) Length: The designed length of the micropile that is not bonded to the 

surrounding ground or grout during stressing. 

Maximum Test Load: The maximum load to which the micropile is subjected during 

testing. 

Micropile: A small-diameter (typically less than 300 mm) drilled and grouted replacement 

pile which is typically reinforced. 

Non-cohesive Soils: Granular soils that are generally nonplastic. 

Overburden: Material, natural or placed, that requires cased drilling methods to provide an 

open borehole to underlying strata. 

Permanent Micropile: Any micropile for permanent use, generally with more than a 24-

month service life. May require special design, corrosion protection, and supervision 

during installation. 

Plunge Length: The length that the pile casing is inserted into the bond zone. 

Post-grouting: The injection of additional grout into the load transfer length of a micropile 

after the primary grout has set. Also known as regrouting or secondary grouting. 

Preloading: Loading the micropile prior to the connection to the structure, to minimize or 

eliminate any structural movement in service. 
FHWA NHI-05-039 Glossary 

Micropile Design & Construction Glossary-3 December 2005 

Primary Grout: Portland-cement-based grout injected into the micropile hole prior to or 

after the installation of the reinforcement to direct the load transfer to the surrounding 

ground. 

Proof Test: Incremental loading of a production micropile, recording the total movement at 

each increment. 

Reinforcement: The steel component of the micropile that accepts and/or resists applied 

loadings. 

Residual Movement: The nonrecoverable movement of a micropile measured during load 

testing. 

Sheath: A smooth or corrugated pipe or tube that protects the reinforcing steel against 

corrosion. 

Single-tube Drilling: The advancement of a steel casing through overburden, usually aided 

by water flushing through the casing. The water may or may not return to the surface 

around the casing, depending largely on the permeability of the overburden. 

Spacer: A device to separate elements of a multiple-element reinforcement to ensure full 

bond development of each steel element. 

Temporary Micropile: Any micropile for temporary use, generally with less than a 24-

month service life. 

Ultimate Grout-to-Ground Bond Values: The estimated ultimate geotechnical unit groutto-ground bond strength selected for use in design. 

Verification Load Test: Non-production (sacrificial) pile load test performed to verify the 

design of the pile system and the construction methods proposed, prior to installation 

of production piles. 

Working Load: Equivalent term of Design Load. 
FHWA NHI-05-039 Glossary 

Micropile Design & Construction Glossary-4 December 2005
FHWA NHI-05-039 Appendix A 

Micropile Design & Construction A-1 December 2005

APPENDIX A 

DESIGN CONCEPT OF 

CASE 2 MICROPILE NETWORKS 

FOR SLOPE STABILIZATION
FHWA NHI-05-039 Appendix A 

Micropile Design & Construction A-2 December 2005

The CASE 2 micropile network design concept developed by Dr. Lizzi and illustrated in 

Figure 3-14 consists of “a three-dimensional lattice structure built into the soil according to a 

pre-established scheme depending on the purpose that the structure has to carry out,” (Lizzi 

1971). The purpose of the micropile network for slope stability is two fold: 

a) The micropiles must retain the soil and prevent its “flow” through the network 

formed by the piles, which would cause a reduction of the continuity and the unity of 

the composite gravity structure. 

b) The micropiles must supply a nailing of the various soil layers by providing 

additional shear resistance along the possible critical sliding surfaces. 

The soil-pile interaction for such micropile networks is very complex and there are many 

factors whose influence on the final behavior of the structure cannot be conveniently 

assessed. Lizzi suggested that designs be based on “some simple assumptions” using the 

concept of reinforced soil, and those used for reinforced concrete. The soil supplies the 

weight in a manner more or less as supplied in a monolithic gravity wall, whereas the 

micropiles, introducing reinforcing elements into the soil, supply the lines of force, allowing 

the composite mass to support compression, tension, and shear stresses. The system is based 

on the micropile-soil interaction, which results in a network (or “knot”) effect provided the 

micropiles are not too far apart. 

The first official test on a full-size reticulated micropile structure was performed in 1957 for 

the Milan, Italy subway system. The knot affect has been confirmed by both model and 

earlier field tests (Lizzi 1978, Plumelle 1984, and Korfiatis 1984). Apart from several earlier 

tests on models and full-scale structures, a recent French National Project on micropiles 

(FOREVER 2003) includes experimental studies on the behavior of micropile networks. The 

findings of this research indicates that in loose to medium dense granular soils, a positive 

network effect can be obtained if adequate densification of the soil is assured and if the 

micropiles are concentrated as much as possible under the applied load. According to the 

researchers, this implies that the micropiles do not move apart or diverge from the surface of 

the foundation but, rather turn inwards in order to ensure a maximum densification of the 

soil. No design guidelines have been developed as yet from this project. 

The design of Case 2 micropiles assumes a highly redundant system in which no tension is 

applied to any of the piles. Therefore, the system is subjected to compression and shear and 

the micropile network provides confinement to the in-situ soil, thereby improving its 

deformation modulus and increasing its shear resistance. The behavior of this system 

depends to a great extent on the knot effect concept and the reinforced concrete analogy. 

Once the knot effect is assured, the micropile enclosed soil mass behaves as a coherent body 
FHWA NHI-05-039 Appendix A 

Micropile Design & Construction A-3 December 2005

and is analyzed as a gravity retaining structure. Using this concept, the following steps can 

be followed for preliminary design of Case 2 micropile networks: 

1. Conduct a slope stability analysis to determine the increased resistance required (Hreq) 

along an existing failure surface to provide a specified target factor of safety, FSTARGET. 

2. Develop the initial geometry of the micropile structure. Assume a pile configuration that 

is dense enough to assure a knot effect and minimize the possibility of plastic flow 

between piles. A preliminary configuration can be based on density of 6 to 7 piles per 

linear meter along the wall alignment. Stability related to the plastic flow of soil between 

piles can be verified using the methods presented in Section 6.6.7. 

3. Check the external stability of the micropile structure 

3.1. Estimate the earth pressure against the micropile structure using conventional 

earth pressure theories. 

 3.2. Check the factor of safety against overturning (FSOV) assuming the micropile 

structure is a rigid body: 

 2.0

M

M FS = overturning

resisting

OV ≥

∑

∑ (Eq. A-1) 

To resist the overturning moment and to maintain compression stresses in the soil 

and in all micropiles, the resultant vertical force (from earth pressures and other 

external forces) should act in the middle third of the micropile structure. 

 3.3. Check the factor of safety against sliding (FSSL): 

1.5

Horizontal Loads

( Vertical Loads)(Shear strength of base soil) + (Shear capacity of piles) FSSL = ≥

∑

∑ (Eq. A-2) 

3.4. Assume a micropile cross section and determine the contact stresses at the edge of 

the base of the micropile structure for a given micropile cross section. The contact 

stresses at the edges of the micropile structure is calculated according to: 





 



 = ±

2

b

I

P e

A

P

trans trans

σ (Eq. A-3) 
FHWA NHI-05-039 Appendix A 

Micropile Design & Construction A-4 December 2005

Where: 

 P = vertical component of the resultant force acting on the structure; 

 e = eccentricity of the force P; 

 Atrans = area of the transformed micropile section; 

 Itrans = moment of inertia at the base of the structure; and 

 b = width of the transformed section. 

 The transformed section area, Atrans is calculated as: 

E

E + A

E

E A = A

soil

stl

stl

soil

conc

trans conc (Eq. A-4) 

Where: 

 Aconc = area of the concrete; 

 Astl = area of the steel; 

 Econc = Young’s modulus of the concrete; 

 Estl = Young’s modulus of the reinforcing steel; and 

 Esoil = Young’s modulus of the soil. 

The moment of inertia at the base at the structure, Itrans, is computed by assigning 

equivalent areas of soil to the concrete and steel based upon the ratios of Young’s 

moduli. 

The minimum stress calculated according to Eq. A-3 should be positive indicating 

that all contact stresses are in compression. 

3.5. Using the stresses computed, determine the maximum compression stresses in 

each component of the composite section (i.e., concrete, steel reinforcement, and 

soil). Check these compression stresses against allowable design values. 

4. Check the internal stability of the micropile structure 

Design each micropile to resist the stresses calculated in Step 3.5. Compute shear 

resistance of the piles and the lateral resistance of the soil in contact with the piles. The 

smaller of the two resistances is considered as the additional shear resistance due to 

micropiles (R1). 
FHWA NHI-05-039 Appendix A 

Micropile Design & Construction A-5 December 2005

5. Determine the number of micropiles (n) for the micropile structure using: 

( )

D

R H

FS req

TARGET

+ = and Hreq = n R1 (Eq. A-5) 

Where: 

R = horizontal component of the soil resisting forces along the critical slip surface; and 

D = horizontal component of the driving force along the critical slip surface. 

The above referenced design procedure has not yet been proven by long term instrumented 

field performance. It is recommended that owners considering the use of these types of 

slope stabilization structures implement a long-term instrumentation program to fully 

understand the behavior and performance of the structure.
FHWA NHI-05-039 Appendix A 

Micropile Design & Construction A-6 December 2005
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-1 December 2005

APPENDIX B

LPILE ANALYSIS RESULTS 

FOR SLOPE STABILIZATION PROBLEM
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-2 December 2005

============================================================== 

 LPILE Plus for Windows, Version 4.0 (4.0.8) 

 Analysis of Individual Piles and Drilled Shafts 

 Subjected to Lateral Loading Using the p-y Method 

 (c) Copyright ENSOFT, Inc., 1985-2003 

 All Rights Reserved 

============================================================== 

Path to file locations: L:\Programs\LPILE\Chapter 6\Ch. 6 Example with P=474.5\ 

Name of input data file: 1st analysis.lpd 

Name of output file: 1st analysis.lpo 

Name of plot output file: 1st analysis.lpp 

Name of runtime file: 1st analysis.lpr 

------------------------------------------------------------------------------ 

 Time and Date of Analysis 

------------------------------------------------------------------------------ 

 Date: May 4, 2005 Time: 15:26: 0 

------------------------------------------------------------------------------ 

 Problem Title 

------------------------------------------------------------------------------ 

1st Analysis 

(To Determine Mult for P=0 and P=Pult Cases) 

------------------------------------------------------------------------------ 

 Program Options 

------------------------------------------------------------------------------ 

Units Used in Computations - SI Units, meters, kilopascals 

Basic Program Options: 

Analysis Type 3: 

- Computation of Nonlinear Bending Stiffness and Ultimate Bending Moment 

 Capacity with Pile Response Computed Using Nonlinear EI 

Computation Options: 

- Only internally-generated p-y curves used in analysis 

- Analysis uses p-y multiplers for group action 

- Analysis assumes no shear resistance at pile tip 

- Analysis for fixed-length pile or shaft only 

- No computation of foundation stiffness matrix elements 

- Output pile response for full length of pile 

- Analysis assumes no soil movements acting on pile 

- Additional p-y curves computed at specified depths 

Solution Control Parameters: 

- Number of pile increments = 145 

- Maximum number of iterations allowed = 100 

- Deflection tolerance for convergence = 10.000E-07 m 

- Maximum allowable deflection = 2.5400E+00 m 

Printing Options: 

- Values of pile-head deflection, bending moment, shear force, and 

 soil reaction are printed for full length of pile. 

- Printing Increment (spacing of output points) = 1 

------------------------------------------------------------------------------ 

 Pile Structural Properties and Geometry 

------------------------------------------------------------------------------ 

Pile Length = 14.50 m 

Depth of ground surface below top of pile = .00 m 

Slope angle of ground surface = .00 deg. 

Structural properties of pile defined using 2 points 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-3 December 2005

Point Depth Pile Moment of Pile Modulus of 

 X Diameter Inertia Area Elasticity 

 m m m**4 Sq. m kN/Sq. m 

----- --------- ----------- ---------- ---------- ----------- 

 1 0.0000 .1778 1.0000 .0248 200000000.000 

 2 14.5000 .1778 1.0000 .0248 200000000.000 

Please note that because this analysis makes computations of ultimate 

moment capacity and pile response using nonlinear bending stiffness 

that the above values of moment of inertia and modulus of are not used 

for any computations other than total stress due to combined axial 

loading and bending. 

------------------------------------------------------------------------------ 

 Soil and Rock Layering Information 

------------------------------------------------------------------------------ 

The soil profile is modelled using 3 layers 

Layer 1 is stiff clay without free water 

Distance from top of pile to top of layer = .000 m 

Distance from top of pile to bottom of layer = 4.700 m 

p-y subgrade modulus k for top of soil layer = 1.000 kN/ m**3 

p-y subgrade modulus k for bottom of layer = 1.000 kN/ m**3 

Layer 2 is stiff clay without free water 

Distance from top of pile to top of layer = 4.700 m 

Distance from top of pile to bottom of layer = 10.000 m 

p-y subgrade modulus k for top of soil layer = 1.000 kN/ m**3 

p-y subgrade modulus k for bottom of layer = 1.000 kN/ m**3 

Layer 3 is stiff clay without free water 

Distance from top of pile to top of layer = 10.000 m 

Distance from top of pile to bottom of layer = 16.000 m 

p-y subgrade modulus k for top of soil layer = 1.000 kN/ m**3 

p-y subgrade modulus k for bottom of layer = 1.000 kN/ m**3 

(Depth of lowest layer extends 1.50 m below pile tip) 

------------------------------------------------------------------------------ 

 Effective Unit Weight of Soil vs. Depth 

------------------------------------------------------------------------------ 

Distribution of effective unit weight of soil with depth 

is defined using 6 points 

Point Depth X Eff. Unit Weight 

 No. m kN/ m**3 

----- ---------- ---------------- 

 1 .00 21.20000 

 2 4.70 21.20000 

 3 4.70 11.40000 

 4 10.00 11.40000 

 5 10.00 13.20000 

 6 16.00 13.20000 

------------------------------------------------------------------------------ 

 Shear Strength of Soils 

------------------------------------------------------------------------------ 

Distribution of shear strength parameters with depth 

defined using 6 points 

Point Depth X Cohesion c Angle of Friction E50 or RQD 

 No. m kN/ m**2 Deg. k_rm % 

----- -------- ---------- ------------------ ------ ------ 

 1 .000 120.00000 .00 .00500 .0 

 2 4.700 120.00000 .00 .00500 .0 

 3 4.700 168.00000 .00 .00400 .0 

 4 10.000 168.00000 .00 .00400 .0 

 5 10.000 480.00000 .00 .00250 .0 

 6 16.000 480.00000 .00 .00250 .0 

Notes: 

(1) Cohesion = uniaxial compressive strength for rock materials. 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-4 December 2005

(2) Values of E50 are reported for clay strata. 

(3) Default values will be generated for E50 when input values are 0. 

(4) RQD and k_rm are reported only for weak rock strata. 

------------------------------------------------------------------------------ 

 p-y Modification Factors 

------------------------------------------------------------------------------ 

Distribution of p-y multipliers with depth defined using 2 points 

Point Depth X p-mult y-mult 

 No. m 

----- ---------- ---------- ---------- 

 1 .000 1.0000 1.0000 

 2 .000 1.0000 1.0000 

------------------------------------------------------------------------------ 

 Loading Type 

------------------------------------------------------------------------------ 

Static loading criteria was used for computation of p-y curves 

------------------------------------------------------------------------------ 

 Pile-head Loading and Pile-head Fixity Conditions 

------------------------------------------------------------------------------ 

Number of loads specified = 1 

Load Case Number 1 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Shear force at pile head = .000 kN 

Bending moment at pile head = .000 m- kN 

Axial load at pile head = .000 kN 

(Zero moment at pile head for this load indicates a free-head condition) 

------------------------------------------------------------------------------ 

 Output of p-y Curves at Specified Depths 

------------------------------------------------------------------------------ 

p-y curves are generated and printed for verification at 8 depths. 

Depth Depth Below Pile Head Depth Below Ground Surface 

 No. m m 

----- --------------------- -------------------------- 

 1 .000 .000 

 2 1.000 1.000 

 3 2.000 2.000 

 4 4.690 4.690 

 5 4.710 4.710 

 6 9.990 9.990 

 7 10.010 10.010 

 8 14.500 14.500 

------------------------------------------------------------------------------ 

 Computations of Ultimate Moment Capacity and Nonlinear Bending Stiffness 

------------------------------------------------------------------------------ 

Pile Description: 

The sectional shape is a circular shaft with steel casing. 

Outside Diameter = .1778 m 

Wall thickness of steel shell = .0115 m 

Cross-sectional area of shell = .00601 m**2 

Moment of inertia of steel shell = 2.08692E-05 m**4 

Material Properties: 

Compressive Strength of Concrete = 27600.000 kN/ m**2 

Yield Stress of Reinforcement = 0. kN/ m**2 

Steel shell or core yield stress = 552000. kN/ m**2 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-5 December 2005

Modulus of Elasticity of Reinforcement = 200000000. kN/ m**2 

Cover Thickness (edge to bar center) = .000 m 

Number of Reinforcing Bars = 10 

Area of Single Bar = .00000 m**2 

Number of Rows of Reinforcing Bars = 5 

Ultimate Axial Squash Load Capacity = 3758.02 kN 

Distribution and Area of Steel Reinforcement 

 Row Area of Distance to 

Number Reinforcement Centroidal Axis 

 m**2 m 

------ ------------- --------------- 

 1 .000000 .0736 

 2 .000000 .0455 

 3 .000000 .0000 

 4 .000000 -.0455 

 5 .000000 -.0736 

Axial Thrust Force = .00 kN 

 Bending Bending Bending Maximum Neutral Axis 

 Moment Stiffness Curvature Strain Position 

 kN-m kN-m2 rad/m m/m m 

 ------------- ------------- ------------- ------------- ------------- 

 1.73583660 4898.917 .00035433 .00002742 .08889729 

 2.50651820 4897.351 .00051181 .00003961 .08889729 

 3.27670667 4895.785 .00066929 .00005180 .08889729 

 4.04640201 4894.220 .00082677 .00006399 .08889729 

 4.81560422 4892.654 .00098425 .00007618 .08889729 

 5.58431330 4891.088 .00114173 .00008837 .08889729 

 6.35252925 4889.522 .00129921 .00010056 .08889729 

 6.55060560 4496.902 .00145669 .00010411 .08297207 

 7.25778201 4496.284 .00161417 .00011537 .08297207 

 7.96476385 4495.667 .00177165 .00012662 .08297207 

 8.67155112 4495.049 .00192913 .00013788 .08297207 

 9.37814382 4494.431 .00208661 .00014913 .08297207 

 10.085 4493.813 .00224409 .00016039 .08297207 

 10.791 4493.196 .00240157 .00017165 .08297207 

 11.497 4492.578 .00255906 .00018290 .08297207 

 12.203 4491.960 .00271654 .00019416 .08297207 

 12.908 4491.342 .00287402 .00020541 .08297207 

 13.614 4490.725 .00303150 .00021667 .08297207 

 14.319 4490.107 .00318898 .00022792 .08297207 

 15.024 4489.489 .00334646 .00023918 .08297207 

 15.729 4488.871 .00350394 .00025043 .08297207 

 16.433 4488.254 .00366142 .00026169 .08297207 

 17.138 4487.636 .00381890 .00027294 .08297207 

 17.842 4487.018 .00397638 .00028420 .08297207 

 23.118 4482.385 .00515748 .00036862 .08297207 

 28.383 4477.752 .00633858 .00045303 .08297207 

 33.636 4473.118 .00751969 .00053745 .08297207 

 38.879 4468.485 .00870079 .00062186 .08297207 

 44.111 4463.852 .00988189 .00070628 .08297207 

 49.332 4459.219 .01106299 .00079069 .08297207 

 54.542 4454.586 .01224409 .00087511 .08297207 

 57.662 4295.045 .01342520 .00095982 .08299377 

 62.752 4296.211 .01460630 .00104577 .08309687 

 67.845 4297.412 .01578740 .00113196 .08319996 

 72.947 4298.973 .01696850 .00121848 .08330848 

 78.054 4300.601 .01814961 .00130527 .08341700 

 83.173 4302.638 .01933071 .00139241 .08353095 

 88.306 4305.127 .02051181 .00147993 .08365032 

 93.456 4308.127 .02169291 .00156786 .08377512 

 98.635 4312.080 .02287402 .00165633 .08391077 

 103.850 4317.171 .02405512 .00174537 .08405727 

 109.135 4324.538 .02523622 .00183532 .08422548 

 116.274 4401.446 .02641732 .00194228 .08502310 

 121.355 4397.159 .02759843 .00203107 .08509364 

 126.423 4392.803 .02877953 .00212002 .08516418 

 131.480 4388.413 .02996063 .00220914 .08523472 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-6 December 2005

 136.408 4380.233 .03114173 .00229741 .08527270 

 141.002 4362.312 .03232283 .00238314 .08522929 

 145.110 4331.145 .03350394 .00246586 .08509907 

 145.110 4183.660 .03468504 .00250950 .08385108 

 147.008 4098.795 .03586614 .00257802 .08337902 

 153.523 4143.973 .03704724 .00264784 .08297207 

 155.871 4077.375 .03822835 .00273226 .08297207 

 157.833 4004.950 .03940945 .00281667 .08297207 

 159.521 3929.994 .04059055 .00290109 .08297207 

 161.057 3855.647 .04177165 .00298551 .08297207 

 162.411 3781.163 .04295276 .00306992 .08297207 

 163.614 3707.213 .04413386 .00315434 .08297207 

 164.745 3635.565 .04531496 .00323875 .08297207 

 165.711 3563.988 .04649606 .00332317 .08297207 

 166.656 3495.506 .04767717 .00340759 .08297207 

 167.455 3427.355 .04885827 .00349200 .08297207 

 168.240 3362.162 .05003937 .00357642 .08297207 

 168.926 3298.012 .05122047 .00366083 .08297207 

 169.575 3236.065 .05240157 .00374525 .08297207 

 170.188 3176.179 .05358268 .00382966 .08297207 

Ultimate Moment Capacity at a Concrete Strain of 0.003 = 161.289 m- kN 

Axial Thrust Force = 474.50 kN 

 Bending Bending Bending Maximum Neutral Axis 

 Moment Stiffness Curvature Strain Position 

 kN-m kN-m2 rad/m m/m m 

 ------------- ------------- ------------- ------------- ------------- 

 1.69826245 4792.874 .00035433 .00031727 .90691267 

 2.45303965 4792.862 .00051181 .00032949 .65527803 

 3.20781175 4792.848 .00066929 .00034172 .52206775 

 3.96257836 4792.833 .00082677 .00035395 .43960844 

 4.71733626 4792.814 .00098425 .00036619 .38354674 

 5.47208598 4792.792 .00114173 .00037843 .34295465 

 6.22682760 4792.770 .00129921 .00039068 .31220536 

 6.98155916 4792.746 .00145669 .00040293 .28810838 

 7.73628058 4792.720 .00161417 .00041519 .26871577 

 8.49098340 4792.688 .00177165 .00042746 .25277953 

 9.24568013 4792.659 .00192913 .00043973 .23944236 

 10.000 4792.625 .00208661 .00045201 .22812367 

 10.755 4792.590 .00224409 .00046429 .21839481 

 11.510 4792.551 .00240157 .00047658 .20994649 

 12.264 4792.509 .00255906 .00048888 .20253996 

 13.019 4792.470 .00271654 .00050118 .19599075 

 13.774 4792.426 .00287402 .00051348 .19016320 

 14.528 4792.379 .00303150 .00052579 .18494336 

 15.283 4792.326 .00318898 .00053812 .18024442 

 16.035 4791.716 .00334646 .00055042 .17597957 

 16.774 4787.090 .00350394 .00056260 .17206198 

 17.571 4799.091 .00366142 .00057505 .16855677 

 18.301 4792.220 .00381890 .00058745 .16532828 

 19.053 4791.556 .00397638 .00059979 .16233854 

 24.610 4771.704 .00515748 .00068957 .14520315 

 29.767 4696.101 .00633858 .00078032 .13460612 

 35.334 4698.840 .00751969 .00087092 .12731897 

 39.786 4572.710 .00870079 .00095706 .12149685 

 45.804 4635.195 .00988189 .00105014 .11776917 

 50.555 4569.762 .01106299 .00113526 .11411745 

 56.180 4588.341 .01224409 .00122769 .11176798 

 61.386 4572.465 .01342520 .00131523 .10946735 

 64.845 4439.494 .01460630 .00139171 .10678147 

 71.647 4538.208 .01578740 .00149414 .10614120 

 74.736 4404.370 .01696850 .00156633 .10380800 

 81.890 4511.946 .01814961 .00167053 .10354213 

 85.716 4434.167 .01933071 .00175060 .10206082 

 92.018 4486.089 .02051181 .00183074 .10075315 

 97.124 4477.213 .02169291 .00193616 .10075315 

 102.139 4465.294 .02287402 .00202929 .10021598 

 105.295 4377.229 .02405512 .00210249 .09890288 

 109.026 4320.217 .02523622 .00218134 .09793705 

 113.742 4305.584 .02641732 .00227957 .09779054 

 118.611 4297.758 .02759843 .00238148 .09779054 

 127.233 4420.944 .02877953 .00247762 .09758978 

 131.954 4404.252 .02996063 .00257166 .09733476 

 136.319 4377.388 .03114173 .00266730 .09715027 

 140.277 4339.870 .03232283 .00276706 .09710686 

 143.850 4293.538 .03350394 .00287126 .09719911 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-7 December 2005

 147.136 4242.066 .03468504 .00297869 .09737816 

 150.123 4185.651 .03586614 .00308557 .09753009 

 152.748 4123.053 .03704724 .00319502 .09774171 

 152.748 3995.667 .03822835 .00329874 .09779054 

 152.748 3875.917 .03940945 .00340066 .09779054 

 154.387 3803.521 .04059055 .00350258 .09779054 

 155.966 3733.787 .04177165 .00360450 .09779054 

 157.340 3663.103 .04295276 .00370642 .09779054 

 158.551 3592.498 .04413386 .00380833 .09779054 

Ultimate Moment Capacity at a Concrete Strain of 0.003 = 147.732 m- kN 

p-y Curve Computed Using Criteria for Stiff Clay without Free Water 

Soil Layer Number = 1 

Depth below pile head = .000 m 

Depth below ground surface = .000 m 

Equivalent Depth = .000 m 

Diameter = .178 m 

Undrained cohesion, c = 120.00000 kN/ m**2 

Avg. Undrained cohesion, c = 120.00000 kN/ m**2 

Average Eff. Unit Weight = 21.20000 kN/ m**3 

Epsilon-50 = .00500 

Pct = 64.008 kN/ m 

Pcd = 192.024 kN/ m 

y50 = .002 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0000 3.599 

 .0000 5.382 

 .0000 6.401 

 .0000 9.571 

 .0000 11.382 

 .0002 17.021 

 .0004 20.241 

 .0009 25.452 

 .0018 30.268 

 .0027 33.497 

 .0036 35.994 

 .0089 45.260 

 .0178 53.824 

 .0356 64.008 

 .0400 64.008 

 .0445 64.008 

p-y Curve Computed Using Criteria for Stiff Clay without Free Water 

Soil Layer Number = 1 

Depth below pile head = 1.000 m 

Depth below ground surface = 1.000 m 

Equivalent Depth = 1.000 m 

Diameter = .178 m 

Undrained cohesion, c = 120.00000 kN/ m**2 

Avg. Undrained cohesion, c = 120.00000 kN/ m**2 

Average Eff. Unit Weight = 21.20000 kN/ m**3 

Epsilon-50 = .00500 

Pct = 127.777 kN/ m 

Pcd = 192.024 kN/ m 

y50 = .002 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0000 7.185 

 .0000 10.745 

 .0000 12.778 

 .0000 19.107 

 .0000 22.722 

 .0002 33.978 

 .0004 40.407 

 .0009 50.809 

 .0018 60.422 

 .0027 66.868 

 .0036 71.854 

 .0089 90.352 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-8 December 2005

 .0178 107.448 

 .0356 127.777 

 .0400 127.777 

 .0445 127.777 

p-y Curve Computed Using Criteria for Stiff Clay without Free Water 

Soil Layer Number = 1 

Depth below pile head = 2.000 m 

Depth below ground surface = 2.000 m 

Equivalent Depth = 2.000 m 

Diameter = .178 m 

Undrained cohesion, c = 120.00000 kN/ m**2 

Avg. Undrained cohesion, c = 120.00000 kN/ m**2 

Average Eff. Unit Weight = 21.20000 kN/ m**3 

Epsilon-50 = .00500 

Pct = 191.547 kN/ m 

Pcd = 192.024 kN/ m 

y50 = .002 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0000 10.771 

 .0000 16.107 

 .0000 19.155 

 .0000 28.643 

 .0000 34.062 

 .0002 50.935 

 .0004 60.572 

 .0009 76.166 

 .0018 90.577 

 .0027 100.240 

 .0036 107.715 

 .0089 135.444 

 .0178 161.071 

 .0356 191.547 

 .0400 191.547 

 .0445 191.547 

p-y Curve Computed Using Criteria for Stiff Clay without Free Water 

Soil Layer Number = 1 

Depth below pile head = 4.690 m 

Depth below ground surface = 4.690 m 

Equivalent Depth = 4.690 m 

Diameter = .178 m 

Undrained cohesion, c = 120.00000 kN/ m**2 

Avg. Undrained cohesion, c = 120.00000 kN/ m**2 

Average Eff. Unit Weight = 21.20000 kN/ m**3 

Epsilon-50 = .00500 

Pct = 363.086 kN/ m 

Pcd = 192.024 kN/ m 

y50 = .002 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0000 10.798 

 .0000 16.147 

 .0000 19.202 

 .0000 28.714 

 .0000 34.147 

 .0002 51.062 

 .0004 60.723 

 .0009 76.356 

 .0018 90.803 

 .0027 100.490 

 .0036 107.983 

 .0089 135.781 

 .0178 161.472 

 .0356 192.024 

 .0400 192.024 

 .0445 192.024 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-9 December 2005

p-y Curve Computed Using Criteria for Stiff Clay without Free Water 

Soil Layer Number = 2 

Depth below pile head = 4.710 m 

Depth below ground surface = 4.710 m 

Equivalent Depth = 4.710 m 

Diameter = .178 m 

Undrained cohesion, c = 168.00000 kN/ m**2 

Avg. Undrained cohesion, c = 168.00000 kN/ m**2 

Average Eff. Unit Weight = 21.17919 kN/ m**3 

Epsilon-50 = .00400 

Pct = 502.977 kN/ m 

Pcd = 268.834 kN/ m 

y50 = .002 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0000 15.118 

 .0000 22.606 

 .0000 26.883 

 .0000 40.200 

 .0000 47.806 

 .0001 71.487 

 .0003 85.013 

 .0007 106.898 

 .0014 127.124 

 .0021 140.685 

 .0028 151.176 

 .0071 190.094 

 .0142 226.061 

 .0284 268.834 

 .0320 268.834 

 .0356 268.834 

p-y Curve Computed Using Criteria for Stiff Clay without Free Water 

Soil Layer Number = 2 

Depth below pile head = 9.990 m 

Depth below ground surface = 9.990 m 

Equivalent Depth = 9.990 m 

Diameter = .178 m 

Undrained cohesion, c = 168.00000 kN/ m**2 

Avg. Undrained cohesion, c = 168.00000 kN/ m**2 

Average Eff. Unit Weight = 16.01061 kN/ m**3 

Epsilon-50 = .00400 

Pct = 957.200 kN/ m 

Pcd = 268.834 kN/ m 

y50 = .002 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0000 15.118 

 .0000 22.606 

 .0000 26.883 

 .0000 40.200 

 .0000 47.806 

 .0001 71.487 

 .0003 85.013 

 .0007 106.898 

 .0014 127.124 

 .0021 140.685 

 .0028 151.176 

 .0071 190.094 

 .0142 226.061 

 .0284 268.834 

 .0320 268.834 

 .0356 268.834 

p-y Curve Computed Using Criteria for Stiff Clay without Free Water 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-10 December 2005

Soil Layer Number = 3 

Depth below pile head = 10.010 m 

Depth below ground surface = 10.010 m 

Equivalent Depth = 8.863 m 

Diameter = .178 m 

Undrained cohesion, c = 480.00000 kN/ m**2 

Avg. Undrained cohesion, c = 480.00000 kN/ m**2 

Average Eff. Unit Weight = 16.00320 kN/ m**3 

Epsilon-50 = .00250 

Pct = 2408.297 kN/ m 

Pcd = 768.096 kN/ m 

y50 = .001 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0000 43.193 

 .0000 64.589 

 .0000 76.810 

 .0000 114.857 

 .0000 136.589 

 .0001 204.248 

 .0002 242.893 

 .0004 305.422 

 .0009 363.210 

 .0013 401.958 

 .0018 431.932 

 .0044 543.126 

 .0089 645.889 

 .0178 768.096 

 .0200 768.096 

 .0222 768.096 

p-y Curve Computed Using Criteria for Stiff Clay without Free Water 

Soil Layer Number = 3 

Depth below pile head = 14.500 m 

Depth below ground surface = 14.500 m 

Equivalent Depth = 13.353 m 

Diameter = .178 m 

Undrained cohesion, c = 480.00000 kN/ m**2 

Avg. Undrained cohesion, c = 480.00000 kN/ m**2 

Average Eff. Unit Weight = 15.13517 kN/ m**3 

Epsilon-50 = .00250 

Pct = 3496.612 kN/ m 

Pcd = 768.096 kN/ m 

y50 = .001 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0000 43.193 

 .0000 64.589 

 .0000 76.810 

 .0000 114.857 

 .0000 136.589 

 .0001 204.248 

 .0002 242.893 

 .0004 305.422 

 .0009 363.210 

 .0013 401.958 

 .0018 431.932 

 .0044 543.126 

 .0089 645.889 

 .0178 768.096 

 .0200 768.096 

 .0222 768.096 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 1 

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Specified shear force at pile head = .000 kN 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-11 December 2005

Specified bending moment at pile head = .000 m- kN 

Specified axial load at pile head = .000 kN 

(Zero moment for this load indicates free-head conditions) 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 .10000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 .200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 .300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 .400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 .500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 .600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 .700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 .800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 .900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 1.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 2.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 3.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 4.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 5.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 6.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 7.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 7.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-12 December 2005

 7.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 7.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 7.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 7.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 7.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 7.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 7.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 7.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 8.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 9.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 10.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 11.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 12.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.600 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.700 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.800 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 13.900 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 14.000 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 14.100 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 14.200 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 14.300 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 14.400 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

 14.500 0.000 0.0 0.0 0.000 0.0 4898.917 0.000 

Please note that because this analysis makes computations of ultimate moment 

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-13 December 2005

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 1: 

Pile-head deflection = 0.000 m 

Computed slope at pile head = 0.000 

Maximum bending moment = 0.000 kN- m 

Maximum shear force = 0.000 kN 

Depth of maximum bending moment = 0.000 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 5 

Number of zero deflection points = 0 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-14 December 2005

=============================================================== 

 LPILE Plus for Windows, Version 4.0 (4.0.8) 

 Analysis of Individual Piles and Drilled Shafts 

 Subjected to Lateral Loading Using the p-y Method 

 (c) Copyright ENSOFT, Inc., 1985-2003 

 All Rights Reserved 

=============================================================== 

Path to file locations: L:\Programs\LPILE\Chapter 6\Ch. 6 Example with P=474.5\P=0 case\ 

Name of input data file: Up analysis(P=0)2.lpd 

Name of output file: Up analysis(P=0)2.lpo 

Name of plot output file: Up analysis(P=0)2.lpp 

Name of runtime file: Up analysis(P=0)2.lpr 

------------------------------------------------------------------------------ 

 Time and Date of Analysis 

------------------------------------------------------------------------------ 

 Date: May 4, 2005 Time: 16:58:55 

------------------------------------------------------------------------------ 

 Problem Title 

------------------------------------------------------------------------------ 

Up Analysis with P=0 case 

------------------------------------------------------------------------------ 

 Program Options 

------------------------------------------------------------------------------ 

Units Used in Computations - SI Units, meters, kilopascals 

Basic Program Options: 

Analysis Type 3: 

- Computation of Nonlinear Bending Stiffness and Ultimate Bending Moment 

 Capacity with Pile Response Computed Using Nonlinear EI 

Computation Options: 

- User-specified p-y curves used in analysis 

- Analysis uses p-y multiplers for group action 

- Analysis assumes no shear resistance at pile tip 

- Analysis for fixed-length pile or shaft only 

- No computation of foundation stiffness matrix elements 

- Output pile response for full length of pile 

- Analysis assumes no soil movements acting on pile 

- Additional p-y curves computed at specified depths 

Solution Control Parameters: 

- Number of pile increments = 145 

- Maximum number of iterations allowed = 100 

- Deflection tolerance for convergence = 2.5400E-07 m 

- Maximum allowable deflection = 2.5400E+00 m 

Printing Options: 

- Values of pile-head deflection, bending moment, shear force, and 

 soil reaction are printed for full length of pile. 

- Printing Increment (spacing of output points) = 1 

------------------------------------------------------------------------------ 

 Pile Structural Properties and Geometry 

------------------------------------------------------------------------------ 

Pile Length = 10.00 m 

Depth of ground surface below top of pile = .00 m 

Slope angle of ground surface = .00 deg. 

Structural properties of pile defined using 2 points 

Point Depth Pile Moment of Pile Modulus of 

 X Diameter Inertia Area Elasticity 

 m m m**4 Sq. m kN/Sq. m 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-15 December 2005

----- --------- ----------- ---------- ---------- ----------- 

 1 0.0000 .17780000 1.0000 .024800 200000000.000 

 2 10.0000 .17780000 1.0000 .024800 200000000.000 

Please note that because this analysis makes computations of ultimate 

moment capacity and pile response using nonlinear bending stiffness 

that the above values of moment of inertia and modulus of are not used 

for any computations other than total stress due to combined axial 

loading and bending. 

------------------------------------------------------------------------------ 

 Soil and Rock Layering Information 

------------------------------------------------------------------------------ 

The soil profile is modelled using 4 layers 

Layer 1 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = .000 m 

Distance from top of pile to bottom of layer = 5.290 m 

Layer 2 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = 5.290 m 

Distance from top of pile to bottom of layer = 5.310 m 

Layer 3 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = 5.310 m 

Distance from top of pile to bottom of layer = 8.000 m 

Layer 4 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = 8.000 m 

Distance from top of pile to bottom of layer = 10.000 m 

(Depth of lowest layer extends .00 m below pile tip) 

------------------------------------------------------------------------------ 

 Effective Unit Weight of Soil vs. Depth 

------------------------------------------------------------------------------ 

Distribution of effective unit weight of soil with depth 

is defined using 8 points 

Point Depth X Eff. Unit Weight 

 No. m kN/ m**3 

----- ---------- ---------------- 

 1 .00 11.40000 

 2 5.29 11.40000 

 3 5.29 11.40000 

 4 5.31 21.20000 

 5 5.31 21.20000 

 6 8.00 21.20000 

 7 8.00 21.20000 

 8 10.00 21.20000 

------------------------------------------------------------------------------ 

 Shear Strength of Soils 

------------------------------------------------------------------------------ 

Distribution of shear strength parameters with depth 

defined using 0 points 

Point Depth X Cohesion c Angle of Friction E50 or RQD 

 No. m kN/ m**2 Deg. k_rm % 

----- -------- ---------- ------------------ ------ ------ 

Notes: 

(1) Cohesion = uniaxial compressive strength for rock materials. 

(2) Values of E50 are reported for clay strata. 

(3) Default values will be generated for E50 when input values are 0. 

(4) RQD and k_rm are reported only for weak rock strata. 

------------------------------------------------------------------------------ 

 p-y Modification Factors 

------------------------------------------------------------------------------ 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-16 December 2005

Distribution of p-y multipliers with depth defined using 5 points 

Point Depth X p-mult y-mult 

 No. m 

----- ---------- ---------- ---------- 

 1 .000 1.0000 1.0000 

 2 5.290 1.0000 1.0000 

 3 5.310 1.0000 1.0000 

 4 8.000 1.0000 1.0000 

 5 10.000 1.0000 1.0000 

------------------------------------------------------------------------------ 

 User-specified p-y Curves 

------------------------------------------------------------------------------ 

User-specified p-y curves defined using 8 curves. 

User-specified curve number 1 at depth = .000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 92.072 

 3 .0004 109.493 

 4 .0009 137.680 

 5 .0018 163.731 

 6 .0027 181.198 

 7 .0037 194.710 

 8 .0092 244.834 

 9 .0183 291.159 

 10 .0366 346.248 

 11 .0412 346.248 

 12 .0458 346.248 

User-specified curve number 2 at depth = 5.290 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 92.072 

 3 .0004 109.493 

 4 .0009 137.680 

 5 .0018 163.731 

 6 .0027 181.198 

 7 .0037 194.710 

 8 .0092 244.834 

 9 .0183 291.159 

 10 .0366 346.248 

 11 .0412 346.248 

 12 .0458 346.248 

User-specified curve number 3 at depth = 5.290 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 92.072 

 3 .0004 109.493 

 4 .0009 137.680 

 5 .0018 163.731 

 6 .0027 181.198 

 7 .0037 194.710 

 8 .0092 244.834 

 9 .0183 291.159 

 10 .0366 346.248 

 11 .0412 346.248 

 12 .0458 346.298 

User-specified curve number 4 at depth = 5.310 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-17 December 2005

 1 .0000 .000 

 2 .0002 65.766 

 3 .0005 78.209 

 4 .0011 98.343 

 5 .0023 116.950 

 6 .0034 129.427 

 7 .0046 139.078 

 8 .0115 174.882 

 9 .0229 207.971 

 10 .0458 247.320 

 11 .0515 247.320 

 12 .0573 247.320 

User-specified curve number 5 at depth = 5.310 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 65.766 

 3 .0005 78.209 

 4 .0011 98.343 

 5 .0023 116.950 

 6 .0034 129.427 

 7 .0046 139.078 

 8 .0115 174.882 

 9 .0229 207.971 

 10 .0458 247.320 

 11 .0515 247.320 

 12 .0573 247.320 

User-specified curve number 6 at depth = 8.000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 56.414 

 3 .0005 67.088 

 4 .0011 84.358 

 5 .0023 100.319 

 6 .0034 111.022 

 7 .0046 119.300 

 8 .0115 150.012 

 9 .0229 178.396 

 10 .0458 212.150 

 11 .0515 212.150 

 12 .0573 212.150 

User-specified curve number 7 at depth = 8.000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 56.414 

 3 .0005 67.088 

 4 .0011 84.358 

 5 .0023 100.319 

 6 .0034 111.022 

 7 .0046 119.300 

 8 .0115 150.012 

 9 .0229 178.396 

 10 .0458 212.150 

 11 .0515 212.150 

 12 .0573 212.150 

User-specified curve number 8 at depth = 10.000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0005 26.070 

 3 .0011 32.781 

 4 .0020 21.922 

 5 .0023 38.983 

 6 .0034 43.142 

 7 .0046 46.359 

 8 .0115 58.294 

 9 .0151 82.440 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-18 December 2005

 10 .0229 69.324 

 11 .0458 82.440 

 12 .0573 82.440 

------------------------------------------------------------------------------ 

 Loading Type 

------------------------------------------------------------------------------ 

Static loading criteria was used for computation of p-y curves 

------------------------------------------------------------------------------ 

 Pile-head Loading and Pile-head Fixity Conditions 

------------------------------------------------------------------------------ 

Number of loads specified = 1 

Load Case Number 1 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Shear force at pile head = 365.000 kN 

Bending moment at pile head = -83.500 m- kN 

Axial load at pile head = .000 kN 

Non-zero moment at pile head for this load case indicates the pile-head 

may rotate under the applied pile-head loading, but is not a free-head 

(zero moment) condition. 

------------------------------------------------------------------------------ 

 Output of p-y Curves at Specified Depths 

------------------------------------------------------------------------------ 

p-y curves are generated and printed for verification at 5 depths. 

Depth Depth Below Pile Head Depth Below Ground Surface 

 No. m m 

----- --------------------- -------------------------- 

 1 .000 .000 

 2 5.290 5.290 

 3 5.310 5.310 

 4 8.000 8.000 

 5 10.000 10.000 

------------------------------------------------------------------------------ 

 Computations of Ultimate Moment Capacity and Nonlinear Bending Stiffness 

------------------------------------------------------------------------------ 

Pile Description: 

The sectional shape is a circular shaft with steel casing. 

Outside Diameter = .1778 m 

Wall thickness of steel shell = .0115 m 

Cross-sectional area of shell = .00601 m**2 

Moment of inertia of steel shell = 2.08692E-05 m**4 

Material Properties: 

Compressive Strength of Concrete = 27600.000 kN/ m**2 

Yield Stress of Reinforcement = 0. kN/ m**2 

Steel shell or core yield stress = 552000. kN/ m**2 

Modulus of Elasticity of Reinforcement = 200000000. kN/ m**2 

Cover Thickness (edge to bar center) = .000 m 

Number of Reinforcing Bars = 10 

Area of Single Bar = .00000 m**2 

Number of Rows of Reinforcing Bars = 5 

Ultimate Axial Squash Load Capacity = 3758.02 kN 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-19 December 2005

Distribution and Area of Steel Reinforcement 

 Row Area of Distance to 

Number Reinforcement Centroidal Axis 

 m**2 m 

------ ------------- --------------- 

 1 .000000 .0736 

 2 .000000 .0455 

 3 .000000 .0000 

 4 .000000 -.0455 

 5 .000000 -.0736 

Axial Thrust Force = .00 kN 

 Bending Bending Bending Maximum Neutral Axis 

 Moment Stiffness Curvature Strain Position 

 kN-m kN-m2 rad/m m/m m 

 ------------- ------------- ------------- ------------- ------------- 

 1.73583660 4898.917 .00035433 .00002742 .08889729 

 2.50651820 4897.351 .00051181 .00003961 .08889729 

 3.27670667 4895.785 .00066929 .00005180 .08889729 

 4.04640201 4894.220 .00082677 .00006399 .08889729 

 4.81560422 4892.654 .00098425 .00007618 .08889729 

 5.58431330 4891.088 .00114173 .00008837 .08889729 

 6.35252925 4889.522 .00129921 .00010056 .08889729 

 6.55060560 4496.902 .00145669 .00010411 .08297207 

 7.25778201 4496.284 .00161417 .00011537 .08297207 

 7.96476385 4495.667 .00177165 .00012662 .08297207 

 8.67155112 4495.049 .00192913 .00013788 .08297207 

 9.37814382 4494.431 .00208661 .00014913 .08297207 

 10.085 4493.813 .00224409 .00016039 .08297207 

 10.791 4493.196 .00240157 .00017165 .08297207 

 11.497 4492.578 .00255906 .00018290 .08297207 

 12.203 4491.960 .00271654 .00019416 .08297207 

 12.908 4491.342 .00287402 .00020541 .08297207 

 13.614 4490.725 .00303150 .00021667 .08297207 

 14.319 4490.107 .00318898 .00022792 .08297207 

 15.024 4489.489 .00334646 .00023918 .08297207 

 15.729 4488.871 .00350394 .00025043 .08297207 

 16.433 4488.254 .00366142 .00026169 .08297207 

 17.138 4487.636 .00381890 .00027294 .08297207 

 17.842 4487.018 .00397638 .00028420 .08297207 

 23.118 4482.385 .00515748 .00036862 .08297207 

 28.383 4477.752 .00633858 .00045303 .08297207 

 33.636 4473.118 .00751969 .00053745 .08297207 

 38.879 4468.485 .00870079 .00062186 .08297207 

 44.111 4463.852 .00988189 .00070628 .08297207 

 49.332 4459.219 .01106299 .00079069 .08297207 

 54.542 4454.586 .01224409 .00087511 .08297207 

 57.662 4295.045 .01342520 .00095982 .08299377 

 62.752 4296.211 .01460630 .00104577 .08309687 

 67.845 4297.412 .01578740 .00113196 .08319996 

 72.947 4298.973 .01696850 .00121848 .08330848 

 78.054 4300.601 .01814961 .00130527 .08341700 

 83.173 4302.638 .01933071 .00139241 .08353095 

 88.306 4305.127 .02051181 .00147993 .08365032 

 93.456 4308.127 .02169291 .00156786 .08377512 

 98.635 4312.080 .02287402 .00165633 .08391077 

 103.850 4317.171 .02405512 .00174537 .08405727 

 109.135 4324.538 .02523622 .00183532 .08422548 

 116.274 4401.446 .02641732 .00194228 .08502310 

 121.355 4397.159 .02759843 .00203107 .08509364 

 126.423 4392.803 .02877953 .00212002 .08516418 

 131.480 4388.413 .02996063 .00220914 .08523472 

 136.408 4380.233 .03114173 .00229741 .08527270 

 141.002 4362.312 .03232283 .00238314 .08522929 

 145.110 4331.145 .03350394 .00246586 .08509907 

 145.110 4183.660 .03468504 .00250950 .08385108 

 147.008 4098.795 .03586614 .00257802 .08337902 

 153.523 4143.973 .03704724 .00264784 .08297207 

 155.871 4077.375 .03822835 .00273226 .08297207 

 157.833 4004.950 .03940945 .00281667 .08297207 

 159.521 3929.994 .04059055 .00290109 .08297207 

 161.057 3855.647 .04177165 .00298551 .08297207 

 162.411 3781.163 .04295276 .00306992 .08297207 

 163.614 3707.213 .04413386 .00315434 .08297207 

 164.745 3635.565 .04531496 .00323875 .08297207 

 165.711 3563.988 .04649606 .00332317 .08297207 

 166.656 3495.506 .04767717 .00340759 .08297207 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-20 December 2005

 167.455 3427.355 .04885827 .00349200 .08297207 

 168.240 3362.162 .05003937 .00357642 .08297207 

 168.926 3298.012 .05122047 .00366083 .08297207 

 169.575 3236.065 .05240157 .00374525 .08297207 

 170.188 3176.179 .05358268 .00382966 .08297207 

Ultimate Moment Capacity at a Concrete Strain of 0.003 = 161.289 m- kN 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 1 

Depth below ground surface = .000 m 

Depth below pile head = .000 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 140.575 

 .0011 143.795 

 .0022 171.931 

 .0033 189.761 

 .0044 201.500 

 .0056 211.627 

 .0067 221.754 

 .0078 231.882 

 .0089 242.009 

 .0100 248.913 

 .0111 254.570 

 .0122 260.227 

 .0133 265.884 

 .0356 343.117 

 .0667 346.248 

 .0889 346.248 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 2 

Depth below ground surface = 5.290 m 

Depth below pile head = 5.290 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 140.575 

 .0011 143.795 

 .0022 171.931 

 .0033 189.761 

 .0044 201.500 

 .0056 211.627 

 .0067 221.754 

 .0078 231.882 

 .0089 242.009 

 .0100 248.913 

 .0111 254.570 

 .0122 260.227 

 .0133 265.884 

 .0356 343.117 

 .0667 346.248 

 .0889 346.248 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 3 

Depth below ground surface = 5.310 m 

Depth below pile head = 5.310 m 

p-multiplier = 1.00000 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-21 December 2005

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 94.987 

 .0011 98.517 

 .0022 115.748 

 .0033 128.676 

 .0044 137.831 

 .0056 144.040 

 .0067 149.806 

 .0078 155.572 

 .0089 161.339 

 .0100 167.105 

 .0111 172.871 

 .0122 176.983 

 .0133 180.208 

 .0356 229.725 

 .0667 247.320 

 .0889 247.320 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 4 

Depth below ground surface = 8.000 m 

Depth below pile head = 8.000 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 81.480 

 .0011 84.508 

 .0022 99.288 

 .0033 110.377 

 .0044 118.231 

 .0056 123.556 

 .0067 128.502 

 .0078 133.449 

 .0089 138.395 

 .0100 143.341 

 .0111 148.287 

 .0122 151.814 

 .0133 154.581 

 .0356 197.057 

 .0667 212.150 

 .0889 212.150 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 4 

Depth below ground surface = 10.000 m 

Depth below pile head = 10.000 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 31.663 

 .0011 32.645 

 .0022 34.576 

 .0033 42.892 

 .0044 45.943 

 .0056 48.013 

 .0067 49.935 

 .0078 51.857 

 .0089 53.779 

 .0100 55.702 

 .0111 57.624 

 .0122 63.148 

 .0133 70.602 

 .0356 76.575 

 .0667 82.440 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-22 December 2005

 .0889 82.440 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 1 

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Specified shear force at pile head = 365.000 kN 

Specified bending moment at pile head = -83.500 m- kN 

Specified axial load at pile head = .000 kN 

Non-zero moment for this load case indicates the pile-head may rotate under 

the applied pile-head loading, but is not a free-head (zero moment )condition. 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 .047472 -83.5000 365.0 -.035587 7.4232 4295.386 -346.250 

 .06897 .044972 -59.1510 341.1 -.036732 5.2585 4295.386 -346.250 

 .138 .042406 -36.4489 317.2 -.037500 3.2403 4295.386 -346.250 

 .207 .039799 -15.3936 293.4 -.037911 1.3685 4489.165 -346.250 

 .276 .037177 4.0149 269.5 -.038001 .3569 4894.284 -346.250 

 .345 .034558 21.7765 245.8 -.037805 1.9359 4483.564 -340.101 

 .414 .031962 37.9205 222.6 -.037345 3.3711 4469.333 -332.288 

 .483 .029407 52.4840 200.0 -.036646 4.6658 4456.417 -324.595 

 .552 .026907 65.5037 177.9 -.035714 5.8233 4296.860 -317.072 

 .621 .024481 77.0154 156.2 -.034571 6.8467 4300.270 -309.766 

 .690 .022139 87.0537 135.1 -.033256 7.7391 4304.520 -302.717 

 .759 .019894 95.6522 114.5 -.031793 8.5035 4309.804 -295.958 

 .828 .017754 102.8 94.3234 -.030206 9.1427 4316.189 -288.380 

 .897 .015727 108.7 74.7909 -.028518 9.6601 4323.880 -278.063 

 .966 .013820 113.2 55.9489 -.026758 10.0598 4368.125 -268.355 

 1.034 .012036 116.4 37.7548 -.024953 10.3461 4401.357 -259.275 

 1.103 .010378 118.4 20.1648 -.023114 10.5228 4399.681 -250.834 

 1.172 .008848 119.2 3.1833 -.021252 10.5934 4399.011 -241.630 

 1.241 .007447 118.8 -13.0405 -.019387 10.5618 4399.311 -228.860 

 1.310 .006174 117.4 -28.4240 -.017536 10.4335 4400.529 -217.261 

 1.379 .005028 114.9 -43.0474 -.015713 10.2133 4386.630 -206.818 

 1.448 .004007 111.4 -56.9897 -.013927 9.9056 4349.413 -197.509 

 1.517 .003107 107.0 -70.2385 -.012189 9.5145 4321.598 -186.705 

 1.586 .002326 101.7 -82.6744 -.010522 9.0444 4315.109 -173.935 

 1.655 .001656 95.6211 -94.1745 -.008944 8.5007 4309.780 -159.567 

 1.724 .001092 88.7468 -104.6 -.007468 7.8896 4305.384 -143.240 

 1.793 6.26E-04 81.1913 -113.8 -.006107 7.2179 4301.850 -122.234 

 1.862 2.50E-04 73.0544 -121.3 -.004870 6.4945 4299.007 -96.405 

 1.931 -4.58E-05 64.4589 -123.9 -.003767 5.7304 4296.613 21.074 

 2.000 -2.70E-04 55.9637 -119.8 -.002809 4.9752 4384.308 98.154 

 2.069 -4.33E-04 47.9353 -112.6 -.001998 4.2614 4460.460 111.365 

 2.138 -5.46E-04 40.4366 -104.7 -.001316 3.5948 4467.107 117.695 

 2.207 -6.15E-04 33.4977 -96.4211 -7.45E-04 2.9779 4473.241 121.597 

 2.276 -6.48E-04 27.1372 -87.9698 -2.78E-04 2.4125 4478.849 123.492 

 2.345 -6.53E-04 21.3640 -79.4438 9.50E-05 1.8993 4483.926 123.761 

 2.414 -6.35E-04 16.1794 -70.9433 3.84E-04 1.4383 4488.476 122.753 

 2.483 -6.00E-04 11.5787 -62.5457 5.97E-04 1.0293 4492.506 120.779 

 2.552 -5.53E-04 7.5524 -54.3080 7.44E-04 .6714 4496.027 118.113 

 2.621 -4.98E-04 4.0879 -46.2697 8.30E-04 .3634 4894.135 114.997 

 2.690 -4.38E-04 1.1704 -38.4540 8.67E-04 .1040 4898.917 111.657 

 2.759 -3.78E-04 -1.2161 -30.8942 8.67E-04 .1081 4898.917 107.577 

 2.828 -3.19E-04 -3.0909 -23.6529 8.37E-04 .2748 4896.163 102.421 

 2.897 -2.63E-04 -4.4786 -16.7582 7.83E-04 .3981 4893.340 97.525 

 2.966 -2.11E-04 -5.4024 -10.1880 7.14E-04 .4803 4891.459 93.009 

 3.034 -1.64E-04 -5.8838 -4.3749 6.34E-04 .5231 4890.478 75.572 

 3.103 -1.23E-04 -6.0058 .1882 5.50E-04 .5339 4890.229 56.756 

 3.172 -8.83E-05 -5.8579 3.5463 4.67E-04 .5208 4890.531 40.629 

 3.241 -5.89E-05 -5.5167 5.8826 3.86E-04 .4904 4891.226 27.125 

 3.310 -3.50E-05 -5.0465 7.3728 3.12E-04 .4486 4892.184 16.090 

 3.379 -1.59E-05 -4.4997 8.1798 2.45E-04 .4000 4893.297 7.314 

 3.448 -1.20E-06 -3.9182 8.4510 1.85E-04 .3483 4894.480 .551315 

 3.517 9.68E-06 -3.3341 8.3163 1.34E-04 .2964 4895.669 -4.458 

 3.586 1.73E-05 -2.7711 7.8875 9.13E-05 .2464 4896.813 -7.977 

 3.655 2.23E-05 -2.2461 7.2587 5.60E-05 .1997 4897.880 -10.257 

 3.724 2.51E-05 -1.7699 6.5074 2.77E-05 .1573 4898.847 -11.532 

 3.793 2.61E-05 -1.3486 5.6954 5.76E-06 .1199 4898.917 -12.016 

 3.862 2.58E-05 -.9844 4.8707 -1.07E-05 8.75E-02 4898.917 -11.898 

 3.931 2.46E-05 -.6767 4.0694 -2.23E-05 6.02E-02 4898.917 -11.340 

 4.000 2.28E-05 -.4231 3.3171 -3.01E-05 3.76E-02 4898.917 -10.479 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-23 December 2005

 4.069 2.05E-05 -.2192 2.6306 -3.46E-05 1.95E-02 4898.917 -9.429 

 4.138 1.80E-05 -6.02E-02 2.0199 -3.66E-05 5.35E-03 4898.917 -8.281 

 4.207 1.54E-05 5.94E-02 1.4893 -3.66E-05 5.28E-03 4898.917 -7.106 

 4.276 1.29E-05 .1452 1.0388 -3.51E-05 1.29E-02 4898.917 -5.958 

 4.345 1.06E-05 .2027 .6652 -3.27E-05 1.80E-02 4898.917 -4.875 

 4.414 8.43E-06 .2370 .3633 -2.96E-05 2.11E-02 4898.917 -3.882 

 4.483 6.51E-06 .2528 .1261 -2.62E-05 2.25E-02 4898.917 -2.995 

 4.552 4.83E-06 .2544 -5.37E-02 -2.26E-05 2.26E-02 4898.917 -2.221 

 4.621 3.39E-06 .2454 -.1842 -1.91E-05 2.18E-02 4898.917 -1.561 

 4.690 2.20E-06 .2290 -.2729 -1.57E-05 2.04E-02 4898.917 -1.011 

 4.759 1.22E-06 .2077 -.3271 -1.27E-05 1.85E-02 4898.917 -.562507 

 4.828 4.50E-07 .1838 -.3536 -9.90E-06 1.63E-02 4898.917 -.207195 

 4.897 -1.43E-07 .1590 -.3585 -7.48E-06 1.41E-02 4898.917 .065948 

 4.966 -5.82E-07 .1344 -.3470 -5.42E-06 1.19E-02 4898.917 .268043 

 5.034 -8.91E-07 .1111 -.3236 -3.69E-06 9.88E-03 4898.917 .410071 

 5.103 -1.09E-06 8.98E-02 -.2922 -2.28E-06 7.98E-03 4898.917 .502444 

 5.172 -1.20E-06 7.08E-02 -.2557 -1.15E-06 6.29E-03 4898.917 .554701 

 5.241 -1.25E-06 5.45E-02 -.2167 -2.66E-07 4.84E-03 4898.917 .575313 

 5.310 -1.24E-06 4.09E-02 -.1828 4.06E-07 3.64E-03 4898.917 .408260 

 5.379 -1.19E-06 2.93E-02 -.1553 9.00E-07 2.60E-03 4898.917 .391097 

 5.448 -1.12E-06 1.95E-02 -.1292 1.24E-06 1.73E-03 4898.917 .364773 

 5.517 -1.02E-06 1.15E-02 -.1051 1.46E-06 1.02E-03 4898.917 .332477 

 5.586 -9.16E-07 4.99E-03 -8.34E-02 1.58E-06 4.44E-04 4898.917 .296806 

 5.655 -8.05E-07 -5.84E-05 -6.43E-02 1.61E-06 5.19E-06 4898.917 .259826 

 5.724 -6.94E-07 -3.87E-03 -4.76E-02 1.58E-06 3.44E-04 4898.917 .223131 

 5.793 -5.86E-07 -6.62E-03 -3.34E-02 1.51E-06 5.89E-04 4898.917 .187906 

 5.862 -4.86E-07 -8.48E-03 -2.16E-02 1.40E-06 7.54E-04 4898.917 .154992 

 5.931 -3.93E-07 -9.60E-03 -1.19E-02 1.28E-06 8.54E-04 4898.917 .124939 

 6.000 -3.10E-07 -1.01E-02 -4.26E-03 1.14E-06 9.00E-04 4898.917 .098061 

 6.069 -2.36E-07 -1.02E-02 1.69E-03 9.94E-07 9.06E-04 4898.917 .074488 

 6.138 -1.72E-07 -9.90E-03 6.13E-03 8.53E-07 8.80E-04 4898.917 .054201 

 6.207 -1.18E-07 -9.34E-03 9.28E-03 7.17E-07 8.31E-04 4898.917 .037077 

 6.276 -7.34E-08 -8.62E-03 1.13E-02 5.91E-07 7.66E-04 4898.917 .022912 

 6.345 -3.69E-08 -7.78E-03 1.25E-02 4.76E-07 6.92E-04 4898.917 .011456 

 6.414 -7.83E-09 -6.89E-03 1.30E-02 3.72E-07 6.12E-04 4898.917 .002426 

 6.483 1.45E-08 -5.98E-03 1.29E-02 2.82E-07 5.32E-04 4898.917 -.004472 

 6.552 3.10E-08 -5.10E-03 1.25E-02 2.04E-07 4.54E-04 4898.917 -.009532 

 6.621 4.26E-08 -4.27E-03 1.17E-02 1.38E-07 3.79E-04 4898.917 -.013035 

 6.690 5.00E-08 -3.49E-03 1.07E-02 8.31E-08 3.10E-04 4898.917 -.015249 

 6.759 5.41E-08 -2.79E-03 9.61E-03 3.89E-08 2.48E-04 4898.917 -.016415 

 6.828 5.54E-08 -2.17E-03 8.47E-03 4.04E-09 1.93E-04 4898.917 -.016752 

 6.897 5.46E-08 -1.62E-03 7.32E-03 -2.26E-08 1.44E-04 4898.917 -.016453 

 6.966 5.23E-08 -1.16E-03 6.22E-03 -4.22E-08 1.03E-04 4898.917 -.015683 

 7.034 4.88E-08 -7.64E-04 5.17E-03 -5.57E-08 6.79E-05 4898.917 -.014584 

 7.103 4.46E-08 -4.42E-04 4.21E-03 -6.42E-08 3.93E-05 4898.917 -.013272 

 7.172 3.99E-08 -1.83E-04 3.35E-03 -6.86E-08 1.63E-05 4898.917 -.011843 

 7.241 3.51E-08 1.92E-05 2.58E-03 -6.97E-08 1.70E-06 4898.917 -.010372 

 7.310 3.03E-08 1.72E-04 1.91E-03 -6.84E-08 1.53E-05 4898.917 -.008918 

 7.379 2.57E-08 2.83E-04 1.35E-03 -6.52E-08 2.52E-05 4898.917 -.007525 

 7.448 2.13E-08 3.58E-04 8.73E-04 -6.07E-08 3.18E-05 4898.917 -.006224 

 7.517 1.73E-08 4.04E-04 4.85E-04 -5.53E-08 3.59E-05 4898.917 -.005033 

 7.586 1.37E-08 4.25E-04 1.74E-04 -4.95E-08 3.78E-05 4898.917 -.003966 

 7.655 1.05E-08 4.28E-04 -6.68E-05 -4.35E-08 3.80E-05 4898.917 -.003026 

 7.724 7.71E-09 4.16E-04 -2.47E-04 -3.75E-08 3.70E-05 4898.917 -.002213 

 7.793 5.33E-09 3.93E-04 -3.76E-04 -3.18E-08 3.50E-05 4898.917 -.001522 

 7.862 3.32E-09 3.64E-04 -4.61E-04 -2.65E-08 3.24E-05 4898.917 -9.45E-04 

 7.931 1.67E-09 3.30E-04 -5.10E-04 -2.16E-08 2.93E-05 4898.917 -4.74E-04 

 8.000 3.41E-10 2.94E-04 -5.30E-04 -1.72E-08 2.61E-05 4898.917 -9.62E-05 

 8.069 -7.05E-10 2.57E-04 -5.27E-04 -1.34E-08 2.28E-05 4898.917 1.93E-04 

 8.138 -1.50E-09 2.21E-04 -5.06E-04 -1.00E-08 1.96E-05 4898.917 4.00E-04 

 8.207 -2.08E-09 1.87E-04 -4.74E-04 -7.13E-09 1.66E-05 4898.917 5.38E-04 

 8.276 -2.49E-09 1.56E-04 -4.34E-04 -4.72E-09 1.38E-05 4898.917 6.22E-04 

 8.345 -2.74E-09 1.27E-04 -3.89E-04 -2.73E-09 1.13E-05 4898.917 6.63E-04 

 8.414 -2.86E-09 1.02E-04 -3.43E-04 -1.12E-09 9.05E-06 4898.917 6.71E-04 

 8.483 -2.89E-09 7.97E-05 -2.98E-04 1.59E-10 7.09E-06 4898.917 6.55E-04 

 8.552 -2.84E-09 6.08E-05 -2.54E-04 1.15E-09 5.40E-06 4898.917 6.21E-04 

 8.621 -2.73E-09 4.47E-05 -2.12E-04 1.89E-09 3.98E-06 4898.917 5.76E-04 

 8.690 -2.58E-09 3.15E-05 -1.75E-04 2.43E-09 2.80E-06 4898.917 5.23E-04 

 8.759 -2.40E-09 2.07E-05 -1.40E-04 2.79E-09 1.84E-06 4898.917 4.67E-04 

 8.828 -2.19E-09 1.21E-05 -1.10E-04 3.02E-09 1.08E-06 4898.917 4.10E-04 

 8.897 -1.98E-09 5.47E-06 -8.38E-05 3.15E-09 4.86E-07 4898.917 3.54E-04 

 8.966 -1.76E-09 5.33E-07 -6.12E-05 3.19E-09 4.74E-08 4898.917 3.01E-04 

 9.034 -1.54E-09 -2.97E-06 -4.22E-05 3.17E-09 2.64E-07 4898.917 2.51E-04 

 9.103 -1.32E-09 -5.28E-06 -2.64E-05 3.12E-09 4.70E-07 4898.917 2.05E-04 

 9.172 -1.11E-09 -6.62E-06 -1.37E-05 3.03E-09 5.88E-07 4898.917 1.63E-04 

 9.241 -9.04E-10 -7.18E-06 -3.74E-06 2.93E-09 6.38E-07 4898.917 1.26E-04 

 9.310 -7.05E-10 -7.13E-06 3.80E-06 2.83E-09 6.34E-07 4898.917 9.27E-05 

 9.379 -5.13E-10 -6.65E-06 9.18E-06 2.74E-09 5.91E-07 4898.917 6.34E-05 

 9.448 -3.28E-10 -5.87E-06 1.27E-05 2.65E-09 5.22E-07 4898.917 3.79E-05 

 9.517 -1.48E-10 -4.90E-06 1.45E-05 2.57E-09 4.36E-07 4898.917 1.59E-05 

 9.586 2.72E-11 -3.86E-06 1.50E-05 2.51E-09 3.43E-07 4898.917 -2.72E-06 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-24 December 2005

 9.655 1.99E-10 -2.84E-06 1.43E-05 2.46E-09 2.52E-07 4898.917 -1.82E-05 

 9.724 3.67E-10 -1.90E-06 1.26E-05 2.43E-09 1.69E-07 4898.917 -3.08E-05 

 9.793 5.34E-10 -1.10E-06 1.01E-05 2.41E-09 9.81E-08 4898.917 -4.05E-05 

 9.862 6.99E-10 -5.02E-07 7.07E-06 2.40E-09 4.47E-08 4898.917 -4.76E-05 

 9.931 8.65E-10 -1.28E-07 3.64E-06 2.39E-09 1.13E-08 4898.917 -5.19E-05 

 10.000 1.03E-09 0.0 0.0 2.39E-09 0.0 4898.917 -5.37E-05 

Please note that because this analysis makes computations of ultimate moment 

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 1: 

Pile-head deflection = .04747209 m 

Computed slope at pile head = -.03558708 

Maximum bending moment = 119.161 kN- m 

Maximum shear force = 365.000 kN 

Depth of maximum bending moment = 1.17241379 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 37 

Number of zero deflection points = 6 

------------------------------------------------------------------------------ 

 Summary of Pile-head Response 

------------------------------------------------------------------------------ 

Definition of symbols for pile-head boundary conditions: 

y = pile-head displacment, m 

M = pile-head moment, kN- m 

V = pile-head shear force, kN 

S = pile-head slope, radians 

R = rotational stiffness of pile-head, m- kN/rad 

 BC Boundary Boundary Axial Pile Head Maximum Maximum 

Type Condition Condition Load Deflection Moment Shear 

 1 2 kN m m- kN kN 

---- ------------ ------------ ----------- ----------- ----------- ----------- 

 1 V = 365.000 M = -83.500 0.0000 .047472 119.1608 365.0000
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-25 December 2005

=============================================================== 

 LPILE Plus for Windows, Version 4.0 (4.0.8) 

 Analysis of Individual Piles and Drilled Shafts 

 Subjected to Lateral Loading Using the p-y Method 

 (c) Copyright ENSOFT, Inc., 1985-2003 

 All Rights Reserved 

=============================================================== 

Path to file locations: L:\Programs\LPILE\Chapter 6\Ch. 6 Example with P=474.5\P=0 case\ 

Name of input data file: Down analysis(P=0)2.lpd 

Name of output file: Down analysis(P=0)2.lpo 

Name of plot output file: Down analysis(P=0)2.lpp 

Name of runtime file: Down analysis(P=0)2.lpr 

------------------------------------------------------------------------------ 

 Time and Date of Analysis 

------------------------------------------------------------------------------ 

 Date: May 4, 2005 Time: 16:57:32 

------------------------------------------------------------------------------ 

 Problem Title 

------------------------------------------------------------------------------ 

Down Analysis with P=0 Case 

------------------------------------------------------------------------------ 

 Program Options 

------------------------------------------------------------------------------ 

Units Used in Computations - SI Units, meters, kilopascals 

Basic Program Options: 

Analysis Type 3: 

- Computation of Nonlinear Bending Stiffness and Ultimate Bending Moment 

 Capacity with Pile Response Computed Using Nonlinear EI 

Computation Options: 

- User-specified p-y curves used in analysis 

- Analysis uses p-y multiplers for group action 

- Analysis assumes no shear resistance at pile tip 

- Analysis for fixed-length pile or shaft only 

- No computation of foundation stiffness matrix elements 

- Output pile response for full length of pile 

- Analysis assumes no soil movements acting on pile 

- Additional p-y curves computed at specified depths 

Solution Control Parameters: 

- Number of pile increments = 145 

- Maximum number of iterations allowed = 100 

- Deflection tolerance for convergence = 2.5400E-07 m 

- Maximum allowable deflection = 2.5400E+00 m 

Printing Options: 

- Values of pile-head deflection, bending moment, shear force, and 

 soil reaction are printed for full length of pile. 

- Printing Increment (spacing of output points) = 1 

------------------------------------------------------------------------------ 

 Pile Structural Properties and Geometry 

------------------------------------------------------------------------------ 

Pile Length = 4.50 m 

Depth of ground surface below top of pile = .00 m 

Slope angle of ground surface = .00 deg. 

Structural properties of pile defined using 2 points 

Point Depth Pile Moment of Pile Modulus of 

 X Diameter Inertia Area Elasticity 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-26 December 2005

 m m m**4 Sq. m kN/Sq. m 

----- --------- ----------- ---------- ---------- ----------- 

 1 0.0000 .17780000 1.0000 .024800 200000000.000 

 2 4.5000 .17780000 1.0000 .024800 200000000.000 

Please note that because this analysis makes computations of ultimate 

moment capacity and pile response using nonlinear bending stiffness 

that the above values of moment of inertia and modulus of are not used 

for any computations other than total stress due to combined axial 

loading and bending. 

------------------------------------------------------------------------------ 

 Soil and Rock Layering Information 

------------------------------------------------------------------------------ 

The soil profile is modelled using 1 layers 

Layer 1 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = .000 m 

Distance from top of pile to bottom of layer = 6.000 m 

(Depth of lowest layer extends 1.50 m below pile tip) 

------------------------------------------------------------------------------ 

 Effective Unit Weight of Soil vs. Depth 

------------------------------------------------------------------------------ 

Distribution of effective unit weight of soil with depth 

is defined using 2 points 

Point Depth X Eff. Unit Weight 

 No. m kN/ m**3 

----- ---------- ---------------- 

 1 .00 12.20000 

 2 6.00 12.20000 

------------------------------------------------------------------------------ 

 Shear Strength of Soils 

------------------------------------------------------------------------------ 

Distribution of shear strength parameters with depth 

defined using 0 points 

Point Depth X Cohesion c Angle of Friction E50 or RQD 

 No. m kN/ m**2 Deg. k_rm % 

----- -------- ---------- ------------------ ------ ------ 

Notes: 

(1) Cohesion = uniaxial compressive strength for rock materials. 

(2) Values of E50 are reported for clay strata. 

(3) Default values will be generated for E50 when input values are 0. 

(4) RQD and k_rm are reported only for weak rock strata. 

------------------------------------------------------------------------------ 

 p-y Modification Factors 

------------------------------------------------------------------------------ 

Distribution of p-y multipliers with depth defined using 2 points 

Point Depth X p-mult y-mult 

 No. m 

----- ---------- ---------- ---------- 

 1 .000 1.0000 1.0000 

 2 6.000 1.0000 1.0000 

------------------------------------------------------------------------------ 

 User-specified p-y Curves 

------------------------------------------------------------------------------ 

User-specified p-y curves defined using 2 curves. 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-27 December 2005

User-specified curve number 1 at depth = .000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0001 263.064 

 3 .0002 312.838 

 4 .0006 393.373 

 5 .0011 467.802 

 6 .0017 517.708 

 7 .0023 556.313 

 8 .0057 699.527 

 9 .0115 831.882 

 10 .0229 989.280 

 11 .0258 989.280 

 12 .0286 989.280 

User-specified curve number 2 at depth = 6.000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0001 263.064 

 3 .0002 312.838 

 4 .0006 393.373 

 5 .0011 467.802 

 6 .0017 517.708 

 7 .0023 556.313 

 8 .0057 699.527 

 9 .0115 831.882 

 10 .0229 989.280 

 11 .0258 989.280 

 12 .0286 989.280 

------------------------------------------------------------------------------ 

 Loading Type 

------------------------------------------------------------------------------ 

Static loading criteria was used for computation of p-y curves 

------------------------------------------------------------------------------ 

 Pile-head Loading and Pile-head Fixity Conditions 

------------------------------------------------------------------------------ 

Number of loads specified = 1 

Load Case Number 1 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Shear force at pile head = 365.000 kN 

Bending moment at pile head = 83.550 m- kN 

Axial load at pile head = .000 kN 

Non-zero moment at pile head for this load case indicates the pile-head 

may rotate under the applied pile-head loading, but is not a free-head 

(zero moment) condition. 

------------------------------------------------------------------------------ 

 Output of p-y Curves at Specified Depths 

------------------------------------------------------------------------------ 

p-y curves are generated and printed for verification at 2 depths. 

Depth Depth Below Pile Head Depth Below Ground Surface 

 No. m m 

----- --------------------- -------------------------- 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-28 December 2005

 1 .000 .000 

 2 4.500 4.500 

------------------------------------------------------------------------------ 

 Computations of Ultimate Moment Capacity and Nonlinear Bending Stiffness 

------------------------------------------------------------------------------ 

Pile Description: 

The sectional shape is a circular shaft with steel casing. 

Outside Diameter = .1778 m 

Wall thickness of steel shell = .0115 m 

Cross-sectional area of shell = .00601 m**2 

Moment of inertia of steel shell = 2.08692E-05 m**4 

Material Properties: 

Compressive Strength of Concrete = 27600.000 kN/ m**2 

Yield Stress of Reinforcement = 0. kN/ m**2 

Steel shell or core yield stress = 552000. kN/ m**2 

Modulus of Elasticity of Reinforcement = 200000000. kN/ m**2 

Cover Thickness (edge to bar center) = .000 m 

Number of Reinforcing Bars = 10 

Area of Single Bar = .00000 m**2 

Number of Rows of Reinforcing Bars = 5 

Ultimate Axial Squash Load Capacity = 3758.02 kN 

Distribution and Area of Steel Reinforcement 

 Row Area of Distance to 

Number Reinforcement Centroidal Axis 

 m**2 m 

------ ------------- --------------- 

 1 .000000 .0736 

 2 .000000 .0455 

 3 .000000 .0000 

 4 .000000 -.0455 

 5 .000000 -.0736 

Axial Thrust Force = .00 kN 

 Bending Bending Bending Maximum Neutral Axis 

 Moment Stiffness Curvature Strain Position 

 kN-m kN-m2 rad/m m/m m 

 ------------- ------------- ------------- ------------- ------------- 

 1.73583660 4898.917 .00035433 .00002742 .08889729 

 2.50651820 4897.351 .00051181 .00003961 .08889729 

 3.27670667 4895.785 .00066929 .00005180 .08889729 

 4.04640201 4894.220 .00082677 .00006399 .08889729 

 4.81560422 4892.654 .00098425 .00007618 .08889729 

 5.58431330 4891.088 .00114173 .00008837 .08889729 

 6.35252925 4889.522 .00129921 .00010056 .08889729 

 6.55060560 4496.902 .00145669 .00010411 .08297207 

 7.25778201 4496.284 .00161417 .00011537 .08297207 

 7.96476385 4495.667 .00177165 .00012662 .08297207 

 8.67155112 4495.049 .00192913 .00013788 .08297207 

 9.37814382 4494.431 .00208661 .00014913 .08297207 

 10.085 4493.813 .00224409 .00016039 .08297207 

 10.791 4493.196 .00240157 .00017165 .08297207 

 11.497 4492.578 .00255906 .00018290 .08297207 

 12.203 4491.960 .00271654 .00019416 .08297207 

 12.908 4491.342 .00287402 .00020541 .08297207 

 13.614 4490.725 .00303150 .00021667 .08297207 

 14.319 4490.107 .00318898 .00022792 .08297207 

 15.024 4489.489 .00334646 .00023918 .08297207 

 15.729 4488.871 .00350394 .00025043 .08297207 

 16.433 4488.254 .00366142 .00026169 .08297207 

 17.138 4487.636 .00381890 .00027294 .08297207 

 17.842 4487.018 .00397638 .00028420 .08297207 

 23.118 4482.385 .00515748 .00036862 .08297207 

 28.383 4477.752 .00633858 .00045303 .08297207 

 33.636 4473.118 .00751969 .00053745 .08297207 

 38.879 4468.485 .00870079 .00062186 .08297207 

 44.111 4463.852 .00988189 .00070628 .08297207 

 49.332 4459.219 .01106299 .00079069 .08297207 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-29 December 2005

 54.542 4454.586 .01224409 .00087511 .08297207 

 57.662 4295.045 .01342520 .00095982 .08299377 

 62.752 4296.211 .01460630 .00104577 .08309687 

 67.845 4297.412 .01578740 .00113196 .08319996 

 72.947 4298.973 .01696850 .00121848 .08330848 

 78.054 4300.601 .01814961 .00130527 .08341700 

 83.173 4302.638 .01933071 .00139241 .08353095 

 88.306 4305.127 .02051181 .00147993 .08365032 

 93.456 4308.127 .02169291 .00156786 .08377512 

 98.635 4312.080 .02287402 .00165633 .08391077 

 103.850 4317.171 .02405512 .00174537 .08405727 

 109.135 4324.538 .02523622 .00183532 .08422548 

 116.274 4401.446 .02641732 .00194228 .08502310 

 121.355 4397.159 .02759843 .00203107 .08509364 

 126.423 4392.803 .02877953 .00212002 .08516418 

 131.480 4388.413 .02996063 .00220914 .08523472 

 136.408 4380.233 .03114173 .00229741 .08527270 

 141.002 4362.312 .03232283 .00238314 .08522929 

 145.110 4331.145 .03350394 .00246586 .08509907 

 145.110 4183.660 .03468504 .00250950 .08385108 

 147.008 4098.795 .03586614 .00257802 .08337902 

 153.523 4143.973 .03704724 .00264784 .08297207 

 155.871 4077.375 .03822835 .00273226 .08297207 

 157.833 4004.950 .03940945 .00281667 .08297207 

 159.521 3929.994 .04059055 .00290109 .08297207 

 161.057 3855.647 .04177165 .00298551 .08297207 

 162.411 3781.163 .04295276 .00306992 .08297207 

 163.614 3707.213 .04413386 .00315434 .08297207 

 164.745 3635.565 .04531496 .00323875 .08297207 

 165.711 3563.988 .04649606 .00332317 .08297207 

 166.656 3495.506 .04767717 .00340759 .08297207 

 167.455 3427.355 .04885827 .00349200 .08297207 

 168.240 3362.162 .05003937 .00357642 .08297207 

 168.926 3298.012 .05122047 .00366083 .08297207 

 169.575 3236.065 .05240157 .00374525 .08297207 

 170.188 3176.179 .05358268 .00382966 .08297207 

Ultimate Moment Capacity at a Concrete Strain of 0.003 = 161.289 m- kN 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 1 

Depth below ground surface = .000 m 

Depth below pile head = .000 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 452.916 

 .0011 468.738 

 .0022 551.327 

 .0033 599.856 

 .0044 646.664 

 .0056 693.472 

 .0067 721.605 

 .0078 746.964 

 .0089 772.322 

 .0100 797.681 

 .0111 823.039 

 .0122 841.875 

 .0133 857.218 

 .0356 989.280 

 .0667 989.280 

 .0889 989.280 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 1 

Depth below ground surface = 4.500 m 

Depth below pile head = 4.500 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-30 December 2005

 .0000 .000 

 .0010 452.916 

 .0011 468.738 

 .0022 551.327 

 .0033 599.856 

 .0044 646.664 

 .0056 693.472 

 .0067 721.605 

 .0078 746.964 

 .0089 772.322 

 .0100 797.681 

 .0111 823.039 

 .0122 841.875 

 .0133 857.218 

 .0356 989.280 

 .0667 989.280 

 .0889 989.280 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 1 

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Specified shear force at pile head = 365.000 kN 

Specified bending moment at pile head = 83.550 m- kN 

Specified axial load at pile head = .000 kN 

Non-zero moment for this load case indicates the pile-head may rotate under 

the applied pile-head loading, but is not a free-head (zero moment )condition. 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 .018217 83.5500 365.0 -.034791 7.4276 4308.873 -924.626 

 .03103 .017146 94.4323 336.5 -.034150 8.3950 4308.873 -909.848 

 .06207 .016097 104.4 308.5 -.033434 9.2846 4308.873 -895.361 

 .09310 .015071 113.6 281.0 -.032654 10.0974 4372.671 -881.196 

 .124 .014070 121.9 253.8 -.031821 10.8349 4396.710 -867.377 

 .155 .013096 129.3 227.1 -.030934 11.4980 4390.275 -853.926 

 .186 .012150 136.0 200.8 -.029995 12.0880 4380.956 -840.867 

 .217 .011234 141.8 175.0 -.029009 12.6061 4356.298 -825.824 

 .248 .010350 146.8 149.6 -.027949 13.0534 4107.092 -805.638 

 .279 .009499 151.1 124.9 -.026826 13.4318 4127.178 -786.238 

 .310 .008685 154.6 100.8 -.025675 13.7428 4114.353 -767.642 

 .341 .007906 157.3 77.2742 -.024485 13.9881 4023.546 -749.872 

 .372 .007165 159.4 54.2647 -.023250 14.1692 3936.500 -732.961 

 .403 .006463 160.7 31.7662 -.021978 14.2875 3873.168 -716.940 

 .434 .005801 161.4 9.7508 -.020682 14.3445 3840.358 -701.832 

 .466 .005179 161.3 -11.6541 -.019378 14.3413 3842.253 -677.591 

 .497 .004598 160.6 -32.3029 -.018084 14.2802 3877.346 -653.111 

 .528 .004057 159.3 -52.2180 -.016814 14.1631 3939.755 -630.311 

 .559 .003554 157.4 -71.4511 -.015579 13.9920 4021.915 -609.152 

 .590 .003090 154.9 -90.0521 -.014386 13.7688 4106.068 -589.582 

 .621 .002661 151.8 -108.1 -.013231 13.4951 4132.105 -571.541 

 .652 .002268 148.2 -125.5 -.012101 13.1725 4106.921 -554.288 

 .683 .001910 144.0 -142.4 -.011026 12.8024 4339.559 -531.243 

 .714 .001584 139.3 -158.5 -.010017 12.3868 4368.838 -508.070 

 .745 .001289 134.2 -173.9 -.009047 11.9278 4383.952 -483.492 

 .776 .001023 128.5 -188.5 -.008118 11.4273 4390.966 -456.274 

 .807 7.85E-04 122.5 -202.1 -.007231 10.8877 4396.200 -420.874 

 .838 5.74E-04 116.0 -214.6 -.006390 10.3122 4398.493 -388.085 

 .869 3.88E-04 109.1 -226.1 -.005589 9.7033 4324.687 -350.722 

 .900 2.27E-04 102.0 -236.5 -.004830 9.0645 4315.330 -318.257 

 .931 8.83E-05 94.4704 -245.0 -.004124 8.3984 4308.902 -232.174 

 .962 -2.92E-05 86.7542 -247.4 -.003471 7.7124 4304.375 76.704 

 .993 -1.27E-04 79.1119 -242.0 -.002872 7.0330 4301.022 276.556 

 1.024 -2.07E-04 71.7359 -232.8 -.002328 6.3773 4298.603 314.318 

 1.055 -2.72E-04 64.6627 -222.8 -.001836 5.7485 4296.661 327.253 

 1.086 -3.21E-04 57.9047 -212.5 -.001393 5.1477 4295.101 337.267 

 1.117 -3.58E-04 51.4715 -201.9 -.001005 4.5758 4457.318 344.665 

 1.148 -3.84E-04 45.3703 -191.2 -6.68E-04 4.0334 4462.736 349.823 

 1.179 -4.00E-04 39.6060 -180.3 -3.72E-04 3.5210 4467.843 353.010 

 1.210 -4.07E-04 34.1817 -169.3 -1.16E-04 3.0388 4472.637 354.477 

 1.241 -4.07E-04 29.0988 -158.3 1.03E-04 2.5869 4477.121 354.462 

 1.272 -4.00E-04 24.3573 -147.3 2.89E-04 2.1654 4481.295 353.187 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-31 December 2005

 1.303 -3.89E-04 19.9560 -136.4 4.42E-04 1.7741 4485.163 350.857 

 1.334 -3.73E-04 15.8926 -125.5 5.66E-04 1.4129 4488.728 347.665 

 1.366 -3.54E-04 12.1641 -114.8 6.63E-04 1.0814 4491.994 343.786 

 1.397 -3.32E-04 8.7666 -104.2 7.35E-04 .7794 4494.966 339.382 

 1.428 -3.08E-04 5.6961 -93.7483 7.83E-04 .5064 4890.861 334.599 

 1.459 -2.83E-04 2.9478 -83.4419 8.11E-04 .2621 4896.454 329.591 

 1.490 -2.58E-04 .5169 -73.2928 8.22E-04 4.60E-02 4898.917 324.466 

 1.521 -2.32E-04 -1.6014 -63.3030 8.18E-04 .1424 4898.917 319.321 

 1.552 -2.07E-04 -3.4122 -53.4719 8.03E-04 .3033 4895.509 314.239 

 1.583 -1.82E-04 -4.9204 -43.8773 7.76E-04 .4374 4892.440 304.075 

 1.614 -1.59E-04 -6.1357 -34.6228 7.41E-04 .5455 4889.964 292.328 

 1.645 -1.36E-04 -7.0694 -25.7235 6.97E-04 .6285 4496.449 281.182 

 1.676 -1.16E-04 -7.7323 -17.1585 6.46E-04 .6874 4495.870 270.789 

 1.707 -9.63E-05 -8.1344 -9.0255 5.91E-04 .7231 4495.518 253.333 

 1.738 -7.88E-05 -8.2925 -1.8770 5.35E-04 .7372 4495.380 207.349 

 1.769 -6.31E-05 -8.2509 3.9169 4.78E-04 .7335 4495.416 166.039 

 1.800 -4.92E-05 -8.0494 8.5010 4.21E-04 .7156 4495.593 129.379 

 1.831 -3.70E-05 -7.7232 12.0177 3.67E-04 .6866 4495.878 97.255 

 1.862 -2.64E-05 -7.3034 14.6051 3.15E-04 .6493 4496.244 69.484 

 1.893 -1.74E-05 -6.8167 16.3944 2.66E-04 .6060 4496.670 45.829 

 1.924 -9.89E-06 -6.2859 17.5092 2.23E-04 .5588 4889.658 26.015 

 1.955 -3.60E-06 -5.7299 18.0596 1.85E-04 .5094 4890.791 9.457 

 1.986 1.57E-06 -5.1649 18.1423 1.50E-04 .4592 4891.942 -4.131 

 2.017 5.72E-06 -4.6039 17.8447 1.19E-04 .4093 4893.085 -15.045 

 2.048 8.96E-06 -4.0573 17.2454 9.16E-05 .3607 4894.197 -23.575 

 2.079 1.14E-05 -3.5335 16.4140 6.76E-05 .3141 4895.263 -30.005 

 2.110 1.32E-05 -3.0385 15.4115 4.67E-05 .2701 4896.269 -34.605 

 2.141 1.43E-05 -2.5769 14.2905 2.89E-05 .2291 4897.208 -37.633 

 2.172 1.50E-05 -2.1515 13.0963 1.39E-05 .1913 4898.072 -39.329 

 2.203 1.52E-05 -1.7640 11.8667 1.54E-06 .1568 4898.859 -39.911 

 2.234 1.50E-05 -1.4150 10.6332 -8.53E-06 .1258 4898.917 -39.580 

 2.266 1.46E-05 -1.1040 9.4213 -1.65E-05 9.81E-02 4898.917 -38.518 

 2.297 1.40E-05 -.8302 8.2513 -2.26E-05 7.38E-02 4898.917 -36.885 

 2.328 1.32E-05 -.5919 7.1386 -2.71E-05 5.26E-02 4898.917 -34.823 

 2.359 1.23E-05 -.3871 6.0946 -3.02E-05 3.44E-02 4898.917 -32.455 

 2.390 1.14E-05 -.2136 5.1272 -3.21E-05 1.90E-02 4898.917 -29.886 

 2.421 1.03E-05 -6.89E-02 4.2413 -3.30E-05 6.12E-03 4898.917 -27.207 

 2.452 9.31E-06 4.97E-02 3.4391 -3.31E-05 4.41E-03 4898.917 -24.492 

 2.483 8.29E-06 .1446 2.7207 -3.25E-05 1.29E-02 4898.917 -21.803 

 2.514 7.29E-06 .2185 2.0847 -3.13E-05 1.94E-02 4898.917 -19.188 

 2.545 6.34E-06 .2740 1.5280 -2.98E-05 2.44E-02 4898.917 -16.687 

 2.576 5.45E-06 .3134 1.0467 -2.79E-05 2.79E-02 4898.917 -14.327 

 2.607 4.61E-06 .3390 .6362 -2.58E-05 3.01E-02 4898.917 -12.130 

 2.638 3.84E-06 .3529 .2911 -2.37E-05 3.14E-02 4898.917 -10.108 

 2.669 3.14E-06 .3570 5.98E-03 -2.14E-05 3.17E-02 4898.917 -8.268 

 2.700 2.51E-06 .3532 -.2249 -1.92E-05 3.14E-02 4898.917 -6.613 

 2.731 1.95E-06 .3431 -.4073 -1.69E-05 3.05E-02 4898.917 -5.140 

 2.762 1.46E-06 .3280 -.5467 -1.48E-05 2.92E-02 4898.917 -3.845 

 2.793 1.03E-06 .3091 -.6486 -1.28E-05 2.75E-02 4898.917 -2.720 

 2.824 6.67E-07 .2877 -.7181 -1.09E-05 2.56E-02 4898.917 -1.755 

 2.855 3.57E-07 .2646 -.7598 -9.17E-06 2.35E-02 4898.917 -.937989 

 2.886 9.81E-08 .2405 -.7784 -7.57E-06 2.14E-02 4898.917 -.258135 

 2.917 -1.13E-07 .2162 -.7778 -6.12E-06 1.92E-02 4898.917 .297320 

 2.948 -2.82E-07 .1923 -.7617 -4.82E-06 1.71E-02 4898.917 .740935 

 2.979 -4.12E-07 .1690 -.7333 -3.68E-06 1.50E-02 4898.917 1.085 

 3.010 -5.10E-07 .1467 -.6957 -2.68E-06 1.30E-02 4898.917 1.342 

 3.041 -5.79E-07 .1258 -.6512 -1.82E-06 1.12E-02 4898.917 1.523 

 3.072 -6.23E-07 .1063 -.6022 -1.08E-06 9.45E-03 4898.917 1.639 

 3.103 -6.46E-07 8.84E-02 -.5504 -4.65E-07 7.86E-03 4898.917 1.700 

 3.134 -6.52E-07 7.21E-02 -.4974 4.31E-08 6.41E-03 4898.917 1.715 

 3.166 -6.43E-07 5.75E-02 -.4445 4.54E-07 5.12E-03 4898.917 1.692 

 3.197 -6.24E-07 4.46E-02 -.3928 7.77E-07 3.96E-03 4898.917 1.641 

 3.228 -5.95E-07 3.32E-02 -.3431 1.02E-06 2.95E-03 4898.917 1.566 

 3.259 -5.60E-07 2.33E-02 -.2959 1.20E-06 2.07E-03 4898.917 1.473 

 3.290 -5.21E-07 1.48E-02 -.2518 1.32E-06 1.31E-03 4898.917 1.369 

 3.321 -4.78E-07 7.64E-03 -.2110 1.39E-06 6.79E-04 4898.917 1.257 

 3.352 -4.34E-07 1.69E-03 -.1738 1.42E-06 1.51E-04 4898.917 1.142 

 3.383 -3.90E-07 -3.15E-03 -.1402 1.42E-06 2.80E-04 4898.917 1.025 

 3.414 -3.46E-07 -7.01E-03 -.1101 1.39E-06 6.23E-04 4898.917 .910081 

 3.445 -3.04E-07 -9.99E-03 -8.36E-02 1.33E-06 8.88E-04 4898.917 .798699 

 3.476 -2.63E-07 -1.22E-02 -6.05E-02 1.26E-06 1.08E-03 4898.917 .692482 

 3.507 -2.25E-07 -1.37E-02 -4.06E-02 1.18E-06 1.22E-03 4898.917 .592574 

 3.538 -1.90E-07 -1.47E-02 -2.36E-02 1.09E-06 1.31E-03 4898.917 .499773 

 3.569 -1.58E-07 -1.52E-02 -9.42E-03 9.95E-07 1.35E-03 4898.917 .414584 

 3.600 -1.28E-07 -1.53E-02 2.25E-03 8.99E-07 1.36E-03 4898.917 .337260 

 3.631 -1.02E-07 -1.51E-02 1.16E-02 8.02E-07 1.34E-03 4898.917 .267849 

 3.662 -7.84E-08 -1.46E-02 1.90E-02 7.09E-07 1.30E-03 4898.917 .206231 

 3.693 -5.78E-08 -1.39E-02 2.46E-02 6.18E-07 1.23E-03 4898.917 .152152 

 3.724 -4.00E-08 -1.31E-02 2.86E-02 5.33E-07 1.16E-03 4898.917 .105257 

 3.755 -2.48E-08 -1.21E-02 3.12E-02 4.53E-07 1.08E-03 4898.917 .065112 

 3.786 -1.19E-08 -1.11E-02 3.27E-02 3.80E-07 9.88E-04 4898.917 .031234 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-32 December 2005

 3.817 -1.18E-09 -1.01E-02 3.32E-02 3.13E-07 8.97E-04 4898.917 .003106 

 3.848 7.53E-09 -9.05E-03 3.30E-02 2.52E-07 8.05E-04 4898.917 -.019805 

 3.879 1.45E-08 -8.04E-03 3.21E-02 1.98E-07 7.15E-04 4898.917 -.038032 

 3.910 1.98E-08 -7.06E-03 3.07E-02 1.50E-07 6.28E-04 4898.917 -.052101 

 3.941 2.38E-08 -6.14E-03 2.89E-02 1.08E-07 5.46E-04 4898.917 -.062516 

 3.972 2.65E-08 -5.27E-03 2.68E-02 7.20E-08 4.69E-04 4898.917 -.069757 

 4.003 2.82E-08 -4.47E-03 2.46E-02 4.11E-08 3.98E-04 4898.917 -.074271 

 4.034 2.91E-08 -3.74E-03 2.23E-02 1.51E-08 3.33E-04 4898.917 -.076472 

 4.066 2.92E-08 -3.09E-03 1.99E-02 -6.55E-09 2.75E-04 4898.917 -.076737 

 4.097 2.87E-08 -2.51E-03 1.75E-02 -2.43E-08 2.23E-04 4898.917 -.075404 

 4.128 2.77E-08 -2.00E-03 1.52E-02 -3.86E-08 1.78E-04 4898.917 -.072772 

 4.159 2.63E-08 -1.57E-03 1.30E-02 -4.99E-08 1.39E-04 4898.917 -.069104 

 4.190 2.46E-08 -1.19E-03 1.09E-02 -5.86E-08 1.06E-04 4898.917 -.064628 

 4.221 2.26E-08 -8.85E-04 9.02E-03 -6.52E-08 7.87E-05 4898.917 -.059533 

 4.252 2.05E-08 -6.34E-04 7.26E-03 -7.00E-08 5.64E-05 4898.917 -.053981 

 4.283 1.83E-08 -4.35E-04 5.68E-03 -7.34E-08 3.86E-05 4898.917 -.048101 

 4.314 1.60E-08 -2.82E-04 4.28E-03 -7.57E-08 2.50E-05 4898.917 -.041996 

 4.345 1.36E-08 -1.69E-04 3.07E-03 -7.71E-08 1.50E-05 4898.917 -.035745 

 4.376 1.12E-08 -9.10E-05 2.06E-03 -7.79E-08 8.09E-06 4898.917 -.029407 

 4.407 8.75E-09 -4.11E-05 1.25E-03 -7.83E-08 3.66E-06 4898.917 -.023022 

 4.438 6.32E-09 -1.35E-05 6.33E-04 -7.85E-08 1.20E-06 4898.917 -.016615 

 4.469 3.88E-09 -1.82E-06 2.17E-04 -7.86E-08 1.62E-07 4898.917 -.010202 

 4.500 1.44E-09 0.0 0.0 -7.86E-08 0.0 4898.917 -.003788 

Please note that because this analysis makes computations of ultimate moment 

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 1: 

Pile-head deflection = .01821670 m 

Computed slope at pile head = -.03479080 

Maximum bending moment = 161.355 kN- m 

Maximum shear force = 365.000 kN 

Depth of maximum bending moment = .43448276 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 24 

Number of zero deflection points = 5 

------------------------------------------------------------------------------ 

 Summary of Pile-head Response 

------------------------------------------------------------------------------ 

Definition of symbols for pile-head boundary conditions: 

y = pile-head displacment, m 

M = pile-head moment, kN- m 

V = pile-head shear force, kN 

S = pile-head slope, radians 

R = rotational stiffness of pile-head, m- kN/rad 

 BC Boundary Boundary Axial Pile Head Maximum Maximum 

Type Condition Condition Load Deflection Moment Shear 

 1 2 kN m m- kN kN 

---- ------------ ------------ ----------- ----------- ----------- ----------- 

 1 V = 365.000 M = 83.550 0.0000 .018217 161.3551 365.0000 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-33 December 2005

============================================================================== 

 LPILE Plus for Windows, Version 4.0 (4.0.8) 

 Analysis of Individual Piles and Drilled Shafts 

 Subjected to Lateral Loading Using the p-y Method 

 (c) Copyright ENSOFT, Inc., 1985-2003 

 All Rights Reserved 

============================================================================== 

Path to file locations: L:\Programs\LPILE\Chapter 6\Ch. 6 Example with P=474.5\P=Pult\ 

Name of input data file: Up analysis.lpd 

Name of output file: Up analysis.lpo 

Name of plot output file: Up analysis.lpp 

Name of runtime file: Up analysis.lpr 

------------------------------------------------------------------------------ 

 Time and Date of Analysis 

------------------------------------------------------------------------------ 

 Date: May 4, 2005 Time: 17: 5:12 

------------------------------------------------------------------------------ 

 Problem Title 

------------------------------------------------------------------------------ 

Up Analysis for P=474.5 Case 

------------------------------------------------------------------------------ 

 Program Options 

------------------------------------------------------------------------------ 

Units Used in Computations - SI Units, meters, kilopascals 

Basic Program Options: 

Analysis Type 3: 

- Computation of Nonlinear Bending Stiffness and Ultimate Bending Moment 

 Capacity with Pile Response Computed Using Nonlinear EI 

Computation Options: 

- User-specified p-y curves used in analysis 

- Analysis uses p-y multiplers for group action 

- Analysis assumes no shear resistance at pile tip 

- Analysis for fixed-length pile or shaft only 

- No computation of foundation stiffness matrix elements 

- Output pile response for full length of pile 

- Analysis assumes no soil movements acting on pile 

- Additional p-y curves computed at specified depths 

Solution Control Parameters: 

- Number of pile increments = 145 

- Maximum number of iterations allowed = 100 

- Deflection tolerance for convergence = 2.5400E-07 m 

- Maximum allowable deflection = 2.5400E+00 m 

Printing Options: 

- Values of pile-head deflection, bending moment, shear force, and 

 soil reaction are printed for full length of pile. 

- Printing Increment (spacing of output points) = 1 

------------------------------------------------------------------------------ 

 Pile Structural Properties and Geometry 

------------------------------------------------------------------------------ 

Pile Length = 10.00 m 

Depth of ground surface below top of pile = .00 m 

Slope angle of ground surface = .00 deg. 

Structural properties of pile defined using 2 points 

Point Depth Pile Moment of Pile Modulus of 

 X Diameter Inertia Area Elasticity 

 m m m**4 Sq. m kN/Sq. m 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-34 December 2005

----- --------- ----------- ---------- ---------- ----------- 

 1 0.0000 .17780000 1.0000 .024800 200000000.000 

 2 10.0000 .17780000 1.0000 .024800 200000000.000 

Please note that because this analysis makes computations of ultimate 

moment capacity and pile response using nonlinear bending stiffness 

that the above values of moment of inertia and modulus of are not used 

for any computations other than total stress due to combined axial 

loading and bending. 

------------------------------------------------------------------------------ 

 Soil and Rock Layering Information 

------------------------------------------------------------------------------ 

The soil profile is modelled using 4 layers 

Layer 1 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = .000 m 

Distance from top of pile to bottom of layer = 5.290 m 

Layer 2 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = 5.290 m 

Distance from top of pile to bottom of layer = 5.310 m 

Layer 3 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = 5.310 m 

Distance from top of pile to bottom of layer = 8.000 m 

Layer 4 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = 8.000 m 

Distance from top of pile to bottom of layer = 10.000 m 

(Depth of lowest layer extends .00 m below pile tip) 

------------------------------------------------------------------------------ 

 Effective Unit Weight of Soil vs. Depth 

------------------------------------------------------------------------------ 

Distribution of effective unit weight of soil with depth 

is defined using 8 points 

Point Depth X Eff. Unit Weight 

 No. m kN/ m**3 

----- ---------- ---------------- 

 1 .00 11.40000 

 2 5.29 11.40000 

 3 5.29 11.40000 

 4 5.31 21.20000 

 5 5.31 21.20000 

 6 8.00 21.20000 

 7 8.00 21.20000 

 8 10.00 21.20000 

------------------------------------------------------------------------------ 

 Shear Strength of Soils 

------------------------------------------------------------------------------ 

Distribution of shear strength parameters with depth 

defined using 0 points 

Point Depth X Cohesion c Angle of Friction E50 or RQD 

 No. m kN/ m**2 Deg. k_rm % 

----- -------- ---------- ------------------ ------ ------ 

Notes: 

(1) Cohesion = uniaxial compressive strength for rock materials. 

(2) Values of E50 are reported for clay strata. 

(3) Default values will be generated for E50 when input values are 0. 

(4) RQD and k_rm are reported only for weak rock strata. 

------------------------------------------------------------------------------ 

 p-y Modification Factors 

------------------------------------------------------------------------------ 

Distribution of p-y multipliers with depth defined using 5 points 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-35 December 2005

Point Depth X p-mult y-mult 

 No. m 

----- ---------- ---------- ---------- 

 1 .000 1.0000 1.0000 

 2 5.290 1.0000 1.0000 

 3 5.310 1.0000 1.0000 

 4 8.000 1.0000 1.0000 

 5 10.000 1.0000 1.0000 

------------------------------------------------------------------------------ 

 User-specified p-y Curves 

------------------------------------------------------------------------------ 

User-specified p-y curves defined using 8 curves. 

User-specified curve number 1 at depth = .000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 92.072 

 3 .0004 109.493 

 4 .0009 137.680 

 5 .0018 163.731 

 6 .0027 181.198 

 7 .0037 194.710 

 8 .0092 244.834 

 9 .0183 291.159 

 10 .0366 346.248 

 11 .0412 346.248 

 12 .0458 346.248 

User-specified curve number 2 at depth = 5.290 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 92.072 

 3 .0004 109.493 

 4 .0009 137.680 

 5 .0018 163.731 

 6 .0027 181.198 

 7 .0037 194.710 

 8 .0092 244.834 

 9 .0183 291.159 

 10 .0366 346.248 

 11 .0412 346.248 

 12 .0458 346.248 

User-specified curve number 3 at depth = 5.290 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 92.072 

 3 .0004 109.493 

 4 .0009 137.680 

 5 .0018 163.731 

 6 .0027 181.198 

 7 .0037 194.710 

 8 .0092 244.834 

 9 .0183 291.159 

 10 .0366 346.248 

 11 .0412 346.248 

 12 .0458 346.298 

User-specified curve number 4 at depth = 5.310 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-36 December 2005

 1 .0000 .000 

 2 .0002 65.766 

 3 .0005 78.209 

 4 .0011 98.343 

 5 .0023 116.950 

 6 .0034 129.427 

 7 .0046 139.078 

 8 .0115 174.882 

 9 .0229 207.971 

 10 .0458 247.320 

 11 .0515 247.320 

 12 .0573 247.320 

User-specified curve number 5 at depth = 5.310 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 65.766 

 3 .0005 78.209 

 4 .0011 98.343 

 5 .0023 116.950 

 6 .0034 129.427 

 7 .0046 139.078 

 8 .0115 174.882 

 9 .0229 207.971 

 10 .0458 247.320 

 11 .0515 247.320 

 12 .0573 247.320 

User-specified curve number 6 at depth = 8.000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 56.414 

 3 .0005 67.088 

 4 .0011 84.358 

 5 .0023 100.319 

 6 .0034 111.022 

 7 .0046 119.300 

 8 .0115 150.012 

 9 .0229 178.396 

 10 .0458 212.150 

 11 .0515 212.150 

 12 .0573 212.150 

User-specified curve number 7 at depth = 8.000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0002 56.414 

 3 .0005 67.088 

 4 .0011 84.358 

 5 .0023 100.319 

 6 .0034 111.022 

 7 .0046 119.300 

 8 .0115 150.012 

 9 .0229 178.396 

 10 .0458 212.150 

 11 .0515 212.150 

 12 .0573 212.150 

User-specified curve number 8 at depth = 10.000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0005 26.070 

 3 .0011 32.781 

 4 .0020 21.922 

 5 .0023 38.983 

 6 .0034 43.142 

 7 .0046 46.359 

 8 .0115 58.294 

 9 .0151 82.440 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-37 December 2005

 10 .0229 69.324 

 11 .0458 82.440 

 12 .0573 82.440 

------------------------------------------------------------------------------ 

 Loading Type 

------------------------------------------------------------------------------ 

Static loading criteria was used for computation of p-y curves 

------------------------------------------------------------------------------ 

 Pile-head Loading and Pile-head Fixity Conditions 

------------------------------------------------------------------------------ 

Number of loads specified = 1 

Load Case Number 1 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Shear force at pile head = 330.000 kN 

Bending moment at pile head = -76.200 m- kN 

Axial load at pile head = 474.500 kN 

Non-zero moment at pile head for this load case indicates the pile-head 

may rotate under the applied pile-head loading, but is not a free-head 

(zero moment) condition. 

------------------------------------------------------------------------------ 

 Output of p-y Curves at Specified Depths 

------------------------------------------------------------------------------ 

p-y curves are generated and printed for verification at 5 depths. 

Depth Depth Below Pile Head Depth Below Ground Surface 

 No. m m 

----- --------------------- -------------------------- 

 1 .000 .000 

 2 5.290 5.290 

 3 5.310 5.310 

 4 8.000 8.000 

 5 10.000 10.000 

Depth of ground surface below top of pile = .00 m 

------------------------------------------------------------------------------ 

 Computations of Ultimate Moment Capacity and Nonlinear Bending Stiffness 

------------------------------------------------------------------------------ 

Pile Description: 

The sectional shape is a circular shaft with steel casing. 

Outside Diameter = .1778 m 

Wall thickness of steel shell = .0115 m 

Cross-sectional area of shell = .00601 m**2 

Moment of inertia of steel shell = 2.08692E-05 m**4 

Material Properties: 

Compressive Strength of Concrete = 27600.000 kN/ m**2 

Yield Stress of Reinforcement = 0. kN/ m**2 

Steel shell or core yield stress = 552000. kN/ m**2 

Modulus of Elasticity of Reinforcement = 200000000. kN/ m**2 

Cover Thickness (edge to bar center) = .000 m 

Number of Reinforcing Bars = 10 

Area of Single Bar = .00000 m**2 

Number of Rows of Reinforcing Bars = 5 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-38 December 2005

Ultimate Axial Squash Load Capacity = 3758.02 kN 

Distribution and Area of Steel Reinforcement 

 Row Area of Distance to 

Number Reinforcement Centroidal Axis 

 m**2 m 

------ ------------- --------------- 

 1 .000000 .0736 

 2 .000000 .0455 

 3 .000000 .0000 

 4 .000000 -.0455 

 5 .000000 -.0736 

Axial Thrust Force = 474.50 kN 

 Bending Bending Bending Maximum Neutral Axis 

 Moment Stiffness Curvature Strain Position 

 kN-m kN-m2 rad/m m/m m 

 ------------- ------------- ------------- ------------- ------------- 

 1.69826245 4792.874 .00035433 .00031727 .90691267 

 2.45303965 4792.862 .00051181 .00032949 .65527803 

 3.20781175 4792.848 .00066929 .00034172 .52206775 

 3.96257836 4792.833 .00082677 .00035395 .43960844 

 4.71733626 4792.814 .00098425 .00036619 .38354674 

 5.47208598 4792.792 .00114173 .00037843 .34295465 

 6.22682760 4792.770 .00129921 .00039068 .31220536 

 6.98155916 4792.746 .00145669 .00040293 .28810838 

 7.73628058 4792.720 .00161417 .00041519 .26871577 

 8.49098340 4792.688 .00177165 .00042746 .25277953 

 9.24568013 4792.659 .00192913 .00043973 .23944236 

 10.000 4792.625 .00208661 .00045201 .22812367 

 10.755 4792.590 .00224409 .00046429 .21839481 

 11.510 4792.551 .00240157 .00047658 .20994649 

 12.264 4792.509 .00255906 .00048888 .20253996 

 13.019 4792.470 .00271654 .00050118 .19599075 

 13.774 4792.426 .00287402 .00051348 .19016320 

 14.528 4792.379 .00303150 .00052579 .18494336 

 15.283 4792.326 .00318898 .00053812 .18024442 

 16.035 4791.716 .00334646 .00055042 .17597957 

 16.774 4787.090 .00350394 .00056260 .17206198 

 17.571 4799.091 .00366142 .00057505 .16855677 

 18.301 4792.220 .00381890 .00058745 .16532828 

 19.053 4791.556 .00397638 .00059979 .16233854 

 24.610 4771.704 .00515748 .00068957 .14520315 

 29.767 4696.101 .00633858 .00078032 .13460612 

 35.334 4698.840 .00751969 .00087092 .12731897 

 39.786 4572.710 .00870079 .00095706 .12149685 

 45.804 4635.195 .00988189 .00105014 .11776917 

 50.555 4569.762 .01106299 .00113526 .11411745 

 56.180 4588.341 .01224409 .00122769 .11176798 

 61.386 4572.465 .01342520 .00131523 .10946735 

 64.845 4439.494 .01460630 .00139171 .10678147 

 71.647 4538.208 .01578740 .00149414 .10614120 

 74.736 4404.370 .01696850 .00156633 .10380800 

 81.890 4511.946 .01814961 .00167053 .10354213 

 85.716 4434.167 .01933071 .00175060 .10206082 

 92.018 4486.089 .02051181 .00183074 .10075315 

 97.124 4477.213 .02169291 .00193616 .10075315 

 102.139 4465.294 .02287402 .00202929 .10021598 

 105.295 4377.229 .02405512 .00210249 .09890288 

 109.026 4320.217 .02523622 .00218134 .09793705 

 113.742 4305.584 .02641732 .00227957 .09779054 

 118.611 4297.758 .02759843 .00238148 .09779054 

 127.233 4420.944 .02877953 .00247762 .09758978 

 131.954 4404.252 .02996063 .00257166 .09733476 

 136.319 4377.388 .03114173 .00266730 .09715027 

 140.277 4339.870 .03232283 .00276706 .09710686 

 143.850 4293.538 .03350394 .00287126 .09719911 

 147.136 4242.066 .03468504 .00297869 .09737816 

 150.123 4185.651 .03586614 .00308557 .09753009 

 152.748 4123.053 .03704724 .00319502 .09774171 

 152.748 3995.667 .03822835 .00329874 .09779054 

 152.748 3875.917 .03940945 .00340066 .09779054 

 154.387 3803.521 .04059055 .00350258 .09779054 

 155.966 3733.787 .04177165 .00360450 .09779054 

 157.340 3663.103 .04295276 .00370642 .09779054 

 158.551 3592.498 .04413386 .00380833 .09779054 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-39 December 2005

Ultimate Moment Capacity at a Concrete Strain of 0.003 = 147.732 m- kN 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 1 

Depth below ground surface = .000 m 

Depth below pile head = .000 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 140.575 

 .0011 143.795 

 .0022 171.931 

 .0033 189.761 

 .0044 201.500 

 .0056 211.627 

 .0067 221.754 

 .0078 231.882 

 .0089 242.009 

 .0100 248.913 

 .0111 254.570 

 .0122 260.227 

 .0133 265.884 

 .0356 343.117 

 .0667 346.248 

 .0889 346.248 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 2 

Depth below ground surface = 5.290 m 

Depth below pile head = 5.290 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 140.575 

 .0011 143.795 

 .0022 171.931 

 .0033 189.761 

 .0044 201.500 

 .0056 211.627 

 .0067 221.754 

 .0078 231.882 

 .0089 242.009 

 .0100 248.913 

 .0111 254.570 

 .0122 260.227 

 .0133 265.884 

 .0356 343.117 

 .0667 346.248 

 .0889 346.248 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 3 

Depth below ground surface = 5.310 m 

Depth below pile head = 5.310 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 94.987 

 .0011 98.517 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-40 December 2005

 .0022 115.748 

 .0033 128.676 

 .0044 137.831 

 .0056 144.040 

 .0067 149.806 

 .0078 155.572 

 .0089 161.339 

 .0100 167.105 

 .0111 172.871 

 .0122 176.983 

 .0133 180.208 

 .0356 229.725 

 .0667 247.320 

 .0889 247.320 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 4 

Depth below ground surface = 8.000 m 

Depth below pile head = 8.000 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 81.480 

 .0011 84.508 

 .0022 99.288 

 .0033 110.377 

 .0044 118.231 

 .0056 123.556 

 .0067 128.502 

 .0078 133.449 

 .0089 138.395 

 .0100 143.341 

 .0111 148.287 

 .0122 151.814 

 .0133 154.581 

 .0356 197.057 

 .0667 212.150 

 .0889 212.150 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 4 

Depth below ground surface = 10.000 m 

Depth below pile head = 10.000 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 31.663 

 .0011 32.645 

 .0022 34.576 

 .0033 42.892 

 .0044 45.943 

 .0056 48.013 

 .0067 49.935 

 .0078 51.857 

 .0089 53.779 

 .0100 55.702 

 .0111 57.624 

 .0122 63.148 

 .0133 70.602 

 .0356 76.575 

 .0667 82.440 

 .0889 82.440 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 1 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-41 December 2005

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Specified shear force at pile head = 330.000 kN 

Specified bending moment at pile head = -76.200 m- kN 

Specified axial load at pile head = 474.500 kN 

Non-zero moment for this load case indicates the pile-head may rotate under 

the applied pile-head loading, but is not a free-head (zero moment )condition. 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 .039554 -76.2000 330.0 -.030915 1.91E+04 4578.630 -346.250 

 .06897 .037382 -53.2344 306.1 -.031890 1.91E+04 4578.630 -346.250 

 .138 .035155 -31.8893 282.4 -.032531 1.91E+04 4578.630 -341.900 

 .207 .032895 -12.1547 259.0 -.032858 1.91E+04 4792.515 -335.096 

 .276 .030623 5.9918 236.2 -.032903 1.91E+04 4792.777 -328.257 

 .345 .028357 22.5742 213.8 -.032697 1.91E+04 4778.996 -321.435 

 .414 .026113 37.6172 191.8 -.032254 1.91E+04 4635.213 -314.680 

 .483 .023908 51.1451 170.4 -.031588 1.91E+04 4571.717 -308.042 

 .552 .021756 63.1827 149.3 -.030719 1.91E+04 4504.909 -301.564 

 .621 .019671 73.7543 128.8 -.029664 1.91E+04 4448.408 -295.287 

 .690 .017665 82.8840 108.6 -.028456 1.91E+04 4492.096 -287.925 

 .759 .015746 90.6026 89.1283 -.027121 1.91E+04 4474.516 -278.158 

 .828 .013924 96.9526 70.2648 -.025676 1.91E+04 4477.512 -268.882 

 .897 .012204 102.0 52.0230 -.024142 1.91E+04 4465.687 -260.130 

 .966 .010594 105.7 34.3658 -.022521 1.91E+04 4371.015 -251.930 

 1.034 .009098 108.2 17.2680 -.020826 1.91E+04 4333.193 -243.906 

 1.103 .007721 109.5 .8796 -.019091 1.91E+04 4318.897 -231.358 

 1.172 .006465 109.6 -14.6813 -.017343 1.91E+04 4318.567 -219.908 

 1.241 .005329 108.6 -29.4905 -.015603 1.91E+04 4327.408 -209.558 

 1.310 .004313 106.5 -43.6234 -.013895 1.91E+04 4358.842 -200.295 

 1.379 .003413 103.5 -57.1104 -.012247 1.91E+04 4429.278 -190.827 

 1.448 .002623 99.4374 -69.8877 -.010675 1.91E+04 4471.724 -179.714 

 1.517 .001940 94.5144 -81.8245 -.009181 1.91E+04 4481.754 -166.453 

 1.586 .001357 88.7521 -92.7682 -.007767 1.91E+04 4459.308 -150.915 

 1.655 8.69E-04 82.2272 -102.7 -.006452 1.91E+04 4505.249 -135.925 

 1.724 4.67E-04 75.0145 -111.3 -.005235 1.91E+04 4408.633 -113.290 

 1.793 1.47E-04 67.2246 -117.5 -.004131 1.91E+04 4474.417 -67.540 

 1.862 -1.02E-04 59.0795 -118.2 -.003168 1.91E+04 4579.515 47.154 

 1.931 -2.90E-04 51.1296 -113.1 -.002337 1.91E+04 4571.665 99.928 

 2.000 -4.25E-04 43.6298 -105.8 -.001625 1.91E+04 4612.790 110.890 

 2.069 -5.14E-04 36.6360 -98.0281 -.001028 1.91E+04 4662.822 115.942 

 2.138 -5.67E-04 30.1760 -89.9306 -5.36E-04 1.91E+04 4696.303 118.887 

 2.207 -5.88E-04 24.2669 -81.6894 -1.39E-04 1.91E+04 4772.936 120.108 

 2.276 -5.86E-04 18.9176 -73.4109 1.73E-04 1.91E+04 4791.676 119.967 

 2.345 -5.64E-04 14.1299 -65.1787 4.10E-04 1.91E+04 4792.404 118.767 

 2.414 -5.29E-04 9.9005 -57.0566 5.83E-04 1.91E+04 4792.629 116.776 

 2.483 -4.84E-04 6.2219 -49.0908 6.99E-04 1.91E+04 4792.770 114.232 

 2.552 -4.33E-04 3.0836 -41.3125 7.66E-04 1.91E+04 4792.850 111.339 

 2.621 -3.78E-04 .4735 -33.7626 7.92E-04 1.91E+04 4792.874 107.609 

 2.690 -3.24E-04 -1.6251 -26.5060 7.84E-04 1.91E+04 4792.874 102.832 

 2.759 -2.70E-04 -3.2338 -19.5740 7.49E-04 1.91E+04 4792.848 98.195 

 2.828 -2.20E-04 -4.3740 -12.9522 6.94E-04 1.91E+04 4792.822 93.838 

 2.897 -1.75E-04 -5.0657 -6.9450 6.26E-04 1.91E+04 4792.804 80.372 

 2.966 -1.34E-04 -5.3729 -2.0475 5.51E-04 1.91E+04 4792.795 61.656 

 3.034 -9.86E-05 -5.3842 1.6440 4.73E-04 1.91E+04 4792.795 45.396 

 3.103 -6.86E-05 -5.1771 4.2988 3.97E-04 1.91E+04 4792.801 31.595 

 3.172 -4.38E-05 -4.8173 6.0834 3.26E-04 1.91E+04 4792.811 20.159 

 3.241 -2.37E-05 -4.3593 7.1552 2.60E-04 1.91E+04 4792.823 10.924 

 3.310 -7.99E-06 -3.8473 7.6588 2.00E-04 1.91E+04 4792.835 3.680 

 3.379 3.92E-06 -3.3160 7.7235 1.49E-04 1.91E+04 4792.846 -1.806 

 3.448 1.25E-05 -2.7918 7.4620 1.05E-04 1.91E+04 4792.856 -5.777 

 3.517 1.84E-05 -2.2936 6.9707 6.84E-05 1.91E+04 4792.865 -8.472 

 3.586 2.20E-05 -1.8348 6.3296 3.87E-05 1.91E+04 4792.872 -10.120 

 3.655 2.37E-05 -1.4231 5.6038 1.53E-05 1.91E+04 4792.874 -10.929 

 3.724 2.41E-05 -1.0628 4.8445 -2.63E-06 1.91E+04 4792.874 -11.089 

 3.793 2.34E-05 -.7548 4.0910 -1.57E-05 1.91E+04 4792.874 -10.763 

 3.862 2.19E-05 -.4975 3.3719 -2.47E-05 1.91E+04 4792.874 -10.092 

 3.931 2.00E-05 -.2880 2.7069 -3.04E-05 1.91E+04 4792.874 -9.193 

 4.000 1.77E-05 -.1222 2.1084 -3.33E-05 1.91E+04 4792.874 -8.164 

 4.069 1.54E-05 4.94E-03 1.5828 -3.42E-05 1.91E+04 4792.874 -7.078 

 4.138 1.30E-05 9.84E-02 1.1320 -3.34E-05 1.91E+04 4792.874 -5.995 

 4.207 1.08E-05 .1633 .7544 -3.15E-05 1.91E+04 4792.874 -4.956 

 4.276 8.67E-06 .2045 .4458 -2.89E-05 1.91E+04 4792.874 -3.992 

 4.345 6.78E-06 .2266 .2005 -2.58E-05 1.91E+04 4792.874 -3.122 

 4.414 5.12E-06 .2338 1.16E-02 -2.25E-05 1.91E+04 4792.874 -2.355 

 4.483 3.68E-06 .2297 -.1280 -1.91E-05 1.91E+04 4792.874 -1.695 

 4.552 2.48E-06 .2174 -.2258 -1.59E-05 1.91E+04 4792.874 -1.140 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-42 December 2005

 4.621 1.49E-06 .1996 -.2887 -1.29E-05 1.91E+04 4792.874 -.684197 

 4.690 6.94E-07 .1785 -.3233 -1.02E-05 1.91E+04 4792.874 -.319626 

 4.759 7.95E-08 .1557 -.3356 -7.79E-06 1.91E+04 4792.874 -.036584 

 4.828 -3.81E-07 .1327 -.3308 -5.72E-06 1.91E+04 4792.874 .175332 

 4.897 -7.10E-07 .1104 -.3135 -3.97E-06 1.91E+04 4792.874 .326633 

 4.966 -9.29E-07 8.97E-02 -.2875 -2.53E-06 1.91E+04 4792.874 .427481 

 5.034 -1.06E-06 7.09E-02 -.2560 -1.38E-06 1.91E+04 4792.874 .487352 

 5.103 -1.12E-06 5.45E-02 -.2214 -4.73E-07 1.91E+04 4792.874 .514809 

 5.172 -1.12E-06 4.04E-02 -.1858 2.10E-07 1.91E+04 4792.874 .517375 

 5.241 -1.09E-06 2.88E-02 -.1507 7.09E-07 1.91E+04 4792.874 .501465 

 5.310 -1.03E-06 1.96E-02 -.1217 1.06E-06 1.91E+04 4792.874 .337408 

 5.379 -9.43E-07 1.20E-02 -9.94E-02 1.28E-06 1.91E+04 4792.874 .309101 

 5.448 -8.49E-07 5.81E-03 -7.92E-02 1.41E-06 1.91E+04 4792.874 .277110 

 5.517 -7.49E-07 9.61E-04 -6.13E-02 1.46E-06 1.91E+04 4792.874 .243469 

 5.586 -6.47E-07 -2.74E-03 -4.57E-02 1.45E-06 1.91E+04 4792.874 .209761 

 5.655 -5.49E-07 -5.43E-03 -3.23E-02 1.39E-06 1.91E+04 4792.874 .177171 

 5.724 -4.56E-07 -7.28E-03 -2.12E-02 1.30E-06 1.91E+04 4792.874 .146551 

 5.793 -3.70E-07 -8.43E-03 -1.20E-02 1.19E-06 1.91E+04 4792.874 .118470 

 5.862 -2.92E-07 -9.02E-03 -4.71E-03 1.06E-06 1.91E+04 4792.874 .093267 

 5.931 -2.24E-07 -9.15E-03 9.57E-04 9.29E-07 1.91E+04 4792.874 .071096 

 6.000 -1.64E-07 -8.95E-03 5.20E-03 7.99E-07 1.91E+04 4792.874 .051968 

 6.069 -1.13E-07 -8.49E-03 8.23E-03 6.73E-07 1.91E+04 4792.874 .035784 

 6.138 -7.11E-08 -7.86E-03 1.02E-02 5.56E-07 1.91E+04 4792.874 .022370 

 6.207 -3.67E-08 -7.11E-03 1.14E-02 4.48E-07 1.91E+04 4792.874 .011500 

 6.276 -9.34E-09 -6.31E-03 1.19E-02 3.51E-07 1.91E+04 4792.874 .002915 

 6.345 1.18E-08 -5.50E-03 1.19E-02 2.67E-07 1.91E+04 4792.874 -.003658 

 6.414 2.74E-08 -4.69E-03 1.15E-02 1.93E-07 1.91E+04 4792.874 -.008491 

 6.483 3.84E-08 -3.93E-03 1.08E-02 1.31E-07 1.91E+04 4792.874 -.011850 

 6.552 4.55E-08 -3.22E-03 9.86E-03 7.98E-08 1.91E+04 4792.874 -.013985 

 6.621 4.94E-08 -2.57E-03 8.86E-03 3.81E-08 1.91E+04 4792.874 -.015126 

 6.690 5.08E-08 -2.00E-03 7.80E-03 5.21E-09 1.91E+04 4792.874 -.015479 

 6.759 5.01E-08 -1.50E-03 6.74E-03 -2.00E-08 1.91E+04 4792.874 -.015226 

 6.828 4.80E-08 -1.07E-03 5.72E-03 -3.84E-08 1.91E+04 4792.874 -.014524 

 6.897 4.48E-08 -7.07E-04 4.75E-03 -5.12E-08 1.91E+04 4792.874 -.013509 

 6.966 4.10E-08 -4.10E-04 3.86E-03 -5.92E-08 1.91E+04 4792.874 -.012291 

 7.034 3.67E-08 -1.71E-04 3.06E-03 -6.34E-08 1.91E+04 4792.874 -.010960 

 7.103 3.22E-08 1.61E-05 2.35E-03 -6.45E-08 1.91E+04 4792.874 -.009589 

 7.172 2.78E-08 1.57E-04 1.73E-03 -6.33E-08 1.91E+04 4792.874 -.008234 

 7.241 2.35E-08 2.59E-04 1.21E-03 -6.03E-08 1.91E+04 4792.874 -.006935 

 7.310 1.95E-08 3.28E-04 7.75E-04 -5.60E-08 1.91E+04 4792.874 -.005723 

 7.379 1.58E-08 3.70E-04 4.19E-04 -5.10E-08 1.91E+04 4792.874 -.004615 

 7.448 1.24E-08 3.90E-04 1.34E-04 -4.55E-08 1.91E+04 4792.874 -.003624 

 7.517 9.48E-09 3.92E-04 -8.54E-05 -3.99E-08 1.91E+04 4792.874 -.002753 

 7.586 6.92E-09 3.80E-04 -2.49E-04 -3.44E-08 1.91E+04 4792.874 -.002001 

 7.655 4.74E-09 3.59E-04 -3.65E-04 -2.91E-08 1.91E+04 4792.874 -.001364 

 7.724 2.91E-09 3.32E-04 -4.41E-04 -2.41E-08 1.91E+04 4792.874 -8.35E-04 

 7.793 1.41E-09 3.00E-04 -4.84E-04 -1.95E-08 1.91E+04 4792.874 -4.04E-04 

 7.862 2.17E-10 2.66E-04 -5.00E-04 -1.55E-08 1.91E+04 4792.874 -6.16E-05 

 7.931 -7.17E-10 2.32E-04 -4.95E-04 -1.19E-08 1.91E+04 4792.874 2.03E-04 

 8.000 -1.42E-09 1.99E-04 -4.74E-04 -8.77E-09 1.91E+04 4792.874 4.01E-04 

 8.069 -1.93E-09 1.67E-04 -4.42E-04 -6.13E-09 1.91E+04 4792.874 5.28E-04 

 8.138 -2.27E-09 1.38E-04 -4.03E-04 -3.93E-09 1.91E+04 4792.874 6.03E-04 

 8.207 -2.47E-09 1.12E-04 -3.60E-04 -2.13E-09 1.91E+04 4792.874 6.38E-04 

 8.276 -2.56E-09 8.87E-05 -3.16E-04 -6.87E-10 1.91E+04 4792.874 6.41E-04 

 8.345 -2.56E-09 6.84E-05 -2.73E-04 4.43E-10 1.91E+04 4792.874 6.21E-04 

 8.414 -2.50E-09 5.10E-05 -2.31E-04 1.30E-09 1.91E+04 4792.874 5.86E-04 

 8.483 -2.38E-09 3.64E-05 -1.92E-04 1.93E-09 1.91E+04 4792.874 5.40E-04 

 8.552 -2.23E-09 2.44E-05 -1.57E-04 2.37E-09 1.91E+04 4792.874 4.88E-04 

 8.621 -2.06E-09 1.46E-05 -1.25E-04 2.65E-09 1.91E+04 4792.874 4.33E-04 

 8.690 -1.87E-09 6.94E-06 -9.72E-05 2.81E-09 1.91E+04 4792.874 3.79E-04 

 8.759 -1.67E-09 1.04E-06 -7.29E-05 2.86E-09 1.91E+04 4792.874 3.25E-04 

 8.828 -1.47E-09 -3.30E-06 -5.22E-05 2.85E-09 1.91E+04 4792.874 2.75E-04 

 8.897 -1.28E-09 -6.34E-06 -3.48E-05 2.78E-09 1.91E+04 4792.874 2.29E-04 

 8.966 -1.09E-09 -8.29E-06 -2.05E-05 2.67E-09 1.91E+04 4792.874 1.86E-04 

 9.034 -9.09E-10 -9.34E-06 -8.97E-06 2.54E-09 1.91E+04 4792.874 1.48E-04 

 9.103 -7.38E-10 -9.69E-06 8.98E-08 2.41E-09 1.91E+04 4792.874 1.15E-04 

 9.172 -5.77E-10 -9.49E-06 6.97E-06 2.27E-09 1.91E+04 4792.874 8.49E-05 

 9.241 -4.25E-10 -8.88E-06 1.19E-05 2.14E-09 1.91E+04 4792.874 5.92E-05 

 9.310 -2.82E-10 -7.98E-06 1.53E-05 2.02E-09 1.91E+04 4792.874 3.70E-05 

 9.379 -1.47E-10 -6.91E-06 1.72E-05 1.91E-09 1.91E+04 4792.874 1.81E-05 

 9.448 -1.84E-11 -5.74E-06 1.79E-05 1.82E-09 1.91E+04 4792.874 2.12E-06 

 9.517 1.04E-10 -4.56E-06 1.75E-05 1.74E-09 1.91E+04 4792.874 -1.12E-05 

 9.586 2.22E-10 -3.44E-06 1.64E-05 1.69E-09 1.91E+04 4792.874 -2.22E-05 

 9.655 3.37E-10 -2.41E-06 1.46E-05 1.64E-09 1.91E+04 4792.874 -3.09E-05 

 9.724 4.49E-10 -1.54E-06 1.22E-05 1.62E-09 1.91E+04 4792.874 -3.77E-05 

 9.793 5.60E-10 -8.36E-07 9.43E-06 1.60E-09 1.91E+04 4792.874 -4.25E-05 

 9.862 6.70E-10 -3.39E-07 6.40E-06 1.59E-09 1.91E+04 4792.874 -4.55E-05 

 9.931 7.79E-10 -5.82E-08 3.21E-06 1.59E-09 1.91E+04 4792.874 -4.68E-05 

 10.000 8.89E-10 0.0 0.0 1.59E-09 1.91E+04 4792.874 -4.63E-05 

Please note that because this analysis makes computations of ultimate moment 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-43 December 2005

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 1: 

Pile-head deflection = .03955380 m 

Computed slope at pile head = -.03091492 

Maximum bending moment = 109.560 kN- m 

Maximum shear force = 330.000 kN 

Depth of maximum bending moment = 1.17241379 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 34 

Number of zero deflection points = 6 

------------------------------------------------------------------------------ 

 Summary of Pile-head Response 

------------------------------------------------------------------------------ 

Definition of symbols for pile-head boundary conditions: 

y = pile-head displacment, m 

M = pile-head moment, kN- m 

V = pile-head shear force, kN 

S = pile-head slope, radians 

R = rotational stiffness of pile-head, m- kN/rad 

 BC Boundary Boundary Axial Pile Head Maximum Maximum 

Type Condition Condition Load Deflection Moment Shear 

 1 2 kN m m- kN kN 

---- ------------ ------------ ----------- ----------- ----------- ----------- 

 1 V = 330.000 M = -76.200 474.5000 .039554 109.5597 330.0000 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-44 December 2005

=============================================================== 

 LPILE Plus for Windows, Version 4.0 (4.0.8) 

 Analysis of Individual Piles and Drilled Shafts 

 Subjected to Lateral Loading Using the p-y Method 

 (c) Copyright ENSOFT, Inc., 1985-2003 

 All Rights Reserved 

=============================================================== 

Path to file locations: L:\Programs\LPILE\Chapter 6\Ch. 6 Example with P=474.5\P=Pult\ 

Name of input data file: Down analysis.lpd 

Name of output file: Down analysis.lpo 

Name of plot output file: Down analysis.lpp 

Name of runtime file: Down analysis.lpr 

------------------------------------------------------------------------------ 

 Time and Date of Analysis 

------------------------------------------------------------------------------ 

 Date: May 4, 2005 Time: 17: 4:52 

------------------------------------------------------------------------------ 

 Problem Title 

------------------------------------------------------------------------------ 

Down Analysis for P=474.5 Case 

------------------------------------------------------------------------------ 

 Program Options 

------------------------------------------------------------------------------ 

Units Used in Computations - SI Units, meters, kilopascals 

Basic Program Options: 

Analysis Type 3: 

- Computation of Nonlinear Bending Stiffness and Ultimate Bending Moment 

 Capacity with Pile Response Computed Using Nonlinear EI 

Computation Options: 

- User-specified p-y curves used in analysis 

- Analysis uses p-y multiplers for group action 

- Analysis assumes no shear resistance at pile tip 

- Analysis for fixed-length pile or shaft only 

- No computation of foundation stiffness matrix elements 

- Output pile response for full length of pile 

- Analysis assumes no soil movements acting on pile 

- Additional p-y curves computed at specified depths 

Solution Control Parameters: 

- Number of pile increments = 145 

- Maximum number of iterations allowed = 100 

- Deflection tolerance for convergence = 2.5400E-07 m 

- Maximum allowable deflection = 2.5400E+00 m 

Printing Options: 

- Values of pile-head deflection, bending moment, shear force, and 

 soil reaction are printed for full length of pile. 

- Printing Increment (spacing of output points) = 1 

------------------------------------------------------------------------------ 

 Pile Structural Properties and Geometry 

------------------------------------------------------------------------------ 

Pile Length = 4.50 m 

Depth of ground surface below top of pile = .00 m 

Slope angle of ground surface = .00 deg. 

Structural properties of pile defined using 2 points 

Point Depth Pile Moment of Pile Modulus of 

 X Diameter Inertia Area Elasticity 

 m m m**4 Sq. m kN/Sq. m 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-45 December 2005

----- --------- ----------- ---------- ---------- ----------- 

 1 0.0000 .17780000 1.0000 .024800 200000000.000 

 2 4.5000 .17780000 1.0000 .024800 200000000.000 

Please note that because this analysis makes computations of ultimate 

moment capacity and pile response using nonlinear bending stiffness 

that the above values of moment of inertia and modulus of are not used 

for any computations other than total stress due to combined axial 

loading and bending. 

------------------------------------------------------------------------------ 

 Soil and Rock Layering Information 

------------------------------------------------------------------------------ 

The soil profile is modelled using 1 layers 

Layer 1 is modelled using user-specied p-y curves 

Distance from top of pile to top of layer = .000 m 

Distance from top of pile to bottom of layer = 6.000 m 

(Depth of lowest layer extends 1.50 m below pile tip) 

------------------------------------------------------------------------------ 

 Effective Unit Weight of Soil vs. Depth 

------------------------------------------------------------------------------ 

Distribution of effective unit weight of soil with depth 

is defined using 2 points 

Point Depth X Eff. Unit Weight 

 No. m kN/ m**3 

----- ---------- ---------------- 

 1 .00 12.20000 

 2 6.00 12.20000 

------------------------------------------------------------------------------ 

 Shear Strength of Soils 

------------------------------------------------------------------------------ 

Distribution of shear strength parameters with depth 

defined using 0 points 

Point Depth X Cohesion c Angle of Friction E50 or RQD 

 No. m kN/ m**2 Deg. k_rm % 

----- -------- ---------- ------------------ ------ ------ 

Notes: 

(1) Cohesion = uniaxial compressive strength for rock materials. 

(2) Values of E50 are reported for clay strata. 

(3) Default values will be generated for E50 when input values are 0. 

(4) RQD and k_rm are reported only for weak rock strata. 

------------------------------------------------------------------------------ 

 p-y Modification Factors 

------------------------------------------------------------------------------ 

Distribution of p-y multipliers with depth defined using 2 points 

Point Depth X p-mult y-mult 

 No. m 

----- ---------- ---------- ---------- 

 1 .000 1.0000 1.0000 

 2 6.000 1.0000 1.0000 

------------------------------------------------------------------------------ 

 User-specified p-y Curves 

------------------------------------------------------------------------------ 

User-specified p-y curves defined using 2 curves. 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-46 December 2005

User-specified curve number 1 at depth = .000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0001 263.064 

 3 .0002 312.838 

 4 .0006 393.373 

 5 .0011 467.802 

 6 .0017 517.708 

 7 .0023 556.313 

 8 .0057 699.527 

 9 .0115 831.882 

 10 .0229 989.280 

 11 .0258 989.280 

 12 .0286 989.280 

User-specified curve number 2 at depth = 6.000 m 

Point y p, 

 No. m kN/ m 

----- ---------- ---------- 

 1 .0000 .000 

 2 .0001 263.064 

 3 .0002 312.838 

 4 .0006 393.373 

 5 .0011 467.802 

 6 .0017 517.708 

 7 .0023 556.313 

 8 .0057 699.527 

 9 .0115 831.882 

 10 .0229 989.280 

 11 .0258 989.280 

 12 .0286 989.280 

------------------------------------------------------------------------------ 

 Loading Type 

------------------------------------------------------------------------------ 

Static loading criteria was used for computation of p-y curves 

------------------------------------------------------------------------------ 

 Pile-head Loading and Pile-head Fixity Conditions 

------------------------------------------------------------------------------ 

Number of loads specified = 1 

Load Case Number 1 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Shear force at pile head = 330.000 kN 

Bending moment at pile head = 76.200 m- kN 

Axial load at pile head = 474.500 kN 

Non-zero moment at pile head for this load case indicates the pile-head 

may rotate under the applied pile-head loading, but is not a free-head 

(zero moment) condition. 

------------------------------------------------------------------------------ 

 Output of p-y Curves at Specified Depths 

------------------------------------------------------------------------------ 

p-y curves are generated and printed for verification at 2 depths. 

Depth Depth Below Pile Head Depth Below Ground Surface 

 No. m m 

----- --------------------- -------------------------- 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-47 December 2005

 1 .000 .000 

 2 4.500 4.500 

------------------------------------------------------------------------------ 

 Computations of Ultimate Moment Capacity and Nonlinear Bending Stiffness 

------------------------------------------------------------------------------ 

Pile Description: 

The sectional shape is a circular shaft with steel casing. 

Outside Diameter = .1778 m 

Wall thickness of steel shell = .0115 m 

Cross-sectional area of shell = .00601 m**2 

Moment of inertia of steel shell = 2.08692E-05 m**4 

Material Properties: 

Compressive Strength of Concrete = 27600.000 kN/ m**2 

Yield Stress of Reinforcement = 0. kN/ m**2 

Steel shell or core yield stress = 552000. kN/ m**2 

Modulus of Elasticity of Reinforcement = 200000000. kN/ m**2 

Cover Thickness (edge to bar center) = .000 m 

Number of Reinforcing Bars = 10 

Area of Single Bar = .00000 m**2 

Number of Rows of Reinforcing Bars = 5 

Ultimate Axial Squash Load Capacity = 3758.02 kN 

Distribution and Area of Steel Reinforcement 

 Row Area of Distance to 

Number Reinforcement Centroidal Axis 

 m**2 m 

------ ------------- --------------- 

 1 .000000 .0736 

 2 .000000 .0455 

 3 .000000 .0000 

 4 .000000 -.0455 

 5 .000000 -.0736 

Axial Thrust Force = 474.50 kN 

 Bending Bending Bending Maximum Neutral Axis 

 Moment Stiffness Curvature Strain Position 

 kN-m kN-m2 rad/m m/m m 

 ------------- ------------- ------------- ------------- ------------- 

 1.69826245 4792.874 .00035433 .00031727 .90691267 

 2.45303965 4792.862 .00051181 .00032949 .65527803 

 3.20781175 4792.848 .00066929 .00034172 .52206775 

 3.96257836 4792.833 .00082677 .00035395 .43960844 

 4.71733626 4792.814 .00098425 .00036619 .38354674 

 5.47208598 4792.792 .00114173 .00037843 .34295465 

 6.22682760 4792.770 .00129921 .00039068 .31220536 

 6.98155916 4792.746 .00145669 .00040293 .28810838 

 7.73628058 4792.720 .00161417 .00041519 .26871577 

 8.49098340 4792.688 .00177165 .00042746 .25277953 

 9.24568013 4792.659 .00192913 .00043973 .23944236 

 10.000 4792.625 .00208661 .00045201 .22812367 

 10.755 4792.590 .00224409 .00046429 .21839481 

 11.510 4792.551 .00240157 .00047658 .20994649 

 12.264 4792.509 .00255906 .00048888 .20253996 

 13.019 4792.470 .00271654 .00050118 .19599075 

 13.774 4792.426 .00287402 .00051348 .19016320 

 14.528 4792.379 .00303150 .00052579 .18494336 

 15.283 4792.326 .00318898 .00053812 .18024442 

 16.035 4791.716 .00334646 .00055042 .17597957 

 16.774 4787.090 .00350394 .00056260 .17206198 

 17.571 4799.091 .00366142 .00057505 .16855677 

 18.301 4792.220 .00381890 .00058745 .16532828 

 19.053 4791.556 .00397638 .00059979 .16233854 

 24.610 4771.704 .00515748 .00068957 .14520315 

 29.767 4696.101 .00633858 .00078032 .13460612 

 35.334 4698.840 .00751969 .00087092 .12731897 

 39.786 4572.710 .00870079 .00095706 .12149685 

 45.804 4635.195 .00988189 .00105014 .11776917 

 50.555 4569.762 .01106299 .00113526 .11411745 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-48 December 2005

 56.180 4588.341 .01224409 .00122769 .11176798 

 61.386 4572.465 .01342520 .00131523 .10946735 

 64.845 4439.494 .01460630 .00139171 .10678147 

 71.647 4538.208 .01578740 .00149414 .10614120 

 74.736 4404.370 .01696850 .00156633 .10380800 

 81.890 4511.946 .01814961 .00167053 .10354213 

 85.716 4434.167 .01933071 .00175060 .10206082 

 92.018 4486.089 .02051181 .00183074 .10075315 

 97.124 4477.213 .02169291 .00193616 .10075315 

 102.139 4465.294 .02287402 .00202929 .10021598 

 105.295 4377.229 .02405512 .00210249 .09890288 

 109.026 4320.217 .02523622 .00218134 .09793705 

 113.742 4305.584 .02641732 .00227957 .09779054 

 118.611 4297.758 .02759843 .00238148 .09779054 

 127.233 4420.944 .02877953 .00247762 .09758978 

 131.954 4404.252 .02996063 .00257166 .09733476 

 136.319 4377.388 .03114173 .00266730 .09715027 

 140.277 4339.870 .03232283 .00276706 .09710686 

 143.850 4293.538 .03350394 .00287126 .09719911 

 147.136 4242.066 .03468504 .00297869 .09737816 

 150.123 4185.651 .03586614 .00308557 .09753009 

 152.748 4123.053 .03704724 .00319502 .09774171 

 152.748 3995.667 .03822835 .00329874 .09779054 

 152.748 3875.917 .03940945 .00340066 .09779054 

 154.387 3803.521 .04059055 .00350258 .09779054 

 155.966 3733.787 .04177165 .00360450 .09779054 

 157.340 3663.103 .04295276 .00370642 .09779054 

 158.551 3592.498 .04413386 .00380833 .09779054 

Ultimate Moment Capacity at a Concrete Strain of 0.003 = 147.732 m- kN 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 1 

Depth below ground surface = .000 m 

Depth below pile head = .000 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 452.916 

 .0011 468.738 

 .0022 551.327 

 .0033 599.856 

 .0044 646.664 

 .0056 693.472 

 .0067 721.605 

 .0078 746.964 

 .0089 772.322 

 .0100 797.681 

 .0111 823.039 

 .0122 841.875 

 .0133 857.218 

 .0356 989.280 

 .0667 989.280 

 .0889 989.280 

p-y Curve Computed by Interpolation from User-input Curves 

Soil Layer Number = 1 

Depth below ground surface = 4.500 m 

Depth below pile head = 4.500 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

 y, m p, kN/ m 

---------------- ---------------- 

 .0000 .000 

 .0010 452.916 

 .0011 468.738 

 .0022 551.327 

 .0033 599.856 

 .0044 646.664 

 .0056 693.472 

 .0067 721.605 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-49 December 2005

 .0078 746.964 

 .0089 772.322 

 .0100 797.681 

 .0111 823.039 

 .0122 841.875 

 .0133 857.218 

 .0356 989.280 

 .0667 989.280 

 .0889 989.280 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 1 

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Specified shear force at pile head = 330.000 kN 

Specified bending moment at pile head = 76.200 m- kN 

Specified axial load at pile head = 474.500 kN 

Non-zero moment for this load case indicates the pile-head may rotate under 

the applied pile-head loading, but is not a free-head (zero moment )condition. 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 .014998 76.2000 330.0 -.029550 1.91E+04 4440.259 -880.191 

 .03103 .014089 86.4487 302.9 -.028982 1.91E+04 4440.259 -867.643 

 .06207 .013199 95.8529 276.1 -.028344 1.91E+04 4440.259 -855.355 

 .09310 .012330 104.4 249.8 -.027641 1.91E+04 4402.137 -843.353 

 .124 .011484 112.2 223.8 -.026869 1.91E+04 4310.471 -831.519 

 .155 .010662 119.1 198.3 -.026036 1.91E+04 4304.934 -812.777 

 .186 .009868 125.2 173.3 -.025165 1.91E+04 4392.860 -794.642 

 .217 .009100 130.6 148.9 -.024263 1.91E+04 4409.035 -777.134 

 .248 .008362 135.2 125.1 -.023324 1.91E+04 4384.290 -760.277 

 .279 .007653 139.1 101.7 -.022350 1.91E+04 4351.532 -744.098 

 .310 .006975 142.2 78.8937 -.021343 1.91E+04 4315.407 -728.621 

 .341 .006328 144.6 56.5102 -.020308 1.91E+04 4282.247 -713.869 

 .372 .005714 146.3 34.5731 -.019250 1.91E+04 4255.618 -699.859 

 .403 .005133 147.3 13.2288 -.018178 1.91E+04 4239.142 -675.661 

 .434 .004586 147.6 -7.3822 -.017097 1.91E+04 4232.741 -652.603 

 .466 .004072 147.3 -27.2996 -.016017 1.91E+04 4238.305 -630.961 

 .497 .003592 146.4 -46.5672 -.014943 1.91E+04 4253.508 -610.730 

 .528 .003144 144.9 -65.2286 -.013883 1.91E+04 4277.471 -591.895 

 .559 .002730 142.8 -83.3268 -.012843 1.91E+04 4307.612 -574.434 

 .590 .002347 140.1 -100.9 -.011828 1.91E+04 4341.609 -558.318 

 .621 .001996 136.9 -117.9 -.010842 1.91E+04 4372.296 -536.749 

 .652 .001674 133.1 -134.2 -.009887 1.91E+04 4397.257 -515.586 

 .683 .001382 128.8 -149.8 -.008964 1.91E+04 4415.342 -491.280 

 .714 .001118 124.1 -164.8 -.008072 1.91E+04 4376.125 -469.311 

 .745 8.81E-04 118.8 -178.8 -.007203 1.91E+04 4300.982 -435.230 

 .776 6.71E-04 113.2 -191.8 -.006366 1.91E+04 4307.350 -403.939 

 .807 4.86E-04 107.1 -203.8 -.005577 1.91E+04 4349.681 -370.427 

 .838 3.25E-04 100.7 -214.8 -.004845 1.91E+04 4468.752 -337.979 

 .869 1.85E-04 93.9248 -224.8 -.004170 1.91E+04 4482.780 -305.510 

 .900 6.59E-05 86.8575 -232.2 -.003542 1.91E+04 4443.643 -173.263 

 .931 -3.46E-05 79.6145 -233.5 -.002963 1.91E+04 4478.130 91.121 

 .962 -1.18E-04 72.4510 -227.9 -.002437 1.91E+04 4504.740 271.981 

 .993 -1.86E-04 65.5422 -218.9 -.001959 1.91E+04 4449.767 305.793 

 1.024 -2.40E-04 58.9212 -209.2 -.001531 1.91E+04 4579.999 320.786 

 1.055 -2.81E-04 52.6032 -199.1 -.001153 1.91E+04 4576.541 329.109 

 1.086 -3.11E-04 46.5970 -188.8 -8.18E-04 1.91E+04 4624.438 335.201 

 1.117 -3.32E-04 40.9090 -178.3 -5.23E-04 1.91E+04 4584.479 339.339 

 1.148 -3.44E-04 35.5438 -167.8 -2.67E-04 1.91E+04 4693.099 341.745 

 1.179 -3.48E-04 30.5042 -157.1 -4.89E-05 1.91E+04 4696.464 342.682 

 1.210 -3.47E-04 25.7917 -146.5 1.36E-04 1.91E+04 4754.616 342.359 

 1.241 -3.40E-04 21.4065 -135.9 2.90E-04 1.91E+04 4783.170 340.984 

 1.272 -3.29E-04 17.3477 -125.4 4.15E-04 1.91E+04 4795.724 338.741 

 1.303 -3.14E-04 13.6134 -114.9 5.15E-04 1.91E+04 4792.435 335.796 

 1.334 -2.97E-04 10.2013 -104.5 5.93E-04 1.91E+04 4792.615 332.301 

 1.366 -2.77E-04 7.1083 -94.2721 6.49E-04 1.91E+04 4792.742 328.392 

 1.397 -2.56E-04 4.3309 -84.1457 6.86E-04 1.91E+04 4792.823 324.196 

 1.428 -2.35E-04 1.8653 -74.1523 7.06E-04 1.91E+04 4792.871 319.825 

 1.459 -2.13E-04 -.2925 -64.2957 7.11E-04 1.91E+04 4792.874 315.378 

 1.490 -1.91E-04 -2.1464 -54.6200 7.03E-04 1.91E+04 4792.867 308.163 

 1.521 -1.69E-04 -3.7034 -45.2231 6.84E-04 1.91E+04 4792.838 297.413 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-50 December 2005

 1.552 -1.48E-04 -4.9735 -36.1541 6.56E-04 1.91E+04 4792.806 287.034 

 1.583 -1.28E-04 -5.9668 -27.3995 6.20E-04 1.91E+04 4792.778 277.152 

 1.614 -1.10E-04 -6.6925 -18.9423 5.79E-04 1.91E+04 4792.755 267.867 

 1.645 -9.23E-05 -7.1596 -11.0162 5.35E-04 1.91E+04 4792.740 242.930 

 1.676 -7.65E-05 -7.3920 -4.1248 4.87E-04 1.91E+04 4792.732 201.179 

 1.707 -6.21E-05 -7.4299 1.5314 4.39E-04 1.91E+04 4792.731 163.335 

 1.738 -4.92E-05 -7.3099 6.0742 3.92E-04 1.91E+04 4792.735 129.420 

 1.769 -3.78E-05 -7.0645 9.6244 3.45E-04 1.91E+04 4792.743 99.369 

 1.800 -2.78E-05 -6.7227 12.2999 3.01E-04 1.91E+04 4792.754 73.052 

 1.831 -1.91E-05 -6.3099 14.2138 2.58E-04 1.91E+04 4792.768 50.289 

 1.862 -1.17E-05 -5.8480 15.4730 2.19E-04 1.91E+04 4792.781 30.862 

 1.893 -5.52E-06 -5.3559 16.1773 1.83E-04 1.91E+04 4792.796 14.526 

 1.924 -3.89E-07 -4.8493 16.4186 1.50E-04 1.91E+04 4792.810 1.022 

 1.955 3.77E-06 -4.3412 16.2805 1.20E-04 1.91E+04 4792.823 -9.919 

 1.986 7.06E-06 -3.8423 15.8386 9.35E-05 1.91E+04 4792.835 -18.564 

 2.017 9.57E-06 -3.3609 15.1598 7.01E-05 1.91E+04 4792.845 -25.179 

 2.048 1.14E-05 -2.9034 14.3033 4.99E-05 1.91E+04 4792.854 -30.017 

 2.079 1.27E-05 -2.4746 13.3205 3.24E-05 1.91E+04 4792.862 -33.320 

 2.110 1.34E-05 -2.0776 12.2555 1.77E-05 1.91E+04 4792.868 -35.314 

 2.141 1.38E-05 -1.7144 11.1456 5.43E-06 1.91E+04 4792.874 -36.211 

 2.172 1.38E-05 -1.3860 10.0220 -4.61E-06 1.91E+04 4792.874 -36.201 

 2.203 1.35E-05 -1.0922 8.9100 -1.26E-05 1.91E+04 4792.874 -35.459 

 2.234 1.30E-05 -.8326 7.8301 -1.89E-05 1.91E+04 4792.874 -34.139 

 2.266 1.23E-05 -.6057 6.7979 -2.35E-05 1.91E+04 4792.874 -32.379 

 2.297 1.15E-05 -.4099 5.8253 -2.68E-05 1.91E+04 4792.874 -30.299 

 2.328 1.06E-05 -.2433 4.9207 -2.89E-05 1.91E+04 4792.874 -28.002 

 2.359 9.72E-06 -.1037 4.0893 -3.00E-05 1.91E+04 4792.874 -25.576 

 2.390 8.78E-06 1.14E-02 3.3340 -3.03E-05 1.91E+04 4792.874 -23.096 

 2.421 7.84E-06 .1042 2.6556 -3.00E-05 1.91E+04 4792.874 -20.622 

 2.452 6.92E-06 .1771 2.0532 -2.91E-05 1.91E+04 4792.874 -18.202 

 2.483 6.04E-06 .2325 1.5244 -2.77E-05 1.91E+04 4792.874 -15.877 

 2.514 5.20E-06 .2725 1.0658 -2.61E-05 1.91E+04 4792.874 -13.674 

 2.545 4.42E-06 .2994 .6734 -2.42E-05 1.91E+04 4792.874 -11.615 

 2.576 3.69E-06 .3150 .3424 -2.23E-05 1.91E+04 4792.874 -9.715 

 2.607 3.03E-06 .3213 6.78E-02 -2.02E-05 1.91E+04 4792.874 -7.981 

 2.638 2.44E-06 .3198 -.1556 -1.81E-05 1.91E+04 4792.874 -6.417 

 2.669 1.91E-06 .3122 -.3331 -1.61E-05 1.91E+04 4792.874 -5.022 

 2.700 1.44E-06 .2996 -.4699 -1.41E-05 1.91E+04 4792.874 -3.792 

 2.731 1.03E-06 .2834 -.5710 -1.22E-05 1.91E+04 4792.874 -2.721 

 2.762 6.84E-07 .2646 -.6411 -1.04E-05 1.91E+04 4792.874 -1.799 

 2.793 3.87E-07 .2439 -.6848 -8.79E-06 1.91E+04 4792.874 -1.018 

 2.824 1.39E-07 .2223 -.7063 -7.28E-06 1.91E+04 4792.874 -.364770 

 2.855 -6.48E-08 .2003 -.7093 -5.91E-06 1.91E+04 4792.874 .170530 

 2.886 -2.28E-07 .1785 -.6973 -4.68E-06 1.91E+04 4792.874 .599935 

 2.917 -3.55E-07 .1572 -.6735 -3.60E-06 1.91E+04 4792.874 .934996 

 2.948 -4.51E-07 .1368 -.6406 -2.64E-06 1.91E+04 4792.874 1.187 

 2.979 -5.20E-07 .1175 -.6010 -1.82E-06 1.91E+04 4792.874 1.367 

 3.010 -5.64E-07 9.95E-02 -.5567 -1.12E-06 1.91E+04 4792.874 1.484 

 3.041 -5.89E-07 8.30E-02 -.5096 -5.27E-07 1.91E+04 4792.874 1.549 

 3.072 -5.97E-07 6.79E-02 -.4612 -3.85E-08 1.91E+04 4792.874 1.570 

 3.103 -5.91E-07 5.43E-02 -.4127 3.57E-07 1.91E+04 4792.874 1.555 

 3.134 -5.75E-07 4.23E-02 -.3651 6.70E-07 1.91E+04 4792.874 1.512 

 3.166 -5.50E-07 3.17E-02 -.3192 9.09E-07 1.91E+04 4792.874 1.446 

 3.197 -5.18E-07 2.24E-02 -.2757 1.08E-06 1.91E+04 4792.874 1.363 

 3.228 -4.82E-07 1.45E-02 -.2348 1.20E-06 1.91E+04 4792.874 1.269 

 3.259 -4.44E-07 7.82E-03 -.1970 1.28E-06 1.91E+04 4792.874 1.167 

 3.290 -4.03E-07 2.25E-03 -.1625 1.31E-06 1.91E+04 4792.874 1.060 

 3.321 -3.62E-07 -2.30E-03 -.1312 1.31E-06 1.91E+04 4792.874 .952991 

 3.352 -3.22E-07 -5.93E-03 -.1033 1.28E-06 1.91E+04 4792.874 .846726 

 3.383 -2.83E-07 -8.75E-03 -7.86E-02 1.23E-06 1.91E+04 4792.874 .743596 

 3.414 -2.45E-07 -1.08E-02 -5.71E-02 1.17E-06 1.91E+04 4792.874 .645089 

 3.445 -2.10E-07 -1.23E-02 -3.85E-02 1.10E-06 1.91E+04 4792.874 .552316 

 3.476 -1.77E-07 -1.33E-02 -2.27E-02 1.01E-06 1.91E+04 4792.874 .466057 

 3.507 -1.47E-07 -1.38E-02 -9.44E-03 9.26E-07 1.91E+04 4792.874 .386811 

 3.538 -1.20E-07 -1.39E-02 1.45E-03 8.37E-07 1.91E+04 4792.874 .314838 

 3.569 -9.51E-08 -1.37E-02 1.02E-02 7.47E-07 1.91E+04 4792.874 .250203 

 3.600 -7.33E-08 -1.33E-02 1.71E-02 6.60E-07 1.91E+04 4792.874 .192806 

 3.631 -5.41E-08 -1.27E-02 2.23E-02 5.76E-07 1.91E+04 4792.874 .142423 

 3.662 -3.75E-08 -1.19E-02 2.60E-02 4.97E-07 1.91E+04 4792.874 .098729 

 3.693 -2.33E-08 -1.11E-02 2.85E-02 4.22E-07 1.91E+04 4792.874 .061326 

 3.724 -1.13E-08 -1.01E-02 2.99E-02 3.54E-07 1.91E+04 4792.874 .029765 

 3.755 -1.36E-09 -9.20E-03 3.04E-02 2.91E-07 1.91E+04 4792.874 .003565 

 3.786 6.75E-09 -8.26E-03 3.02E-02 2.35E-07 1.91E+04 4792.874 -.017769 

 3.817 1.32E-08 -7.33E-03 2.94E-02 1.84E-07 1.91E+04 4792.874 -.034735 

 3.848 1.82E-08 -6.44E-03 2.81E-02 1.39E-07 1.91E+04 4792.874 -.047825 

 3.879 2.19E-08 -5.59E-03 2.65E-02 1.01E-07 1.91E+04 4792.874 -.057509 

 3.910 2.44E-08 -4.80E-03 2.46E-02 6.69E-08 1.91E+04 4792.874 -.064237 

 3.941 2.60E-08 -4.07E-03 2.26E-02 3.82E-08 1.91E+04 4792.874 -.068428 

 3.972 2.68E-08 -3.40E-03 2.04E-02 1.40E-08 1.91E+04 4792.874 -.070469 

 4.003 2.69E-08 -2.80E-03 1.82E-02 -6.09E-09 1.91E+04 4792.874 -.070712 

 4.034 2.64E-08 -2.27E-03 1.60E-02 -2.25E-08 1.91E+04 4792.874 -.069474 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-51 December 2005

 4.066 2.55E-08 -1.81E-03 1.39E-02 -3.57E-08 1.91E+04 4792.874 -.067036 

 4.097 2.42E-08 -1.41E-03 1.19E-02 -4.61E-08 1.91E+04 4792.874 -.063644 

 4.128 2.26E-08 -1.07E-03 9.97E-03 -5.41E-08 1.91E+04 4792.874 -.059508 

 4.159 2.08E-08 -7.85E-04 8.20E-03 -6.01E-08 1.91E+04 4792.874 -.054808 

 4.190 1.89E-08 -5.56E-04 6.58E-03 -6.45E-08 1.91E+04 4792.874 -.049693 

 4.221 1.68E-08 -3.75E-04 5.12E-03 -6.75E-08 1.91E+04 4792.874 -.044283 

 4.252 1.47E-08 -2.37E-04 3.83E-03 -6.95E-08 1.91E+04 4792.874 -.038676 

 4.283 1.25E-08 -1.35E-04 2.72E-03 -7.07E-08 1.91E+04 4792.874 -.032943 

 4.314 1.03E-08 -6.58E-05 1.79E-03 -7.13E-08 1.91E+04 4792.874 -.027138 

 4.345 8.10E-09 -2.23E-05 1.04E-03 -7.16E-08 1.91E+04 4792.874 -.021299 

 4.376 5.87E-09 6.32E-07 4.66E-04 -7.17E-08 1.91E+04 4792.874 -.015448 

 4.407 3.65E-09 8.71E-06 7.74E-05 -7.16E-08 1.91E+04 4792.874 -.009597 

 4.438 1.43E-09 7.55E-06 -1.30E-04 -7.16E-08 1.91E+04 4792.874 -.003751 

 4.469 -7.95E-10 2.77E-06 -1.56E-04 -7.15E-08 1.91E+04 4792.874 .002091 

 4.500 -3.01E-09 0.0 0.0 -7.15E-08 1.91E+04 4792.874 .007931 

Please note that because this analysis makes computations of ultimate moment 

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 1: 

Pile-head deflection = .01499829 m 

Computed slope at pile head = -.02954991 

Maximum bending moment = 147.640 kN- m 

Maximum shear force = 330.000 kN 

Depth of maximum bending moment = .43448276 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 22 

Number of zero deflection points = 5 

------------------------------------------------------------------------------ 

 Summary of Pile-head Response 

------------------------------------------------------------------------------ 

Definition of symbols for pile-head boundary conditions: 

y = pile-head displacment, m 

M = pile-head moment, kN- m 

V = pile-head shear force, kN 

S = pile-head slope, radians 

R = rotational stiffness of pile-head, m- kN/rad 

 BC Boundary Boundary Axial Pile Head Maximum Maximum 

Type Condition Condition Load Deflection Moment Shear 

 1 2 kN m m- kN kN 

---- ------------ ------------ ----------- ----------- ----------- ----------- 

 1 V = 330.000 M = 76.200 474.5000 .014998 147.6397 330.0000 
FHWA NHI-05-039 Appendix B 

Micropile Design & Construction B-52 December 2005
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-1 December 2005

APPENDIX C

Micropile Guide Construction Specification 

 [Foundation Support Projects] 

Contractor Design/Build of Micropiles

Metric (SI) Units 

(With Commentary)

(Commentary: Owner-Controlled design specifications can vary in the amount of the design 

to be performed by the Owner’s design engineer and the amount performed by the micropile 

specialty Contractor. This guide specification is set up for the Owner-controlled design 

(Standard Design) method wherein the Owner provides preliminary plans showing the pile 

design loadings, footing design, and pile layout for each footing location. The Owner also 

provides related design criteria and requirements, subsurface data, rights-of-way limits, 

utility locations, site limitations, construction material and testing specifications, and 

required Contractor working drawing/design and construction submittals and review 

requirements. The micropile Contractor designs the individual micropile elements and pile 

top footing connections and selects the micropile construction process and equipment. This 

approach is very similar to that commonly used by many highway agencies for Owner design 

of permanent tieback and permanent soil nail walls. During the bidding process, the 

micropile contractors prepare a preliminary micropile design and a firm cost proposal based 

on the Owner’s preliminary plans and specifications. If the micropile portion of the project is 

to be subcontracted, general contractors will receive bids from the micropile contractors and 

include the best offer and name of the selected micropile contractor in their bid submittal. 

Once the contract is awarded, the selected micropile Contractor prepares detailed micropile 

design calculations and working drawings and submits them to the Engineer for review. 

After acceptance of the design, construction begins.)

1.0 DESCRIPTION 

This work shall consist of constructing micropiles as shown on the contract plans and 

approved working drawings and as specified herein. The micropile specialty Contractor is 

responsible for furnishing of all design, materials, products, accessories, tools, equipment, 

services, transportation, labor and supervision, and manufacturing techniques required for 

design, installation and testing of micropiles and pile top attachments for this project. 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-2 December 2005

The selected micropile Contractor shall select the micropile type, size, pile top attachment, 

installation means and methods, estimate the ground-grout bond value and determine the 

required bond length and final micropile diameter. The micropile Contractor shall design 

and install micropiles that will develop the load capacities indicated on the contract plans. 

The micropile load capacities shall be verified by verification and proof load testing as 

required and must meet the test acceptance criteria specified herein. 

Where the imperative mood is used within this specification, “The Contractor shall” is 

implied. 

(Commentary: Successful design and installation of high-quality micropiles require 

experienced Contractors having the necessary specialty drilling and grouting equipment and 

expertise and experienced work crews. The most important section of the specifications to 

be enforced by the Owner deals with the experience qualifications of the micropile 

Contractor. Failure to enforce the specified experience qualifications opens the door for 

inexperienced Contractors trying to cut costs. The results often are inferior workmanship, 

project delays, and project claims that, more often than not, substantially increase project 

costs. Results like these often discourage project Owners from implementing new 

technology, and draws them back to more traditional methods at any cost. This can be 

avoided with the proper specification implementation and, as importantly, enforcement to 

ensure a mutually successful project.) 

1.1 Micropile Contractor’s Experience Requirements And Submittal. 

The micropile Contractor shall be experienced in the construction and load testing of 

micropiles and have successfully constructed at least 5 projects in the last 5 years involving 

construction totaling at least 100 micropiles of similar capacity to those required in these 

plans and specifications. 

The Contractor shall have previous micropile drilling and grouting experience in soil/rock 

similar to project conditions. The Contractor shall submit construction details, structural 

details and load test results for at least three previous successful micropile load tests from 

different projects of similar scope to this project. 

The Contractor shall assign an Engineer to supervise the work with experience on at least 3 

projects of similar scope to this project completed over the past 5 years. The Contractor shall 

not use consultants or manufacturers’ representatives to satisfy the supervising Engineer 

requirements of this section. The on-site foremen and drill rig operators shall also have 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-3 December 2005

experience on at least 3 projects over the past 5 years installing micropiles of equal or greater 

capacity than required in these plans and specifications. 

The micropiles shall be designed by a Registered Professional Engineer with experience in 

the design of at least 3 successfully completed micropile projects over the past 5 years, with 

micropiles of similar capacity to those required in these plans and specifications. The 

micropile design engineer may be either an employee of the Contractor or a separate 

Consultant design engineer meeting the stated experience requirements. (Commentary: If 

the Owner prepares a fully detailed design, this paragraph can be deleted). 

At least 45 calendar days before the planned start of micropile construction, the Contractor 

shall submit 5 copies of the completed project reference list and a personnel list. The project 

reference list shall include a brief project description with the owner's name and current 

phone number and load test reports. The personnel list shall identify the micropile system 

design engineer (if applicable), supervising project Engineer, drill rig operators, and on-site 

foremen to be assigned to the project. The personnel list shall contain a summary of each 

individual's experience and be complete enough for the Engineer to determine whether each 

individual satisfies the required qualifications. The Engineer will approve or reject the 

Contractor's qualifications within 15 calendar days after receipt of a complete submission. 

Additional time required due to incomplete or unacceptable submittals will not be cause for 

time extension or impact or delay claims. All costs associated with incomplete or 

unacceptable submittals shall be borne by the Contractor. 

Work shall not be started, nor materials ordered, until the Engineer’s written approval of the 

Contractor's experience qualifications is given. The Engineer may suspend the Work if the 

Contractor uses non-approved personnel. If work is suspended, the Contractor shall be fully 

liable for all resulting costs and no adjustment in contract time will result from the 

suspension. 

1.2 Related Specifications 

(Commentary: Engineer to specify all related specifications.) 

1.3 Definitions 

(Commentary: Engineer to specify any additional definitions.) 

Admixture: Substance added to the grout to control bleed and/or shrinkage, improve 

flowability, reduce water content, or retard setting time. 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-4 December 2005

Alignment Load (AL): A minimum initial load (no greater than 10 percent of the Design 

Load) applied to micropile during testing to keep the testing equipment correctly 

positioned. 

Bond Length: The length of the micropile that is bonded to the ground and used to transfer 

the applied axial loads to the surrounding soil or rock. 

Bond-breaker: A sleeve placed over the steel reinforcement to prevent load transfer. 

Casing: Steel tube introduced during the drilling process in overburden soil to temporarily 

stabilize the drill hole. This is usually withdrawn as the pile is grouted, although in 

certain types of micropiles, some casing is permanently left in place to provide added 

pile reinforcement. 

Centralizer: A device to support and position the reinforcing steel in the drill hole and/or 

casing so that a minimum grout cover is provided. 

Contractor: The person/firm responsible for performing the micropile work. 

Coupler: The means by which load capacity can be transmitted from one partial length of 

reinforcement to another. 

Creep Movement: The movement that occurs during the creep test of a micropile under a 

constant load. 

Design Load (DL): The maximum load expected to be applied to the micropile during its 

service life. 

Encapsulation: A corrugated or deformed tube protecting the reinforcing steel against 

corrosion. 

Engineer: The Owner or Owner’s authorized agent. 

Free (unbonded) length: The designed length of the micropile that is not bonded to the 

surrounding ground or grout. 

Micropile: A small-diameter, bored, cast-in-place composite pile, in which the applied load 

is resisted by steel reinforcement, cement grout and frictional grout/ground bond. 

Maximum Test Load: The maximum load to which the micropile is subjected during 

testing. 

Ultimate Grout-to-Ground Bond Values: The estimated ultimate geotechnical unit groutto-ground bond strength selected for use in design. 

Overburden: Material, natural or placed, that may require cased drilling methods to provide 

an open borehole to underlying strata. 

Post-grouting: The injection of additional grout into the load transfer length of a micropile 

after the primary grout has set. Also known as regrouting or secondary grouting. 

Primary Grout: Portland-cement-based grout injected into the micropile hole prior to or 

after the installation of the reinforcement to direct the load transfer to the surrounding 

ground along the micropile. 
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Micropile Design & Construction C-5 December 2005

Proof Load Test: Incremental loading of a production micropile, recording the total 

movement at each increment. 

Reinforcement: The steel component of the micropile that accepts and/or resists applied 

loadings. 

Sheathing: Smooth or corrugated piping or tubing that protects the reinforcing steel against 

corrosion. 

Spacer: A device to separate elements of a multiple-element reinforcement. 

Verification Load Test: Pile load test performed to verify the design of the pile system and 

the construction methods proposed, prior to installation of production piles. 

1.4 Referenced Codes and Standards. 

The following publications form a part of this specification to the extent indicated by the 

references. The latest publication as of the issue date of this specification shall govern, 

unless indicated otherwise. 

1.4.1 American Society for Testing and Materials (ASTM) 

 American Association of State Highway and Transportation Officials (AASHTO) 

ASTM AASHTO SPECIFICATION / TEST 

A36, A572 M183, M223 Structural Steel 

A82 M55 Cold-Drawn Steel Wire for Concrete Reinforcement 

A252 – Welded and Seamless Steel Pipe Piles 

A615 M31 Deformed and Plain Billet Steel Bars for Concrete Reinforcement 

A722 M275 Uncoated High-Strength Steel Bar for Prestressing Concrete 

 A775 – Epoxy -Coated Reinforcing Steel Bars 

A934 – Epoxy-Coated Prefabricated Steel Reinforcing Bars 

C 33 M80 Concrete Aggregates 

C 109 T106 Compressive Strength of Hydraulic Cement Mortar 

C 188 T133 Density of Hydraulic Cement 

C 144 M45 Aggregate for Masonry Mortar 

C 150 M 85 Portland Cement 

C 494 M194 Chemical Admixtures for Concrete 

D 1143 – Method of Testing Piles Under Static Axial Compressive Load 

D 1784 – Polyvinyl Chloride (PVC) Pipe (Class 13464-B) 

D 3350 M 252 Polyethylene Corrugated Tubing 

D 3689 – Method of Testing Individual Piles Under Static Axial Tensile Load 

D 3966 Standard Test Method for Piles Under Lateral Load 

– T 26 Quality of Water to be Used in Concrete 
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Micropile Design & Construction C-6 December 2005

1.4.2 American Welding Society (AWS) 

 D1.1 Structural Welding Code-Steel 

 D1.2 Structural Welding Code-Reinforcing Steel 

1.4.3 American Petroleum Institute (API) 

 5CT (N-80) Specification for casing and tubing 

 RP 13B-1 Recommended Practice – Standard Procedure for Field Testing 

Water Based Drilling Fluids 

1.5 Available Information. 

Available information developed by the Owner, or by the Owner’s duly authorized 

representative include the following items: 

1. Plans prepared by ___________ , dated __________.

2. Geotechnical Report No.(s) ________ titled __________, dated__________. 

(Commentary: The subsurface conditions expected can significantly impact the contractor's 

choice of procedures, methods, or equipment, the bidding process, and contract 

administration. Experience has proven that use of a geotechnical summary is advantageous 

toward achieving a successful contract. It is recommended that advisory wording be inserted 

into the contract special provisions to "red flag" the conditions to bidders. Such a summary 

may become part of the contract special provisions, making it a legal part of the contract 

documents. The purpose is to alert and be fair to bidders, and thus prevent/minimize 

differing site condition construction claims and dispute.)

1.6 Construction Site Survey 

Before bidding the Work, the Contractor shall review the available subsurface information 

and visit the site to assess the site geometry, equipment access conditions, and location of 

existing structures and above ground facilities. 

The Contractor is responsible for field locating and verifying the location of all utilities 

shown on the plans prior to starting the Work. Maintain uninterrupted service for those 

utilities designated to remain in service throughout the Work. Notify the Engineer of any 

utility locations different from shown on the plans that may require micropile relocations or 

structure design modification. Subject to the Engineer’s approval, additional cost to the 

Contractor due to micropile relocations and/or structure design modification resulting from 

utility locations different from shown on the plans, will be paid as Extra Work. 

(Commentary: The location of both active and abandoned buried utilities within the ground 

mass to receive micropiles can have a profound impact on the design and construction of the 
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Micropile Design & Construction C-7 December 2005

micropiles. Careful consideration of the presence and location of all utilities is required for 

successful design and installation of micropiles.)

Prior to start of any micropile construction activity, the Contractor and Engineer shall jointly 

inspect the site to observe and document the pre-construction condition of the site, existing 

structures and facilities. 

1.7 Micropile Design Requirements. 

The micropiles shall be designed to meet the specified loading conditions, as shown on the 

contract plans and approved working drawings. Design the micropiles and pile top to footing 

connections using the procedures contained in the FHWA “Micropile Design and 

Construction”, Report No. FHWA NHI-05-039. 

The required geotechnical factors of safety shall be in accord with the FHWA manual, unless 

specified otherwise. Estimated soil/rock design shear strength parameters, unit weights, 

applied foundation loadings, slope and external surcharge loads, corrosion protection 

requirements, known utility locations, easements, right-of-ways and other applicable design 

criteria will be as shown on the plans or specified herein. 

Structural design of any individual micropile structure elements not covered in the FHWA 

manual shall be by the service load design method in conformance with appropriate articles 

of the most current Edition of the AASHTO Standard Specifications for Highway Bridges, 

including current interim specifications. 

Where required as shown on the contract plans, corrosion protection of the internal steel 

reinforcing bars, consisting of either encapsulation, epoxy coating, or grout, shall be provided 

in accordance with Materials Section 2.0. Where permanent casing is used for a portion of 

the micropile, encapsulation shall extend at least 1.5 m into the casing. 

(Commentary: The previous paragraph is not comprehensive. Corrosion protection 

requirements need to be evaluated on a project-specific basis and detailed specifications and 

drawings depicting the corrosion protection requirements should be provided.) 

(Commentary: When installation of micropiles provides additional support for existing 

structures, such as for seismic retrofit or underpinning applications, the structural designer 

should add appropriate specification verbiage and design criteria into this specification to 

cover the penetration of the existing structural elements and the top of pile anchorage to the 

existing structure.) 
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Micropile Design & Construction C-8 December 2005

1.7.1 Micropile Design Submittals. 

At least 21 calendar days before the planned start of micropile structure construction, submit 

complete design calculations and working drawings to the Engineer for review and approval. 

Include all details, dimensions, quantities, ground profiles, and cross-sections necessary to 

construct the micropile structure. Verify the limits of the micropile structure and ground 

survey data before preparing the detailed working drawings. 

The drawings and calculations shall be signed and sealed by the contractor’s Professional 

Engineer or by the Consultant designer’s Professional Engineer (if applicable), previously 

approved by the owner’s Engineer. If the micropile contractor uses a consultant design 

engineer to prepare the design, the micropile contractor shall still have overall contract 

responsibility for both the design and the construction. 

1.7.2 Design Calculations. 

Design calculations shall include, but not be limited to, the following items: 

1. A written summary report which describes the overall micropile design. 

2. Applicable code requirements and design references. 

3. Micropile structure critical design cross-section(s) geometry including soil/rock strata 

and piezometric levels and location, magnitude and direction of design applied 

loadings, including slope or external surcharge loads. 

4. Design criteria including, soil/rock shear strengths (friction angle and cohesion), unit 

weights, and ground-grout bond values and micropile drillhole diameter assumptions 

for each soil/rock strata. 

5. Factors of safety and allowable stresses used in the design on the ground-grout bond 

values, surcharges, soil/rock and material unit weights, steel, grout, and concrete 

materials. 

6. Seismic design earthquake acceleration coefficient. 

7. Design calculation sheets (both static and seismic) with the project number, micropile 

structure location, designation, date of preparation, initials of designer and checker, 

and page number at the top of each page. Provide an index page with the design 

calculations. 

8. Design notes including an explanation of any symbols and computer programs used in 

the design. 

9. Pile to footing connection calculations. 

(Commentary: If the contract allows the Contractor to provide alternative number of 

micropiles (e.g., provide fewer high capacity micropiles as compared to what is provided in 

plans, then the Contractor should also provide calculations for footing reinforcement (if 

different than that provided in the plans))). 
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Micropile Design & Construction C-9 December 2005

1.7.3 Working Drawings. 

The working drawings shall include all information required for the construction and quality 

control of the piling. Working drawings shall include, but not be limited to, the following 

items unless provided in the contract plans: 

1. A plan view of the micropile structure(s) identifying: 

(a) A reference baseline and elevation datum. 

(b) The offset from the construction centerline or baseline to the face of the 

micropile structure at all changes in horizontal alignment. 

 (c) Beginning and end of micropile structure stations. 

(d) Right-of-way and permanent or temporary construction easement limits, 

location of all known active and abandoned existing utilities, adjacent structures 

or other potential interferences. The centerline of any drainage structure or 

drainage pipe behind, passing through, or passing under the micropile structure. 

(e) Subsurface exploration locations shown on a plan view of the proposed 

micropile structure alignment with appropriate reference base lines to fix the 

locations of the explorations relative to the micropile structure. 

2. An elevation view of the micropile structure(s) identifying: 

(a) Elevation view showing micropile locations and elevations; vertical and 

horizontal spacing; batter and alignment and the location of drainage elements 

(if applicable). 

(b) Existing and finish grade profiles both behind and in front of the micropile 

structure. 

3. Design parameters and applicable codes. 

4. General notes for constructing the micropile structure including construction 

sequencing or other special construction requirements. 

5. Horizontal and vertical curve data affecting the micropile structure and micropile 

structure control points. Match lines or other details to relate micropile structure 

stationing to centerline stationing. 

6. A listing of the summary of quantities on the elevation drawing of each micropile 

structure showing pay item estimated quantities. 

7. Micropile typical sections including micropile spacing and inclination; minimum 

drillhole diameter; pipe casing and reinforcing bar sizes and details; splice types and 

locations; centralizers and spacers; grout bond zone and casing plunge lengths (if 

used); corrosion protection details; and connection details to the substructure footing, 

anchorage, plates, etc. 

8. A typical detail of verification and production proof test micropiles defining the 

micropile length, minimum drillhole diameter, inclination, and load test bonded and 

unbonded test lengths. 
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Micropile Design & Construction C-10 December 2005

9. Details, dimensions, and schedules for all micropiles, casing and reinforcing steel, 

including reinforcing bar bending details. 

10. Details for constructing micropile structures around drainage facilities (if applicable). 

The working drawings and design calculations shall be signed and sealed by the Contractor’s 

Professional Engineer or by the Consultant designer’s Professional Engineer (if applicable), 

by the Owner. If the micropile Contractor uses a Consultant design engineer to prepare the 

design, the micropile Contractor shall still have overall contract responsibility for both the 

design and the construction. 

Submit 5 sets of the working drawings with the initial submission. Drawing sheet size shall 

be 550 by 850 mm. One set will be returned with any indicated corrections. The Engineer 

will approve or reject the Contractor's submittal within 15 calendar days after receipt of a 

complete submission. If revisions are necessary, make the necessary corrections and 

resubmit 5 revised sets. When the drawings are approved, furnish 5 sets and a Mylar sepia 

set of the approved drawings. The Contractor will not be allowed to begin micropile structure 

construction or incorporate materials into the work until the submittal requirements are 

satisfied and found acceptable to the Engineer. Changes or deviations from the approved 

submittals must be re-submitted for approval. No adjustments in contract time or delay or 

impact claims will be allowed due to incomplete submittals. (Commentary: Submittals 

procedures shall be coordinated with Owner/Agency procedures).

Revise the drawings when plan dimensions are changed due to field conditions or for other 

reasons. Within 30 days after completion of the work, submit as-built drawings to the 

Engineer. Provide revised design calculations signed by the approved Registered 

Professional Engineer for all design changes made during the construction of the micropile 

structure. 

1.8 Construction Submittals. 

The Contractor shall prepare and submit to the Engineer, for review of completeness, 5 

copies of the following for the micropile system or systems to be constructed: 

1. Detailed step-by-step description of the proposed micropile construction procedure, 

including personnel, testing and equipment to assure quality control. This step-by-step 

procedure shall be shown on the working drawings in sufficient detail to allow the 

Engineer to monitor the construction and quality of the micropiles. 

2. Proposed start date and time schedule and micropile installation schedule providing 

the following: 

 Micropile number 

 Micropile design load 
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Micropile Design & Construction C-11 December 2005

 Type and size of reinforcing steel 

 Minimum bond length 

 Total micropile length 

 Micropile top footing attachment 

3. If welding of casing is proposed, submit the proposed welding procedure, certified by 

a qualified welding specialist. 

4. Information on headroom and space requirements for installation equipment that 

verify the proposed equipment can perform at the site. 

5. Plan describing how surface water, drill flush, and excess waste grout will be 

controlled and disposed. 

6. Certified mill test reports for the reinforcing steel or coupon test results for permanent 

casing without mill certification. The ultimate strength, yield strength, elongation, and 

material properties composition shall be included. For API N-80 pipe casing, coupon 

test results may be submitted in lieu of mill certification. 

7. Proposed Grouting Plan. The grouting plan shall include complete descriptions, 

details, and supporting calculations for the following: 

(a) Grout mix design and type of materials to be used in the grout including 

certified test data and trial batch reports. 

(b) Methods and equipment for accurately monitoring and recording the grout 

depth, grout volume and grout pressure as the grout is being placed. 

(c) Grouting rate calculations, when requested by the Engineer. The calculations 

shall be based on the initial pump pressures or static head on the grout and 

losses throughout the placing system, including anticipated head of drilling fluid 

(if applicable) to be displaced. 

(d) Estimated curing time for grout to achieve specified strength. Previous test 

results for the proposed grout mix completed within one year of the start of 

grouting may be submitted for initial verification and acceptance and start of 

production work. During production, grout shall be tested in accord with 

Section 3.4.5. 

(e) Procedure and equipment for Contractor monitoring of grout quality. 

8. Detailed plans for the proposed micropile load testing method. This shall include all 

drawings, details, and structural design calculations necessary to clearly describe the 

proposed test method, reaction load system capacity and equipment setup, types and 

accuracy of apparatus to be used for applying and measuring the test loads and pile top 

movements in accordance with Section 3.6, Pile Load Tests. 

9. Calibration reports and data for each test jack, pressure gauge and master pressure 

gauge and electronic load cell to be used. The calibration tests shall have been 
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Micropile Design & Construction C-12 December 2005

performed by an independent testing laboratory, and tests shall have been performed 

within 90 calendar days of the date submitted. Testing shall not commence until the 

Engineer has reviewed and accepted the jack, pressure gauge, master pressure gauge 

and electronic load cell calibration data. 

Work other than test pile installation shall not begin until the construction submittals have 

been received, reviewed, and accepted in writing by the Engineer. Provide submittal items 1 

through 5 at least 21 calendar days prior to initiating micropile construction, item 7 as the 

work progresses for each delivery and submittal items 6, 8 and 9 at least 7 days prior to start 

of micropile load testing or incorporation of the respective materials into the work. The 

Contractor shall allow the Engineer 7 calendar days to review the construction submittals 

after a complete set has been received. Additional time required due to incomplete or 

unacceptable submittals shall not be cause for delay or impact claims. All costs associated 

with incomplete or unacceptable Contractor submittals shall be the responsibility of the 

Contractor. 

1.9 Pre-construction Meeting. 

A pre-construction meeting will be scheduled by the Engineer and held prior to the start of 

micropile construction. The Engineer, prime Contractor, micropile specialty Contractor, 

micropile design engineer, excavation Contractor and geotechnical instrumentation specialist 

(if applicable) shall attend the meeting. Attendance is mandatory. The pre-construction 

meeting will be conducted to clarify the construction requirements for the work, to 

coordinate the construction schedule and activities, and to identify contractual relationships 

and delineation of responsibilities amongst the prime Contractor and the various 

Subcontractors - specifically those pertaining to excavation for micropile structures, 

anticipated subsurface conditions, micropile installation and testing, micropile structure 

survey control and site drainage control. 

2.0 MATERIALS. 

Furnish materials new and without defects. Remove defective materials from the jobsite at 

no additional cost. Materials for micropiles shall consist of the following: 

Admixtures for Grout: Admixtures shall conform to the requirements of ASTM C 

494/AASHTO M194. Admixtures that control bleed, improve flowability, reduce water 

content, and retard set may be used in the grout, subject to the review and acceptance of the 

Engineer. Admixtures shall be compatible with the grout and mixed in accordance with the 

manufacturer’s recommendations. Expansive admixtures shall only be added to the grout 
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Micropile Design & Construction C-13 December 2005

used for filling sealed encapsulations and anchorage covers. Accelerators are not permitted. 

Admixtures containing chlorides are not permitted. 

Cement: All cement shall be Portland cement conforming to ASTM C 150/AASHTO M85, 

Types I, II, III or V. 

Centralizers and Spacers: Centralizers and spacers shall be fabricated from schedule 40 

PVC pipe or tube, steel, or material non-detrimental to the reinforcing steel. Wood shall not 

be used. 

Encapsulation: Encapsulation (double corrosion protection) shall be shop fabricated using 

high-density, corrugated polyethylene tubing conforming to the requirements of ASTM 

D3350/AASHTO M252 with a nominal wall thickness of 0.8 mm. The inside annulus 

between the reinforcing bars and the encapsulating tube shall be a minimum of 5mm and be 

fully grouted with non-shrink grout conforming to Materials Section 2.0. 

Epoxy Coating: The minimum thickness of coating applied electrostatically to the 

reinforcing steel shall be 0.3 mm. Epoxy coating shall be in accordance with ASTM A775 or 

ASTM A934. Bend test requirements are waived. Bearing plates and nuts encased in the pile 

concrete footing need not be epoxy coated unless the footing reinforcement is epoxy coated. 

Fine Aggregate: If sand - cement grout is used, sand shall conform to ASTM C 

144/AASHTO M45. 

Galvanization: If used, galvanization shall meet the requirements of ASTM A-153. 

Grout: Neat cement or sand/cement mixture with a minimum 3-day compressive strength of 

14 MPa and a 28-day compressive strength of 28 MPa per AASHTO T106/ASTM C109. 

(Commentary: Note to designers/specifiers. A 28-day grout strength of 28 MPa is common 

for micropiles. If the micropile design calls for higher grout strength, revise the specification 

accordingly.)

Permanent Casing Pipe: Permanent steel casing/pipe shall have the diameter and at least 

minimum wall thickness shown on the approved Working Drawings. The permanent steel 

casing/pipe: 

1. shall meet the Tensile Requirements of ASTM A252, Grade 3, except the yield 

strength shall be a minimum of 345 MPa to 552 MPa as used in the design submittal. 
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Micropile Design & Construction C-14 December 2005

2. may be new "Structural Grade" (a.k.a. "Mill Secondary" ) steel pipe meeting above but 

without Mill Certification, free from defects (dents, cracks, tears) and with two coupon 

tests per truckload delivered to the fabricator. 

For permanent casing/pipe that will be welded for structural purposes, the following material 

conditions apply: 

1. the carbon equivalency (CE) as defined in AWS D1.l, Section XI5.1, shall not exceed 

0.45, as demonstrated by mill certifications 

2. the sulfur content shall not exceed 0.05%, as demonstrated by mill certifications 

For permanent casing/pipe that will be shop or field welded, the following fabrication or 

construction conditions apply: 

1. the steel pipe shall not be joined by welded lap splicing 

2. welded seams and splices shall be complete penetration welds 

3. partial penetration welds may be restored in conformance with AWS D1.1 

4. the proposed welding procedure certified by a welding specialist shall be submitted for 

approval 

Threaded casing joints shall develop at least the required compressive, tensile, and/or 

bending strength used in the design of the micropile. 

(Commentary: From a practical standpoint, the adequacy of pipe and reinforcing bar splices 

and threaded joint connections will be verified by the verification and proof load testing).

Plates and Shapes: Structural steel plates and shapes for pile top attachments shall conform 

to ASTM A 36/AASHTO M183, or ASTM A 572/AASHTO M223, Grade 350. 

Reinforcing Bars: Reinforcing steel shall be deformed bars in accordance with ASTM 

A 615/AASHTO M31, Grade 420 or Grade 520 or ASTM A 722/AASHTO M275, Grade 

1035. When a bearing plate and nut are required to be threaded onto the top end of 

reinforcing bars for the pile top to footing anchorage, the threading may be continuous spiral 

deformed ribbing provided by the bar deformations (e.g., Dywidag or Williams continuous 

threadbars) or may be cut into a reinforcing bar. If threads are cut into a reinforcing bar, the 

next larger bar number designation from that shown on the Plans shall be provided, at no 

additional cost. 

Bar tendon couplers, if required, shall develop the ultimate tensile strength of the bars 

without evidence of any failure. 
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Micropile Design & Construction C-15 December 2005

Reinforcing Bar Corrosion Protection:

(Commentary: Corrosion protection requirements vary between Transportation Agencies. 

The most common and simplest tests utilized to measure the aggressiveness of the soil 

environment include electrical resistivity, pH, chloride, and sulfate. Per FHWA NHI-05-039, 

the ground is considered aggressive if any one of these indicators show critical values as 

detailed below: 

PROPERTY TEST DESIGNATION* CRITICAL VALUES* 

Resistivity AASHTO T-288 below 3,000 ohm-cm

pH AASHTO T-289 below 5 or above 10

Sulfates AASHTO T-290 above 200 ppm

Chlorides AASHTO T-291 above 100 ppm

* Specifier should check test standards for latest updates and individual transportation 

agencies may have limits on critical values different than tabulated above. Standard 

specifications or test methods for any of the above items which are common to your 

agency can be referenced in lieu of the above listed AASHTO/ASTM references.

Sheathing: Smooth plastic sheathing, including joints, shall be watertight. Polyvinyl chloride 

(PVC) sheathing shall conform to ASTM D 1784, Class 13464-B. 

Water: Water used in the grout mix shall conform to AASHTO T 26 and shall be potable, 

clean, and free from substances that may be injurious to cement and steel. 

3.0 CONSTRUCTION REQUIREMENTS 

3.1 Site Drainage Control. 

The Contractor shall control and properly dispose of drill flush and construction related 

waste, including excess grout, in accord with the standard specifications and all applicable 

local codes and regulations. Provide positive control and discharge of all surface water that 

will affect construction of the micropile installation. Maintain all pipes or conduits used to 

control surface water during construction. Repair damage caused by surface water at no 

additional cost. Upon substantial completion of the Work, remove surface water control pipes 

or conduits from the site. Alternatively, with the approval of the Engineer, pipes or conduits 

that are left in place, may be fully grouted and abandoned or left in a way that protects the 
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Micropile Design & Construction C-16 December 2005

structure and all adjacent facilities from migration of fines through the pipe or conduit and 

potential ground loss. 

Immediately contact the Engineer if unanticipated existing subsurface drainage structures are 

discovered during excavation or drilling. Suspend work in these areas until remedial 

measures meeting the Engineer’s approval are implemented. Cost of remedial measures or 

repair work resulting from encountering unanticipated subsurface drainage structures, will be 

paid for as Extra Work. 

3.2 Excavation 

Coordinate the work and the excavation so the micropile structures are safely constructed. 

Perform the micropile construction and related excavation in accordance with the Plans and 

approved submittals. No excavations steeper than those specified herein or shown on the 

Plans will be made above or below the micropile structure locations without written approval 

of the Engineer. 

3.3 Micropile Allowable Construction Tolerances 

1. Centerline of piling shall not be more than 75 mm from indicated plan location. 

2. Pile shall be plumb within 2 percent of total-length plan alignment. 

3. Top elevation of pile shall be plus 25 mm or minus 50 mm maximum from vertical 

elevation indicated. 

4. Centerline of reinforcing steel shall not be more than 19 mm from indicated 

location. 

(Commentary: The tolerances provided in this Section are maxima. Depending on the 

structural requirements, the actual values set for a particular project may need to be lower.)

3.4 Micropile Installation 

The micropile Contractor shall select the drilling method, the grouting procedure, and the 

grouting pressure used for the installation of the micropiles. The micropile Contractor shall 

also determine the micropile casing size, final drillhole diameter and bond length, and central 

reinforcement steel sizing necessary to develop the specified load capacities and load testing 

requirements. The micropile Contractor is also responsible for estimating the grout take. 

There will be no extra payment for grout overruns. (Commentary: Note, extra payment for 

grout takes is appropriate for micropiles in Karst. Otherwise, the bid price of these piles will 

be artificially high to cover risk of high grout loss.)
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Micropile Design & Construction C-17 December 2005

3.4.1 Drilling 

The drilling equipment and methods shall be suitable for drilling through the conditions to be 

encountered, without causing damage to any overlying or adjacent structures or services. 

The drillhole must be open along its full length to at least the design minimum drillhole 

diameter prior to placing grout and reinforcement. (Commentary: When micropile 

construction will occur in close proximity to settlement sensitive structures, recommend 

including the following sentence in the specification - Vibratory pile driving hammers shall 

not be used to advance casing.)

Temporary casing or other approved method of pile drillhole support will be required in 

caving or unstable ground to permit the pile shaft to be formed to the minimum design 

drillhole diameter. The Contractor’s proposed method(s) to provide drillhole support and to 

prevent detrimental ground movements shall be reviewed by the Engineer. Detrimental 

ground movement is defined as movement which requires remedial repair measures. Use of 

drilling fluid containing bentonite is not allowed. (Commentary: The specification verbiage 

related to drillhole support methods and difficulty of drilling may vary project to project 

depending on the subsurface conditions revealed by the subsurface investigation data. It is 

the micropile specialty contractor’s responsibility to select the proper drilling equipment and 

methods for the site conditions. It is the owner’s responsibility to provide the available 

subsurface information. For projects with difficult ground conditions, use of an “advisory 

specification” included in the contract documents is recommended).

Costs of removal or remedial measures due to encountering unanticipated subsurface 

obstructions will be paid for as Extra Work. 

3.4.2 Ground Heave or Subsidence. 

During construction, the Contractor shall observe the conditions in the vicinity of the 

micropile construction site on a daily basis for signs of ground heave or subsidence. 

Immediately notify the Engineer if signs of movements are observed. Contractor shall 

immediately suspend or modify drilling or grouting operations if ground heave or subsidence 

is observed, if the micropile structure is adversely affected, or if adjacent structures are 

damaged from the drilling or grouting. If the Engineer determines that the movements require 

corrective action, the Contractor shall take corrective actions necessary to stop the movement 

or perform repairs. When due to the Contractor’s methods or operations or failure to follow 

the specified/approved construction sequence, as determined by the Engineer, the costs of 

providing corrective actions will be borne by the Contractor. When due to differing site 

conditions, as determined by the Engineer, the costs of providing corrective actions will be 

paid as Extra Work. 
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Micropile Design & Construction C-18 December 2005

3.4.3 Pipe Casing and Reinforcing Bars Placement and Splicing. 

Reinforcement may be placed either prior to grouting or placed into the grout - filled 

drillhole before temporary casing (if used) is withdrawn. Reinforcement surface shall be free 

of deleterious substances such as soil, mud, grease or oil that might contaminate the grout or 

coat the reinforcement and impair bond. Pile cages and reinforcement groups, if used, shall 

be sufficiently robust to withstand the installation and grouting process and the withdrawal of 

the drill casings without damage or disturbance. 

The Contractor shall check pile top elevations and adjust all installed micropiles to the 

planned elevations. 

Centralizers and spacers (if used) shall be provided at 3-m centers maximum spacing. The 

upper and lower most centralizer shall be located a maximum of 1.5 m from the top and 

bottom of the micropile. Centralizers and spacers shall permit the free flow of grout without 

misalignment of the reinforcing bar(s) and permanent casing. The central reinforcement bars 

with centralizers shall be lowered into the stabilized drillhole and set. The reinforcing steel 

shall be inserted into the drill hole to the desired depth without difficulty. Partially inserted 

reinforcing bars shall not be driven or forced into the hole. Contractor shall redrill and 

reinsert reinforcing steel when necessary to facilitate insertion. 

Lengths of casing and reinforcing bars to be spliced shall be secured in proper alignment and 

in a manner to avoid eccentricity or angle between the axes of the two lengths to be spliced. 

Splices and threaded joints shall meet the requirements of Materials Section 2.0. Threaded 

pipe casing joints shall be located at least two casing diameters (OD) from a splice in any 

reinforcing bar. When multiple bars are used, bar splices shall be staggered at least 0.3 

meters. 

3.4.4 Grouting. 

Micropiles shall be primary grouted the same day the load transfer bond length is drilled. The 

Contractor shall use a stable neat cement grout or a sand cement grout with a minimum 28-

day unconfined compressive strength of 28 MPa. Admixtures, if used, shall be mixed in 

accordance with manufacturer’s recommendations. The grouting equipment used shall 

produce a grout free of lumps and undispersed cement. The Contractor shall have means and 

methods of measuring the grout quantity and pumping pressure during the grouting 

operations. The grout pump shall be equipped with a pressure gauge to monitor grout 

pressures. A second pressure gauge shall be placed at the point of injection into the pile top. 

The pressure gauges shall be capable of measuring pressures of at least 1 MPa or twice the 

actual grout pressures used, whichever is greater. The grout shall be kept in agitation prior to 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-19 December 2005

mixing. Grout shall be placed within one hour of mixing. The grouting equipment shall be 

sized to enable each pile to be grouted in one continuous operation. 

The grout shall be injected from the lowest point of the drill hole and injection shall continue 

until uncontaminated grout flows from the top of the pile. The grout may be pumped through 

grout tubes, casing, hollow-stem augers, or drill rods. Temporary casing, if used, shall be 

extracted in stages ensuring that, after each length of casing is removed the grout level is 

brought back up to the ground level before the next length is removed. The tremie pipe or 

casing shall always extend below the level of the existing grout in the drillhole. The grout 

pressures and grout takes shall be controlled to prevent excessive heave or fracturing of rock 

or soil formations. Upon completion of grouting, the grout tube may remain in the hole, but 

must be filled with grout. 

Grout within the micropiles shall be allowed to attain the required design strength prior to 

being loaded. 

If the Contractor elects to use a postgrouting system, Working Drawings and details shall be 

submitted to the Engineer for review in accordance with Section 1.8, Pre-installation 

Submittals. 

3.4.5 Grout Testing 

Grout within the micropile verification and proof test piles shall attain the minimum required 

3-day compressive strength of 14 MPa prior to load testing. Previous test results for the 

proposed grout mix completed within one year of the start of work may be submitted for 

initial verification of the required compressive strengths for installation of pre-production 

verification test piles and initial production piles. During production, micropile grout shall be 

tested by the Contractor for compressive strength in accordance with AASHTO T106/ASTM 

C109 at a frequency of no less than one set of three 50-mm grout cubes from each grout plant 

each day of operation or per every 10 piles, whichever occurs more frequently. The 

compressive strength shall be the average of the 3 cubes tested. 

Grout consistency as measured by grout density shall be determined by the Contractor per 

ASTM C 188/AASHTO T 133 or API RP-13B-1 at a frequency of at least one test per pile, 

conducted just prior to start of pile grouting. The Baroid Mud Balance used in accordance 

with API RP-13B-1 is an approved device for determining the grout density of neat cement 

grout. The measured grout density shall be between ________ kg/m3 and ________ kg/m3

. 

Grout samples shall be taken directly from the grout plant. Provide grout cube compressive 

strength and grout density test results to the Engineer within 24 hours of testing. 

(Commentary: If the Engineer will perform the grout testing, revise this section 

accordingly).
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-20 December 2005

3.5 Micropile Installation Records. 

Contractor shall prepare and submit to the Engineer full-length installation records for each 

micropile installed. The records shall be submitted within one work shift after that pile 

installation is completed. The data shall be recorded on the micropile installation log. A 

separate log shall be provided for each micropile. (Commentary: In addition to the expertise 

of the micropile specialty Contractor, the quality of the individual construction elements is 

directly related to the final product overall quality. As with other drilled pile systems, the 

actual load carrying capacity of a micropile can only be definitively proven by pile load 

tests. It is not practical or economical to test every pile installed. Therefore, inspection by 

the Contractor and Owner's Engineer is needed to assure that each individual micropile is 

well constructed and to justify load testing only a small number, e.g., 5%, of the total number 

of production piles installed.)

3.6 Pile Load Tests 

Perform verification and proof testing of piles at the locations specified herein or designated 

by the Engineer. Perform compression load testing in accord with ASTM D1143, tension 

load testing in accord with ASTM D3689, and lateral load testing in accord with ASTM 

D3966, except as modified herein. 

(Commentary: Specifier/design engineer needs to determine and write into this portion of the 

specification the number of required verification and proof tests. The total number of load 

tests and maximum test loads to be specified can vary on a project-by-project basis. They 

are dependent on ground type and variability, required pile capacity, pile loading type (i.e., 

static or seismic), total number of piles, criticality of the structure and available site access 

and work space. Guideline criteria for estimating the total number of verification and proof 

test piles are given in Chapter 7 of FHWA NHI-05-039. If pile capacity demands are greatest 

in compression, the piles should be load tested in compression. If the pile capacity demands 

are equal for both compression and tension, or greater in tension, it is recommended that 

tension testing alone be conducted, to reduce costs). 

(Commentary: Specifier - Indicate here which types of load tests are required for the 

project).

3.6.1 Verification Load Tests 

Perform pre-production verification pile load testing to verify the design of the pile system 

and the construction methods proposed prior to installing any production piles. __________ 

sacrificial verification test piles shall be constructed in conformance with the approved 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-21 December 2005

Working Drawings. Verification test pile(s) shall be installed at the following locations 

___________. 

Verification load tests shall be performed to verify that the Contractor installed micropiles 

will meet the required compression and tension load capacities and load test acceptance 

criteria and to verify that the length of the micropile bond zone is adequate. The micropile 

verification load test results must verify the Contractor's design and installation methods, and 

be reviewed and accepted by the Engineer prior to beginning installation of production 

micropiles. 

The drilling-and-grouting method, casing length and outside diameter, reinforcing bar 

lengths, and depth of embedment for the verification test pile(s) shall be identical to those 

specified for the production piles at the given locations. The verification test micropile 

structural steel sections shall be sized to safely resist the maximum test load. (Commentary:

Note that if additional steel area is provided in the verification test, the measured deflection 

will be lower than production piles.)

The maximum verification and proof test loads applied to the micropile shall not exceed 80 

percent of the structural capacity of the micropile structural elements, to include steel yield in 

tension, steel yield or buckling in compression, or grout crushing in compression. Any 

required increase in strength of the verification test pile elements above the strength required 

for the production piles shall be provided for in the contractor’s bid price. 

The jack shall be positioned at the beginning of the test such that unloading and repositioning 

during the test will not be required. When both compression and tension load testing is to be 

performed on the same pile, the pile shall be tested under compression loads prior to testing 

under tension loads. 

3.6.2 Testing Equipment and Data Recording. 

Testing equipment shall include dial gauges, dial gauge support, jack and pressure gauge, 

electronic load cell, and a reaction frame. The load cell is required only for the creep test 

portion of the verification test. (Commentary: The purpose and value of an electronic load 

cell is to measure small changes in load for load tests where the load is held for a long 

duration, such as during verification or creep testing. It is not intended to be used during 

proof testing, including the short term creep portion. Experience has proven that load cells 

have been problematic under field conditions, yet even with errors resulting from cell 

construction, off-center loading, and other effects, a load cell is very sensitive to small 

changes in load and is strongly recommended for creep testing.) The contractor shall 

provide a description of test setup and jack, pressure gauge and load cell calibration curves in 

accordance with the Submittals Section. 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-22 December 2005

Design the testing reaction frame to be sufficiently rigid and of adequate dimensions such 

that excessive deformation of the testing equipment does not occur. Align the jack, bearing 

plates, and stressing anchorage such that unloading and repositioning of the equipment will 

not be required during the test. 

Apply and measure the test load with a hydraulic jack and pressure gauge. The pressure 

gauge shall be graduated in 500 kPa increments or less. The jack and pressure gauge shall 

have a pressure range not exceeding twice the anticipated maximum test pressure. Jack ram 

travel shall be sufficient to allow the test to be done without resetting the equipment. Monitor 

the creep test load hold during verification tests with both the pressure gauge and the 

electronic load cell. Use the load cell to accurately maintain a constant load hold during the 

creep test load hold increment of the verification test. 

Measure the pile top movement with a dial gauge capable of measuring to 0.025 mm. The 

dial gauge shall have a travel sufficient to allow the test to be done without having to reset 

the gauge. Visually align the gauge to be parallel with the axis of the micropile and support 

the gauge independently from the jack, pile or reaction frame. Use a minimum of two dial 

gauges when the test setup requires reaction against the ground or single reaction piles on 

each side of the test pile. (Commentary: Experience with testing piles reacting against the 

ground, or against single reaction piles on each side of the test pile, has resulted in racking 

and misalignment of the system on some projects. Two dial gauges are recommended for this 

test setup to determine if racking is occurring and to provide a more accurate average 

micropile head movement measurement). 

The required load test data shall be recorded by the Engineer. 

3.6.3 Verification Test Loading Schedule. 

Test verification piles designated for compression or tension load testing to a maximum test 

load of 2.0 times the micropile Design Load shown on the Plans or Working Drawings. 

(Commentary: The maximum test load shall be at least to the Design Load multiplied by the 

factor of safety used to estimate the bond length of the micropile. In some cases, e.g., 

potentially creeping ground, this factor of safety may be as high as 2.5.) The verification 

pile load tests shall be made by incrementally loading the micropile in accordance with the 

following cyclic load schedule for both compression and tension loading: 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-23 December 2005

Step Loading Applied Load Hold Time (min.) 

1 Apply AL 2.5 

2 Cycle 1 

0.15 DL 

0.30 DL 

0.45 DL 

AL 

2.5 

2.5 

2.5 

1 

3 Cycle 2 

0.15 DL 

0.30 DL 

0.45 DL 

0.60 DL 

0.75 DL 

0.90 DL 

1.00 DL 

AL 

1 

1 

2.5 

2.5 

2.5 

2,5 

2.5 

1 

4 Cycle 3 

0.15 DL 

1.00 DL 

1.15 DL 

1.30 DL 

1.45 DL 

AL 

1 

1 

2.5 

10 to 60 minutes 

2.5 

1 

5 Cycle 4 

0.15 DL 

1.45 DL 

1.60 DL 

1.75 DL 

1.90 DL 

2.00 DL 

1.50 DL 

1.00 DL 

0.50 DL 

AL 

1 

1 

1 

2.5 

2.5 

10 

5 

5 

5 

5 

Pile top movement shall be measured at each load increment. The load-hold period shall 

start as soon as each test load increment is applied. The verification test pile shall be 

monitored for creep at the 1.30 Design Load (DL). Pile movement during the creep test shall 

be measured and recorded at 1, 2, 3, 4, 5, 6, 10, 20, 30, 50, and 60 minutes. The alignment 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-24 December 2005

load shall not exceed 5 percent of the DL load. Dial gauges shall be reset to zero after the 

initial AL is applied. 

The acceptance criteria for micropile verification load tests are: 

1. The pile shall sustain the first compression or tension 1.0 DL test load with no more 

than _______mm total vertical movement at the top of the pile, relative to the position 

of the top of the pile prior to testing. (Commentary: Structural designer to determine 

maximum allowable total pile top structural axial displacement at 1.0 DL test load 

based on structural design requirements. The allowable displacement should also 

consider long term pile group settlements at the Design Load. Also, if the verification 

test pile has to be upsized structurally to accommodate the maximum required 

verification test load, this provision will not apply. Only the proof tested production 

piles will then be subject to this criterion.). 

2. At the end of the 1.30 DL creep test load increment, test piles shall have a creep rate 

not exceeding 1 mm/log cycle time (1 to 10 minutes) or 2 mm/log cycle time (6 to 60 

minutes or the last log cycle if held longer). The creep rate shall be linear or 

decreasing throughout the creep load hold period. 

3. Failure does not occur at the 2.0 DL maximum test load. Failure is defined as load 

where the slope of the load versus head settlement curve first exceeds 0.15 mm/kN. 

The Engineer will provide the Contractor written confirmation of the micropile design and 

construction within 3 working days of the completion of the verification load tests. This 

written confirmation will either confirm the capacities and bond lengths specified in the 

Working Drawings for micropiles or reject the piles based upon the verification test results. 

3.6.4 Verification Test Pile Rejection 

If a verification-tested micropile fails to meet the acceptance criteria, the Contractor shall 

modify the design, the construction procedure, or both. These modifications may include 

modifying the installation methods, increasing the bond length, or changing the micropile 

type. Any modification that necessitates changes to the structure shall require the Engineer’s 

prior review and acceptance. Any modifications of design or construction procedures or cost 

of additional verification test piles and load testing shall be at the Contractor’s expense. At 

the completion of verification testing, test piles shall be removed down to the elevation 

specified by the Engineer. 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-25 December 2005

3.6.5 Proof Load Tests 

Perform proof load tests on the first set of production piles installed at each designated 

substructure unit prior to the installation of the remaining production piles in that unit. The 

first set of production piles is the number required to provide the required reaction capacity 

for the proof tested pile. The initial proof test piles shall be installed at the following 

substructure units ______________. Proof testing shall be conducted at a frequency of 

________________. Location of additional proof test piles shall be as designated by the 

Engineer. (Commentary: Guidance on the number of proof tests to be performed is provided 

in Chapter 7 of FHWA NHI-05-039.)

3.6.6 Proof Test Loading Schedule 

Test piles designated for compression or tension proof load testing to a maximum test load of 

1.60 times the micropile Design Load shown on the Plans or Working Drawings. Proof tests 

shall be made by incrementally loading the micropile in accordance with the following 

schedule, to be used for both compression and tension loading: 

Step Loading Applied Load Hold Time (min.) 

1 Apply AL 2.5 

2 Load Cycle 

0.15 DL 

0.30 DL 

0.45 DL 

0.60 DL 

0.75 DL 

0.90 DL 

1.00 DL 

1.15 DL 

1.30 DL 

1.45 DL 

1.60 DL 

2.5 

2.5 

2.5 

2.5 

2.5 

2.5 

2.5 

2.5 

10 to 60 minutes 

2.5 

2.5 

3 Unload Cycle 

1.30 DL 

1.00 DL 

0.75 DL 

0.50 DL 

0.25 DL 

AL 

4 

4 

4 

4 

4 

4 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-26 December 2005

Depending on performance, either a 10 minute or 60 minute creep test shall be performed at 

the 1.30DL Test Load. Where the pile top movement between 1 and 10 minutes exceeds 1 

mm, the Maximum Test Load shall be maintained an additional 50 minutes. Movements 

shall be recorded at 1, 2, 3, 5, 6, 10, 20, 30, 50 and 60 minutes. The alignment load shall not 

exceed 5 percent of DL. Dial gauges shall be reset to zero after the initial AL is applied. 

The acceptance criteria for micropile proof load tests are: 

1. The pile shall sustain the compression or tension 1.0 DL test load with no more than 

______ mm total vertical movement at the top of the pile, relative to the position of the 

top of the pile prior to testing. (Commentary: Structural designer to determine 

maximum allowable total pile top structural axial displacement at 1.0 DL test load 

based on structural design requirements. The allowable displacement should also 

consider long term pile group settlements at the Design Load.)

2. At the end of the 1.30DL creep test load increment, test piles shall have a creep rate 

not exceeding 1 mm/log cycle time (1 to 10 minutes) or 2 mm/log cycle time (6 to 60 

minutes).The creep rate shall be linear or decreasing throughout the creep load hold 

period. 

3. Failure does not occur at the 1.60DL maximum test load. Failure is defined as load 

where the slope of the load versus head settlement curve first exceeds 0.15 mm/kN. 

3.6.7 Proof Test Pile Rejection 

If a proof-tested micropile fails to meet the acceptance criteria, the Contractor shall 

immediately proof test another micropile within that footing. For failed piles and further 

construction of other piles, the Contractor shall modify the design, the construction 

procedure, or both. These modifications may include installing replacement micropiles, 

incorporating piles at not more than 50% of the maximum load attained, postgrouting, 

modifying installation methods, increasing the bond length, or changing the micropile type. 

Any modification that necessitates changes to the structure design shall require the 

Engineer’s prior review and acceptance. Any modifications of design or construction 

procedures, or cost of additional verification test piles and verification and/or proof load 

testing, or replacement production micropiles, shall be at the Contractor’s expense. 

4.0 METHOD OF MEASUREMENT. 

Measurement will be made as follows for the quantity, as specified or directed by the 

Engineer: 

• Mobilization will be measured on a lump-sum basis. 

• Micropiles will be measured per each, installed, and accepted. 

• Micropile verification load testing will be measured per each. 

• Micropile proof load testing will be measured per each. 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-27 December 2005

The final pay quantities will be the design quantity increased or decreased by any changes 

authorized by the Engineer. 

5.0 BASIS OF PAYMENT 

The quantities accepted for payment will be paid for at the contract unit prices for the 

following items:

Pay Item Unit 

Mobilization and Demobilization ............................. Lump Sum 

Micropile Verification Load Test .............................. Each 

Micropile Proof Load Test Each 

Micropiles ................................................................ Each* 

Micropiles Variations in Length to Top of Rock ...... LF** 

Unexpected Obstruction Drilling ............................. Hour*** 

*For the option where the contractor designs the footing and number of piles, the foundation 

system should be bid as lump sum and a schedule of values established for progress payments 

after award. 

**Where piles are founded in rock, micropiles will be paid on a per each basis assuming Rock 

at Elevation _____. Additional length or shorter length due to variations in the top of rock will 

be paid on an add or deduct lineal foot basis where the linear footage = Elevation ___ minus 

Elevation of As-Built Rock. 

***If “obstructions” are not defined in the Standard Specifications, a definition should be added.

The contract unit prices for the above items will be full and complete payment for providing 

all design, materials, labor, equipment, and incidentals to complete the work. 

Where verification test piles are designated as sacrificial, the micropile verification load test 

bid item shall include the cost of the sacrificial micropile. 

The unit contract amount for “Micropiles” shall include the drilling, furnishing, and placing 

the reinforcing steel and casing, grouting, and pile top attachments. The micropile Contractor 

is also responsible for estimating the grout take. There will be no extra payment for grout 

overruns. 
FHWA NHI-05-039 Appendix C – Guide Specification 

Micropile Design & Construction C-28 December 2005
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-1 December 2005

SAMPLE PROBLEM NO. 1 – BRIDGE ABUTMENT FOUNDATION SUPPORT 

The following sample problem illustrates the design of foundation support for a bridge abutment 

using micropiles. This sample problem is intended to illustrate the quantification of typical 

abutment loads and the design of a micropile foundation for non-seismic load groups. In the 

example, seismic loads are provided and the example could be repeated using these loads. 

Practitioners typically follow different procedures around the United States in the design of 

bridge abutments, and therefore this sample problem is not intended to depict a “standard 

abutment” or a “standard abutment design procedure.” For simplicity, this example problem 

considers only a portion of the longitudinal forces and no transverse forces. Abutment designs, 

which include wind or seismic forces, for example, would have transverse as well as longitudinal 

forces. This example also does not illustrate construction load cases (e.g., full backfill prior to 

girder placement) that need to be incorporated into actual designs. 

Problem Statement 

The structure is a simply supported, single-span bridge, 30 meters long, supported on concrete 

retaining abutments. The superstructure consists of 5 AASHTO Type IV precast - prestressed 

concrete girders with a cast-in-place concrete deck. 

The bridge abutment length is 10.5 meters. The abutment wall backfill material is medium dense 

sand with an angle of internal friction of 35 degrees and a unit weight of 17.5 kN/m3

. The unit 

weight of the concrete is 23.6 kN/m3. Figure S1-1 shows the dimensions of the abutment. The 

pile details are shown on Figure S1-2. 

A summary of loading applied to the bridge abutment is shown in Figure S1-3. All load values 

are per 1-meter length of the abutment. The seismic site coefficient is 0.1 g. 

The foundation soil conditions are described in the boring log contained in Figure S1-4. These 

soils consist of 2.5 meters of loose sandy gravel underlain by moderately compressible soft, 

brown, fine sandy silt, which is 1.5 meters thick. The silt is underlain by dense to very dense 

gravel with cobbles and boulders that extends to a maximum depth of 30 meters. Ground water 

is 4 meters below the top of footing. Type B3 (pressure grouted through the casing during casing 

withdrawal) micropiles will be used. The bond length will be formed in the dense gravel. 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-2 December 2005

Figure S1-1. Sample Problem No. 1 - Abutment Section Detail 

(unless noted, all length dimensions in mm) 

200

250

460

3

1

700

300 300

2450

BORING

B – 1

LOOSE TO MEDIUM DENSE SANDY

GRAVEL (GW)

SOFT, BROWN FINE

SANDY SILT (ML)

DENSE TO VERY DENSE SANDY

GRAVEL AND COBBLES WITH

BOULDERS UP TO 1-METER (GW)

1700

2900

1500

2500

26 m

5250

MICROPILE

TYPE B3

400 1350

650

BACKFILL MATERIAL:

MEDIUM DENSE SAND

( = 17.5 kN/m3 ; N = 35E

1850

20E
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-3 December 2005

Figure S1-2. Sample Problem No. 1 – Pile Details 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-4 December 2005

Figure S1-3. Sample Problem No. 1 – Summary of Abutment Loads 

HL

PE

PEQ

VL

VDL+VLL

h/3 = 1750

DC

IA

DS

IS

DC = Dead load of concrete abutment

DS = Dead load of soil

VDL = 178.70 kN/m (dead load from bridge structure)

VLL = 73.00 kN/m (live load from bridge structure)

HL = Earth pressure due to live load surcharge VL

VL = Live load surcharge = 0.6 m thick equivalent soil surcharge

(not included in this example)

PE = Active earth pressure

PEQ = Seismic earth pressure

IA = 30.9 kN/m (seismic inertia force of concrete abutment and soil weight)

IS = 26.8 kN/m (seismic inertia force of the superstructure)
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-5 December 2005

Figure S1-4. Sample Problem No. 1 – Soil Boring Log 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-6 December 2005

STEP 1 – ABUTMENT DESIGN LOADS 

The magnitude and point of application for the active earth pressure, earth pressure due to 

live load surcharge, and seismic earth pressure is determined in this section. Calculations 

for the remaining components of the abutment loading are not included. The magnitude, 

point of application, and resulting moment on the abutment for the entire load 

components are summarized in Table S1-1. The moments are taken about the center 

point of the base of the abutment footing.

Active Earth Pressure - PE

 

Soil internal friction angle φ = 35 degrees 

Unit weight of soil γsoil = 17.5 kN / m3 

Coefficient of active soil pressure 0.271

2

tan 45 2 =



 



 Κ = ° − φ a

 3 Κ a γ soil = 4.74 kΝ / m

Resultant load ( ) m k m

m

k PE 0.5 4.74 5.25 65.32 / 2

3 × = Ν Ν = ×

Moment about centroid k m m

m

m

k 114.31 /

3

5.25 65.32 × = Ν − Ν

Earth Pressure Due to Live Load Surcharge - HL 

Surcharge pressure Κ a ×γ soil × 0.6m = 2.84 kPa

Surcharge load 2.84 kΝ × 5.25m = 14.91 kΝ / m

Moment about centroid k m m

m

m

k 39.1 /

2

5.25 14.91 × = Ν Ν
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-7 December 2005

Table S1-1. Sample Problem No. 1- Summary of Abutment Loads Per Meter Length 

Load Moment Arm Moment* 

Load Description Type Fx

(kN) 

Fy

(kN) 

X 

(m) 

Y 

(m) 

M 

(kN-m) 

Dc

Dead load of concrete 

abutment D 97.00 0.27 26.19 

DS Dead load of soil E 108.68 -0.55 -59.77 

VDL

Dead load from bridge 

superstructure 

D 178.70 0.58 103.65 

VLL

Live load from bridge 

superstructure 

L 73.00 0.58 42.34 

HL

Earth pressure due to 

live load surcharge L 14.91 2.63 39.13 

PE Earth pressure E 65.32 1.75 114.31 

PEQ-H Seismic earth pressure EQ 15.91 3.15 50.12 

IA

Seismic inertial force of 

concrete & soil weight EQ 30.9 2.35 72.50 

IS

Seismic inertial force of 

the superstructure EQ 26.8 3.55 95.14 

 *Moment is calculated about the center of the footing at its base. 

Seismic Earth Pressure - PEQ 

See “Seismic Design of Bridges - Design Example No. 3" Publication No. FHWA-SA97-008 for a description of the following Mononobe - Okabe lateral seismic earth over 

pressure and the seismic inertia forces from the abutment self-weight and the soil resting 

on the abutment footing. 

Seismic acceleration coefficient: A = 0.10 

Seismic coefficients 15 = 1.5× Α = 0. h k and 0 kv = (assumed value) 

Reference AASHTO Sec. 6.4.3 (A) Div. 1A. 

 

Slope of soil face: β = 0° 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-8 December 2005

Backfill slope angle: i = 0° 

Friction angle between soil and abutment: δ = 1⁄2 φ = 17.5°

 Seismic inertia angle = ° 



 





− = − 8.531

tan 1

v

h

k

k θ

 Seismic earth pressure coefficient 

( )( )

( ) () 2.65

cos cos

sin sin 1

2

 =



 





+ + × −

+ × − − Ψ = +

δ β θ β

φ δ φ θ

i

i

 

( )

() ( ) 0.34

cos cos

cos 2

 =



 





Ψ × × +

− Κ = θ θ δ

φ θ

AE

Seismic earth pressure 3 Κ AEγ soil = 5.95 kΝ / m

Resultant seismic force ( ) m k m

m

k

Q 0.5 5.95 5.25 16.68 / 2

3 − Ρ = Ν 



 





×

Ν ΡΕ = × Ε

Since this force is at angle δ to the horizontal, 

( ) k m

m

k

Q 16.68 cos = 15.91 Ν / Ν ΡΕ −Η = δ 

To be conservative, neglect the vertical portion of PEQ over the footing heel. 

Seismic Inertia Forces 

I A = kh ()( ) DC + DS = 0.15× 97.0 +108.68 = 30.9kΝ / m

I S = kh ( ) VDL = 0.15×178.70 = 26.8kN / m

Moment about centroid: 

m

k m

m

m

k Ν

× × = Ν 16 .68 0.6 5.25 52.54
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-9 December 2005

STEP 2 – DETERMINE PILE DESIGN LOADS PER METER LENGTH

The Group I loads per AASHTO Table 3.22.1A are calculated from the abutment loads 

shown in Table 5-4. 

Fy = sum of vertical loads 

Fx = sum of horizontal loads 

M = sum of moments about the center of the footing at its base. 

Fy = DC + DS + VDL + VLL

Fy = 97.0 + 108.7 + 178.7 + 73.0 = 457.4 kN/m 

Fx = HL + PE

Fx = 15.0 + 65.3 = 80.3 kN/m 

M = DC + DS + VDL + VLL + HL + PE

M = 26.2 - 59.8 + 103.7 + 42.3 + 39.3 + 114.3 = 266.0 kN/m 

Determine Pile Group Properties Per Meter Length 

Centroid of Pile Group (from front pile) 

Front piles: 1/1.5 × 0.0 = 0.0 

Rear piles: 1 / 2.25 × 1.85 = 0.822

Sum: 1.111 0.822

So centroid is (0.822/1.111) = 0.74 m from front pile. 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-10 December 2005

 e 0.74 0.185m

2

1.85 = − =

Pile Group I about centroid 

 ( ) ( ) 1.11 0.9127

2.25

1 0.74

1.5

1 2 2 Ι = + =

 Rear Pile Vertical Load = ( ) 



 



 Μ − − 0.9127

1.11

1.111

Fy F ey

 Front Pile Vertical Load = ( ) 



 



 Μ − +

0.9127

0.74

1.111

Fy F ey 

Group I Pile Design Loads 

Rear Pile Vertical Load = [ ] = Ν 



 



 − × − 191k

0.9127

266 457.4 0.185 1.11

1.111

457.4

Front Pile Vertical Load = [ ] = Ν 



 



 − ×

+ 559k

0.9127

266 457.4 0.185 0.74

1.111

457.4

Front Pile Axial Load = ( ) = Ν ° 595 k

cos 20

559 compression 

(Controlling Group 1, non-seismic, axial design load per pile) 

A more refined analysis would utilize the vertical stiffness of the batter pile. 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-11 December 2005

STEP 3 – EVALUATE ALLOWABLE STRUCTURAL CAPACITY OF CASED 

LENGTH 

A single pile design is used that can support the maximum compression load that acts on 

the front row of battered piles. 

For the permanent casing reinforcement, a yield strength of 241 MPa is used for design. 

To maintain strain compatibility between the reinforcing bar and casing in the upper pile 

length, a yield strength (Fy-steel) of 241 MPa is used for both members. The use of a 

higher strength casing, such as API N80 (Fy = 552 MPa) would greatly increase the 

structural capacity of this section of the pile. These calculations do not address the 

capacity of the casing joint. 

If the project incorporated a larger number of piles, savings could be realized by the use 

of separate designs for the front and rear piles. For example, a smaller casing size and a 

shorter bond length may be used on the rear piles due to the lower required capacity. The 

use of separate designs could increase the amount of load testing required at the start of 

the project, which the potential savings on a larger piling job could support. 

Consideration must also be given to maintaining simple pile construction. Mixing 

different reinforcing sizes and pile depths can occasionally lead to errors during pile 

installation. Also, if the overall stiffness (load versus pile top deflection) of the pile is 

changed, then the centroid and load per pile must be reevaluated. 

Pile Cased Length Allowable Load 

 Material dimensions and properties

 

Casing - Use 141 mm outside diameter x 9.5 mm wall thickness. 

 

Reduce outside diameter by 1.6 mm to account for corrosion. 

 

 Casing outside diameter ODcasing = 141 mm - 2 x 1.6 mm = 137.8 mm 

 

Pile casing inside diameter IDcasing = 141 mm - 2 x 9.5 mm = 122 mm 

Pile casing steel area [ ] 2

sin

2

sin

2

sin 3,224

4

Aca g = ΟD ca g − ΙD ca g = mm

π

Casing yield strength Fy−ca sin g = 241ΜΡa 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-12 December 2005

Radius of gyration mm

D D

rca g 46

4

2 2

sin = Ο + Ι = 

Reinforcing bar - Use 43 mm grade 520 steel reinforcing bar. 

 

Bar area A bar = 1,452 mm2

 

Bar steel yield strength Fy-bar = 520 MPa 

Grout area 2

sin

2 10,240

4

Agrout = ΙD ca g − Abar = mm

π 

Grout compressive strength f c grout 34.5 MPa '

− =

For strain compatibility between casing and rebar, use for steel yield stress: 

 Fy-steel = the minimum of Fy-bar and Fy casing = 241 MPa 

Allowable Tension Load

 

Ρt −allowable = 0.55Fy−steel(Abar + Aca sin g ) = 620kN

Allowable Compression Load

Pc allowable [0.4 f c grout Agrout 0.47 Fy steel (Abar Aca sin g )] 671kN '

− = − × + − + =

 

STEP 4 – EVALUATE ALLOWABLE STRUCTURAL CAPACITY OF UNCASED 

LENGTH 

Pile Uncased Length Allowable Load 

Material dimensions and properties

Soil conditions and the method of pile installation can affect the resulting diameter of the 

pile bond length. For this example, assume a drill-hole diameter of 50 mm greater than 

the casing outside diameter (OD). 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-13 December 2005

Using a casing OD = 141mm 

 

Therefore, Grout Db = 141 mm + 50 mm = 191 mm (0.191 m) 

Bond length grout area 2 2 27,200

4

Agrout = D b − Abar = mm

π

Allowable Tension Load

 Pt allowable 0.55Fy bar Abar (0.55 520MPa 1,452mm ) 415kN 2

− = − × = × × =

Allowable Compression Load

 

( )

P ( ) MPa mm MPa mm kN

P f A F A

c allowable

c allowable c grout y bar bar

0.4 34.5 27,200 0.47 520 1,452 730

0.4 0.47

2 2

'

= × × + × × =

= × + ×

−

− −

STEP 5 – EVALUATE ALLOWABLE GEOTECHNICAL CAPACITY 

Allowable Load – Geotechnical Capacity 

The micropile bond length will be located in the dense to very dense sandy gravel with 

cobbles and boulders starting approximately 3.35 m below the bottom of footing 

elevation. The pile bond length shall be installed using a Type B pressure grouting 

methodology. 

From Table 5-3 select an ultimate unit grout-to-ground bond strength α bond = 265 kPa. 

This represents an approximate average value for gravels. 

The controlling non-seismic micropile loading is 595 kN per pile. Therefore, an 

allowable geotechnical bond load PG-allowable ≥ 595 kN/pile must be provided to support 

the structural loading. 

Provide: PG-allowable ≥ 595 kN/pile

Compute the bond length, Lb, required to provide PG-allowable as follows: 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-14 December 2005

bond b

G allowable

b D

P FS

L

× ×

× = −

α π

 

m

kPa m

kN Lb 7.48

265 0.191

595 2.0 = × ×

× = π

Select Bond Length = 7.5 m 

m m kN kPa PG allowable 3.14 0.191 7.5 596

2.0

265 − = × × × =

STEP 6 – VERIFY ALLOWABLE LOADS 

The controlling axial design load for the pile is 595 kN (compression). The summary of 

the pile allowable loads is: 

 

Structural Upper Cased Length = 671 kN (compression) 

Structural Lower Uncased Length = 730 kN (compression) 

Geotechnical Bond Length = 596 kN (compression) 

The allowable loads are all greater than the 595 kN design load, therefore the pile axial 

design is OK. 

The controlling lateral design load is 80.3 kN/m. Check to see if the batter piles carry 

lateral loads. The front row of piles are battered at 20° from vertical and each pile carries 

the following ratio of the vertical pile load as a lateral resisting load. 

Lateral resisting load = 559kN ×tan(20 ) = 204 kN o per pile 

The lateral design load per pile ( ) m kN

m

kN = 80.3 × 1.5 = 120 per pile 

The lateral resisting load is greater than the lateral design load therefore the pile lateral 

design is OK. 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-15 December 2005

STEP 7 – ESTIMATE MICROPILE SETTLEMENT 

Settlements resulting from consolidation of soil layers below the micropile group are not 

anticipated as these soils are not cohesive in nature. Herein, elastic settlements are 

calculated. 

Casing Length Elastic Stiffness 

 

Front pile batter angle Φ = 20° batter

Max pile length from footing to top of gravel m

m L

batter

upper 3.6

cos( )

3.35 = Φ =

Casing insertion into bond length Linsert = 1.0 m

Pile casing length Lca sin g = Lupper + Linsert = 4.6 m

 Steel modulus of elasticity Esteel = 200,000 MPa 

 Grout modulus of elasticity Egrout = 31,000 MPa

 Area of Grout 2 Agrout = 10,240 mm 

Asteel = Abar + Acasing = 1,452 mm2

 + 3,224 mm2 = 4,676 mm2

Pile compression stiffness value 

EAcased length = Agrout ×Egrout + Asteel ×Esteel =1,252,000kN

Uncased Length Elastic Stiffness 

Pile uncased length (bond length) Lb = 7.5 m 

Asteel = Abar = 1,452 mm2

Agrout = 27,200 mm2

 

Pile compression stiffness value 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-16 December 2005

EAuncased length = Agrout ×Egrout + Asteel ×Esteel =1,133,000kN

Elastic Displacement 

Elastic displacement (cased length) 

mm

kN

kN m

AE

P L

t

cased length

compression ca g

elastic 2.2

1,252,000

sin 595 4.6 = × = ×

∆ =

Elastic displacement (uncased length) 

mm

kN

kN m

AE

P L

t

uncased length

compression b

elastic 2.0

1,133,000

595 (1/ 2 7.5 )

= × × = ×∆ =

STEP 8 – MICROPILE TO FOOTING CONNECTION DESIGN 

Design calculations are completed for the detail shown in Figure S1-5 for connection of 

the pile top to the abutment footing. 

Required Design Loads and Dimensions 

 

 Group I service load, compression Pc-service = 595 kN 

 

Abutment concrete compressive strength f’c = 27.6 MPa 

 

Casing outside diameter ODcasing = 141 mm 

Pile area 2

sin

2 15,615

4

Areapile = OD ca g = mm

π 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-17 December 2005

Figure S1-5. Pile Top to Abutment Footing Connection Detail 

Required Plate Area

 

 Assume a 254 mm square plate 2 2 Areaplate = Plate width = 64,516mm 

Check Cone Shear 

 

Pcone allowable ≥ Pc-service = 595 kN 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-18 December 2005

Equivalent diameter for 254 mm2

 plate, 286mm

4 2542

= × = π 

[ ] [ ] 2 2 2 2

1

2

2 1086 286 862,053

4 4

ACP = d − d = − = mm

π π

Use ACI 349 Appendix B for cone shear 

 

 Pcone design strength c psiCP x Acp f ' = 4 φ

 ( ) c x Acp psi

kPa 4 f psi 6.89476 ' = φ

 c ACP = f kPa × ' 10.5 φ

Pcone nominal strength c ACP = f kPa × ' 10.5 φ

 6 10 1000 10.5 27.6 −  × ×



 



 = ACP mPa

kPa mPa

 = 1,504 kN

 FS

P

P come noninal strength

come allowable =

φ

LF FS =

[ ]

[ ] D L E

D D L L E E

Q Q Q

B Q B Q B Q LF Combined load factor

+ +

+ + = = γ

Where: γ = 1.3; BD = 1; BL = 1.67; BE = 1.3 

and with Q D = 0.62; Q L = 0.16; Q E = 0.22 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-19 December 2005

= 0.62

D + L + E

D

Q Q Q

Q

= 0.16

D + L + E

L

Q Q Q

Q

= 0.22

D + L + E

E

Q Q Q

Q

LF = 1.3 [1.0 × 0.62 + 1.67 × 0.16 + 1.3 × 0.22] = 1.53 

 φ = 0.65 for unreinforced shear cone per ACI 349 Appendix B 

 2.35

0.65

1.53 FS = =

kN kN OK kN Pcone allowable 640 594.6 . . . . 2.35

1,504 = = >

Note – edge distance limitations and other requirements of ACI 349 Appendix B must be 

satisfied. 

Required Plate Thickness 

Actual bearing stress, compression MPa

Area

P Bearing

plate

c service

compression = = 9.22 −

 

Plate bending moment for 10 mm width 

Bearing kNm

Plate OD

M mm compression

width ca g 0.147

2 2

1 10

2

sin

max  × =



 



 − = ×

Note - use of this cantilever moment was determined to be a conservative approximation 

of the maximum moment in the plate due to a compression pile load by comparison to a 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-20 December 2005

more accurate formula shown in Roark and Young (1975). Plate bending from a tension 

pile load or with different plate support details must be further analyzed. 

 

 Allowable bending stress - Fy MPa and Fb 55Fy = 345 = 0.

Note - Allowable stresses should be increased by the appropriate % factor (AASHTO 

Table 3.22.1A column 14) depending on which load group produces controlling load 

condition. For this example, the Group I load produces the controlling condition (% = 

100%). 

max 3 775mm

F

M S

b

x−req = =

Required plate thickness - mm

mm

S

t x req

req 21.6

10

6 = = − 

 

Use 254 mm square x 25.4 mm thick top plate.

Required Weld Size:

 

 Tensile strength of E70 electrode, Fuweld = 483 MPa 

 

 Minimum tensile strength of connected parts (ASTM A53 Grade B Casing) 

 Fupart = 414 MPa 

 Fillet weld strength ΦF = 0.27Fu part = 111.8 MPa

 Top weld size tweld −top = 6.35mm

 Stiffener plate size tstiff = 12.7 mm Wstiff = 100 mm Lstiff = 150 mm

 Top weld strength Lweld = π O Dcasimg − 4tstiff + 8Wstiff = 1,190 mm

 Top weld strength 

 Pweld −top = 0.707 tweld −topΦ F Lweld = 598 kN > 595 kN . . . OK
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-21 December 2005

Stiffener plate side weld dimensions tweld −side = 6.35mm

 Lweld = 8 Lstiff = 1,200 mm

 Stiffener plate side weld strength 

 Pweld −side = 0.707 tweld −sideΦFweld Lweld = 603 kN

 > 0.707 tweld −topΦF ×8 Wstiff = 402 kN . . . . OK

 

 Use 6.35 mm fillet weld for welding top and stiffener plates. 

Note - this example ignored bending stresses on the welds which is considered 

appropriate for a compression pile load with the weld details shown. Weld bending stress 

must be analyzed for other conditions. 

STEP 9 – CHECK STRUCTURAL CAPACITY TO RESIST TEST LOADS 

The controlling axial design load for the pile is 595 kN (compression). 

 

Verification Test Load = 2.0 × Design Load 

 

 = 2.0 × 595 kN = 1,190 kN 

 

Proof Test Load = 1.6 × Design Load 

 

 = 1.6 × 595 kN = 952 kN 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-22 December 2005

Cased Length Uncased Length

OD* = 141mm 

ID = 122 mm (9.5 mm wall) 

A casing = 3,925 mm2 A grout = 27,200 mm2

Fy-casing = 241 MPa 

(use for casing and bar) 

f’c-grout = 34.5 MPa 

A bar = 1,452 mm2 Abar = 1,452 mm2

Fy-bar = 520 MPa Fy-bar = 520 MPa 

A grout = 10,240 mm2 

f’c-grout = 34.5 MPa 

*

 Do not reduce by 1.6 mm for corrosion. 

Pile Cased Length Allowable Load 

( )



 



 = + + − − − bar ca g

y ca g

grout c grout c allowable A A

F

P f A sin

' sin

1.25

0.68

( ) mm mm kN MPa Pc allowable MPa mm 1,452 3,925 1,277

1.25

241 0.68 34.5 10,240 2 2 2 =



 



 − = × × + +

Pile Uncased Length Allowable Load 

 

grout y bar bar c grout Pc−allowable = 0.68 f − A + 0.80F − A '

 Pc allowable 0.68 34.5MPa 27,200mm 0.80 520MPa 1,452mm 1,242kN 2 2

− = × × + × × =

The design pile is OK for the proof test at 952 kN and the verification test at 1,190 kN. 

STEP 10 – PREPARE DRAWINGS 

The following detail drawings (Figures S1-6 and S1-7) show the pile design. 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-23 December 2005

Figure S1-6. Page 1 of Sample Problem No.1 – Working Drawing Submittal 
FHWA NHI-05-039 Appendix D – Sample Problem No.1 

Micropile Design & Construction D-24 December 2005

Figure S1-7. Page 2 of Sample Problem No. 1 – Working Drawing Submittal 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-1 December 2005

SAMPLE PROBLEM NO. 2 – LATERALLY LOADED MICROPILE 

Micropiles are being considered to support loads for a new multi-story building. The site 

is underlain by approximately 6 m of undocumented and variable fill overlying partially 

weathered rock. The soil matrix of the fill is characterized as loose to very dense silty to 

clayey sand. Approximately 3 m of new fill will be placed over the existing fill to 

establish foundation grades. 

The micropile section shown in Figure S2-1 is proposed for the project. The micropiles 

are required to carry a design axial compression load of 1,423 kN and a design lateral 

groundline shear load of 44.48 kN. 

Perform a laterally loaded pile analysis and evaluate: 

1. structural capacity of the cased length of the micropile 

2. reduced section modulus of the casing joint and proposed bending moment 

limit at the casing joints 

Micropile Section Properties 

1. Casing outside diameter (OD) = 0.1969 m. 

2. Casing wall thickness (tw) = 0.0151 m. 

3. Casing yield strength (Fy) = 552 MPa 

4. Grout compressive strength (f’c) = 27.6 MPa 

Determine: (1) casing area, Acasing; (2) casing moment of inertia, Icasing; (3) casing section 

modulus, Scasing; and (4) area of grout, Agrout. 

( ) ( ( ) ) 2 2 2 2 2 2 2

sin 0.1969 0.1969 2(0.0151) 0.00863

4 4

Aca g = OD − ID = m − − m = m

π π

( ) ( ( ) ) 4 4 4 4 4 4 4

sin 0.1969 . 0.1969 2(0.0151) . 0.00003587

64 64

I ca g = OD − ID = in − − m = m

π π

3

4

sin

sin 0.000364

(0.1969 / 2)

0.00003587 .

/ 2

m

m

m

OD

I

S ca g

ca g = = =

2 2 2 2

sin

2 (0.1969 ) 0.00863 0.0218

4 ( ) 4

Agrout = OD − Aca g = m − m = m

π π
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-2 December 2005

1 in. = 25.4 mm 

1 ksi = 6.89 MPa 

Figure S2-1. Micropile Detail for Sample Problem 2.
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-3 December 2005

Laterally Loaded Pile Analysis 

The computer program LPILE is used to evaluate the maximum bending moment in the 

cased length of the micropile. For the purposes of this example, both 50% fixity and 

fixed head (100% fixity) conditions are analyzed. The micropile cap will be embedded 

0.91 m below the ground surface. For the analysis, a 0.305-m embedment depth was 

conservatively assumed. 

For the analysis, a 12.2-m length of the micropile was modeled. Default LPILE p-y 

curves for sand above the water table were used to model the soil profile. The upper 3.35 

m of the profile was modeled with a soil friction angle of 32 degrees and the remaining 

portion of the profile (representing the existing fill layer) was modeled with a soil friction 

angle of 30 degrees. Other soil parameters are provided in the LPILE output file. 

LPILE Analysis Results 

The results of the LPILE analysis are provided below and the bending moment diagram 

and lateral deflection profile are provided in Figures S2-2 and S2-3. 

Axial 

Load 

(kN) 

Fixity 

Condition 

Pile Head 

Deflection 

(mm) 

Maximum 

Shear Load 

(kN) 

Maximum 

Bending 

Moment 

(kN-m) 

1,423 100% 3.3 44.48 -37.3 

1,423 50% 8.4 44.48 27.2 

Structural Capacity Evaluation (Eq. 5-3) 

1.0

1 '

≤















 −

+

b

e

a

b

a

a

F

F

f

f

F

f

Where 

MPa

m

kN

A

P

f

ca g

c

a 164.89

0.00863

1,423

2

sin

= = =

MPa

m

kN m

S

M

f

ca g

b 102.47

0.000364

37.3

3

sin

max = − = =
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-4 December 2005

F F MPa MPa

F F MPa MPa

b y

a y

0.55 0.55(552 ) 303.6

0.47 0.47 (552 ) 259.44

= = =

= = =

Assume buckling potential is negligible, F′e >>> fa 

Therefore, 

OK

MPa

MPa

MPa

MPa 0.97 1.0

303.6

102.47

259.44

164.89

+ = <

Structural Capacity Evaluation (Eq. 5-6) 

1.0 max + ≤

c−allowable allowable

c

M

M

P

P

Where 

[ ]

MPa m MPa m kN

Pc allowable f c Agrout Fy Aca g

0.4(27.6 )(0.0218 ) 0.47(552 )(0.00863 ) 2,479

0.4 0.47

2 2

sin

'

= + =

− = × +

0.55 0.55(552 )(0.000364 ) 110.5 . 3 M allowable = Fy Sca sin g = MPa m = kN − m

Therefore, 

OK

kN m

kN m

kN

kN 0.91 1.0

110.5

37.3

2,479

1,423 = < −

− +

Section Modulus at the Joint (Eq. 5-26 ) 

( ) ( )

3

4 4 4 4

int

int 0.000173

(0.1969 0.0151 )/ 2

((0.1969 0.0151 ) (0.1667 ) 64

/ 2

(( ) ) 64

/ 2

m

m m

m m m

OD t

OD t ID

OD t

I

S

w

w

w

jo

jo = −

− −

= −

− −

= − =

π π

Maximum Bending Moment at the Joint (Eq. 5-27) 

MPa kN m

MPa

MPa F m

F

f

F

f M S b

e

a

a

a

jo jo × = − 













 = × − 















× − 













 = × − 303.6 19.2

259.44

164.89 1 1 0.000173 1 3

' max ( int) int

Using the reduced section modulus at a joint indicates that the combined stress criterion 

can only be satisfied at the location of a threaded connection (i.e., joint) if the maximum 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-5 December 2005

bending moment is 19.2 kN-m or less. This result indicates that threaded connections 

should not be placed from the bottom of the pile cap to approximately 0.5 m below the 

ground surface where the micropile-footing connection achieves 100% fixity. For the 

50% fixity condition, positive bending moments greater than 19.2 kN-m are computed 

between a depth of approximately 0.75 to 2.1 m. 

Alternatively, if the maximum bending moment needs to be resisted over these depths, 

the following options could be considered: (1) use a larger casing (with a larger cross 

sectional area of steel) over this depth range; or (2) place an additional steel casing at 

least over this length. On projects where a second casing is used, the design should 

require that joints from the two casings be staggered by at least 1 m. 

For the 50% fixity case, a 3-m long casing could be used at the ground surface so that the 

first threaded connection would be located in an area where acceptable bending resistance 

could be developed. 

0

1

2

3

4

5

6

-40 -20 0 20 40 60

Bending Moment (kN-m)

Depth (m)

Fixed Head

50% Fixity

Free Head

Figure S2-2. Bending Moment Diagram for Sample Problem No. 2. 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-6 December 2005

0

1

2

3

4

5

6

-5 0 5 10 15 20

Deflection (mm)

Depth (m)

Fixed Head

50% Fixity

Free Head

Figure S2-3. Lateral Deflection Profile for Sample Problem No. 2. 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-7 December 2005

LPILE ANALYSIS RESULTS 

FOR 

SAMPLE PROBLEM 2 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-8 December 2005

============================================================================== 

 LPILE Plus for Windows, Version 4.0 (4.0.8) 

 Analysis of Individual Piles and Drilled Shafts 

 Subjected to Lateral Loading Using the p-y Method 

 (c) Copyright ENSOFT, Inc., 1985-2003 

 All Rights Reserved 

============================================================================== 

This program is licensed to: 

Paul Sabatini 

GeoSyntec 

Path to file locations: G:\CWP\CHE8123 - NHI Micropiles\400 - Technical\402 - 

Revised Manual\Draft 100% Manual\Ch. 5\LPILE Analysis\ 

Name of input data file: 004SI.lpd 

Name of output file: 004SI.lpo 

Name of plot output file: 004SI.lpp 

Name of runtime file: 004SI.lpr 

------------------------------------------------------------------------------ 

 Time and Date of Analysis 

------------------------------------------------------------------------------ 

 Date: May 24, 2005 Time: 16:51:45 

------------------------------------------------------------------------------ 

 Problem Title 

------------------------------------------------------------------------------ 

Micropile Manual - Sand Profile 

------------------------------------------------------------------------------ 

 Program Options 

------------------------------------------------------------------------------ 

Units Used in Computations - SI Units, meters, kilopascals 

Basic Program Options: 

Analysis Type 3: 

- Computation of Nonlinear Bending Stiffness and Ultimate Bending Moment 

 Capacity with Pile Response Computed Using Nonlinear EI 

Computation Options: 

- Only internally-generated p-y curves used in analysis 

- Analysis does not use p-y multipliers (individual pile or shaft action only) 

- Analysis assumes no shear resistance at pile tip 

- Analysis includes automatic computation of pile-top deflection vs. 

 pile embedment length 

- No computation of foundation stiffness matrix elements 

- Output pile response for full length of pile 

- Analysis assumes no soil movements acting on pile 

- Additional p-y curves computed at specified depths 

Solution Control Parameters: 

- Number of pile increments = 100 

- Maximum number of iterations allowed = 100 

- Deflection tolerance for convergence = 2.5400E-07 m 

- Maximum allowable deflection = 2.5400E+00 m 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-9 December 2005

Printing Options: 

- Values of pile-head deflection, bending moment, shear force, and 

 soil reaction are printed for full length of pile. 

- Printing Increment (spacing of output points) = 1 

------------------------------------------------------------------------------ 

 Pile Structural Properties and Geometry 

------------------------------------------------------------------------------ 

Pile Length = 12.19 m 

Depth of ground surface below top of pile = -.30 m 

Slope angle of ground surface = .00 deg. 

Structural properties of pile defined using 2 points 

Point Depth Pile Moment of Pile Modulus of 

 X Diameter Inertia Area Elasticity 

 m m m**4 Sq. m kN/Sq. m 

----- --------- ----------- ---------- ---------- ----------- 

 1 0.0000 .19685000 3.58667E-05 .008626 199947980.000 

 2 14.5000 .19685000 3.58667E-05 .008626 199947980.000 

Please note that because this analysis makes computations of ultimate 

moment capacity and pile response using nonlinear bending stiffness 

that the above values of moment of inertia and modulus of are not used 

for any computations other than total stress due to combined axial 

loading and bending. 

------------------------------------------------------------------------------ 

 Soil and Rock Layering Information 

------------------------------------------------------------------------------ 

The soil profile is modelled using 2 layers 

Layer 1 is sand, p-y criteria by Reese et al., 1974 

Distance from top of pile to top of layer = -.305 m 

Distance from top of pile to bottom of layer = 3.048 m 

p-y subgrade modulus k for top of soil layer = 24430.244 kN/ m**3 

p-y subgrade modulus k for bottom of layer = 24430.244 kN/ m**3 

Layer 2 is sand, p-y criteria by Reese et al., 1974 

Distance from top of pile to top of layer = 3.048 m 

Distance from top of pile to bottom of layer = 12.192 m 

p-y subgrade modulus k for top of soil layer = 16286.830 kN/ m**3 

p-y subgrade modulus k for bottom of layer = 16286.830 kN/ m**3 

(Depth of lowest layer extends .00 m below pile tip) 

------------------------------------------------------------------------------ 

 Effective Unit Weight of Soil vs. Depth 

------------------------------------------------------------------------------ 

Distribution of effective unit weight of soil with depth 

is defined using 4 points 

Point Depth X Eff. Unit Weight 

 No. m kN/ m**3 

----- ---------- ---------------- 

 1 -.30 18.83843 

 2 3.05 18.83843 

 3 3.05 17.64407 

 4 12.19 17.64407 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-10 December 2005

------------------------------------------------------------------------------ 

 Shear Strength of Soils 

------------------------------------------------------------------------------ 

Distribution of shear strength parameters with depth 

defined using 4 points 

Point Depth X Cohesion c Angle of Friction E50 or RQD 

 No. m kN/ m**2 Deg. k_rm % 

----- -------- ---------- ------------------ ------ ------ 

 1 -.305 .00000 32.00 ------ ------ 

 2 3.048 .00000 32.00 ------ ------ 

 3 3.048 .00000 30.00 ------ ------ 

 4 12.192 .00000 30.00 ------ ------ 

Notes: 

(1) Cohesion = uniaxial compressive strength for rock materials. 

(2) Values of E50 are reported for clay strata. 

(3) Default values will be generated for E50 when input values are 0. 

(4) RQD and k_rm are reported only for weak rock strata. 

------------------------------------------------------------------------------ 

 Loading Type 

------------------------------------------------------------------------------ 

Static loading criteria was used for computation of p-y curves 

------------------------------------------------------------------------------ 

 Pile-head Loading and Pile-head Fixity Conditions 

------------------------------------------------------------------------------ 

Number of loads specified = 5 

Load Case Number 1 

Pile-head boundary conditions are Shear and Slope (BC Type 2) 

Shear force at pile head = 44.482 kN 

Slope at pile head = .000 m/ m 

Axial load at pile head = 1423.431 kN 

(Zero slope for this load indicates fixed-head condition) 

Load Case Number 2 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Shear force at pile head = 44.482 kN 

Bending moment at pile head = .000 m- kN 

Axial load at pile head = 1423.431 kN 

(Zero moment at pile head for this load indicates a free-head condition) 

Load Case Number 3 

Pile-head boundary conditions are Shear and Rotational Stiffness (BC Type 3) 

Shear force at pile head = 44.482 kN 

Rotational stiffness = 88964.449 m- kN 

Axial load at pile head = 1423.431 kN 

Load Case Number 4 

Pile-head boundary conditions are Shear and Rotational Stiffness (BC Type 3) 

Shear force at pile head = 44.482 kN 

Rotational stiffness = 889644.490 m- kN 

Axial load at pile head = 1423.431 kN 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-11 December 2005

Load Case Number 5 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Shear force at pile head = 44.482 kN 

Bending moment at pile head = -18.642 m- kN 

Axial load at pile head = 1423.431 kN 

Non-zero moment at pile head for this load case indicates the pile-head 

may rotate under the applied pile-head loading, but is not a free-head 

(zero moment) condition. 

------------------------------------------------------------------------------ 

 Output of p-y Curves at Specified Depths 

------------------------------------------------------------------------------ 

p-y curves are generated and printed for verification at 7 depths. 

Depth Depth Below Pile Head Depth Below Ground Surface 

 No. m m 

----- --------------------- -------------------------- 

 1 .000 .305 

 2 2.020 2.325 

 3 4.690 4.995 

 4 4.710 5.015 

 5 9.990 10.295 

 6 10.010 10.315 

 7 12.192 12.497 

Depth of ground surface below top of pile = -.30 m 

  WARNING ** ** 

An unreasonable input value for yield strength of reinforcing steel has been 

specified. The input value is either smaller than 262,000 kN/m2 or larger 

than 551,600 kN/m2. You should check you input for correctness. 

  WARNING ** ** 

An unreasonable input value for concrete cover thickness has been specified. 

The input value is either smaller than 0.02 meters or larger than 0.2 meters. 

You should check your input for correctness. 

------------------------------------------------------------------------------ 

 Computations of Ultimate Moment Capacity and Nonlinear Bending Stiffness 

------------------------------------------------------------------------------ 

Pile Description: 

The sectional shape is a circular shaft with steel casing. 

Outside Diameter = .1969 m 

Wall thickness of steel shell = .0151 m 

Cross-sectional area of shell = .00863 m**2 

Moment of inertia of steel shell = 3.58702E-05 m**4 

Material Properties: 

Compressive Strength of Concrete = 27579.034 kN/ m**2 

Yield Stress of Reinforcement = 27579. kN/ m**2 

Steel shell or core yield stress = 551581. kN/ m**2 

Modulus of Elasticity of Reinforcement = 199948000. kN/ m**2 

Cover Thickness (edge to bar center) = .000 m 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-12 December 2005

Number of Reinforcing Bars = 1 

Area of Single Bar = .00000 m**2 

Number of Rows of Reinforcing Bars = 1 

Ultimate Axial Squash Load Capacity = 5270.58 kN 

Distribution and Area of Steel Reinforcement 

 Row Area of Distance to 

Number Reinforcement Centroidal Axis 

 m**2 m 

------ ------------- --------------- 

 1 .000000 .0000 

Axial Thrust Force = .00 kN 

 Bending Bending Bending Maximum Neutral Axis 

 Moment Stiffness Curvature Strain Position 

 kN-m kN-m2 rad/m m/m m 

 ------------- ------------- ------------- ------------- ------------- 

 1.61543650 8206.417 .00019685 .00001640 .09842200 

 2.90699392 8204.183 .00035433 .00002952 .09842200 

 4.19784752 8201.948 .00051181 .00004264 .09842200 

 5.48799731 8199.714 .00066929 .00005576 .09842200 

 6.77744329 8197.479 .00082677 .00006888 .09842200 

 8.06618545 8195.244 .00098425 .00008200 .09842200 

 9.35422380 8193.010 .00114173 .00009512 .09842200 

 10.642 8190.775 .00129921 .00010824 .09842200 

 10.924 7499.209 .00145669 .00011327 .09287117 

 12.105 7499.108 .00161417 .00012553 .09288319 

 13.286 7499.006 .00177165 .00013780 .09289520 

 14.466 7498.500 .00192913 .00015006 .09290121 

 15.646 7498.397 .00208661 .00016234 .09291322 

 16.827 7498.295 .00224409 .00017462 .09292524 

 18.007 7498.192 .00240157 .00018690 .09293725 

 19.187 7497.684 .00255906 .00019917 .09294326 

 20.367 7497.581 .00271654 .00021146 .09295528 

 21.548 7497.478 .00287402 .00022375 .09296729 

 22.728 7497.375 .00303150 .00023605 .09297931 

 23.907 7496.866 .00318898 .00024833 .09298531 

 25.088 7496.762 .00334646 .00026064 .09299733 

 26.268 7496.658 .00350394 .00027294 .09300934 

 27.448 7496.554 .00366142 .00028526 .09302136 

 28.628 7496.450 .00381890 .00029757 .09303337 

 29.807 7495.940 .00397638 .00030986 .09303938 

 38.654 7494.751 .00515748 .00040234 .09312348 

 47.499 7493.562 .00633858 .00049501 .09320759 

 56.340 7492.380 .00751969 .00058788 .09329169 

 65.179 7491.214 .00870079 .00068095 .09337579 

 74.016 7490.072 .00988189 .00077422 .09345990 

 82.855 7489.387 .01106299 .00086775 .09355001 

 91.693 7488.762 .01224409 .00096149 .09364012 

 100.537 7488.652 .01342520 .00105553 .09373624 

 109.382 7488.664 .01460630 .00114980 .09383235 

 118.136 7482.927 .01578740 .00124306 .09385038 

 126.884 7477.638 .01696850 .00133646 .09387441 

 135.737 7478.784 .01814961 .00143145 .09398254 

 144.598 7480.243 .01933071 .00152669 .09409067 

 153.504 7483.692 .02051181 .00162256 .09421683 

 162.450 7488.599 .02169291 .00171886 .09434899 

 171.554 7499.959 .02287402 .00181643 .09452320 

 181.768 7556.318 .02405512 .00192092 .09496775 

 190.497 7548.547 .02523622 .00201690 .09503383 

 199.203 7540.624 .02641732 .00211304 .09509991 

 207.887 7532.571 .02759843 .00220867 .09514196 

 216.202 7512.356 .02877953 .00230320 .09514196 

 223.884 7472.618 .02996063 .00239574 .09507588 

 228.487 7337.017 .03114173 .00247204 .09449317 

 232.667 7198.231 .03232283 .00254929 .09398254 

 236.784 7067.337 .03350394 .00263238 .09368217 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-13 December 2005

 240.174 6924.418 .03468504 .00271455 .09337579 

 243.147 6779.298 .03586614 .00279815 .09312949 

 245.703 6632.145 .03704724 .00288206 .09290722 

 247.960 6486.275 .03822835 .00296751 .09273901 

 250.011 6343.943 .03940945 .00305375 .09260084 

 251.825 6204.036 .04059055 .00313918 .09245066 

 253.433 6067.107 .04177165 .00322600 .09234252 

 254.956 5935.730 .04295276 .00331258 .09223439 

 256.253 5806.259 .04413386 .00339969 .09214428 

 257.514 5682.756 .04531496 .00348631 .09204816 

 258.584 5561.408 .04649606 .00357383 .09197607 

 259.626 5445.491 .04767717 .00366089 .09189798 

 266.840 5461.521 .04885827 .00374982 .09186193 

 267.799 5351.757 .05003937 .00384047 .09186193 

Ultimate Moment Capacity at a Concrete Strain of 0.003 = 248.732 m- kN 

Axial Thrust Force = 444.82 kN 

 Bending Bending Bending Maximum Neutral Axis 

 Moment Stiffness Curvature Strain Position 

 kN-m kN-m2 rad/m m/m m 

 ------------- ------------- ------------- ------------- ------------- 

 1.59641069 8109.766 .00019685 .00021404 1.10243780 

 2.87353417 8109.752 .00035433 .00022719 .65629032 

 4.15065210 8109.736 .00051181 .00024034 .48470288 

 5.42776291 8109.716 .00066929 .00025350 .39387121 

 6.70486558 8109.694 .00082677 .00026666 .33764809 

 7.98195810 8109.669 .00098425 .00027983 .29942310 

 9.25904000 8109.642 .00114173 .00029301 .27174708 

 10.536 8109.610 .00129921 .00030619 .25078731 

 11.813 8109.575 .00145669 .00031938 .23436312 

 13.090 8109.543 .00161417 .00033256 .22114086 

 14.367 8109.501 .00177165 .00034577 .21027951 

 15.644 8109.460 .00192913 .00035897 .20119034 

 16.933 8114.997 .00208661 .00037169 .19324257 

 18.216 8117.216 .00224409 .00038490 .18662843 

 19.414 8083.775 .00240157 .00039833 .18097548 

 20.715 8094.734 .00255906 .00041140 .17587521 

 21.918 8068.234 .00271654 .00042454 .17139370 

 23.319 8113.629 .00287402 .00043745 .16732070 

 24.592 8112.165 .00303150 .00045098 .16387847 

 25.869 8112.108 .00318898 .00046422 .16068254 

 26.853 8024.180 .00334646 .00047669 .15755870 

 27.976 7984.229 .00350394 .00048897 .15466314 

 29.265 7992.743 .00366142 .00050220 .15227220 

 30.576 8006.552 .00381890 .00051480 .14991730 

 31.519 7926.605 .00397638 .00052712 .14767655 

 40.618 7875.591 .00515748 .00062325 .13595614 

 49.161 7755.812 .00633858 .00071659 .12816456 

 58.415 7768.317 .00751969 .00081316 .12325052 

 66.923 7691.622 .00870079 .00090617 .11926162 

 75.868 7677.494 .00988189 .00100140 .11645016 

 85.876 7762.426 .01106299 .00110135 .11466597 

 92.645 7566.527 .01224409 .00118687 .11204675 

 103.624 7718.590 .01342520 .00129208 .11135590 

 110.324 7553.198 .01460630 .00137732 .10940950 

 118.090 7479.987 .01578740 .00147068 .10826810 

 130.093 7666.740 .01696850 .00157887 .10815997 

 136.846 7539.876 .01814961 .00166478 .10683834 

 144.490 7474.616 .01933071 .00175488 .10589518 

 152.218 7420.983 .02051181 .00184584 .10510221 

 160.622 7404.371 .02169291 .00194965 .10498807 

 169.126 7393.816 .02287402 .00205580 .10498807 

 182.567 7589.521 .02405512 .00215675 .10477180 

 188.707 7477.637 .02523622 .00223839 .10381062 

 196.615 7442.638 .02641732 .00233268 .10341413 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-14 December 2005

 204.416 7406.814 .02759843 .00242603 .10301765 

 212.036 7367.603 .02877953 .00252277 .10277134 

 219.353 7321.374 .02996063 .00262432 .10270526 

 226.068 7259.311 .03114173 .00273039 .10278937 

 231.848 7172.897 .03232283 .00283997 .10297559 

 236.792 7067.588 .03350394 .00295038 .10317384 

 241.025 6948.953 .03468504 .00306085 .10336007 

 244.630 6820.653 .03586614 .00317025 .10350424 

 247.638 6684.389 .03704724 .00327777 .10358835 

 250.262 6546.509 .03822835 .00338410 .10363641 

 252.618 6410.091 .03940945 .00349103 .10369648 

 254.611 6272.667 .04059055 .00359565 .10369648 

 256.423 6138.679 .04177165 .00370028 .10369648 

 258.080 6008.462 .04295276 .00380594 .10372051 

Ultimate Moment Capacity at a Concrete Strain of 0.003 = 238.693 m- kN 

Axial Thrust Force = 1645.84 kN 

 Bending Bending Bending Maximum Neutral Axis 

 Moment Stiffness Curvature Strain Position 

 kN-m kN-m2 rad/m m/m m 

 ------------- ------------- ------------- ------------- ------------- 

 1.54081874 7827.359 .00019685 .00077499 3.95205263 

 2.77346952 7827.347 .00035433 .00078813 2.23939590 

 4.00611524 7827.333 .00051181 .00080128 1.58069174 

 5.23875301 7827.313 .00066929 .00081444 1.23198105 

 6.47138493 7827.294 .00082677 .00082760 1.01611167 

 7.70400607 7827.270 .00098425 .00084076 .86933022 

 8.93661679 7827.244 .00114173 .00085394 .76304456 

 10.169 7827.213 .00129921 .00086712 .68253058 

 11.402 7827.183 .00145669 .00088030 .61942600 

 12.634 7827.144 .00161417 .00089350 .56864407 

 13.867 7827.109 .00177165 .00090669 .52688673 

 15.099 7827.066 .00192913 .00091989 .49195379 

 16.332 7827.022 .00208661 .00093310 .46229533 

 17.564 7826.971 .00224409 .00094632 .43680599 

 18.797 7826.923 .00240157 .00095953 .41465676 

 20.029 7826.866 .00255906 .00097277 .39524089 

 21.262 7826.814 .00271654 .00098599 .37807179 

 22.494 7826.756 .00287402 .00099923 .36278900 

 23.727 7826.691 .00303150 .00101247 .34909817 

 24.959 7826.627 .00318898 .00102572 .33675900 

 26.191 7826.557 .00334646 .00103898 .32558526 

 27.424 7826.488 .00350394 .00105224 .31541476 

 28.656 7826.415 .00366142 .00106550 .30612133 

 29.888 7826.338 .00381890 .00107878 .29759685 

 31.120 7826.253 .00397638 .00109207 .28975121 

 40.360 7825.558 .00515748 .00119185 .24620367 

 49.598 7824.700 .00633858 .00129195 .21893615 

 58.831 7823.657 .00751969 .00139242 .20028322 

 68.130 7830.283 .00870079 .00149190 .18658037 

 77.203 7812.526 .00988189 .00159226 .17624166 

 85.907 7765.272 .01106299 .00169251 .16810166 

 94.717 7735.752 .01224409 .00179186 .16145749 

 103.868 7736.770 .01342520 .00189309 .15612293 

 112.002 7668.060 .01460630 .00198917 .15129900 

 122.167 7738.241 .01578740 .00209217 .14763450 

 130.935 7716.336 .01696850 .00219303 .14435446 

 139.679 7695.962 .01814961 .00228615 .14107443 

 146.230 7564.663 .01933071 .00238336 .13840715 

 155.542 7583.033 .02051181 .00248623 .13632259 

 162.189 7476.597 .02169291 .00259016 .13451437 

 170.646 7460.258 .02287402 .00269161 .13278424 

 175.764 7306.735 .02405512 .00279548 .13132445 

 180.600 7156.368 .02523622 .00293046 .13123433 

 188.135 7121.651 .02641732 .00304746 .13047140 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-15 December 2005

 191.931 6954.404 .02759843 .00316879 .12993073 

 195.595 6796.323 .02877953 .00329230 .12951021 

 199.081 6644.766 .02996063 .00341967 .12925190 

 202.390 6499.001 .03114173 .00355037 .12911973 

 205.538 6358.908 .03232283 .00368405 .12908970 

 208.542 6224.398 .03350394 .00382068 .12914977 

Ultimate Moment Capacity at a Concrete Strain of 0.003 = 185.078 m- kN 

p-y Curve in Sand Computed Using Reese Criteria 

Soil Layer Number = 1 

Depth below pile head = .000 m 

Depth below ground surface = .305 m 

Equivalent Depth (see note) = .305 m 

Pile Diameter = .197 m 

Angle of Friction = 32.000 deg. 

Avg. Eff. Unit Weight = 18.83843 kN/ m**3 

k = 24430.244 kN/m3 

A (static) = 1.7329 

B (static) = 1.2487 

Pst = 7.324 kN/ m 

Psd = 41.611 kN/ m 

Ps = 7.324 kN/ m 

pu = 12.692 kN/ m 

Cbar = 53.9219 

n = 3.2237 

m = 864.7227 

yk = .0008 m 

ym = .0033 m 

yu = .0074 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

If Psd <= Pst then actual depth is used in place of equivalent depth in 

computations. 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0003 2.036 

 .0005 4.072 

 .0008 5.949 

 .0011 6.504 

 .0014 6.971 

 .0016 7.376 

 .0019 7.737 

 .0022 8.065 

 .0025 8.365 

 .0027 8.643 

 .0030 8.902 

 .0033 9.146 

 .0074 12.692 

 .2042 12.692 

 .4011 12.692 

 .5979 12.692 

p-y Curve in Sand Computed Using Reese Criteria 

Soil Layer Number = 1 

Depth below pile head = 2.020 m 

Depth below ground surface = 2.325 m 

Equivalent Depth (see note) = 2.325 m 

Pile Diameter = .197 m 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-16 December 2005

Angle of Friction = 32.000 deg. 

Avg. Eff. Unit Weight = 18.83843 kN/ m**3 

k = 24430.244 kN/m3 

A (static) = .8800 

B (static) = .5000 

Pst = 257.686 kN/ m 

Psd = 317.379 kN/ m 

Ps = 257.686 kN/ m 

pu = 226.764 kN/ m 

Cbar = 4171.9895 

n = 1.6447 

m = 23877.0680 

yk = .0013 m 

ym = .0033 m 

yu = .0074 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

If Psd <= Pst then actual depth is used in place of equivalent depth in 

computations. 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0003 15.528 

 .0005 31.056 

 .0008 46.584 

 .0011 62.112 

 .0014 75.665 

 .0016 84.535 

 .0019 92.841 

 .0022 100.693 

 .0025 108.168 

 .0027 115.324 

 .0030 122.204 

 .0033 128.843 

 .0074 226.764 

 .2042 226.764 

 .4011 226.764 

 .5979 226.764 

p-y Curve in Sand Computed Using Reese Criteria 

Soil Layer Number = 2 

Depth below pile head = 4.690 m 

Depth below ground surface = 4.995 m 

Equivalent Depth (see note) = 5.449 m 

Pile Diameter = .197 m 

Angle of Friction = 30.000 deg. 

Avg. Eff. Unit Weight = 18.44579 kN/ m**3 

k = 16286.830 kN/m3 

A (static) = .8800 

B (static) = .5000 

Pst = 1099.854 kN/ m 

Psd = 521.333 kN/ m 

Ps = 521.333 kN/ m 

pu = 458.773 kN/ m 

Cbar = 8440.4724 

n = 1.6447 

m = 48306.3849 

yk = .0025 m 

ym = .0033 m 

yu = .0074 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-17 December 2005

If Psd <= Pst then actual depth is used in place of equivalent depth in 

computations. 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0003 24.265 

 .0005 48.529 

 .0008 72.794 

 .0011 97.058 

 .0014 121.323 

 .0016 145.587 

 .0019 169.852 

 .0022 194.116 

 .0025 218.381 

 .0027 233.315 

 .0030 247.235 

 .0033 260.666 

 .0074 458.773 

 .2042 458.773 

 .4011 458.773 

 .5979 458.773 

p-y Curve in Sand Computed Using Reese Criteria 

Soil Layer Number = 2 

Depth below pile head = 4.710 m 

Depth below ground surface = 5.015 m 

Equivalent Depth (see note) = 5.469 m 

Pile Diameter = .197 m 

Angle of Friction = 30.000 deg. 

Avg. Eff. Unit Weight = 18.44260 kN/ m**3 

k = 16286.830 kN/m3 

A (static) = .8800 

B (static) = .5000 

Pst = 1107.556 kN/ m 

Psd = 523.330 kN/ m 

Ps = 523.330 kN/ m 

pu = 460.530 kN/ m 

Cbar = 8472.8005 

n = 1.6447 

m = 48491.4045 

yk = .0025 m 

ym = .0033 m 

yu = .0074 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

If Psd <= Pst then actual depth is used in place of equivalent depth in 

computations. 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0003 24.354 

 .0005 48.707 

 .0008 73.061 

 .0011 97.414 

 .0014 121.768 

 .0016 146.122 

 .0019 170.475 

 .0022 194.829 

 .0025 219.183 

 .0027 234.209 

 .0030 248.182 

 .0033 261.665 

 .0074 460.530 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-18 December 2005

 .2042 460.530 

 .4011 460.530 

 .5979 460.530 

p-y Curve in Sand Computed Using Reese Criteria 

Soil Layer Number = 2 

Depth below pile head = 9.990 m 

Depth below ground surface = 10.295 m 

Equivalent Depth (see note) = 10.749 m 

Pile Diameter = .197 m 

Angle of Friction = 30.000 deg. 

Avg. Eff. Unit Weight = 18.03305 kN/ m**3 

k = 16286.830 kN/m3 

A (static) = .8800 

B (static) = .5000 

Pst = 4085.048 kN/ m 

Psd = 1050.477 kN/ m 

Ps = 1050.477 kN/ m 

pu = 924.420 kN/ m 

Cbar = 17007.4142 

n = 1.6447 

m = 97336.5779 

yk = .0026 m 

ym = .0033 m 

yu = .0074 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

If Psd <= Pst then actual depth is used in place of equivalent depth in 

computations. 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0003 47.865 

 .0005 95.729 

 .0008 143.594 

 .0011 191.459 

 .0014 239.324 

 .0016 287.188 

 .0019 335.053 

 .0022 382.918 

 .0025 430.783 

 .0027 470.126 

 .0030 498.174 

 .0033 525.239 

 .0074 924.420 

 .2042 924.420 

 .4011 924.420 

 .5979 924.420 

p-y Curve in Sand Computed Using Reese Criteria 

Soil Layer Number = 2 

Depth below pile head = 10.010 m 

Depth below ground surface = 10.315 m 

Equivalent Depth (see note) = 10.769 m 

Pile Diameter = .197 m 

Angle of Friction = 30.000 deg. 

Avg. Eff. Unit Weight = 18.03229 kN/ m**3 

k = 16286.830 kN/m3 

A (static) = .8800 

B (static) = .5000 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-19 December 2005

Pst = 4099.902 kN/ m 

Psd = 1052.474 kN/ m 

Ps = 1052.474 kN/ m 

pu = 926.177 kN/ m 

Cbar = 17039.7421 

n = 1.6447 

m = 97521.5966 

yk = .0026 m 

ym = .0033 m 

yu = .0074 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

If Psd <= Pst then actual depth is used in place of equivalent depth in 

computations. 

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0003 47.954 

 .0005 95.908 

 .0008 143.861 

 .0011 191.815 

 .0014 239.769 

 .0016 287.723 

 .0019 335.677 

 .0022 383.630 

 .0025 431.584 

 .0027 471.020 

 .0030 499.121 

 .0033 526.237 

 .0074 926.177 

 .2042 926.177 

 .4011 926.177 

 .5979 926.177 

p-y Curve in Sand Computed Using Reese Criteria 

Soil Layer Number = 2 

Depth below pile head = 12.192 m 

Depth below ground surface = 12.497 m 

Equivalent Depth (see note) = 12.951 m 

Pile Diameter = .197 m 

Angle of Friction = 30.000 deg. 

Avg. Eff. Unit Weight = 17.96451 kN/ m**3 

k = 16286.830 kN/m3 

A (static) = .8800 

B (static) = .5000 

Pst = 5882.580 kN/ m 

Psd = 1270.322 kN/ m 

Ps = 1270.322 kN/ m 

pu = 1117.883 kN/ m 

Cbar = 20566.7358 

n = 1.6447 

m = 117707.2342 

yk = .0026 m 

ym = .0033 m 

yu = .0074 m 

p-multiplier = 1.00000 

y-multiplier = 1.00000 

If Psd <= Pst then actual depth is used in place of equivalent depth in 

computations. 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-20 December 2005

 y, m p, kN/ m 

---------------- ----------------- 

 .0000 .000 

 .0003 57.670 

 .0005 115.340 

 .0008 173.010 

 .0011 230.680 

 .0014 288.350 

 .0016 346.020 

 .0019 403.690 

 .0022 461.360 

 .0025 519.030 

 .0027 568.515 

 .0030 602.432 

 .0033 635.161 

 .0074 1117.883 

 .2042 1117.883 

 .4011 1117.883 

 .5979 1117.883 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 1 

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Slope (BC Type 2) 

Specified shear force at pile head = 44.482 kN 

Specified slope at pile head = 0.000E+00 m/ m 

Specified axial load at pile head = 1423.431 kN 

(Zero slope for this load indicates fixed-head conditions) 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 .003403 -37.2932 44.4822 -7.11E-18 2.67E+05 7844.083 -9.251 

 .122 .003367 -31.8884 43.1608 -5.38E-04 2.53E+05 7844.083 -12.426 

 .244 .003271 -26.5823 41.5111 -9.92E-04 2.38E+05 7844.083 -14.636 

 .366 .003125 -21.4220 39.6064 -.001365 2.24E+05 7871.775 -16.608 

 .488 .002939 -16.4510 37.5126 -.001658 2.10E+05 7880.353 -17.741 

 .610 .002721 -11.6996 35.1507 -.001875 1.97E+05 7879.471 -21.004 

 .732 .002481 -7.2289 32.3918 -.002022 1.85E+05 7879.576 -24.253 

 .853 .002228 -3.0994 29.2195 -.002102 1.74E+05 7879.641 -27.787 

 .975 .001969 .6255 25.6391 -.002121 1.67E+05 7879.657 -30.947 

 1.097 .001711 3.8886 21.7048 -.002086 1.76E+05 7879.631 -33.592 

 1.219 .001460 6.6420 17.4867 -.002005 1.83E+05 7879.588 -35.601 

 1.341 .001222 8.8483 13.0688 -.001885 1.89E+05 7879.543 -36.871 

 1.463 .001001 10.4828 8.5461 -.001735 1.94E+05 7879.503 -37.320 

 1.585 7.99E-04 11.5345 4.0222 -.001565 1.97E+05 7879.476 -36.890 

 1.707 6.19E-04 12.0068 -8.16E-02 -.001383 1.98E+05 7879.462 -30.429 

 1.829 4.62E-04 11.9945 -3.4043 -.001197 1.98E+05 7879.462 -24.077 

 1.951 3.27E-04 11.5921 -5.9714 -.001015 1.97E+05 7879.474 -18.035 

 2.073 2.15E-04 10.8905 -7.8304 -8.41E-04 1.95E+05 7879.493 -12.461 

 2.195 1.22E-04 9.9745 -9.0454 -6.79E-04 1.92E+05 7879.516 -7.469 

 2.316 4.89E-05 8.9206 -9.6917 -5.33E-04 1.90E+05 7879.541 -3.134 

 2.438 -7.63E-06 7.7963 -9.8515 -4.04E-04 1.86E+05 7879.565 .511606 

 2.560 -4.95E-05 6.6585 -9.6092 -2.92E-04 1.83E+05 7879.588 3.464 

 2.682 -7.88E-05 5.5544 -9.0475 -1.97E-04 1.80E+05 7879.606 5.750 

 2.804 -9.76E-05 4.5209 -8.2451 -1.19E-04 1.77E+05 7879.622 7.414 

 2.926 -1.08E-04 3.5854 -7.2740 -5.67E-05 1.75E+05 7879.635 8.517 

 3.048 -1.11E-04 2.7669 -6.3336 -7.52E-06 1.73E+05 7879.645 6.909 

 3.170 -1.10E-04 2.0436 -5.4843 2.97E-05 1.71E+05 7879.652 7.022 

 3.292 -1.04E-04 1.4193 -4.6372 5.65E-05 1.69E+05 7879.657 6.874 

 3.414 -9.60E-05 .8933 -3.8206 7.44E-05 1.67E+05 7879.657 6.522 

 3.536 -8.60E-05 .4618 -3.0561 8.49E-05 1.66E+05 7879.657 6.019 

 3.658 -7.53E-05 .1186 -2.3591 8.93E-05 1.65E+05 7879.657 5.414 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-21 December 2005

 3.780 -6.43E-05 -.1444 -1.7395 8.91E-05 1.65E+05 7879.657 4.750 

 3.901 -5.35E-05 -.3365 -1.2022 8.54E-05 1.66E+05 7879.657 4.063 

 4.023 -4.34E-05 -.4672 -.7483 7.92E-05 1.66E+05 7879.657 3.383 

 4.145 -3.42E-05 -.5464 -.3754 7.14E-05 1.67E+05 7879.657 2.733 

 4.267 -2.60E-05 -.5835 -7.89E-02 6.26E-05 1.67E+05 7879.657 2.131 

 4.389 -1.89E-05 -.5874 .1478 5.36E-05 1.67E+05 7879.657 1.588 

 4.511 -1.30E-05 -.5661 .3125 4.46E-05 1.67E+05 7879.657 1.113 

 4.633 -8.06E-06 -.5267 .4234 3.62E-05 1.66E+05 7879.657 .707571 

 4.755 -4.14E-06 -.4754 .4893 2.84E-05 1.66E+05 7879.657 .371913 

 4.877 -1.12E-06 -.4173 .5182 2.15E-05 1.66E+05 7879.657 .103024 

 4.999 1.11E-06 -.3565 .5181 1.55E-05 1.66E+05 7879.657 -.104035 

 5.121 2.67E-06 -.2963 .4962 1.05E-05 1.66E+05 7879.657 -.255553 

 5.243 3.67E-06 -.2392 .4588 6.35E-06 1.66E+05 7879.657 -.358621 

 5.364 4.22E-06 -.1867 .4113 3.06E-06 1.66E+05 7879.657 -.420666 

 5.486 4.41E-06 -.1399 .3583 5.33E-07 1.65E+05 7879.657 -.449073 

 5.608 4.35E-06 -9.95E-02 .3034 -1.32E-06 1.65E+05 7879.657 -.450887 

 5.730 4.09E-06 -6.55E-02 .2495 -2.60E-06 1.65E+05 7879.657 -.432598 

 5.852 3.71E-06 -3.77E-02 .1988 -3.39E-06 1.65E+05 7879.657 -.399996 

 5.974 3.27E-06 -1.58E-02 .1526 -3.81E-06 1.65E+05 7879.657 -.358083 

 6.096 2.79E-06 7.85E-04 .1118 -3.93E-06 1.65E+05 7879.657 -.311050 

 6.218 2.31E-06 1.28E-02 7.68E-02 -3.82E-06 1.65E+05 7879.657 -.262281 

 6.340 1.85E-06 2.08E-02 4.78E-02 -3.56E-06 1.65E+05 7879.657 -.214403 

 6.462 1.44E-06 2.57E-02 2.44E-02 -3.20E-06 1.65E+05 7879.657 -.169348 

 6.584 1.07E-06 2.79E-02 6.23E-03 -2.79E-06 1.65E+05 7879.657 -.128437 

 6.706 7.61E-07 2.82E-02 -7.24E-03 -2.35E-06 1.65E+05 7879.657 -.092472 

 6.828 5.00E-07 2.70E-02 -1.66E-02 -1.93E-06 1.65E+05 7879.657 -.061825 

 6.949 2.91E-07 2.48E-02 -2.26E-02 -1.53E-06 1.65E+05 7879.657 -.036527 

 7.071 1.28E-07 2.20E-02 -2.59E-02 -1.16E-06 1.65E+05 7879.657 -.016356 

 7.193 6.99E-09 1.89E-02 -2.69E-02 -8.49E-07 1.65E+05 7879.657 -9.05E-04 

 7.315 -7.87E-08 1.57E-02 -2.63E-02 -5.81E-07 1.65E+05 7879.657 .010349 

 7.437 -1.35E-07 1.26E-02 -2.46E-02 -3.62E-07 1.65E+05 7879.657 .017992 

 7.559 -1.67E-07 9.82E-03 -2.21E-02 -1.88E-07 1.65E+05 7879.657 .022627 

 7.681 -1.81E-07 7.31E-03 -1.92E-02 -5.60E-08 1.65E+05 7879.657 .024844 

 7.803 -1.81E-07 5.14E-03 -1.62E-02 4.04E-08 1.65E+05 7879.657 .025193 

 7.925 -1.71E-07 3.34E-03 -1.32E-02 1.06E-07 1.65E+05 7879.657 .024170 

 8.047 -1.55E-07 1.89E-03 -1.04E-02 1.47E-07 1.65E+05 7879.657 .022203 

 8.169 -1.35E-07 7.68E-04 -7.81E-03 1.67E-07 1.65E+05 7879.657 .019652 

 8.291 -1.14E-07 -6.77E-05 -5.58E-03 1.73E-07 1.65E+05 7879.657 .016810 

 8.412 -9.31E-08 -6.53E-04 -3.71E-03 1.67E-07 1.65E+05 7879.657 .013904 

 8.534 -7.33E-08 -1.03E-03 -2.19E-03 1.54E-07 1.65E+05 7879.657 .011101 

 8.656 -5.55E-08 -1.24E-03 -9.90E-04 1.36E-07 1.65E+05 7879.657 .008517 

 8.778 -4.01E-08 -1.32E-03 -9.12E-05 1.17E-07 1.65E+05 7879.657 .006226 

 8.900 -2.71E-08 -1.30E-03 5.48E-04 9.63E-08 1.65E+05 7879.657 .004265 

 9.022 -1.66E-08 -1.22E-03 9.69E-04 7.68E-08 1.65E+05 7879.657 .002644 

 9.144 -8.38E-09 -1.09E-03 1.21E-03 5.89E-08 1.65E+05 7879.657 .001351 

 9.266 -2.22E-09 -9.43E-04 1.32E-03 4.32E-08 1.65E+05 7879.657 3.63E-04 

 9.388 2.15E-09 -7.86E-04 1.32E-03 2.98E-08 1.65E+05 7879.657 -3.55E-04 

 9.510 5.04E-09 -6.32E-04 1.24E-03 1.88E-08 1.65E+05 7879.657 -8.43E-04 

 9.632 6.74E-09 -4.89E-04 1.12E-03 1.01E-08 1.65E+05 7879.657 -.001140 

 9.754 7.51E-09 -3.62E-04 9.76E-04 3.56E-09 1.65E+05 7879.657 -.001286 

 9.876 7.61E-09 -2.53E-04 8.17E-04 -1.20E-09 1.65E+05 7879.657 -.001317 

 9.997 7.22E-09 -1.62E-04 6.60E-04 -4.40E-09 1.65E+05 7879.657 -.001265 

 10.119 6.53E-09 -9.01E-05 5.12E-04 -6.35E-09 1.65E+05 7879.657 -.001157 

 10.241 5.67E-09 -3.50E-05 3.80E-04 -7.32E-09 1.65E+05 7879.657 -.001016 

 10.363 4.75E-09 5.09E-06 2.65E-04 -7.55E-09 1.65E+05 7879.657 -8.60E-04 

 10.485 3.83E-09 3.24E-05 1.70E-04 -7.26E-09 1.65E+05 7879.657 -7.02E-04 

 10.607 2.98E-09 4.91E-05 9.39E-05 -6.63E-09 1.65E+05 7879.657 -5.51E-04 

 10.729 2.21E-09 5.75E-05 3.50E-05 -5.81E-09 1.65E+05 7879.657 -4.14E-04 

 10.851 1.56E-09 5.97E-05 -8.21E-06 -4.90E-09 1.65E+05 7879.657 -2.95E-04 

 10.973 1.02E-09 5.72E-05 -3.81E-05 -4.00E-09 1.65E+05 7879.657 -1.95E-04 

 11.095 5.86E-10 5.18E-05 -5.68E-05 -3.15E-09 1.65E+05 7879.657 -1.13E-04 

 11.217 2.50E-10 4.45E-05 -6.67E-05 -2.41E-09 1.65E+05 7879.657 -4.88E-05 

 11.339 -1.65E-12 3.64E-05 -6.96E-05 -1.78E-09 1.65E+05 7879.657 3.26E-07 

 11.460 -1.85E-10 2.81E-05 -6.74E-05 -1.28E-09 1.65E+05 7879.657 3.68E-05 

 11.582 -3.15E-10 2.04E-05 -6.13E-05 -9.09E-10 1.65E+05 7879.657 6.33E-05 

 11.704 -4.06E-10 1.35E-05 -5.24E-05 -6.47E-10 1.65E+05 7879.657 8.25E-05 

 11.826 -4.72E-10 7.82E-06 -4.15E-05 -4.82E-10 1.65E+05 7879.657 9.68E-05 

 11.948 -5.24E-10 3.56E-06 -2.89E-05 -3.94E-10 1.65E+05 7879.657 1.08E-04 

 12.070 -5.68E-10 8.97E-07 -1.51E-05 -3.59E-10 1.65E+05 7879.657 1.19E-04 

 12.192 -6.11E-10 0.0 0.0 -3.52E-10 1.65E+05 7879.657 1.29E-04 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-22 December 2005

Please note that because this analysis makes computations of ultimate moment 

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 1: 

Pile-head deflection = .00340258 m 

Computed slope at pile head = -7.11419E-18 

Maximum bending moment = -37.293 kN- m 

Maximum shear force = 44.482 kN 

Depth of maximum bending moment = 0.000 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 10 

Number of zero deflection points = 5 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 2 

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Specified shear force at pile head = 44.482 kN 

Specified bending moment at pile head = .000 m- kN 

Specified axial load at pile head = 1423.431 kN 

(Zero moment for this load indicates free-head conditions) 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 .014724 5.52E-12 44.4822 -.010991 1.65E+05 7879.576 -12.692 

 .122 .013384 7.2364 42.6455 -.010935 1.85E+05 7879.576 -17.437 

 .244 .012057 14.1941 40.2756 -.010769 2.04E+05 7879.576 -21.439 

 .366 .010758 20.7951 37.3520 -.010498 2.22E+05 7873.895 -26.520 

 .488 .009497 26.9459 33.7804 -.010128 2.39E+05 7859.268 -32.069 

 .610 .008288 32.5476 29.3418 -.009666 2.54E+05 7843.367 -40.743 

 .732 .007140 37.4558 23.8529 -.009122 2.68E+05 7838.035 -49.298 

 .853 .006064 41.5301 17.5993 -.008508 2.79E+05 7832.013 -53.287 

 .975 .005066 44.7001 10.9265 -.007836 2.88E+05 7824.059 -56.174 

 1.097 .004153 46.9142 3.9683 -.007122 2.94E+05 7818.495 -57.970 

 1.219 .003329 48.1397 -3.1475 -.006381 2.97E+05 7815.411 -58.759 

 1.341 .002597 48.3615 -10.2836 -.005628 2.98E+05 7814.853 -58.304 

 1.463 .001957 47.5856 -17.2581 -.004880 2.96E+05 7816.806 -56.106 

 1.585 .001407 45.8469 -23.8505 -.004151 2.91E+05 7821.178 -52.038 

 1.707 9.45E-04 43.2107 -29.8236 -.003457 2.84E+05 7827.798 -45.946 

 1.829 5.64E-04 39.7748 -34.4167 -.002811 2.74E+05 7835.513 -29.401 

 1.951 2.59E-04 35.7944 -37.0790 -.002224 2.63E+05 7839.841 -14.272 

 2.073 2.18E-05 31.5052 -38.0263 -.001701 2.51E+05 7844.499 -1.268 

 2.195 -1.56E-04 27.1123 -37.5242 -.001245 2.39E+05 7858.247 9.504 

 2.316 -2.82E-04 22.7876 -35.8446 -8.59E-04 2.28E+05 7879.844 18.049 

 2.438 -3.65E-04 18.6700 -33.2530 -5.38E-04 2.16E+05 7875.716 24.465 

 2.560 -4.13E-04 14.8659 -29.9993 -2.78E-04 2.06E+05 7879.373 28.910 

 2.682 -4.33E-04 11.4516 -26.3110 -7.48E-05 1.96E+05 7879.478 31.594 

 2.804 -4.31E-04 8.4762 -22.3882 7.93E-05 1.88E+05 7879.551 32.756 

 2.926 -4.14E-04 5.9649 -18.4013 1.91E-04 1.81E+05 7879.599 32.646 

 3.048 -3.85E-04 3.9229 -14.9571 2.68E-04 1.76E+05 7879.631 23.853 

 3.170 -3.48E-04 2.2250 -12.1440 3.15E-04 1.71E+05 7879.650 22.293 

 3.292 -3.08E-04 .8524 -9.5469 3.39E-04 1.67E+05 7879.657 20.311 

 3.414 -2.66E-04 -.2206 -7.2079 3.44E-04 1.66E+05 7879.657 18.059 

 3.536 -2.24E-04 -1.0245 -5.1518 3.34E-04 1.68E+05 7879.657 15.669 

 3.658 -1.84E-04 -1.5928 -3.3887 3.14E-04 1.69E+05 7879.656 13.253 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-23 December 2005

 3.780 -1.47E-04 -1.9598 -1.9163 2.86E-04 1.70E+05 7879.653 10.900 

 3.901 -1.14E-04 -2.1595 -.7226 2.55E-04 1.71E+05 7879.651 8.682 

 4.023 -8.54E-05 -2.2244 .2121 2.21E-04 1.71E+05 7879.650 6.650 

 4.145 -6.06E-05 -2.1844 .9125 1.87E-04 1.71E+05 7879.650 4.839 

 4.267 -3.99E-05 -2.0666 1.4065 1.54E-04 1.71E+05 7879.652 3.265 

 4.389 -2.31E-05 -1.8948 1.7236 1.23E-04 1.70E+05 7879.653 1.937 

 4.511 -9.89E-06 -1.6890 1.8935 9.53E-05 1.70E+05 7879.655 .848990 

 4.633 1.35E-07 -1.4661 1.9445 7.09E-05 1.69E+05 7879.657 -.011839 

 4.755 7.39E-06 -1.2395 1.9033 5.00E-05 1.68E+05 7879.657 -.664099 

 4.877 1.23E-05 -1.0194 1.7939 3.25E-05 1.68E+05 7879.657 -1.131 

 4.999 1.53E-05 -.8133 1.6374 1.83E-05 1.67E+05 7879.657 -1.436 

 5.121 1.68E-05 -.6264 1.4519 7.17E-06 1.67E+05 7879.657 -1.607 

 5.243 1.71E-05 -.4618 1.2523 -1.25E-06 1.66E+05 7879.657 -1.668 

 5.364 1.65E-05 -.3206 1.0505 -7.31E-06 1.66E+05 7879.657 -1.643 

 5.486 1.53E-05 -.2031 .8556 -1.14E-05 1.66E+05 7879.657 -1.554 

 5.608 1.37E-05 -.1081 .6742 -1.38E-05 1.65E+05 7879.657 -1.421 

 5.730 1.19E-05 -3.39E-02 .5107 -1.49E-05 1.65E+05 7879.657 -1.260 

 5.852 1.01E-05 2.16E-02 .3677 -1.50E-05 1.65E+05 7879.657 -1.085 

 5.974 8.28E-06 6.09E-02 .2462 -1.43E-05 1.65E+05 7879.657 -.907652 

 6.096 6.59E-06 8.66E-02 .1460 -1.32E-05 1.65E+05 7879.657 -.735564 

 6.218 5.06E-06 .1011 6.61E-02 -1.17E-05 1.65E+05 7879.657 -.575335 

 6.340 3.73E-06 .1068 4.76E-03 -1.01E-05 1.65E+05 7879.657 -.431104 

 6.462 2.60E-06 .1058 -4.01E-02 -8.47E-06 1.65E+05 7879.657 -.305266 

 6.584 1.66E-06 10.0E-01 -7.09E-02 -6.88E-06 1.65E+05 7879.657 -.198795 

 6.706 9.17E-07 9.09E-02 -8.98E-02 -5.41E-06 1.65E+05 7879.657 -.111541 

 6.828 3.44E-07 7.99E-02 -9.92E-02 -4.08E-06 1.65E+05 7879.657 -.042518 

 6.949 -7.85E-08 6.81E-02 -.1012 -2.94E-06 1.65E+05 7879.657 .009850 

 7.071 -3.72E-07 5.63E-02 -9.77E-02 -1.98E-06 1.65E+05 7879.657 .047503 

 7.193 -5.60E-07 4.50E-02 -9.03E-02 -1.19E-06 1.65E+05 7879.657 .072569 

 7.315 -6.63E-07 3.47E-02 -8.06E-02 -5.76E-07 1.65E+05 7879.657 .087215 

 7.437 -7.01E-07 2.56E-02 -6.96E-02 -1.10E-07 1.65E+05 7879.657 .093536 

 7.559 -6.90E-07 1.78E-02 -5.82E-02 2.25E-07 1.65E+05 7879.657 .093476 

 7.681 -6.46E-07 1.13E-02 -4.71E-02 4.50E-07 1.65E+05 7879.657 .088769 

 7.803 -5.80E-07 6.12E-03 -3.67E-02 5.85E-07 1.65E+05 7879.657 .080917 

 7.925 -5.03E-07 2.13E-03 -2.75E-02 6.48E-07 1.65E+05 7879.657 .071172 

 8.047 -4.22E-07 -8.01E-04 -1.94E-02 6.59E-07 1.65E+05 7879.657 .060544 

 8.169 -3.43E-07 -2.83E-03 -1.27E-02 6.31E-07 1.65E+05 7879.657 .049814 

 8.291 -2.68E-07 -4.12E-03 -7.25E-03 5.77E-07 1.65E+05 7879.657 .039556 

 8.412 -2.02E-07 -4.80E-03 -3.00E-03 5.08E-07 1.65E+05 7879.657 .030163 

 8.534 -1.45E-07 -5.02E-03 1.72E-04 4.32E-07 1.65E+05 7879.657 .021877 

 8.656 -9.66E-08 -4.91E-03 2.41E-03 3.55E-07 1.65E+05 7879.657 .014816 

 8.778 -5.80E-08 -4.56E-03 3.86E-03 2.82E-07 1.65E+05 7879.657 .009004 

 8.900 -2.79E-08 -4.07E-03 4.68E-03 2.15E-07 1.65E+05 7879.657 .004391 

 9.022 -5.53E-09 -3.49E-03 5.00E-03 1.57E-07 1.65E+05 7879.657 8.81E-04 

 9.144 1.03E-08 -2.90E-03 4.95E-03 1.07E-07 1.65E+05 7879.657 -.001655 

 9.266 2.06E-08 -2.32E-03 4.65E-03 6.67E-08 1.65E+05 7879.657 -.003360 

 9.388 2.65E-08 -1.79E-03 4.17E-03 3.48E-08 1.65E+05 7879.657 -.004382 

 9.510 2.91E-08 -1.32E-03 3.61E-03 1.08E-08 1.65E+05 7879.657 -.004862 

 9.632 2.91E-08 -9.14E-04 3.01E-03 -6.49E-09 1.65E+05 7879.657 -.004932 

 9.754 2.75E-08 -5.81E-04 2.43E-03 -1.81E-08 1.65E+05 7879.657 -.004706 

 9.876 2.47E-08 -3.16E-04 1.88E-03 -2.50E-08 1.65E+05 7879.657 -.004285 

 9.997 2.14E-08 -1.14E-04 1.39E-03 -2.83E-08 1.65E+05 7879.657 -.003748 

 10.119 1.78E-08 3.23E-05 9.68E-04 -2.90E-08 1.65E+05 7879.657 -.003159 

 10.241 1.43E-08 1.32E-04 6.18E-04 -2.77E-08 1.65E+05 7879.657 -.002567 

 10.363 1.11E-08 1.93E-04 3.40E-04 -2.52E-08 1.65E+05 7879.657 -.002007 

 10.485 8.19E-09 2.23E-04 1.26E-04 -2.20E-08 1.65E+05 7879.657 -.001500 

 10.607 5.72E-09 2.31E-04 -3.00E-05 -1.84E-08 1.65E+05 7879.657 -.001059 

 10.729 3.69E-09 2.22E-04 -1.37E-04 -1.49E-08 1.65E+05 7879.657 -6.90E-04 

 10.851 2.08E-09 2.03E-04 -2.03E-04 -1.17E-08 1.65E+05 7879.657 -3.93E-04 

 10.973 8.48E-10 1.77E-04 -2.37E-04 -8.71E-09 1.65E+05 7879.657 -1.62E-04 

 11.095 -4.72E-11 1.48E-04 -2.46E-04 -6.20E-09 1.65E+05 7879.657 9.11E-06 

 11.217 -6.63E-10 1.19E-04 -2.37E-04 -4.13E-09 1.65E+05 7879.657 1.29E-04 

 11.339 -1.05E-09 9.18E-05 -2.17E-04 -2.49E-09 1.65E+05 7879.657 2.08E-04 

 11.460 -1.27E-09 6.72E-05 -1.89E-04 -1.26E-09 1.65E+05 7879.657 2.53E-04 

 11.582 -1.36E-09 4.62E-05 -1.57E-04 -3.86E-10 1.65E+05 7879.657 2.74E-04 

 11.704 -1.37E-09 2.91E-05 -1.23E-04 1.97E-10 1.65E+05 7879.657 2.77E-04 

 11.826 -1.31E-09 1.61E-05 -8.98E-05 5.47E-10 1.65E+05 7879.657 2.69E-04 

 11.948 -1.23E-09 7.06E-06 -5.78E-05 7.26E-10 1.65E+05 7879.657 2.55E-04 

 12.070 -1.14E-09 1.77E-06 -2.78E-05 7.95E-10 1.65E+05 7879.657 2.37E-04 

 12.192 -1.04E-09 0.0 0.0 8.08E-10 1.65E+05 7879.657 2.19E-04 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-24 December 2005

Please note that because this analysis makes computations of ultimate moment 

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 2: 

Pile-head deflection = .01472369 m 

Computed slope at pile head = -.01099103 

Maximum bending moment = 48.361 kN- m 

Maximum shear force = 44.482 kN 

Depth of maximum bending moment = 1.34112000 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 16 

Number of zero deflection points = 5 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 3 

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Rotational Stiffness (BC Type 3) 

Specified shear force at pile head = 44.482 kN 

Specified rotational stiffness = 88964.449 m- kN/rad 

Specified axial load at pile head = 1423.431 kN 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 .003792 -35.7869 44.4822 -4.02E-04 2.63E+05 7855.921 -9.588 

 .122 .003709 -30.3169 43.1143 -9.15E-04 2.48E+05 7855.921 -12.853 

 .244 .003569 -24.9563 41.4085 -.001344 2.34E+05 7855.921 -15.128 

 .366 .003381 -19.7533 39.4373 -.001691 2.19E+05 7875.828 -17.208 

 .488 .003156 -14.7531 37.2627 -.001958 2.06E+05 7879.377 -18.465 

 .610 .002904 -9.9877 34.8067 -.002149 1.92E+05 7879.515 -21.824 

 .732 .002632 -5.5199 31.9438 -.002269 1.80E+05 7879.606 -25.140 

 .853 .002351 -1.4109 28.6613 -.002323 1.69E+05 7879.657 -28.706 

 .975 .002066 2.2751 24.9689 -.002316 1.71E+05 7879.649 -31.866 

 1.097 .001786 5.4813 20.9246 -.002256 1.80E+05 7879.607 -34.478 

 1.219 .001516 8.1604 16.6026 -.002150 1.87E+05 7879.557 -36.420 

 1.341 .001261 10.2761 12.0911 -.002008 1.93E+05 7879.508 -37.587 

 1.463 .001026 11.8056 7.4896 -.001837 1.97E+05 7879.468 -37.898 

 1.585 8.13E-04 12.7400 2.9059 -.001647 2.00E+05 7879.440 -37.294 

 1.707 6.25E-04 13.0858 -1.2391 -.001447 2.01E+05 7879.429 -30.701 

 1.829 4.61E-04 12.9402 -4.5741 -.001246 2.01E+05 7879.434 -24.007 

 1.951 3.21E-04 12.4029 -7.1154 -.001050 1.99E+05 7879.450 -17.681 

 2.073 2.05E-04 11.5696 -8.9176 -8.64E-04 1.97E+05 7879.475 -11.882 

 2.195 1.10E-04 10.5285 -10.0518 -6.93E-04 1.94E+05 7879.502 -6.723 

 2.316 3.55E-05 9.3592 -10.6001 -5.40E-04 1.91E+05 7879.531 -2.273 

 2.438 -2.15E-05 8.1310 -10.6509 -4.04E-04 1.87E+05 7879.558 1.439 

 2.560 -6.31E-05 6.9024 -10.2940 -2.88E-04 1.84E+05 7879.583 4.416 

 2.682 -9.17E-05 5.7209 -9.6169 -1.90E-04 1.81E+05 7879.603 6.691 

 2.804 -1.09E-04 4.6235 -8.7021 -1.10E-04 1.78E+05 7879.620 8.316 

 2.926 -1.19E-04 3.6373 -7.6246 -4.64E-05 1.75E+05 7879.634 9.360 

 3.048 -1.21E-04 2.7804 -6.5974 3.28E-06 1.73E+05 7879.644 7.491 

 3.170 -1.18E-04 2.0274 -5.6813 4.05E-05 1.71E+05 7879.652 7.537 

 3.292 -1.11E-04 1.3810 -4.7757 6.68E-05 1.69E+05 7879.657 7.319 

 3.414 -1.01E-04 .8397 -3.9090 8.40E-05 1.67E+05 7879.657 6.897 

 3.536 -9.04E-05 .3987 -3.1029 9.36E-05 1.66E+05 7879.657 6.327 

 3.658 -7.87E-05 5.06E-02 -2.3724 9.71E-05 1.65E+05 7879.657 5.658 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-25 December 2005

 3.780 -6.68E-05 -.2135 -1.7265 9.58E-05 1.66E+05 7879.657 4.936 

 3.901 -5.53E-05 -.4037 -1.1698 9.10E-05 1.66E+05 7879.657 4.197 

 4.023 -4.46E-05 -.5303 -.7023 8.38E-05 1.66E+05 7879.657 3.472 

 4.145 -3.49E-05 -.6040 -.3210 7.50E-05 1.67E+05 7879.657 2.784 

 4.267 -2.63E-05 -.6347 -2.02E-02 6.55E-05 1.67E+05 7879.657 2.151 

 4.389 -1.89E-05 -.6316 .2075 5.57E-05 1.67E+05 7879.657 1.584 

 4.511 -1.27E-05 -.6034 .3705 4.61E-05 1.67E+05 7879.657 1.090 

 4.633 -7.65E-06 -.5573 .4779 3.71E-05 1.67E+05 7879.657 .671482 

 4.755 -3.64E-06 -.4997 .5388 2.90E-05 1.66E+05 7879.657 .327315 

 4.877 -5.86E-07 -.4360 .5620 2.17E-05 1.66E+05 7879.657 .053792 

 4.999 1.65E-06 -.3702 .5558 1.55E-05 1.66E+05 7879.657 -.154750 

 5.121 3.19E-06 -.3058 .5278 1.02E-05 1.66E+05 7879.657 -.305287 

 5.243 4.15E-06 -.2451 .4845 5.98E-06 1.66E+05 7879.657 -.405540 

 5.364 4.65E-06 -.1898 .4315 2.62E-06 1.66E+05 7879.657 -.463495 

 5.486 4.79E-06 -.1408 .3736 6.34E-08 1.65E+05 7879.657 -.487017 

 5.608 4.66E-06 -9.87E-02 .3144 -1.79E-06 1.65E+05 7879.657 -.483553 

 5.730 4.35E-06 -6.35E-02 .2569 -3.04E-06 1.65E+05 7879.657 -.459915 

 5.852 3.92E-06 -3.50E-02 .2031 -3.81E-06 1.65E+05 7879.657 -.422140 

 5.974 3.42E-06 -1.27E-02 .1545 -4.18E-06 1.65E+05 7879.657 -.375413 

 6.096 2.90E-06 4.12E-03 .1118 -4.24E-06 1.65E+05 7879.657 -.324044 

 6.218 2.39E-06 1.61E-02 7.55E-02 -4.08E-06 1.65E+05 7879.657 -.271489 

 6.340 1.91E-06 2.40E-02 4.56E-02 -3.78E-06 1.65E+05 7879.657 -.220402 

 6.462 1.47E-06 2.85E-02 2.16E-02 -3.37E-06 1.65E+05 7879.657 -.172713 

 6.584 1.08E-06 3.04E-02 3.15E-03 -2.91E-06 1.65E+05 7879.657 -.129714 

 6.706 7.58E-07 3.03E-02 -1.04E-02 -2.44E-06 1.65E+05 7879.657 -.092161 

 6.828 4.89E-07 2.87E-02 -1.97E-02 -1.99E-06 1.65E+05 7879.657 -.060368 

 6.949 2.73E-07 2.62E-02 -2.54E-02 -1.56E-06 1.65E+05 7879.657 -.034304 

 7.071 1.07E-07 2.30E-02 -2.84E-02 -1.18E-06 1.65E+05 7879.657 -.013682 

 7.193 -1.52E-08 1.97E-02 -2.91E-02 -8.52E-07 1.65E+05 7879.657 .001968 

 7.315 -1.01E-07 1.63E-02 -2.82E-02 -5.75E-07 1.65E+05 7879.657 .013226 

 7.437 -1.55E-07 1.30E-02 -2.61E-02 -3.48E-07 1.65E+05 7879.657 .020730 

 7.559 -1.85E-07 1.00E-02 -2.33E-02 -1.70E-07 1.65E+05 7879.657 .025129 

 7.681 -1.97E-07 7.38E-03 -2.01E-02 -3.56E-08 1.65E+05 7879.657 .027051 

 7.803 -1.94E-07 5.12E-03 -1.68E-02 6.11E-08 1.65E+05 7879.657 .027077 

 7.925 -1.82E-07 3.26E-03 -1.36E-02 1.26E-07 1.65E+05 7879.657 .025725 

 8.047 -1.63E-07 1.77E-03 -1.06E-02 1.65E-07 1.65E+05 7879.657 .023443 

 8.169 -1.42E-07 6.19E-04 -7.91E-03 1.83E-07 1.65E+05 7879.657 .020603 

 8.291 -1.19E-07 -2.25E-04 -5.58E-03 1.86E-07 1.65E+05 7879.657 .017505 

 8.412 -9.63E-08 -8.07E-04 -3.64E-03 1.78E-07 1.65E+05 7879.657 .014379 

 8.534 -7.53E-08 -1.17E-03 -2.07E-03 1.63E-07 1.65E+05 7879.657 .011394 

 8.656 -5.65E-08 -1.37E-03 -8.46E-04 1.43E-07 1.65E+05 7879.657 .008665 

 8.778 -4.03E-08 -1.43E-03 6.39E-05 1.22E-07 1.65E+05 7879.657 .006263 

 8.900 -2.68E-08 -1.40E-03 7.03E-04 9.98E-08 1.65E+05 7879.657 .004221 

 9.022 -1.60E-08 -1.29E-03 1.12E-03 7.90E-08 1.65E+05 7879.657 .002545 

 9.144 -7.56E-09 -1.15E-03 1.34E-03 6.01E-08 1.65E+05 7879.657 .001219 

 9.266 -1.31E-09 -9.86E-04 1.43E-03 4.36E-08 1.65E+05 7879.657 2.14E-04 

 9.388 3.07E-09 -8.17E-04 1.41E-03 2.97E-08 1.65E+05 7879.657 -5.08E-04 

 9.510 5.92E-09 -6.52E-04 1.32E-03 1.83E-08 1.65E+05 7879.657 -9.90E-04 

 9.632 7.53E-09 -5.00E-04 1.18E-03 9.38E-09 1.65E+05 7879.657 -.001275 

 9.754 8.21E-09 -3.66E-04 1.02E-03 2.67E-09 1.65E+05 7879.657 -.001405 

 9.876 8.19E-09 -2.52E-04 8.49E-04 -2.11E-09 1.65E+05 7879.657 -.001418 

 9.997 7.69E-09 -1.58E-04 6.81E-04 -5.29E-09 1.65E+05 7879.657 -.001348 

 10.119 6.90E-09 -8.43E-05 5.24E-04 -7.16E-09 1.65E+05 7879.657 -.001222 

 10.241 5.95E-09 -2.81E-05 3.85E-04 -8.03E-09 1.65E+05 7879.657 -.001065 

 10.363 4.94E-09 1.23E-05 2.65E-04 -8.15E-09 1.65E+05 7879.657 -8.95E-04 

 10.485 3.96E-09 3.94E-05 1.67E-04 -7.75E-09 1.65E+05 7879.657 -7.25E-04 

 10.607 3.05E-09 5.56E-05 8.80E-05 -7.02E-09 1.65E+05 7879.657 -5.64E-04 

 10.729 2.25E-09 6.33E-05 2.79E-05 -6.10E-09 1.65E+05 7879.657 -4.20E-04 

 10.851 1.56E-09 6.46E-05 -1.57E-05 -5.11E-09 1.65E+05 7879.657 -2.95E-04 

 10.973 1.00E-09 6.13E-05 -4.54E-05 -4.13E-09 1.65E+05 7879.657 -1.91E-04 

 11.095 5.54E-10 5.49E-05 -6.35E-05 -3.24E-09 1.65E+05 7879.657 -1.07E-04 

 11.217 2.12E-10 4.69E-05 -7.26E-05 -2.45E-09 1.65E+05 7879.657 -4.13E-05 

 11.339 -4.26E-11 3.81E-05 -7.46E-05 -1.79E-09 1.65E+05 7879.657 8.40E-06 

 11.460 -2.25E-10 2.93E-05 -7.13E-05 -1.27E-09 1.65E+05 7879.657 4.48E-05 

 11.582 -3.52E-10 2.11E-05 -6.43E-05 -8.78E-10 1.65E+05 7879.657 7.07E-05 

 11.704 -4.39E-10 1.40E-05 -5.45E-05 -6.06E-10 1.65E+05 7879.657 8.91E-05 

 11.826 -5.00E-10 8.05E-06 -4.29E-05 -4.36E-10 1.65E+05 7879.657 1.02E-04 

 11.948 -5.45E-10 3.65E-06 -2.97E-05 -3.46E-10 1.65E+05 7879.657 1.13E-04 

 12.070 -5.84E-10 9.21E-07 -1.54E-05 -3.10E-10 1.65E+05 7879.657 1.22E-04 

 12.192 -6.21E-10 0.0 0.0 -3.03E-10 1.65E+05 7879.657 1.31E-04 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-26 December 2005

Please note that because this analysis makes computations of ultimate moment 

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 3: 

Pile-head deflection = .00379184 m 

Computed slope at pile head = -.00040226 

Maximum bending moment = -35.787 kN- m 

Maximum shear force = 44.482 kN 

Depth of maximum bending moment = 0.000 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 10 

Number of zero deflection points = 5 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 4 

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Rotational Stiffness (BC Type 3) 

Specified shear force at pile head = 44.482 kN 

Specified rotational stiffness = 889644.490 m- kN/rad 

Specified axial load at pile head = 1423.431 kN 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 .003443 -37.1359 44.4822 -4.17E-05 2.67E+05 7844.262 -9.286 

 .122 .003403 -31.7243 43.1559 -5.77E-04 2.52E+05 7844.262 -12.470 

 .244 .003302 -26.4125 41.5004 -.001029 2.38E+05 7844.262 -14.687 

 .366 .003152 -21.2478 39.5888 -.001398 2.23E+05 7872.070 -16.671 

 .488 .002961 -16.2738 37.4864 -.001689 2.10E+05 7880.216 -17.817 

 .610 .002740 -11.5209 35.1146 -.001904 1.97E+05 7879.476 -21.090 

 .732 .002497 -7.0506 32.3448 -.002048 1.84E+05 7879.580 -24.346 

 .853 .002241 -2.9233 29.1609 -.002125 1.73E+05 7879.643 -27.883 

 .975 .001979 .7975 25.5688 -.002141 1.67E+05 7879.657 -31.043 

 1.097 .001719 4.0546 21.6230 -.002104 1.76E+05 7879.629 -33.685 

 1.219 .001466 6.8002 17.3941 -.002020 1.84E+05 7879.585 -35.687 

 1.341 .001226 8.9970 12.9665 -.001897 1.90E+05 7879.540 -36.945 

 1.463 .001003 10.6205 8.4356 -.001746 1.94E+05 7879.499 -37.380 

 1.585 8.01E-04 11.6599 3.9055 -.001573 1.97E+05 7879.472 -36.932 

 1.707 6.20E-04 12.1190 -.2025 -.001389 1.98E+05 7879.458 -30.457 

 1.829 4.62E-04 12.0928 -3.5263 -.001202 1.98E+05 7879.459 -24.069 

 1.951 3.27E-04 11.6763 -6.0907 -.001018 1.97E+05 7879.472 -17.997 

 2.073 2.13E-04 10.9610 -7.9436 -8.43E-04 1.95E+05 7879.491 -12.400 

 2.195 1.21E-04 10.0319 -9.1501 -6.81E-04 1.93E+05 7879.514 -7.391 

 2.316 4.75E-05 8.9661 -9.7862 -5.34E-04 1.90E+05 7879.540 -3.043 

 2.438 -9.08E-06 7.8309 -9.9346 -4.04E-04 1.87E+05 7879.565 .608417 

 2.560 -5.09E-05 6.6837 -9.6803 -2.91E-04 1.83E+05 7879.587 3.563 

 2.682 -8.01E-05 5.5716 -9.1066 -1.97E-04 1.80E+05 7879.605 5.848 

 2.804 -9.88E-05 4.5314 -8.2925 -1.18E-04 1.77E+05 7879.622 7.508 

 2.926 -1.09E-04 3.5907 -7.3103 -5.56E-05 1.75E+05 7879.635 8.604 

 3.048 -1.12E-04 2.7682 -6.3609 -6.39E-06 1.73E+05 7879.645 6.970 

 3.170 -1.11E-04 2.0419 -5.5047 3.08E-05 1.71E+05 7879.652 7.076 

 3.292 -1.05E-04 1.4152 -4.6515 5.76E-05 1.69E+05 7879.657 6.920 

 3.414 -9.65E-05 .8877 -3.8297 7.54E-05 1.67E+05 7879.657 6.561 

 3.536 -8.65E-05 .4552 -3.0609 8.58E-05 1.66E+05 7879.657 6.051 

 3.658 -7.56E-05 .1115 -2.3604 9.02E-05 1.65E+05 7879.657 5.440 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-27 December 2005

 3.780 -6.45E-05 -.1516 -1.7381 8.98E-05 1.65E+05 7879.657 4.770 

 3.901 -5.37E-05 -.3435 -1.1988 8.60E-05 1.66E+05 7879.657 4.077 

 4.023 -4.35E-05 -.4738 -.7434 7.97E-05 1.66E+05 7879.657 3.392 

 4.145 -3.43E-05 -.5524 -.3697 7.18E-05 1.67E+05 7879.657 2.738 

 4.267 -2.61E-05 -.5888 -7.28E-02 6.29E-05 1.67E+05 7879.657 2.133 

 4.389 -1.89E-05 -.5920 .1540 5.38E-05 1.67E+05 7879.657 1.588 

 4.511 -1.29E-05 -.5700 .3185 4.48E-05 1.67E+05 7879.657 1.111 

 4.633 -8.01E-06 -.5299 .4291 3.63E-05 1.66E+05 7879.657 .703775 

 4.755 -4.09E-06 -.4779 .4944 2.85E-05 1.66E+05 7879.657 .367242 

 4.877 -1.07E-06 -.4192 .5228 2.16E-05 1.66E+05 7879.657 .097879 

 4.999 1.17E-06 -.3579 .5221 1.55E-05 1.66E+05 7879.657 -.109326 

 5.121 2.72E-06 -.2973 .4995 1.05E-05 1.66E+05 7879.657 -.260736 

 5.243 3.72E-06 -.2398 .4614 6.31E-06 1.66E+05 7879.657 -.363506 

 5.364 4.26E-06 -.1870 .4134 3.01E-06 1.66E+05 7879.657 -.425121 

 5.486 4.45E-06 -.1400 .3598 4.84E-07 1.65E+05 7879.657 -.453017 

 5.608 4.38E-06 -9.94E-02 .3045 -1.37E-06 1.65E+05 7879.657 -.454280 

 5.730 4.12E-06 -6.53E-02 .2503 -2.64E-06 1.65E+05 7879.657 -.435433 

 5.852 3.74E-06 -3.75E-02 .1992 -3.44E-06 1.65E+05 7879.657 -.402292 

 5.974 3.28E-06 -1.55E-02 .1528 -3.85E-06 1.65E+05 7879.657 -.359878 

 6.096 2.80E-06 1.13E-03 .1118 -3.96E-06 1.65E+05 7879.657 -.312394 

 6.218 2.32E-06 1.31E-02 7.67E-02 -3.85E-06 1.65E+05 7879.657 -.263232 

 6.340 1.86E-06 2.12E-02 4.75E-02 -3.58E-06 1.65E+05 7879.657 -.215021 

 6.462 1.44E-06 2.60E-02 2.41E-02 -3.22E-06 1.65E+05 7879.657 -.169692 

 6.584 1.08E-06 2.82E-02 5.91E-03 -2.80E-06 1.65E+05 7879.657 -.128565 

 6.706 7.60E-07 2.84E-02 -7.57E-03 -2.36E-06 1.65E+05 7879.657 -.092436 

 6.828 4.99E-07 2.71E-02 -1.70E-02 -1.93E-06 1.65E+05 7879.657 -.061670 

 6.949 2.89E-07 2.49E-02 -2.29E-02 -1.53E-06 1.65E+05 7879.657 -.036294 

 7.071 1.26E-07 2.21E-02 -2.61E-02 -1.17E-06 1.65E+05 7879.657 -.016076 

 7.193 4.67E-09 1.89E-02 -2.71E-02 -8.49E-07 1.65E+05 7879.657 -6.05E-04 

 7.315 -8.10E-08 1.58E-02 -2.65E-02 -5.81E-07 1.65E+05 7879.657 .010649 

 7.437 -1.37E-07 1.27E-02 -2.48E-02 -3.61E-07 1.65E+05 7879.657 .018277 

 7.559 -1.69E-07 9.84E-03 -2.23E-02 -1.87E-07 1.65E+05 7879.657 .022887 

 7.681 -1.82E-07 7.31E-03 -1.93E-02 -5.38E-08 1.65E+05 7879.657 .025073 

 7.803 -1.82E-07 5.14E-03 -1.63E-02 4.25E-08 1.65E+05 7879.657 .025389 

 7.925 -1.72E-07 3.34E-03 -1.32E-02 1.08E-07 1.65E+05 7879.657 .024331 

 8.047 -1.56E-07 1.88E-03 -1.04E-02 1.48E-07 1.65E+05 7879.657 .022331 

 8.169 -1.36E-07 7.52E-04 -7.82E-03 1.69E-07 1.65E+05 7879.657 .019751 

 8.291 -1.15E-07 -8.41E-05 -5.58E-03 1.74E-07 1.65E+05 7879.657 .016882 

 8.412 -9.34E-08 -6.69E-04 -3.70E-03 1.68E-07 1.65E+05 7879.657 .013953 

 8.534 -7.35E-08 -1.05E-03 -2.17E-03 1.55E-07 1.65E+05 7879.657 .011131 

 8.656 -5.56E-08 -1.25E-03 -9.75E-04 1.37E-07 1.65E+05 7879.657 .008532 

 8.778 -4.01E-08 -1.33E-03 -7.50E-05 1.17E-07 1.65E+05 7879.657 .006229 

 8.900 -2.71E-08 -1.31E-03 5.64E-04 9.67E-08 1.65E+05 7879.657 .004260 

 9.022 -1.65E-08 -1.23E-03 9.85E-04 7.70E-08 1.65E+05 7879.657 .002633 

 9.144 -8.29E-09 -1.10E-03 1.23E-03 5.91E-08 1.65E+05 7879.657 .001338 

 9.266 -2.13E-09 -9.48E-04 1.33E-03 4.32E-08 1.65E+05 7879.657 3.48E-04 

 9.388 2.25E-09 -7.89E-04 1.33E-03 2.98E-08 1.65E+05 7879.657 -3.71E-04 

 9.510 5.13E-09 -6.34E-04 1.25E-03 1.88E-08 1.65E+05 7879.657 -8.58E-04 

 9.632 6.82E-09 -4.90E-04 1.13E-03 1.01E-08 1.65E+05 7879.657 -.001154 

 9.754 7.59E-09 -3.62E-04 9.81E-04 3.46E-09 1.65E+05 7879.657 -.001299 

 9.876 7.67E-09 -2.52E-04 8.21E-04 -1.29E-09 1.65E+05 7879.657 -.001328 

 9.997 7.27E-09 -1.62E-04 6.62E-04 -4.50E-09 1.65E+05 7879.657 -.001274 

 10.119 6.57E-09 -8.94E-05 5.14E-04 -6.44E-09 1.65E+05 7879.657 -.001164 

 10.241 5.70E-09 -3.43E-05 3.80E-04 -7.40E-09 1.65E+05 7879.657 -.001021 

 10.363 4.77E-09 5.84E-06 2.65E-04 -7.61E-09 1.65E+05 7879.657 -8.64E-04 

 10.485 3.84E-09 3.31E-05 1.70E-04 -7.31E-09 1.65E+05 7879.657 -7.04E-04 

 10.607 2.98E-09 4.98E-05 9.32E-05 -6.67E-09 1.65E+05 7879.657 -5.52E-04 

 10.729 2.22E-09 5.81E-05 3.43E-05 -5.84E-09 1.65E+05 7879.657 -4.15E-04 

 10.851 1.56E-09 6.02E-05 -8.99E-06 -4.92E-09 1.65E+05 7879.657 -2.95E-04 

 10.973 1.02E-09 5.77E-05 -3.88E-05 -4.01E-09 1.65E+05 7879.657 -1.94E-04 

 11.095 5.82E-10 5.21E-05 -5.75E-05 -3.16E-09 1.65E+05 7879.657 -1.12E-04 

 11.217 2.46E-10 4.47E-05 -6.73E-05 -2.41E-09 1.65E+05 7879.657 -4.80E-05 

 11.339 -5.93E-12 3.65E-05 -7.01E-05 -1.78E-09 1.65E+05 7879.657 1.17E-06 

 11.460 -1.89E-10 2.82E-05 -6.78E-05 -1.28E-09 1.65E+05 7879.657 3.76E-05 

 11.582 -3.19E-10 2.04E-05 -6.16E-05 -9.05E-10 1.65E+05 7879.657 6.40E-05 

 11.704 -4.10E-10 1.35E-05 -5.26E-05 -6.42E-10 1.65E+05 7879.657 8.32E-05 

 11.826 -4.75E-10 7.84E-06 -4.16E-05 -4.77E-10 1.65E+05 7879.657 9.74E-05 

 11.948 -5.26E-10 3.57E-06 -2.90E-05 -3.89E-10 1.65E+05 7879.657 1.09E-04 

 12.070 -5.70E-10 9.00E-07 -1.51E-05 -3.54E-10 1.65E+05 7879.657 1.19E-04 

 12.192 -6.12E-10 0.0 0.0 -3.47E-10 1.65E+05 7879.657 1.29E-04 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-28 December 2005

Please note that because this analysis makes computations of ultimate moment 

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 4: 

Pile-head deflection = .00344303 m 

Computed slope at pile head = -.00004174 

Maximum bending moment = -37.136 kN- m 

Maximum shear force = 44.482 kN 

Depth of maximum bending moment = 0.000 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 10 

Number of zero deflection points = 5 

------------------------------------------------------------------------------ 

 Computed Values of Load Distribution and Deflection 

 for Lateral Loading for Load Case Number 5 

------------------------------------------------------------------------------ 

Pile-head boundary conditions are Shear and Moment (BC Type 1) 

Specified shear force at pile head = 44.482 kN 

Specified bending moment at pile head = -18.642 m- kN 

Specified axial load at pile head = 1423.431 kN 

Non-zero moment for this load case indicates the pile-head may rotate under 

the applied pile-head loading, but is not a free-head (zero moment )condition. 

 Depth Deflect. Moment Shear Slope Total Flx. Rig. Soil Res 

 X y M V S Stress EI p 

 m m kN- m kN Rad. kN/ m**2 kN- m**2 kN/ m 

-------- --------- --------- --------- --------- --------- --------- --------- 

 0.000 .008366 -18.6425 44.4822 -.005045 2.16E+05 7879.449 -12.692 

 .122 .007733 -12.4130 42.6455 -.005285 1.99E+05 7879.449 -17.437 

 .244 .007077 -6.4094 40.3063 -.005431 1.83E+05 7879.449 -20.935 

 .366 .006409 -.6998 37.5515 -.005486 1.67E+05 7879.657 -24.256 

 .488 .005740 4.6512 34.4402 -.005455 1.78E+05 7879.620 -26.783 

 .610 .005079 9.5916 30.9157 -.005345 1.91E+05 7879.525 -31.034 

 .732 .004436 14.0449 26.8966 -.005162 2.04E+05 7879.401 -34.896 

 .853 .003820 17.9417 22.4119 -.004915 2.14E+05 7879.417 -38.672 

 .975 .003238 21.2156 17.5017 -.004612 2.23E+05 7872.199 -41.876 

 1.097 .002696 23.8100 12.2492 -.004263 2.30E+05 7879.577 -44.288 

 1.219 .002199 25.6821 6.7662 -.003880 2.35E+05 7871.866 -45.656 

 1.341 .001750 26.8065 1.1874 -.003473 2.39E+05 7860.126 -45.859 

 1.463 .001352 27.1771 -4.3393 -.003054 2.40E+05 7857.847 -44.803 

 1.585 .001005 26.8086 -9.6556 -.002636 2.39E+05 7860.113 -42.406 

 1.707 7.09E-04 25.7375 -14.3645 -.002228 2.36E+05 7871.103 -34.840 

 1.829 4.62E-04 24.0794 -17.9549 -.001843 2.31E+05 7879.547 -24.057 

 1.951 2.60E-04 21.9990 -20.2933 -.001486 2.25E+05 7875.595 -14.303 

 2.073 9.91E-05 19.6470 -21.5162 -.001164 2.19E+05 7875.660 -5.757 

 2.195 -2.42E-05 17.1565 -21.7769 -8.79E-04 2.12E+05 7880.563 1.480 

 2.316 -1.15E-04 14.6420 -21.2368 -6.33E-04 2.05E+05 7879.380 7.380 

 2.438 -1.79E-04 12.1979 -20.0572 -4.25E-04 1.98E+05 7879.456 11.971 

 2.560 -2.19E-04 9.8990 -18.3930 -2.55E-04 1.92E+05 7879.517 15.328 

 2.682 -2.41E-04 7.8013 -16.3880 -1.18E-04 1.86E+05 7879.565 17.563 

 2.804 -2.48E-04 5.9437 -14.1706 -1.12E-05 1.81E+05 7879.599 18.810 

 2.926 -2.43E-04 4.3498 -11.8527 6.84E-05 1.77E+05 7879.625 19.213 

 3.048 -2.31E-04 3.0298 -9.8084 1.25E-04 1.73E+05 7879.642 14.322 

 3.170 -2.13E-04 1.9146 -8.1051 1.64E-04 1.70E+05 7879.653 13.619 

 3.292 -1.91E-04 .9966 -6.5065 1.86E-04 1.68E+05 7879.657 12.605 

 3.414 -1.67E-04 .2634 -5.0445 1.96E-04 1.66E+05 7879.657 11.377 

 3.536 -1.43E-04 -.3014 -3.7401 1.96E-04 1.66E+05 7879.657 10.021 

 3.658 -1.20E-04 -.7165 -2.6044 1.88E-04 1.67E+05 7879.657 8.609 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-29 December 2005

 3.780 -9.75E-05 -1.0017 -1.6405 1.75E-04 1.68E+05 7879.657 7.204 

 3.901 -7.71E-05 -1.1771 -.8445 1.58E-04 1.68E+05 7879.657 5.854 

 4.023 -5.90E-05 -1.2624 -.2075 1.39E-04 1.68E+05 7879.657 4.596 

 4.145 -4.33E-05 -1.2759 .2833 1.19E-04 1.69E+05 7879.657 3.456 

 4.267 -2.99E-05 -1.2346 .6434 9.98E-05 1.68E+05 7879.657 2.451 

 4.389 -1.89E-05 -1.1536 .8896 8.13E-05 1.68E+05 7879.657 1.588 

 4.511 -1.01E-05 -1.0459 1.0393 6.43E-05 1.68E+05 7879.657 .868339 

 4.633 -3.27E-06 -.9225 1.1098 4.90E-05 1.68E+05 7879.657 .286930 

 4.755 1.84E-06 -.7924 1.1172 3.58E-05 1.67E+05 7879.657 -.165391 

 4.877 5.46E-06 -.6625 1.0766 2.45E-05 1.67E+05 7879.657 -.500797 

 4.999 7.82E-06 -.5384 1.0013 1.52E-05 1.66E+05 7879.657 -.733351 

 5.121 9.17E-06 -.4236 .9031 7.78E-06 1.66E+05 7879.657 -.878038 

 5.243 9.72E-06 -.3209 .7917 2.03E-06 1.66E+05 7879.657 -.949962 

 5.364 9.66E-06 -.2313 .6750 -2.25E-06 1.66E+05 7879.657 -.963702 

 5.486 9.17E-06 -.1555 .5594 -5.24E-06 1.65E+05 7879.657 -.932834 

 5.608 8.39E-06 -9.31E-02 .4495 -7.16E-06 1.65E+05 7879.657 -.869593 

 5.730 7.42E-06 -4.34E-02 .3487 -8.22E-06 1.65E+05 7879.657 -.784673 

 5.852 6.38E-06 -5.23E-03 .2589 -8.59E-06 1.65E+05 7879.657 -.687122 

 5.974 5.33E-06 2.27E-02 .1814 -8.46E-06 1.65E+05 7879.657 -.584349 

 6.096 4.32E-06 4.20E-02 .1164 -7.96E-06 1.65E+05 7879.657 -.482185 

 6.218 3.39E-06 5.39E-02 6.36E-02 -7.22E-06 1.65E+05 7879.657 -.385002 

 6.340 2.56E-06 6.00E-02 2.20E-02 -6.34E-06 1.65E+05 7879.657 -.295877 

 6.462 1.84E-06 6.15E-02 -9.20E-03 -5.40E-06 1.65E+05 7879.657 -.216761 

 6.584 1.24E-06 5.96E-02 -3.15E-02 -4.46E-06 1.65E+05 7879.657 -.148666 

 6.706 7.56E-07 5.53E-02 -4.61E-02 -3.57E-06 1.65E+05 7879.657 -.091855 

 6.828 3.72E-07 4.96E-02 -5.45E-02 -2.76E-06 1.65E+05 7879.657 -.046004 

 6.949 8.26E-08 4.30E-02 -5.80E-02 -2.04E-06 1.65E+05 7879.657 -.010372 

 7.071 -1.26E-07 3.61E-02 -5.76E-02 -1.43E-06 1.65E+05 7879.657 .016068 

 7.193 -2.66E-07 2.94E-02 -5.46E-02 -9.24E-07 1.65E+05 7879.657 .034506 

 7.315 -3.51E-07 2.32E-02 -4.96E-02 -5.17E-07 1.65E+05 7879.657 .046200 

 7.437 -3.93E-07 1.75E-02 -4.36E-02 -2.03E-07 1.65E+05 7879.657 .052399 

 7.559 -4.01E-07 1.26E-02 -3.71E-02 3.03E-08 1.65E+05 7879.657 .054286 

 7.681 -3.85E-07 8.45E-03 -3.06E-02 1.93E-07 1.65E+05 7879.657 .052941 

 7.803 -3.54E-07 5.07E-03 -2.43E-02 2.98E-07 1.65E+05 7879.657 .049311 

 7.925 -3.13E-07 2.41E-03 -1.86E-02 3.56E-07 1.65E+05 7879.657 .044204 

 8.047 -2.67E-07 3.98E-04 -1.36E-02 3.77E-07 1.65E+05 7879.657 .038282 

 8.169 -2.21E-07 -1.04E-03 -9.33E-03 3.72E-07 1.65E+05 7879.657 .032070 

 8.291 -1.76E-07 -2.01E-03 -5.79E-03 3.49E-07 1.65E+05 7879.657 .025964 

 8.412 -1.36E-07 -2.58E-03 -2.98E-03 3.13E-07 1.65E+05 7879.657 .020248 

 8.534 -9.98E-08 -2.84E-03 -8.21E-04 2.71E-07 1.65E+05 7879.657 .015106 

 8.656 -6.94E-08 -2.87E-03 7.49E-04 2.27E-07 1.65E+05 7879.657 .010644 

 8.778 -4.44E-08 -2.74E-03 1.82E-03 1.84E-07 1.65E+05 7879.657 .006902 

 8.900 -2.46E-08 -2.49E-03 2.48E-03 1.43E-07 1.65E+05 7879.657 .003874 

 9.022 -9.52E-09 -2.18E-03 2.80E-03 1.07E-07 1.65E+05 7879.657 .001517 

 9.144 1.47E-09 -1.85E-03 2.88E-03 7.58E-08 1.65E+05 7879.657 -2.36E-04 

 9.266 8.97E-09 -1.51E-03 2.78E-03 4.99E-08 1.65E+05 7879.657 -.001465 

 9.388 1.36E-08 -1.19E-03 2.55E-03 2.91E-08 1.65E+05 7879.657 -.002253 

 9.510 1.61E-08 -8.95E-04 2.25E-03 1.30E-08 1.65E+05 7879.657 -.002686 

 9.632 1.68E-08 -6.42E-04 1.91E-03 1.07E-09 1.65E+05 7879.657 -.002842 

 9.754 1.63E-08 -4.29E-04 1.57E-03 -7.21E-09 1.65E+05 7879.657 -.002794 

 9.876 1.50E-08 -2.56E-04 1.24E-03 -1.25E-08 1.65E+05 7879.657 -.002604 

 9.997 1.33E-08 -1.22E-04 9.40E-04 -1.54E-08 1.65E+05 7879.657 -.002324 

 10.119 1.13E-08 -2.17E-05 6.77E-04 -1.65E-08 1.65E+05 7879.657 -.001997 

 10.241 9.23E-09 4.89E-05 4.54E-04 -1.63E-08 1.65E+05 7879.657 -.001654 

 10.363 7.29E-09 9.47E-05 2.73E-04 -1.52E-08 1.65E+05 7879.657 -.001320 

 10.485 5.52E-09 1.21E-04 1.31E-04 -1.36E-08 1.65E+05 7879.657 -.001011 

 10.607 3.98E-09 1.31E-04 2.44E-05 -1.16E-08 1.65E+05 7879.657 -7.37E-04 

 10.729 2.69E-09 1.31E-04 -5.12E-05 -9.58E-09 1.65E+05 7879.657 -5.03E-04 

 10.851 1.64E-09 1.22E-04 -1.01E-04 -7.63E-09 1.65E+05 7879.657 -3.11E-04 

 10.973 8.29E-10 1.09E-04 -1.29E-04 -5.84E-09 1.65E+05 7879.657 -1.58E-04 

 11.095 2.19E-10 9.27E-05 -1.42E-04 -4.28E-09 1.65E+05 7879.657 -4.24E-05 

 11.217 -2.15E-10 7.57E-05 -1.42E-04 -2.98E-09 1.65E+05 7879.657 4.20E-05 

 11.339 -5.07E-10 5.92E-05 -1.33E-04 -1.94E-09 1.65E+05 7879.657 9.99E-05 

 11.460 -6.87E-10 4.39E-05 -1.19E-04 -1.14E-09 1.65E+05 7879.657 1.37E-04 

 11.582 -7.85E-10 3.06E-05 -1.01E-04 -5.61E-10 1.65E+05 7879.657 1.58E-04 

 11.704 -8.24E-10 1.96E-05 -8.08E-05 -1.73E-10 1.65E+05 7879.657 1.67E-04 

 11.826 -8.27E-10 1.10E-05 -6.03E-05 6.37E-11 1.65E+05 7879.657 1.69E-04 

 11.948 -8.09E-10 4.86E-06 -3.98E-05 1.86E-10 1.65E+05 7879.657 1.67E-04 

 12.070 -7.81E-10 1.22E-06 -1.96E-05 2.33E-10 1.65E+05 7879.657 1.63E-04 

 12.192 -7.52E-10 0.0 0.0 2.43E-10 1.65E+05 7879.657 1.59E-04 
FHWA NHI-05-039 Appendix E – Sample Problem No.2 

Micropile Design & Construction E-30 December 2005

Please note that because this analysis makes computations of ultimate moment 

capacity and pile response using nonlinear bending stiffness that the above 

values of total stress due to combined axial stress and bending may not be 

representative of actual conditions. 

Output Verification: 

Computed forces and moments are within specified convergence limits. 

Output Summary for Load Case No. 5: 

Pile-head deflection = .00836608 m 

Computed slope at pile head = -.00504485 

Maximum bending moment = 27.177 kN- m 

Maximum shear force = 44.482 kN Depth of maximum bending moment = 

1.46304000 m 

Depth of maximum shear force = 0.000 m 

Number of iterations = 13 

Number of zero deflection points = 5 

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 Summary of Pile-head Response 

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Definition of symbols for pile-head boundary conditions: 

y = pile-head displacment, m 

M = pile-head moment, kN- m 

V = pile-head shear force, kN 

S = pile-head slope, radians 

R = rotational stiffness of pile-head, m- kN/rad 

 BC Boundary Boundary Axial Pile Head Maximum Maximum 

Type Condition Condition Load Deflection Moment Shear 

 1 2 kN m m- kN kN 

---- ------------ ------------ ----------- ----------- ----------- ----------- 

 2 V= 44.482 S= 0.000 1423.4310 .003403 -37.2932 44.4822 

 1 V= 44.482 M= 0.000 1423.4310 .014724 48.3615 44.4822 

 3 V= 44.482 R= 88964.449 1423.4310 .003792 -35.7869 44.4822 

 3 V= 44.482 R= 8.90E+05 1423.4310 .003443 -37.1359 44.4822 

 1 V= 44.482 M= -18.642 1423.4310 .008366 27.1771 44.4822 

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 Pile-head Deflection vs. Pile Length 

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Boundary Condition Type 2, Shear and Slope 

Shear = 44. kN 

Slope = .00000 

Axial Load = 1423. kN 

 Pile Pile Head Maximum Maximum 

 Length Deflection Moment Shear 

 m m m- kN kN 

----------- ------------ ------------ ------------ 

 12.192 .00340258 -37.293 44.482 

 11.582 .00340004 -37.279 44.482 

 10.973 .00339741 -37.272 44.482 

 10.363 .00339593 -37.273 44.482 

 9.754 .00339785 -37.294 44.482 

 9.144 .00339393 -37.277 44.482 

 8.534 .00339252 -37.271 44.482 

 7.925 .00339051 -37.270 44.482 

 7.315 .00338987 -37.266 44.482 

 6.706 .00338885 -37.267 44.482