GEOTECHNICAL ENGINEERING 

CIRCULAR (GEC) No. 8 

__________ 

DESIGN AND CONSTRUCTION 

OF CONTINUOUS 

FLIGHT AUGER PILES 

FINAL 

April 2007 
 

 

1. Report No. FHWA-HIF-07-03 2 . Government Accession No. 3. Recipients Catalog No. 

4. Title and Subtitle 5. Report Date 

GEOTECHNICAL ENGINEERING CIRCULAR NO. 8 6. Performing Organization Code 

Design and Construction of Continuous Flight Auger (CFA) Piles 

7. Author(s) 8. Performing Organization Report No. 

Dan A. Brown, Ph.D., P.E., Steven D. Dapp, Ph.D., P.E., 

W. Robert Thompson, III, P.E., and Carlos A. Lazarte, Ph.D., P.E. 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

GeoSyntec Consultants 

10015 Old Columbia Road, Suite A-200 11. Contract or Grant No. 

Columbia, Maryland 21046-1760 

12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered 

Office of Technology Application Technical Report 

Office of Engineering/Bridge Division 

Federal Highway Administration 14. Sponsoring Agency Code 

U.S. Department of Transportation 

400 Seventh Street, S.W. 

Washington D.C., 20590 

15. Supplementary Notes 

FHWA Technical Consultant: J.A. DiMaggio, P.E., S.C. Nichols, P.E. 

16. Abstract 

This manual presents the state-of-the-practice for design and construction of continuous flight auger 

(CFA) piles, including those piles commonly referred to as augered cast-in-place (ACIP) piles, drilled 

displacement piles, and screw piles. CFA pile types, materials, and construction equipment and 

procedures are discussed. A performance-based approach is presented to allow contractors greater 

freedom to compete in providing the most cost-effective and reliable foundation system, and a rigorous 

construction monitoring and testing program to verify the performance. Quality control (QC)/quality 

assurance (QA) procedures are discussed, and general requirements for a performance specification are 

given. 

Methods to estimate the static axial capacity of single piles are recommended based on a thorough 

evaluation and comparison of various methods used in the United States and Europe. Group effects for 

axial capacity and settlement, and lateral load capacities for single piles and pile groups are discussed. A 

generalized step-by-step method for selecting and designing CFA piles is presented, along with example 

calculations. An Allowable Stress Design (ASD) procedure is used. 

17. Key Word 18. Distribution Statement 

Continuous flight auger piles, CFA, augered cast-in-place piles, ACIP, No Restrictions. 

drilled displacement piles, screw piles, deep foundation, testing, 

automated monitoring, performance specification. 

19. Security Classification (of this report) 20. Security Classification (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 
ENGLISH TO METRIC (SI) CONVERSION FACTORS 

The primary metric (SI) units used in civil and structural engineering are: 

•	 meter (m) 

•	 kilogram (kg) 

•	 second (s) 

•	 Newton (N) 

•	 Pascal (Pa) 

The following are the conversion factors for units presented in this manual: 

Quantity From English 

Units 

To Metric 

(SI) Units Multiply by For Aid to Quick Calculations 

Mass lb Kg 0.453592 1 lb(mass) = 0.5 kg 

Force lb 

kip 

N 

kN 

4.44822 

4.44822 

1 lb(force) = 4.5 N 

1 kip(force) = 4.5 kN 

Force/Unit Length plf 

klf 

N/m 

kN/m 

14.5939 

14.5939 

1 plf = 14.5 N/m 

1 klf = 14.5 kN/m 

Pressure, Stress, 

Modulus of 

Elasticity 

psf 

ksf 

psi 

ksi 

Pa 

kPa 

kPa 

MPa 

47.8803 

47.8803 

6.89476 

6.89476 

1 psf = 48 Pa 

1 ksf = 48 kPa 

1 psi = 6.9 kPa 

1 ksi = 6.9 MPa 

Length 

inch 

foot 

foot 

mm 

m 

mm 

25.4 

0.3048 

304.8 

1 in = 25 mm 

1 ft = 0.3m 

1 ft = 300 mm 

Area 

square inch 

square foot 

square yard 

mm2 

m2 

m2 

645.16 

0.09290304 

0.83612736 

1 sq in = 650 mm2 

1 sq ft = 0.09 m2 

1 sq yd = 0.84 m2 

Volume 

cubic inch 

cubic foot 

cubic yard 

mm3 

m3 

m3 

16386.064 

0.0283168 

0.764555 

1 cu in = 16,400 mm3 

1 cu ft = 0.03 m3 

1 cu yd = 0.76 m3 

A few points to remember: 

1.	 In a “soft” conversion, an English measurement is mathematically converted to its exact 

metric (SI) equivalent. 

2.	 In a “hard” conversion, a new rounded metric number is created that is convenient to work 

with and remember. 

3.	 Use only the meter and millimeter for length (avoid centimeter). 

4.	 The Pascal (Pa) is the unit for pressure and stress (Pa and N/m2

). 

5.	 Structural calculations should be shown in MPa or kPa. 

6.	 A few basic comparisons worth remembering to help visualize metric dimensions are: 

• One mm is about 1/25 inch, or slightly less than the thickness of a dime. 

• One m is the length of a yardstick plus about 3 inches. 

• One inch is just a fraction (1/64 inch) longer than 25 mm (1 inch = 25.4 mm). 

• Four inches are about 1/16 inch longer than 100 mm (4 inches = 101.6 mm). 

• One foot is about 3/16 inch longer than 300 mm (12 inches = 204.8 mm). 
ACKNOWLEDGEMENTS 

The authors express their appreciation to Mr. Jerry A. DiMaggio, P.E. of the Federal Highway 

Administration (FHWA), Office of Bridge Technology, Mr. Silas Nichols, P.E., of the FHWA 

Resource Center, and Mr. Chien-Tan Chang of the FHWA Office of Bridge Technology for 

providing valuable technical assistance, review, and project overview during this project. The 

authors thank the following individuals that served on the Technical Working Group for this 

project: 

• Silas Nichols FHWA Resource Center 

• Benjamin Rivers FHWA Resource Center 

• Khalid Mohamed FHWA Eastern Federal Lands Highway Division 

• Rich Barrows FHWA Western Federal Lands Highway Division 

• James Brennan Kansas DOT 

• Mark McClelland Texas DOT 

The authors thank the following organizations and individuals for providing valuable information 

and reviewing this manual: 

•	 International Association of Foundation Drilling (ADSC-IAFD) - Emerging Technologies 

Task Force 

• Deep Foundations Institute (DFI) - Augered Cast-In-Place Pile Committee 

In addition, the authors thank the following organizations and individuals for providing valuable 

information for the preparation of this document: 

• Applied Foundation Testing, Green Cove Springs, Florida 

• Bauer Maschinen GmbH, Schrobenhause, Germany 

• Berkel and Company Contractors, Inc., Bonner Springs, Kansas 

• British Research Establishment, U.K. 

• Cementation Foundations Skanska, U.K. 

• DGI-Menard, Inc., Bridgeville, Pennsylvania 

• Franki Geotechnics B, Belgium 

• Jean Lutz, S.A., France 

• Morris-Shea Bridge Company, Inc., Irondale, Alabama 

• Pile Dynamics, Inc., Cleveland, Ohio 

• Societa Italiana Fondazioni (SIF), S.p.A, Italy 

• Soilmec, S.p.A., Italy 

• Soletanche Bachy, France 

• STS Consultants, Vernon Hills, Illinois 

• Trevi, S.p.A., Italy 

• Prof. A. Mandolini, Second University of Naples, Naples, Italy 

• Prof. W. Van Impe, Ghent University, Ghent, Belgium 

• Prof. C. Vipulanandan, University of Houston, Houston, Texas 

• Prof. Michael O’Neill (deceased), University of Houston, Houston, Texas 

Finally, the authors thank Ms. Lynn Johnson, of Geosyntec Consultants, for word processing, 

editing, and assisting in the layout of the document. 

i 
PREFACE
	

The purpose of this document is to develop a state-of-the-practice manual for the design and 

construction of continuous flight auger (CFA) piles, including those piles commonly referred to as 

augered cast-in-place (ACIP) piles, drilled displacement (DD) piles, and screw piles. An Allowable 

Stress Design (ASD) procedure is presented in this document as resistance (strength reduction) 

factors have not yet been calibrated for CFA piles for a Load Resistance Factored Design (LRFD) 

approach. The intended audience for this document is engineers and construction specialists 

involved in the design, construction, and contracting of foundation elements for transportation 

structures. 

CFA piles have been used in the U.S. commercial market but have not been used frequently for 

support of transportation structures in the United States. This underutilization of a viable 

technology is a result of perceived difficulties in quality control, and the difficulties associated with 

incorporating a rapidly developing (and often proprietary) technology into the traditional, 

prescriptive design-bid-build concept. Recent advances in automated monitoring and recording 

devices will alleviate concerns of quality control, as well as provide an essential tool for a 

performance-based contracting process. 

This document provides descriptions of the basic mechanisms involving CFA piles, CFA pile types, 

applications for transportation projects, common materials, construction equipment, and procedures 

used in this technology. Recommendations are made for methods to estimate the static axial 

capacity of single piles. A thorough evaluation and comparison of various existing methods used in 

the United States and Europe is also presented. Group effects for axial capacity and settlement are 

discussed, as well as lateral load capacities for both single piles and pile groups. A generalized 

step-by-step method for the selection and design of CFA piles is presented. Quality control 

(QC)/quality assurance (QA) procedures are discussed, and a performance specification is provided. 

This generic specification may be adapted to specific project requirements. 

A list of the references used in the development of this manual is presented. These references 

include the key publications on the design of augered pile foundations. Existing Federal Highway 

Administration (FWHA) and American Association of State Highway Officials (AASHTO) 

publications that include engineering principles related to the subject of CFA piles are also included 

in the references. 

ii 
TABLE OF CONTENTS 

CHAPTER 1 INTRODUCTION............................................................................................. 1 

1.1 PURPOSE ....................................................................................................................... 1 

1.2 BACKGROUND............................................................................................................. 1 

1.3 RELEVANT PUBLICATIONS ...................................................................................... 2 

1.4 DOCUMENT ORGANIZATION ................................................................................... 2 

CHAPTER 2 DESCRIPTION OF CONTINUOUS FLIGHT AUGER PILE TYPES 

AND BASIC MECHANISMS.......................................................................... 3 

2.1 INTRODUCTION........................................................................................................... 3 

2.2 CONSTRUCTION SEQUENCE .................................................................................... 6 

2.2.1 Drilling.................................................................................................................... 6 

2.2.2 Grouting .................................................................................................................. 8
 

2.2.2.1 General Sequence.......................................................................................... 8 

2.2.2.2 Start of Grouting ........................................................................................... 9 

2.2.2.3 Withdrawal of Auger .................................................................................... 9 

2.2.2.4 Grout vs. Concrete ...................................................................................... 11 

2.2.2.5 Reinforcement (Rebar)................................................................................ 13 

2.3 SUMMARY .................................................................................................................. 14
 

CHAPTER 3 APPLICATIONS FOR TRANSPORTATION PROJECTS ...................... 15 

3.1 INTRODUCTION......................................................................................................... 15 

3.2 ADVANTAGES AND LIMITATIONS OF CFA PILES............................................. 15 

3.2.1 Background........................................................................................................... 15 

3.2.2 Geotechnical Conditions Affecting the Selection and Use of CFA Piles ............. 16 

3.2.2.1 Favorable Geotechnical Conditions ............................................................ 16 

3.2.2.2 Unfavorable Geotechnical Conditions........................................................ 17 

3.2.3 Project Conditions Affecting the Selection and Use of CFA Piles....................... 20 

3.3 ADVANTAGES AND LIMITATIONS OF DRILLED DISPLACEMENT PILES .... 23 

3.4 APPLICATIONS .......................................................................................................... 24 

3.4.1 Soundwalls............................................................................................................ 24 

3.4.2 Bridge Piers and Abutments ................................................................................. 25 

3.4.3 Retaining Structures.............................................................................................. 29 

3.4.4 Pile-Supported Embankments............................................................................... 30 

3.5 CONSTRUCTION COST EVALUATION.................................................................. 31 

iii 
TABLE OF CONTENTS (continued) 

CHAPTER 4 CONSTRUCTION TECHNIQUES AND MATERIALS ........................... 33 

4.1 INTRODUCTION......................................................................................................... 33 

4.2 CONSTRUCTION EQUIPMENT ................................................................................ 33 

4.2.1 Drilling Rigs.......................................................................................................... 33
 

4.2.2 Augers and Drilling Tools .................................................................................... 38 

4.2.3 Equipment for Concrete/Grout and Reinforcement Placement ............................ 48 

4.2.3.1 Auger Plug .................................................................................................. 48 

4.2.3.2 Pumping Equipment.................................................................................... 49 

4.2.3.3 Finishing the Top of the Pile....................................................................... 51 

4.3 CONSTRUCTION MATERIALS ................................................................................ 52 

4.3.1 Grout and Concrete............................................................................................... 52 

4.3.1.1 Cement ........................................................................................................ 55 

4.3.1.2 Pozzolanic Additives .................................................................................. 55 

4.3.1.3 Water........................................................................................................... 56 

4.3.1.4 Aggregate.................................................................................................... 56 

4.3.1.5 Fluidifiers for Grout and Water Reducing Admixtures for Concrete ......... 56 

4.3.1.6 Retarders ..................................................................................................... 57 

4.3.1.7 Air Entraining Agents................................................................................. 57 

4.3.1.8 Sampling and Testing ................................................................................. 58 

4.3.2 Reinforcing Steel .................................................................................................. 59 

4.3.2.1 Reinforcing Steel Materials ........................................................................ 59 

4.3.2.2 Reinforcing Cage/Section ........................................................................... 59 

4.4 SUMMARY OF RECOMMENDED PRACTICES ..................................................... 61 

CHAPTER 5 EVALUATION OF STATIC CAPACITY OF CONTINUOUS 

FLIGHT AUGERED PILES ......................................................................... 64 

5.1 INTRODUCTION......................................................................................................... 64 

5.2 DEVELOPMENT OF SIDE-SHEAR AND END-BEARING RESISTANCE 

WITH PILE DISPLACEMENT.................................................................................... 65 

5.3 RECOMMENDED METHODS FOR ESTIMATING STATIC AXIAL 

CAPACITY OF CFA PILES ........................................................................................ 66 

5.3.1 Cohesive Soils....................................................................................................... 68 

5.3.1.1 Recommended Method for Side-Shear and End-Bearing Estimates 

using Undrained Shear Strength ................................................................. 68 

5.3.1.2 Alternative Methods for Side-Shear Estimates using Undrained Shear 

Strength....................................................................................................... 69 

iv 
TABLE OF CONTENTS (continued) 

5.3.1.3 Alternative Method for End-Bearing Estimates using Dynamic Cone 

Penetrometer ............................................................................................... 71 

5.3.1.4 Alternative Method for Side-Shear and End-Bearing Estimates using 

SPT-N Values ............................................................................................. 71 

5.3.1.5 Alternative Method for Side-Shear and End-Bearing Estimates 

using CPT Values ....................................................................................... 71 

5.3.2 Cohesionless Soils ................................................................................................ 72 

5.3.2.1 Recommended Method for Side-Shear Estimates using Pile Depth 

and End-Bearing Estimates using SPT-N Values ....................................... 72 

5.3.2.2 Alternative Methods for Side-Shear using Pile Depth................................ 73 

5.3.2.3 Alternative Method for Side-Shear and End-Bearing Estimates 

using CPT Values ....................................................................................... 74 

5.3.3 Other Geo-Materials ............................................................................................. 75 

5.3.3.1 Introduction................................................................................................. 75 

5.3.3.2 Vuggy Limestone ........................................................................................ 76 

5.3.3.3 Clay-Shale................................................................................................... 78 

5.4 STATIC AXIAL CAPACITY OF DRILLED DISPLACEMENT PILES ................... 82 

5.4.1 Introduction........................................................................................................... 82
 

5.4.2 Recommended Method Using SPT-N Values or CPT Data ................................. 82 

5.4.3 Amelioration ......................................................................................................... 87 

5.5 GROUP EFFECTS ON STATIC AXIAL COMPRESSION LOAD RESISTANCE OF 

CFA PILES ................................................................................................................... 87 

5.5.1 Introduction........................................................................................................... 87
 

5.5.2 Group Efficiencies ................................................................................................ 89 

5.5.2.1 Conventional CFA Pile Groups .................................................................. 89 

5.5.2.2 Drilled Displacement Pile Groups .............................................................. 94 

5.5.3 Settlement of Pile Groups ..................................................................................... 95 

5.5.3.1 Elastic Compression of the Pile .................................................................. 96 

5.5.3.2 Compression Settlement in Cohesionless Soils .......................................... 98 

5.5.3.3 Consolidation Settlement in Cohesive Soils ............................................... 99 

5.5.4 Uplift of Single CFA Piles and CFA Pile Groups .............................................. 103 

5.6 LATERAL RESISTANCE AND STRUCTURAL CAPACITY OF CFA PILES ..... 104 

5.6.1 Behavior and Limitations of CFA Piles .............................................................. 104 

5.6.2 Lateral Analyses Using the p-y Method ............................................................. 105 

5.6.3 Lateral Analyses of CFA Pile Groups ................................................................ 111 

5.6.4 Structural Capacity.............................................................................................. 113 

5.6.4.1 Longitudinal Reinforcement ..................................................................... 114 

5.6.4.2 Shear Reinforcement................................................................................. 117 

5.6.5 Concrete or Grout Cover and Cage Centering Devices ...................................... 120 

v 
TABLE OF CONTENTS (continued) 

5.6.6 Seismic Considerations ....................................................................................... 120 

5.7 DOWNDRAG IN CFA PILES ................................................................................... 121 

5.8 EXAMPLE PROBLEMS: AXIAL CAPACITY OF SINGLE PILES ....................... 125 

5.8.1 Conventional CFA Pile in Cohesive Soils.......................................................... 125 

5.8.2 Conventional CFA and Drilled Displacement Piles in Cohesionless Soils ........ 127 

CHAPTER 6 RECOMMENDED DESIGN METHOD.................................................... 133 

6.1 STEP 1: INITIAL DESIGN CONSIDERATIONS .................................................... 133 

6.1.1 General Structural Foundation Requirements..................................................... 133 

6.1.2 Site Geology and Subsurface Conditions ........................................................... 134 

6.2 STEP 2: COMPARISON AND SELECTION OF DEEP FOUNDATION 

ALTERNATIVES....................................................................................................... 134 

6.3 STEP 3: SELECT PILE LENGTH AND CALCULATE PERFORMANCE 

UNDER SPECIFIED LOADS .................................................................................... 136 

6.3.1 Limit States for Design ....................................................................................... 136 

6.3.2 Design Procedures .............................................................................................. 139 

6.4 STEP 4: CONSTRUCTABILITY REVIEW ............................................................. 144 

6.5 STEP 5: PREPARE PLANS AND CONSTRUCTION SPECIFICATIONS, 

SET FIELD QC/QA AND LOAD TESTING REQUIREMENTS............................. 145 

6.6 EXAMPLE PROBLEM .............................................................................................. 145 

6.6.1 Introduction......................................................................................................... 145 

6.6.2 Step 1: Initial Design Considerations ................................................................. 145 

6.6.2.1 General Structural Foundation Requirements........................................... 145 

6.6.2.2 Site Geology and Subsurface Conditions ................................................. 145 

6.6.3 Step 2: Comparison and Selection of Deep Foundation Alternatives................. 146 

6.6.4 Step 3: Select Pile Length and Calculate Performance Under 

Specified Loads................................................................................................... 147 

6.6.5 Step 4: Constructability Review ......................................................................... 159 

6.6.6 Step 5: Prepare Plans and Construction Specifications, Set Field QC/QA 

and Load Testing Requirements ......................................................................... 159 

CHAPTER 7 QUALITY CONTROL (QC) / QUALITY ASSURANCE (QA) 

PROCEDURES............................................................................................. 160 

7.1 INTRODUCTION....................................................................................................... 160 

7.2 THE ROLE OF THE INSPECTOR ............................................................................ 160 

7.3 PRE-CONSTRUCTION PLANNING ........................................................................ 162 

7.3.1 Owner-Supplied Information .............................................................................. 162 

7.3.2 CFA Contractor Experience................................................................................ 163 

vi 
TABLE OF CONTENTS (continued) 

7.3.3 Design Submittals ............................................................................................... 163 

7.3.3.1 Design Calculations .................................................................................. 164 

7.3.3.2 Working Drawings .................................................................................... 164 

7.3.4 Pile Installation Plan ........................................................................................... 165 

7.3.5 Testing Plan ........................................................................................................ 167 

7.3.5.1 Pre-Production Testing ............................................................................. 167 

7.3.5.2 Conformance Monitoring and Verification Tests ..................................... 168 

7.3.5.3 Materials Testing ...................................................................................... 170 

7.4 PERFORMANCE MONITORING AND CONTROL DURING 

CONSTRUCTION ...................................................................................................... 170 

7.4.1 Monitoring and Control of the Drilling Phase .................................................... 171 

7.4.2 Monitoring and Control of the Grouting/Concreting Phase ............................... 172 

7.4.3 Finishing the Pile Top and Installing Reinforcement ......................................... 178 

7.4.4 Sampling and Testing of the Grout or Concrete ................................................. 180 

7.5 POST-CONSTRUCTION INTEGRITY TESTING................................................... 183 

7.5.1 Use of Integrity Testing ...................................................................................... 183 

7.5.2 Integrity Testing by Surface Methods................................................................. 184 

7.5.3 Integrity Testing using Downhole Techniques................................................... 186 

7.6 LOAD TESTING ........................................................................................................ 188 

7.6.1 Considerations in Planning a CFA Pre-Production Test Pile Program............... 188 

7.6.2 Proof Tests on Production Piles.......................................................................... 189 

7.7 SUMMARY OF RECOMMENDED QC/QA PROCEDURES ................................. 191 

7.7.1 Prior to Construction........................................................................................... 191 

7.7.2 On-site Review of Contractor’s Equipment........................................................ 192 

7.7.3 During Drilling.................................................................................................... 192 

7.7.4 During Grout/Concrete Placement...................................................................... 192 

7.7.5 During Reinforcement Placement and Pile Top Finishing ................................. 193 

7.7.6 Post-Installation .................................................................................................. 193 

CHAPTER 8 GUIDE CONSTRUCTION SPECIFICATIONS FOR CONTINUOUS 

FLIGHT AUGER (CFA) PILES ................................................................. 194 

8.1 DESCRIPTION........................................................................................................... 195 

8.1.1 Definitions........................................................................................................... 195
 

8.1.2 Related Specifications......................................................................................... 196 

8.1.3 Reference Codes and Standards.......................................................................... 196 

8.1.4 Available Information ......................................................................................... 196 

8.1.5 Project Site Survey.............................................................................................. 197 

8.1.6 CFA Pile Contractors Experience and Submittal of Experience ........................ 198 

vii 
TABLE OF CONTENTS (continued) 

8.1.6.1 Experience Requirements ......................................................................... 198 

8.1.6.2 Experience Requirements and Submittal .................................................. 198 

8.1.7 CFA Pile Design Requirements .......................................................................... 199 

8.1.7.1 CFA Pile Design Submittals ..................................................................... 199 

8.1.7.2 Design Calculations .................................................................................. 200 

8.1.7.3 Working Drawings .................................................................................... 201 

8.1.8 Construction Submittals...................................................................................... 202 

8.1.8.1 Pile Installation Plan ................................................................................. 202 

8.1.8.2 Conformance Testing Plan........................................................................ 204 

8.1.9 Pre-Construction Meeting ................................................................................... 204 

8.2 MATERIALS .............................................................................................................. 205 

8.3 CONSTRUCTION REQUIREMENTS ...................................................................... 206 

8.3.1 Site Preparation and Protection of Adjacent Structures...................................... 206 

8.3.1.1 Site Preparation ......................................................................................... 206 

8.3.1.2 Protection of Adjacent Structures ............................................................. 206 

8.3.2 Grout or Concrete ............................................................................................... 207 

8.3.2.1 Mix Design – Grout .................................................................................. 208 

8.3.2.2 Mix Design – Concrete ............................................................................. 209 

8.3.2.3 Field Operations ........................................................................................ 210 

8.3.2.4 Grout or Concrete Sampling and Testing ................................................. 211 

8.3.3 Auger Equipment ................................................................................................ 212 

8.3.4 Automatic Measurement and Recording Equipment .......................................... 213 

8.3.5 Drilling................................................................................................................ 213 

8.3.6 Placement of Grout or Concrete ......................................................................... 215 

8.3.7 Pile Head Finishing and Protection..................................................................... 216 

8.3.8 Reinforcing Steel Placement ............................................................................... 217 

8.3.9 Pile Cut-Off......................................................................................................... 218 

8.3.10 Inspection and Records....................................................................................... 218 

8.3.11 Testing................................................................................................................. 219 

8.3.11.1 Pre-Production Testing ............................................................................. 219 

8.3.11.2 Verification Load Testing ......................................................................... 220 

8.3.12 Integrity Testing.................................................................................................. 221 

8.3.13 Unacceptable Piles .............................................................................................. 222 

8.4 MEASUREMENT ...................................................................................................... 223 

8.5 PAYMENT.................................................................................................................. 223 

CHAPTER 9 REFERENCES.............................................................................................. 224 

viii 
TABLE OF CONTENTS (continued) 

LIST OF TABLES 

Table 5.1 Relationship between Undrained Shear Strength, Rigidity Index, and Bearing 

Capacity Factor for Cohesive Soils for FHWA 1999 Method ...................................69 

Table 5.2 Soil Conditions Investigated for Drilled Displacement Piles.....................................83 

Table 5.3 Efficiency (η) for Model Drilled Shafts Spaced 3 Diameters Center-to-Center 

in Various Group Configurations in Clayey Sand (Senna et al., 1993) .....................92 

Table 5.4 P-Multipliers (Pm) for Design of Laterally Loaded Pile Groups..............................112 

Table 6.1 Design Consideration for Foundation Selection of CFA and DD Piles ...................135 

Table 6.2 Pile Group Settlement Computation ........................................................................157 

Table 7.1 General Guidelines for Auger Penetration Rate for CFA Piles ...............................171 

Table A.1 Soil-Pile Friction Angle, Limiting Unit Side-Shear Resistance, 

and Limiting End-Bearing Values (API, 1993) .................................................... A-15 

Table A.2 Total Resistance - Results from Five Methods (McVay et al., 1994) ................... A-17 

Table A.3 Total Resistance - Results from Eight Different Methods 

(Zelada and Stephenson, 2000) ............................................................................. A-20 

Table A.4 Total Resistance - Results from Eight Methods 

(Zelada and Stephenson, 2000) ............................................................................. A-21 

Table A.5 Side-Shear Resistance - Results from Eight Methods 

(Zelada and Stephenson, 2000) ............................................................................. A-21 

Table A.6 End-Bearing Resistance - Results from Eight Methods 

(Zelada and Stephenson, 2000) ............................................................................. A-22 

LIST OF FIGURES 

Figure 2.1 CFA Pile Rig..............................................................................................................3 

Figure 2.2 Schematic of CFA Pile Construction .........................................................................4 

Figure 2.3 Schematic of Typical Drilled Shaft vs. CFA Foundation ..........................................5 

Figure 2.4 Group of CFA Piles with Form for Pile Cap .............................................................5 

Figure 2.5 Effect of Over-Excavation using CFA Piles ..............................................................6 

Figure 2.6 Displacement Pile ......................................................................................................7 

Figure 2.7 Hole at Base of Auger for Concrete...........................................................................8 

Figure 2.8 Grout Delivered to Pump ...........................................................................................8 

Figure 2.9 Grout at Surface after Auger Withdrawal ................................................................11 

Figure 2.10 Finishing Pile and Reinforcement Placement ..........................................................11 

Figure 2.11 Placement of a Single Full-Length Bar....................................................................13 

Figure 2.12 Vibratory Drive Head Used to Install Rebar Cage ..................................................13 

Figure 3.1 Use of CFA Piles for Commercial Building Projects ..............................................16 

Figure 3.2 Examples of Difficult Conditions for Augured Piles...............................................18 

ix 
TABLE OF CONTENTS (continued) 

Figure 3.3 CFA Piles at Bridge Interchange .............................................................................20 

Figure 3.4 Low Headroom CFA Pile Application ....................................................................21 

Figure 3.5 Secant Pile Wall with CFA Pile Construction .........................................................22 

Figure 3.6 CFA Piles for Soundwall along Highway................................................................22 

Figure 3.7 Pilecaps on CFA Piles For A Pile-Supported Embankment ....................................23 

Figure 3.8 Drilled Displacement Piles Limit Spoil Removal....................................................24 

Figure 3.9 CFA Pile Foundation for Soundwall........................................................................25 

Figure 3.10 Schematic Diagram of the Foundation on CFA Piles for the 

Krenek Road Bridge ................................................................................................26 

Figure 3.11 CFA Piles at the Krenek Road Bridge Site..............................................................27 

Figure 3.12 Comparison of Measured Settlements and Test Pile, Krenek Road Bridge Site .....28 

Figure 3.13 Secant CFA Pile Wall for a Light Rail System in Germany....................................29 

Figure 3.14 Schematic Plan View of a Secant Pile Wall ............................................................30 

Figure 3.15 Drilling CFA Piles through Guide for Secant Wall .................................................30 

Figure 3.16 Diagram of Pile-Supported Embankment for Italian Railway Project ....................32 

Figure 4.1 Typical Crane-Mounted CFA Rig ...........................................................................34 

Figure 4.2 Photo of Crane-Attached CFA System ....................................................................35 

Figure 4.3 Low Headroom CFA Pile Rig..................................................................................36 

Figure 4.4 Low Headroom Rig with Segmental Augers ...........................................................36 

Figure 4.5 Hydraulic Rig Drilling on M25 Motorway in England ...........................................37 

Figure 4.6 Soilmec Hydraulic CFA Rig with Kelley Extension ...............................................38 

Figure 4.7 Augers for Different Soil Conditions.......................................................................38 

Figure 4.8 Auger for Use in Clay with Auger Cleaner Attachment ..........................................39 

Figure 4.9 Cutter Heads for Hard Material and Soil .................................................................39 

Figure 4.10 Hardened Cutting Head............................................................................................40
 

Figure 4.11 DeWaal Drilled Displacement Pile ..........................................................................41 

Figure 4.12 Omega Screw Pile....................................................................................................42 

Figure 4.13 Fundex Screw Pile ...................................................................................................43 

Figure 4.14 Drilled Displacement Piles ......................................................................................44 

Figure 4.15 Additional Drilled Displacement Piles ....................................................................45 

Figure 4.16 Double Rotary Cased CFA Piles..............................................................................46 

Figure 4.17 Double Rotary Fixed Drive System.........................................................................46 

Figure 4.18 Double Rotary System with Kelly-Bar Extension ...................................................47 

Figure 4.19 Typical Concrete/Grout Pumps................................................................................50 

Figure 4.20 In-Line Flowmeter ...................................................................................................51 

Figure 4.21 Sensor for Concrete Pressure at Auger Tip..............................................................52 

Figure 4.22 Completion of Pile Top Prior to Installation of Reinforcement ..............................53 

Figure 4.23 Sand-Cement Grout Mixes ......................................................................................54 

Figure 4.24 Machine-Welded Reinforcement Cage on Project Site in Germany .......................60 

Figure 4.25 Use of Steel Pipe to Reinforce a CFA Pile for a Wall.............................................60 

Figure 4.26 Installation of Reinforcement Cage into Battered CFA Pile ...................................61 

x 
TABLE OF CONTENTS (continued) 

Figure 5.1 Load-Displacement Relationships ...........................................................................67 

Figure 5.2 Relationship for the α Factor with Su for Calculating the Unit Side-Shear for 

Cohesive Soils for the Coleman and Arcement (2002) Method ..............................70 

Figure 5.3 Unit Side-Shear Resistance as a Function of Cone Tip Resistance for 

Cohesive Soils – LPC Method.................................................................................72 

Figure 5.4 Relationship for the β Factor for Calculating the Unit Side-Shear for 

Cohesionless Soils for the FHWA 1999 and Coleman and Arcement Methods .....74 

Figure 5.5 Unit Side-Shear as a Function of Cone Tip Resistance for 

Cohesionless Soils - LPC Method ...........................................................................75 

Figure 5.6 Unconfined Compressive Strength vs. Ultimate Unit Side-Shear for Drilled 

Shafts in Florida Limestone .....................................................................................77 

Figure 5.7 Correlation of Ultimate Unit Side-Shear Resistance for South Florida 

Limestone with SPT-N60 Value ...............................................................................77 

Figure 5.8 Side-Shear Development with Displacement for South Florida Limestone ............78 

Figure 5.9 Relative Load Capacity vs. Relative Displacement for CFA Sockets in ClayShale.........................................................................................................................79 

Figure 5.10 Hyperbolic Model Parameter QULT as a Function of the Unconfined 

Compressive Strength (QU) for CFA Sockets in Clay-Shale...................................80 

Figure 5.11 Parameter Ρ50/D as a Function of Unconfined Compressive Strength for CFA 

Sockets in Clay-Shale ..............................................................................................81 

Figure 5.12 Ultimate Unit Side-Shear Resistance for Drilled Displacement Piles for 

Nesmith (2002) Method ...........................................................................................85 

Figure 5.13 Ultimate Unit End-Bearing Resistance for Drilled Displacement Piles for 

Nesmith (2002) Method ...........................................................................................86 

Figure 5.14 Overlapping Zones Of Influence in A Frictional Pile Group ..................................88 

Figure 5.15 Efficiency (Η) Vs. Center-To-Center Spacing (S), Normalized By Shaft 

Diameter (BSHAFT), for Underreamed Model Drilled Shafts in Compression in 

Moist, Silty Sand......................................................................................................91 

Figure 5.16 Relative Unit Side and Base Resistances for Model Single Shaft and Typical 

Shaft in a Nine-Shaft Group in Moist Alluvial Silty Sand ......................................91 

Figure 5.17 Block Type Failure Mode ........................................................................................93 

Figure 5.18 Deeper Zone of Influence for End-Bearing Pile Group than for a Single Pile ........96 

Figure 5.19 Equivalent Footing Concept for Pile Groups .........................................................100 

Figure 5.20 Pressure Distribution Below Equivalent Footing for Pile Group ..........................101 

Figure 5.21 Typical e vs. Log p Curve from Laboratory Consolidation Testing ......................102 

Figure 5.22 p-y Soil Response of Laterally Loaded Pile Model ...............................................106 

Figure 5.23 Example Deflection and Moment Response of Laterally Loaded Pile Model ......108 

Figure 5.24 Typical Stress-Strain Relationship Used for Steel Reinforcement ........................109 

Figure 5.25 Typical Stress-Strain Relationship Used for Concrete ..........................................109 

Figure 5.26 Variation of Pile Stiffness (EI) with Bending Moment and Axial Load ...............111 

Figure 5.27 The p-multiplier (Pm) .............................................................................................112 

Figure 5.28 Circular Column (Pile) with Compression Plus Bending ......................................115 

Figure 5.29 Example Interaction Diagram for Combined Axial Load and Flexure..................116 

xi 
TABLE OF CONTENTS (continued) 

Figure 5.30 Examples of Cases of Downdrag ...........................................................................122 

Figure 5.31 Potential Geotechnical Limit States for Piles Experiencing Downdrag ................123 

Figure 5.32 Mechanics of Downdrag: Estimating the Depth to the Neutral Plane ...................124 

Figure 5.33 Mechanics of Downdrag in a Pile Group...............................................................124 

Figure 5.34 Soil Profile Su vs. Depth for Example Problem of CFA Pile in Cohesive Soil .....128 

Figure 5.35 Soil Profile SPT-N vs. Depth for Example Problem of CFA Pile and DD Pile 

in Cohesionless Soil ...............................................................................................129 

Figure 6.1 GULS and Short Term SLS for Axial Load on a Single CFA Pile .......................137 

Figure 6.2 Typical Conditions at the Project Site ...................................................................146 

Figure 6.3 Idealized Soil Profile for Design............................................................................148 

Figure 6.4 Five-Pile Footing Layout .......................................................................................149 

Figure 6.5 Computed Lateral Load vs. Deflection ..................................................................151 

Figure 6.6 Deflection and Bending Moments vs. Depth for Example Problem .....................152 

Figure 6.7 Maximum Bending Moments as a Function of Pile Top Deflection .....................152 

Figure 6.8 Bending Moment vs. Curvature for a 18-in. diameter Pile with 6 #7’s .................153 

Figure 6.9 Computed Axial Resistance vs. Depth...................................................................156 

Figure 7.1 Operator with Cab Mounted Display Used to Control Drilling.............................172 

Figure 7.2 Depth Encoder Mounted on Crane Boom..............................................................175 

Figure 7.3 In-line Flowmeter...................................................................................................175 

Figure 7.4 Pressure Sensors on Hydraulics to Monitor Rig Forces ........................................176 

Figure 7.5 Display Panel for Observation by Inspector ..........................................................176 

Figure 7.6 Example Data Sheet from Project ..........................................................................177 

Figure 7.7 Dipping Grout to Remove Contamination .............................................................178 

Figure 7.8 Cleaning the Top of a CFA Concrete Pile .............................................................179 

Figure 7.9 Placement of Reinforcing Cage with Plastic Spacers ............................................180 

Figure 7.10 Cubes for Grout Testing.........................................................................................182 

Figure 7.11 Sonic Echo Testing Concept..................................................................................184 

Figure 7.12 Sonic Echo Testing of Long Piles..........................................................................185 

Figure 7.13 Downhole Sonic Logging Concept (SSL) .............................................................187 

Figure 7.14 Gamma-Gamma Testing Via Downhole Tube ......................................................187 

Figure 7.15 Static Load Test Setup on CFA Piles.....................................................................190 

Figure 7.16 Proof Testing of Production Piles with Statnamic (RLT) Device .........................190 

Figure 7.17 Effect of Multiple Load Cycles on a CFA Pile ......................................................191 

Figure A.1 β Factor vs. Pile Length (Neely, 1991) ................................................................. A-5 

Figure A.2 α vs. Undrained Shear Strength - Clayey Soils (Clemente et al., 2000) .............. A-6 

Figure A.3 β Factor vs. Depth - Zelada and Stephenson (2000) and 

FHWA 1999 Methods........................................................................................... A-8 

Figure A.4 Ultimate Unit End-Bearing Resistance vs. SPT-N Values -

Zelada and Stephenson (2000) and Other Methods .............................................. A-9 

xii 
TABLE OF CONTENTS (continued) 

Figure A.5 Normalized Load-Settlement Relationship for Design of CFA Piles - 

Clay Soils of Texas Gulf Coast (O’Neill et al., 2002)........................................ A-10 

Figure A.6 α vs. Average Undrained Shear Strength along Pile Length 

(Coyle and Castello, 1981) ................................................................................. A-13 

Figure A.7 Unit Side-Shear and End-Bearing Capacities - Cohesionless Soils 

(Coyle and Castello, 1981) ................................................................................. A-13 

Figure A.8 Relationship between SPT-N Values and φ (Coyle and Castello, 1981) ............ A-14 

Figure A.9 Summary of Total Resistance - Results from Five Methods 

(McVay et al., 1994) ........................................................................................... A-19 

Figure A.10 Summary of Total Resistance - Results from Eight Methods (Zelada and 

Stephenson, 2000)............................................................................................... A-20 

Figure A.11 Summary of Total Resistance - Results from Four Methods (Coleman and 

Arcement, 2002) ................................................................................................. A-23 

Figure A.12 Total Capacity - Results from FHWA 1999 Method 

(Coleman and Arcement, 2002) .......................................................................... A-24 

Figure A.13 Total Capacity Results - Coleman and Arcement (2002) Method...................... A-24 

Figure A.14 Effective Lateral Earth Pressure near a CFA Pile during Construction 

(O’Neill et al., 2002)........................................................................................... A-25 

Figure A.15 Total Resistance - Results from Four Methods................................................... A-26 

Figure A.16 Comparison of Study Results - Axial Capacity in Cohesive Soils ..................... A-27 

Figure A.17 Comparison of Study Results - Axial Capacity in Cohesionless Soils ............... A-28 

LIST OF APPENDICES 

APPENDIX A: COMPARISONS OF METHODS FOR ESTIMATING THE STATIC 

AXIAL CAPACITY OF CFA PILES 

A.1 INTRODUCTION....................................................................................................... A-1 

A.2 METHODS FOR AXIAL CAPACITY OF CFA PILES ............................................ A-2 

A.2.1 Wright and Reese (1979) Method ..................................................................... A-2 

A.2.2 Douglas (1983) Method .................................................................................... A-2 

A.2.3 Rizkalla (1988) Method .................................................................................... A-3 

A.2.4 Neely (1991) Method........................................................................................ A-4 

A.2.5 Viggiani (1993) Method ................................................................................... A-4 

A.2.6 Decourt (1993) Method..................................................................................... A-5 

A.2.7 Clemente et al. (2000) Method ......................................................................... A-6 

A.2.8 Frizzi and Meyer (2000) Method ...................................................................... A-7 

A.2.9 Zelada and Stephenson (2000) Method ............................................................ A-7 

A.2.10 Coleman and Arcement (2002) Method ........................................................... A-8 

A.2.11 O’Neill et al. (2002) Method ............................................................................ A-9 

A.3 METHODS FOR AXIAL CAPACITY OF DRILLED SHAFTS 

APPLICABLE CFA PILES ...................................................................................... A-10 

xiii 
TABLE OF CONTENTS (continued) 

A.3.1 TxDOT Method (1972)................................................................................... A-10 

A.3.2 FHWA 1999 Method ...................................................................................... A-11 

A.4 METHODS FOR DRIVEN PILES APPLICABLE TO CFA PILES ....................... A-11 

A.4.1 Coyle and Castello (1981) Method................................................................. A-11 

A.4.2 American Petroleum Institute (API) (1993) Method ...................................... A-12 

A.5 METHOD FOR DRILLED SHAFTS AND DRIVEN PILES APPLICABLE 

TO CFA PILES ......................................................................................................... A-15 

A.6 COMPARISON OF DESIGN METHODS FOR AXIAL CAPACITY 

OF CFA PILES ......................................................................................................... A-16 

A.6.1 Comparison of Five Methods in Predominantly Sandy Soils 

(McVay et al., 1994) ....................................................................................... A-16 

A.6.2 Comparison of Eight Methods in Predominantly Sandy Soils 

(Zelada and Stephenson, 2000)....................................................................... A-16 

A.6.3 Comparison of Four Methods in Mixed Soil Conditions 

(Coleman and Arcement, 2002) ...................................................................... A-18 

A.6.4 Comparison of Seven Methods - Sandy and Clay Soils 

(O’Neill et al., 1999)....................................................................................... A-22 

A.6.5 Summary of Comparison Study Results for Cohesive Soils .......................... A-25 

A.6.6 Summary of Comparison Study Results for Cohesionless Soils .................... A-25 

APPENDIX B		 EXAMPLE PROBLEMS: SPREADSHEET SOLUTIONS FOR 

AXIAL CAPACITY OF SINGLE PILES WITH DEPTH ....................... B-1 

B.1 CONVENTIONAL CFA PILE IN COHESIVE SOIL ............................................... B-1 

B.2 CONVENTIONAL CFA AND DRILLED DISPLACEMENT PILES IN 

COHESIONLESS SOILS ........................................................................................... B-7 

xiv 
TABLE OF CONTENTS (continued) 

LIST OF ABBREVIATIONS 

AASHTO American Association of State Highway and Transportation Officials 

ACI American Concrete Institute 

ACIP Augered cast-in-place 

API American Petroleum Institute 

ASCE American Society of Civil Engineers 

ASD Allowable stress design 

ASTM American Society of Testing Materials 

bpf Blows per foot 

CFA Continuous flight auger 

CIP Cast-in-place 

CSL Cross-hole sonic logging 

DD Drilled displacement 

DFI Deep Foundations Institute 

DLT Dynamic load test 

DOT Department of Transportation 

FDOT Florida Department of Transportation 

FWHA Federal Highway Administration 

GULS Geotechnical ultimate limit state 

GWT Ground water table 

H2SO4 Sulphuric acid 

IGM Intermediate geotechnical material 

kcf Kips per cubic foot 

kPa KiloPascal 

ksi Kips per square inch 

LPC Laboratorie Des Ponts et Chausses 

LRFD Load and Resistance Factor Design 

MPa Megapascal 

Na2SO4 Sodium sulphate 

NaCl Sodium chloride 

NGES National Geotechnical Experimentation Site 

NHI National Highway Institute 

pcy Pounds per cubic yard 

pH Hydrogen potential 

ppm Parts per million 

psi pounds per square inch 

PVC Polyvinyl chloride 

xv 
TABLE OF CONTENTS (continued) 

QA/QC Quality Assurance/Quality Control 

RLT Rapid load test 

SLD Service load design 

SLS Service limit state 

SPT Standard penetration test 

SSL Single-hole sonic logging 

SULS Structural ultimate limit state 

tsf Tons per square foot 

TSL Total service load 

TXDOT Texas Department of Transportation 

VMA Viscosity-modifying admixtures 

W/C Water-to-cement ratio 

xvi 
TABLE OF CONTENTS (continued) 

LIST OF SYMBOLS
	

Ac Cross-sectional area of concrete inside spiral steel 

Ai Average cross-sectional area for pile segment “i” 

Ag Gross area 

Ag’ Effective area 

Apile Cross-sectional area of single pile 

Apiles Cross-sectional area of all piles in a group 

Agroup Cross-sectional area of pile group, not including overhanging cap area 

As Cross-sectional area of reinforced steel 

Av Effective cross-sectional area in resisting shear 

Avs Required area of transverse steel 

Bshaft Shaft diameter 

B Width of block 

B Pile diameter 

C Wave propagation velocity 

Cc Compression index 

Cr Recompression index 

d Pile diameter 

dc Depth of concrete cover 

db Diameter of longitudinal bars 

dpile Distance normal to neutral axis of outer piles 

D Pile diameter 

D Depth of block 

DB Diameter of pile at the base 

Di Diameter of pile segment “i” 

e Void ratio 

eo Initial void ratio 

E Elastic modulus 

Ec Initial tangent slope 

Ec Young’s Modulus of concrete or grout 

Ee Average Young’s Modulus of equivalent pier within compressible layer 

Ei Average composite modulus for pile segment “i” 

EI Flexural rigidity of pile/beam 

Epile Average Young’s modulus of pile 

Es Undrained Young’s modulus or secant modulus 

Esoil Soil average Young’s modulus 

Est Young’s Modulus of geomaterial between piles 

xvii 
TABLE OF CONTENTS (continued) 

f Side-Shear resistance 

f’c Concrete compressive strength 

f”c Ultimate compressive strength 

fmax Ultimate Side-Shear resistance 

fs Ultimate unit Side-Shear resistance 

fs-ave Average unit Side-Shear resistance 

fs,i Unit Side-Shear resistance of segment “i” 

fy Steel yield stress 

Fpile Axial force on pile 

H Original thickness of layer 

i Generic pile segment number 

If Influence factor for group embedment 

Ir Rigidity index 

k Subgrade modulus 

K, Ks, K’ Lateral earth pressure coefficient 

Ko In-situ lateral earth pressure coefficient 

Ka Active lateral earth pressure coefficient 

Kp Passive lateral earth pressure coefficient 

L Pile embedment length below top of grade 

L Pile socket length 

Li Length of pile segment “i” 

Lpile Pile length 

M, Mt Moment 

Moverturn Overturning moment 

Mx Nominal ultimate flexural resistance 

N Number of pile segments 

N SPT blow-count 

Neq Average equivalent N value 

N60 SPT-N value (bpf) corrected for 60% efficiency 

N 60 ' Average corrected SPT-N value 

Nc CPT cone factor 

N *

C , Nq Bearing capacity factor 

NTxDOT Value obtained from the Texas Cone Penetrometer 

p Vertical effective consolidation stress 

p Lateral soil reaction 

pc Preconsolidation pressure 

pf Foundation pressure 

xviii 
TABLE OF CONTENTS (continued) 

po Effective overburden or vertical pressure 

P Compressive force 

Pa, Patm Standard atmospheric pressure 

Pm P-multiplier 

Pn Nominal ultimate axial resistance 

Pt Lateral force 

Px Axial load 

Px Nominal ultimate axial resistance 

qc CPT tip resistance 

q c Average CPT tip resistance 

qp Ultimate unit end-bearing resistance 

qu Unconfined compressive strength 

Q Pile total resistance 

Qi Average axial load at pile segment “i” 

Qi Value of load of type “i” 

Qt Ultimate total load 

Qt, Qult, Qmax Ultimate resistance 

rls Radius of rings formed along centroids of longitudinal bars 

R Computed resistance at GULS 

Rallowable Allowable static axial resistance 

RB, RBd End-bearing resistance 

RBlock Resistance of the block 

RS Side-shear resistance 

RT Total axial compressive resistance 

Rug Ultimate resistance of pile group 

Ru,i Ultimate resistance of “i” in pile group 

S Pile spacing 

S Pile slope 

S Longitudinal spacing of reinforcement ties (spiral pitch) 

Sgroup Total settlement of pile group 

Si Total settlement 

SF Safety factor 

SR Stiffness ratio 

Su Soil undrained shear strength 

Sua Average undrained shear strength along pile length 

Su ave Average soil undrained shear strength 

V Shear force 

xix 
TABLE OF CONTENTS (continued) 

Vc Concrete shear strength 

Vn Nominal shear resistance of concrete section 

Vsteel	 Nominal shear resistance of transverse steel 

w Load along pile length 

W Pile displacement 

WS	 Correlation constant 

WT	 Correlation constant 

x Coordinate along pile length 

y Lateral deflection at a point with coordinate x 

zsoil, i	 Thickness of soil layer “i” 

zw	 Depth below watertable 

Z Length of block 

Z Depth from ground surface to middle of a soil layer or pile segment (in ft) 

Zm	 Depth from ground surface to middle of a soil layer or pile segment (in m) 

α	 Reduction factor 

β	 Pile segment factor 

β Reduction factor 

γ Soil unit weight 

γsoil, i Unit weight of soil layer “i” 

γw Water unit weight 

δ Soil-to-pile interface friction angle 

∆ Elastic compression of pile 

∆p Change in overburden pressure 

ε50 Strain at 50% of compressive strength in compression load tests 

εy Yield strain 

η	 Pile efficiency 

ηg Pile group efficiency 

ρ	 Pile displacement 

σ′v Vertical effective stress 

φ	 Soil drained angle of internal friction 

φ Resistance factor 

Ψ	 Ratio of undrained shear strength and vertical effective stress in soil 

xx 
CHAPTER 1 INTRODUCTION 

1.1 PURPOSE 

The purpose of this document is to develop a state-of-the-practice manual for the design and 

construction of continuous flight auger (CFA) piles, including those piles commonly referred to 

as augered cast-in-place (ACIP) piles, drilled displacement (DD) piles, and screw piles. An 

Allowable Stress Design (ASD) procedure is presented in this document as resistance (strength 

reduction) factors have not yet been calibrated for CFA piles for a Load Resistance Factored 

Design (LRFD) approach. The intended audience for this document is engineers and 

construction specialists involved in the design, construction, and contracting of foundation 

elements for transportation structures. 

1.2 BACKGROUND 

CFA piles have been used worldwide and also in the U.S. commercial market, but have not been 

used frequently for support of transportation structures in the United States. This 

underutilization of a viable technology is a result of perceived difficulties in quality control and 

of the difficulties associated with incorporating a rapidly developing (and often proprietary) 

technology into the traditional, prescriptive design-bid-build concept. Recent advances in 

automated monitoring and recording devices will alleviate concerns of quality control, as well as 

provide an essential tool for a performance-based contracting process. 

A performance-based approach is presented to allow the specialty contractors greater freedom to 

compete in providing the most cost-effective foundation system while satisfying the project 

requirements. The performance specification places a greater responsibility for the resulting 

foundation performance on the contractor or design-build team. Rather than rigorous 

prescriptive specifications, a comprehensive testing program is used to verify performance. 

Full-scale load testing is used to verify the load carrying capabilities of the foundations provided. 

Automatic monitoring and recording devices are used during construction of both test piles and 

production piles to establish construction parameters (down-force, torque, grout take, etc.), and 

to verify that these parameters are met for every production pile. Full-scale load testing may be 

performed on production piles throughout the project, as selected by the owner. 

This document provides descriptions of CFA pile types, materials, construction equipment, and 

procedures. Quality control (QC)/quality assurance (QA) procedures are discussed. 

A performance specification is provided in a format that may be adapted to specific project 

requirements. Recommendations are made for methods to estimate the static axial capacity of 

single piles. A thorough evaluation and comparison of various existing methods used in the 

United States and Europe is presented. Group effects for axial capacity and settlement are 

discussed, as well as lateral load capacities for both single piles and pile groups. A generalized 

step-by-step method for the selection and design of CFA piles is presented. 

1 
1.3 RELEVANT PUBLICATIONS 

A list of the references used in the development of this manual is presented in Chapter 9. These 

references include key publications on the design of augered pile foundations. Existing Federal 

Highway Administration (FWHA) and American Association of State Highway Officials 

(AASHTO) publications that include engineering principles related to the subject of CFA piles 

are also included in the references. 

1.4 DOCUMENT ORGANIZATION 

The remainder of this document is organized as follows. 

•	 Chapter 2 – Description of Continuous Flight Auger Pile Types and Basic Mechanisms. 

This chapter provides a general overview of CFA piles, including a description of the 

main system components, typical equipment, and the sequence of construction. 

•	 Chapter 3 – Applications for Transportation Projects. This chapter presents advantages 

and limitations of CFA piles in transportation projects, describes favorable and 

unfavorable project and geotechnical conditions, and illustrates applications of CFA 

piles in transportation projects. 

•	 Chapter 4 – Construction Techniques and Materials. This chapter provides details on 

construction techniques, materials, and recommended practice for the construction of 

CFA piles in transportation projects. 

•	 Chapter 5 – Evaluation of Static Capacity of Continuous Flight Augered Piles. This 

chapter presents an evaluation and comparison of various existing methods used in the 

United States and Europe to calculate the static capacity of CFA piles. 

•	 Chapter 6 – Recommended Design Method. This chapter presents a step-by-step 

generalized method for the selection and design of CFA piles. An annotated example is 

included in this chapter. 

•	 Chapter 7 – Quality Control (QC)/Quality Assurance (QA) Procedures. This chapter 

discusses the use of automated QC/QA equipment and presents guidelines. 

•	 Chapter 8 – Guide Construction Specifications for Continuous Flight Auger Piles. This 

chapter presents a performance specification for CFA piles. 

•	 Chapter 9 – References. A list of the references used in this document is presented. 

•	 Appendix A – Comparisons of Methods for Estimating the Static Axial Capacity of CFA 

Piles. 

•	 Appendix B – Spreadsheet Solutions for Axial Capacity of Single CFA Piles. 

2 
 

CHAPTER 2 DESCRIPTION OF CONTINUOUS FLIGHT AUGER 

PILE TYPES AND BASIC MECHANISMS 

This chapter provides a general overview of continuous flight auger (CFA) piles. CFA piles 

have also been referred to as auger-cast, augered-cast-in-place, auger-pressure grout, and screw 

piles. The term CFA is used to generally refer to these types of piles constructed according to 

the recommendations in this document. This overview includes: (1) a description of the main 

components of a CFA pile; (2) typical drilling and grouting equipment used; and (3) a 

description of the sequence of construction. 

A comparison of CFA piles with common deep foundations is presented to provide context for 

readers who are more familiar with driven piles and drilled shafts. Considerations are presented 

for: (1) initial hole drilling; (2) potential soil caving or mining; and (3) subsequent grout or 

concrete placement, including reinforcement placement. Additionally, basic information 

regarding the effects of soil type (i.e., clay, sand, or mixed) on load transfer will also be 

presented. 

2.1 INTRODUCTION 

CFA piles are a type of drilled 

foundation in which the pile is drilled to 

the final depth in one continuous 

process using a continuous flight auger 

(Figure 2.1). While the auger is drilled 

into the ground, the flights of the auger 

are filled with soil, providing lateral 

support and maintaining the stability of 

the hole (Figure 2.2a). At the same time 

the auger is withdrawn from the hole, 

concrete or a sand/cement grout is 

placed by pumping the concrete/grout 

mix through the hollow center of the 

auger pipe to the base of the auger 

(Figure 2.2b). Simultaneous pumping 

of the grout or concrete and 

withdrawing of the auger provides 

continuous support of the hole. 

Reinforcement for steel-reinforced CFA 

piles is placed into the hole filled with 

fluid concrete/grout immediately after 

withdrawal of the auger (Figure 2.2c). Source: Cementation Foundation Skanska 

Figure 2.1: CFA Pile Rig 

3 
Source: Bauer Maschinen 

Figure 2.2: Schematic of CFA Pile Construction 

CFA piles are typically installed with diameters ranging from 0.3 to 0.9 m (12 to 36 in.) and 

lengths of up to 30 m (100 ft), although longer piles have occasionally been used. In the United 

States, the practice has typically tended toward smaller piles having diameters of 0.3 to 0.6 m 

(12 to 24 in.) primarily because less powerful rigs have typically been used for commercial 

practice with these piles in the United States. European practice tends toward larger diameters 

[up to 1.5 m (60 in.)]. In recent years, the trend in the United States has been toward increased 

use of CFA piles in the 0.6 to 0.9 m (24 to 36 in.) diameter range. 

The reinforcement is often confined to the upper 10 to 15 m (33 to 50 ft) of the pile for ease of 

installation and also due to the fact that in many cases, relatively low bending stresses are 

transferred below these depths. In some cases, full-length reinforcement is used, as is most 

common with drilled shaft foundations. 

CFA piles can be constructed as single piles (similar to drilled shafts), for example, for 

soundwall or light pole foundations. For bridges or other large structural foundations, CFA piles 

are most commonly installed as part of a pile group in a manner similar to that of driven pile 

foundations as illustrated in Figures 2.3 and 2.4. Similarly to driven piles, the top of a group of 

CFA piles is terminated with a cap (Figure 2.4). Typical minimum center-to-center spacing is 3 

to 5 pile diameters. 

CFA piles differ from conventional drilled shafts or bored piles, and exhibit both advantages and 

disadvantages over conventional drilled shafts. The main difference is that the use of casing or 

4 
Single 

Drilled 

Shaft 

CFA 

Group 

Single 

Colum Single 

Colum 

Figure 2.3: Schematic of Typical Drilled Shaft vs. CFA Foundation 

slurry to temporarily support the hole is avoided. Drilling the hole in one continuous process is 

faster than drilling a shaft excavation, an operation that requires lowering the drilling bit multiple 

times to complete the excavation. In contrast, the torque requirement to install the continuous 

auger is high compared with a conventional drilled shaft of similar diameter; therefore, the 

diameter and length of CFA piles are generally less than drilled shafts. The use of a continuous 

auger for installation also limits CFA piles to soil or very weak rock profiles, while drilled shafts 

are often socketed into rock or other very hard bearing materials. 

Figure 2.4: Group of CFA Piles with Form for Pile Cap
	

5 
 

Because CFA piles are drilled and cast in place rather than being driven, as are driven piles, 

noise and vibration due to pile driving are minimized. CFA piles also eliminate splices and 

cutoffs. Soil heave due to driving can be eliminated when non-displacement CFA piles are used. 

A disadvantage of CFA piles compared to driven piles is that the available QA methods to verify 

the structural integrity and pile bearing capacity for CFA piles are less reliable than those for 

driven piles. Another disadvantage of CFA piles is that CFA piles generate soil spoils that 

require collection and disposal. Handling of spoils can be a significant issue when the soils are 

contaminated or if limited room is available on the site for the handling of material. Certain 

types of CFA piles that do not generate spoils will be discussed later in this document. 

The remainder of this chapter provides an overview of the construction process of CFA piles. 

2.2 CONSTRUCTION SEQUENCE 

2.2.1 Drilling 

The key component of the CFA pile system, 

contributing to the speed and economy of these piles, 

is that the pile is drilled in one continuous operation 

using a continuous flight auger, thus reducing the time 

required to drill the hole. While advancing the auger 

to the required depth, it is essential that the auger 

flights be filled with soil so that the stability of the 

hole is maintained. If the auger turns too rapidly, with 

respect to the rate of penetration into the ground, then 

the continuous auger acts as a sort of “Archimedes 

pump” and conveys soil to the surface. As illustrated 

in Figure 2.5, this action can result in a reduction of 

the horizontal stress necessary to maintain stability of 

the hole. Consequently, lateral movement of soil 

towards the hole and material loss due to overexcavation can result in ground subsidence at the 

surface and reduced confinement of nearby installed 

piles. The top of Figure 2.5 represents an auger 

having balanced auger rotation and penetration rates, 

so that the flights are filled from the digging edge at 

the base of the auger with no lateral “feed”. The 

bottom of Figure 2.5 illustrates an auger having an 

excessively slow penetration rate and an insufficient 

base feed to keep the auger flights full; as a result, the 

auger feeds from the side with attendant decompression 

of the ground. 

As the auger cuts the soil at the base of the tool, material is loaded onto the flights of the auger. 

The volume of soil through which the auger has penetrated will tend to “bulk” and take up a 

larger volume after cutting than the in-situ volume. Some of the bulk volume is also due to the 

After Fleming (1995) 

Figure 2.5: Effect of OverExcavation using CFA Piles 

6 
volume of the auger itself, including the hollow center tube. Thus, it is necessary that some soil 

is conveyed up the auger during drilling. To maintain a stable hole at all times, it is necessary to 

move only enough soil to offset the auger volume and material bulking without exceeding this 

volume. Controlling the rate of penetration helps to avoid lateral decompression of the ground 

inside the hole, the loosening of the in-situ soil around the hole, and ground subsidence adjacent 

to the pile. 

The proper rate of penetration may be difficult to maintain if the rig does not have adequate 

torque and down-force to rotate the auger. When a soil profile being drilled has mixed soil 

conditions (e.g., weak and strong layers), difficulties may arise. For example, if a rig having a 

low torque-capacity is used for drilling through a mostly-hard profile, difficulties can arise when 

drilling through a weak, embedded stratum to penetrate the strong soil. If the rig cannot 

penetrate the strong soil stratum at the proper rate, the augers can “mine” the overlying weak soil 

to the surface and cause subsidence. 

One solution to properly balance soil removal and penetration rate is to use auger tools that 

actually displace soil laterally during drilling. In this construction technique, these types of piles 

are more commonly described as Drilled Displacement (DD) piles. DD piles include a variety of 

patented systems, which typically consist of a center pipe within the auger, an auger of larger 

diameter than that of conventional CFA equipment (Figure 2.6), and some type of bulge or plug 

within the auger string to force the soil laterally as it passes (not shown in Figure 2.6). The 

advantage of this system is that soil mining is avoided. In addition, the soil around the pile tends 

to be densified and the lateral stresses at the pile/soil wall are increased, thus leading to soil 

improvement and increased pile capacity for a given length. The main disadvantage is that the 

demand for torque and down-force from the rig is greater and this creates a limitation on the 

ability to install piles to great depths, as well as in very firm to dense soils. 

Large-Diameter Auger 

Drilling Bit 

Figure 2.6: Displacement Pile 

7 
For some soil conditions, the concern for soil mining and the need to establish a good penetration 

rate is not as critical. CFA piles have been successfully installed in many geologic formations 

without any consideration of the rate of penetration or soil mining. Where soils are stable due to 

cohesion, cementation, and/or apparent cohesion due to low groundwater levels, and pile lengths 

are relatively short, it may be feasible to neglect some of the considerations of drilling rate and 

soil mining. For example, residual soil, weak limestone formations, and cemented sands are soil 

types that favor easy construction. In such instances, the continuous auger is essentially used to 

construct a small open-hole, drilled shaft, or bored pile. However, such practice should be 

allowed only after the completion of successful test installations and after load tests have 

confirmed that satisfactory results are obtained and that with no adverse effects from ground 

subsidence will take place. 

2.2.2 Grouting 

When the drilling stage is complete and the auger has penetrated to the required depth, the 

grouting stage must begin immediately. Grout or concrete is pumped under pressure through a 

hose to the top of the rig and delivered to the base of the auger via the hollow center of the auger 

stem. The generic term grout will be mostly used in the remainder of this document; however, it 

is understood that grout or concrete can be used in this process. Figure 2.7 shows the hole at the 

base of the auger stem. Figure 2.8 shows grout being delivered to the project site by truck to a 

pump located near the drill rig. 

Figure 2.7: Hole at Base of Auger for Concrete Figure 2.8: Grout Delivered to Pump 

2.2.2.1 General Sequence 

The general grouting sequence is as follows: 

•	 Upon achieving the design pile tip elevation, the auger is lifted a short distance 

[typically 150 to 300 mm (6 to 12 in.)] and grout is pumped under pressure to expel the 

plug at the base of the internal pipe and commence the flow. The auger is then screwed 

8 
back down to the original pile tip elevation to establish a small head of grout or 

concrete on the auger and to achieve a good bearing contact at the pile tip. 

•	 The grout is pumped continuously under pressure [typically up to 2 MPa (300 psi) 

measured at the top of the auger] while the auger is lifted smoothly in one continuous 

operation. 

•	 Simultaneously, as the auger is lifted, the soil is removed from the flights at the ground 

surface so that soil cuttings are not lifted high into the air (potential safety hazard). 

•	 After the auger has cleared the ground surface and the grouting/concrete procedure is 

completed, any remaining soil cuttings are removed from the area at the top of the pile 

and the top of the pile is cleared of debris and contamination. 

•	 The reinforcement cage is lowered into the fluid grout/concrete to the required depth 

and tied off at the ground surface to maintain the proper reinforcement elevation. 

2.2.2.2 Start of Grouting 

It is essential that the grouting process begin immediately upon reaching the pile tip elevation; if 

there is any delay the auger may potentially become stuck and impossible to retrieve. To avoid 

“hanging” the auger (i.e., getting the auger stuck), some contractors may wish to maintain a slow 

steady rotation of the auger while waiting for delivery of grout; this rotation without penetration 

may lead to soil mining as described in the previous section and should be avoided. Another 

concern with excess rotation is degradation and subsequent reduction or loss of side friction 

capacity. The practice of maintaining rotation without penetration is not recommended. The best 

way to avoid such problems is to not start the drilling of a pile until an adequate amount of 

concrete/grout is available at the jobsite to complete the pile. 

After reaching the pile tip elevation, the operator typically must lift the auger about 150 mm 

(6 in.) and pump grout/concrete under pressure to expel the plug used as a stopper in the bottom 

of the hollow auger. This operation is typically called “clearing the bung” or “blowing the plug” 

among contractors. Occasionally, some contractors lift the auger up to about 300 mm (12 in.), 

although a distance limited to 150 mm (6 in.) is preferable. Lifting of the auger prior to blowing 

the plug must be limited to 150 mm (6 in.) because a greater lift-up distance does not favor the 

development of good end-bearing in the pile. If the lift-up distance is excessive, the stress relief 

in the hole walls below the auger may be large, the bearing surface may be disturbed, and this 

may result in mixing of grout with loose soil at the pile toe. Prior to starting withdrawal, the 

auger is re-penetrated to the original pile tip elevation while maintaining pressure on the grout. 

2.2.2.3 Withdrawal of Auger 

Grout should be pumped to develop pressure at the start of the grouting operation. The pressure 

developed should be monitored to ensure that an adequate value is maintained. The grouting 

pressure typically depends on the equipment being used, but commonly, the applied grouting 

pressure is in the range of 1.0 to 1.7 MPa (150 to 250 psi) as measured at the top of the auger. 

9 
As a minimum, the pressure must be in excess of the overburden pressure at the discharge point 

at the tip of the auger after accounting for elevation head differences between the measurement 

point and the auger tip. The grouting pressure must be maintained as the auger is slowly and 

smoothly withdrawn. This pressure replaces the soil-filled auger as the lateral support 

mechanism in the hole. When the grout pressure is applied, the grout also pushes up the auger 

flights and presses the soil against the auger. 

If over-rotation has been applied during drilling, it could be difficult to maintain the grout 

pressure during withdrawal. Over-rotation refers to the excess rotation of the auger relative to 

the depth penetrated for each turn. During over-rotation, the auger does not have a sufficient 

feed of soil from the cutting edge to maintain the flights full of soil and to prevent soil from 

loading the auger from the side. Over-rotation of the augers during drilling tends to clear the 

auger of soil and permits the concrete or grout to flow up the auger flights rather than remaining 

below the base of the auger under pressure. If grout flows up the auger flights for a large 

distance, it will be vented to the surface while the auger is still in the ground and at that point it 

will no longer be possible to maintain pressure in excess of surrounding overburden stress. 

As the auger is slowly and steadily withdrawn, an adequate and controlled volume of 

grout/concrete must be delivered at the same time to replace the volume of soil and auger being 

removed. An overrun in the grout replacement volume of about 15 to 20% above the theoretical 

volume of the pile should be required. The necessary volume of grout must be delivered 

continuously as the auger is removed, and this volume should be measured and monitored to 

ensure that an adequate volume of concrete/grout is delivered. If the auger is pulled too fast in 

relation to the ability of the pump to deliver volume, the soil will tend to collapse inward and 

form a neck in the pile. Continuous monitoring of the volume is required to avoid the possibility 

that the rig operator could pull too fast for a short segment and then slow down for the volume to 

“catch up”. This discontinuous withdrawal could result in the pile being constructed as a series 

of necks and bulges rather than the uniform structural section that is desired. 

During grouting, the auger should be pulled with either no rotation or slow continuous rotation in 

the direction of drilling. A static pull with no rotation can help maintain a static condition at the 

base of the auger against which the grout pressure acts. Some contractors prefer to slowly rotate 

the auger during withdrawal to minimize the risk of having the auger flight getting stuck. In 

addition, some augers have an off-center discharge plug at the base and slow rotation may help 

avoid concentrating the distribution of the grout pressure to an off-center location within the 

hole. If rotation is used, it must be very slow so that the auger does not tend to conduct the soil 

on the auger flights to the surface ahead of the auger. When the grout reaches the surface, the 

grout pressure is vented, and the high pressure under the auger can no longer be maintained. At 

this point, it is important that the proper volume of grout be continuously delivered per increment 

of length as the auger is removed, and the grout that is on the augers should not be allowed to 

flow back into the hole. If grout and soil become mixed on the auger during this process, the soil 

and contaminated grout could fall into the top of the pile and be difficult to remove. 

After withdrawal of the auger and removal of spoil, it is necessary that the top of the pile be 

cleared of debris and any soil contamination be removed. The use of a small form is 

recommended to provide definition of the top of the pile prior to placement of the reinforcement. 

10 
 

As seen in Figure 2.9, the top of the pile can be 

difficult to find among the surface disturbance. 

Attention to detail in the final preparation of the 

surface is critical to ensure that structural integrity 

is maintained. Figure 2.10 shows a sequence of the 

final preparation of the pile surface and placement 

of the reinforcement. A dipping tool is typically 

used to remove any soil contamination near the top 

of the pile (top two photos of Figure 2.10) before 

placing reinforcement into the fluid grout (bottom 

two photos). Figure 2.9: Grout at Surface after 

Auger Withdrawal 

Figure 2.10: Finishing Pile and Reinforcement Placement 

2.2.2.4 Grout vs. Concrete 

In the current U.S. practice, the majority of work is completed using a sand/cement grout 

mixture. In European practice, concrete is used almost exclusively. In the United States, 

contractors are starting to use concrete more frequently. Successful projects have been 

completed using both materials. Some of the advantages of each material are discussed below. 

Details of these materials are provided in Chapter 4. 

11 
 

Grout has been used since the early days of CFA pile construction in the United States because 

of the fluidity and ease of installation of reinforcement. The typical range of compressive 

strength of grout in transportation projects is 28 to 35 MPa (4,000 to 5,000 pounds per square 

inch [psi]). Grouts used with CFA piles are usually rich in cement, having 8 to 11 sacks per 0.76 

cubic meter (1 cubic yard). Aggregate is generally limited to sand with the gradation of concrete 

sand. A Fluidifier is often used as a pumping aid, to act as a retardant, and to help control 

shrinkage because the mix is so rich in cement. Fly ash and slag are often substituted for a 

portion of the cement. Typical percentages for fly ash and slag are around 12% to 15%, for a 

combined replacement of cement of 24% to 30%. When only fly ash is used to partly replace the 

cement, its content can range commonly between 25 and 70 lbs per cubic yard (pcy) of concrete, 

with 40 lbs per cubic yard being a typical quantity. 

The partial replacement of cement with fly ash and slag tends to produce mixes with higher 

workability and pumpability, reduced bleeding, and reduced shrinkage. Fly ash and/or slag tend 

to slightly retard the early strength gain of the grout mix relative to an equivalent mix using only 

Portland cement, although long-term strength (e.g., 56 days) may be comparable. If fly ash 

and/or slag are used in the mix, the submittal of the grout mix design should include information 

on strength development vs. time. 

Grout is so fluid that the workability is typically measured using a flow cone (as described in 

Chapter 7) in lieu of the slump measurement that is typical for concrete mixes. With the use of 

grout aids (which provide some retarding effect) and the relatively rapid construction of these 

piles (casting is normally completed in a matter of minutes), the loss of workability during the 

placement operations is not normally a significant consideration and retarding admixtures are not 

commonly used. However, the mix must remain fluid during rebar placement. 

Workability during time after placement of the grout is important in CFA pile construction 

because of the need to place reinforcement within the pile soon after completion. It is considered 

good practice to start drilling only after the concrete or grout has arrived on the project site and 

delivery of the full volume needed for completion of the pile without interruption is assured. 

The characteristics of the soil at the site play a significant role in the workability of the grout 

during rebar placement. Rebar may be easy to install for up to 30 minutes after grout casting for 

piles in saturated clays; on the other hand, dry sandy soils may tend to dewater the grout very 

quickly. If sandy soils are producing rapid dewatering of the grout, conventional measurements 

of concrete setting time alone may not provide a reliable indication of the ability to place the 

reinforcing cage. Retarding admixtures or anti-washout agents [such as viscosity-modifying 

admixtures (VMA)] may be needed for piles with long rebar cages constructed in sandy soils. 

The use of test pile installations, together with a willingness to adjust the mix characteristics 

based on observations, are important components of achieving constructability. 

The concrete used by most European and some U.S. contractors generally uses a pea-gravel size 

aggregate with around 42% sand used in the mix. Concrete is cited as being less costly than 

grout, less prone to overrun volume, and is considered to be more stable in the hole when 

constructing piles through soft ground. Concrete slump for CFA construction is similar to that of 

wet-hole drilled shaft construction, with target slump values in the 200 mm ± 25 mm (8 in. ± 1 in.) 

range. Considerations for rebar placement are similar to those for sand/cement grout cited above. 

12 
 

2.2.2.5 Reinforcement (Rebar) 

Reinforcement is placed into the fluid 

grout/concrete immediately after the auger is 

removed. In general, reinforcement lengths 

between 10 and 15 m (33 and 50 ft) are 

considered feasible, depending on soil conditions. 

However, longer reinforcement has been used. 

Contractors often install a single, full-length bar 

(i.e., it extends the entire depth of the pile) into 

the center of the pile (Figure 2.11) and a cage of 

partial-length bars around the perimeter of the 

pile. The full-length bar provides continuity and 

acts as a guide for the cage. A full-length bar is 

also used for tension resistance. In this case, a 

wire “football” is installed on the end of the bar to 

anchor the bar in the grout. A minimum cover of 

75 mm (3 in.) is commonly adopted for most 

applications. Difficulties in placing the cage can 

arise if the concrete starts to set and loses 

workability. Soil conditions can also have an 

effect on the reinforcement placement, as a free 

draining sand or dry soil can tend to dewater the 

concrete rapidly and lead to increased difficulty in 

placing the cage. 

A common practice in Europe is to utilize a small 

vibratory drive head to install the cage. The photo in 

Figure 2.12 is from a project in Munich, in which 1-m 

(3-ft) diameter piles were used to construct a wall 

through gravelly sand, and 18-m (60-ft) long cages 

were installed along the entire length of the pile to 

provide flexural strength. These cages were machinewelded using weldable reinforcement and the piles 

were constructed using concrete. The use of a 

vibratory drive head could lead to problems with 

cages that are not securely tied or welded, and could 

also produce segregation and bleeding if the concrete 

mix is not well proportioned. The system appeared to 

work very well on this project, as the concrete in the 

exposed piles appeared to be sound and free of 

segregation or voids. 

Figure 2.11: Placement of a Single 

Full-Length Bar 

Figure 2.12: Vibratory Drive Head 

Used to Install Rebar Cage 

It is worth noting the differences in grout placement for a CFA pile in contrast with that of a 

drilled shaft foundation. Concrete used for a drilled shaft is placed through a tremie pipe into a 

fluid-filled hole or via a drop chute into a dry open hole. In each case, the inspector and 

13 
contractor have some means of observing the location of the concrete relative to the surface 

and/or tremie. Additionally, the reinforcement cage is pre-positioned and held in place, often 

with some access tubes for subsequent non-destructive testing to verify structural integrity. The 

concrete must maintain workability to pass through the cage and fill the hole. The placement of 

grout in CFA piles can only be monitored remotely and indirectly by measurement of the volume 

delivered through the auger at any given time and the pressure at which it was pumped. The 

grout must maintain workability so that the cage can pass through the grout. Quality control 

issues are present with both systems and difficulties can arise with either system. The CFA pile 

system is particularly dependent upon operator control during grout placement and auger 

withdrawal. 

2.3 SUMMARY 

This chapter provides a general overview of CFA piles, including the general construction 

sequence used and potential limitations and/or difficulties using the technique. CFA piles have 

some significant advantages in terms of speed and cost effectiveness if used in favorable 

circumstances, and can clearly pose difficulties in terms of quality control if careful construction 

practices are not followed. The following chapter will describe potential applications of this 

technology in transportation related projects and will outline favorable and unfavorable project 

and geotechnical conditions for CFA piles. 

14 
CHAPTER 3 APPLICATIONS FOR TRANSPORTATION 

PROJECTS 

3.1 INTRODUCTION 

This chapter presents several advantages and limitations of using CFA piles, and provides 

information on project and geotechnical conditions that may be favorable or problematic for this 

type of pile. This chapter also illustrates applications of CFA piles on transportation projects, 

including bridge piers and abutments, soundwalls, earth retaining structures, and pile-supported 

embankments. At the end of this chapter, several examples of typical costs for CFA piles in U.S. 

construction are provided, which can be beneficial when considering CFA as an alternative 

foundation to more traditional methods. 

3.2 ADVANTAGES AND LIMITATIONS OF CFA PILES 

3.2.1 Background 

CFA piles have been more widely used in private, commercial work in the United States and 

abroad than in transportation work. Several factors appear to contribute to this trend; some 

factors are inherently associated with CFA pile technology and some are institutional 

perceptions. The factors that might have contributed to a wider acceptance of CFA piles in 

commercial applications than in transportation projects are: 

•	 Simple foundation requirements: a large number of piles are commonly used in a 

compact area (Figure 3.1) primarily to support large concentrated dead loads. 

•	 Speed of installation of CFA piles over other pile types. 

•	 Increased use of design-build contracting in private work, in which contractors are 

highly motivated toward speed, economy, and innovations to those means. 

•	 Increased requirements to minimize noise and vibrations from pile installation in 

heavily populated areas. 

•	 A reluctance by many owners to utilize CFA piles because of concerns about quality 

control and structural integrity. 

•	 The typical demand on bridges for uplift and lateral load capacity, scour considerations, 

and/or seismic considerations, require pile diameters and possibly lengths up to a range 

not commonly used with CFA piles in private commercial work in U.S. markets. 

The following sections describe advantages and limitations of CFA piles and present 

geotechnical and project conditions that affect the selection and use of these piles. 

15 
Figure 3.1: Use of CFA Piles for Commercial Building Projects 

3.2.2 Geotechnical Conditions Affecting the Selection and Use of CFA Piles 

3.2.2.1 Favorable Geotechnical Conditions 

CFA piles generally work well in the following types of soil conditions: 

•	 Medium to very stiff clay soils. In these soils, the side-shear resistance can provide the 

needed capacity within a depth of approximately 25 m (80 ft) below the ground surface. 

The major advantage of cohesive soils for CFA pile construction is that clays are 

generally stable during drilling and less subject to concerns about soil mining during 

drilling. 

•	 Cemented sands or weak limestone. These soils are favorable if the materials do not 

contain layers that are too strong to be drilled using continuous flight augers. In 

cemented materials, it is not so critical that the cuttings on the auger maintain stability of 

the hole. In addition, CFA piles can often produce excellent side-shear resistance in 

cemented materials because of the high side resistance created by the rough sidewall and 

good bond achieved using cast-in-place grout or concrete. 

•	 Residual soils. Residual soils, particularly silty or clayey soils that have a small amount 

of cohesion, are favorable for CFA pile installation because installation can be 

particularly fast and economical. 

16 
•	 Medium dense to dense silty sands and well-graded sands. These sands, even when 

containing some gravel, are commonly favorable. This is especially true if the 

groundwater table is deeper than the pile length. 

•	 Rock overlain by stiff or cemented deposits. CFA piles can achieve significant 

end-bearing capacity on rock, provided that the overlying soil deposits are sufficiently 

competent to allow installation to the rock without excessive flighting. Flighting is the 

lifting of soil on the auger as the auger turns, in the manner of an Archimedes pump. 

Rock that is directly overlain by strong material or a transitional zone is well suited. 

3.2.2.2 Unfavorable Geotechnical Conditions 

The installation of CFA piles can be problematic in the following types of soil conditions: 

•	 Very soft soils. In these soils, the installation of CFA piles can present problems 

concerning ground stability due to soft-ground conditions, which can produce necks or 

structural defects in the pile. Even with oversupply of concrete or grout (which is a 

costly measure and the piles become less economical), the result is a bulge in the very 

soft zones that can cause an increase in downdrag loads. Under these conditions, it is 

difficult to reliably control the volume per unit length of the pile during withdrawal of the 

auger. 

•	 Loose sands or very clean uniformly graded sands under groundwater. Clean, loose 

sands with shallow groundwater are unfavorable because the potential for soil mining is 

high. Therefore, under these conditions, the control of the penetration rate during drilling 

and grout placement is extremely critical. For these soil conditions, DD piles are likely 

to be more reliable because this type of pile tends to densify the surrounding loose soil. 

•	 Geologic formations containing voids, pockets of water, lenses of very soft soils, and/or 

flowing water. These subsurface conditions may cause the hole to collapse, initiate 

problems during drilling and grouting, and make the penetration and grouting rates hard 

to control. For example, solution cavities in limestone are a common source of such 

difficulties. 

•	 Hard soil or rock overlain by soft soil or loose, granular soil. The installation of CFA 

piles is typically difficult in a soil profile in which it is necessary to drill into a hard 

bearing stratum overlain by soft soil or loose granular soil (Figure 3.2a). The problem 

occurs when the hard stratum is encountered and the rate of penetration is slowed because 

of the difficult drilling; the overburden soils are then flighted by side loading of the auger 

above the hard stratum. Decompression of the ground above the hard stratum and ground 

subsidence can result in the case of a stiff clay layer underlying a water-bearing sand 

deposit, even if the stiff clay can be drilled without great difficulty. The rate of 

penetration required for the stiff clay is lower than that for the sand, and the sand will 

tend to flight during drilling of the clay. 

17 
In addition, a hard rock layer overlain by soft material presents a quality assurance 

concern in that there is difficulty ensuring that the pile has sound bearing on the rock 

formation. Piles are typically driven to a resistance that ensures sound bearing, and 

drilled shafts are typically socketed a short depth into the rock. 

The potential for difficult drilling conditions also exists when a sand stratum is 

sandwiched between an upper and a deeper clay deposit; in this case, the sand also 

tends to be flighted and a cone of sand tends to collapse and displace toward the hole. 

This cone of depression in the sand deposit is caused by over-removal of the sand, 

which may not be visible at the surface, but could result in: (1) a void beneath the upper 

clay; (2) loosening of the sand; and (3) over consumption of concrete or grout. 

In comparison, these soil conditions are more favorable for the use of driven piles or 

drilled shafts, for which cases drilling through sands can be controlled using casing or 

slurry. 

 

 

 

 loose 

sand 

loose 

sand 

hard 

clay 

stiff 

clay 

a) sand overlying hard clay b) sand bea ring stratum 

underlying stiff clay 

Figure 3.2: Examples of Difficult Conditions for Augured Piles 

•	 Sand-bearing stratum underlying stiff clay. When the bearing stratum is composed of 

clean, dense, water-bearing sand and is overlain by a stiff clay deposit, pile installation 

may be difficult (Figure 3.2b). In this case, the slower rate of penetration (relative to the 

rate of turning of the auger) used in the clay can cause loosening of the sand stratum 

below when this stratum is encountered, and this results in excessive flighting of the sand 

from the stratum intended as the primary bearing formation. Excessive flighting occurs 

when the auger is rotated too much in proportion to the penetration into the soil, such that 

too much soil is flighted towards the surface and the auger flights do not maintain 

adequate soil to provide lateral support for the hole. The water pressure in a confined 

18 
aquifer may contribute to this problem. The result is that the pile does not support the 

load at the tip in the deeper sand as intended, but almost solely relies on side-shear 

resistance in the clay. Under these conditions, it is better that the pile either terminate in 

the clay (assuming an appropriate design capacity is achieved) or the pile be drilled into 

the sand. 

•	 Highly variable ground conditions. When highly variable ground conditions exist, in 

which one of the cases noted above may be encountered at some locations across the site, 

it is more difficult to provide a relatively uniform drilling criteria for the site. Having 

varying drilling criteria across the site can lead to problems with quality control and 

quality assurance, particularly if the wrong criteria are applied to individual piles. Highly 

variable ground conditions also create additional problems with respect to reliability of 

capacity predictions. 

•	 Conditions requiring penetration of very hard strata. When a stratum is very hard to 

penetrate (e.g., rock), drilling of CFA piles would be very difficult. This condition 

requires a modification to the CFA pile design so that penetration in the rock is avoided 

or the use of drilled shafts socketed into the material or driven piles driven to refusal on 

the material are employed. CFA piles designed to bear on hard rock that cannot be 

penetrated with an auger must be designed for a smaller bearing value than the rock may 

be capable of sustaining in other conditions because of the difficulty in achieving sound 

contact at the pile/rock bearing surface. 

•	 Ground conditions requiring uncommonly long piles. CFA piles longer than 30 m 

(100 ft) require unusual equipment for this technique; however, there have been isolated 

circumstances in which CFA piles longer than 30 m (100 ft) have been used. CFA piles 

of such length are uncommon, and may require equipment with unusually high torque, 

high lifting capacity, and tall leads 

•	 Ground conditions with deep scour or liquefiable sand layers. In these circumstances, 

where a total or near-total loss of lateral support may occur at significant depths, the piles 

may be subject to high bending stresses at great depths. CFA piles are most efficient in 

relatively smaller diameters, and placement of a rebar cage to great depths can be 

difficult. CFA piles also are not typically designed with reinforcement to achieve high 

bending resistance. If ground conditions exist where deep loss of support may occur, this 

condition tends to favor the use of larger diameter drilled shafts or large driven piles. 

CFA piles may require structural steel inserts, such as steel pipe or H sections, to achieve 

adequate bending resistance through a zone where loss of support may occur. 

Design applications requiring significant shear, bending, or uplift resistance may not be suitable 

for CFA piles, regardless the type of soil conditions at the site. The limitations associated with 

reinforcement installation typically restrict the use of CFA piles in these applications. In some 

cases, groups of CFA piles can provide adequate shear, bending, or uplift resistance; however, 

another deep foundation system may be more economical. 

19 
3.2.3 Project Conditions Affecting the Selection and Use of CFA Piles 

CFA piles may be a viable alternative for projects with the following conditions: 

•	 Projects where speed of installation is important. CFA piles can be installed very quickly, 

provided the rig has a good working platform on which to move around the site and the 

geotechnical conditions are otherwise favorable (Figure 3.3). For projects requiring a large 

number of piles and on projects where 

high production rates are important, CFA 

piles can have advantages over drilled 

shafts or some types of driven piles. 

Typical production rates on private 

projects for piles having diameters of 300 

to 450 mm (12 to 18 in.) and lengths of 

less than 20 m (65 ft) are about 300 to 450 

m (1,000 to 1,500 ft) per day. These rates 

are achievable on private projects, such as 

large buildings, where most of the piles on 

the project are relatively close together, 

reducing the amount of movement of the 

rig between piles. Lower production 

rates, such as 60 to 150 m (200 to 500 ft) 

per day, should be expected for 

transportation projects where pile groups 

supporting bridge bents are spread across 

a large project area, or a significant 

number of battered piles are installed. 

•	 Batter Piles Required. Although not 

commonly a viable alternative, it is also 

possible to install CFA piles on a batter, Figure 3.3: CFA Piles at Bridge 

but the speed of installation decreases and Interchange
	

these piles are more difficult to construct 

in other ways. For example, the drill rig capability is diminished when working on a 

batter and the reinforcing cage is more difficult to install with proper cover. Pile batter 

should generally be limited to 1 (horizontal):4 (vertical) or steeper for bearing piles. 

Greater batter angles ranging to even horizontal can be used to install anchor piles in 

competent, non-caving soil, but these are typically not designed to support large axial 

compression loads. 

•	 Projects where large numbers of piles are required. The costs for CFA piles reflect the 

high productivity for projects where large numbers of piles are required. Prices for CFA 

piles are often a few dollars per foot less than prestressed concrete or steel piles of similar 

size and axial capacity, assuming both pile types meet the project performance criteria. 

20 
•	 Low headroom conditions. Low headroom equipment can be used effectively with CFA 

piles and is often more cost effective than high strength micropiles if the ground 

conditions are favorable for CFA pile installation (Figure 3.4). Note that continuous 

placement of grout is not possible when the auger string must be broken during 

withdrawal. Therefore, this technique should only be used in favorable ground 

conditions and with close control to maintain grout pressure and volume during 

extraction. 

Figure 3.4: Low Headroom CFA Pile Application 

•	 Secant or tangent pile walls up to 10 m (33 ft) of exposed wall height. When CFA piles 

of less than 1.2 m (4 ft) in diameter can be used for a retaining wall, and when 

geotechnical conditions are otherwise favorable, CFA piles can be a viable alternative to 

drilled shafts or slurry walls (Figure 3.5). For this application, it is important to utilize 

heavy drilling equipment, which can maintain good vertical alignment. A structural steel 

section may be used for pile reinforcement rather than a reinforcing cage. The CFA 

drilling technique has been used successfully on many such projects with both anchored 

earth retention and cantilever walls. Higher walls are possible with the use of tiebacks. 

•	 Soundwalls in favorable soil conditions. Because soundwalls tend to have large numbers 

of relatively short piles, CFA piles can be quite fast and economical. Figure 3.6 

illustrates an example of a long row of CFA piles for a soundwall along a highway. 

•	 Pile-supported embankments. Although this type of construction commonly takes place 

in relatively soft soils, the loading demands on a per pile basis are not particularly very 

large. The speed and economy of CFA piles especially DD piles, make them a 

potentially effective alternative to ground modification (Figure 3.7). CFA piles have 

been utilized for embankment support to limit excessive settlement from soft or 

21 
compressible foundation soils. This is a special application of CFA piles that requires 

consideration of edge stability, design of the individual pile caps (if any) and reinforced 

embankment overlying the piles, as well as the magnitude and time rate of settlement. 

The reader is referred to Collin (2004) and Han and Akins (2004) for further details. 

Figure 3.5: Secant Pile Wall with CFA Pile Construction
	

Figure 3.6: CFA Piles for Soundwall (at right) along Highway (out of view to left) 

22 
3.3 ADVANTAGES AND LIMITATIONS OF DRILLED DISPLACEMENT PILES 

Drilled displacement (DD) piles have many of the same features, advantages, and limitations as 

CFA piles. Some of the factors that may differ for DD piles compared to CFA piles are outlined 

below. 

•	 Better performance in loose sandy soils. DD piles increase the horizontal stress in the 

ground and densify sandy soils around the pile during installation (Figure 3.8). 

Figure 3.7: Pilecaps on CFA Piles for a Pile-Supported Embankment 

Therefore, this technique achieves some ground improvement around the pile. This 

improvement leads to higher values of side-shear resistance in granular soils, especially 

in loose to medium dense sands. DD piles are less subject to the problems of soil 

flighting, described previously for CFA piles. Hence, mixed soil profiles having loose 

granular soils interbedded with clays are less of a concern. In general, DD piles will 

achieve a given load carrying capacity at a shorter length than for a CFA pile of similar 

diameter. 

•	 Little or no spoil removed from site. In areas where contaminated ground exists or it is 

desirable to limit the spoil removed from the site, DD piles are more advantageous than 

CFA piles or drilled shafts because little or no spoil is generated. 

•	 Difficult to penetrate dense or hard soils and more limited depth range. Because of the 

much greater torque required for DD piles relative to CFA piles, it may be impossible 

or impractical to penetrate deeply into soils with strong resistance. In general, DD piles 

are not installed as deep as CFA piles and lengths greater than about 20 to 25 m (65 to 

80 ft) are not very common. DD piles are not used in rock (a condition favoring drilled 

shafts), or even weak rock or hard cemented soils (where CFA piles may be used). 

23 
•	 Effect of displacement. In confined areas or areas in close proximity to utilities or 

sensitive structures, the use of DD piles can pose potential problems for affecting these 

structures. Closely spaced DD piles can also cause large pore pressures in loose fine 

grained soils. Partial displacement piles may work better in this application. 

Figure 3.8: Drilled Displacement Piles Limit Spoil Removal 

3.4 APPLICATIONS 

In this section, several typical applications of CFA piles for transportation projects are described. 

3.4.1 Soundw alls 

The use of CFA pile foundations for soundwalls represents an easy-to-implement application. 

Soundwall foundations are commonly characterized by single piles at each column location and 

by the use of reinforcement or anchor bolts designed to make a moment connection to the 

column. Figure 3.9 provides an illustration of the standard design detail used by the Florida 

Department of Transportation (FDOT). These piles are relatively lightly loaded, with the 

foundation design controlled by overturning from wind loads. A typical foundation has a 

diameter of 450 to 900 mm (18 to 36 in.) and a depth of 4 to 8 m (13 to 26 ft). CFA piles are an 

alternative to drilled shafts for these foundations. 

24 
Figure 3.9: CFA Pile Foundation for Soundwall 

3.4.2 Bridge Piers and Abutments 

Where conditions are favorable, the use of CFA pile foundations is a feasible alternative to other 

types of deep foundations for bridges. Most often, the type of bridge most suited for the use of 

CFA foundations are interchange structures (where scour is not a major issue), approach 

structures, or those involving bridge widening. CFA piles may be favored in areas where pile 

driving vibrations or noise requirements cannot be met or simply for situations where cost or 

speed advantages can be achieved. 

As of this writing, there have been relatively few cases of bridge structures supported on CFA 

pile foundations in the United States. An example is provided by Vipulanandan et al. (2004) for 

a bridge at the Krenek Road site in Crosby, Texas, constructed in the Pleistocene soils of the 

Gulf coast region. The Texas Department of Transportation (TXDOT) constructed this bridge 

25 
entirely using CFA piles as an implementation project to provide a comparison of the CFA 

alternative to driven piles. The project included load tests up to failure on instrumented piles as 

well as instrumentation on production piles to monitor pile performance in service. The CFA 

bridge project is located a short distance [about 1 km (0.6 mile)] from the Runneburg Road 

Bridge site, where a bridge was constructed using driven piles in very similar soil conditions. An 

examination of the two projects provides a comparison of CFA and driven pile alternates on two 

very similar projects. 

The Krenek Road site for the CFA pile-supported bridge was underlain predominantly by stiff 

clays with two thin layers of sand and the groundwater table located about 1.5 m (5 ft) below the 

ground surface. The bridge was founded on 64 CFA piles, 17 to 19 m (56 to 62 ft) long and 

450 mm (18 in.) in diameter. A schematic diagram is presented in Figure 3.10. The abutment 

piles were installed on a batter of 1:4. Intermediate bent columns were founded on 4-pile groups 

of vertical piles. The piles were designed to terminate in a dense sand stratum (Figure 3.11). 

Side-shear and end-bearing resistance provide a design axial capacity of 810 kN (90 tons). There 

was no significant design uplift or lateral load requirements for these piles. 

Vipulanandan et al. (2004) 

Figure 3.10: Schematic Diagram of the Foundation on CFA Piles for the 

Krenek Road Bridge 

The foundation for the Runneburg Road Bridge was almost identical to the Krenek Road Bridge, 

except that the Runneburg Road Bridge was founded on 400 mm (16 in.) square prestressed 

concrete piles driven to a depth of 14 m (46 ft). The piles of the Runneburg Road Bridge were 

terminated entirely within the stiff clay formation and designed to support the design axial load 

of 810 kN (90 tons) primarily using side friction. 

26 
Source: University of Houston 

Figure 3.11: CFA Piles at the Krenek Road Bridge Site 

Each vertical CFA pile of the Krenek Road Bridge was installed relatively fast, within about 

15 minutes. For this project, the time needed to move the rig was a significant factor to the 

schedule, especially for the driven piles, which experienced equipment delays during installation 

of the central bent piles. The cycle time for the battered abutment piles was about 45 minutes for 

each type. For the driven piles, about one third of this time was due to the required pre-boring. 

Vipulanandan et al. (2004) noted some construction issues for the installation of CFA piles. In 

several cases, the contractor had difficulty installing the full-length cages due to excessive grout 

viscosity and/or lack of timely work to install the cages immediately after completion of the 

grouting. On numerous occasions, the contractor was observed slowly turning the auger with the 

auger in the borehole and without either excavating or pumping grout. This operation was 

performed because grout was not available in a timely fashion and the operator could not stop 

rotation and risked seizing the auger in the ground. This practice increased soil mining, 

particularly in the sand strata. 

Load tests were conducted on test piles at both sites, and the CFA piles were instrumented to 

determine the distribution of side-shear and end-bearing resistance. Although the designers had 

anticipated higher side-shear strength values for the driven piles, the CFA piles actually 

mobilized higher side friction than the driven prestressed piles. Note that this conclusion is 

27 
based on an estimated distribution of side-shear and end-bearing in the driven piles, because the 

driven piles were not fully instrumented. The base resistance for CFA piles was virtually zero, 

probably reflecting the effect of decompression of the dense sand-bearing stratum during 

installation of the pile through the stiff clay. The CFA piles actually provided the needed axial 

capacity, but through higher than anticipated side-shear resistance and much lower than 

anticipated end-bearing resistance. 

Twelve production piles were instrumented and monitored during construction and load testing 

using trucks. The results from the pile instrumentation suggest that the piles supported the fully 

loaded bridge entirely by mobilizing side friction alone and with very small [around 3 mm 

(0.1 in.)] movements (Figure 3.12). A lesson learned from this project is that CFA piles would 

have been better designed to terminate in the clay rather than attempting to mobilize end-bearing 

in a water-bearing sand stratum below the stiff clay. 

Vipulanandan et al., (2004) 

Figure 3.12: Comparison of Measured Settlements and Test Pile, Krenek Road 

Bridge Site 

The unit cost of CFA piles was approximately $65 per linear meter ($20 per linear foot). The 

instrumentation and full-length cage, required for the instrumentation, affected the unit cost, 

which was estimated to be about $7 higher per linear meter ($2 per linear foot) than would 

normally be anticipated for production piles. Cost per pile for CFA piles at the central bent was 

$1,140 per pile. The cost for the driven piles at the central bent of the Runneburg Road Bridge 

was less than the CFA pile cost at the Krenek Road Bridge; however, the load tests indicated that 

a higher factor of safety was achieved for the CFA piles than for the driven piles and, if the 

lengths were adjusted to provide a similar factor of safety for axial loading, the unit cost of the 

CFA piles would have been about 8% less. 

The comparison study between these two bridges suggests that CFA piles can provide a viable 

alternative to conventional driven pile foundations. As a result of these experiences, TXDOT 

plans to utilize CFA piles on other future bridge projects where conditions appear favorable. 

28 
3.4.3 Retaining Structures 

CFA piles can be used to construct secant or tangent pile walls in a manner very similar to that of 

drilled shaft walls, which can be designed as cantilever or anchored walls. The most significant 

distinction relating to CFA piles, as opposed to other types of vertical elements, is the 

construction method for the vertical element. The CFA piles are intended to provide a reinforced 

vertical wall member having a similar function as that of a drilled shaft, slurry wall section, or 

sheet pile. In almost all such cases, the contractor provides designs of CFA piles for retaining 

structures as a design-build option. Figure 3.13 illustrates a typical CFA secant pile wall. 

Figure 3.13: Secant CFA Pile Wall for a Light Rail System in Germany 

The major differences for CFA pile wall systems as compared to other pile types are discussed 

below. 

•	 Diameters of CFA piles are generally limited to about 1 m (40 in.). 

•	 Maximum depths for CFA piles are generally no more than 10 to 18 m (33 to 60 ft) 

with wall heights generally around 12 m (40 ft) or less. This limitation is not only 

related to machine capability, but also due to the fact that the reinforcement must be 

placed into the fluid concrete and verticality of the piles can be difficult to maintain for 

long piles. 

•	 Control of verticality is critical to keep the piles aligned, especially if a watertight 

structure is needed; some of the hydraulic rigs equipped with inclinometers are 

well-suited for this construction. 

•	 For secant pile systems, the sequencing of pile installation and set time and initial 

strength characteristics of the concrete is critical so that the excavation equipment can 

cut into previously drilled piles. Some contractors install primary piles using a weaker 

concrete mix and utilize a stronger mix for the secondary piles, which provide the main 

structural strength of the wall (see Figures 3.14 and 3.15). Large, high torque-capacity 

rigs are necessary, especially when cutting into existing concrete piles. 

29 
• Placement of reinforcement can be more difficult in a CFA pile than in a conventional 

drilled shaft or slurry wall, in which the reinforcement is placed ahead of the concrete. 

Primary Piles 

(drilled first) 

Secondary 

Piles 

Figure 3.14: Schematic Plan View of a Secant Pile Wall 

Figure 3.15: Drilling CFA Piles through Guide for Secant Wall 

3.4.4 Pile-Supported Embankments 

The use of CFA piles for a pile-supported embankment may represent a cost-effective alternative 

to ground modification or embankment support using driven piles. The use of pile support for 

embankments is likely to be considered only when the foundation strata consist of weak and 

compressible subsoils, which would take a long time to consolidate. Furthermore, there is an 

interest in minimizing post-construction settlements of the embankment or accelerating 

construction. Examples include, widening of existing embankments (where the additional fill 

may result in costly or disruptive damage to the existing structure); a fill supporting a 

30 
transportation facility that is particularly sensitive to settlements (such as a high-speed rail); or 

the fill approach to a pile-supported structure (where differential settlements may be a problem). 

Accelerated construction is required for projects where additional cost due to traffic shifts, 

geotechnical instrumentation, and related time delays present an unacceptable situation to project 

owners. 

CFA piles offer the advantages of installation speed and economy (cycle times of 15 minutes or 

less per pile are not uncommon), and costs on the order of $40 per linear meter ($12 per linear 

foot) are feasible on a large volume project using many small diameter [i.e., 300 to 350 mm 

(12 to 14 in.)] CFA piles. 

A diagram of a pile-supported embankment for a railway project in Italy is illustrated in Figure 

3.16. This embankment was designed as part of a widening project to increase traffic capacity. 

The pile support was used to limit settlements produced by the new fill on the existing railway 

structure and the new rail line. The piles were capped using precast cylinder sections filled with 

concrete (shown previously in Figure 3.7), and the fill overlying the pile caps was reinforced 

using geotextiles. 

3.5 CONSTRUCTION COST EVALUATION 

Because the use of CFA piles in U.S. transportation facilities has been very limited, there are few 

records of cost data for transportation projects. Costs of CFA piles on private projects often 

range from approximately $40 to $60 per linear meter ($12 to $20 per linear foot) for 300- to 

450-mm (12- to 18- in.) diameter piles. However, these projects typically include much greater 

quantities of piling and fewer moves across the site than is typical for a bridge or soundwall; 

prices on transportation projects are likely to be higher. In addition, costs relating to 

performance and integrity testing are likely to be higher on transportation projects. A major 

factor on transportation projects is the impact of site constraints on productivity. Many variables 

affect pile costs, including length, diameter, reinforcement, and grout strength. Costs will also 

vary according to region of the country, as well as the size of the project. 

The aforementioned project in Texas has been followed by another bridge project on State 

Highway 7 in Houston County, which was awarded in early 2005. This project includes 24 

760-mm (30-in.) diameter piles. The bid price was $200 per linear meter ($60 per linear foot) 

for 237 linear meters (778 linear feet) of piling, along with a mobilization cost of $25,000 and a 

cost of $25,000 each for two static load tests. 

The Kansas DOT has used CFA piles on only a few projects, including two bridges and a secant 

pile wall. These projects utilized 400- to 450-mm (16- to 18-in.) diameter piles, with typical 

costs in the range of $72 to $85 per linear meter ($22 to $26 per linear foot). Some low 

headroom work was bid at $320 per linear meter ($98 per linear foot). According to Jim 

Brennan, Kansas State Geotechnical Engineer, the prices are quite sensitive to mobilization costs 

and the numbers of piles on the project, with fewer piles resulting in higher unit costs. 

31 
Figure 3.16: Diagram of Pile-Supported Embankment for Italian Railway Project 

The Florida DOT has used CFA piles for soundwalls, usually in the 760- to 900-mm (30- to 

36-in.) diameter range and for depths typically less than 9 m (30 ft). Bid prices on these projects 

are typically in the range of $200 to $260 per linear meter ($60 to $80 per linear foot). 

Production ranges from 6 to 15 piles per day. Frizzi and Vedula (2004) identify relative costs of 

CFA piles vs. driven precast concrete piles for a project in south Florida. Details of their cost 

comparison can be found in their paper. 

32 
CHAPTER 4 CONSTRUCTION TECHNIQUES AND MATERIALS 

4.1 INTRODUCTION 

This chapter provides details of the construction techniques, materials, and recommended 

practice for the construction of CFA piles for transportation projects. The guide specification 

included in Chapter 8 of this manual is a performance-based specification that allows the 

contractor to select the equipment, materials, and techniques to install a pile to provide the 

foundation capacity required for the job. This chapter is thus written with the performance-based 

specification in mind. Many types of equipment for installing CFA piles are presented, including 

some that are proprietary, which have been difficult to fit into the traditional design-bid-build 

project delivery method. Using a performance-based specification will allow for these systems 

to be considered more often because the contractor is bidding to provide the pile that meets the 

performance specifications at the least cost, regardless of pile type. 

4.2 CONSTRUCTION EQUIPMENT 

This chapter describes various types of drilling equipment used for the construction of CFA piles 

and DD piles, and provides details of tools, grouting/concrete equipment. Advantages and 

limitations of various types of drilling rigs are discussed, particularly with respect to torque 

capabilities. 

4.2.1 Drilling Rigs 

A typical crane-mounted drill rig for CFA piles is illustrated in Figures 4.1 and 4.2. The 

continuous-flight hollow-stem auger is driven by a hydraulic gearbox located at the top of the 

auger. The only downward force (referred to as “crowd” or “downcrowd” among contractors) 

that can be applied by such a system is via the total weight of the gearbox, augers above ground, 

and any soil on the auger flights. Typical crowd values are in the range between 13 and 45 kN 

(3,000 and 10,000 lbs) and typically are around 22 kN (5,000 lbs). 

The pile leads, which are similar to those used by driven pile rigs, serve to provide a guide for 

the auger. The leads may hang freely from the crane boom or be fixed to the crane. The torque 

arm, or stabilizing arm, holds the leads at a point near the ground surface and absorbs torque 

from the drilling operation. A hydraulic spotter may be used to install batter piles. 

The top of the auger is held into the leads via the attached gearbox. The swivel at the top of the 

auger provides for freedom of rotation of the auger without disconnecting the grout/concrete line, 

so that grout placement can begin immediately after completion of the drilling. The auger is 

hollow to act as a conduit for grout/concrete placement. Grout, rather than concrete, is more 

common with this type of rig, and is delivered from a piston pump through the grout hose, as 

shown in Figure 4.1. 

33 
Source: Deep Foundations Institute 

Figure 4.1: Typical Crane-Mounted CFA Rig 

In the current U.S. practice, torque capacities for crane-attached rigs range from 20 to 120 kN-m 

(15,000 to 90,000 ft-lbs); rigs in the range of 27 to 50 kN-m (20,000 to 36,000 ft-lbs) are most 

common for private commercial work. Auger diameters of up to 450 mm (18 in.) are most 

common with these rigs, although diameters of 600 mm (24 in.) are possible with crane-mounted 

rigs at the higher end of the range of torque. 

For CFA piles used on transportation projects, a suggested minimum torque capacity of 40 kN-m 

(30,000 ft-lbs) should be required. This value may not be sufficient to avoid soil mining for 

some pile lengths and diameters and soil conditions. Under a performance-based project 

delivery method, the contractor will have the responsibility of selecting the appropriate rig torque 

capacity for the project requirements to ensure that piles are installed properly and without soil 

mining. The minimum torque capacity recommended above may be relaxed for light duty 

projects, including small soundwall piles or low headroom conditions. 

34 
Figure 4.2: Photo of Crane-Attached CFA System 

A diagram of a special CFA pile rig adapted to function in low headroom conditions is provided 

in Figure 4.3. These special rigs avoid using a crane mast and utilize segmental auger sections to 

achieve the low headroom capability (Figure 4.4). The torque capacity and crowd for such rigs 

are limited to about 28 kN-m (21,000 ft-lbs) and 13 kN (3,000 lb), respectively. Because of 

these limitations, the low headroom equipment should only be used in the most favorable soil 

conditions described in Chapter 2, for which minimal risk of soil mining exists. 

35 
Source: Deep Foundations Institute 

Figure 4.3: Low Headroom CFA Pile Rig 

Figure 4.4: Low Headroom Rig with Segmental Augers 

Hydraulic rigs are common in European practice and are readily available in the United States. 

These rigs typically have torque capacities in the range of 90 to 400 kN-m (66,000 to 300,000 ftlbs) and can apply a crowd of up to 270 kN (60,000 lb). The rigs shown in Figures 4.5 and 

4.6 are typical examples. In European practice with this type of equipment, pile diameters 

ranging from 450 mm to 1,200 mm (18 to 48 in.) are possible, with a range of 600 to 900 mm 

(24 to 36 in.) being most common. Lengths are typically less than 28 m (90 ft), although 

somewhat longer piles can be installed with the Kelly-bar extensions, as shown on the rig in 

Figure 4.6. 

36 
Source: Cementation Foundation Skanska 

Figure 4.5: Hydraulic Rig Drilling on M25 Motorway in England 

The hydraulic pressure used to drive the auger can readily be measured and provides an 

indication of applied torque or downward force. Thus, these rigs lend themselves readily to 

computer monitoring and control. Besides the more sophisticated built-in controls, the high 

torque and downward crowd forces offer advantages over conventional crane attachments in the 

ability to drill larger piles and control the tendency for soil mining. The fully hydraulic rigs are 

often used in the United States for installation of DD piles, because of the need for downcrowd 

and greater torque for installation of DD piles. Compared to crane-mounted rigs, the most 

significant disadvantages of the hydraulic rigs are the high cost of the equipment and the greater 

weight of the rig. The heavy rig weight can be a problem on some sites because of the need for a 

more stable working platform than a crane rig may require. Additional significant disadvantages 

include slower drilling rates and a lack of “reach”, which requires that the entire rig be moved 

from pile to pile. These two issues can lead to lower production rates than with a crane rig. 

37 
Figure 4.6: Soilmec Hydraulic CFA Rig with Kelly-Bar Extension 

4.2.2 Augers and Drilling Tools 

A variety of auger types may be used to drill the piles depending on the soil conditions 

encountered. Figures 4.7 through 4.10 illustrate some of the auger types that may be used for 

CFA piles. The pitch for CFA piles is, in general, smaller than that for DD piles (Figure 4.7). 

The augers for drilling in clay soils may tend to have a larger pitch to facilitate removal of the 

cuttings (Figure 4.8). Selecting the correct auger pitch is important because, for a given soil 

type, an excessively large pitch could result in mining of the soil around the pile. 

Figure 4.7: Augers for Different Soil Conditions: Auger for CFA Piles in Sandy Soil (Top) 

and Augers for DD Piles (Bottom) 

38 
Figure 4.8: Auger for Use in Clay, with Auger Cleaner Attachment 

The base of the auger is usually a double start, with two cutting faces merging into a single flight 

auger a short distance above the tip. The double start cutting head helps keep vertical alignment 

better than a single cutting face, but can tend to pack with clay where the two flights merge. The 

cutting teeth on the base of the auger may utilize hardened points for drilling weak rock (Figures 

4.9 and 4.10). 

Figure 4.9: Cutter Heads for Hard Material (left) and Soil (right) 

39 
Discharge Point 

Figure 4.10: Hardened Cutting Head 

The augers and tools in Figures 4.11 through 4.15 are for use with full or partial displacement 

piles in which all or a portion of the soil is displaced laterally rather than excavated. These 

systems have advantages in many circumstances over conventional CFA piles as described in 

previous chapters. 

Virtually all of these displacement-drilling systems are proprietary in some form or another. 

Some types of DD piles are designed to allow placement of reinforcement inside the tool prior to 

concreting. Some have a sacrificial shoe that is left in place on the bearing surface and may help 

provide improved end-bearing capacity and result in less chances of a soft toe condition. 

The common characteristics of DD piles include greater requirements for torque and downforce 

compared to conventional CFA tools that do not displace soil. The depth to which a pile can be 

installed is limited by the capability of the rig. The greater torque demand due to rig capabilities 

for DD piles can be more significant for limiting pile depth than for conventional CFA piles. At 

the same rig capacity, partial displacement systems can generally penetrate more deeply than full 

displacement systems because there is some opportunity to drill through dense soil layers. The 

level of soil removal for partial displacement systems can vary widely depending on the rig 

operator controlling the rate of penetration. 

The DeWaal displacement pile, which is installed in the United States by the Morris-Shea Bridge 

Co. of Alabama, utilizes a short section of screw auger below the soil displacement bulge in the 

drill pipe (Figure 4.11). This pile type uses a sacrificial shoe, which is usually knocked out with 

a full-length center bar, and grout, which is placed by gravity through the center of the pipe. 

40 
Base 

Source: Prof. W. Van Impe of Ghent University, Belgium 

Figure 4.11: DeWaal Drilled Displacement Pile 

Another term used for DD piles is screw piles. The Omega pile, which is an European pile type, 

is an example of a screw pile. This system uses a short, tapered screw section leading into the 

displacement bulge (Figure 4.12). A small reinforcement cage is placed through the hollow 

auger prior to concrete placement. Omega piles are installed in the U.S. market by L.G. Barcus 

& Sons. 

41 
Source: Prof. W. Van Impe of Ghent University, Belgium 

Figure 4.12: Omega Screw Pile 

The Fundex screw pile is one of the oldest types of screw piles in use. American Pile Driving, 

Inc., of California, is the U.S. representative for this technology. Fundex piles are installed with 

an over-sized sacrificial shoe and a full-length cage that is placed in advance of grout/concrete 

placement. Concrete is placed by gravity through the hollow pipe. The pipe is oscillated as it is 

42 
removed, and the oversized shoe on the bottom of the pipe is intended to provide a rough texture 

to the hole and thus to the surface of the pile. 

Source: Prof. W. Van Impe of Ghent University, Belgium 

Figure 4.13: Fundex Screw Pile 

Berkel and Company Contractors, Inc. of Kansas, has developed their own proprietary tools for 

installing full and partial displacement piles. The full displacement pile in Figure 4.14a is 

similar to others in outward appearance, but uses pressure grouting to construct the pile with 

reinforcement placed after completion of grouting. The partial displacement pile in Figure 4.14b 

43 
is intended to provide partial displacement of soil but still allowing some soil removal via the 

flights on the enlarged auger above the short screw section at the bottom. Partial displacement 

techniques are intended to allow pile penetration to depths beyond those possible with full 

displacement piles, because the removal of some soil can allow easier penetration. The full and 

partial displacement piles shown in Figure 4.15 are manufactured by Bauer Maschinen of 

Germany, and are sold to multiple contractors in the U.S. using Bauer equipment. 

(a) Full Displacement Pile 

(b) Partial Displacement Pile 

Figure 4.14: Drilled Displacement Piles 

44 
(a) Full Displacement Augers 

(b) Partial Displacement Auger 

Source: Bauer Maschinen 

Figure 4.15: Additional Drilled Displacement Piles 

The double rotary system represents another class of augering equipment (Figures 4.16 through 

4.18). These rigs include a full-length casing, which is advanced simultaneously with the auger, 

generally by rotating the casing in the opposite direction of the auger. This technique is 

especially useful for constructing secant pile walls using CFA piles, as the fully cased system 

provides stability for the hole, allows rapid drilling without the need for drilling fluid, and 

increases the verticality of the piles. The casing makes the system quite stiff, and the casing 

itself acts as a type of core barrel for cutting through hard materials, including the secondary 

concrete piles. 

45 
(a) Movable Rotary Drive (b) Fixed Twin Drive 

Figure 4.16: Double Rotary Cased CFA Piles 

The double rotary can have independent movable rotary drives (Figure 4.16a) or fixed twin 

drives (Figure 4.16b and 4.17). The movable drive system works more like a conventional 

drilled shaft in that the two drive motors can move independent of each other, allowing the auger 

to be removed from the casing while leaving a cased hole. The reinforcement and concrete is 

then placed into the cased hole as with a cased drilled shaft, and the rig reattaches to the casing 

and withdraws the casing. This system has the advantage of pre-placement of the reinforcement 

prior to concrete placement, like a drilled shaft. If the pile is terminated in a water-bearing zone, 

it is necessary to add water or drilling fluid to stabilize the base of the cased excavation and then 

place concrete using a tremie. Double rotary cased CFA drilling systems are manufactured and 

sold in the U.S. by Bauer, Delmag, and Soilmec. 

(a) Cutting Head (b) Concrete Placement (c) Cuttings Discharge 

Figure 4.17: Double Rotary Fixed Drive System 

46 
 

With the fixed twin drives (Figures 4.16b and 4.17), the two motors are not capable of 

independent operation. The auger and casing are advanced together and removed together while 

concrete is pumped through the center of the auger, similar to a conventional CFA pile. The 

control of the rate of rotation of the auger relative to the casing is important; the auger must 

rotate faster so that the proper amount of soil is flighted to the top, which allows the auger to 

advance without hanging up inside the casing, and to maintain soil on the augers to stabilize the 

base of the excavation. The flighted soil is discharged through a discharge chute located at the 

drive head (see Figure 4.16b). In some systems, (Figure 4.17b), the auger/casing system is then 

moved to a location for depositing spoils after concrete placement; then the auger is reversed 

and the soil is discharged from the bottom of the casing (Figure 4.17c). Reinforcement is then 

placed into the fluid concrete. 

Some rigs are equipped with a Kelly-bar extension, which allows the auger to penetrate deeper 

than the casing and extend the hole beyond as a CFA pile (Figure 4.18). This system may be 

advantageous when drilling to form a wall through a granular material by extending the piles to 

depths beyond the capability of the casing. The Kelly-bar extension also allows the contractor 

installing the casing slightly behind the leading edge of the auger and thereby permits the cutting 

of relief prior to forcing the casing forward. 

Source: Bauer Maschinen 

Figure 4.18: Double Rotary System with Kelly-Bar Extension 

47 
4.2.3 Equipment for Concrete/Grout and Reinforcement Placement 

The concrete or grout is normally obtained from a ready-mix plant and delivered to the site by 

trucks. For most CFA pile construction, the concrete or grout is pumped under pressure through 

pump lines to the top of the auger string and through the auger to provide positive pressure at the 

point of discharge at the base of the auger. Some types of DD piles are designed for placement 

of concrete into the top of the large diameter auger tool without pressure (see Figures 4.11 

through 4.13). General reference in this section will be to the more common construction of 

CFA piles or partial DD piles. Most CFA piles in the United States are currently constructed 

using sand-cement grout, while most CFA piles in Europe are constructed using concrete of 

small aggregate. In general, the practices and equipment used in the United States and Europe 

are similar. The terms “grout” and “concrete” will be used interchangeably in this section, 

unless specific differences are referenced. 

4.2.3.1 Auger Plug 

The grout discharge point should be located at the bottom of the auger below the cutting teeth 

(e.g., Figures 2.7 and 4.10). In most cases, this grout discharge point is oriented away from the 

leading edge of the cutter head so that high ground pressures do not press against the plug during 

drilling. Some augers are equipped with a centered plug so that a single bar can be placed 

through the center of the auger string prior to concrete placement. Ordinarily, the pressure of the 

grout blows out the plug. A center plug is usually made of a steel shoe or plug of some other 

hard material. The normal off-centered plug is most often cork or plastic. 

Problems with the plug (or “bung” as it sometimes is called by contractors) can occur if the plug 

does not come out or the plug comes out prematurely and the line fills with soil. In either case, 

pumping grout through the line is no longer possible and the pile must be abandoned and 

re-drilled. If the pile needs to be abandoned, the contractor must reverse the direction of rotation 

and remove the auger while leaving soil behind to keep the hole from collapsing. After 

correcting the problem (e.g., by clearing the discharge point), the pile is re-drilled. The pile can 

be re-drilled a short distance away from the first location, as long as the pile layout allows doing 

so. Alternatively, the pile can be re-drilled in the same location, although it is likely that some 

adverse effect on the subsequent pile performance will occur due to soil disturbance. Depending 

upon conditions, the re-drilled pile may be acceptable as is, may require to be deepened, or 

additional piles may be required to compensate. 

Some contractors have successfully used an auger having no plug in the bit by pumping 

compressed air through the auger during the drilling process. The air pressure can be useful in 

some stiff clays or other difficult drilling conditions in helping prevent the soil from adhering to 

the auger and breaking up the soil as it is cut. This technique is used successfully in some parts 

of the country having stiff cohesive soils, such as Texas and northern Georgia. Soil conditions 

that are more susceptible to mining, such as relatively clean sands, may not be suitable for the 

use of compressed air during pile installation. One case of using compressed air to install 

600-mm (24-in.) diameter piles in northeast Florida showed a significantly lower side-shear 

capacity for a test pile installed using compressed air when compared to a test pile installed 

48 
 

without using compressed air. The contractor used compressed air during installation of a 16.8­

m (55-ft) long, 600-mm (24-in.) diameter piles. Instrumented StatnamicTM load tests were 

performed on two piles installed less than 3 m (10 ft) apart, one installed with compressed air 

and one without. The unit side-shear resistance measured in the pile installed using compressed 

air was about half of that measured in the pile installed without compressed air. The soils 

consisted of relatively clean, poorly-graded fine sands, with the piles tipped into a loose to firm 

clayey sand layer. As with many techniques, the use of compressed air should take into 

consideration the potential impact on pile capacity. With a performance-based specification, a 

contractor could choose to use air, provided that a test pile is successfully load-tested and the pile 

meets the required performance. 

4.2.3.2 Pumping Equipment 

The grout pumping equipment should be a positive displacement pump capable of developing 

pressures at the pump of up to 2.4 MPa (350 psi). The typical grout pump operates with 

reciprocating pistons, each delivering around 10 to 30 liters per stroke (0.4 to 1 ft3

 per stroke). 

The size and capacity of the pump must be suitable for the size of the pile being constructed. 

Several examples of pumps are shown in Figure 4.19. Most commonly, the pump is located 

close to the piling rig with grout lines running to the rig and an operator manning the pump 

(Figures 4.19a and 4.19b). The grout line is typically around 63 to 100 mm (2.5 to 4 in.) in 

diameter and can extend 30 to 60 m (100 to 200 ft) from the pump. Some contractors have the 

pump mounted directly on the rig, which allows pumping to be controlled by the operator 

(Figure 4.19c). The pumping operation shown in Figure 4.19d includes a rotating drum for 

holding a full truck load of grout/concrete [approximately 8 m3 (10 yd3)] on-site so that a 

ready-mix concrete truck can discharge into the holding drum and return to the concrete plant. 

It is important that the pump does not deliver an excessive grout volume with each stroke, which 

would cause the operator to have difficulty controlling the pile grouting operation. In general, a 

pump should deliver a volume per stroke that corresponds to around 100 mm (4 in.) of pile 

length or less. If the volume per stroke is too large in relation to the pile size, the operator cannot 

maintain a steady progress of pumping and cannot construct a uniform pile. If the volume per 

stroke is too small in relation to the pile size, the operation is slow and inefficient. A related 

problem could also be when there is a tendency to withdraw the auger too rapidly in relation to 

the grout volume supplied. 

In order to verify the volume and pressure of grout delivered to the pile, it is necessary that 

instrumentation be provided to monitor the grouting operations. Two methods are available for 

real-time monitoring of grout/concrete volume during installation: stroke count and in-line 

flowmeter. The simplest of these two methods is to count the strokes from the pump, which can 

be automated by using the pressure sensor or a proximity switch. In this method, the cumulative 

volume is determined by multiplying the number of strokes by an estimated volume of 

grout/concrete delivered per stroke. Volume estimation by counting strokes suffers from the 

inaccuracy of assuming a constant volume per stroke, and possibly due to variations in the 

efficiency of the ball-valves sealing off against the seats. Sometimes, the pump strokes are 

inconsistent and the volume delivered per stroke can vary. The automated stroke counter can 

49 
miss strokes or count erratic behavior as multiple strokes. The volume pumped per stroke can 

also vary with the pressure against which the pump is operating, and can vary with time for other 

reasons. With the introduction of modern sensors and monitoring equipment, stroke counting is 

now considered a poor quality control practice. 

(a) Trucks Discharging into Pump (b) Close up View of Grout Pump 

(c) Concrete Pump Mounted on Rig (d) Pump with Rotating Drum On-Site 

Figure 4.19: Typical Concrete/Grout Pumps 

The second and preferred method to monitor volume is to use an in-line magnetic flowmeter, 

shown in Figure 4.20. This device provides a more accurate and reliable indication of the actual 

volume delivered. Flowmeters work by placing a magnetic field around a tube such that the 

conductive medium moving through the tube induces a voltage in the medium. The voltage of 

the medium is proportional to the average flow velocity. The flowmeter thus makes a voltage 

measurement that is proportional to the average velocity of the grout flowing through it; this 

average velocity can be converted to volume using the known cross-sectional area of flow. The 

flowmeter is sensitive only to conductivity of the grout and is independent of density or 

viscosity. The interior of the tube is generally lined with a ceramic material for durability. 

50 
Figure 4.20: In-Line Flowmeter 

A pressure sensor should be mounted in-line to provide a real-time monitor of the pressure being 

delivered to the auger and to ensure that positive grout pressure is maintained in the hole as it is 

being filled. The best place for this sensor would obviously be at the base of the auger, as shown 

in Figure 4.21. This instrument provides a measure of grout pressure inside the auger about 1 m 

(3 ft) above the tip. The system requires an interior mount and a cable extending up through the 

auger and through a slide ring body at the swivel atop the auger. At present, the “in-auger” 

pressure sensors have been difficult to maintain and therefore are not widely used. 

A more common location for measuring pressure is in the line just above the swivel on top of the 

auger string. If the line is completely filled, the pressure at the auger tip should differ by the 

difference in head from the top to bottom, minus a small loss due to flow in the lines. Pressure 

measurements in the line farther away from the auger can be affected by losses between the 

measurement location and the auger, and thus it is preferred that the pressure measurements be 

made as near to the auger as possible. 

The minimum pressure during all grouting operations should be displayed in real-time for 

operator control and inspector observation. This information can be used to immediately correct 

areas of the pile where the pressure has dropped due to grout contamination with soil or other 

problems. These readings should also be recorded for quality control documentation. 

4.2.3.3 Finishing the Top of the Pile 

After the grout placement is complete and the auger is withdrawn, the workers must finish the 

top of the pile prior to reinforcement placement. A recommended procedure is to place a small 

form or casing around the top of the pile to prevent fall-in from surrounding soil. Sheet metal 

ductwork or prefabricated column forms are often used for this purpose, as shown in Figure 4.22. 

While not all contractors use this technique in private contracts, the use of the top form to 

prevent fall-in is required in public projects. Besides the use of the top form, it is also necessary 

to scoop the grout or shovel out the contaminated uppermost portion of grout. The workman in 

Figure 4.22c is using a folding circular screen to remove soil contamination from the fluid grout. 

51 
Source: Bauer Maschinen 

Figure 4.21: Sensor for Concrete Pressure at Auger Tip 

 

4.3 CONSTRUCTION MATERIALS 

The component materials of a CFA pile consist of grout/concrete and reinforcing steel. 

4.3.1 Grout and Concrete 

Both grout and concrete have been successfully used for the construction of CFA piles. Concrete 

used for CFA piles is very similar to the concrete used for wet-hole placement in drilled shafts. 

Grout used for CFA piles is similar to concrete except that the grout mix contains only sand, not 

coarse aggregate. While the grout used for pressure-grouting applications in some types of 

micropiles and other grouting applications is often a mixture of only cement and water; such 

thin, fluid grouts are not used for CFA piles. Both grout and concrete mixes typically contain a 

mixture of Portland cement, fly ash, water, aggregate (fine aggregate only for grout) and 

admixtures. Water reducers are typically added to concrete mixes, and fluidifiers have been 

developed to overcome problems associated with grout placement. Retarders are often added to 

grout or concrete mixes to increase grout flowability or extend the slump loss time of concrete. 

Regardless of whether grout or concrete is used, the mix must be made such that all solids 

remain in suspension without excessive bleed-water. Additionally, the mix must be capable of: 

52 
(1) being pumped without difficulty; (2) penetrating and filling open voids in the adjacent soil; 

and (3) allowing for insertion of the steel reinforcement. 

 

(a) Spoil Removal (b) Clearing Top of Pile and 

Form Placement 

(c) and (d) Contaminated Grout Removal 

Figure 4.22: Completion of Pile Top Prior to Installation of Reinforcement 

While some contractors and engineers have personal preferences for either grout or concrete, 

both have been used successfully in CFA pile applications. In general, the perceived advantages 

and disadvantages of grout relative to concrete may be summarized as follows. 

Advantages: 

•	 Grout mixes are sometimes preferred for easier insertion of steel reinforcement into the 

pile; 

•	 Grout mixes tend to be more fluid and have greater workability; and 

•	 Grout mixes tend to be easier to pump, and many contractors, who have historically used 

grout mixes, have grout pumps and equipment that may not be suitable for use with 

concrete. 

53 
Disadvantages: 

•	 Grout will generally have a higher unit cost than concrete; 

•	 Grout will tend to have a slightly lower elastic modulus than concrete; and 

•	 Grout will tend to be less stable within the hole when drilling through extremely soft soils 

(such as organic clays or silt). 

Grout mixes will tend to be more susceptible to small variations in water content which could 

lead to segregation or excessive bleed water. In general, any mix (concrete or grout) having 

extremely high workability requires greater attentiveness to quality control both at the batch 

plant and at the project site. 

DD piles may induce excess pore water pressures in the surrounding soil that could result in 

water intrusion into a newly constructed pile as the excess pore pressure dissipates. Grout may 

be more susceptible to this effect than concrete. Special fluidifiers are often added to grout 

mixes to counteract these effects, as will be described in Section 4.3.6. 

A grout mix will have a slightly lower elastic modulus than a comparable concrete mix at the 

same compressive strength. While a lower elastic modulus may be of concern in structural 

applications where deflections control the design, it would typically have a relatively small effect 

on the load/settlement characteristics of CFA piles. The elastic shortening of a pile is 

proportional to the modulus of the grout/concrete pile. As CFA piles are relatively short, the 

load/settlement characteristics are predominantly controlled by the interaction between the pile 

and surrounding soil, regardless of whether grout or concrete is used. 

Figure 4.23: Sand-Cement Grout Mixes
	

54 
A study at the University of Houston (O’Neill et al., 1999) compared the chemical resistance of 

auger grout (i.e., grout steel in CFA piles) and conventional Portland cement concrete to 

solutions of acid, sodium sulfate (Na2SO4), and sodium chloride (NaCl). The researchers tested 

samples in chemical solutions over a period of two years and determined the following: 

•	 The grout gained over 3% weight in a solution with 2% of sodium over 2 years. 

By contrast, the concrete gained about 1% in 500 days. 

•	 The sulfate solutions produced a 2% weight loss in a period of 180 to 270 days in the 

auger grout. The concrete had a weight loss of 0.2 to 0.3% in 500 days, indicating a 

faster degradation of auger grout in a sulfate environment. 

•	 Leaching of calcium in sulfates was about five times higher in auger grout than in 

concrete. 

•	 Sulfates produced a slightly increased degradation in pulse velocity in auger grout 

compared to cement concrete. 

•	 There was a notable decrease in compressive strength in auger grouts immersed in 

hydrochloric acid (pH = 2 to 4) or sulfate solutions. Sulfuric acid (H2SO4) at pH = 4 and 

5 parts per million (ppm) of sulfate had minimal effect on the grout and concrete. 

Based on this study, it can be expected that auger grouts will not perform as well as normal 

Portland cement concrete in aggressive soil environments that contain sulfates and acids. 

The following sections describe the components of grout and concrete used for CFA piles. 

4.3.1.1 Cement 

Ordinary Type I or Type I/II Portland cement can normally be used in grout/concrete for CFA 

piles. The cement should meet the requirements of ASTM C 150 or AASHTO M85. Special 

sulfate resistant cements should be considered in environments where the sulfate content of the 

geo-material or groundwater is extremely high. 

4.3.1.2 Pozzolanic Additives 

Both grout and concrete mixes may contain pozzolanic additives. The most commonly used is 

fly ash (ASTM C 618-94 1995); however, finely ground silica fume and blast furnace slag 

(ASTM 989-94 1995) can also be used. The use of pozzolanic additives results in lower 

permeability of the hardened concrete and tends to retard the set time of the cement paste, 

thereby increasing the time that the grout/concrete remains workable. As a consequence of 

providing a more workable mix, the use of fly ash, silica fume, and/or slag will probably 

severely retard the early strength gain of the grout mix, typically until about 10 to 14 days of age. 

If these additives are to be used in the mix, the submitted mix design should include information 

on strength development vs. time so that the design engineer is informed of the delay in strength 

gain corresponding to the mix and make any adjustments, if necessary. 

55 
Fly ash is now widely available in most areas of the United States as a by-product of burning 

coals. ACI 232.2R-96 of the American Concrete Institute (ACI, 2006) provides an excellent 

overview of the use of fly ash in concrete. ASTM C 618 categorizes ash by chemical 

composition. Class C and Class F ashes are most commonly used in concrete and grout mixes. 

As a group, these ashes tend to show different performance characteristics. However, there are 

important differences in fly ash from different sources and the performance of a fly ash is not 

determined solely by its classification as either Class C or Class F. For instance, problems have 

been reported in some cases when power companies turn to scrubber systems to remove sulfur 

dioxide from stack gasses. This occurs when fly ashes are mixed with scrubber products and 

contain free lime and calcium sulfates or sulfites (see p. 95 in Mindess et al., 2003). The mix 

design for CFA piles should be developed specifically for a project site using locally available 

materials. 

4.3.1.3 Water 

Water used for mixing the grout/concrete should be potable (free of organic contamination and 

deleterious material) and should have low chloride and sulfate contents. 

4.3.1.4 Aggregate 

All aggregate should meet the appropriate specifications. Some of the relevant ASTM 

specifications for aggregate are: ASTM C 33-93, Specification for Concrete Aggregate; ASTM 

C 87-90, Test for Effect of Organic Impurities in Fine Aggregate on Strength of Mortar; and 

ASTM C 227-90, ASTM C 289-94, ASTM C 295-90, ASTM C 586-92, all of which address 

tests that measure the alkali susceptibility of aggregates. 

In general, rounded gravel is strongly preferred over crushed stone due to the benefits in terms of 

workability of the mix for pumping and placement. Aggregate gradation will depend upon the 

specific mix design requirements. Concrete mixes having extremely high workability will tend 

to require a greater ratio of fine to coarse aggregate to minimize the tendency for segregation and 

bleeding. 

4.3.1.5 Fluidifiers for Grout and Water Reducing Admixtures for Concrete 

Both low-range and high-range (i.e., superplasticizer) water reducing admixtures have routinely 

been used in concrete mix designs for drilled shafts. ASTM C 494 is a performance 

specification that classifies an admixture as water-reducing if it reduces the water requirements 

by 5%. Thus both low-range and high-range water reducers are specified by ASTM C 494. 

High-range water reducers may also be conveniently specified by requiring that the performance 

specification ASTM C 1017 also be met, as this specification requires that an increase in slump 

of 90 mm (3.5 in.) or greater be obtained. For low-range water reducers, admixture Type D (per 

ASTM C 494) is preferred for piles over admixture Type A to provide some retarding properties 

and reduce slump loss. Similarly, for high-range water reducers (superplasticizers), admixture 

Type G is often preferred over admixture Type F to reduce slump loss, but the newer 

polycarboxylate-based superplasticizers are designed to maintain a high slump for extended 

periods. 

56 
Low-range water reducers can be used to obtain water/cement ratios in the range of 0.40 to 0.45, 

and can consist of lignosulfonates, hydroxylated carboxylic acids, and similar compounds (see 

ASTM C 494). High-range water reducers can be used to obtain water/cement ratios of 0.3 or 

lower while maintaining a high slump (see ASTM C1017). Many of the older naphthalene-based 

superplasticizers had a tendency for rapid slump loss, could even result in a flash set, and thus 

were very risky to use for cast-in-place deep foundations. However, many of the modern 

superplasticizer products are polycarboxylate compounds that lose their effectiveness much 

slower and are very useful for drilled shafts and CFA piles. These products also act as a mild 

retarder. It is important to note that high-slump concrete mixes must be designed carefully to 

avoid problems of segregation and bleeding. Water reducers can be very effective at reducing 

the water/cement ratio for a given workability requirement and thus reducing the tendency for 

segregation and bleeding in the mix. 

Grout fluidifiers have been developed for intrusion grout mixtures to offset the effects of 

bleeding, reduce the water/cement ratio while providing a desired consistency, and retard 

stiffening so that handling times may be extended. A grout fluidifier may be specified by 

meeting the requirements of ASTM C937. Grout fluidifiers typically contain a water reducing 

admixture, a suspending agent, aluminum powder, and a chemical buffer to assure timed reaction 

of the aluminum powder with the alkalies in the Portland cement. 

4.3.1.6 Retarders 

Retarders [described in ASTM C494-92 (ASTM, 2006)] consist of lignosulfonic acids, 

hydroxycarboxylic acids, sugars, and phosphates. Many of these possess water-reducing 

capabilities and can be classified as water-reducing, set-retarding admixtures [Type D in ASTM 

C494 (ASTM, 2006)]. Retarding admixtures may be needed in the grout/concrete mix when it is 

placed during periods of high temperature [> 20o C (68o F)] to reduce the slump loss in the 

period during which the grout/concrete is placed. Some types of retarders slow down the rate of 

early hydration of cement, but hydration proceeds normally after the effect is overcome. Some 

inorganic retarders are more complex and can form coatings around the cement particles that 

severely reduce the rate of reaction. Thus, retarders can slow the rate of early strength 

development. The strength should approach that of unretarded concrete within eight days, unless 

an overdose has been used. Overdosing the mix with retarder can prevent set entirely. 

4.3.1.7 Air Entraining Agents 

Air entraining agents (ASTM C 260-94, 1995) can be used when deterioration of the 

grout/concrete by freeze-thaw action is possible. Entrained air will also improve workability and 

pumpability and reduce bleeding. However, it can produce a slightly more permeable 

grout/concrete and thus be more susceptible to deterioration due to a chemical attack (e.g., 

chlorides). When air is added, about 5% is needed to improve pumpability. Because air tends to 

be lost during the mixing, pumping, and placement processes, much of the entrained air is likely 

to be lost by diffusion by the time the grout/concrete begins to set. 

57 
4.3.1.8 Sampling and Testing 

Representative samples of grout and concrete mixes must be obtained at the project site for 

QA/QC testing, as described in greater detail in Chapter 7. The three parameters most typically 

measured are temperature, workability, and strength. Workability is measured using slump 

testing for concrete and flow cone testing for grout. Strength testing is performed in a laboratory 

after curing samples from the field. 

Typical strength requirements for CFA piles are 27.6 to 34.5 MPa (4,000 to 5,000 psi). Strength 

testing of concrete utilizes conventional 150-mm (6-in.) diameter cylinders. For the sand-cement 

grout often used with CFA piles, some engineers use small cylinders 50 or 75 mm (2 or 3 in.) in 

diameter, but most use 50-mm (2-in.) cubes. There is not a consensus at present on which 

method is preferred, but the cubes are easier to prepare and transport. The compressive strength 

of properly prepared and tested cubes are slightly higher than that of cylinders with a height to 

diameter ratio of 2, so the strength requirement from tests on cubes is typically 10% higher than 

that of cylinders. 

The ideal location and time to obtain samples for testing would be at the point of discharge into 

the soil and after the mix has been pumped through the lines and the auger, as the properties 

(particularly workability) can be altered by pumping extended distances, especially in hot 

weather. However, this location is generally not possible, therefore, samples are typically 

obtained from the discharge location into the pump hopper. Workability and temperature should 

be checked on every truck as a means of verifying consistency of the mix. Because the 

grout/concrete must be placed immediately when the auger achieves the tip elevation, the 

sampling and inspection must be expeditious. 

Slump ranges for concrete for CFA piles should typically be 200 mm +/- 25 mm (8 in. +/- 1 in.), 

similar to that used for drilled shafts constructed using the wet method. Workability of grout is 

tested using a flow cone instead of the conventional slump test used for concrete. Standards 

ASTM C939 and U. S. Army Corps of Engineers CRD-C 611-94 provide specifications for flow 

cone testing in which fluid consistency is described according to an efflux time per standard 

volume. Because the grout mixes used for CFA piles are typically too thick to flow effectively 

from the standard 12 mm (0.5 in.) outlet specified in these standards, it is common practice to 

modify the above specs to provide a 19 mm (0.75 in.) opening. This modification can be made 

by taking out the removable orifice that extends out the bottom of the Corps of Engineers device 

to leave a 19 mm (0.75 in.) opening or to cut the flow cone specified in the ASTM standard to 

modify the outlet diameter. Grouts suitable for CFA pile construction typically have a fluid 

consistency represented by an efflux time of 10 to 25 seconds, when tested in accordance with 

the modifications described above. 

Most standard mix designs will maintain workability for a period of up to 2 hours without any 

additional retarding admixtures (other than the typical grout fluidifier), if agitated continuously 

in the ready-mix truck. Flow cone or slump tests should be performed on site at the time of 

placement to ensure grout/concrete workability over time. If a project has an unusual concern 

for a lengthy time for rebar cage placement or a great depth, additional retarding admixtures may 

58 
 

be used to extend the slump or flow life. Flow cone or slump tests at the time corresponding to 

rebar cage placement may be used to evaluate the workability associated with the mix at this 

critical time. 

Grout or concrete should not be placed when its temperature falls below 4°C (40° F) or exceeds 

38°C (100° F), unless approved procedures for cold or hot weather grouting are followed. 

4.3.2 Reinforcing Steel 

4.3.2.1 Reinforcing Steel Materials 

Reinforcing bars for CFA piles typically consist of ASTM A615 Grade 60 steel, the same as 

those used for drilled shaft construction. Occasionally, CFA piles may be reinforced with 

high-strength threaded bars meeting ASTM A722 (1,035 or 1,100 MPa [150 or 160 ksi]). The 

high-strength bars are normally used where large tensile loads are to be supported. Transverse 

steel may consist of either circular ties or spirals. Steel pipe may be used in cases where large 

bending stresses may occur, such as in a wall. Steel pipe used in CFA piles is steel ASTM A572, 

Grade 50 having a nominal minimal yield strength of 350 MPa (50 ksi) or ASTM A252, Grade 

2, nominal minimal yield strength of 420 MPa (60 ksi or Grade 60). In the case of steel pipes, 

the CFA pile is really designed as a concrete- or grout-filled steel element rather than a 

reinforced concrete member; guidelines suitable for micropile design would be appropriate in 

this case. 

4.3.2.2 Reinforcing Cage/Section 

Reinforcing cages should be fabricated so that lifting and handling does not cause permanent 

distortion or racking. For this reason, it is important that wire ties be used on all longitudinal 

bars at every tie or spiral. Welding is only permitted if weldable reinforcement is specified (see 

Figure 4.24). The use of weldable reinforcement is rare in U.S. practice, but can assist in 

handling the cage with a minimum of distortion. Spliced steel cages and/or coupled threaded 

bars are often necessary to install reinforcement in low headroom applications. 

Where bending stresses are potentially high as in the case for a pile wall or slope stabilization 

scheme, it is possible to construct CFA piles using structural steel sections for reinforcement. 

Figure 4.25 illustrates the use of a steel pipe section within a CFA pile to provide flexural 

strength in a tangent pile wall application. 

Reinforcement cages are normally specified with 75 mm (3 in.) clear cover to the outside of the 

pile. Plastic or cementitious spacers should be placed at intervals of no more than about 3 m 

(10 ft) along the cage to provide cover. Spacers made of steel should not be permitted as they 

may greatly accelerate corrosion of the reinforcing steel, particularly above the groundwater 

table. Centering guides made of steel, such as a wire “basket” or “football” tied at the base of 

single-rod reinforcement may be used. A reinforcing cage may be tied together at the bottom to 

create a “point” to facilitate installation into the pile. If CFA piles are used on a batter, special 

provisions may be necessary to maintain cover. For the project illustrated in Figure 4.26, a 

59 
continuous PVC pipe was used on the bottom side of the cage to maintain cover and act as a 

“runner” to slide the reinforcement cage into position within the grouted pile. 

Figure 4.24: Machine-Welded Reinforcement Cage on Project Site in Germany 

Figure 4.25: Use of Steel Pipe to Reinforce a CFA Pile for a Wall 

60 
Figure 4.26: Installation of Reinforcement Cage into Battered CFA Pile 

Where a single bar is used for tensile reinforcement, centralizers are used at spacing of no more 

than 3 m (10 ft). Some rigs are equipped to install a center bar through the hollow auger prior to 

placement of grout/concrete. These bars cannot be used with a centralizer because the 

centralizer cannot fit through the auger stem while attached to the bar. Splices may sometimes 

be used with CFA piles, but it is better to avoid the use of splices. Splices are common for piles 

supporting tensile forces or for piles reinforced with a single full-length center bar. Mechanical 

splices are preferred in such cases, and high-strength threaded bars are convenient for this 

purpose. 

4.4 SUMMARY OF RECOMMENDED PRACTICES 

This chapter describes equipment, techniques, and materials used to construct CFA piles. 

A wide variety of techniques and equipment have been used to construct these piles. Several 

parameters are summarized below that are key components of good quality construction. The 

specifications section of this document (Chapter 8) provides detailed guidelines. 

•	 Drilling Rigs. The rig must have adequate torque capacity to install the pile without 

excessive flighting of the soil during drilling. While specs may include a minimum torque 

provision, it seems most prudent to set as a performance requirement that the contractor 

provide a rig capable of doing the project. The torque and power of the rig will directly 

affect the depth to which piles can be installed and the resulting axial capacity that can be 

achieved. 

61 
•	 Drilling. In order to avoid excessive flighting and to construct piles of consistent quality 

and axial capacity, target penetration rates must be established and maintained during 

drilling of CFA piles. It is essential that this parameter be controlled by the rig operator 

and monitored for verification. Automated monitoring systems must be used to provide 

direct feedback to the operator and verification of performance. Details of monitoring 

systems will be described in Chapter 7. It is essential that the installation method used for 

construction of production piles be consistent with that used for construction of load test 

(control) piles. 

•	 Cementitious Materials. Either grout or concrete may be used for construction of CFA 

piles. Each has relative advantages under different circumstances. In general it is 

recommended that: (1) the specifications for grout/concrete materials be performancebased verified using strength tests on either cubes or cylinders; and (2) testing for 

workability and mix temperature be routinely performed on each truck as a means of 

monitoring consistency. Mix proportions and characteristics should be established based 

on test piles or control piles and maintained at a consistent quality throughout the project. 

Workability of concrete is monitored using slump tests. Workability of grout is monitored 

using flow cone tests with a modified opening enlarged to 19 mm (0.75 in.). Workability 

of the mix must be maintained for the entire duration of pile construction, including rebar 

installation into the pile. Slump or flow cone tests should be performed at times 

corresponding to rebar cage installation. 

•	 Placement of Grout or Concrete. Placement of grout or concrete through the auger is a 

critical part of the operation and must be monitored using automated systems to ensure 

that adequate volumes are pumped at a positive pressure at all times as auger withdrawal 

is in progress. Slow, steady pulling of the auger at a rate appropriate for the delivery from 

the pump is essential. Some contractors prefer to use a static pull of the auger and some 

prefer a very slow rotation in the direction of drilling. It appears that both methods can be 

used successfully. The auger should never be allowed to turn in place without either 

drilling or pumping taking place. The systems utilizing automated monitoring of volume 

and pressure delivered to the pile as a function of auger tip elevation are the most effective 

to obtain consistent quality and verification. In-line flow meters are the preferred means 

of monitoring volume of grout/concrete over stroke counters. 

•	 Completion of the Pile Top. It is essential that the contractor continue to deliver the 

appropriate volume of grout/concrete to the pile when the auger is close to the surface and 

significant positive pressure can no longer be maintained. The completion of the pile top 

requires manual work to remove any debris or contaminated grout/concrete near the top of 

the pile before reinforcement is placed into the fluid grout/concrete. The use of a small 

form at the pile top extending above grade is recommended to maintain a sound surface. 

If below-grade cutoff is required, it is necessary to complete the pile to grade and then 

chip or cut the top down later. It is necessary to flush the grout/concrete to the surface of 

the working platform to remove any questionable or contaminated material. 

62 
•	 Reinforcement. Installation of reinforcement requires that the grout/concrete mix retain 

adequate workability for the time necessary to install the cage after removal of the auger 

and clearing the top of the pile. The mix requirements with respect to this aspect of the 

work can vary with differing soil conditions, particularly with respect to the tendency of 

dry sandy soils to rapidly dewater the pile. The mix should be developed to demonstrate 

that workability is maintained within the slump or flow cone guidelines for the entire 

duration of time required for drilling and grouting the pile and placing the rebar cage. In 

addition, other measures such as anti-washout admixtures may be required if soil 

conditions cause excessive dewatering of the mix after casting that results in rebar 

installation difficulties. Designers should include reinforcement cages that use: (1) fewer 

heavy bars instead of many smaller bars; (2) are no longer than the minimum necessary to 

provide structural capacity and anchorage; and (3) allow the cage installation proceed with 

minimum difficulty. The contractor should tie the cage to permit handling without 

permanent distortion. 

•	 Installation Plan. The contractor should submit an installation plan including details of 

the equipment and methods proposed for the project. Many aspects of the construction 

work are performance-oriented with respect to the contractor’s equipment requirements 

and methodology. The installation details and monitoring of the installation are key 

components of verifying that the performance requirements are met. Contractors should 

be held accountable for developing an installation plan that will achieve the required 

objective. 

•	 Test Piles and Test Installations. The recommended means of verifying that the 

installation plan will achieve the project requirements is using a carefully monitored test 

pile program. The program should consist of pre-production static load tests, production 

static and/or rapid and/or dynamic load tests, and post-installation integrity tests in 

sufficient quantities to provide the data necessary to demonstrate that the installed piles 

meet the load and deflection criteria established in the project plans with an appropriate 

factor of safety. It is imperative that the demonstrated installation procedure be followed 

for all production pile installations. 

63 
CHAPTER 5 EVALUATION OF STATIC CAPACITY OF 

CONTINUOUS FLIGHT AUGERED PILES 

5.1 INTRODUCTION 

In many respects, the static capacity of a well-constructed continuous flight auger (CFA) pile can 

be considered to fall between that of a drilled shaft and a driven pile. This concept is primarily 

attributed to different changes in lateral stress during the installation of the various pile types. 

During construction of a drilled shaft, the soil stress tends to reduce or remain unchanged in the 

vicinity of the pile excavation. During installation of a driven pile, the pile driving process 

displaces the soil laterally and increases the stresses in the surrounding soil. In the case of 

conventional CFA pile construction, the stresses in the soil tend to remain near the preconstruction stress values (similar to a drilled shaft), while the construction of drilled 

displacement (DD) piles tend to increase the stresses in the surrounding soil (similar to driven 

piles). 

It is reasonable to estimate static capacity of CFA piles using methods developed specifically for 

driven piles and drilled shafts, because the load-settlement behavior of CFA piles are similar. 

Some methods, however, have been developed specifically for CFA piles, and usually take the 

form of modifications made to methods previously developed for drilled shafts or driven piles. 

For these methods, measured pile capacity (via full-scale load-testing) of CFA piles has also 

been correlated to parameters including, SPT blowcount, CPT cone penetration tip resistance, 

and soil undrained shear strength. 

This chapter provides specific methods of estimating static axial capacity for different soil types 

and type of strength data. Four comparison studies are available in which several prediction 

methods were compared to various CFA load-test databases. The methods presented in Section 

5.2 were chosen as those that appeared to generally provide reliable and accurate results for 

conventional CFA piles according to the four studies. Appendix A contains a summary of other 

analysis methods of estimating static axial capacity of CFA piles that are currently or have 

traditionally been used in the United States and abroad, and a summary of the four comparison 

studies to asses the adequacy of various methods. Section 5.3 presents a method for DD piles. 

This chapter also presents information on pile group behavior, settlement, and lateral load 

capacity; this information is also used in Chapter 6 to present a recommended design procedure 

for CFA piles. 

It should be noted that computations of static axial resistance should be considered as estimates 

to be validated and/or modified on a project-specific basis using the results of load-tests. The 

guide specification provided in Chapter 8 is written as a performance-based specification, in 

which the contractor is responsible to compute static resistance, set pile length requirements for a 

given design axial loading, and verify that the performance requirements are achieved via the use 

of load-tests. 

64 
5.2 DEVELOPMENT OF SIDE-SHEAR AND END-BEARING RESISTANCE WITH 

PILE DISPLACEMENT 

Similar to other types of deep foundations, the total axial compressive resistance (RT) of a CFA 

pile is calculated as the combination of the side-shear resistance (RS), and end-bearing resistance 

(RB): 

R T = R	 S + R B (Equation 5.1)

To calculate the total side-shear resistance, the pile length must first be divided into N pile 

segments. The side resistance of a particular pile segment “i” (of length Li, and diameter, Di) is 

obtained by multiplying the unit side-shear resistance (fs,i sometimes referred to as load or 

transfer rate) of the segment by the surface area of the pile segment (π Di Li). The total sideshear resistance is obtained by adding the contribution of all N pile segments as: 

N 

R = ∑ fs,i π Di Li (Equation 5.2) s i 

Some of the methods presented in this chapter and Appendix A use an average unit side-shear 

(fs-ave) for the entire pile length, instead of summing individual pile segments. In these cases, the 

total side-shear resistance is calculated as: 

R S = f s-ave π D L	 (Equation 5.3)

where D is the average diameter of the pile, and L is the pile total embedment length. 

The total end-bearing resistance (RB) is calculated as: 

⎛π D2 ⎞ R = B

B qp ⎜

⎜ ⎟⎟

	 (Equation 5.4)

⎝ 4 ⎠

where qp is the unit end-bearing resistance, and DB is the diameter of the pile at the base. 

The side-shear component is mobilized with relatively small pile vertical displacements relative 

to the surrounding soil, typically less than 10 mm (0.4 in.). The end-bearing component is fully 

mobilized with larger displacements, typically at a pile tip movement in the range of 5% to 10% 

of the pile diameter. Driven piles of comparable axial resistance are likely to mobilize the tip 

resistance at a smaller vertical displacement due to the inherent preloading at the tip that occurs 

during installation. Consequently, the load-settlement curve from a load-test of a CFA pile may 

appear somewhat softer than that of a typical driven pile and methods used to interpret ultimate 

load resistance from load-tests on driven piles could be conservative for CFA piles. 

65 
The mobilized side- and end-bearing resistances can be assessed using Figure 5.1, which is based 

on a study by Reese and O’Neill (1988) for drilled shafts. The CFA pile resistance at any 

desired displacement (expressed as a ratio to the diameter) may be obtained from the calculated 

ultimate resistance for that CFA pile multiplied by the normalized resistance at comparable 

displacement ratio given in the figure. Reese and O’Neill (1988), AASHTO (2006), and others 

consider the ultimate end-bearing capacity to be mobilized at a tip displacement equal to 5% of 

the pile diameter. Many studies of CFA pile resistance use a similar definition and the methods 

presented in this document are also based on the ultimate end-bearing capacity defined at a pile 

tip displacement equal to 5% of the pile diameter, unless otherwise noted. 

Elastic compression of the pile under load can have a small effect on the distribution of 

displacement of the pile relative to the surrounding soil. However, the elastic compression is 

relatively small for the pile lengths and load levels that are typical of CFA piles, and can often be 

disregarded. For instance, consider a load of 445 kN (100 kip) acting on a pile 450 mm (18 in.) 

in diameter and 25 m (82 ft) long, and a pile elastic modulus (E) of 27,500 MPa (4,000 ksi). If 

half of the load goes to the tip and the side-shear is evenly distributed along the pile length, the 

average load in the pile would be 0.75 of the load, or 334 kN (75 kips) and the elastic shortening 

would be 334 kN × 25 m / (ApileE) = 2 mm (0.08 in.), where Apile is the cross-sectional area of the 

pile. Details of the calculation of the elastic compression of a pile are presented in Section 

5.5.3.1. 

5.3 RECOMMENDED METHODS FOR ESTIMATING STATIC AXIAL 

CAPACITY OF CFA PILES 

The recommended methods presented for estimation of static axial capacity of single CFA piles 

assume that a conventional continuous flight auger construction technique will be employed, and 

construction practices and quality assurance procedures consistent with those recommended 

herein are adhered to such extent that excessive flighting of soil and ground loosening is avoided. 

The use of high-displacement auger cast piles (DD piles) and/or the use of amelioration 

(introduction of coarse sand or gravel from the ground surface down into the annular area 

between the borehole wall and the drill stem) could significantly increase the pile capacity, and is 

discussed subsequently in Section 5.4. 

Recommended design procedures are broadly organized by soil type as either cohesive or 

cohesionless in the subsections that follow. Note that silty soils require judgment on the part of 

the engineer to evaluate the most reasonable approach to use. In general, these fine-grained soils 

should be classified in response to the anticipated behavior under the load being considered, as to 

whether the soil is likely to behave more nearly in an undrained or fully drained manner. 

Depending on this clarification, methods for either cohesive of cohesionless soils must be used. 

Recommendations are further categorized by the available type of in-situ or laboratory test data. 

Appendix A summarizes results from comparison studies of different procedures, and provides 

the basis by which the recommended methods were chosen. Appendix A also summarizes other 

methods used to predict CFA pile capacities. 

66 
 

(a) Normalized Load Transfer in Side-Shear (b) Normalized End-Bearing Capacity 

vs. Settlement in Cohesive Soils vs. Settlement in Cohesive Soils 

 

 

(c) Normalized Load Transfer in Side-Shear d) Normalized End-Bearing 

vs. Settlement in Cohesive Soils vs. Settlement in Cohesive Soils 

Source: Reese and O’Neill (1988) 

Figure 5.1: Load-Displacement Relationships 

The design procedures recommended in the following subsections appear to provide good 

correlations to CFA pile capacity for generalized soil types across the broad scope of North 

67 
American practice. The design engineer should consider the specific soil composition and 

construction techniques to be used at their particular site and experience within the local area or 

geology. The design engineer is encouraged to investigate the formulation of alternative design 

procedures in order to identify documented procedures that have a basis that may more closely 

match the specific conditions of their site. While the estimates of capacity derived from static 

analyses are useful for preliminary design, it must also be emphasized that a well designed loadtesting program is a critical and necessary component for the effective use of CFA piles. 

5.3.1 Cohesive Soils 

5.3.1.1 Recommended Method for Side-Shear and End-Bearing Estimates Using Undrained 

Shear Strength 

The FHWA 1999 method for drilled shafts is recommended for prediction of both the side-shear 

and end-bearing resistances for CFA piles in cohesive materials. The FHWA 1999 method was 

originally proposed by Reese and O’Neill (1988) and later modified by O’Neill and Reese 

(1999). 

For a given pile segment, the ultimate unit side-shear resistance (fs) is calculated as: 

fs = α Su	 

 (Equation 5.5)

where Su is the undrained shear strength of the soil at the pile segment location, and α is a 

reduction factor that varies as follows: 

α = 0.55 for Su /Pa ≤ 1.5 (Equation 5.6) 

where Pa is the standard atmospheric pressure (equal to 1 atm or approximately equal to 101 kPa 

[1.06 ton per square foot or tsf]), for 1.5 < Su/Pa ≤ 2.5, α varies linearly from 0.55 to 0.45. 

If the bottom of the pile is bearing on clay, the side-shear contribution to the capacity of the 

bottom one-diameter length of the pile is neglected. If the top layer is clayey, there exists the 

potential for this soil to shrink away from the top of the pile when exposed to the atmosphere. If 

such a condition is suspected, then the side-shear contribution from this layer should be 

neglected in the greater of either the top 1.5 m (5 ft) of soil or the depth of seasonal moisture 

change. 

In the FHWA 1999 method, the ultimate unit end-bearing resistance (qp) is calculated as: 

q = N *	 S (Equation 5.7) p c u 

where Su is the average undrained shear strength of the soil between the pile tip and two-pile 

diameters below the pile tip, and N *

c is the bearing capacity factor. The value of N *c is adopted 

as follows: 

Nc 

* = 9	 (Equation 5.8)

68 
for 200 kPa (2 tsf) ≤ Su ≤ 250 kPa (2.6 tsf), and L ≥ 3D, or 

* Nc = 4 [ ln Ir +1] (Equation 5.9) 3 

for Su < 200 kPa (2 tsf), and L ≥ 3D. 

where L is the pile embedment length below top of grade, and Ir is the rigidity index. 

Note that values of Su greater than 250 kPa (2.6 tsf) are treated as intermediate geo-materials in 

accordance with O’Neill and Reese (1999). The rigidity index (Ir) is calculated as follows: 

ES Ir = 3S (Equation 5.10)

u 

where Su and the undrained Young’s modulus (ES) are those of the soil just below the pile tip. ES 

is best determined from triaxial testing or in-situ testing (such as the pressuremeter test). If ES is 

not measured, it can be assumed with less accuracy to be a function of Su for design purposes by 

interpolating between the values given in Table 5.1 below. 

Table 5.1: Relationship between Undrained Shear Strength, Rigidity Index, and Bearing 

Capacity Factor for Cohesive Soils for FHWA 1999 Method 

Source: O’Neill and Reese (1999) 

Su Ir = Es/(3Su) N* 

c 

25 kPa (0.25 tsf) 50 6.5 

50 kPa (0.50 tsf) 150 8.0 

100 kPa (1.00 tsf) 250 8.7 

200 kPa (2.00 tsf) 300 8.9 

2 ⎡ 1 L ⎤

q = 1 + N * 

p ⎢ ⎥ S for L < 3D (Equation 5.11) 3 ⎣ 6 D ⎦ c u

Although not expected to occur for CFA piles, if the pile embedment length below grade were to 

be less than three pile diameters, the ultimate unit end-bearing resistance (qp) should be reduced 

according to the FHWA 1999 method, as follows: 

5.3.1.2 Alternative Methods for Side-Shear Estimates Using Undrained Shear Strength 

The Coleman and Arcement (2002) method was derived from CFA pile load-tests conducted in 

mixed soil conditions consisting of mostly alluvial and loessial deposits, and interbedded sands 

and clays in Mississippi and Louisiana. Section A.2.10 of Appendix A contains further details of 

the test program. The method may be considered as an alternative for soils of similar geology 

and properties as described in Appendix A and below. This method provides modifications to 

the α factor for clays and silts (exhibiting an undrained condition) that may be utilized for 

69 

 
estimation of side-shear capacities. The ultimate unit side-shear resistance (fs) is again calculated 

from the average undrained shear strength (Su), and the α factor as: 

S f = α S u (Equation 5.12)

α = 56.2 (Su in kPa) (Equation 5.13a) 

u S 

α = 0.56 (Su in tsf) (Equation 5.13b) 

u S 

Coefficients above are rounded from Coleman and Arcement (2002). The valid range of Su for 

this equation is between about 25 and 150 kPa (0.25 to 1.5 tsf), as shown in Figure 5.2. Note that 

in the recommended FHWA 1999 method, α would be constant and equal to 0.55 for soils with Su 

less than approximately 150 kPa [1.5 tsf]), and would reduce to as low as 0.45 for greater values 

of Su. The design engineer may consider the use of this correlation for similar deposits where it is 

anticipated that the FHWA 1999 method may be too conservative for similar deposits of clays and 

silts that are very soft to medium in consistency (i.e., Su up to approximately 50 kPa [0.5 tsf ]). 

4.00 

3.50 

3.00 

2.50 

α 2.00 

1.50 

1.00 

0.50 

0.00 

Silts 

Clays 

0 50 100 150 200 250 300 

Undrained Shear Strength (kPa) 

Source: Coleman and Arcement (2002) 

Figure 5.2: Relationship for the α Factor with Su for Calculating the Unit Side-Shear for 

Cohesive Soils for the Coleman and Arcement (2002) Method 

The TXDOT 1971 Method (Texas Highway Department, 1972) for drilled shafts has shown 

favorable results in predicting the static axial capacity of CFA piles in stiff clays, which have 

been over-consolidated by desiccation. The ultimate unit side-shear resistance (fs) in cohesive 

soils is calculated for a given pile segment simply as a function of Su (i.e., here the α factor is 

constant at 0.7): 

fs = 0.7 Su ≤120 kPa (1.25 tsf) (Equation 5.14) 

70 
5.3.1.3 Alternative Method for End-Bearing Estimates Using Dynamic Cone Penetrometer 

The TXDOT 1971 Method (Texas Highway Department, 1972) for drilled shafts has shown 

favorable results in predicting the static axial capacity of CFA piles in cohesive soils. However, 

the method relies on the use of a Dynamic Cone Penetrometer value (NTxDOT) for estimation of 

ultimate unit end-bearing resistance, which is uncommon in most areas outside of Texas. The 

ultimate unit end-bearing resistance (qp) can be determined using the NTxDOT value as follows: 

N 

q TxDOT

p (tsf ) = 8.25 (Equation 5.15)

5.3.1.4 Alternative Method for Side-Shear and End-Bearing Estimates Using SPT-N Values 

The design methods for prediction of side-shear and end-bearing resistance components in 

cohesive soils rely almost exclusively on undrained shear strength (Su). When no other types of 

geotechnical data other than SPT-N values are available, the undrained shear strength can be 

estimated from SPT-N values using local or published correlations appropriate for the soil 

deposit in question. However, this procedure is recommended only in feasibility studies, and not 

for design, because SPT-N values obtained in soils are not highly-reliable in estimating the 

undrained shear strength. 

5.3.1.5 Alternative Method for Side-Shear and End-Bearing Estimates Using CPT Values 

CPT testing has shown good results in prediction of both end-bearing and side-shear of CFA 

piles, as well as other types of deep foundations. This method of testing has become common in 

geotechnical soil exploration. For many engineers, the CPT is the preferred tool for use in 

predicting pile capacities in soils. Current research is focused on developing improved 

correlations for the use of CPT data in estimating CFA pile capacities, and improved correlations 

may become available as CPT becomes more widespread in the U.S. market. 

The Laboratorie Des Ponts et Chausses (LPC) method for drilled shafts and driven piles, 

developed by Bustamante and Gianeselli (1981, 1982), is recommended to be used over the 

previously presented methods for cohesive soils when cone bearing resistance (qc) data from 

CPT testing. Side-shear resistance estimates can be made using Figure 5.3 for clays and silts 

exhibiting an undrained condition. 

The ultimate unit side-shear in cohesive soils (fs) at a given depth (shown in Figure 5.3 as 

Maximum friction) is determined from the cone bearing resistance (qc) at that depth (as shown 

on the Y-axis), and then by interpolation between the limiting curves shown (qc < 1.2 MPa [12.5 

tsf] and qc > 5 MPa [52 tsf]) based upon the average qc along the pile length or pile segment 

length within a cohesive stratum. 

The ultimate unit end-bearing resistance (qp) in cohesive soils may also be estimated directly 

from the cone tip resistance (qc) from CPT testing: 

q p = 0.15 qc (Equation 5.16)

71 
Source: Bustamante and Gianeselli (1982) 

Figure 5.3: Unit Side-Shear Resistance as a Function of Cone Tip Resistance for Cohesive 

Soils – LPC Method 

The cone tip resistance used in this equation is averaged for a range of two to three pile 

diameters below the pile tip, whichever gives a lesser average value. 

5.3.2 Cohesionless Soils 

5.3.2.1 Recommended Method for Side-Shear Estimates Using Pile Depth and End-Bearing 

Estimates Using SPT-N Values 

The FHWA 1999 method for drilled shafts is recommended for the prediction of CFA pile 

capacity in cohesionless soils. The FHWA 1999 method was originally proposed by Reese and 

O’Neill (1988), and later modified by O’Neill and Reese (1999). This method uses SPT N60 

values (in blows per 0.3 m or per foot [bpf]) for calculations; these values should be based on 

60% hammer efficiency but should not be depth corrected. 

The ultimate unit side-shear resistance (fs) of a pile segment is estimated as: 

fs = K σ v ' tanφ ≤ 200 kPa (2.0 tsf )	 (Equation 5.17) 

72 
Where K is the lateral earth pressure coefficient, σ′v is the vertical effective stress, and φ is the 

soil drained angle of internal friction. The β factor is defined as: 

β = K tanφ (Equation 5.18)

and is limited to 0.25 ≤ β ≤ 1.2. The β factor for a pile segment is estimated as: 

β =1.5 − 0.135 ⋅ Z 0.5 for N ≥ 15 bpf (Equation 5.19a) 

N β = (1.5 − 0.135 Z 0.5 ) for N < 15 bpf (Equation 5.19b) 15 

where Z is the depth (in feet) from the ground surface to the middle of a given soil layer or pile 

segment. 

In the FHWA 1999 method, the ultimate unit end-bearing resistance (qp) is estimated as: 

qp (tsf) = 0.6N60 for 0 ≤ N60 ≤ 75 (Equation 5.20a)

 qp = 4.3 MPa [45 tsf] for N60 > 75 (Equation 5.20b) 

where N60 is the SPT-N value (bpf) at 60% of hammer efficiency near the tip of the pile, which is 

typically taken as the average within the depth interval of approximately 1 pile diameter above, 

to 2 or 3 pile diameters below, the pile tip. 

5.3.2.2 Alternative Methods for Side-Shear Using Pile Depth 

The Coleman and Arcement (2002) method was derived from CFA pile load-tests conducted in 

Mississippi and Louisiana in mixed soil conditions consisting of mostly alluvial, loessial 

deposits, and interbedded sands and clays. Section A.6.3 of Appendix A contains further details 

of the test program. This method provides modifications to the β factor of the recommended 

FHWA 1999 method for sandy soils and silty soils (exhibiting a drained condition) as follows: 

ƒs = β σ v ≤ 200 kPa (2.0 tsf) (Equation 5.21) 

The values of β are computed as follows: 

−0.67 β = 2.27 Zm (for silty soils) (Equation 5.22) 

−1.3 β = 10.72 Zm (for sandy soils) (Equation 5.23) 

Where Zm is the depth (in meters) from the ground surface to the middle of a given soil layer or 

pile segment. The values of β are limited to 0.2 ≤ β ≤ 2.5. 

The resulting β values in this method are shown in Figure 5.4, which also shows β values 

obtained using the FHWA 1999 method for comparison. The higher β factors at shallow depths 

73 
are most likely a result of the weakly cemented deposits (i.e., with a cohesion of approximately 

24 kPa [500 psf]) used in this study; these cemented soils have appreciable strength even when 

the effective overburden stress is low. 

3.00 

2.50 

2.00
 

β 1.50
 

1.00 

0.50 

0.00 

Silts 

Clays 

FHWA 

0 5 10 15 20 25 

Depth (m) 

Source: Coleman and Arcement (2002) 

Figure 5.4: Relationship for the β Factor for Calculating the Unit Side-Shear for 

Cohesionless Soils for the FHWA 1999 and Coleman and Arcement Methods 

5.3.2.3 Alternative Method for Side-Shear and End-Bearing Estimates Using CPT Values 

The LPC method for drilled shafts and driven piles, developed by Bustamante and Gianeselli 

(1981, 1982), is recommended when the capacities are to be estimated directly from the CPT 

cone bearing resistance (qc). These estimates can be made using Figure 5.5 for sands and gravel. 

The ultimate unit side-shear in cohesionless soils (fs) at a given depth (shown on the X-axis as 

Maximum friction) is determined from the cone bearing resistance (qc) at that depth (as shown 

on the Y-axis), and by the interpolating between the limiting curves shown (qc < 3.5 MPa [36 tsf] 

and qc > 5 MPa [52 tsf]) based upon the average qc along the pile length or pile segment length 

within a cohesionless stratum. 

The ultimate unit end-bearing resistance (qp) in cohesionless soils may also be estimated directly 

from the cone bearing resistance (qc) from CPT testing, which is typically averaged over two to 

three pile diameters below the pile tip. According to the LPC method: 

qp (MPa) = 0.375 ⋅ qc (Equation 5.24)

74 
Source: Bustamante and Gianeselli, (1982) 

Figure 5.5: Unit Side-Shear as a Function of Cone Tip Resistance for 

Cohesionless Soils - LPC Method 

5.3.3 Other Geo-Materials 

5.3.3.1 Introduction 

CFA piles have been used with success in strong, non-caving materials including vuggy 

limestones, shales, and other types of weathered or weak rocks. However, it is generally not 

possible to install CFA piles in such hard material while maintaining a rate of penetration that 

would normally be required to penetrate caving soil without mining. The use of continuous 

flight augers to construct CFA piles in weak or weathered rock is thus comparable to drilling an 

open hole drilled shaft without removing the auger. The potential problem of such practice is for 

conditions where non-cohesive overburden soils are present and will be subject to soil mining of 

the overburden as the rock socket is drilled. Where cohesive or stable overburden soils permit 

the installation of CFA piles into weak or weathered rock without problems, it is recommended 

that computational procedures should follow that of drilled shafts as outlined in O’Neill and 

Reese (1999). The following subsections present experience with CFA piles installed in vuggy 

limestone and shale. 

For hard rock overlain by soil materials, it may be difficult to construct a CFA pile with 

sufficient base resistance on the rock without soil mining. Piles should penetrate at least one pile 

diameter into the rock bearing stratum to utilize end-bearing capacity associated with the rock. 

75 
Even when the overlying soil is cohesive and the risk of soil mining is low, the reliability of the 

pile/rock interface is uncertain unless penetration of the rock can be assured. Conditions with 

soil overlying an extremely hard rock formation would be better suited to alternate foundation 

types, such as a drilled shaft, micropile, or driven steel pile. 

5.3.3.2 Vuggy Limestone 

For vuggy limestone formations of South Florida, or for similar formations elsewhere, CFA piles 

may be designed according to the relationships suggested by Frizzi and Meyer (2000). These 

relationships were derived from over 60 load-tests in the Miami limestone and Fort Thompson 

limestone formations found in South Florida (Broward and Miami-Dade Counties). 

Frizzi and Meyer (2000) presented relationships of unconfined compressive strength vs. ultimate 

unit side-shear resistance, shown on Figure 5.6. The relationship shown on that figure by 

Gupton and Logan (1984) was based upon drilled shaft experience in Florida limestone, the 

relationship by Kaderabek and Reynolds (1981) was based on anchor pullout tests performed on 

rock core specimens, and the relationship developed by Ramos et al. (1994) was developed 

primarily from full-scale field grout plug tests and limited CFA load-tests in various Florida 

limestone. The trend lines suggest that the smaller scale anchor tests and grouted plugs tend to 

mobilize higher side-shear resistance than larger foundations when tested in rock at the lower 

end of the unconfined compressive strength range; as the intact rock strength increases, they will 

tend to perform more similarly to drilled shafts. These data suggest that the effect of scale is 

important in interpreting field test data for drilled foundations in Florida limestone, and design 

correlations for CFA piles should be based on tests of full-scale piles. 

In the Frizzi and Meyer (2000) method, the ultimate unit side-shear resistance for a given pile 

segment in either the Miami limestone or Fort Thompson limestone formations are correlated to 

the SPT-N60, as shown in Figure 5.7. SPT-N60 values for calculations should be based on 60% 

hammer efficiency but should not be depth corrected. The data utilized to develop these 

relationships were limited to ultimate unit side-shear resistance values not exceeding 

approximately 9 and 8 MPa (94 to 84 tsf) for the Miami limestone and Fort Thompson limestone 

formations, respectively. Note that the smaller scale plug tests data from Ramos et al. (1986) 

again appears to be unconservative when compared to full-scale field load-test data. 

Figure 5.8 presents a relationship of side-shear stress development with displacement from loadtested CFA piles constructed in the Miami limestone and Fort Thompson limestone formations. 

Note that this data is presented as the ratio of the developed side-shear to the ultimate side-shear 

resistance (f/fmax) vs. the pile displacement (W) expressed as a percentage of the diameter (D). 

This relationship is compared with curves for drilled shafts proposed by Reese and O’Neill 

(1988) and with load-test data published by Semeraro (1982). No modifications or methods for 

predicting the end-bearing capacity were proposed by Frizzi and Meyer (2000). Note that in 

most cases, the CFA piles mobilized a very high load-carrying capacity initially (at a very low 

displacement), after which the load mobilization characteristics become similar to the deflection 

hardening response shown for granular soil. 

76 
0 

2 

4 

6 

8 

10 

12 

14 

16 

18 

20 

Side Shear (tons/ft

2) 

Reynolds and Kaderabek (1980) 

Gupton and Logan (1984) 

Ramos et al. (1994) 

Range of Compressive 

Strength for 

Miami Limestone, 

Prieto-Portar (1982) 

Range of Compressive 

Strength for 

Fort Thompson Limestone, 

Prieto-Portar (1982) 

0 5 10 15 20 25 30 35 40 45 50 

Unconfined Compressive Strength (tons/ft2) 

Source: Frizzi and Meyer (2000) 

Figure 5.6: Unconfined Compressive Strength vs. Ultimate Unit Side-Shear for Drilled 

Shafts in Florida Limestone 

 

0 

2 

4 

6 

8 

10 

12 

14 

16 

18 

20 

Side Shear (tons/ft

2) 

Mobilized (Miami Fmt.) 

Measured Ultimate (Miami Fmt.) 

Calculated Ultimate (Miami Fmt.) 

Mobilized (Fort Thompson) 

Measured Ultimate (Fort Thompson) 

Calculated Ultimate (Fort Thompson) 

Typical Range of 

SPT N-values for 

Miami Formation 

PROPOSED RELATIONSHIP 

FOR 

MIAMI LIMESTONE 

Crapps (1986), Drilled Shafts 

Ramos et al. (1994), 

Plug Tests 

PROPOSED RELATIONSHIP 

FOR 

FORT THOMPSON FORMATION 

0 10 20 30 40 50 60 70 80 90 100 

Standard Penetration Test N-value (blws/0.3 m) 

Source: Frizzi and Meyer (2000) 

Figure 5.7: Correlation of Ultimate Unit Side-Shear Resistance for South Florida 

Limestone with SPT-N60 Value 

77 
 

 

 

0 

0.2 

0.4 

0.6 

0.8 

1 

1.2 

f/f max 

Deflection-Hardening Response- Granular Soil 

(Reese and O,Neill, 1988) 

Drilled Shaft Load Test Data 

(Semeraro, 1982) 

Augercast Pile Load Test Data 

PROPOSED RANGE FOR 

AUGERCAST PILES IN SOUTH FLORIDA ROCK 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 

W/D (%) 

Source: Frizzi and Meyer (2000) 

Figure 5.8: Side-Shear Development with Displacement for South Florida Limestone 

ρ

Q D (Equation 5.25) = Qult ρ 50 + ρ

D D 

5.3.3.3 Clay-Shale 

For CFA piles socketed into clay-shale formations of North-Central Texas, or for similar 

formations elsewhere, the total capacity developed in the socket may be estimated according to 

the relationships suggested by Vipulanandan et al. (2005). These relationships were derived 

from eight load-tests of CFA piles socketed into clay-shale with unconfined compression 

strengths (qu) ranging from 100 to 3,000 kPa (1 to 30 tsf) (measured in situ from a Texas Cone 

Penetrometer value, NTxDOT). Overburden soils were predominantly clay and sandy clay, and 

thus allowed for construction of the socket without appreciable soil mining effects. The diameter 

and length of the CFA piles varied from 450 to 600 mm (18 to 24 in.) and 12 to 25 m (40 to 83 

ft), respectively. 

The load-test results are presented in dimensionless form for all eight test piles as a relative load 

capacity (Q/Qult), which is a function of the relative displacement (ρ/D). This is shown in Figure 

5.9 and is represented by the following hyperbolic function: 

78 
where: 

Q = resistance at the given displacement (in any consistent units); 

Qult = the ultimate resistance that occurs for very large displacements (in the same, 

consistent units of Q); 

ρ = pile displacement (in any consistent units); 

D = diameter of the pile (in the same, consistent units of ρ); and 

ρ50/D = the displacement-to-diameter ratio at Q/Qult = 0.5. 

The parameter Qult was correlated to the unconfined compressive strength (qu) of the clay-shale, 

pile circumference (π D), and socket length (L) and is shown in Figure 5.10 and is represented 

as: 

Qult L = − 0.11 + 0.96 (Equation 5.26)

qu π D L D 

0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0.7 

0.8 

0.9 

1 

 Relative Load Capacity (Q / Qult)

Case No.3 

Case No.4 

Case No.1 

Case No. 2 

Case No.5 

Case No.6 

Case No.7 

Case No.8 

Range of ρ50 / d 

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 

Relative Displacement , ρ / D (%)

Source: Vipulanandan et al. (2004) 

Figure 5.9: Relative Load Capacity vs. Relative Displacement for CFA Sockets in Clay-Shale 

79 
 

Qult / (qu π D L) 

1.0 

0.8 

0.6 

0.4 

0.2 

0 

Case-6 

Minimum 

Recommended 

L/D per TXDOT 

Case-3 

Case-7 

Case-1 

Case-5 

Case-4 

Case-2 

Case-8 

0 1 2 3 4 5 6 7 8 

L/D of Socket in Rock

Source: Vipulanandan et al. (2004) 

Figure 5.10: Hyperbolic Model Parameter Qult as a Function of the Unconfined 

Compressive Strength (qu) for CFA Sockets in Clay-Shale 

The parameter ρ50/D was also correlated to the unconfined compressive strength of the clay-shale 

normalized by the standard atmospheric pressure (in any consistent units) in the equation below. 

ρ 50 15.8 [in %] = (Equation 5.27) D qu 

Patm 

This relationship is shown in Figure 5.11. 

To use the Vipulanandan et al. (2004) method, the unconfined compressive strength obtained 

from the field or laboratory is considered first. After normalizing qu with the atmospheric 

pressure the ratio ρ50/D is obtained form Figure 5.11 or Equation 5.27. The ultimate capacity is 

computed using Figure 5.10 or Equation 5.26. With the pile diameter D and socket length L 

known, and the variables previously presented already determined, the relative load capacity can 

be the computed for a range of pile displacements. An example in English units is provided to 

illustrate the method. 

80 
 

1.4
 

1.2 Case-1

1 

0.8 

ρ50/D 

0.6 

Case-5 

Case-4 

Case-8 

Case-6 

Case-2 

Case-8 

Case-3 

0.4 

 Hyperbolic 0.2
 

0
 

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 

qu / Patm 

Source: Vipulanandan et al. (2004) 

Figure 5.11: Parameter ρ50/d as a Function of Unconfined Compressive Strength for CFA 

Sockets in Clay-Shale 

For: 

•	 a pile with diameter D = 1.5 ft; 

•	 drilled into clay shale of qu = 20 tsf; and 

• a socket L = 3 D = 4.5 ft. 

The following results are obtained using the method described above: 

•	 for ratio qu/Patm = 20; 

• Equation 5.27 results ρ50/D = 0.79%. 

With Equation 5.26, the ultimate capacity is estimated as: 

Qu = qu π D L (-0.11 × L/D + 0.96) = 20 × 3.14 × 1.5 × 4.5 (-0.11 × 3 + 0.96) = 267 tons. 

For a pile displacement of 0.25 in. and using Equation 5.25, the mobilized load capacity is 

estimated to be: 

Q = Qult [ρ/D ÷ (ρ50/D + ρ/D)] = 

= 267 × [0.25/18 ÷ (0.0079 + 0.25/18)] = 0.64 × 267 = 170 tons. 

81 
 

5.4 STATIC AXIAL CAPACITY OF DRILLED DISPLACEMENT PILES 

5.4.1 Introduction 

Numerous construction techniques and tools have been developed to increase the load capacity 

over that which is attained from conventional CFA piles for a given soil condition. Most of these 

systems have been developed by specialty contractors and/or equipment manufacturers, and thus 

may perform differently depending upon the relative volume of soil displaced in proportion to 

the pile volume, the magnitude of the permanent increase in lateral stress or soil improvement at 

the pile/soil interface, the relative roughness of the resulting pile/soil interface, and the effective 

diameter of the resulting pile. Different techniques may achieve superior results in different 

types of soil conditions. For example, increased lateral stress and soil densification may be a 

very desirable effect of installation in sandy soil profiles, while increased roughness or effective 

diameter may be effective in cohesive soils where densification of saturated cohesive soil is 

unlikely to occur. 

Most of these specific techniques and tools share some common features regarding the 

mechanisms by which higher capacities may be realized. In general, in DD piles, the drilling 

spoils and the surrounding soil are displaced laterally or compacted into the borehole wall to 

varying degrees during auger penetration. The relative volume of soil displaced in proportion to 

the pile volume determines whether the technique is termed a “high displacement” or a “partial 

displacement” pile. In cases where an amelioration technique is employed, sand or gravel 

introduced into the top of the borehole may also be compacted into the borehole wall by 

specialty tooling. As a result, localized densification of the soil will occur to some limited extent 

away from the pile, and the effective lateral stresses in the soil surrounding the pile will increase. 

A number of studies have attempted to quantify the effects of displacement on surrounding soils 

during pile construction. Kulhawy (1984) showed that the lateral earth pressure coefficient (Ko) 

may decrease as much as one third (resembling an active lateral earth pressure, Ka) for drilled 

shafts, and may nearly double (resembling a passive lateral earth pressure, Kp) for 

high-displacement driven piles. Displacement effects have also been quantified by other means. 

Webb et al. (1994) indicated an increase of 20 to 50% in CPT resistance over the length of pile 

after the installation of displacement piles in sandy soils. Nataraja and Cook (1983) used SPT to 

quantify the effects of displacement and concluded that the increased stresses were also a 

function of the soil uniformity coefficient, over-consolidation ratio, and effective stress 

conditions before displacement. 

5.4.2 Recommended Method Using SPT-N Values or CPT Data 

The recommended method for estimating axial resistance of DD piles is based on the published 

work of NeSmith (2002). Caution is warranted in using the correlations presented for DD piles, 

as the static axial capacity is very sensitive to the construction technique and tooling, and relies 

heavily on the abilities and experience of the specialty contractors. Improved side-shear 

resistance and end-bearing capacities obtainable with this technique over conventional CFA piles 

must be verified for the specific site, technique, and equipment using full-scale load-testing, 

automated monitoring, and recording equipment for all test and production piles. 

82 
NeSmith (2002) studied the results of 22 full-scale compression load-tests and six full-scale 

pullout tests of DD piles located at 19 different sites throughout the United States. The pile 

diameters ranged from 0.36 to 0.46 m (14 to 18 in.), with the majority at 0.41 m (16 in.). The 

pile lengths ranged from 6 to 21 m (20 to 69 ft), with an average length of approximately 13 m 

(43 ft). A variety of soil conditions were investigated (listed in Table 5.2), which generally 

ranged from clean sands, fine gravels, to silty and clayey sands. Five of the compression test 

piles (included as one site in the Piedmont geologic setting in Table 5.2) were from the research 

conducted by Brown and Drew (2000); the soils at this site consisted of clayey silts to silty clays 

with around 50% passing the #200 sieve, and represent the soil profile with the highest fines 

content in the NeSmith (2002) study. 

Table 5.2: Soil Conditions Investigated for Drilled Displacement Piles 

Source: NeSmith (2002) 

Geologic Setting Sites Major Features 

Alluvium in a major river 

(AR, CA, FL, IA, WA) 5 Loose to dense sand, some gravel, well-graded (primarily), 

clean to some silt and clay 

Post Miocene (FL) 4 Loose (primarily) to medium silty, clayey sand 

Barrier Island (Fl, AL, MD) 4 Medium to very dense sand, uniform, clean 

Piedmont (GA) 3 Loose (primarily), silty sand/sandy silt, micaceous (toe in 

partially weathered rock) 

Glacial Outwash (MN) 1 Loose to medium sand with fine gravel, clean, well-graded 

Gulf Coastal Plain ( FL) 1 Loose to medium silty clayey sand 

Colma Formation (CA) 1 Medium to very dense silty and clayey sand 

NeSmith (2002) defined ultimate pile capacity to occur at displacements of 25.4 mm (1 in.) of tip 

movement, or when the displacement rate of the loading curve reached 0.057 mm/kN (0.02 

in./ton), whichever occurred first. While the two stated failure criteria occasionally occurred 

near the same load, the displacement rate criterion did not govern in any case. In the event that 

the load was not increased to a level sufficient to reach either of the criteria, the load 

displacement relationship was extrapolated to ultimate by the method proposed by Chin (1970), 

and this method was also used to estimate the shaft end-bearing component for test piles where 

no instrumentation was available. 

Figure 5.12 (a) and (b) shows correlations of the ultimate unit side-shear (fs) with CPT tip 

resistance (qc) and SPT-N values, respectively. SPT-N60 values should be based on 60% hammer 

efficiency but should not be depth corrected. These relationships should only be applied to 

cohesionless materials in which displacement of the spoils into the borehole wall during 

construction will result in densification of the surrounding soil. Based on these trends, the 

ultimate unit side-shear resistance (fs) for a given pile section can be correlated with qc or to 

SPT-N60 values as follows: 

f = 0.01 q +W for qc ≤ 200 tsf (20 MPa) (Equation 5.28) S c S 

ƒS (tsf) = 0.05 N + WS for N ≤ 50 (Equation 5.29) 

83 
f S (MPa) = 0.005 ⋅ N +WS for N ≤ 50 

where the correlation constant (Ws) and limiting ultimate unit side-shear (fs) are as follows: 

•	 Ws = 0, and fs ≤ 0.16 MPa (1.7 tsf) for uniform, rounded materials having up to 40% fines. 

•	 Ws = 0.05 MPa (0.5 tsf) and fs ≤ 0.21 MPa (2.2 tsf) for well-graded angular materials having 

up to 10% fines. 

•	 For soil conditions with material properties falling between the provided ranges, a linear 

interpolation between the limiting values should be made. 

Note that the recommended method for estimating the ultimate fs from CPT-qc values for DD 

piles (Figure 5.12), are more than twice that predicted by the alternative method (LPC) for 

computing fs from CPT-qc values for conventional CFA piles (Figure 5.5). 

The ultimate unit end-bearing (qp) was correlated to either CPT-qc or SPT-N values obtained 

near the pile tip. SPT-N60 values should be based on 60% hammer efficiency. These values 

should be obtained between approximately 4D above and 4D below the pile tip. Figure 5.13 (a) 

and (b) show the ultimate unit end-bearing capacity (qp) data, and the correlations with CPT-qc 

and SPT-N values, respectively. Capacities may be estimated according to the following 

relationships: 

qp = 0.4 qc + WT < 19 MPa (200 tsf) (Equation 5.30) 

qp (MPa or tsf) = 0.19 N60 + WT for N60 ≤ 50 (Equation 5.31) 

where the constant (WT) is as follows: 

WT = 0, for qp ≤ 7.2 MPa (75 tsf) and uniform, rounded materials having up to 40% fines. 

WT = 1.34 MPa (14 tsf), for qp ≤ 8.62 MPa (89 tsf) and well-graded angular materials having up 

to 10% fines. 

For soil conditions with material properties falling between the ranges provided above, a linear 

interpolation between the limiting values should be made. 

It is worthwhile comparing the above recommendations for DD piles with that for conventional 

CFA piles as described in the preceding section. For CFA piles, the recommended method and 

the alternative method for computing ultimate unit end-bearing (qp in units of tsf) from SPT-N60 

values ranged from 0.6 N60 to 1.7 N60, respectively. The recommended method for ultimate unit 

end-bearing (qp in units of tsf) from SPT-N60 values for DD piles ranges from 1.9 N60 to 1.9 N60 

+ 14 tsf, depending on soil material properties. Similarly, the alternative method (LPC) for 

computing the ultimate unit end-bearing (qp) from CPT-qc values for conventional CFA piles 

was 0.375 qc. The recommended method for ultimate unit end-bearing (qp) from CPT-qc values 

for DD piles ranged from 0.4 qc to 0.4 qc + 14 tsf, depending on soil material properties. 

84 
CONE TIP RESISTANCE, qc, MPa 

3.83 7.66 11.49 15.32 19.15 4 .383 

40 80 120 160 200 

CONE TIP RESISTANCE, qc, TSF 

NEN 6743 Q1 

Q5 

Q1--qc<1.0MPa (10.44 TSF) 

Q4--qc>3.5MPa (36.54 TSF) 

Q5--qc>8.0MPa (83.52 TSF) 

Q4 

Bustamnate & Gianeselli (1993), 

Screw Piles, Sand and Gravel 

Dutch Standard, NEN 6743, 0.009qc, Screw Piles 

Limit qc to 15 MPa (156.6 TSF) 

RECOMMENDED BASE LINE--DIRTY, ROUNDED, UNIFORM 

Limit fs 0.21 MPa (2.2 TSF) 

Limit fs 0.16 MPa (1.7 TSF) 

Auburn NGES, Brown & Drew (2000) Isolated Pile 

Center of 5-pile group, spaced at 3D 

RECOMMENDED LIMIT--CLEAN, ANGULAR, WELL-GRADED 

NEN 6743 

Berkel Database 

ULTIMATE UNIT SHAFT RESISTANCE, TSF ULTIMATE UNIT SHAFT RESISTANCE, TSF3 

2 

1 

.288 

ULTIMATE UNIT SHAFT RESISTANCE, MPa ULTIMATE UNIT SHAFT RESISTANCE, MPa 

.192 

.096 

0 0 

(a) Correlated to CPT Testing 

4 .383 

10 20 30 40 50 

STANDARD PENETRATION RESISTANCE, N, BLOWS PER 305 mm 

MEYERHOF, Bored Piles

RECOMMENED BASE LINE-- ROUNDED, UNIFORM 

Q1--qc<1.0MPa (10.44 TSF) 

Q4--qc>3.5MPa (36.54 TSF) 

Q5--qc>8.0MPa (83.52 TSF) 

Bustamnate & Gianeselli (1993), 

Screw Piles, Sand and Gravel 

qc/n = +-4 

Meyerhof, 0.0019N (MPa), 0.02N (TSF)--Bored Piles 

Q1 

Q4 

Q5 

Limit fs 0.21 MPa (2.2 TSF) 

Limit fs 0.16 MPa (1.7 TSF) 

pwr 

pwr 

gravel 

Auburn NGES, Brown & Drew Center of 5-pile group, spaced at 3D 

Isolated Pile 

RECOMMENED LIMIT-- ANGULAR, WELL-GRADED 

Berkel Database 3 

2 

1 

.288 

.192 

.096 

0 0 

S f 

(b) Correlated to SPT Testing 

Note: N in Figure above refers to N60. Source: NeSmith (2002) 

Figure 5.12: Ultimate Unit Side-Shear Resistance for Drilled Displacement Piles for 

NeSmith (2002) Method 

85 
 

 

 

CONE TIP RESISTANCE, qc, MPa 

3.83 7.66 11.49 15.33 19.15 

120 11.5 

40 80 120 160 200 

CONE TIP RESISTANCE, qc, TSF 

HIGH FINES CONTENT 

Bustamnate & Gianeselli (1993), Screw Piles, 

Sand and Gravel, qt= 0.50 to 0.75qc--

Ultimate load at displacement of 0.10D, qc 

averaged 1.5D above and below tip 

German Standard, DIN 4014, qt = 0.12qc+.1,(MPa) 

Does not differentiate between augercast and 

displacement 

Douglas, (1983) qt = .25qc 

Ultimate load at 1.2 inches 

Bustamnate & Gianeselli (1993), Upper Limit 

Douglas (1983) 

DIN 4014 

BASE LINE--DIRTY, ROUNDED, UNIFORM 

Berkel Database 

RECOMMENDED LIMIT--CLEAN, ANGULAR, WELL-GRADED 

Limit qt 

7.18 MPa (75 tsf) 

Limit qt 

8.53 MPa (89 tsf) 90 8.62 

ULTIMATE UNIT TOE RESISTANCE, TSF ULTIMATE UNIT SHAFT RESISTANCE, TSF

ULTIMATE UNIT TOE RESISTANCE, MPa ULTIMATE UNIT SHAFT RESISTANCE, MPa 

60 

30 

5.75 

2.87 

0 0 

(a) Correlated to CPT Testing 

4 .383 

10 20 30 40 50 

STANDARD PENETRATION RESISTANCE, N, BLOWS PER 305 mm 

MEYERHOF, Bored Piles

RECOMMENED BASE LINE-- ROUNDED, UNIFORM 

Q1--qc<1.0MPa (10.44 TSF) 

Q4--qc>3.5MPa (36.54 TSF) 

Q5--qc>8.0MPa (83.52 TSF) 

Bustamnate & Gianeselli (1993), 

Screw Piles, Sand and Gravel 

qc/n = +-4 

Meyerhof, 0.0019N (MPa), 0.02N (TSF)--Bored Piles 

Q1 

Q4 

Q5 

Limit fs 0.21 MPa (2.2 TSF) 

Limit fs 0.16 MPa (1.7 TSF) 

pwr 

pwr 

gravel 

Auburn NGES, Brown & Drew Center of 5-pile group, spaced at 3D 

Isolated Pile 

RECOMMENED LIMIT-- ANGULAR, WELL-GRADED 

Berkel Database 3 

2 

1 

.288 

.192 

.096 

0 0 

(b) Correlated to SPT Testing 

Note: N in Figure above refers to N60. Source: NeSmith (2002) 

Figure 5.13: Ultimate Unit End-Bearing Resistance for Drilled Displacement Piles for 

NeSmith (2002) Method 

86 
5.4.3 Amelioration 

The amelioration technique involves introducing coarse sand or gravel into the top of the 

borehole as the specialty tooling is advanced. A section of reversed auger flights (pitched 

opposite to the direction of rotation) is situated above the normal auger flights, and a packer 

(enlarged drill stem) lies in the drill string between these two sets of auger flights. The sand or 

gravel introduced falls down into the annular between the borehole wall and the drill stem. The 

reversed flights catch the introduced granular material and force it into the borehole wall. 

In addition to densifying the surrounding soil and increasing the effective stress, this technique 

was shown by Brown and Drew (2000) to be advantageous in silty clays to clayey silts where the 

soil-to-pile interface friction angle (δ) would have otherwise been smaller. They found 

amelioration with sand to increase an individual pile’s side-shear resistance by approximately 

25% over that of an individual pile constructed without amelioration. However, they found 

amelioration with sand to increase side-shear by only 16% of a single pile tested individually 

within a pile group (spaced at 3 pile diameters center-to-center) over that of a similar single pile 

within a group constructed without amelioration and tested individually within the group. Also, 

they found amelioration with crushed stone (maximum aggregate size typically 10 mm [0.4 in.]) 

to increase side-shear resistance of individual piles by approximately 50% over that of an 

individual pile constructed without amelioration. The introduced free-draining granular material 

may allow for any excess pore pressures around the pile to be dissipated more rapidly than they 

would otherwise, as well as potentially increasing the effective diameter of the pile. While both 

grouping of piles and amelioration both provided marked increases in capacity, their combined 

effects were not as substantial as the simple sum of the two. 

This technique, which may result in substantial improvements to the capacity, relies heavily on 

the abilities and experience of the specialty contractors, and is typically utilized as only a 

contractor-proposed method. However, with the use of performance-based specifications for 

contracting as described in Chapter 8, the use of these innovative pile types may be encouraged. 

Improved capacities obtainable with DD techniques must be verified for the specific site and 

tooling/technique with full-scale load-testing and the use of automated monitoring and recording 

equipment for all test and production piles. Note also that the required resistance may tend to be 

achieved with shorter piles than anticipated with conventional CFA, and thus group effects and 

settlement considerations may be controlling issues in some cases. Effects of installation of DD 

piles with amelioration on adjacent structures may also be a limiting factor in selection of this 

technique. 

5.5 GROUP EFFECTS ON STATIC AXIAL COMPRESSION LOAD RESISTANCE 

OF CFA PILES 

5.5.1 Introduction 

The axial compressive capacity of a pile group is not necessarily the sum of the single pile 

capacity within the group. In pile groups, the zone of influence from an individual pile may 

intersect with other piles, depending on the pile spacing, as illustrated in Figure 5.14. 

Evaluations of pile group capacities should also consider potential block failure of the pile group, 

87 
and the potential contribution of the pile cap to bearing capacity contribution regarding the total 

capacity of the pile group system (termed occasionally as a pile raft). Finally, the designer 

should be aware that settlement of a pile group may often exceed that which would be predicted 

based upon a single pile analysis 

. 

Source: Hannigan et al. (2006) 

Figure 5.14: Overlapping Zones of Influence in a Frictional Pile Group 

88 
5.5.2 Group Efficiencies 

The efficiency of a pile group (ηg) is defined as: 

Rug η g = n 

∑Ru,i 

i=1 (Equation 5.32)

where Rug is the ultimate resistance of the pile group, and Ru,i is the ultimate resistance of a single 

pile “i” in the pile group with a total of n piles in the group. 

Displacement piles (such as driven piles and to a lesser extent DD piles) generally tend to 

increase the effective stress of the surrounding soil, and thus can create a pile group capacity 

greater than the sum of the individual pile capacities when these densified zones of influence 

surrounding the pile overlap. This soil improvement effect creates an efficiency greater than 1.0. 

Conversely, excavated piles (such as drilled shafts and conventional CFA piles), generally tend 

to decrease the effective stress of the surrounding soil, or at best maintain it at the at-rest (Ko) 

condition, creating an efficiency less than or equal to 1.0, respectively. Changes in effective 

stress are more pronounced in cohesionless soils. Note also that installation effects from poorly 

controlled pile construction resulting in soil mining during drilling can adversely affect the 

lateral stress of previously installed piles. 

5.5.2.1 Conventional CFA Pile Groups 

Groups of conventional CFA piles may be designed with drilled shaft group efficiencies that may 

tend to be conservative if proper techniques are used for CFA pile construction, as verified with 

appropriate construction monitoring. However, the reader is strongly cautioned that if soil 

mining were to occur, the resulting efficiency for the CFA group would be substantially less than 

that for a group of drilled shafts in the same soil conditions. Note that cohesionless soils are 

particularly sensitive to this effect. 

The overlapping zones of influence from individual piles in a group, and the tendency for the 

pile cap to bear on the underlying soils (if in contact) tend to cause the piles, pile cap system, 

and the soil surrounding the piles to act as a single unit and exhibit a block-type failure mode 

(i.e., bearing failure). The group capacity should be checked to see if a block-type failure mode 

controls the group capacity, as will be discussed in the next paragraph. 

Block failure mode for pile groups generally will only control the design for pile groups in soft 

cohesive soils or cohesionless soils underlain by a weak cohesive layer. Note that closer spacing 

of the piles in the group will also tend to increase the potential of the block failure mode. 

89 
Cohesionless Soils 

In the absence of site-specific data to indicate otherwise, it is recommended that the AASHTO 

provisions (AASHTO, 2002) for group efficiencies for drilled shafts in cohesionless soils 

(AASHTO 10.8.3.9.3) be followed for conventional CFA piles in the same soils. This provision 

states that regardless of cap contact with the ground: 

η = 0.65 for a center-to-center spacing of 2.5 diameters, 

η = 1.0 for a center-to-center spacing of 6.0 diameters or more, and 

The value of η must be determined by linear interpolation for intermediate spacing. 

There is evidence that the recommended values are most likely conservative for CFA piles in 

cohesionless soils, in circumstances where the pile cap is in firm contact with the ground and 

contributes significantly to the bearing capacity, and/or when the cohesionless soil is not 

loosened by the installation process. Results from small-scale field tests in cohesionless soils 

from diverse locations around the world suggest that an efficiency of 1.0 or greater may be 

obtained with pile center-to-center spacing of approximately 3 to 4 diameters, and that 0.67 may 

be a lower bound for group efficiencies. Note that a typical center-to-center spacing of 3 pile 

diameters would result in a recommended efficiency of 0.7 using the AASHTO (2002) 

provisions cited above. 

Studies of drilled shaft groups in cohesionless soils include Garg (1979), Liu et al. (1985), and 

Senna et al. (1993). The shafts in these studies did not exceed the range of 125 to 330 mm (5 to 

13 in.) in diameter, and from 8 to 24 times their respective diameter in length. While these piles 

may be considered model-scale for drilled shafts, their sizes approached that typical of CFA 

piles. Note that all three of the studies sites were performed in either dry sand or sand with fines 

above the water table. Efficiencies for groups in clean sands below the water table may be lower 

than reported in the cited studies due to a greater potential for relaxation of lateral stress. 

Garg (1979) conducted compression model tests of underreamed shafts in moist, poorly-graded 

silty sand with SPT-N values ranging from 5 to 15. The efficiency vs. the ratio of spacing to 

diameter (S/Bshaft) for 2 and 4 pile groups, both with and without the cap in contact with the 

ground, are shown in Figure 5.15. Note that the efficiency of a group with its pile cap in contact 

with the ground is consistently higher than the efficiency of the group with the cap not in contact 

with the ground. 

Liu et al. (1985) conducted model axial compression tests in moist alluvial silty sand, soil 

density for side-shear resistance was not reported. The group effects on side-shear and 

end-bearing contributions of a 3 by 3 pile group as a function of the ratio of spacing to diameter 

(spacing/B) are shown in Figure 5.16. The relationship is shown for the cases of the pile cap in 

contact or not in contact with the ground. Note that the case of the cap in contact with the 

ground results in lower efficiencies but higher efficiencies for end-bearing than with the cap not 

in contact with the ground for comparable spacing-to-diameter ratios. 

90 
Efficiency, η

2 

1.8 

1.6 

1.4 

1.2 

1 

0.8 

0.6 2-Shaft Grp - Cap in Contact w/ Ground 

0.4 2-Shaft Grp - Cap Suspended above Ground 

4-Shaft Grp - Cap in Contact w/ Ground 0.2 4-Shaft Grp - Cap Suspended above Ground

0
 

23 45 6

s/Bshaft 

Source: O’Neill and Reese (1999) (Modified after Garg, 1979) 

Figure 5.15: Efficiency (η) vs. Center-to-Center Spacing (s), Normalized by Shaft Diameter 

(Bshaft), for Underreamed Model Drilled Shafts in Compression in Moist, Silty Sand 

60 1.4 

1.2 50
 

1
 

40 

fmax (kPa)

s ingle pile 

30 

W eakening Effect 

by Pile Cap 20 

qmax (kPa) 0.8 single pile 

St rengt hening 

0.6 Effect by Pile Cap

0.4 

10 0.2 

0 0 

23456 23456

Spacing / B Spacing / B 

Source: O’Neill and Reese (1999) 

Figure 5.16: Relative Unit Side and Base Resistances for Model Single Shaft and Typical 

Shaft in a Nine-Shaft Group in Moist Alluvial Silty Sand 

7 

91 
Senna et al. (1993) conducted model axial compression tests in clayey sand with SPT-N values 

ranging from approximately 4 at the surface to as high as 18 at the tip depths (6 m [19.7 ft]). 

Four different group configurations were tested and compared to a single pile response with the 

resulting efficiencies as shown in Table 5.3. Note that all groups had center-to-center spacing of 

3 diameters, and all caps were in contact with the ground. 

Table 5.3: Efficiency (η) for Model Drilled Shafts Spaced 3 Diameters Center-to-Center in 

Various Group Configurations in Clayey Sand (Senna et al, 1993) 

Configuration 2 × 1 

Pile Bent 

3 × 1 

Pile Bent 

3 Triangular 

Pile Group 

4 Square 

Pile Group 

Efficiency η = 1.1 η = 1.1 η = 1.04 η = 1.0 

While these studies have limitations with respect to application to CFA pile design in 

cohesionless soils, they suggest that there may be circumstances in which the AASHTO (2002) 

specifications would result in a significantly conservative estimate of group capacity. The group 

effects of CFA pile installation in cohesionless soil are generally attributed to reductions in 

lateral stress and/or reductions in soil relative density. For granular soils with considerable fines 

or light cementation and pile construction that is conducted with care to avoid potential 

reductions in lateral stress, it may be worthwhile to include an evaluation of group effects into 

the test pile program. Effects of pile installation on soil density or stress should be reflected in 

post-construction in-situ tests (SPT or CPT) within the pile group. Likewise, verification tests of 

an interior pile should provide a representative indication of a typical pile within a group after 

installation of the entire group. If reliable interpretations from a well-conceived test pile 

program can demonstrate that negative group effects are less severe than indicated by the 

AASHTO recommendations for drilled shafts, then an alternate approach may be justified on a 

project-specific basis. 

Cohesive Soils 

It is recommended that the AASHTO (2002) provisions for group efficiencies for drilled shafts 

in cohesive soils (AASHTO 10.8.3.9.2) be followed for conventional CFA piles in similar soils. 

This provision states that, regardless of cap contact with the ground, the efficiency should be 

determined from a block failure mode, and that the efficiency be limited to η = 1.0, or: 

Block η g = R 

≤ 1(Equation 5.33)

∑

n 

Ru,i 

i=1 

The resistance of the block failure (RBlock) mode can be simply estimated as the sum of the 

side-shear resistance contribution from the peripheral area of the block, as shown in Figure 5.17, 

and the end-bearing capacity contribution from the block footprint area: 

RBlock =2 fs [D Z + B]+ q p (Z B) (Equation 5.34)

92 
where: D, Z, and B are the depth, length, and width of the block, respectively, fs is the ultimate 

unit side-shear resistance of the block, Ru,i is the individual pile ultimate resistance and qp is the 

ultimate unit end-bearing capacity for the block, Ru,i is estimated as described in Section 5.3 

for conventional CFA piles. 

 

Most often, the limiting pile-to-soil friction angle (δ) is used to conservatively calculate shear 

resistance for the entire peripheral surface of the block at corresponding depths, rather than a 

combination of pile-to-soil (δ) and soil-to-soil (φ) friction angles. The ultimate unit end-bearing 

capacity for the block is similar to that determined for a single pile; however, the ultimate unit 

end-bearing capacity of the block must take into account that the influence zone of the block is 

deeper than that of a single pile. This may be accounted for by assuming a zone of 

approximately 2 to 3 times Z, and determining qp by the methods presented in Section 5.3 for this 

deeper zone of influence. 

Source: Hannigan et al. (2006) 

Figure 5.17: Block Type Failure Mode 

Pile in a Strong Layer with a Weak Underlying Layer 

If a weak formation is present, the group efficiency should be checked to ascertain whether a 

group efficiency of less than 1.0 is warranted. The group efficiency may be checked as 

described in Section 5.5.2.1.2, where the individual pile ultimate resistance (Ru,i) is estimated as 

described in Section 5.3 (for conventional CFA piles) and the block extends to the weak layer. It 

should be noted that a weak layer below the pile group will, in most cases, present a significant 

consideration from the standpoint of group settlement as outlined in section 5.5.3.3. Settlement 

considerations may require that minimum pile penetration be achieved to an elevation below the 

compressible layer. 

93 
5.5.2.2 Drilled Displacement Pile Groups 

The efficiency of DD pile groups are comparable to that of driven displacement pile group. The 

recommendations included in this section are consistent with recommendations for the design of 

driven pile groups. In general, even a modest amount of displacement with intermediate DD 

piles can result in the conditions required to avoid the negative installation effects associated 

with conventional drilled foundations. For conditions where positive displacement of at least 

15% of the pile volume is achieved, the methods in the sections below are recommended. 

Cohesionless Soils 

It is recommended that the AASHTO provisions for group efficiencies for driven piles in 

cohesionless soils (see, AASHTO 10.7.3.10.3 in AASHTO, 1996) be followed for DD piles in 

the same soils. This provision states that η = 1.0 regardless of cap contact with the ground. 

Groups of driven displacement piles typically exhibit a group efficiency greater than 1.0 

(especially for cohesionless soils). However, a group efficiency of 1.0 is typically used in the 

interest of a conservative design. Likewise, groups of DD piles have typically exhibited a group 

efficiency greater than 1.0; however the group efficiency should also be limited to 1.0. Adequate 

spacing for DD piles may be considered to be approximately 3 pile diameters on centers or more. 

For cohesionless soils, the DD pile group efficiency is recommended to be taken as 1.0 if a weak 

deposit is not encountered in the underlying formation. If a weak formation is present, the group 

efficiency should be checked to ascertain whether a group efficiency of less than 1.0 is 

warranted. The group efficiency may be checked with the equation in Section 5.5.2.1 where the 

ultimate resistance of the block (RBlock) is estimated as described in Section 5.5.3, while the 

individual pile ultimate resistance (Ru,i) is estimated as described in Section 5.4 (for auger 

displacement piles). 

Cohesive Soils 

A study by Brown and Drew (2000) of full-scale DD piles in the Piedmont geologic setting of 

the National Geotechnical Experimentation Site (NGES) (clayey silts to silty clays), suggested 

that DD piles behave like neither driven displacement piles nor conventional CFA piles, but inbetween these extremes. Although not tested as a group, comparisons showed an increase in unit 

side-shear resistance of approximately 100% of the single interior pile within a 5-pile group 

(spaced at 3 pile diameters center-to-center) over an isolated pile. Also tested and compared was 

an isolated pile and a 5-pile group (spaced at 3 pile diameters center-to-center), all of which were 

constructed using an amelioration technique with coarse sand. The same comparison yielded an 

increase in unit side-shear resistance of 90% for the single interior central pile of the five-pile 

group over the isolated pile. 

94 
For cohesive soils with undrained shear strengths greater than 100 kPa (1 tsf) or for groups with 

the pile cap in firm contact with the ground, the DD pile group efficiency may be taken as 1.0. 

For the condition of cohesive soils with undrained shear strengths less than 100 kPa (1 tsf) and 

the pile cap not in firm contact with the ground, a group efficiency should be linearly 

interpolated in accordance with the pile spacing as follows: adopt an efficiency of 0.7 for a pile 

spacing of 3 diameters on-centers and increase to an efficiency of 1.0 for a pile spacing of 6 

diameters or greater on-centers. 

In all cases, a block failure mode should be checked to see if it governs the efficiency. The 

group efficiency for this mode should be checked with the equation shown in the previous 

section, where again, the ultimate resistance of the block (RBlock) is estimated as described in 

Section 5.5.3, while the individual pile ultimate resistance (Ru,i) is estimated as described in 

Section 5.4 (for auger displacement piles). 

Piles in a Strong Layer with a Weak Underlying Layer 

If a weak formation is present the group efficiency should be checked to ascertain whether a 

group efficiency of less than 1.0 is warranted. The group efficiency may be checked as 

described in Section 5.5.2.1, where the individual pile ultimate resistance (Ru,i) is estimated as 

described in Section 5.4 (for auger displacement piles). Note that a potentially problematic 

condition may exist if the overlying strong layer is capable of stopping the penetration of DD 

piles. If the piles are terminated at this shallow “refusal” depth, the group effect must be 

checked for punching shear through into the underlying weak layer using the block failure 

concept described in the previous section. However, it is likely that settlement concerns could be 

significant, and these issues must be addressed as outlined in the following sections. 

5.5.3 Settlement of Pile Groups 

The development of resistances with pile displacements of individual piles was discussed in 

Chapter 5.2. Displacements of individual piles at ultimate resistances (or in limited cases the 

load development with pile displacement) derived from many studies and prediction methods 

were presented in Section 5.3 and Appendix A. However, the settlement of a pile group is likely 

to be many times greater than the settlements predicted with the assumption that the piles act 

individually, especially for cases where the soils near the pile tips are more compressible. 

The greater settlement of the pile group is attributed to a deeper zone of influence for the pile 

group than that for a single pile. The group effect of the piles mobilize a much deeper zone that 

that of a single pile, as illustrated in Figure 5.18. 

Settlement of pile groups can be attributed to a combination of elastic compression of the piles 

and settlement of the surrounding soils. Settlement of the surrounding soils primarily consists of 

nearly instantaneous compression for purely cohesionless soils, and primarily time-dependant 

consolidation for purely cohesive soils. Note that layered systems of soils may contain 

appreciable amounts of both compression and consolidation settlements. 

95 
Source: Hannigan et al. (2006), after Tomlinson (1994) 

Figure 5.18: Deeper Zone of Influence for End-Bearing Pile Group than for a Single Pile 

Design engineers, who must consider pile foundation settlements, should carefully consider the 

magnitude and timing of the application of loads and their effect on the structure. For instance, 

the dead load of the column, pier cap, and perhaps other portions of the bridge structure may be 

in place, therefore, settlement due to these loads may be complete before the final connections of 

any settlement-sensitive portions of the structure are made. It may be possible that only 

settlements resulting from loads are imposed after the girder bearing plates are set are of 

significance to the structure. 

Simplified methods for estimating pile group settlement are presented in the following sections. 

The methods presented were formulated for driven pile groups and are considered to be generally 

representative of CFA and DD pile group settlements. The deeper zone of influence for a pile 

group is unlikely to be significantly affected by differences in installation between piles of 

different types, although differences in individual pile stiffness and mobilization of capacity can 

affect settlements to some degree. 

5.5.3.1 Elastic Compression of the Pile 

The elastic compression of the pile is a function of the imposed load, pile stiffness, and the load 

transfer characteristics from the pile to the surrounding soil. 

Defining the stiffness ratio as: 

⎛

⎜

⎜

⎞

⎟

⎟

⎛ L
 E ⎜

⎝

⎞

⎟

⎠

soil 

Epile 

S
 = ⋅ R (Equation 5.35) B ⎝ ⎠

where: L = pile embedment depth, B = pile diameter, Esoil = average Young’s modulus of the 

soil, and Epile = Young’s modulus of the pile. 

96 
For many practical problems, a pile may be considered “rigid” if its stiffness ratio (SR) is 

approximately SR ≤ 0.010. In these cases, the elastic shortening of the pile is likely to be very 

small compared to the settlements of the soil in which the pile is embedded. Otherwise, elastic 

compression (∆) should be estimated and included in settlement calculations. This compression 

should be subtracted from the pile total displacement when determining the development of sideshear or end-bearing developed stresses at values less than ultimate. 

The elastic compression of a pile (∆) may be calculated as the sum of elastic compression of “n” 

pile segments as follows: 

n Q ⋅ L ∆ = ∑ i i (Equation 5.36)

i=1 Ai ⋅ Ei 

Where: Li, Ai, and Ei are the length, average cross-sectional area, and average composite 

modulus, respectively, for each of the pile segments. Qi 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 of the pile to soil system. If downdrag or uplift were 

to occur, the load distribution would be as described in Section 5.7. 

The load imposed to an individual pile could become a complex solution if the pile cap were to 

provide a contribution to the total capacity of the pile group system (i.e., a pile raft as described 

in Section 5.5.4), and the group was subject to eccentric effects. However, to estimate the load 

imposed to the individual pile for purposes of elastic compression calculations, it may be 

sufficient to simply divide the total load of the pile group by the number of piles. 

For many practical problems, an estimate of elastic shortening may be made using simplified 

assumptions regarding the load distribution in the pile. For example, a constant load transfer rate 

(i.e., a uniform unit side-shear stress along the entire length of the pile) and axial load supported 

entirely in side friction would result in a triangular distribution of load in the pile vs. depth 

ranging from the maximum load at the pile top to 0 load at the pile toe. For this condition, the 

elastic compression may be computed as: 

⎛ 1 ⎞ Qmax ⋅ Lpile ∆= ⎜ ⎟⋅ (Equation 5.37) ⎝ 2 ⎠ Apile ⋅ E pile 

Where: Qmax is the total maximum imposed load and Lpile and Apile are the pile total length and 

cross-sectional area, respectively. 

An upper bound (other than the possibility of downdrag) is represented by a pile acting as a 

free-standing column with no load transfer along the entire length of the pile and the total 

maximum imposed load to the pile-supported in end-bearing. For this condition, Equation 5.38 

provides an upper bound estimate of elastic shortening in the pile. 

97 
Q max ⋅ Lpile ∆ = (Equation 5.38) max A pile pile ⋅ E

Note that downdrag or soil swell conditions could present a more significant pile load, and for 

such a case Qmax would be determined as described in Section 5.7. 

Equations 5.37 and 5.38 can be used to quickly estimate the potential magnitude of elastic 

shortening and determine if a more complete evaluation of load distribution is justified for the 

purpose of computing settlement. 

5.5.3.2 Compression Settlement in Cohesionless Soils 

Meyerhof (1976) recommended that the compression settlement of a pile group (Sgroup) in a 

homogeneous sand deposit (not underlain by a more compressible soil at greater depth) be 

conservatively estimated by the correlations to either SPT-N values or to CPT-qc values. If the 

group was underlain by cohesive deposits, time-dependant consolidation settlements would be 

needed, as described in the following section. The method proposed by Meyerhof (1976) does 

not distinguish 60% hammer efficiency for N-values. However, the 60% correction is 

recommended. 

For SPT-N values in cohesionless soils: 

S = 0.96 p f I f B 

for sands (Equation 5.39) group N60 ' 

1.92 p f I f B

S = for silty sands (Equation 5.40) group N60 ' 

For CPT qc values in cohesionless saturated soils: 

42 p f f I B

S = (Equation 5.41) group 

qc 

 

 

 

where: 

Sgroup = estimated total settlement (in.); 

pf = foundation pressure (tsf), which is obtained as the group load divided by group 

area on plan view; 

B = width of pile group (ft); 

D = pile embedment depth below grade (ft) 

If = influence factor for group embedment = 1 – D/(8B) ≥ 0.5; 

N 60' = average corrected SPT-N value (bpf per 0.3 m) within a depth B below the pile tip 

level; and 

qc = average static cone tip resistance (tsf) within a depth B below the pile tip. 

98 
5.5.3.3 Consolidation Settlement in Cohesive Soils 

Consolidation settlement of cohesive soils is generally associated with sustained loads and 

occurs as excess pore pressure dissipates (primary consolidation). For purpose of discussion in 

this section, the time rate of settlement will not be addressed directly. Design for a total 

magnitude of settlement for the full sustained dead load on the structure would represent a 

conservative approach to settlement in cohesive soils. For most structures, a portion of the dead 

load will be in place (pile cap, column, pier cap, etc.), and consolidation for that portion of the 

load may be nearly complete, before settlement-sensitive portions of the structure (above the 

girder bearing plates) are in place. Should computed settlements for total sustained dead load be 

found to significantly affect the design, it may be prudent to evaluate the time rate of the 

settlement for construction loads to more accurately assess the post-construction settlements. 

Time rate of primary consolidation is a topic covered in most geotechnical texts and in the 

FHWA Soils and Foundations Workshop Manual (FHWA NH1-06-088). 

The consolidation settlement is driven by the load exerted on the pile group and resulting stress 

distribution into the soil below and around the pile group. The actual stress distribution in the 

subsurface can be affected by many factors including the soil stratigraphy, relative pile/soil 

stiffness, pile to soil load transfer distribution, pile cap rigidity, and the amount of load sharing 

between the cap and the piles. For most practical problems, a simplified model of stress 

distribution is sufficient to estimate pile group settlements. The equivalent footing method is 

presented below as a simplified method to estimate vertical stress with depth in the soil below 

the pile group. 

Terzaghi and Peck (1967) proposed that pile group settlements could be evaluated using an 

equivalent footing situated 1/3 of the pile embedment depth (D) above the pile toe elevation, and 

this equivalent footing would have a plan area of the pile group equal to the width (B) times the 

pile group length (Z). The pile group load over this plan area is then the bearing pressure 

transferred to the soil through the equivalent footing. The same load is then assumed to spread 

within the frustum of the pyramid of side slopes of 1 (horizontal): 2 (vertical), thus reducing the 

bearing pressure (pd with depth) with depth as the area increases. This concept is illustrated in 

Figure 5.19. 

In some cases, the depth of the equivalent footing should be adjusted based on soil stratigraphy 

and load transfer mechanism to the soil, rather than fixing the equivalent footing at a depth of 1/3 

D above the pile toe for all soil conditions. Figure 5.20 presents the recommended location of 

the equivalent footing for a variety of load transfer and soil resistance conditions. 

The cohesive soils below the equivalent footing elevation are broken into layers, and the total 

consolidation settlement is the sum of the settlements of each layer. A plot of the relationship 

between void ratio (e) and logarithm of the vertical effective consolidation stress (p) determined 

in the laboratory is used to estimate the consolidation settlement. Multiple laboratory curves 

may need to be generated to accommodate the different layers depending on the soil consistency 

and maximum past pressures. The settlement of each layer may be calculated as presented in the 

99 
three following equations. A generic example of this consolidation curve is shown in Figure 

5.21 to illustrate the terms in these equations. 

Source: Hannigan et al. (200

Figure 5.19: Equivalent Footing Concept for Pile Groups 

The settlement (Si) for an overconsolidated cohesive soil layer, where the pressure after the 

foundation pressure increase is greater than the soil preconsolidation pressure (po + ∆p > pc), is 

obtained as: 

⎡ ⎡

⎢

⎢⎣

⎛ ⎤ ⎤ ⎜

⎝

⎜

⎞

⎟

⎠

⎟

⎛

⎜

⎝

⎞

⎟

⎠

⎟

p p σ ∆p 

1 

C C +

p 

S H
 log c 

0 

H
 c log⎜ (Equation 5.42) r ⎢ +

⎢⎣ ⎥

⎥⎦ ⎥

⎥⎦

=
 i 1+ e p + e 0 0 c 

6) 

The settlement (Si) for an overconsolidated cohesive soil layer, where the pressure after the 

foundation pressure increase is less than the soil preconsolidation pressure (po + ∆p < pc), is 

obtained as: 

σ σ

⎡

⎢

⎢⎣

Cr p0 p 

⎜ ⎟ 1 e p 

⎛ ⎤ ⎜

⎝

⎞

⎟

⎠

+ ∆ S
 H
 log ⎥ (Equation 5.43)

⎥⎦

=
 i

+
 

100 
Notes: 

(1) Plan area of perimeter of pile group = (B)(Z). 

(2) Plan area (B1)(Z1) = projection of area (B)(Z) at depth based on shown pressure distribution. 

(3) For relatively rigid pile cap, pressure distribution is assumed to vary with depth as above. 

(4) For flexible slab or group of small separate caps, compute pressures by elastic solutions.

Source: Cheney and Chassie (1993) and Hannigan et al. (2006)

Figure 5.20: Pressure Distribution Below Equivalent Footing for Pile Group 

101 
 

Applied Pressure = p0 + ∆p 

Void Ratio, e 

Virgin Compression Line 

Estimated Preconsolidation 

Pressure, pc 

Recompression Line 

Cc 

1 Cr

 1 

p0 pc p0 +∆p 

Log Pressure, p 

Source: Hannigan et al. (2006) 

Figure 5.21: Typical e vs. Log p Curve from Laboratory Consolidation Testing 

The settlement for a normally consolidated cohesive soil layer (po = pc) is: 

⎡

⎢

⎢⎣

Cc ⎜ ⎟ 1 

⎛

⎜

⎝

⎞

⎟

⎠

po + ∆p S
 H
 log ⎥ (Equation 5.44)

⎥⎦

=
 i + e p o o 

⎤

where: Si = total settlement; 

H = original thickness of layer; 

Cc = compression index; 

Cr = recompression index; 

eo = initial void ratio; 

po = effective overburden pressure at midpoint of stratum, prior to pressure 

increase; 

pc = estimated preconsolidation pressure; and 

∆ = average change in pressure. 

If the soil were underconsolidated (i.e., po > pc), the consolidation process due to loads imposed 

prior to placement of the foundation would continue, and this would result in an additional 

downdrag load to the pile group, as discussed in Section 5.7. 

102 
5.5.4 Uplift of Single CFA Piles and CFA Pile Groups 

CFA piles behave essentially as drilled shafts in response to uplift. CFA piles can be particularly 

efficient in uplift because their long, slender shape maximizes side-shear for a given volume of 

grout or concrete. A limiting factor for uplift may be the ability to place sufficient reinforcing 

steel; however, a single high-strength bar can be placed full length in most circumstances. 

Uplift forces may be exerted on CFA piles by either an applied external uplift force or due to 

swelling of surrounding soils. Note that an uplift resistance is provided in response to the case of 

externally applied loads, while an uplift load is applied to the pile in the case of swelling soils. 

The ultimate upward side-shear resistance may be determined as a portion of the ultimate 

downward side-shear resistance using the methods for axial compression loading on CFA piles 

recommended in this chapter, but with opposite sign (direction). For piles in cohesive soils 

subjected to uplift, the upward resistance may be estimated as the same magnitude as the 

downward resistance. For piles in cohesionless soils subjected to uplift, the upward directed 

side-shear from the pile can produce a potential reduction in effective stress in the vicinity of the 

pile. The ultimate uplift side-shear resistance in cohesionless soils can be maintained up to 

100%. However, it has been determined in numerous studies that the remaining side-shear 

resistance range from about 70 to 100% of the downward ultimate resistance. It is recommended 

that to obtain the ultimate side-shear resistance in cohesionless soils for uplift the side-shear 

resistance used for compressive loading be multiplied by a factor of 0.8. Note that appropriate 

safety factors still need to be applied to obtain the allowable uplift resistance. 

The uplift resistance of a pile group should be determined in accordance with AASHTO (1996) 

for service load design that states that the group uplift should be determined as the lesser of: 

(1) The design allowable uplift capacity of a single pile times the number of piles in the 

group. The design uplift capacity of a single pile has been specified above. The design 

allowable uplift should be taken as one third of the ultimate, if determined by a static 

analysis method, or one half, if determined by a load test. 

(2) Two thirds of the effective weight of the group and soil contained within a block 

defined by the perimeter of the pile group and the embedded length of the piles (see 

Figure 5.17). 

(3) One half of the effective weight of the pile group and soil contained within a block 

defined by the perimeter of the pile group and the embedded pile length plus one half of 

the total soil shear resistance on the peripheral surface of the pile group (see 

Figure 5.17). 

Soil uplift on a pile is most often caused by the swelling of expansive soils, or may also occur 

through ice jacking (frost heave, or upward load imposed from an ice sheet frozen to the pile or 

column/pier). When the uplift force is caused by the swelling of surrounding soils, it should be 

considered as a load to the pile and may be determined equal to the ultimate downward side103 
shear values on the CFA piles, using the methods recommended herein [but opposite sign 

(direction)]. Note that a reduction factor should not be applied to cohesionless soils when the 

uplift is a soil load because the reduction in effective stress around the pile would not be 

anticipated in such a condition. 

5.6 LATERAL RESISTANCE AND STRUCTURAL CAPACITY OF CFA PILES 

5.6.1 Behavior and Limitations of CFA Piles 

Although published results are limited, lateral load-tests have shown that CFA piles behave 

essentially like drilled shafts when the differences between the pile material properties are 

accounted for (i.e., differences in grout or concrete used for CFA piles and amount of reinforcing 

steel). References for lateral load-tests on CFA piles include O’Neill et al. (2000) in 

over-consolidated clays in Coastal Texas, and Frizzi and Meyer (2000) in the dense Pamlico 

sand and Miami limestone (vuggy) formations are typical of South Florida. 

Because of structural capacity limitations related to reinforcement, CFA piles generally do not 

provide large resistances to lateral loading compared to that which can typically be developed 

with drilled shafts and driven pile groups. Typically, a reinforcing cage is set to only a sufficient 

depth to accommodate the section of pile where the bending stresses are at or near the maximum, 

with a single bar often set through the centerline of the pile to the full pile depth. For 

applications requiring greater reinforcement than is practical from reinforcing cages, it is 

possible to reinforce CFA piles with structural steel sections such as H or pipe, similar to 

micropile construction techniques. 

In the construction of CFA piles, the reinforcing cages are typically set into the freshly placed 

grout or concrete except for the special case of some types of screw piles where the cage is 

placed through the hollow auger. Placing the reinforcing cages in freshly placed grout can limit 

the amount of steel that can be penetrated into the grout to the pile full depth. This limitation is 

affected by soil conditions and the concrete or grout mix properties. 

CFA piles constructed in cohesive soils generally provide for greater penetration ability for a full 

reinforcing steel cage (often to 45 m [150 ft] or more), as the water in the concrete or grout mix 

is better retained and thus workability is better maintained. Conversely, free-draining 

cohesionless soil will allow bleed water from the concrete or grout mix to escape into the 

surrounding soil; this rapid fluid loss limits the in-situ workability of the remaining grout. 

Penetration ability for a full reinforcing steel cage in free-draining soils (e.g., sand) may thus be 

limited, especially if the sand is dry. 

CFA piles typically have a diameter in the range of 0.35 to 0.60 m (14 to 24 in.) and are rarely 

constructed in excess of 0.9 m (36 in.) in diameter. When accounting for concrete cover of the 

reinforcing steel (particularly in aggressive environments), this leaves little room for a rebar cage 

diameter to provide a cross-sectional moment to resist the bending stresses. 

It is possible to design groups of CFA piles to include batter piles to enhance lateral stiffness and 

capacity of the group, as may be done with driven piles. Analyses of a CFA pile group may be 

104 
performed in a similar manner to other deep foundation types, using computer codes such as 

GROUP (Ensoft, 2006) or FB-Pier (BSI, 2003). However, the use of batter piles can be limited 

by concerns relating to ground movement from settlement and by the increased construction 

difficulty associated with placing a rebar cage within a batter CFA pile. The use of batter piles 

over water is not a typical CFA pile application. 

In the special case of a secant or tangent pile wall constructed using CFA piles, the procedures 

for analysis are similar to other types of deep foundation elements. The differences for CFA 

piles are in the sizes and depth limitations, along with the need to install reinforcement after the 

grout or concrete is in place. 

5.6.2 Lateral Analyses Using the p-y Method 

The p-y method is recommended for lateral load analyses of vertical CFA piles and pile groups. 

The p-y method is a general method for analyzing laterally loaded piles with combined axial and 

lateral loads, including distributed loads along the pile, non-linear bending characteristics 

(including cracked sections), layered soils and/or rock, and non-linear soil response. The method 

utilizes a numerical solution to the governing equations, and a variety of software is available to 

perform the analyses. 

A physical model for a vertical laterally loaded pile is shown in Figure 5.22. The pile is modeled 

as a simple beam with boundary condition specified as pile head loads, as shown. The soil has 

been idealized by a series of non-linear springs with depth that provide reaction to the external 

loading imposed at the head. At each pile depth (x) the soil reaction (p) resisting force per unit 

length along the pile) is a nonlinear function of (y) lateral deflection, which is dependent on the 

soil shear strength and stiffness, piezometric surface, pile diameter, depth, and whether the 

loading is static (monotonic) or cyclic. 

Although the curves have been shown as bi-linear in the preceding figure, actual p-y curves used 

for design are usually more complex-curvilinear functions. The nonlinear soil resistance (p) as a 

function of displacement (y) has been derived from instrumented full-scale load-tests in a variety 

of soils. From these instrumented tests and simple theory of passive earth pressure response 

around a pile, empirical correlations of p-y response with soil properties have been developed for 

different soil types. Computer programs for lateral load analyses of piles contain many of these 

models, and allow the user to input a user-developed curve of any shape (presumably based on 

local experience, correlations with in-situ tests, latest research in a specific geology, etc.). 

Lateral models for soils are correlated with basic strength and stiffness information obtained 

during the geotechnical investigation. For example, cohesive soils will require input profiles to 

the depth along the pile of shear strength (Su), a stiffness parameter associated with strain at a 

compressive stress equal to 50% of the compressive strength from uniaxial strength testing (ε50), 

and unit weight (γ). Cohesionless soils will require input profiles of soil friction angle (φ), 

subgrade modulus (k), and unit weight (γ). Ground water elevation must also be defined. 

105 
Source: O’Neill and Reese (1999) 

Figure 5.22: p-y Soil Response of Laterally Loaded Pile Model 

A more detailed description of many lateral soil models may be found in Reese (1986) and 

O’Neill and Reese (1999). 

Note that loss of soil resistance due to scour or liquefaction must be considered as a part of the 

lateral load analysis. In some cases, it may be necessary to consider the loss of soil resistance 

when calculating the axial capacity of piles. Conditions in which liquefaction results in loss of 

soil resistance along a significant portion of the pile length could be problematic for CFA piles of 

small diameter due to the inherent limitations of bending capacity and reinforcement in small 

diameter piles. 

For these analyses, the pile is modeled as a beam-column with a distributed load along the length 

of the beam produced by the elastic (spring) foundation. The governing differential equations 

for the solution of a beam on an elastic foundation were derived by Hetenyi (1946). For the 

general case of combined lateral and axial loading, the following governing differential equation 

applies: 

d 4 y d 2 

y EI + P − p − w = 0 (Equation 5.45) dx 4 x dx 2 

106 
where: x = distance along pile length; 

Px = axial load; 

y = lateral deflection at a point with coordinate x; 

p = lateral soil reaction, (measured as a force per unit length of pile); 

EI = flexural rigidity of pile; 

E = pile elastic modulus; 

I = movement of inertia of pile cross-section; and 

w = distributed load along the length of the pile (due to either soil or water, if any). 

Available computer codes typically discretize the pile and soil into a number of segments and 

nodes (i.e., finite difference, finite elements) via numerical methods to obtain solutions to 

complex problems. The numerical methods can handle great complexity and offer the advantage 

of their relative simplicity to the user. In these models, the solution produces computed soil 

resistance (p), shear (V), moment (M), pile slope (S), and pile deflection (y) at each node along 

the pile. The beam equations for shear, moment, and slope are derived as follows (FHWA-RD85-106): 

d 3 y V = EI (Equation 5.46) dx 3 

M = EI (Equation 5.47) dx 2 

d 2 y

dy S = (Equation 5.48) dx 

In addition to the axial load, the boundary conditions at the pile head must be specified by a 

lateral force (Pt) and a moment (Mt), as shown in Figure 5.22. Alternatively, these conditions 

may be specified in terms of lateral displacement, slope, or a rotational restraint, relating the 

slope at the top of the pile to the pile head moment. A free-head condition is represented by a 

specified lateral force and moment, as shown in Figure 5.22. This condition might be 

representative of a CFA pile used to support a soundwall, sign, light pole, or any similar freestanding structure that is cantilevered above a single CFA pile. For groups of CFA piles 

incorporated into a rigid cap, the rotational stiffness of the group and a full moment connection 

into the cap would result in a pile top condition approaching that of a fixed head pile (i.e., pile 

head is completely restrained). A fixed-head condition might be specified by using a lateral 

force and a slope at the pile head of zero. Computer software for modeling pile groups can be 

used to specify the group loads and incorporate the appropriate boundary condition for each pile 

into the group solution. 

107 
Figure 5.23 illustrates a computed solution for a pile that is restrained against rotation at the pile 

head and is subjected to a lateral shear force. The moment is observed to be a maximum at the 

pile head due to the rotational restraint; the pile slope approaches zero at the pile head. 

0 

-5 

-10 

-15 

-20 

-25 

-30 

-35 

-5 

-10 

-15 

-20 

-25 

-30 

-35 

Deflection, inches Bending Moment, inch-kips 

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 -600 -400 -200 0 200 400 

0 

Depth, ft 

Depth, ft 

-40 -40 

Figure 5.23: Example Deflection and Moment Response of Laterally Loaded Pile Model 

The nonlinear p-y relationship described earlier is implemented at each node by using a secant 

modulus (Es), as indicated below: 

p Es = (Equation 5.49)

y 

Therefore, at each node (i) along the length of the pile, the value of soil reaction (pi) is expressed 

as the secant modulus multiplied by the deflection (or Esi yi). Because the p-y response is 

nonlinear, an iterative solution is used to repetitively update the secant modulus so as to track the 

nonlinear relation of p at a range of differing values of y. This method of successive 

approximation using a secant modulus is computationally intense but very stable, and allows p-y 

curves to incorporate features such as strain-softening, loss of resistance due to cyclic loading, 

and other deflection-dependent effects on soil resistance that may be observed in experiments. 

Non-linear stress-strain relationships are also available for both the steel and the concrete 

materials in a computer solution. The assumed stress strain relationship built into most programs 

for the steel is shown in Figure 5.24, while that for concrete is shown in Figure 5.25. 

108 
Source: O’Neill and Reese (1999) 

Figure 5.24: Typical Stress-Strain Relationship Used for Steel Reinforcement 

For steel, the value of yield stress (fy) is the same in compression (positive or +, in the sign 

convention adopted herein) and in tension. Reinforcing steel used is usually Grade 60 with a 

yield stress of 413 MPa (60 ksi) and a modulus (E) of 200,000 MPa (2,900 ksi). By definition, 

the yield strain is the yield stress divided by the modulus (εy = fy /E). 

Source: O’Neill and Reese (1999) 

Figure 5.25: Typical Stress-Strain Relationship Used for Concrete 

For concrete, the compressive strength depends on the mobilized compressive strain. First, the 

compressive strength increases up to the reduced ultimate compressive strength (f′′c), which is 

taken as a percentage of the 28-day cylinder compressive strength. The strength is expressed as 

109 
 

⎡ 2 ⎤ ⎛ ε ⎞ ⎛ ε ⎞ f c = f '' c ⎢2 ⎜

⎜ ⎟

⎟ − ⎜⎜ ⎟

⎟ ⎥ for: ε < ε o (Equation 5.50a) ⎢ ⎝ ε o ⎠ ⎝ ε o ⎠ ⎥ ⎣ ⎦

f c = 0.85 f '' c for: ε = 0.038 (Equation 5.50b)

f c = linearly interpolated for ε o < ε < 0.038 

With: 

f '' c = 0.85 f ' c (Equation 5.51)

1.7 f ' c ε o = (Equation 5.52) Ec 

Where fc ’ is the concrete compressive strength at 28 days, and Ec is the initial tangent slope of the 

stress-strain area. The value Ec can be estimated as: 

Ec = 57,000 f ' c (psi) (Equation 5.53a)

or Ec = 151,000 f ' c (kPa) (Equation 5.53b)

The ultimate tensile strength of concrete (fr) is estimated as 

fr = 7.5 f ' c (psi) (Equation 5.54a)

or fr = 19.7 f ' c (kPa) (Equation 5.54b)

The authors’ experience from observed behavior of instrumented load-tests on drilled shafts 

suggests that the computed modulus using the equations above tends to be somewhat 

conservative for concrete. Sand cement grout without coarse aggregate may have a slightly 

lower modulus than that of concrete of similar strength. 

The bending stiffness (EI) of the beam column system is not actually constant once cracking 

occurs in the concrete or grout. As the bending moment at any of the steel reinforced sections 

increases to the point at which tensile stresses at one side of the pile exceeds the tensile strength 

of the concrete or grout, the section cracks, and the value of EI is reduced significantly at that 

cracked section. Note that a uniform, concentric axial compressive load (Px) will produce a 

uniform compressive stress (Px × Area). The superposition of this uniform compressive stress to 

the stress distribution produced by the bending moment on the uncracked section will allow for a 

larger bending moment at the point of crack initiation and beyond. Computer programs for 

lateral load analyses can include the reduction in stiffness. Figure 5.26 illustrates an example of 

computed EI as a function of moment for the case of an axial load of varying magnitude. 

110 
 

0.0E+00 

1.0E+07 

2.0E+07 

3.0E+07 

4.0E+07 

5.0E+07 

6.0E+07 

7.0E+07 

E I (ksi)

Px = 0 

Px = 60 kips Ultimate Moment 

Capacity 

(Plastic Hinges) 

Cracking Moments 

Section: 24-inch diameter CFA pile with 

six #8 bars uniformly spaced around a circle, 

(3-inches of concrete cover over bars). 

f'c = 6,000 psi, and f y = 60,000 psi

 Axial Load 

0 500 1,000 1,500 2,000 2,500 3,000 3,500 

Moment (in-kips) 

Figure 5.26: Variation of Pile Stiffness (EI) with Bending Moment and Axial Load 

5.6.3 Lateral Analyses of CFA Pile Groups 

The p-multiplier (Pm) method is recommended to account for group effects on lateral load 

response. For closely spaced piles in a group, values of soil resistance for a given p-y 

relationship are multiplied by a p-multiplier less than 1 (i.e., Pm<1), as shown in Figure 5.27. 

Therefore, the lateral capacity of the pile group at a given deflection level is less than the sum of 

the individual pile lateral capacities at that deflection. Also, the lateral deflection at a given load 

is greater than the deflection of an individual pile at the same load per pile. The value of this 

multiplier is dependent on the location of the pile within the group and the spacing of the pile 

group. “Front Row” piles are those that push into the soil without any piles ahead of them, and 

thus are the least affected by the presence of the other piles. “Second Row” piles are affected to 

a greater extent than the front row piles; “Third and Subsequent Rows” piles are the most 

affected by the group interaction. The group interaction may be described as the piles in the 

back pushing the soil forward into the area that is being vacated by the piles in front of them 

(often referred to as a “shadowing” effect). 

Values of p-multipliers (Pm) are provided in Table 5.4 for cyclic loading and static loading. 

111 
Source: Hannigan et al. (2006) 

Figure 5.27: The p-multiplier (Pm) 

Table 5.4: P-Multipliers (Pm) for Design of Laterally Loaded Pile Groups 

Soil Type (1) Test Type Pile Spacing 

(Cent.-Cent.) 

Pm for Rows: 

1 2 3+ 

Reported

Lateral Group 

Efficiencies 

Deflection

(mm) Reference 

Stiff Clay Field Study 3B .70 .50 .40 N/A 51 Brown et al. (1987) 

Stiff Clay Field Study 3B .70 .60 .50 N/A 30 Brown et al. (1987) 

Medium Clay Scale Model 

(Cyclic Load) 3B .60 .45 .40 N/A 600 (at 50 

cycles) Moss (1997) 

Clayey Silt Field Study 3B .60 .40 .40 N/A 25-60 Rollins et al. (1998) 

V. Dense Sand Field Study 3B .80 .40 .30 75% 25 Brown et al. (1998) 

M. Dense Sand Centrifuge Model 3B .80 .40 .30 74% 76 McVay et al. (1995) 

M. Dense Sand Centrifuge Model 5B 1.0 .85 .70 95% 76 McVay et al. (1995) 

Loose M. Sand Centrifuge Model 3B .65 .45 .35 73% 76 McVay et al. (1995) 

Loose M. Sand Centrifuge Model 5B 1.0 .85 .70 92% 76 McVay et al. (1995) 

Loose F. Sand Field Study 3B .80 .70 .30 80% 25-75 Ruesta and Townsend 

(1997) 

Note: (1) V = very, M = medium, F = fine 

112 
Computer programs such as GROUP (Ensoft, 2006) or FB-Pier (BSI, 2003) may be used to 

analyze the entire group of piles for a given axial, lateral, and moment loading applied to the pile 

cap. These codes compute the group p-multipliers by multiplying individual p-multipliers (Pm) and 

p-y curves for individual piles. Recent studies (Brown and O’Neill 2003) suggest that a simplified 

approach to the use of p-multipliers is suitable for design, particularly when considering that the 

direction of loading may not be known. A single p-multiplier equal to the average value of all the 

pile row p-multipliers in the group provides a reasonably accurate indication of the overall group 

deflection and stiffness. The shear and maximum moment distribution in individual piles within 

the group was found to deviate from the computed average response using the simplified method 

by no more than 20% in typical cases. The simplified analysis also allows the analysis of a single 

pile to be used to anticipate the lateral response of a typical pile within the group, with a 20% 

increase in computed maximum bending moment recommended for design in order to account for 

variations within the pile group. 

Analyses of an individual pile within the group can be performed using a computer code such as 

LPILE (Ensoft, 2006), but with p-multipliers applied to the individual p-y curves to account for 

group action. Within a group of piles connected to a common cap, a full moment connection to 

the cap would provide rotational restraint to the top of the pile so that the horizontal translation 

of the cap is modeled as a lateral shear or displacement at the pile head combined with a slope of 

zero. The lateral load resistance of the pile group is then equal to the sum of the lateral load 

resistance of the individual piles. 

5.6.4 Structural Capacity 

The structural capacity of CFA piles should be checked in the same manner, and to the same 

requirements as drilled shafts. While both types of foundations are reinforced, cast-in-place 

structural elements, some differences exist. Drilled shafts often have larger diameters and 

consist of non-redundant single shafts designed to support individual columns. On the other 

hand, CFA piles are typically used in groups with relatively small lateral and bending stresses on 

a per-pile basis. However, CFA piles can also be used as individual foundations for soundwalls, 

signs, or light pole structures where the design is dominated by flexure. The structural integrity 

should be checked for axial loading (including potential uplift loads), as well as bending and 

shear induced by lateral loading. 

The following sections describe the necessary steps for structural analysis and design of CFA 

piles based on the axial load requirements and bending stresses computed as a result of the lateral 

analyses using the p-y method. Note that the geotechnical design of CFA piles is outlined in 

accordance with allowable stress design (ASD). However, most states use the load and 

resistance factor design AASHTO specifications (AASHTO, 2006) for the structural design of 

reinforced concrete members. Structural design of CFA piles is outlined in accordance with 

LRFD as is typical of structural design of other reinforced concrete members in AASHTO 

(2006). To compute bending moments in the pile for structural design, the lateral load analyses 

must include factored load cases. 

113 
5.6.4.1 Longitudinal Reinforcement 

Reinforcing steel for CFA piles typically consists of two different sections: 1) a top section that 

consists of a full cage configuration of multiple longitudinal bars and transverse spirals or ties; 

and 2) a bottom section that consists of a single longitudinal bar along the centerline of the pile 

that extends the full length of the pile. 

An adequate section of steel reinforcement of CFA piles for the purpose of axial uplift loading is 

often accomplished by the insertion of a single bar down the center of the freshly placed grout or 

concrete column. Virtually any size bar needed to satisfy the structural requirements can 

typically be inserted to full depth. High-strength, threaded rods can be used in CFA piles 

similarly to the use with micropiles. 

The top section of reinforcement must extend to a depth that is below the area where large 

bending moments take place. It is recommended that the depth of full cage reinforcement be set 

to the inflexion point in the displacement profile (i.e., second point of zero displacement with 

depth), obtained from lateral load analysis. For instance, the pile shown in Figure 5.23 would 

require a reinforcing cage extending to approximately 7.5 m (25 ft) below the top of the pile. If 

this were a pile that extended to a depth of 15 or 18 m (50 or 60 ft) below grade, it would be 

unnecessary to install a full length cage. When relatively short piles are used and the computed 

deflection profile does not cross the zero axis at a second point, a full length reinforcing cage 

should be used. 

For ease of cage installation with both a top section cage and central bar only, the transverse 

reinforcement is often not included in approximately the bottom 1.2 m (4 ft) of the cage, and the 

longitudinal bars are bent inward toward the single bar at the center of the shaft to form a 

“tapered section” in the cage. In such case, the tapered section should not be counted as part of 

the cage length to the required minimum depth. 

Within the zone where the full cage is installed, the minimum longitudinal reinforcement area 

should be not less than 1% of the gross concrete area (Ag) of the pile. However, in the event that 

the pile size is larger than necessary to support the computed loads from a structural (not 

geotechnical) standpoint, then a reduced effective area (Ag’) may be used to determine the 

minimum longitudinal reinforcement and design strength as outlined in the O’Neill and Reese 

(1999) recommendations for drilled shafts and per section 10.8.4 of the ACI code (ACI, 2004). 

The reduced effective area (Ag’) is the area of concrete sufficient to provide the required axial 

strength and, in all cases, must be limited to not less than one half of the gross concrete area (Ag). 

If the reinforcement includes a central bar, this bar must extend throughout the top section cage. 

If a central bar is used, the area of the central bar may be included in the analysis of structural 

capacity and minimum requirements of the top cage section. 

The design of reinforced concrete piles for bending and axial forces follows procedures used for 

analysis and design of short columns. Figure 5.28a schematically illustrates the section of a 

reinforced concrete column loaded parallel to its axis by a compressive force P and moment M. 

The distribution of strains across the cross section at the instant the ultimate load is reached are 

114 
shown in Figure 5.28b. The internal forces within the pile, shown in Figure 5.28c, must be in 

equilibrium with the nominal strength, represented by the combined P and M. The internal forces 

are related to the strains by the modulus. For any of the bars with strains in excess of the yield 

strain (i.e., equal to the yield strength divided by the elastic modulus), the stress at failure is 

taken as the yield stress of the bar. 

3 2

a) cross section of 

4 1 circular reinforced 

concrete column; 

3 2 hatched section is 

uncracked concrete 

in compression 

ε

ε 1 

2 εc = 0.003 

b) strains 

ε4 ε3 

M 

P 

c) stresses and forces .85f’c 

As2fs2 

As4fs4 A f A f s1 s1 

s3 s3 

Figure 5.28: Circular Column (Pile) with Compression Plus Bending 

The analysis of the combinations of P and M to produce failure is called a strain compatibility 

analysis; the plot of these load combinations at failure is an interaction diagram. Details and 

examples of the calculations involved in the analysis described above is covered in most 

textbooks on reinforced concrete design. 

Satisfactory pile designs are those where all combinations of axial loads and bending moments 

are contained within the factored ultimate resistance interaction diagram for all critical pile 

sections, and where the transverse shear requirements are met. The interaction diagram is a plot 

of all combinations of axial and bending forces on a column that would result in structural yield 

of the column. The factored interaction diagram would lie inside the interaction diagram of 

ultimate resistance and are obtained by multiplying the “ultimate” interaction diagram by 

resistance factors for axial and bending. 

115 
To calculate the required amount of longitudinal reinforcement, the interaction diagram must be 

determined. The maximum bending moment and axial load calculated from the lateral analysis 

of the pile foundation are compared against the factored interaction diagram. Figure 5.29 shows 

a typical interaction diagram, both with the nominal and the factored ultimate resistances. 

The nominal ultimate resistance interaction diagram, shown as the solid line in Figure 5.29, 

should be obtained for all critical pile sections. Computer programs for lateral analyses typically 

include options for generating this interaction diagram at specified pile sections. 

 

Px 

M 

0.9 M (nom.) (P = 0) x

P = 0.85 f ' s c g s y s (A - A ) + f A

Pn s = β P Nominal ultimate 

resistance 

interaction diagram 

Factored ultimate 

resistance 

interaction diagram 

NOT TO SCALE 

P' = 0.133 f c 

' Ag 

Pr = φ Px 

(nom.) 

Mr = φ Mx 

(nom.) 

Permissible

Source: O’Neill and Reese (1999) 

Figure 5.29: Example Interaction Diagram for Combined Axial Load and Flexure 

The factored axial resistance (i.e., the intersection of the solid line with the Px-axis for axial 

compressive load only) is obtained as follows: 

Pn = β PS = β [0.85 ƒc' (Ag – As) + ƒy AS] (Equation 5.55) 

where: Pn = nominal ultimate axial resistance; 

fc ’ = compressive concrete strength at 28-days; 

fy = yield strength of the longitudinal reinforcing steel; 

Ag = gross cross-sectional area of concrete; 

116 
 

As = cross-sectional area of the reinforcing steel; and 

β = reduction factor to account for the possibility of small axial load eccentricities. 

β = 0.85 for spiral transverse reinforcement, and β = 0.80 for tied transverse 

reinforcement. 

Because resistance factors are different for pure axial and bending, the interaction diagram used 

for design involves transitional factors for cases with combined axial and bending. A transition 

point is defined by the axial load P’ in Figure 5.29, which is defined as: 

P’ = 0.133 fc’ Ag (Equation 5.56) 

The factored resistance interaction diagram (shown as the dashed line in Figure 5.29) is obtained 

above the P’ line by simultaneously multiplying the nominal ultimate axial resistance (Px) and 

the nominal ultimate flexural resistance (Mx) by a resistance factor (φ), 

P = φ P and M = φ M (Equation 5.57) r x r x 

where φ = 0.75 for either spiral or tied transverse reinforcement (AASHTO, 2006) 

The factored flexural resistance for pure flexure (i.e., Px = 0) is determined as 0.9 of the nominal 

ultimate flexural resistance, or 0.9 M. For locations between Px = 0 and Px = P’, the factored 

resistance is obtained by multiplying the nominal ultimate flexural resistance by a factor linearly 

interpolated between φ = 0.9 (for Px = 0) and φ = 0.75 (for Px = P’). In most cases for CFA 

piles with large bending moments, bending controls the structural design and the computed 

combinations of axial forces and bending moments lie close to the Px = 0 side of the diagram. 

5.6.4.2 Shear Reinforcement 

The pile design should first be checked to determine if the concrete section has adequate shear 

capacity without shear reinforcement. The factored shear resistance (φ Vn) of the concrete 

section can be determined as follows: 

φ V = φ V A (Equation 5.58) n c V 

Where: Vn = nominal (computed, unfactored) shear resistance of section; 

 φ = capacity reduction factor for shear, usually equal to 0.85; 

AV = cross-sectional area that is effective in resisting shear; and 

Vc = concrete shear strength. 

The cross-sectional area that is effective in resisting shear can be evaluated for a circular CFA 

pile as: 

117 
⎡B ⎤ AV = B + 0.58 rls (Equation 5.59) ⎢

⎣ 2 ⎥

⎦

where 

B db rls = − dc − (Equation 5.60) 2 2 

where: rls = radius of the ring formed along the centroids of the longitudinal bars; 

B = pile diameter; 

dc = depth of concrete cover; and 

db = diameter of longitudinal bars. 

The concrete shear strength can be estimated as: 

⎛ P ⎞

VC = ⎜

⎜

1+ 0.00019 φ ⎟

⎟ f c ' (fc ’ in psi) (Equation 5.61a) A ⎝ g ⎠

⎛ P ⎞

VC = ⎜0.166 +φ 0.000032 ⎟ f c ' (fc ’ in MPa) (Equation 5.61b) ⎜ A ⎟ ⎝ g ⎠

Where P = axial load and Ag = gross concrete area. 

For a pure bending case (i.e., Px = 0), this reduces to: V C = f c ' (fc ’ in psi) or V C = 0.166 f c ' 

(fc ’ in MPa). 

If the factored shear resistance is greater than the factored shear load for the critical sections (as 

determined from p-y analyses), the minimum area of transverse reinforcement recommended 

below is adequate. If the factored shear resistance is less than the factored shear load, then: a) 

the pile diameter should be increased; or b) the shear reinforcing must be analyzed specifically to 

ensure that sufficient shear capacity is provided. The latter is likely to be an unusual 

circumstance for a CFA pile under normal conditions because bending moments associated with 

high shears are likely to control pile diameter. 

If a spiral is used for the transverse reinforcement, the minimum reinforcement ratio (ρ) will be 

determined in accordance with the AASHTO code as: 

⎛ Ag ⎞ ⎛ f c ' ⎞

ρ S = 0.45 ⎜

⎜ −1⎟

⎟ ⎜ ⎟ (Equation 5.62) A f ⎜ ⎟ ⎝ c ⎠ ⎝ y ⎠

118 
where: ρS = Volume of spiral steel per turn/Volume of concrete core per turn; 

 Volume of spiral steel per turn = area of bar × π × diameter of spiral hoop; 

 volume per turn of concrete core = Ac × pitch of spiral; 

Ac = cross-sectional area of concrete inside spiral steel = 0.25 × π × (core diameter)2

; 

A = gross cross-sectional area of concrete of pile cross section; 

fc ′ = concrete compressive strength at 28-days; and 

fy = yield strength of the spiral reinforcing steel. 

If a tied bar is used for the transverse reinforcement, the minimum requirement is: 

• #3 tied bars may be used for cages with longitudinal reinforcing smaller than # 11 bars 

• #4 tied bars may be used for cages with longitudinal reinforcing of #11 bars or larger. 

The vertical spacing of the tied bars shall not exceed the lesser of: 

• the pile diameter; or 

• 300 mm (12 in.). 

Where the pile with minimum transverse reinforcement has inadequate shear resistance, the pile 

design may be changed to: (1) a larger diameter pile; (2) higher concrete compressive strength; 

or (3) transverse reinforcement greater than the minimum to increase the shear resistance. The 

required area of transverse steel is determined as follows: 

S V A steel vs = (Equation 5.63) ⎡B ⎤ f y + 0.58 r ⎢

⎣ ls ⎥ 2 ⎦

Where: Avs = required area of transverse steel; 

S = longitudinal spacing of the ties (spiral pitch); 

Vsteel = nominal shear resistance of transverse steel (equal to total nominal shear 

resistance needed less shear resistance provided by concrete); 

fy = yield strength of steel; and 

rls = radius of the ring formed along the centroids of the longitudinal bars on 

cross section. 

119 
5.6.5 Concrete or Grout Cover and Cage Centering Devices 

The concrete cover requirements of Section 5.12.3 AASHTO (AASHTO, 2006) apply for CFA 

piles. For water-to-cement ratios (W/C) between 0.40 and 0.50, the minimum cover of concrete 

or grout over the longitudinal bars must be 75 mm (3 in.) and 100 mm (4 in.) for aggressive 

environments (e.g., exposure to salt water). The required cover for transverse reinforcement may 

be less than that required for longitudinal bars by no more than 12 mm (0.5 in.). Transverse 

reinforcement greater than 13 mm (0.5 in.) would thus necessitate greater cover than longitudinal 

bars. This is rarely the case for CFA piles, as they typically have transverse reinforcement no 

greater than 13 mm (0.5 in.). 

For W/C ratios greater than or equal to 0.50, the cover requirements must be increased by a 

factor of 1.2. For W/C ratios less than or equal to 0.40, the cover requirements may be decreased 

by a factor of 0.8. However, low W/C ratios can pose constructability problems with 

reinforcement. 

Centering devices must be used with CFA pile construction to maintain alignment of the steel 

reinforcing cages that are being inserted into the freshly placed concrete or grout. The centering 

devices for full cages are similar to the centering devices used for drilled shaft construction, and 

most often plastic “wheels” that are installed around the transverse reinforcement. The central 

longitudinal bar is typically centered with a set of skids such that the arrangement of skids is 

axis-symmetric around the central bar. Note that the orientation of either wheels or skids must 

be such that they roll or easily slide, respectively, along the borehole wall without scraping into 

the soil. 

5.6.6 Seismic Considerations 

Where seismic loadings govern design, there may be several considerations that influence the 

design of a deep foundation. A complete discussion of the design of deep foundations for 

seismic loading is beyond the scope of this manual. However, it is appropriate to summarize 

herein the major points that may affect the selection and design of CFA piles for projects where 

seismic loads are significant. 

For many transportation structures, design for seismic loading may only include a simple 

equivalent static analysis of lateral loads at the top of the foundation due to inertial effects on the 

structure. For such cases, the analysis and design may proceed as outlined in Sections 5.6.2 and 

5.6.3. It is possible that seismic loads could include a component of pile uplift load in some 

cases. If piles are subjected to uplift loading, a full length center bar may be required as 

described in Section 5.6.4.1. 

Where seismic loads and soft ground conditions are present, it may be necessary to consider 

bending stresses in the pile due to seismically-induced lateral ground movements. The most 

significant in this case is liquefaction and lateral spreading. Seismically-induced lateral ground 

movements could produce large bending stresses at great depth below the top of the pile. 

Therefore, reinforcement may need to be installed at great depths in a CFA pile to ensure that the 

pile retains axial load capacity during and after the seismic event. A single center bar is not 

120 
sufficient in such cases. The use of a continuous steel pipe for reinforcement can provide good 

flexural capacity and ductility in such cases and may be considered where deep reinforcing cages 

may be problematic to install. 

5.7 DOWNDRAG IN CFA PILES 

CFA piles will be subjected to a downdrag load (i.e., shear stress reversal) when the soils in 

contact with the upper portion of the pile move downward relative to the pile. Downdrag loads 

are fully developed at relatively small displacements, of only approximately 2.5 to 13 mm (0.1 to 

0.5 in.). CFA piles behave similarly to drilled shafts in response to downdrag and analysis 

should be conducted in accordance with the methods of determining the ultimate side-shear 

values on the CFA piles as recommended herein. One difference with CFA piles is that they will 

always be used in groups and group behavior for downdrag and uplift may control. 

Some examples of cases where downdrag can occur are illustrated in Figure 5.30. Note that 

overlying loose sand, shown as case (a), may be especially problematic if the loose sand is 

submerged and is in a seismically active area. A high liquefaction potential, coupled with the 

limited flexural capacity of CFA piles at great depths may preclude their use. Overlying soft 

clay, shown as case (b), may only be a problem if a surface load is added or if excess pore 

pressures exist within the clay following the CFA pile installation to drive the consolidation 

process. Recently placed fill, shown as case (c), may most commonly be encountered in 

highway design when an abutment and fill are placed around the CFA columns or the supported 

column/pier. 

The range of forces that may develop against vertical piles when downdrag is occurring is shown 

schematically in Figure 5.31. The limit-state on the left occurs when the combination of the 

applied load and downdrag load produces both side-shear and end-bearing resistance failures in 

the founding stratum. The limit-state on the right occurs when a greater load is applied to the 

same pile shown on the left. The load on the right has been increased a sufficient amount such 

that the increased pile deflection is then greater than the settlement of the surrounding soil, and 

thus the entire pile has now been moved down relative to the soil. In such a case, downdrag no 

longer acts to load the pile. 

Although the limit-state on the right side of Figure 5.31 represents the true ultimate geotechnical 

limit-state for strength, this condition can only exist when the settlement of the pile exceeds that 

of the ground surface that may be on the order of several inches to several feet. Therefore, the 

limit-state on the left side is customarily considered to be the strength limit-state for sustained 

loads. Downdrag conditions can be such that settlement considerations (i.e., serviceability limit 

state) rather than geotechnical strength conditions control design. Downdrag forces can add 

significantly to axial forces within the pile and thus can have a significant effect on pile 

structural design and material strength requirements. 

121 
Source: O’Neill and Reese (1999) 

Figure 5.30: Examples of Cases of Downdrag 

The downdrag force should be considered as a permanent load for analysis. This force is the 

force added to the pile above the neutral plane (defined below) by way of negative 

(i.e., downward) side-shear. The pile resistance is then the positive (upward) side-shear and 

end-bearing located below the neutral plane. To correctly differentiate between the downdrag 

loads and pile resistances, the location of the neutral plane must be determined. The neutral 

plane is defined at the depth along the pile where there is zero relative movement between the 

soil and the pile. Therefore, at the neutral plane, there is no load transfer from the soil to the pile. 

It may be sufficient to assume that the neutral point lies at the top surface of the strong lower 

layer in Figure 5.32 if the top layer is relatively weak and causes the downdrag. Note that this 

assumption is conservative. This condition is shown as details (c) and (d) in Figure 5.32 and is 

discussed in O’Neill and Reese (1999). Figure 5.32(c) shows the relative movement between the 

pile and the soil (i.e., negative sign means downdrag). Figure 5.32(d) shows the distribution of 

resistances along the pile. Better estimates of the neutral point may be obtained with the iterative 

methodology, as shown in parts (e) and (f) in Figure 5.32. In this case, the neutral point will be 

located where the end-bearing resistance (RBd) matches that value predicted by static analyses or 

load-tests. The location of the neutral point may be obtained after only a few trial depths 

provided that the pile behaves elastically and the load transfer functions are simple. 

122 
Source: O’Neill and Reese (1999) 

Figure 5.31: Potential Geotechnical Limit States for Piles Experiencing Downdrag 

When downdrag is anticipated to occur around a pile group, it is usually sufficient for design 

purposes to use an equivalent pier method where the depth of the pier is the same as for 

individual piles, and the perimeter of the pier is that of the pile group, as shown in Figure 5.33. 

The neutral plane may then be determined by the iterative procedure previously described with 

the equivalent pier dimensions and the equivalent elastic modulus (Ee) calculated as follows: 

⎛ A piles ⎞ ⎛ A ⎞

E E ⎜ ⎟ ⎜ e = c + Est 1− piles ⎟ (Equation 5.64) ⎜ A ⎟ ⎜ A ⎟ ⎝ group ⎠ ⎝ group ⎠

Where: Ee = average Young’s modulus of equivalent pier within the compressible layer; 

Ec = Young’s modulus of pile (concrete or grout); 

Est = Young’s modulus of geomaterial between piles; 

Apiles = cross-sectional area of all the piles in the group; and 

Agroup = cross-sectional area of the pile group, not including overhanging cap area. 

Note that for typical spacing of 3 pile diameters center-to-center in groups of piles, the downdrag 

loads occur only around the perimeter of the group, and do not develop against interior piles. 

123 
Source: O’Neill and Reese (1999) 

Figure 5.32: Mechanics of Downdrag: Estimating the Depth to the Neutral Plane 

Source: O’Neill and Reese (1999) 

Figure 5.33: Mechanics of Downdrag in a Pile Group 

124 
5.8 EXAMPLE PROBLEMS: AXIAL CAPACITY OF SINGLE PILES 

This section presents two example problems that illustrate the estimation of the axial capacity of 

CFA piles. The first example is on the estimation of the axial capacity of a conventional CFA 

pile in cohesive soils. The second example is on the estimation of the axial capacity of 

conventional CFA and DD piles in cohesionless soils. In these example problems, all quantities 

are expressed in English units only. 

Problem Statement 

Conventional CFA piles of 18 in. nominal diameter are being considered for use to provide 

support for a highway interchange in a Coastal Plains area. A subsurface investigation, as 

described in the example problem of Chapter 6 (section 6.7.4, part A), provided information 

necessary to develop the generalized soil profile at the pier location shown in Figure 5.34. The 

bottom of the proposed pile cap is at a depth of 4 ft. An allowable stress design (ASD) is to be 

used with a safety factor of 2.0, as detailed in Chapter 6 (section 6.7.4 Part D). Note that a safety 

factor of 2.0 is used, as full-scale load-testing will be implemented to verify (or modify if 

necessary) the pile capacity estimates. Details of the safety factor selection criteria will be 

presented subsequently in Chapter 6. Provide a hand calculation of the allowable static axial 

capacity at a pile depth of 60 ft. 

5.8.1 Conventional CFA Pile in Cohesive Soils 

Solution 

The side-shear resistance (RS) for a pile embedment depth of 60 ft is estimated with the use of the 

recommended method detailed in Section 5.3.1.1. Note that a spreadsheet solution for the 

capacity with a range of pile depths is given in Appendix B. The side-shear contributions from 

the top soil layer (classified as medium gray clay or CH), and the bottom soil layer (classified as 

stiff to very stiff tan clay or CL to CH) are estimated. The top 5 ft of side-shear is disregarded 

from the top soil layer estimate, and the bottom 1-diameter (1.5 ft) of side-shear is disregarded 

from the bottom soil layer estimate, as per the recommended method. Note that if either the 

bottom of the pile cap (at a depth of 4 ft for this example) or an evaluation of the depth of 

seasonal moisture change were at a depth in excess of 5 ft, then this larger depth would be 

discounted from the contribution to the side-shear resistance. From Equation 5.2: 

N 

R = ∑ f s, i π D i L i = f s s (Top Layer ) π D L (Top Layer ) + f s(Bottom Layer ) π D L (Bottom Lay er ) 

i 

where: D = 1.5 ft (the same for both top and bottom layers); 

L(Top Layer) = 29 ft - 5 ft = 24 ft (note the top 5 ft are disregarded for side-shear resistance); 

L(Bottom Layer) = 60 ft - 1.5 ft - 29 ft = 29.5 ft (note the bottom 1 diameter or 1.5 ft is 

disregarded for side-shear resistance); 

125 
fs = α Su,ave; fs is estimated from Equation 5.5 for both the top and bottom layers, as 

shown below. Note that this will yield an ultimate unit side-shear resistance. 

The maximum undrained shear strength, Su,max, for this profile is 2.5 ksf, which yields a ratio of 

Su,max/Pa ≈ 1.25. Therefore, α = α(Top Layer) = α(Bottom Layer) = 0.55, from Equation 5.6. 

Su,ave (Top Layer) = 0.6 ksf from the idealized soil profile shown in Figure 5.34. Note that the stiffer, 

desiccated surficial soils (within the top 5 ft zone) were not included in this average in the 

idealized soil profile. 

Su,ave (Bottom Layer) = (1.50 ksf + 2.07 ksf)/2 = 1.79 ksf from the idealized soil profile shown in 

Figure 5.34. Note that 2.07 ksf in the above calculation was linearly interpolated at a depth of 

58.5 ft (60 ft embedment depth - 1.5 ft exclusion zone at tip). 

fs (Top Layer) = 0.55 × (0.60 ksf) = 0.33 ksf 

fs (Bottom Layer) = 0.55 × (1.79 ksf) = 0.98 ksf 

Then, it results: 

RS = (0.33 ksf) × π × (1.5 ft) × (24 ft) + (0.98 ksf) × π × (1.5 ft) × (29.5 ft) 

RS = 37.3 kips + 136.2 kips = 173.5 kips 

The end-bearing resistance (RB) for a pile embedment depth of 60 ft is estimated per the 

recommended method detailed in Section 5.3.1.1. The end-bearing resistance is estimated for 

the bottom soil layer according to Equation 5.4: 

⎛ π D 2 ⎞ R B = q p ⎜

⎜ ⎟

⎟ ⎝ 4 ⎠

where: D = 1.5 ft, the nominal diameter of the pile 

q p = N*

cS u from Equation 5.7

Su(ave) = (2.10 ksf + 2.14 ksf) / 2 = 2.12 ksf = 1.06 tsf from the idealized soil profile 

shown in Figure 5.34. The values 2.10 ksf and 2.14 ksf in the above calculation 

were linearly interpolated at depths of 60 ft (pile tip) and 63 ft (2 diameters 

below the pile tip), respectively 

N * 

c = 8.71, as interpolated from Table 5.1 for an undrained shear strength of 2.12 ksf 

= 1.06 tsf 

qp = (8.71) × (2.12 ksf) = 18.46 ksf 

RB = (18.46 ksf) × (π/4) × (1.5 ft)2

 = 32.6 kips 

126 
The total axial resistance (RT) for a pile embedment depth of 60 ft is the sum of the side-shear 

resistance and the end-bearing resistance, according to Equation 5.1: 

RT = RS + RB = 173.5 kips + 32.6 kips = 206.1 kips 

Note that this is the ultimate geotechnical axial resistance. 

The allowable static axial resistance (Rallowable) is obtained in accordance with ASD and a Safety 

Factor, SF = 2.0. 

Rallowable = RT / SF = (206.1 kips) / 2.0 = 103.1 kips 

5.8.2 Conventional CFA and Drilled Displacement Piles in Cohesionless Soils 

Problem Statement 

Both conventional CFA piles and DD piles, both with a nominal diameter of 18 in., are being 

considered for use to provide support for a bridge over a small stream within a flood plain. 

A subsurface investigation provided information to develop the generalized soil profile at the 

pier location, shown in Figure 5.35, in terms of SPT-N values, soil descriptions, and unit 

weights. N values are assumed to correspond to 60% hammer efficiency. While the pier 

location is usually accessible by track-mounted equipment, extreme high tides have been known 

to bring the water level up to that indicated on the figure. The hydraulic engineer for the project 

has indicated that potential scour exists at the pier to a depth of 6 ft. The bottom of the proposed 

pile cap is also proposed at a depth of 6 ft. An ASD is used with a safety factor of 2.5. Details 

of the safety factor selection criteria will be presented subsequently in Chapter 6. Provide a hand 

calculation of the ultimate static axial resistance and the allowable static axial resistance for both 

pile types at a depth of 17 ft in accordance with ASD. 

Solution 

Hand solutions for conventional CFA piles and DD piles are presented subsequently, both at a 

pile depth of 17 ft. Note that spreadsheet solutions of both piles types are given in Appendix B 

for the capacity with a range of pile depths. 

For both pile types, the pile will be divided into 6 segments with the bottom of these segments at 

depths of 3.25, 5.75, 8.25, 10.75, 13.25, and 17 ft, respectively. These depths correspond to the 

midpoint between depths of reported SPT-N values. It follows then that the midpoint of each 

pile segment is at depths of 1.63, 4.5, 7.0, 9.5, 12.0, and 15.1 ft, respectively. 

127 
-10
 

-5
 

Su from Boring-1 

0
 

Column

Su from Boring-2
 

Su from Boring-3
 

5 

Cap 

10 

15 

20 

Su(ave) = 0.6 ksf 

Below 5 ft 

Top Soil Layer 

(Medium Clay) 

25 Exclusion Zone Saturated Unit W eight = 110 pcf 

30 

35 CFA Pile 

(18-inch Diam.) 

40 

45 

50 

55 

Bottom Soil Layer 

(Stiff to Very Stiff Clay) 

Saturated Unit W eight = 120 pcf 

60 

65 Su Linearly Increases with Depth 

70 Su = 1.5 ksf @ depth of 29 ft 

75 

Su = 2.5 ksf @ depth of 80 ft

80 

0 0.5 1 1.5 2 2.5 3 

Undrained Shear Strength, Su (ksf) 

Depth (ft) 

Figure 5.34: Soil Profile Su vs. Depth for Example Problem of CFA Pile in Cohesive Soil 

Conventional CFA Pile Calculations

The side-shear resistance (RS) for a pile embedment depth of 17 ft is estimated following the 

recommended method detailed in Section 5.3.2.1. The pile cap and the potential scour both 

dictate that the side-shear contribution be discounted to a depth of 6 ft. Further, the solution in 

this example has assumed a worst-case “bed” scour, where the top 6 ft has been disregarded in 

the calculation of the effective stress distribution and β with depth. Note that if the scour was 

anticipated to be only “localized”, the top 6 ft do not need to be disregarded in calculating 

effective stresses and β. From Equation 5.2: 

N 

R = ∑ fs,i π Di L

s i 

i 

128 
SPT-"N" Value (blows/ft) 

0 10 20 30 40 50 60 70 80 90 100 

-10 

Flood -5 

Plain

0 

Scour 

5 

Column 

Cap Light Brown Fine Sand (SP) 

Depth (ft) 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

Well Rounded 

Approx 4 % fines Content 

Sat. Unit Weight = 120 pcf 

Greenish-Grey Silty Fine Sand (SM)
 

W ell Rounded
 

Approx. 17 % Fines Content
 

Sat. Unit Weight = 118 pcf
 

Greyish-White Shelly Sand (SW)
 

Very Angular
 

Approx. 3 % Fines Content
 

Sat. Unit Weight = 134 pcf
 

CFA Pile or
 

Drilled Displacement Pile 

(18-inch Diam.)
 

Figure 5.35: Soil Profile SPT-N vs. Depth for Example Problem of CFA Pile and DD Pile 

in Cohesionless Soil 

For this example with N = 6 pile segments and a constant nominal pile diameter, it results: 

6 

R s D ∑ fs,i Li 

i 

where: D = 1.5 ft (the same for both top and bottom layers) 

fs = K σv ’ tan φ = β σv ’ from Equations 5.17 and 5.18 

and β = 1.5 − 0.135Z 0.5 (from Equation 5.19) and Z is the depth to the middle of each 

pile segment (in ft). Note that β is limited to the following range 

0.25 < β < 1.2, and 

σv ’ = (γsat – γwater) Z = (120 pcf – 62.4 pcf) Z (ft) 

129 
Pile Segment 1: Disregarded (above scour and pile cap) 

Pile Segment 2: Disregarded (above scour and pile cap) 

Pile Segment 3: fs(3) = (1.2) × (0.120 - 0.0624 kcf) × (7 - 6 ft) = 0.07 ksf (β limited to 1.2) 

Pile Segment 4: fs(4) = (1.2) × (0.120 - 0.0624 kcf) × (9.5 - 6 ft) = 0.24 ksf (β limited to 1.2) 

Pile Segment 5: fs(5) = [1.5 - 0.135 × (12 - 6)0.5] × (0.120 - 0.0624 kcf) × (12 - 6 ft) = 0.40 ksf 

Pile Segment 6: fs(6) = [1.5 – 0.135 × (15.1 - 6)0.5] × (0.120 - 0.0624 kcf) × (15.1 - 6 ft) = 0.57 ksf 

RS = π (1.5 ft) × {(0.07 ksf) × [(2.5 ft - (6 - 5.75 ft)] + (0.24 ksf) × (2.5 ft) + (0.40 ksf) × (2.5 ft) + 

(0.57 ksf) × (3.75 ft)} 

RS = 18.4 kips 

The end-bearing resistance (RB) for a pile embedment depth of 17 ft is estimated following the 

recommended method detailed in Section 5.3.2.1. From Equation 5.4: 

⎛ π D 2 ⎞ R B = q p ⎜

⎜ ⎟⎟ ⎝ 4 ⎠

where: D = 1.5 ft is the nominal diameter of the pile 

qp (ksf) = 0.6 Nave from Equation 5.20 

Nave = (22 + 26 blows/ft)/2 = 24 blows/ft, from the N values at the tip and 5 ft 

below the tip. 

qp = 0.6 × (24) × (2 ksf/ 1 tsf) = 28.8 ksf 

RB = (28.8 ksf) × (π/4) × (1.5 ft)2

 = 50.9 kips 

The total axial resistance (RT) for a pile embedment depth of 17 ft is the sum of the side-shear 

resistance and the end-bearing resistance, according to Equation 5.1: 

RT = RS + RB = 18.4 kips + 50.9 kips = 69.3 kips 

Note that this is the ultimate geotechnical axial resistance. 

The allowable static axial resistance (Rallowable) is obtained for a Safety Factor, SF = 2.5: 

Rallowable = RT / SF = 69.3 kips / 2.5 = 27.7 kips 

130 
DD Pile Calculations 

The side-shear resistance (RS) for a pile embedment depth of 17 ft is estimated following the 

recommended method detailed in Section 5.4.2. The pile cap and the potential scour both dictate 

that the side-shear contribution be discounted to a depth of 6 ft. From Equation 5.2: 

R = s ∑

N 

fs,i π Di Li

i 

For this example with N = 6 pile segments and a constant nominal pile diameter is results: 

= π D∑

6 

R fs,i Li s 

i 

where: D = 1.5 ft (the same for both top and bottom layers) 

fs (ksf) = (0.05 N) (2 ksf/ 1 tsf) + WT, from Equation 5.31, and limited to N60 ≤ 50. 

WT = 0 for 6-pile segments, all lying within the soil layer (silty fine sand). Note 

that fs would be limited to 3.4 ksf for well-rounded and poorly-graded soils, 

and limited to 4.4 ksf for angular well-graded soils. If the pile segments had 

been into the last layer (i.e., Shelly sand), WT = 1 ksf for these angular, wellgraded soils. See Section 5.4.2 for details pertaining to the selection of WT. 

Pile Segment 1: Disregarded (above scour and pile cap) 

Pile Segment 2: Disregarded (above scour and pile cap) 

Pile Segment 3: fs(3) = (0.05) × (19 blows/ft) × (2 ksf/1 tsf) + (0 ksf) = 1.90 ksf 

Pile Segment 4: fs(4) = (0.05) × (24 blows/ft) × (2 ksf/1 tsf) + (0 ksf) = 2.40 ksf 

Pile Segment 5: fs(5) = (0.05) × (25 blows/ft) × (2 ksf/1 tsf) + (0 ksf) = 2.50 ksf 

Pile Segment 6: fs(6) = (0.05) × (22 blows/ft) × (2 ksf/1 tsf) + (0 ksf) = 2.20 ksf 

RS = π × (1.5 ft) × [(1.90 ksf) × (2.5 ft-(6 - 5.75 ft)) + (2.40 ksf)(2.5 ft) + (2.50 ksf)(2.5 ft)+ 

(2.20 ksf)(3.75 ft)] 

RS = 116.7 kips 

131 
The end-bearing resistance (RB) for a pile embedment depth of 17 ft is estimated according to the 

recommended method detailed in Section 5.4.2. From Equation 5.4: 

⎛ π D 2 ⎞ R B = q p ⎜ ⎟ ⎜ ⎟ ⎝ 4 ⎠

where: D = 1.5 ft, the nominal diameter of the pile 

qp ( ksf ) = 1.9N( ave ) (2 ksf/1 tsf) + WT, from Equation 5.33 and limited to N60 ≤ 50. 

Nave = (25 + 22 + 26 + 9) / 4 = 20.5 blows/ft, from the SPT-N values 6.25 ft above 

and 10 ft below the tip. Note that qp would be limited to 150 ksf for wellrounded and poorly-graded soils and limited to 178 ksf for angular, 

well-graded soils. 

qp = 1.9 × (20.5) × (2 ksf/1 tsf) + 0 = 77.9 ksf 

RB = (77.9 ksf) × (π/4) × 2 (1.5 ft) = 137.7 kips
 

The total axial resistance (RT) for a pile embedment depth of 17 ft is the sum of the side-shear 

resistance and the end-bearing resistance according to Equation 5.1: 

RT = RS + RB = 116.7 kips + 137.7 kips = 254.4 kips 

Note that this is the ultimate geotechnical axial resistance. 

The allowable static axial resistance (Rallowable) is obtained in for a Safety Factor (SF = 2.5). 

Rallowable = RT/SF = 254.4 kips / 2.5 = 101.7 kips 

132 
CHAPTER 6 RECOMMENDED DESIGN METHOD 

The purpose of this chapter is to present a step-by-step generalized method for the selection and 

design of CFA piles. 

The process consists of the following design steps: 

Step 1:		 Initial Design Considerations 

Step 2: Comparison and Selection of Deep Foundation Alternatives 

Step 3: Selection of Pile Length and A ssessment of Pile Performance under Specified 

Loads: 

• Calculation of Pile Length 

• Verification of Capacity and Performance for Axial and Lateral Loads 

• Verification of Pile Group Capacity and Group Settlement Calculations 

• Pile Structural Design 

• Miscellaneous Considerations 

Step 4:		 Review of Constructability 

Step 5: Preparation of Plans and Constr uction Specifications, Set QC/QA and Load 

Testing Requirements 

The remainder of this chapter presents an outline of each of the design steps listed above and 

presents preliminary discussions of the most salient aspects of the design. 

6.1 STEP 1: INITIAL DESIGN CONSIDERATIONS 

The initial design considerations include a review of structure-specific and site-specific 

conditions for the project that are necessary for any foundation design. In this chapter, attention 

is focused specifically on those items that establish or preclude suitability of CFA piles for the 

project. Step 1 is subdivided into several components as described below. 

6.1.1 General Structural Foundation Requirements 

The first step in the entire process is to determine the general structural requirements for the 

foundation. Some important considerations include the following: 

•	 Project type: new bridge, replacement bridge, bridge widening, retaining wall, noise 

wall, sign or light standard. CFA piles may be considered for any of the above. 

•	 Construction sequencing: phased construction or all at once. Neither condition either 

precludes or favors CFA piles. 

•	 General structure layout and approach grades. 

•	 Surficial site characteristics. A stable working platform is required for CFA pile 

construction. 

133 
•	 Special design events such as seismic, scour, vessel impact, etc. These factors should 

be considered in planning the site investigation and can have a significant effect on the 

selection of CFA piles. 

•	 Possible modifications to the structure that may be desirable for the site under 

consideration. 

•	 Approximate foundation loads and limitations on deformation. 

6.1.2 Site Geology and Subsurface Conditions 

A comprehensive review of this component of Step 1 is the subject of other FHWA publications 

(e.g., “Subsurface Investigations,” document FHWA-HI-97-021, and National Highway Institute 

[NHI] Workshop on Soils and Foundations, document FHWA-NHI-66-083, and 

GEC No. 5: “Evaluation of Soil and Rock Properties, document FHWA-IF-02-034 authored by 

Sabatini et al. [2002]) and will not be repeated here in detail. In general, the components of the 

site characterization include a review of the site geology and foundation experience in the area, 

followed by a carefully planned and executed subsurface exploration program. In general, the 

consideration of CFA piles does not require specialized investigation techniques differing from 

those used for driven pile foundations. Important considerations for CFA piles include the 

general site stratigraphy and soil classification, the depth and characteristics of the most likely 

bearing formation, groundwater conditions, variability, and the presence and extent of unusual 

geologic features such as solution cavities, boulders, lenses, or layers of hard rock. 

The use of cone penetration testing (CPT) is generally considered to be particularly well suited 

for design procedures used for CFA piles, but especially for drilled displacement (DD) piles. 

CPT soundings provide a continuous record of a strength measurement that correlates well with 

CFA and DD pile performance, CPT soundings can generally be performed in soils where CFA 

or DD piles are to be considered. It is also a very cost-effective tool compared to conventional 

borings for sounding a large area. Where conditions are such that CFA piles may be considered 

as a viable foundation alternates, the use of CPT soundings is recommended and encouraged as a 

part of the exploration program. 

6.2 STEP 2: COMPARISON AND SELECTION OF DEEP FOUNDATION 

ALTERNATIVES 

The information from Step 1 must be evaluated and a foundation system selected. Alternatives 

to deep foundations may be considered, including shallow foundation systems and the potential 

use of ground improvement techniques to allow the use of shallow foundations. Where deep 

foundations are required, alternatives include driven piles, drilled shafts, micropiles, and CFA 

piles including both conventional CFA piles and DD piles. The selection of the optimum deep 

foundation system for a given project includes consideration of multiple factors and requires 

experience and judgment on the part of the designer. Table 6.1 outlines many of the 

considerations involved in the foundation selection process with respect to CFA piles. 

134 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 6.1: Design Consideration for Foundation Selection of CFA and DD Piles 

Stratigraphic 

Favorable Ground 

Conditions? Type of Profile GWT Location Other Factors 

Predominantly Clays: 

favor CFA 

Very soft surface may 

be unfavorable due to 

poor working platform 

If below existing 

grade, not much of a 

factor in clays. 

Depth to competent 

material > 30 m 

(100 ft): not favorable 

Sands: favor DD 

Uniform or similar 

strata: favorable 

GWT depth > 3m 

(10 ft): favorable 

Boulders, rock layers 

or lenses: not 

favorable 

Highly variable drilling 

resistance: not 

favorable 

Artesian conditions: 

not favorable 

Good working 

platform is especially 

important for DD 

because DD rigs are 

usually heavier than 

CFA 

Cemented soils, weak 

rock: favor CFA 

Highly variable drilling 

resistance: not 

favorable 

Artesian conditions: 

not favorable 

Boulders, rock layers 

or lenses: not 

favorable 

Rock: not favorable for 

CFA or DD -- -- --

Structural 

Loading Conditions Other Conditions 

Approximate maximum ultimate lateral loads per 

vertical pile (kip) vs. recommended diameter (in.) • Low headroom requirements: may 

favor CFA piles 

• Close proximity to existing structures: 

not favorable to CFA or DD due to 

potential ground movements during 

construction 

• Noise and vibration considerations: 

may favor CFA or DD piles vs. driven 

piles 

• Potential obstructions below grade: not 

favorable to CFA or DD piles 

soft or loose soil: 

12 kip - 18” dia. 

20 kip - 24” dia. 

30 kip - 30” dia. 

45 kip - 36” dia. 

Stiff or dense soil: 

20 kip - 18” dia. 

35 kip - 24” dia. 

50 kip - 30” dia. 

70 kip - 36” dia. 

Approximate maximum ultimate axial 

compressive loads per pile (kip) vs. 

recommended diameter 

400 kip - 18” dia. 

700 kip ­ 24” dia. 

1,000 kip ­ 30” dia. 

1,500 kip ­ 36” dia. 

Special 

Considerations 

Seismic Scour Contaminated Spoils Over Water 

Lateral subsurface soil 

movements from seismic 

events produce lateral 

load conditions not 

favorable to CFA or DD 

Deep scour may result 

in high moments at 

depth: not favorable to 

CFA or DD 

Contaminated 

ground conditions: 

may favor DD due to 

avoidance of spoils 

Work over water: not 

favorable to CFA or 

DD piles 

Economic 

Factors 

Qualified Local 

Subcontractors 

Available? 

Relative Numbers of 

Piles Project Size 

Necessary for CFA or 

DD 

Large numbers of 

piles: favorable to CFA 

or DD 

Small project with few piles and many moves: 

may not favor CFA or DD 

135 
The subsequent steps are presented for CFA piles and DD piles. Alternative deep foundation 

types are described in existing FHWA design manuals for drilled shaft foundations (e.g., FHWA 

Report No. IF-99-025 by O’Neill and Reese [1999]), for driven pile foundations (e.g., 

Publication for NHI Course FHWA-NHI-132021 by Hannigan et al. [2006]), and for micropile 

foundations (e.g., Publication NHI-05-039 by Sabatini et al. [2005]). 

6.3 STEP 3: SELECT PILE LENGTH AND CALCULATE PERFORMANCE 

UNDER SPECIFIED LOADS 

6.3.1 Limit States for Design 

The design method presented is based on an Allowable Stress Design (ASD) for geotechnical 

conditions, in which a factor of safety is applied to ultimate limit state conditions to obtain 

allowable resistance values for design. Resistance factors for Load Resistance Factored Design 

(LRFD) have not been calibrated for geotechnical aspects of CFA pile design. Structural design 

of the pile is in accordance with LRFD (AASHTO, 2004) as for other reinforced concrete 

structural elements. 

In general, there are three limit state conditions that must be satisfied for design of CFA and 

other deep foundations: 

1.	 Geotechnical Ultimate Limit State (GULS). The pile should have a load resistance 

that is greater than the expected loads (service loads) by an adequate margin to 

provide a required level of safety (safety factor). For axial compressive loads, the 

GULS is defined as the load resistance at a displacement equal to 5% of the pile 

diameter in an axial static load test, as shown in Figure 6.1. The Davisson criterion, 

commonly used for driven piles, and shown for reference in Figure 6.1, will 

sometimes underestimate the ultimate resistance and is not appropriate for CFA 

piles. For lateral loads, the GULS may be defined as a push-over failure of the 

foundation or alternately as some deflection limit at which collapse of the structure 

above the foundation may occur. Uplift loading conditions and group behavior for 

axial, rotation, or lateral are additional geotechnical ultimate limit states that may 

control in some cases. The GULS for preliminary design is determined by 

calculations, and these calculations may be refined based on site-specific load 

testing. Note that the GULS is often referenced using the words “capacity” or 

“failure”, which are a poor choice of words, because no collapse or condition of 

plunging may exist at the GULS and the pile may have a capacity to support 

additional loads beyond the GULS. The state of deformation associated with the 

GULS is not to be confused with deformations at service load levels. The GULS 

provides a definition of foundation resistance. 

2.	 Service Limit State (SLS). The pile should undergo deformations at service load 

levels that are within the tolerable limits appropriate for the structure. The actual 

definition of the service limits should be determined by a rational assessment of the 

sensitivity of the structure to deformations. Short-term deformations for transient 

loadings are a function of the mobilization of pile resistance as indicated in Figure 

6.1. However, long-term settlements under structural dead loads are a function of 

136 
group settlements and should be computed accordingly (as described in Chapter 5). 

For bridge structures, the serviceability requirements for deformations are in 

accordance with AASHTO (2002) Section 4.4.7.2.5. Settlements should generally be 

such that angular distortions between adjacent foundations do not exceed 0.008 in 

simple spans and 0.004 in continuous spans. It should be noted that only postconstruction settlements affect serviceability of the bridge structure. Tolerable 

movement criteria for lateral displacement should be developed considering the 

effects of combined lateral and vertical displacements on the structure. AASHTO 

(2002) Section 4.4.7.2.5 requires that horizontal movements be limited to 25 mm 

(1 in.) where combined horizontal and vertical movements are possible, and be 

limited to 38 mm (1.5 in.) when vertical movements are small relative to horizontal 

movements. 

3.	 Structural Ultimate Limit State (SULS). The pile must have sufficient structural 

capacity when the pile is subjected to combined axial and flexural loads such that 

structural yielding of the pile is avoided. The SULS provides a second definition of 

foundation strength. 

SLS (short-term 

loading only) GULS 

PL/AE + d/120 in. + 0.15 in. 

(Davisson Criterion) 

Load (P)
 

Displacement
 

Limit at 

Service Load 

L = Pile Length 

A = Pile Area 

E = Pile Modulus 

d = Pile Diameter (in.) 

The “ultimate” resistance 

Measured in the Davisson criterion 

Curve is defined as point at 

which Davisson line 

0.05d 

Displacement intersects measured load 

vs. deflection curve 

Figure 6.1: GULS and Short-Term SLS for Axial Load on a Single CFA Pile 

Most engineers using ASD methods are familiar with the concept of a factor of safety, which 

divides the resistance at the GULS to determine an allowable load per pile. The service 

(unfactored design) loads are compared against the allowable loads per pile to evaluate strength 

and provide the margin of safety against the limit-state condition (often referred to as “failure”). 

137 
For design of CFA piles using ASD, the resistance computed at the GULS is compared with 

service loads such that: 

∑Qi < R / SF (Equation 6.1)

Where: 

Qi	 = value of service (unfactored) load of type i 

R = computed resistance at GULS 

SF	 = factor of safety 

CFA piles should generally be designed having a factor of safety of at least 2.5. Lower factors of 

safety are warranted where site-specific load tests are performed and QA/QC systems are used to 

provide verification that the performance of production piles is reasonably consistent with that of 

the test pile(s). A factor of safety of 2.0 may be used for design for axial loads provided that the 

following conditions are met: 

1.	 At least one conventional static load test (per ASTM Standard D1143-81) is performed at 

the site, to a load exceeding the computed ultimate by 50% or to a load producing 

displacement equal to 5% of the pile diameter, whichever comes first. Multiple load tests 

are required where the site extends for a great distance of roadway structure or if, in the 

judgment of the project geotechnical engineer, the site spans across significant geologic 

or stratigraphic differences in site conditions. Dynamic or rapid load tests, as described 

in Chapter 7, may be substituted for some of the conventional static load tests and their 

results can be correlated to static test or local conditions. 

2.	 Automated monitoring systems are used on production piles to verify that production 

piles are constructed in a similar way and to achieve similar performance in the test 

pile(s). 

3.	 The site geology, stratigraphy, and soil properties are not highly variable. Engineering 

judgment must apply in this instance, and higher factors of safety for design are 

warranted for conditions with unusual variability in soil properties or geologic conditions. 

It is acceptable to use a higher factor of safety for some portion of the computed 

resistance. For example, base resistance or the resistance within some deeper strong 

layer may be considered as more variable than other portions of the profile that contribute 

to resistance and therefore, an engineer may apply judgment to assign a higher factor of 

safety to this portion of the resistance. 

4.	 The site conditions do not pose difficult construction conditions for CFA piles. 

Note that load testing and monitoring as described above should be required on all transportation 

projects constructed using CFA or DD piles. Exceptions may include soundwalls, sign 

foundations, or similar structures for which the design is not controlled by axial resistance. 

It is also important to note that the foundation design engineer should consider the factors of 

safety cited above as minimum values, and should use a higher factor of safety in any 

circumstance where there exists concerns for site variability, lack of redundancy, or potentially 

138 
 

difficult construction conditions. An especially critical structure such as a lifeline structure for 

hurricane evacuation or seismic safety concerns may also warrant a higher safety factor. The 

values suggested above are for typical conditions and routine projects. 

6.3.2 Design Procedures 

To complete a design, it is necessary to perform static analyses and estimate pile lengths and pile 

diameters necessary to provide the required compression, lateral, and uplift load capacity. For 

most routine projects, it is anticipated that the ultimate limit state (capacity) conditions usually 

control the design of individual CFA piles rather than serviceability (deflection) requirements, 

therefore, the most efficient approach for design is to check first ultimate limit state conditions 

and then serviceability. Note that some instances of serviceability may control, such as with 

large pile groups over a deeper compressible stratum. 

In general, smaller diameter and greater length piles tend to be more economical than larger 

diameter, shorter length piles with similar axial resistance. However, pile diameter is often 

controlled by lateral shear and bending moment considerations. Lateral load considerations 

almost never control the length of CFA piles because the soil resistance mobilized to resist 

lateral loads tends to be within the shallow strata extending to a depth no more than about 10-pile 

diameters. If significant lateral loads (per pile) are anticipated, the design is accomplished by 

first performing an initial analysis of lateral loading to define the required diameter and also the 

depth to the point where calculated bending moments are negligible. This lateral check is 

followed by static analysis of axial load capacity to define the pile length requirements. 

Note that a range of diameters and lengths may be considered for groups of piles, as it is feasible 

to consider foundations with larger numbers of smaller capacity piles vs. fewer numbers of larger 

capacity piles. At this stage in the design, it is appropriate to consider a range of pile capacities 

for possible different group configurations. The procedures described in Chapter 5 are used to 

perform the analyses associated with determining axial and lateral resistance of various design 

alternatives. 

The recommended procedure for performing a foundation design of CFA or DD piles is outlined 

below. This outline is developed for the design of a foundation for a structure such as a bridge. 

A similar procedure for sign foundations or wall components may differ in specifics of some 

components, but will follow a similar general outline. 

A. Develop Idealiz ed Profile. Using the borings and geologic descriptions from the site 

investigation program, group the borings into zones for foundation design according to 

similarities in the soil profile and properties, and establish idealized geotechnical design 

profiles for each representative zone at the site. The differing zones should adequately 

cover the range of conditions at the site, and the designers may develop multiple profiles 

for each zone to evaluate the possible range of geotechnical (and groundwater) conditions 

within each identified zone. It may also be necessary to consider several cases of scour 

associated with different loading conditions. The layers and characterization of soils 

should be consistent with the methods for estimating axial and lateral load transfer as 

outlined in Chapter 5 of this document. 

139 
B. Develop Geotechnica l Design Parameters. For each stratum defined in the idealized 

profiles, evaluate the geotechnical strength and stiffness parameters to establish design 

parameters for each layer. These may include: 

a.		 Soil strength parameters such as undrained shear strength and drained friction 

angle or other measurements, such as SPT-N60 values and cone tip resistance. 

These strength parameters will be used either directly or through correlations to 

estimate unit side-shear and end-base resistances and to develop p-y curves for 

lateral loading. 

b.		 Soil stiffness or modulus and other parameters related to deformation 

characteristics for use in developing p-y curves for lateral loading and performing 

settlement analyses of pile groups. 

c.		 Other soil properties that may be needed for design, such as unit weights and 

index tests for classification. 

Note that the actual values used for design are typically based on judgment and 

experience along with an understanding of the site geology and potential variability 

(Sabatini et al., 2002). 

C. Obtain the Loadings for the Foundation. The design loadings will likely include 

several cases of both axial and lateral loads. Many different load combinations exist of 

dead loads, traffic loads, wind loads, etc. Some cases may be combined with scour and 

some may include extreme event loadings. If downdrag or uplift due to expansive soils is 

to be considered, these should be noted at this time for inclusion where appropriate into 

subsequent analysis and design steps. Analyses of the load combinations will reveal the 

maximum axial and lateral loads imposed to the pile and represent the critical design 

cases. 

D. Safety Fac tor(s) for Design. The safety factors cited in the previous section are 

suggested for general use in design for strength, and differ depending on the level of sitespecific testing and quality control. Large values may be applied in cases where unusual 

variability in subsurface conditions exist, difficult construction conditions are likely, or if 

other considerations for the structure dictate. For example, where base resistance 

contributes a large portion of the axial resistance and the properties of the bearing stratum 

are quite variable, it may be appropriate to use a significantly greater safety factor on 

base resistance than side-shear even where a load test is performed. 

E. Select a Trial Design P ile Group t o Establish Individual Pile Loads . The geometry 

and layout of the pile group, along with the number of piles used to support the 

foundation loadings will determine individual loads per pile. At this point in the process, 

experience and/or some preliminary estimates should suggest some reasonable values of 

nominal axial and lateral resistance for single piles so that an efficient layout can be 

developed. Engineers are encouraged to evaluate numerous alternatives in the 

preliminary design stage. 

140 
F. Select a Trial Design for Individual CFA or Drilled Displacement Piles. 

a.		 Design for Lateral Loading. Lateral analyses may only be needed if lateral loads 

are significant. As a guide, lateral shear forces on vertical piles that are less than 

about 9 to 22 kN (2 to 5 kips) per pile for 460 to 915 mm (18 to 36-in.) diameter 

piles, would probably not justify lateral analysis at this point in the design process 

and the designer could skip the lateral analyses and move on to design for axial 

load. If battered piles are used to resist lateral forces these guidelines apply to the 

resulting forces transverse to the pile axis and the longitudinal component of the 

force on the battered pile is considered in design for axial loading. 

Select a diameter that is sufficient to provide the necessary nominal lateral load 

resistance and service load requirements for deflection. Note that when lateral 

loads are significant, the final design of CFA piles for lateral loading is typically 

controlled by structural design considerations and the necessary flexural strength 

and reinforcement. At this point in the design process, it is prudent to consider 

lateral loading because it may control the pile diameter (but usually not the 

length). Note that high bending stresses combined with unsupported length due to 

scour or liquefaction may preclude the use of CFA piles altogether. 

A preliminary lateral analysis using a computer code as described in Chapter 5 is 

warranted at this step in the process. The relative significance of lateral load 

magnitude is certainly dependent upon soil conditions, and weak surficial soils 

tend to result in more significant bending moments for a given lateral shear force. 

Batter piles may also be considered for large lateral forces if downdrag or 

constructability considerations do not preclude their use, and groups of piles 

including batter piles are best analyzed using 3-D group analysis programs such 

as GROUP (Ensoft, 2006) or FB-Pier (BSI, 2003). 

The lateral load analysis of a trial pile design should proceed as follows: 

i.	 Select a trial pile diameter and length (although the design is generally not 

sensitive to length for CFA piles having length/diameter ratios of 20 or 

more). Select a trial longitudinal reinforcement. A longitudinal 

reinforcement with a cross-sectional area of around 1% of the pile crosssectional area is typically a good initial value to consider. Construct a 

computer model with p-y curves for the load conditions likely to be most 

critical for lateral load considerations. 

ii.	 With the pile modeled as a linear elastic beam, evaluate foundation 

strength conditions by computing the foundation response of the pile due 

to service loads multiplied by a factor of at least 2.5 to ensure that the pile 

embedment into the soil has adequate reserve capacity. Service load 

deflections or structural strength requirements generally control design, 

but this “push-over” type analysis is performed to ensure that adequate 

reserve strength exists with respect to the soil resistance. At the same 

time, service load and factored load cases can be computed to provide 

design information that will be used in subsequent steps. Note that there 

may be several different load combinations to be evaluated, although there 

141 
is usually a clearly dominant lateral loading case. This check is to ensure 

that push-over conditions do not control the design. As mentioned earlier, 

normally service deflections or structural limit state will control lateral 

load design. The strength check ensures that the available soil resistance 

exceeds the structural capacity of the pile in flexure and thus the 

foundation should have ductility. Note that for analysis of a single pile 

that will be representative of a group of piles, it is appropriate to include a 

p-multiplier (less than 1.0) which is equal to the average p-multiplier for 

the group. The p-multiplier concept is described in Chapter 5 and other 

references, and is incorporated into most computer programs for lateral 

analysis using p-y curves. 

iii.	 Verify that the magnitude and depth of longitudinal reinforcement is 

adequate for the maximum bending stress computed with the computer 

program used in step ii. Details of structural design and adequacy are 

contained in Section 5.6.4. Check to see that the reinforcing design is 

constructible, as discussed in Section 2.2.2.5. 

iv.	 With the pile modeled as a nonlinear reinforced concrete beam, evaluate 

foundation deflections by computing the foundation response of the pile, 

or pile cap (when pile groups are used), due to service loads. If the 

deflections are larger than the service load requirements, the pile diameter 

may need to be increased (go back to step 3.F.a.i) or the layout changed 

(go back to step 3.E). If the lateral loads are very high, it may be 

appropriate to consider batter piles, CFA piles reinforced with steel pipe, 

or alternative deep foundations. 

v.	 Note that if seismic loads are an important component of lateral load 

considerations, the possibility of subsurface ground movements must be 

considered, as briefly described in Chapter 5. Although the recommended 

procedure for design of CFA piles is with ASD using the AASHTO 

(2002), sections of the AASHTO (2006) design code address issues 

relating to subsurface ground movements, the effect on pile foundations, 

and ductility requirements for piles. Subsurface ground movements, 

which can occur at large depths, may subject CFA piles to significant 

bending stresses at locations well below the ground surface. Installation 

of conventional reinforcement in CFA piles may be problematic in such 

conditions. The use of structural steel pipe or H sections for 

reinforcement in CFA piles, or selection of alternative deep foundation 

systems should be considered. 

b.		 Design for Axial Loading. After the diameter is selected, determine the length of 

pile required to provide the necessary axial resistance. Analyses of ultimate axial 

resistance are performed using the methods outlined in Chapter 5. This step may 

be a trial and error process. Many engineers may prefer to automate the 

computations using a spreadsheet or other computer solution that incorporates the 

methods outlined in Chapter 5. These methods produce profiles with depth of the 

142 
nominal and allowable axial resistance for each of the idealized profiles, and 

loading conditions, and foundation location established for the project. The 

allowable axial resistance (ultimate axial resistance divided by the factor of 

safety) is compared to the service loads to ensure that the design meets strength 

requirements. 

c.		 At this point it is also prudent to consider constructability, and cost effectiveness 

of the pile length determined. If the design is problematic from either standpoint, 

go back to step 3.E and consider an alternative pile layout or alternate deep 

foundation types. 

G. Pile Group Capacity. The pile group capacities may be evaluated by hand calculations 

for simple load conditions and soil layering, as is detailed in Section 5.5.2. However, for 

pile groups with complex 3-D load conditions or soil layering, the pile group capacity 

may require analyses using computer codes such as FB-Pier, GROUP, or similar 

computer-based pile group analysis methods. These tools can be effectively used to 

optimize foundation layout and load distribution to the piles. 

H. Pile Group Sett lements. For groups of piles subject to sustained permanent loads, 

long-term settlements in excess of the short-term deformations associated with individual 

pile load-deflection response (i.e., due to the deeper influence of the pile group) will 

present a service load condition that should be considered. The group settlement may be 

evaluated by hand calculations for simple load conditions and soil layering, as is detailed 

in Section 5.5.3. However, for pile groups with complex 3-D load conditions or soil 

layering, the pile group capacity may also require computer-based pile group analysis 

methods. It is noted that the advantages of DD piles in achieving high capacity at 

shallow depth may be offset by settlement considerations if relatively compressible strata 

exist at depth. Where downdrag loading is relevant, this should be assessed as outlined in 

Chapter 5 and design modifications maybe be required. If necessary, longer piles may be 

required to accommodate settlement or downdrag concerns and the design process may 

require returning to step 3.E. 

I.		 Pile Group Lateral Behavior . The group behavior was taken into account using p-y 

multipliers during the preliminary analyses of single piles (see step F.a.ii). This may be 

sufficient for most pile groups, and a sensitivity analysis may be considered to determine 

primarily the effect of the pile-head fixicity. However, for pile groups with complex soilpile interaction or cap designs, the pile group lateral capacity may also require computerbased pile group analysis methods. 

J.		 Structural Design. After the design has been selected to satisfy considerations of 

geotechnical strength (GULS) and serviceability (SLS), the final structural design of the 

piles and pile cap must be completed. This step will involve the final lateral pile analysis 

or verification and the pile structural design, including reinforcement and grout or 

concrete material requirements. The structural design for CFA piles is very similar to 

that of drilled shaft foundations, except for slight differences in properties of grout 

compared to concrete and the tendency to use a rebar cage that does not extend the full 

length of the pile. The structural design for the pile is detailed in Section 5.6.4. 

143 
6.4 STEP 4: CONSTRUCTABILITY REVIEW 

An evaluation of constructability is an integral part of the design process and constructability 

factors should have been considered already in making foundation type selection. A final review 

of constructability should be performed at this point, including a review of the checklist below 

for items for evaluating constructability of CFA piles and, if appropriate, DD piles. Note that 

there are always concerns of some type about constructability, and special concerns should be 

noted and identified on plan notes and special provisions. It is helpful to highlight these issues to 

potential bidders so that responsible bids can be prepared and special concerns addressed in the 

successful bidder’s installation plan. A checklist of items to consider follows. 

a.	 Are pile length and diameters appropriate? Typical CFA pile diameters are 

typically 0.4 to 0.6 m (16 to 24 in.), and are rarely constructed in excess of 0.9 m 

(36 in.) in diameter. Typical DD pile diameters are 0.4 to 0.6 m (16 to 24 in.). 

Lengths of over 30 m (100 ft) are generally undesirable and not optimum. 

b.	 Can bearing strata be penetrated to depth indicated? Avoid designs that require 

penetration into hard materials to achieve capacity if the overburden soils may be 

subject to soil mining or if the bearing stratum is too hard to drill effectively. 

c.	 Is there a risk of soil mining due to loose water-bearing sands? Avoid CFA in 

such materials; DD piles may be more effective. 

d.	 Is there a potential effect on nearby structures? Drilling in close proximity to 

nearby structures can be risky due to potential subsidence. 

e.	 Is the rebar cage appropriate? Rebar cage length less than about 12 m (40 ft) is 

preferable. 

f.	 Is there a pile cutoff detail? Avoid pile cutoff more than a few feet below the 

working grade if possible. Deeper cutoff will require casting the pile to the 

surface and chipping down after the grout or concrete has set. 

g.	 Is construction sequence is feasible? Consider site access, existing structures, 

obstructions, pile cap footprint. Avoid installing CFA or DD piles over water. A 

stable working platform is necessary, especially for DD piles which require 

larger, heavier rigs than conventional CFA piles. 

h.	 Are low headroom conditions required? Low headroom working conditions are 

best if avoided. If it is necessary to use low headroom construction, use smaller 

piles (usually 0.45 m [18 in.] diameter or less) and smaller working loads per pile 

to avoid installation problems with small lightweight rigs. 

i.	 Is there a plan for resolving construction questions prior to production? 

144 
6.5 STEP 5: PREPARE PLANS AND CO NSTRUCTION SPECIFI CATIONS, SET 

QC/QA AND LOAD TESTING REQUIREMENTS 

At this step, general specifications should be reviewed, and project special provisions and plan 

notes should be developed if needed for incorporation into the project plans and specifications. 

Guide construction specifications are provided in Chapter 8. Field QC/QA requirements will 

vary depending on the project type, (e.g., soundwall foundations in favorable soil conditions may 

have minimal requirements, whereas bridge structure foundations will include extensive 

monitoring). Load testing requirements should be established, consistent with the design 

considerations and factor of safety. 

6.6 EXAMPLE PROBLEM 

6.6.1 Introduction 

This example problem is intended to demonstrate the step-by-step design methodology for CFA 

piles described in the previous sections. In the interest of brevity, the design will focus on the 

foundation for a single column of one pier, for a single load case. An actual project would utilize 

the methodology for a variety of foundation locations, additional load cases and alternate 

subsurface profiles as may occur across the project site for the structure in question. The 

example problem is developed in English units only. 

6.6.2 Step 1: Initial Design Considerations 

6.6.2.1 General Structural Foundation Requirements 

This project will consist of a series of new bridges to be constructed as a part of an interchange. 

The layout is such that relatively good access is available and a large number of foundations are 

required. The magnitude of the axial and lateral loads per each foundation is not unusually large. 

The working platform is relatively soft in some areas, but suitable for equipment; timber crane 

mats may be needed. 

6.6.2.2 Site Geology and Subsurface Conditions 

The site is in the coastal plains, at a location where relatively soft to medium strength alluvial 

sediments are present at shallow depths. This soil is predominantly cohesive, but with frequent 

silt or sand layers. Groundwater is typically present at depths ranging from 6 to 10 ft below 

existing grade, leaving the cohesive soils in the upper 5 ft, which exhibit a stiffer crust due to 

desiccation. The shallow sediments are underlain by older, more competent overconsolidated 

clays of Pleistocene age. The stiff clays extend to depths of engineering significance for this 

project. The general conditions for the entire site, as indicated by the site investigation, is shown 

in Figure 6.2. The relatively low strength and high compressibility of the shallow alluvial 

sediments require that deep foundation support be utilized. 

145 
Figure 6.2: Typical Conditions at the Project Site 

Medium gray clay (CH) with 

silt and sand layers 

Su = 0.5 to 1 ksf 

w/c = 35 to 50% 

Stiff to very stiff tan clay 

(CL to CH) with sand 

pockets and layers 

Su = 1.5 to 3 ksf 

w/c = 25 to 35% 

20 to 40 ft GWT

6.6.3 Step 2: Comparison and Selection of Deep Foundation Alternatives 

A number of deep foundation alternatives may be considered for this site, including driven piles, 

drilled shafts, and CFA piles. Because the soils are predominantly clays and no strong bearing 

stratum is present, deep foundations will derive the majority of capacity from side-shear. This 

type of profile favors the use of CFA piles, although prestressed concrete piles may be a feasible 

alternative. Drilled shafts are also a viable alternative, but because of the shallow groundwater 

and frequent sand layers it is likely that dry hole construction may not be possible and slurry 

drilling would be required. CFA piles are likely to be very cost-effective in the conditions 

described in Step 1 and will thus be considered further. The cohesive soils do not favor the use 

of DD piles as their strength is not appreciably improved from the construction process nor does 

it benefit from the higher lateral stress attained. 

Possible difficulties with the use of CFA piles for this site are: 

• If extremely soft organic layers were present within the alluvium, these could pose 

stability problems with fluid grout. However, no substantial thicknesses (more than a 

few feet thick) of organics were evident. 

• Large lateral loads could be detrimental to CFA piles due to the soft shallow stratum 

and the limited strength in flexure for these piles. 

• Downdrag could be problematic for CFA piles at the abutments, where fill will likely 

produce significant settlement. This is a consideration for any type of deep 

foundation, however, and does not preclude the use of CFA piles. 

146 
6.6.4 Step 3: Select Pile Length and Calculate Performance Under Specified Loads 

For this step in the design process, one intermediate bent will be selected and a design developed 

for the columns at that bent. This bent is to be constructed as a two-column pier, with each 

column supported by a pile footing. The design will be completed using ASD methods. 

Step-By-Step Design Procedure for Axial and Lateral Loads. 

6.6.4.A Develop idealized profile. Based on the borings at the intermediate bent 

location with consideration of nearby borings and engineering judgment, the profile 

shown in Figure 6.3 is developed for this location. Note that this is the same profile used 

for one of the examples in Chapter 5. 

6.6.4.B Develop geotechnical design parameters. Undrained shear strengths have 

been obtained based on unconsolidated, undrained triaxial tests, and a design strength 

profile is developed as shown below. Note that a pile footing is anticipated, with the 

base of the cap at 4 ft below grade. This elevation will be the top of the pile for analysis 

purposes. 

For settlement considerations of pile groups installed into the deeper stiff clay, this clay 

is heavily overconsolidated with a recompression index, Cr of 0.015. The void ratio 

averages approximately 0.6. Consolidation settlements of the shallow clay will be of 

interest to parts of the project, but will not directly affect the deep foundation 

calculations in this example. 

6.6.4.C Obtain the nominal loadings for the foundation. At this interchange, there is 

no waterway to cause scour and extreme event loadings are not significant. Axial loads 

are controlled by combined dead load and live load, and lateral loads are produced by 

wind. Although there are typically a number of load cases to be considered, this 

simplified problem will consider foundation loads as follows for each of the two 

columns: 

•	 Group Vertical service load (dead + live) = 500 kips 

•	 Dead Load / Live Load = 2.5 

•	 Horizontal service load (due to wind) = 50 kips 

•	 Overturning moments at the base of the column = 250 ft-kips service loads 

(transient) 

Post-construction axial settlements should not exceed 0.5 in. under service dead loads 

and lateral deflections at the pile cap should not exceed 0.25 in. 

6.6.4.D Establish Factor of Safety for Design. For this project, an extensive field load 

test program will be developed and used, so that a factor of safety of 2.0 may be used. 

6.6.4.E Select a trial design pile group to establish individual pile loads. Several 

different pile layouts may be used, but as a first trial consider a 5 pile group of 18-in. 

diameter CFA piles. With piles spaced at 3 diameters on center (i.e., 4.5 ft center-tocenter), the layout of such a group is shown in Figure 6.4. 

147 
-10
 

-5
 

Su from Boring-1 

Depth (ft) 

0
 

Column 

Su from Boring-2
 

Su from Boring-3
 

Cap 

5 

10 

15 Su(ave) = 0.6 ksf Top Soil Layer 

20 (Medium Clay) 

Exclusion Zone 

Below 5 ft 

Saturated Unit Weight = 110 pcf 25 

30 

CFA Pile 35 (18-inch Diam.) 

40 

45 

Bottom Soil Layer 50 

(Stiff to Very Stiff Clay) 

55 Saturated Unit W eight = 120 pcf 

60 

65 Su Linearly Increases with Depth 

Su = 1.5 ksf @ depth of 29 ft 70 

Su = 2.5 ksf @ depth of 80 ft

75 

80 

0 0.5 1 1.5 2 2.5 3 

Undrained Shear Strength, Su (ksf) 

Figure 6.3: Idealized Soil Profile for Design 

The five-pile layout provides some redundancy in the foundation and distributes the 

resistance over a broad footprint so that the moment on the column is resisted by axial 

forces in the piles. A preliminary estimate of individual pile factored loads is as follows: 

Axial pile force due to axial column load: 

500 kip per column/5 piles = 100 kips/pile 

The axial pile force (Fpile) due to the overturning moment on column (Moverturn) can be 

computed from static equilibrium as follows: only Npiles = 4 piles contribute to moment 

as the center piles lies along the neutral axis. The distance normal to the neutral axis of 

the outer four piles (dpile) is used for calculation. 

148 
 

4.5 ft 

10 ft 

Figure 6.4: Five-Pile Footing Layout 

For static equilibrium about the center of the group, the applied overturning moment 

must equal the overturning moment resulting from pile axial forces as follows: 

Moverturn = Npiles × Fpile × dpile 

Load per pile due to moment = 250 kip-ft / [(4 piles) × (4.5 ft) (cos 45°)] = +/-20 

kips/pile 

Cap weight (assume a 2.5-ft thick cap): 

10 ft × 10 ft × 2.5 ft × 0.15 kip/ft3

 / 4 piles = 8 kips/pile 

Total axial load per pile = 

Axial force due to column load + Load due to moment + Cap weight = 100 + 20 + 8 kips 

= 128 kips/pile 

Note that piles at the opposite side of the group are those with the minimum load, and 

are 40 kips/pile less than the maximum. In some cases, the pile cap may not need to be 

included in the load. 

For design, round off and use 130 kips/pile as the required allowable pile capacity 

For lateral loads due to wind, use lateral load per pile = 50 kips/5 piles = 10 kips/pile 

6.6.4.F Select a trial design for individual CFA pile. Because lateral loads may 

control pile diameter, check lateral loading first. Note that combined lateral and axial 

loading could be evaluated using pile group design software, such as FB-Pier (BSI, 

2003) or GROUP (Ensoft, 2006). In many simple cases and in this simple example, an 

149 
analysis can be performed on a single pile that is representative of the group behavior. 

For this example, a single pile is evaluated using LPILE (Ensoft, 2006) to demonstrate 

the calculation methods and design philosophy. It is obvious that the piles will need to 

extend for some length into the stiff Pleistocene clay stratum to generate axial resistance; 

however, the lateral response is unlikely to be affected by this length because the length 

to diameter ratio for an 18-in. diameter CFA pile will be large. A 40-ft long pile is used 

for lateral analysis, even though a longer pile will likely be required for axial loading 

considerations. 

a. Design for Lateral Loading 

LPILE is used to compute the response of a single linear elastic pile of 18 in. in diameter 

that extends into the stiff clay stratum for a short distance. Analyses are performed for a 

range of loads, including loads up to twice the service load of 10 kips per pile, in order 

to verify that a ductile lateral load vs. deflection response is obtained (e.g., the pile has 

greater capacity in excess of the design loads with increasing deflection). The top of the 

pile is assumed to be restrained against rotation; i.e., the pile has a full moment 

connection and is fixed to the cap by connecting the reinforcement into the cap. The cap 

will resist rotation because of the rotational stiffness from the axial resistance of the 

piles. To account for lateral group effects, an average P-multiplier for the pile group is 

used. P-multipliers range from 0.4 to 0.8 for piles within a group spaced at 3-diameters 

on center in clay soils (see Section 5.6.3 for a discussion of P-multipliers). 

First, a linear elastic analyses (concrete and steel strength are assumed to be linearly 

elastic with no cracking) with a p-multiplier at the mid-range of 0.6 is performed to 

verify that the lateral deflections are small and the 18-in. diameter pile has adequate 

lateral resistance. Subsequently, the model is revised to include nonlinear behavior of 

the reinforced concrete pile. As a first try, a rebar cage having longitudinal steel equal to 

at least 1% of the cross-sectional area (i.e., Ds = 2.54 in.2

) is used. Six #7 bars provide a 

total of 3.6 in.2 area and are used for subsequent analyses. Grade 60 reinforcement of 

fy = 60 ksi and fc ’ = 4,000 psi concrete or grout is used for this design. Note that 

repeated analyses with a range of values are very easy once the basic model is 

established. 

The results of these analyses are illustrated using Figures 6.5 through 6.8. The design 

engineer can quickly evaluate results graphically on the computer screen and revise the 

analyses as required without lengthy printouts. The figures are used in this example to 

illustrate the design process. 

The lateral load vs. deflection response shown in Figure 6.5 indicates that the piles in the 

group should support a lateral shear of 10 kips with a deflection of around 0.2 in. or 

slightly less at the pile top. The curve for the linear elastic pile case was performed to 

provide an initial evaluation of soil response without regards to the structural capacity of 

the pile. The nonlinear analyses should be expected to provide a more realistic estimate 

of actual pile response. Note that this does not include any potential contribution from 

the pile cap which is typically bearing against the soil; therefore, this analysis is likely 

conservative. The actual distribution of forces in the piles in the group may range from 

around 8 to 12 kips for a displacement of 0.2 in., depending on the row position, and 

150 
p-multiplier used, as was discussed in Section 5.6.3. The consideration of the average 

condition is sufficient for this illustration problem. 

0 

5 

10 

15 

20 

0 0.1 0.2 0.3 0.4 0.5 0.6 

Deflection, inches 

Shear, kips

NL, Pm=.8 

L.E. 

NL, Pm=.6 

NL,Pm=.4 

Figure 6.5: Computed Lateral Load vs. Deflection Response. NL = nonlinear pile 

behavior, L.E. = linear elastic beam 

The resulting deflection profiles illustrate the length of pile over which the lateral soil 

resistance is mobilized. Deflection vs. depth for the mid range of the p-multipliers used 

(Pm = 0.6) is shown for a 10 kip lateral load (mid-range from 8 to 12 kips range) in 

Figure 6.6. This is considered representative of the average pile case. Bending moments 

in the pile vs. depth for that case are also shown in Figure 6.6. The maximum bending 

moment occurs at the top of the pile, at the connection to the pile cap. Both deflections 

and bending moments indicate that depths below 30 ft are relatively unaffected by lateral 

loads applied at the pile top. 

An evaluation of bending moments for the range of lateral loads from 8 to 12 kips 

corresponds to the range of maximum bending stresses in the piles of the group at a 

deflection of approximately 0.2 in. Maximum bending moments vs. deflection for the 

range of p-multiplier values used is illustrated in Figure 6.7. The maximum value for 

use in design (i.e., for a deflection of 0.2 in.) is around 700 in.-kips. Note that the stiffer 

pile (Pm = 0.8) has the highest moment at a given deflection, because this stiffer pile is 

supporting a larger share of the lateral load. In any event, it is appropriate to design all 

of the piles to encompass the maximum possible range of conditions. If the simplified 

method had been used with calculations performed only for the average p-multiplier of 

0.6, the estimated deflection would have been almost the same to that obtained using the 

row-dependent p-multipliers. The maximum moment would have been calculated at 

720 in.-kips, based on the 600 in.-kips for the average pile, with a 20% increase to 

account for variations in pile stiffness. 

151 
-5 

-10 

-15 

-20 

-25 

-30 

-35 

-5 

-10 

-15 

-20 

-25 

-30 

-35 

Deflection, inches Bending Moment, inch-kips 

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 -600 -400 -200 0 200 400 

0 0 

Depth, ft 

Depth, ft 

-40 -40

Figure 6.6: Deflection and Bending Moments vs. Depth for Example Problem 

(lateral load = 10 kips) 

0 

200 

400 

600 

800 

1000 

1200 

0 0.1 0.2 0.3 0.4 0.5 0.6 

Deflection, inches 

Max Moment, inch-kips 

NL, Pm=.8 

NL, Pm=.6 

NL,Pm=.4 

Figure 6.7: Maximum Bending Moments as a Function of Pile Top Deflection 

Figure 6.8 shows the moment vs. curvature relationship computed with LPILE for an 

18 in.-diameter pile reinforced with 6 #7 bars, and with 3 in. of cover. The range of 80 

to 130 kips of axial force encompasses the anticipated range of axial pile loads and 

provides a structural check on combined axial and flexural responses. This figure 

152 
2000 

Bending Moment, inch-kips 

1500 

1000 

500 

0 

80 k Axial 

130 k Axial 

0 1 2 3 4 5 

Curvature, in/in x .0001 

Figure 6.8: Bending Moment vs. Curvature for a 18-in. diameter Pile with 6 #7’s 

suggests that the maximum bending moments computed in the 700 in.-kip range are well 

within the factored moment resistance of this pile for purposes of preliminary design. 

The ultimate moment resistance is in the 1,500 to 1,800 in.-kip range, as is evident by 

the large increase in curvature with little increase in bending moment (approximate 

curvature of 0.0003). 

At this point, the preliminary evaluation of an 18-in. diameter pile for lateral loads is 

completed. Before completing a final design considering lateral loads, the design for 

axial resistance should be performed. Note also that by evaluating a range of lateral 

loads at this preliminary design stage, it would be easy to re-evaluate lateral load 

response for pile groups with different numbers of piles or for different loads that may 

be representative of other foundation cases on the project. 

b. Design for Axial Loading 

The maximum service loads were determined to be 130 kips per pile. Using a factor of 

safety of 2.0, the ultimate pile resistance required for this design is 260 kips, 

corresponding to a tip embedment of 69 ft below grade. Computations of axial 

resistance with depth for an 18-in. diameter pile in this soil profile were made in Section 

B.1 of Appendix B. The results of these calculations are reproduced as Figure 6-9. 

Axial structural capacity was considered in combination with flexure in the previous 

step. 

Note that load testing of a pile with similar characteristics and soil conditions is required 

to utilize the safety factor of 2.0 selected for design. The load test must be designed to 

test the pile load resistance to at least 390 kips, i.e., 3 times the design load. 

153 
c. Consider Constructability and Cost Effectiveness. 

The required embedment depth of 69 ft below grade is fairly deep, but well within the 

range for which CFA piles of this size can be constructed efficiently. It is possible to 

consider using 24-in. diameter piles of shorter length, for which a 4–pile group could be 

easily constructed. It is also feasible to increase the design group to a 6–pile 

arrangement of 18 in. piles to use shorter piles which may require a rig with less torque 

or crowd. 

Another constructability issue to consider is the rebar cage. The calculations for bending 

moments suggest that a cage needs to extend to a depth of 30 ft, which is within the 

range of embedment that is relatively easy to construct. Without significant tensile 

forces or seismic ground motions that could produce significant bending stresses at 

greater depth, there is no necessity to install a deeper cage. The six bar cage developed 

in this preliminary design step does not appear to pose a constructability problem. 

It may be noted that the great majority of the resistance of the proposed design comes 

from side-shear, with relatively little contribution from end-bearing resistance. Of most 

significance is the embedment into the stiff Pleistocene clay stratum, a point which 

should be made via the project documents so that the inspection team can specifically 

seek to verify the embedment into the Pleistocene. It generally should be possible to 

note a change in drilling resistance when this significantly stiffer stratum is encountered 

below the alluvium. 

6.6.4.G Pile Group Capacity. Limiting pile group capacity may be estimated using the 

block failure concept outlined in Section 5.5.2.1.2. This rarely controls but must be 

checked. A quick check can be made on the side-shear on the block in the stiff clay 

stratum only, without even considering the base resistance of the block. The width of 

the outside of the 5-pile group is 2 times the projected distance from the center pile to 

the center of the corner piles plus one pile diameter or: 

2 × (4.5 cos 45°) + 1.5 = 7.9 ft 

The group is embedded 69 – 29 = 40 ft into the stiff clay. Therefore, the surface area of 

the block resisting in side-shear is: 

4 × 7.9 × 40 = 1,264 ft2 

The average undrained shear strength within 29 and 69 ft below grade is 1.9 ksf. 

Therefore, the side-shear resistance on the block is: 

1,264 ft2 × 1.9 ksf = 2,402 kip. 

This resistance is substantially larger than the resistance of the 5 individual piles, 

indicating that block failure of the group does not control. Base resistance can be added 

if necessary, but this quick check is sufficient to verify the block failure does not control 

design. 

154 
6.6.4.H Pile Group Settlements. Long-term settlements in clay soils resulting from 

dead load are a consideration, as these sustained loads may result in significant 

compression or consolidation settlement of the underlying soils. The step-by-step 

procedure outlined in Section 5.5.3.3 is followed for this calculation. 

a.	 The depth of the “equivalent footing” is approximately 2/3 of the depth within 

the stiff clay stratum. Because the pile extends to 69 ft below grade and the stiff 

clay starts at a depth of 29 ft below grade, the equivalent footing is located at: 

b.	 2/3 × (69 – 29 ft) = 0.67 × 40 = 56 ft, or 27 ft into the stiff clay deposit or 56 ft 

below the ground surface. The side of the equivalent footing for a 5-pile group 

shown in Figure 6-4 is 2 × (4.5 cos 45°) + 1.5 = 7.9 ft. Because the DL/LL ratio 

is 2.5, the sustained dead load (SDL) is the total service load (TSL) times the 

ratio to the dead load of the total service load or: 

SDL = 500 × 2.5/(1+2.5) = 357 kips 

the cap weight is assumed to be = 10 × 10 × 2.5 × 0.15 = 37.5 kip 

Therefore, the total dead weight causing long-term settlement is 395 kip. 

The bearing pressure on the equivalent footing is thus 395 kip/7.92 = 6.33 ksf. 

c.	 The soil is divided into 6-ft thick layers below the equivalent footing. The first 

of three layers will have an effective vertical stress, po, at the center of the layer 

(or at depth of 56 + 3 = 59 ft) equal to: 

6 

po = ∑ (γsoil zsoil,i) – γw zw where: 

i
 

γsoil = soil unit weight of layer i 

zsoil,i = soil layer thickness of layer i 

γw = unit weight of water 

zw = depth below the groundwater table 

= 29 ft × 0.110 kcf + 30 ft × 0.120 kcf – 52 ft × 0.0624 kcf = 3.55 ksf 

Load spreading at a 1H:2V ratio at the center of the first layer produces a stress change, 

∆p, of 395k/(7.9 + 3)2

 = 3.32 ksf and a final stress, pf = po + ∆p = 3.32 + 3.55 = 6.87 ksf. 

The settlement, S, of this layer is: 

S1 = H [(Cr/(1+eo)) log (p f /po)], where 

H = layer thickness = 6 ft = 72 in. 

155 
Resistance (kips) 

0 50 100 150 200 250 300 

0 

5 

CFA Pile Embedment Depth (ft) 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

75 

80 

Allowable Total Resistance (RT(Allow)) 

Minimum 

Required Pile 

Embedment 

Depth (Lmin) 

Allowable End Bearing RB(Allow) Ultimate End Bearing RB 

Allowable Side Shear RS(Allow) Ultimate Side Shear RS 

Allowable Total RT(Allow) Ultimate Total RT 

CFA Pile 

with an 18-inch 

Nominal Diameter 

Top Soil Layer 

(Soft Clay) 

Bottom Soil Layer 

(Medium to Stiff Clay) 

Figure 6.9: Computed Axial Resistance vs. Depth 

Cr = recompression index = 0.015 

eo = void ratio = 0.6 

S1 = 72 [(0.015 / 1.6) log (6.87/3.55)] = 0.19 in. 

For other layers, the computation follows in Table 6.2. Note that the calculation is 

performed until a depth at which ∆p/po < 10% 

156 
 

Table 6.2: Pile Group Settlement Computation
	

Layer 

Number 

Depth 

Interval 

(ft) 

Thickness 

(in.) po (ksf) ∆p (ksf) S (in.) 

1 56 - 62 72 3.55 3.32 0.19 

2 62 – 68 72 3.9 1.38 0.09 

3 68 – 74 72 4.24 0.75 0.05 

4 74 – 80 72 4.59 0.47 0.03 

TOTAL: 0.36 

Add to the consolidation settlement above the theoretical elastic shortening (Sel) of the 

piles acting as a column above the equivalent footing. These piles support a total load of 

395 kips with an area equal to that of 5 piles; therefore, using an estimated elastic 

modulus for the piles of 3,000 ksi, it results 

S × 254 in.2 

el = (1/2) × (PL/AE) = 1/2 × [(395 kip × 56 ft × 12 in./ft) / (5 × 3,000 

ksi)] = 0.04 in. 

Long-term settlements under dead load for this foundation are thereby estimated at no 

more than 0.36 + 0.04 = 0.40 in., or about 0.5 in. It should be noted that a portion of the 

dead load is applied onto the piles before the pier cap and girder bearing plates are 

finalized, and the portion of the settlement that occurs during this period will not affect 

the bridge structure. Therefore, if the long-term settlements due to total dead load 

appear to be too high, it would be prudent for the design engineer to re-evaluate the 

settlements to estimate the actual magnitude of the post-construction portion of the total 

settlement. 

 6.6.4.I Pile Group Lateral Behavior. Lateral deflections have already been estimated in 

the previous step (6.6.4.F.a) at less than 0.2 in. for the design lateral loads using 

appropriate P-multipliers to account for group effects. A full 3-D computer model of the 

proposed foundation may be analyzed using GROUP (Ensoft, 2006) or FB-Pier (BSI, 

2003) or similar software. The use of these sophisticated programs is not necessary for 

this simple problem but may be a convenience for users who are familiar and efficient in 

using such software. 

6.6.4.J Finalize Structural Design. The design satisfies geotechnical limit states and 

serviceability limit states. The final sub-step in designing the piles is to finalize the 

structural design of the pile and select reinforcement. Structural design follows the 

procedures outlined in Section 5.6.4. 

The depth required for the full cage section must first be determined. It was seen in 

Figure 6.6 that the pile clearly exhibited “long pile” behavior, and the depth to the 

counter-flexure point in the displacement profile (second point of zero displacement with 

157 
depth) was approximately 25 ft. The cage may thus terminate at this depth because the 

piles are not bearing in weak rock or intermediate geotechnical material (IGM) sockets. 

Longitudinal reinforcement was chosen as the recommended minimum of 1%, as has 

been determined previously in computations of lateral resistance to provide adequate 

lateral structural resistance. Combined axial force and flexure was considered in the 

analysis presented in Figure 6.8. 

For the maximum computed shear force in any pile, check to determine if the concrete 

section has adequate shear capacity without shear reinforcement (Chapter 5, Section 

5.6.4.2). 

With 6 #7’s bars and 3-in. cover on the longitudinal reinforcing, the radius of the ring 

formed by the centroids of the longitudinal bars is (Eq. 5.59): 

rls = B/2 – dc – db/2 = 9 – 3 – 0.44 = 5.56 in. 

The area of the cross-section that is effective in resisting shear is (Eq. 5.59): 

Av = B[B/2 + 0.5756 × rls] = 219 in.2 

The concrete shear strength using the average axial force of 100 kips is (Eq. 5.61a): 

Vc = [1 + φ × 0.00019 (P/A 0.

g)] × (fc ’) 5 

 = [1 + 0.85 × 0.00019 × 100,000 / (π × 92

)] × (4,000)0.5 = 68 psi 

Note that the maximum shear will likely occur on a front row pile with greater axial 

force. 

Note that ignoring the effect of axial force and computing Vc = (fc ’)

 0.5,a value of 63 psi 

is obtained, which is slightly conservative but generally sufficient for design. 

The factored shear resistance provided by the concrete is thus: 

φ Vn = φ Vc Av = 0.85 × 68 × 219 / 1,000 (lb/kip) = 12.6 kips > 12 kips (max. shear) 

Thus, shear reinforcement is not required and the transverse reinforcement can consist of 

the minimum recommended of #3 ties at 12 in. spacing. 

A single center longitudinal bar will extend to the full length of the CFA pile. Because 

these piles are not subject to uplift forces, the longitudinal bar may be a # 9 bar 

(minimum size allowed). Note that this bar must extend through the full cage section to 

the top of the shaft, and would be allowed to contribute to the structural capacity of the 

top cage section if the design engineer elects to do so in the analyses. 

158 
6.6.5 Step 4: Constructability Review 

Finally, a brief check on constructability issues is provided in a question and answer format: 

a. Are pile length and diameters appropriate? Yes, 18 in. diameter and less than 70 ft 

embedded length is within normal sizes. 

b. Can the bearing strata be penetrated to depth indicated? Avoid designs which require 

penetration into hard materials to achieve capacity if the overburden soils may be 

subject to soil mining or if the bearing stratum is too hard to drill effectively. Yes. 

c. Is there a risk of soil mining due to loose water-bearing sands? Yes, if soils are 

cohesive. 

d. Is there potential effect on nearby structures? No. 

e. Is the rebar cage appropriate? Yes. 

f. Is there a pile cutoff detail? Yes. Avoid pile cutoff more than a few feet below the 

working grade if possible. Deeper cutoff will require casting the pile to the surface 

and chipping down after the grout or concrete has set. These piles may be formed to 

the surface and cut down later. If the contractor chooses to dip the pile down while 

still fluid, there must be a temporary form provided to prevent cave-ins from 

contaminating the top of the pile. 

g. Is construction sequence feasible? Yes. Consider existing structures, obstructions, 

pile cap footprint. Avoid installing CFA or DD piles over water. A stable working 

platform is necessary, especially for DD piles, which require larger, heavier rigs than 

conventional CFA piles. The working pad may require stabilization; this is worthy of 

a note on the plans that the surface may be soft. 

h. Are low headroom conditions required? No. 

i. Is there a plan for resolving construction questions prior to production? Yes. Include 

pre-construction meeting discussion. 

6.6.6 Step 5: Prepare Plans and Construction Specifications, Set Field QC/QA and Load 

Testing Requirements 

These items follow the general work for developing plans and specifications for transportation 

projects involving deep foundation work. The following two chapters are focused on the aspects 

of inspection, testing, and specifications for CFA projects. Note that for this example, a load 

testing program is required because the design relied on the use of a lower factor of safety and 

because of the increased reliability of a design that must be validated by site-specific load test data. 

159 
CHAPTER 7 QUALITY CONTROL (QC) / QUALITY 

ASSURANCE (QA) PROCEDURES 

7.1 INTRODUCTION 

Continuous flight auger (CFA) piles have a history of use in the U.S. commercial market but 

have been used infrequently on public works transportation projects. This under-utilization of a 

viable technology is at least partly the result of perceived difficulties in quality control on the 

part of transportation agencies. In addition, the proprietary systems used for the installation of 

drilled displacement piles are not easily incorporated into traditional design-bid-build delivery 

systems for public works projects. 

The guide specification included in Chapter 8 of this document is performance-based in which 

the contractor is responsible for the final determination of pile lengths. The approach requires 

that the contractor provide the quality control and performance measurement parameters 

necessary to ensure that the owner is provided with the pile capacity and structural integrity that 

is required for the job. The key for the owner is that the specifications require measurements that 

provide a reliable indication of performance. With reliable performance indicators, this approach 

can allow contractors to exercise ingenuity and seek the most cost-effective and timely solutions 

to achieve the project requirements. 

General quality control/quality assurance (QA/QC) practices for deep foundation installation that 

have been used in the U.S. and abroad are reviewed in this chapter to provide the background for 

understanding QA/QC issues with CFA piles. Recommended “best practices” for QA/QC for 

CFA piles on transportation projects are included in each section. The last section summarizes 

the recommended practices. 

7.2 THE ROLE OF THE INSPECTOR 

The inspector on a CFA pile project has a significant role in the observation and recording of the 

contractor’s QA/QC practices. As outlined in this chapter and in the guide specification in 

Chapter 8, a significant amount of testing, data collection by automated equipment, and manual 

data will be recorded for pile installation. The inspector will be required to: (a) understand the 

basic fundamentals of CFA pile installation; (b) verify that good construction practices are 

followed; and (c) understand the data collected. The inspector may also be collecting manual 

data, such as is done in much of current commercial practice, to duplicate or to backup the data 

recorded and submitted by the contractor. 

While much of the data collected during pile installation may be recorded by the contractor, the 

inspector needs to ensure that the data is collected. Many agencies have standard protocols for 

record keeping and submittals, delineating responsibilities among the contractor and inspector. 

Some agencies may require that the inspector duplicate some or all manual data collection. The 

recommended records for pile installation are: 

160 
1.	 Pile location and plumbness; 

2.	 Ground surface elevation; 

3.	 Pile toe (bottom) depth/elevation; 

4.	 Depth/Elevation of top of grout/concrete; 

5.	 Pile length; 

6.	 Auger diameter; 

7.	 Details of the reinforcing steel (number, size, and grade of longitudinal bars, size and 

spacing of transverse steel; outside diameter and length of cage); 

8.	 Flow cone efflux time and volume of grout placed, or slump and volume of concrete 

placed; 

9.	 Theoretical volume of excavation (theoretical diameter = diameter of auger); 

10. Depth/Elevation to which reinforcing steel was placed; 

11. Date/Time of beginning of drilling; 

12. Date/Time of completion of drilling; 

13. Date/Time grout or concrete was mixed; 

14. Date/Time ready-mix grout or concrete truck arrived at project site, and copies of all 

grout or concrete batch tickets used for the pile construction; 

15. Date/Time of beginning of grout or concrete pumping; 

16. Date/Time of completion of grout or concrete pumping; 

17. Date/Time of placement of reinforcing steel; 

18. Weather conditions, including air temperature, at time of grout or concrete placement; 

19. Identification of all grout or concrete samples taken from the pile; 

20. All other pertinent data relative to the pile installation; and 

21. All readings made by the automated measuring and recording equipment to include as 

a minimum: 

a.	 auger rotation vs. depth for every 0.6-m (2-ft) increment, or less, of pile 

advancement during the drilling process, and during placement of grout or 

concrete (if auger is rotated during this placement); and 

b.	 volume of grout or concrete placed versus depth of outlet orifice for every 0.6-m 

(2-ft) increment, or less, of pile placed; 

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c.	 Average maximum and minimum pump stroke pressures at ground level for every 

0.6-m (2-ft) increment, or less, of pile placed; 

d.	 Average maximum and minimum pump stroke pressure at or near the auger head 

for every 0.6-m (2-ft) increment, or less, of pile placed, if directed by the 

engineer; and 

e.	 Additionally, the engineer may also specify that the torque and crowd force 

(downward thrust on auger) measurements be made at every 0.6-m (2-ft) 

increment, or less, of pile advancement during the drilling process. 

7.3 PRE-CONSTRUCTION PLANNING 

Effective QA/QC begins with proper planning prior to construction. Under the performancebased specification model, the contractor will be required to submit design calculations, working 

drawings, a detailed pile installation plan, and a conformance testing plan. The owner and its 

engineer(s) and inspector(s) will need to review the submittals as part of the project planning 

process. The owner will also have to provide some level of information for the contractor to 

perform the design and develop their installation plans. 

Owner-controlled design specifications can vary in the amount of design performed by the 

owner’s design engineer and the amount performed by the CFA pile specialty contractor. For the 

method recommended in Chapter 8, the owner provides preliminary design information. The 

contractor designs the individual piles and pile cap connections and selects the CFA construction 

process and equipment. 

During the bid process, qualified CFA pile contractors prepare a preliminary CFA pile design 

based on the owner’s preliminary plans and specifications. The submittal design will occur with 

the bid. Once the contract is awarded, the selected CFA pile contractor prepares detailed CFA 

pile design calculations and working drawings and submits them for review. 

7.3.1 Owner-Supplied Information 

The owner should provide preliminary design information for the contractor during the pre-bid 

process. The complete list of items will vary according to project and local procedures, but will 

generally include: 

1.	 plans showing the pile design loadings, minimum pile diameter, pile tip elevation, 

minimum reinforcement, pile to footing/cap connection design, and pile layout for 

each footing/cap location; 

2.	 design criteria and requirements, such as design loads and maximum allowable 

displacements, safety factor; 

3.	 any geotechnical reports for the project containing the results of exploratory borings, 

test pits, or other subsurface data collected in the vicinity of the pile locations; 

4.	 site information, such as rights-of-way limits, utility locations, site limitation; 

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5.	 material requirement for grout/concrete and reinforcement and testing specifications; 

and 

6.	 requirements for submittal and review of contractor design, working drawing, and 

construction submittals. 

The subsurface conditions expected at the site can significantly impact the contractor’s choice of 

procedures, methods, equipment, the biding process, and contract administration. The 

geotechnical report should be a factual document describing the subsurface conditions revealed 

by the investigation and should be included in the contract special provisions. This report should 

alert bidders of the subsurface conditions and reduce the potential for differing site conditions 

construction claims and disputes. By including the report in the contract special provisions, it 

becomes a legal part of the contract documents. 

7.3.2 CFA Contractor Experience 

The quality of CFA piles is highly dependent upon the skill of the contractor and the specific 

crew that is assigned to the project. It is essential that the contractor demonstrate competence to 

perform the work by providing documentation of successful completion of prior projects of a 

similar nature to the project being bid. Only experienced contractors will be allowed to perform 

the work and all contractors will be required to construct a test pile. 

For transportation projects, the recommended experience requirements for contractors and their 

personnel are as follows. 

1.	 The contractor should have completed a minimum of three projects in the two-year 

period preceding the bid date in which CFA piles were installed successfully under 

subsurface and project conditions similar to those of the current project; 

2.	 The designated job site supervisor (foreman or crew chief) should have a minimum of 

three years of experience in the supervision of the installation of CFA piles; 

3.	 Drill rig operators should have a minimum of three years of experience installing 

CFA piles; and 

4.	 The designated project manager should have a minimum of three years experience 

with CFA projects of similar size and scope. 

The contractor should be required to submit a list of personnel to be used on the project and 

provide documentation of experience. 

7.3.3 Design Submittals 

The CFA piles shall be designed by a licensed Professional Engineer (Design Engineer) that is 

licensed in the state where the project is located. The Design Engineer should have experience 

in the design of at least three successfully completed CFA pile projects over the past five years 

with CFA piles of similar capacity to those required for the project. 

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Revisions to the design due to field conditions will need to be documented through submittals of 

revised calculations and/or working drawings in the affected portion of the project. It is 

recommended that the contractor be required to submit as-built drawings upon completion of the 

pile installation. 

7.3.3.1 Design Calculations 

Design calculations should include, but not be limited to, the following items: 

1.	 A written summary report that describes the overall CFA pile design; 

2.	 CFA pile structure critical design cross-section(s) including soil/rock strata, 

piezometric levels, and location, magnitude and direction of applied loads; 

3.	 Design criteria, including soil/rock shear strengths (friction angle and cohesion), unit 

weights, unit skin friction values, and unit end-bearing values. Any additional 

subsurface borings, laboratory work, or other subsurface data collected for the design 

beyond what was provided by the owner; 

4.	 Safety factors used in the design; 

5.	 Seismic design earthquake acceleration coefficient or other seismic design criteria 

applicable for the geographic area of the project; 

6.	 Design calculation sheets (both static and seismic) with the project number, CFA pile 

structure location, designation, date of preparation, initials of designer and checker, 

and page number at the top of each page. An index page should be provided with the 

design calculations; 

7.	 Design notes including an explanation of any symbols and computer programs used 

in the design; and 

8.	 Pile to cap/footing calculations. 

7.3.3.2 Working Drawings 

Working drawings should include, but not be limited to, the following items unless provided in 

the contract plans: 

1.	 A plan view of the CFA pile structure(s) identifying: 

a.	 A reference baseline datum; 

b.	 The offset from the construction centerline or baseline to the face of the CFA pile 

structure at all changes in horizontal alignment; 

c.	 Beginning and end station of CFA pile structures; 

d.	 CFA pile locations with center-to-center pile spacing; 

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e.	 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; 

f.	 The centerline of any drainage structures or drainage pipes behind, passing 

through, or passing under the CFA pile structure; and 

g.	 Subsurface exploration locations shown on a plan view of the proposed CFA 

structure alignment with appropriate reference base lines to fix the locations of the 

explorations relative to the CFA structure. 

2.	 An elevation view of the CFA pile structure(s) identifying: 

a.	 CFA pile locations and elevations with vertical and horizontal spacing; and 

b.	 Existing and finish grade profiles both behind and in front of the CFA pile 

structure. 

3.	 General notes for constructing the CFA piles including construction sequencing or 

other special construction requirements. 

4.	 Horizontal and vertical curve data affecting the CFA pile structure and control points, 

including match lines or other details to relate CFA pile structure stationing to 

centerline stationing. 

5.	 A listing of the summary of quantities. 

6.	 CFA pile typical sections including spacing; diameter; reinforcing bar sizes, 

locations, and details; centralizers and spacers; and connection details to the 

substructure footing/pile cap. 

7.	 Typical details of verification and proof load test piles, including reaction systems. 

8.	 Details, dimensions, and schedules for all CFA piles and reinforcing steel. 

3.4 Pile Installation Plan 

e Pile Installation Plan is used by the contractor to demonstrate the acceptability of the 

uipment, techniques, and source of materials to be used on the project. This plan should 

clude, but not be limited to, the following items: 

1.	 List and sizes of proposed equipment, including drilling rigs, augers and other drilling 

tools, pumps for grout or concrete, mixing equipment, automated monitoring 

equipment, and similar equipment to be used in construction, including details of 

procedures for calibrating equipment as required; 

2.	 Step-by-step description of pile installation procedures; 

3.	 A plan of the sequence of pile installation; 

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4.	 Target drilling and grouting parameters (along with acceptable ranges) for pile 

installation, including auger rotation speed, drilling penetration rates, torque, applied 

crowd pressures, grout pressures, and grout volume factors; 

5.	 Details of methods of reinforcement placement, including support for reinforcing 

cages at the top of the pile and methods for centering the cages within the grout or 

concrete column; 

6.	 Mix designs for all grout or concrete to be used on the project, including slump loss 

vs. time curves and strength development vs. time curves for mixes with fly ash 

and/or slag; 

7.	 Equipment and procedures for monitoring and recording auger rotation speed, auger 

penetration rates, auger depths, and crowd pressures during installation; 

8.	 Equipment and procedures for monitoring and recording grout or concrete pressures 

and volumes placed during installation; 

9.	 Contingency plans for equipment failures during drilling or grouting operations (grout 

pump, monitoring equipment, etc.); 

10. Procedures for protecting adjacent structures, on or off the right-of-way, that may be 

adversely affected by foundation construction operations, including a monitoring plan 

as required in Section 3.1; and 

11. Other required submittals shown on the plans or requested by the engineer. 

A clearly written pile installation plan can be very effective in reducing misunderstandings 

between the engineer, inspector, and the CFA pile contractor and can form the basis for solving 

potential problems before they occur, thus keeping the project on schedule and minimizing 

claims. The specific time allowance for review and approval should be clearly defined in the 

contract documents; 14 days is considered suitable for most routine projects. In reviewing the 

pile contractor’s submittal, the key information regarding the equipment that should be 

scrutinized is: 

1.	 the rated capacity and boom lengths of the drill rig; 

2.	 the torque, rotational speed and down crowd capacity of the drilling machine; 

3.	 the horsepower of the hydraulic power unit used to turn the auger; and 

4.	 the positive displacement piston-ball valve pump, pump stroke displacements, engine 

horsepower and pump pressures of the grout pump to be used. 

With respect to the above parameters, the installation plan should include documentation that the 

proposed drilling equipment has been demonstrated effective on similar size piles in similar soil 

conditions. 

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7.3.5 Testing Plan 

The testing plan should be a requirement of the contract provided by the owner. The CFA pile 

contractor should include a plan for constructing and performing the required tests to meet the 

requirements of the testing plan along with the Pile Installation Plan. The testing program should 

consist of pre-production static load tests, production static and/or rapid and/or dynamic load 

tests, and post-installation integrity tests in sufficient quantities to provide the data necessary to 

demonstrate that the installed piles meet the load and deflection criteria established in the project 

plans with an appropriate factor of safety. 

The intent of the pre-production testing program is to install test piles to establish and/or verify 

installation means and methods, as well as load capacity. The results of the pre-production test 

program will then be used during production pile installation to ensure that the contractor is 

consistently installing acceptable piles (i.e., all production piles are the same as a test pile). The 

use of automated monitoring equipment provides a means of evaluating each pile for 

conformance to the installation criteria. Verification load tests and structural integrity tests 

during construction will be used to verify that the contractor is producing acceptable piles. 

Sections 7.4 through 7.6 provide detailed discussions and recommended practices of each of the 

components of a testing program. The remainder of this section will outline the general 

requirements for the contractor’s pre-construction submittal. 

7.3.5.1 Pre-Production Testing 

Pre-production load test program will generally consist of a single or multiple static load tests 

and will depend on the number of piles to be installed, the range of design pile capacities, and the 

variation of subsurface conditions at the site. Lateral and uplift load tests may be included as 

well. For very large projects, pre-production testing may include a single static load test 

supplemented with several piles tested by the rapid load test (RLT) (usually StatnamicTM) or 

dynamic load test (DLT) methods. Performing rapid or dynamic tests during the pre-production 

testing program will allow these methods to be “calibrated” against static load tests results prior 

to production pile installation. A discussion of various load test methods is contained in 

Section 7.6. 

Piles installed for pre-production testing (including any reaction piles required for static load 

testing) should include all construction, monitoring, testing, and inspection requirements of 

production piles. The results of the installation and testing will be used to: 

1.	 establish target drilling penetration rate(s) for the various subsurface conditions on 

the site; 

2.	 establish pressure/volume relations for placement of grout/concrete. The grout factor 

(i.e., ratio of used volume of grout/concrete to theoretical volume for the specified 

pile size) ±7.5% that is calculated on the test pile(s) should be used for the installation 

of the production piles; 

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3.	 establish target values for torque and downward thrust or crowd for displacement or 

partial displacement piles; 

4.	 establish mix design parameters such as grout flow, necessary admixtures, etc.; and 

5.	 evaluate design correlations of side and base resistance with the site specific soil 

parameters. 

Because a major advantage of CFA piles is speed of installation, the pre-production load test 

program may be performed concurrent with the start of production piles to reduce additional 

mobilization or delay costs; however, the ability to modify the design based on the results of the 

load test may be limited in this case. For very large projects, the ability to modify the design 

based on the pre-production tests may make the separate mobilization for pre-production testing 

less of cost consideration. 

7.3.5.2 Conformance Monitoring and Verification Tests 

Conformance monitoring includes the use of automated measuring and recording equipment to 

confirm the pile installation criteria, integrity testing, and verification tests on production piles to 

demonstrate that the installed production piles meet the established load-deflection criteria. 

Installation Automated Monitoring 

Automated monitoring equipment provides “real time” evaluation of each pile on a project. 

Section 7.4 outlines the types of equipment and their application. Automated monitoring is a 

contract requirement. Therefore, the contract documents should outline the data to be collected 

and submitted. The installation plan should include type of monitoring equipment, 

manufacturer, data to be collected, current calibration records, and sample data records. As a 

minimum, the monitoring equipment should have the capability to monitor and record the 

following: 

1.	 auger rotation; 

2.	 depth of the auger injection point; 

3.	 torque delivered to the auger; and 

4.	 crowd force (downward thrust on auger). 

All measurements should be referenced to (or plotted against) the depth of the auger injection 

point. This can be accomplished with a rotational position indicator on the auger head system 

and an electronic position indicator on the crane line or boom holding the auger. Torque and 

thrust load cells should be positioned on the auger head system. 

As a minimum, the following automatic measurements should be recorded during the grouting or 

concreting operation: 

1.	 volume of grout or concrete; 

2.	 maximum and minimum grout or concrete pressure; 

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3. auger rotation (if rotated); and 

4. depth of the injection point. 

ll measurements should be referenced to (or plotted against) the depth of the auger injection 

oint. This can be accomplished with electronic flowmeters and electronic pressure transducers 

laced in the grout or concrete pressure line, an electronic position indicator on the crane line or 

oom holding the auger, and a rotational position indicator on the auger system. 

alibration should be made on all monitoring equipment at the beginning of the project in 

ccordance with the equipment manufacturer’s specifications. The values indicated by the 

onitoring equipment should be within three percent of the manufacturer recommendations. 

ntegrity Testing 

ost-installation integrity tests are valuable in establishing that the contractor’s procedures are 

roducing acceptable piles on any given project. The most reliable of the post-installation 

ntegrity tests for identifying anomalies within the pile are those that use down-tube instruments, 

uch as the cross-hole sonic (CSL) test, single-hole sonic test, the backscatter gamma test, and 

he fiber-optic television camera test. However, these types of tests are costly and utilize 

ntrusive tubes, and thus not generally practical for CFA piles of less than 760 mm (30 in.) in 

iameter. The piles that will include any access tubes should be noted in the test program. Sonic 

cho tests performed from the pile top are also available to check pile integrity, and may be more 

ractical for routine use to verify the overall structural integrity of the piles in the upper 10 to 20 

iameters, though the results may not be as reliable as down-tube tests under certain conditions. 

escriptions of tests applicable to CFA piles and a discussion of their use are included in 

ection 7.5. Piles that have installation records out of specification or that otherwise appear 

bnormal can be selected for integrity tests or verification load tests to determine if they should 

e accepted or rejected. Integrity tests along with careful monitoring of installation would then 

e used to verify pile capacity based on comparison to the pre-production test results. 

ecommended frequency of integrity testing is given in Section 7.3.3. 

erification Testing 

erification tests should be performed on a minimum of two percent of production piles, or at a 

reater frequency if required by the engineer. For smaller projects (i.e., less than about 50 piles), 

 minimum of one or two verification tests should be specified; the actual minimum is dependent 

pon the variability of site conditions, experience in the area, and other factors as may be 

onsidered relevant by the engineer. Verification tests can also be used to determine if a 

uestionable pile should be accepted or rejected. Verification tests can be performed using static 

oad tests, RLTs, or DLTs. Combinations of the various test methods may also be used as 

ppropriate for the project. Section 7.6 includes discussions of common RLTs and DLTs 

vailable. 

 single pre-production test only demonstrates the performance of the test pile. Performing 

erification tests periodically throughout production pile installation will verify that the pile 

nstallation techniques continue to provide adequate pile capacities. The use of RLTs (e.g., 

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StatnamicTM) or DLTs (e.g., drop hammer) can often test a large number of piles more efficiently 

in both time and cost compared to static load test methods. Calibrating the RLT or DLT results 

with static load test results during the pre-production test program should be part of the testing 

program, unless comparative tests have been performed on previous projects in similar soil 

conditions. 

7.3.5.3 Materials Testing 

Requirements for sampling and testing of grout and concrete materials used on the project should 

be included in the owner’s bid package. The general requirements for materials testing in the 

State DOT Standard Specifications should be referenced, along with any additional materials 

testing the contractor is required to perform. Requirements would include the test type and 

frequency. The tasks for materials testing may be performed solely by the owner, by an 

independent testing firm working for the contractor, or a combination, and will be addressed in 

the project specifications. Requirements for grout or concrete testing are discussed in Chapter 4 

and in Section 7.4 

7.4 PERFORMANCE MONITORING AND CONTROL DURING CONSTRUCTION 

The construction of continuous flight auger piles is hidden from the view of the operator as well 

as the inspector. Past practice has emphasized the importance of a skilled operator using visual 

observations of the drilling and inaccurate estimates of grout/concrete pumped to construct a 

“good” pile. A skilled operator and experienced CFA contractors are important to achieve a 

good end result, but the reliance upon visual observations alone is insufficient to provide quality 

assurance and quality control (QA/QC) for transportation projects. Technology is available to 

obtain the measurements and feedback needed to: (a) provide operators with information needed 

to develop judgment and control; and (b) provide inspectors and owners with documentation that 

the pile was constructed with proper practices in accordance with specifications. Much of the 

equipment used for this purpose has been described in Chapter 4 of this document. This section 

will summarize the requirements for performance monitoring and control during construction. 

Post-construction techniques for integrity and load testing are described in subsequent sections of 

this chapter. 

It is important to remember that automated monitoring should not be viewed as the sole record 

for CFA pile QA/QC. Critical information that supplements automated monitoring includes: 

visual record of the completion of the top of the pile, notes of the workmanship of clearing debris 

and forming the pile top, descriptions of the successes and difficulties in installing the rebar 

cage, and notes of difficulties encountered and the methods used to resolve any problems. 

Complementary manual checks of the data collected by the automated equipment should also be 

performed periodically by the inspector to verify that the equipment is working reliably and 

accurately. The manual/visual observations outlined in this chapter that are typical of 

commercial practice in the United States would be appropriate for this task. The level of 

duplicate data will vary according to the confidence level of the owner agency and the 

complexity of the project. In the event that the automated equipment malfunctions during 

production, pile installation should stop until repairs are made. 

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7.4.1 Monitoring and Control of the Drilling Phase 

The drilling phase of construction should be controlled to ensure that excessive flighting of soil 

does not occur with conventional CFA piles and that the appropriate level of soil displacement 

occurs with drilled displacement piles. The operator and inspector should observe and record the 

depth of the auger, the speed of the auger, the rate at which the auger penetrates into the ground, 

and the torque with which the auger is rotated. 

There is always some uncertainty as to the proper rate of penetration during construction. The 

penetration rate will be estimated by the contractor during the design phase and included in the 

installation plan. Table 7.1 lists some general guidelines for penetration rates that are based on 

experience. The actual rate to be used can be affected by other factors, such as the pitch on the 

auger flights. The pre-production installation and testing of piles will either confirm the 

estimated penetration rate or provide the necessary data to modify the penetration rate to an 

acceptable value for the production piles. The same construction practices used during 

installation of successful test piles should be used for all production piles unless there is a 

significant change in subsurface conditions, such as differing soil types, soils more susceptible to 

mining, etc. 

Table 7.1: General Guidelines for Auger Penetration Rate for CFA Piles 

Soil Type Rate of Penetration 

(Revolutions per Auger Pitch) 

Clay soils 2 to 3 

Cohesionless soils 1.5 to 2 

When penetrating mixed soil profiles, the higher rate of penetration (lower revolutions) should 

control. For example, in a mix of layers of cohesionless and clay soil, the use of the slower 

penetration rate appropriate for the clay (2 to 3 revolutions per pitch) could result in excessive 

flighting of the sand strata. For partial displacement drilled piles, the rate of penetration will 

affect how much relative displacement occurs, and this parameter has a significant effect on axial 

resistance. For drilled full displacement piles, the rate of penetration is usually dictated by the 

need to displace the soil. 

In the manual control system that is widely used in commercial construction, the auger speed is 

predetermined by the gearbox setting, the depth of penetration is monitored by direct observation 

of the top of the auger in the leads, and the rate of penetration is observed using a stopwatch. 

These data should be documented in the inspector’s notes. This approach is not sufficientl y 

accurate fo r transpor tation proje cts and sh ould not b e used as the primary means of 

QA/QC for the drillin g process. These manual observations should be made by the inspector 

during drilling as a check and/or backup to the automated systems. 

The recommended system for transportation projects uses a depth encoder and revolution counter 

to monitor and display the rate of penetration graphically to the operator in units of revolutions 

per meter (or foot) of penetration (or meters (or feet) of penetration per revolution), and 

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simultaneously records this information for plotting after the pile is complete. This system is 

most often used with hydraulic fixed mast drilling equipment, in which the operator has control 

of the crowd on the tool, the torque applied, and the speed of revolution (see Figure 7.1). The 

cab mounted display and monitoring paramet ers of the drilling sy stem are required for 

drilled displacement piles and fo r CFA piles in non-cohesive soils . CFA piles may be 

installed without monitoring and control of the drilling phase only in soils that are demonstrated 

to be non-caving and not subject to flighting (similar to the contraction of drilled shafts in dry, 

open holes). 

When crane-mounted drilling systems are used instead for CFA piles, the operator has no ability 

to apply crowd to the auger other than the dead weight of the system. A monitoring system 

typically used on one of these rigs uses a depth encoder and a clock to monitor the rate of 

penetration which produce a printed record of depth at various time increments to document the 

results. The speed of auger rotation is controlled via the gearbox and recorded. This system 

provides documentation of the operation and a simple visual control. This system does not 

provide the level of control that should be expected for most transportation projects, but may be 

acceptable in some cases of non-critical foundations such as soundwalls or other systems 

installed to shallow depths in favorable (non-caving) soil conditions. 

Figure 7.1: Operator with Cab Mounted Display Used to Control Drilling 

7.4.2 Monitoring and Control of the Grouting/Concreting Phase 

Control of the grouting/concreting phase of construction may be the most important aspect of 

QA/QC for CFA piles. The obvious objective is that adequate grout or concrete be delivered to 

the discharge point of the auger at the proper pressure to complete the pile. Poor 

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grouting/concreting can result in a pile that cannot perform as intended in supporting the 

structure, including both geotechnical and structural failure. 

For the operator to have control and documentation of the operation requires that the pressure 

and volume be monitored as a function of auger depth. In addition, it is desirable to monitor that 

the auger is extracted in a slow, continuous manner without excessive or reverse rotation. Upon 

reaching the required tip elevation, the contractor should establish a flow of concrete or grout 

with minimal lifting of the auger, typically 150 to 300 mm (6 to 12 in.). After the plug is blown, 

an initial charge of grout or concrete should be pumped before starting the auger lifting process 

to develop pressure in the grout or concrete at the bottom of the hole. Some of the initial volume 

of grout will probably push up the auger flights. The volume of grout/concrete delivered to the 

lowermost 0.9 to 1.8 m (3 to 6 ft) of pile length should be over-supplied by approximately twice 

the theoretical volume required to fill the pile for that length. 

During the lifting process, the operator must control the lift speed of the auger so that the proper 

volume of concrete is delivered under sufficient pressure. The auger should be pulled smoothly 

at a steady speed while grout/concrete is continuously pumped under pressure. Some contractors 

may slowly rotate the auger in the direction of drilling, while some may pull without rotation. 

To monitor and control this operation, it is important to observe and document the following: 

(1) position of the auger tip, (2) lifting speed, (3) volume of grout/concrete that is delivered, and 

(4) pressure with which the grout/concrete is delivered. In the event that the operator pulls the 

auger too quickly and the grout/concrete pressure drops below allowable levels, a common 

practice is to immediately re-drill down 1.5-m (5-ft) below the point where the pressure drop 

occurred and rebuild the pile from that point up. The operator should be able to observe the 

pressure drop within seconds and allow the re-drilling and grouting to take place almost 

immediately. 

The manual method of monitoring and documenting the grouting/concrete operation involves the 

following: 

•	 the position of the auger tip is monitored visually by observing the height of the auger 

in the leads; 

•	 the lifting speed is controlled by the operator by feel and by observing the height of 

the auger in the leads while timing the withdrawal using a stopwatch; 

•	 the volume of grout is measured by estimating the volume per stroke of the pump, and 

by manually counting the pump strokes; and 

•	 the pressure with which the grout is delivered is monitored by a gauge in the line near 

the pump. 

The only means of documenting the operation using the above technique is by the inspector 

manually recording the observations. The rig operator depends on estimating volumes and 

manually observing the auger withdrawal, and on signals from the pump operator that the 

pressure and volume delivered are consistent. 

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In general, the simple manual observation and contr ol system described above is not 

considered to provide sufficient control for transportation projects. These manual 

observations can be made by the inspector during grouting/concreting as a check and/or backup 

to the automated systems. They may be sufficient for non-critical foundations such as 

soundwalls or other shallow foundations in favorable soil conditions. 

The system recommended for transportation projects includes automated monitoring of the auger 

position; volume of grout/concrete that is delivered; pressure with which it is delivered; and 

rotation and lifting speed of the auger. Such system should provide the following: 

•	 the position of the auger tip [monitored automatically by a position sensor (shown in 

Figure 7.2)]; 

•	 the volume of grout [measured by an in-line flowmeter (see Figure 7.3) that provides a 

reliable and accurate measure of the grout/concrete that is delivered in real time]; 

•	 the pressure with which the grout/concrete is delivered [monitored using a gauge in the 

line near the swivel at the top of the auger, or in the auger itself near the tip (latter 

option is better)]; 

•	 the rotation of the auger [monitored by a sensor]; 

•	 the lifting speed [controlled by the operator based on real time observation of the 

control parameters noted above, displayed graphically in the cab of the rig, and 

compared to target values]; and 

•	 the entire operation [recorded as a part of the documentation process]. 

There are several methods for providing each of the above measurements, and a variety of 

different in-cab display systems. Some contractors use electronic monitoring of pressure pulses 

along with a calibration of volume per pump stroke to determine volume. With the pumps most 

commonly used, this system is inferior to an in-line flow meter because of possible missed 

strokes, variable volume per stroke, and other inconsistencies. The pressure in the line can be 

monitored at a range of locations. The best location is at the tip of the auger inside the auger 

itself (see Figure 4.20). Although such a system exists, it is not widely available and requires 

augers equipped with cabling, sensor cutouts, and a means of transmitting the signal through the 

swivel. The location of the sensor near the swivel at the top of the line is the next best position. 

The location of pressure sensors in the line near the pump is least effective because of the 

potential for losses between the measurement point and the auger. 

Hydraulic rigs are typically equipped with pressure sensors in the hydraulic lines (see 

Figure 7.4), which provide feedback and documentation of the torque and crowd force used 

during drilling. These parameters can be very useful to monitor rig performance and drilling 

resistance in the soil, particularly for drilled displacement piles. It is quite possible that future 

research could develop correlations between such drilling parameters and axial resistance of the 

completed pile. 

174 
Figure 7.2: Depth Encoder Mounted on Crane Boom 

Figure 7.3: In-line Flowmeter 

175 
Figure 7.4: Pressure Sensors on Hydraulics to Monitor Rig Forces 

Figure 7.5 shows a display panel mounted outside of the cab of the rig for observation by the 

inspector. This allows the inspector to make periodic checks of the data being recorded during 

pile installation. An example of the documentation of a production pile is illustrated in Figure 

7.6. Other systems may present the information differently, but similar information should be 

presented. The top of the data sheet provides project and pile information, and start and finish 

times. The leftmost column indicates, in a graphical way, the volume of concrete delivered as a 

function of depth, having a line indicating the target volume. The pile had an over consumption 

of concrete of 17% above the theoretical volume, which is comparable to a target value of 15% 

(15 to 20% is typical for CFA piles). Graphical representation of concrete pressures, forces in 

the rig (measured hydraulic pressures in psi), and rates of lifting and drilling are also provided. 

Note that a harder layer appears to have been penetrated at depths of around 46 to 54 ft, as 

indicated by the higher torque and thrust used in attempting to maintain the rotation and drill rate 

here. At this location, the rotation and drill rates drop slightly. 

Figure 7.5: Display Panel for Observation by Inspector
	

176 
Source: Jean Lutz S.A 

Figure 7.6: Example Data Sheet from Project 

177 
7.4.3 Finishing the Pile Top and Installing Reinforcement 

Inspection of the installation of reinforcement and completion of the pile top are not subject to 

automated monitoring and depend wholly on the observation of the inspector. It is particularly 

important that the inspector note the point at which grout/concrete appears at the surface relative 

to the embedment of the tip of the auger. If grout/concrete has pushed far up the auger flights 

from the tip (more than about 3 m [10 ft]), it may be a sign that the auger has not remained 

charged with soil. The point at which grout/concrete first appears should be noted and should be 

relatively consistent from pile to pile. When grout/concrete appears at the surface, it will be no 

longer possible for the operator to maintain excess positive pressure at the tip because the 

grout/concrete is now vented to the surface. Therefore, it is particularly important that the 

volume of flow be consistent to ensure that the auger is not pulled too fast from this point on. 

When the auger is removed, it is possible for some soil to spill into the top of the pile and 

contaminate the grout or concrete. The inspector should observe that the contractor dips out any 

contamination and finishes the pile with good quality grout or concrete, as shown in Figures 7.7 

and 7.8. A small surface casing is normally required to stabilize the top of the hole. 

Figure 7.7: Dipping Grout to Remove Contamination 

Installation of reinforcement should proceed immediately after the pile top is prepared. 

Reinforcement should be clean and free of rust or contamination, of the size and dimensions 

indicated on the plans, and equipped with appropriate centering devices. These are normally 

plastic or sometimes made of mortar or grout. Centering devices should not be made of metal 

because of potential corrosion and contact with the rebar cage. Welding of the cage is permitted 

only if weldable reinforcing steel is used; however, this reinforcement is not common in the 

United States at present. 

178 
Reinforcement should be lowered into the fluid grout or concrete by gravity or, if necessary, with 

an additional gentle push as shown in Figure 7.9. Reinforcement should not be driven, 

hammered, or vibrated unless specifically permitted by the contract documents; vibration is 

normally permitted only for fully welded cages. If the cage cannot be placed to the full required 

depth, the actual installation depth should be recorded and the engineer notified. After 

installation, the cage should be supported at the ground surface for a sufficient amount of time 

(typically a few hours, depending on the setting of the grout/concrete mix) to avoid it settling 

into the pile. The cage is often kept in place by using wire to tie it to timber supports. 

Figure 7.8: Cleaning the Top of a CFA Concrete Pile 

Difficulties in placing the reinforcement may occur if the grout or concrete does not maintain 

sufficient workability for the duration of time required for placement. In addition, sandy soil 

profiles can promote rapid dewatering of the grout or concrete in the pile such that reinforcement 

placement is difficult even with a properly retarded mix. In such cases, anti-washout additives or 

viscosity modifying admixtures may be helpful in reducing water loss from the grout/concrete. 

Installation of rebar to depths in excess of 18 m (60 ft) is possible under favorable circumstances, 

although significant bending stresses rarely occur at such depths for foundation piles. 

Most often, piles are connected to a pile cap, with the base of the cap lying below existing 

construction grade. This below-grade cutoff is typically constructed by excavating for the pile 

cap, chipping the top of the hardened pile down to the required elevation, and cutting the rebar, 

as necessary. If the shallow soils are cohesive and the cutoff elevation is within a few feet of the 

surface, it may be possible to dip the grout/concrete down to the desired depth. In the latter case, 

a surface casing must be used to maintain a stable hole above the cutoff elevation and prevent 

surficial soils from sloughing into the fluid grout or concrete and contaminating the top of the 

pile. 

179 
Figure 7.9: Placement of Reinforcing Cage with Plastic Spacers 

7.4.4 Sampling and Testing of the Grout or Concrete 

Sampling and testing of the grout/concrete are important parts of QA/QC. The samples may be 

obtained for testing directly by the inspector or by the contractor under the direct supervision of 

inspectors. The general approach to QA/QC for the grout/concrete is that the mix design and the 

quality of the mix is the contractor’s responsibility and the inspector obtains samples for testing 

to verify that the requirements for the project are met. Strength tests are the control parameter of 

most concern for design, while workability is measured in the field to ensure that the 

construction goes smoothly and that the mix characteristics are consistent. 

For concrete, 150 mm (6 in.) diameter by 300-mm (12-in.) high cylinders (ASTM C 31. [ASTM, 

2006]) should be made from samples of the mix from the field in the same manner as for per 

most other cast-in-place concrete construction including drilled shaft construction. Samples 

should be cured and tested according to ASTM C39 (ASTM, 2006) or the agency’s normal 

procedures. Concrete compressive strength requirements for CFA piles are typically 24 to 31 

MPa (3,000 to 4,500 psi) and will be specified according to the project requirements. Typical 

specifications require a set of at least six samples for each 40 m3 (about 50 yd3

) of concrete 

placed, but no less than one set per day or per batch of concrete, if batch plant operations are 

started and stopped more than once per day. 

180 
For grout, 50 mm (2 in.) cubes are most often used for strength testing, (see Figure 7.10) per 

ASTM C109 (ASTM, 2006). These are small and easy to handle and transport, and are 

considered adequate for testing grout without coarse aggregate in the mix. If the grout mix has 

pea gravel as aggregate, the mix should be considered concrete and thereby tested using 

cylinders as outlined above. Because grout cubes are small, it is easy for small misalignment in 

the testing apparatus or uneven surfaces to result in incorrect dimensions and thereby 

unrepresentative low measured strengths. For this reason and also because the samples are 

small, it is prudent to make extra samples during field operations so that any discrepancies can 

be re-evaluated. Some engineers prefer to use 75 mm (3 in.) diameter by 150 mm (6 in.) high or 

50 mm (2 in.) diameter by 100 mm (4 in.) high cylinders. In such cases, careful attention is 

necessary to the relationship between maximum aggregate size and the height-to-diameter ratio 

of the sample. If the samples are cast using a method or sample different than that used for the 

mix design, a relationship between the compressive strengths obtained by the methods will be 

required. 

Compressive strength requirements for CFA piles constructed with grout are similar to that for 

piles constructed with concrete, as noted above. However, it should be noted that the 

compressive strength of properly tested cubes are slightly higher than that of cylinders with a 

height-to-diameter ratio of two, therefore, the strength requirement from tests on cubes are 

typically 10% greater than that of cylinders. 

Workability and consistency of concrete are monitored by performing slump tests on samples of 

the mix at the site. Slump measurements (ASTM C 143, [ASTM, 2006]) should be made on 

each truck on the project to ensure that consistent mixes are delivered. A slump of 

approximately 200 +/- 25 mm (8 +/- 1 in.) is typical for CFA piles, as is for drilled shaft 

placement in wet hole conditions. The relationship of slump loss over time should be established 

as part of the mix design and included in the approved installation plan. In general, a mix should 

be developed such that it maintains slump (or flow for grout) for a period of at least two hours 

for routine projects. The workability as a function of time is highly temperature-dependent and 

adjustments to the mix may be needed in warm weather. The contractor should place concrete 

quickly to avoid a decrease in workability over time as the cementitious material hydrates. 

The addition of water at the project site should only be permitted through the approved 

installation plan or with prior approval by the engineer, and only to the extent that the 

water-cementitious material ratio does not exceed the ratio of the approved design mix. If the 

slump of the mix as delivered is not suitable, adjustments should be made at the plant unless the 

project is specifically planned for water to be held back and added at the site. In any case, it is 

critical that the mix have adequate workability; sometimes it may be necessary for the contractor 

to adjust the mix with water at the site rather than complete a pile with inadequate workability in 

the mix. Such practice should be a rare exception and corrections must be made to the operation. 

If water is added at the site, the inspector should have samples made and/or tests performed after 

the water has been added and the mix ready for placement. 

181 
Figure 7.10: Cubes for Grout Testing 

Similar to the case of concrete, the workability and consistency of grout must be monitored by 

performing flow cone tests on samples of the mix at the jobsite. Flow cone measurements 

should be made on each truck on the job, to ensure that consistent mixes are delivered. As with 

concrete, water should not be added at the jobsite unless specifically allowed in the project 

specifications. The preferred practice is that water should not be added at the project site without 

approval from the project engineer. If the workability of the mix is not suitable as delivered, 

adjustments should be made at the plant. Nevertheless, it is critical that the mix have adequate 

workability. Sometimes it may be necessary to adjust the mix with water at the site rather than 

complete a pile with inadequate workability in the mix. Such practice should be a rare exception 

and corrections to the grout mix must be made to the operation. Sometimes, grout additives are 

added at the project site. If so, the specific manufacturer’s recommendations must be followed. 

ASTM C 939 (ASTM, 2006) or U.S. Army Corps of Engineers CRD 611-94 (USACE, 1994) 

provide specifications for flow cone testing in which fluid consistency is described according to 

an efflux time per standard volume (time for a specific volume to flow out of the cone). As the 

grout mixes used for CFA piles are typically too thick to flow effectively from the standard 

12-mm (0.5-in.) outlet specified in these standards, it is common practice to modify the above 

specifications and use a 19-mm (0.75-in.) opening. This modification can be made by: (a) 

removing the removable orifice that extends out the bottom of the Corps of Engineers device to 

leave a 19 mm (0.75 in.) opening; or (b) cutting the flow cone specified in the ASTM standard to 

modify the outlet diameter. Grouts that are suitable for CFA pile construction typically have a 

fluid consistency represented by an efflux time of 10 to 25 seconds when tested in accordance 

with the modifications described above. Grouts that are suitable for CFA pile construction 

182 
should maintain fluid consistency within this range for a period of at least two hours, but in no 

case less than the time required to complete a pile and place reinforcement. 

7.5 POST-CONSTRUCTION INTEGRITY TESTING 

Post-construction integrity tests are used to supplement the installation monitoring to establish 

that a contractor’s procedures are producing acceptable piles. There are several types of integrity 

tests that are useful for CFA or drilled displacement piles, most using technologies already in use 

on transportation projects for drilled shaft foundations. Several references are available that 

describe a wide variety of integrity test methods in greater detail. Two of these references are 

O’Neill and Reese (1999) and (DFI (2005). 

7.5.1 Use of Integrity Testing 

Integrity test methods require careful interpretation, which should be performed by experienced 

personnel. However, integrity testing personnel cannot always determine whether an anomalous 

reading is a defect within the pile; therefore, the final decision on acceptability of the pile must 

be made by the design engineer based on the site specific soil conditions, construction records, 

the post-installation integrity testing report, and analysis of the possible effect on foundation 

performance. 

As discussed previously, the most reliable means of achieving consistent QA/QC is automated 

monitoring and control during construction, with documentation of the installation via these 

measurements. The use of post-construction integrity testing is best utilized to verify that the 

installation parameters used for control (i.e., penetration speed, grout or concrete pressures and 

volumes during auger withdrawal) are appropriate for the site-specific project conditions. 

Integrity tests can also be used to further evaluate piles that did not meet drilling or grouting 

criteria. Coring of the piles can be used to supplement or to provide a visual check of suspected 

defects detected by integrity testing. 

The necessary frequency of post-construction integrity testing is left to the judgment of the 

owner and can vary from project to project. A frequency of 10% to 20% of production piles 

subjected to integrity testing is typical. In addition, all preproduction and verification test piles 

should be tested. When agencies have little experience with CFA piles, particularly difficult 

project conditions exist, or project or site conditions give reason to expect problems with pile 

integrity, integrity testing of more than 20% of production piles may be required. A typical 

reasonable approach for load-bearing piles is to subject the first 10 to 15 piles to be constructed 

on a project to integrity tests to establish that the contractor’s construction practice at the site is 

adequate. Thereafter, the frequency of such tests can be set to meet the specified frequency 

criteria, can be reduced, or even perhaps eliminate further integrity tests if the construction 

records for the remaining production piles are similar to those of the initial piles that were 

subjected to integrity tests. 

183 
7.5.2 Integrity Testing by Surface Methods 

The most commonly available, economical, and easily applied type of integrity test is the sonic 

echo test. The advantage of the method is that a test can be performed rapidly, inexpensively, 

and without any internal instrumentation or tubes in the pile. In general, the sonic echo test is the 

recommended method for routine testing of CFA piles of 760 mm (30 in.) diameter or less. 

This test is performed by striking the top of the pile with a small instrumented hammer (Figure 

7.11, left). A sonic, compressive wave travels down the length of the pile and is reflected by an 

anomaly in the pile, or the pile tip if the pile is free of defects, and travels back to the top where 

it is picked up by a receiver on top of the pile. The reflections are used to indicate major changes 

in cross sectional dimensions or material properties. Wave propagation through the pile is 

affected by the pile impedance, which is defined mathematically as EA/C, where E is the elastic 

modulus of the pile, A is the area of the cross section, and C is the wave propagation velocity, 

which is related to the elastic modulus and mass density of the pile. 

Impedance changes occur where there is a change in cross-sectional area of the pile. A bulge 

(increase in cross-sectional area) or a neck (reduction in cross-sectional area) can be detected by 

an increase or decrease, respectively, in impedance of the signal. Changes in impedance also 

indicate where a change in grout/concrete density occurs, indicating a possible defect in the 

grout/concrete. Other types of processing are sometimes used to interpret the measurements of 

reflections including impulse response and impedance logging. Figure 7.11 (right) provides a 

simplified illustration of the sonic echo test. The displacement record shown in the figure 

indicates the reflection off the base of a pile of the length, L, embedded in sound rock. The 

reflection occurring at a time shorter than 2L/C (i.e., first upward spike of record) suggests an 

impedance change in the pile above the pile toe. 

Figure 7.11: Sonic Echo Testing Concept
	

184 
Although sonic echo testing is an economical and rather simple test, there are some important 

limitations to consider. As the sound wave travels along the pile, it loses energy and the strength 

of the reflected signal can become very weak. This means that for very long piles 

(i.e., depth-to-diameter ratio of greater than 30), the tip of the pile and anomalies or defects 

occurring at great depths will likely go undetected. Due to the nature of the design of CFA piles, 

the integrity of the upper 6 m (20 ft) is most critical for structural capacity, particularly for shear 

and bending moment. As sonic echo testing is more reliable at shallower depths, this limitation 

is not as significant as for long drilled shafts. This makes testing using sonic echo quite useful 

for rapidly evaluating a large number of piles. The hypothetical example shown in Figure 7.12 

illustrates this concept. The long pile (A) has a weak reflection from the toe that may not be 

detectable. The short pile (B) has a strong reflection from the toe that is readily detected. Pile C 

illustrates a long pile containing a defect at a shallow depth. Although the reflection from the toe 

may be difficult to detect (as for pile A) as would a deep defect, the shallow reflection is readily 

detected. 

A B C 

A: long pile, weak reflection from toe at 2LA/C 

B: short pile, strong reflection from toe at 2LB/C 

C: long pile, strong reflection from defect at 2LC/C 

LC 

A 

LB
 

B
 

C 

LA 

Figure 7.12: Sonic Echo Testing of Long Piles 

Time axis 

Another important limitation of sonic echo testing is that the wave energy is not likely to detect 

anomalies or defects unless these are large compared to the wave length generated by the impact. 

Some research indicates that defects that are shorter than 0.25 of the wave length are generally 

not detected. A typical hammer for sonic echo tests generates a wave length of approximately 

1.6 m (5.3 ft), which means that defects or anomalies less than 0.4 m (15- to 16-in.) thick will go 

undetected. For most CFA pile diameters, this threshold of detection should be appropriate. 

185 
7.5.3 Integrity Testing using Downhole Techniques 

The most reliable of the post-installation integrity tests for identifying anomalies within cast-inplace deep foundations are those that use down-tube instruments, such as the cross-hole sonic 

logging (CSL) test, single-hole sonic logging (SSL) test, and the backscatter gamma test. 

However, due to the difficulty and expense of downhole methods on routine projects, these 

methods are recommended for use on piles where bending moments are unusually high and/or 

piles larger than 760 mm (30 in.) in diameter are used. 

CSL is performed using a source in one tube and a receiver in another to provide a measure of 

the wave speed of the material between the tubes. A strong signal measurement with an arrival 

time consistent with the wave speed of good grout/concrete is indicative of sound grout/concrete 

between the tubes. The SSL test (shown in Figure 7.13) utilizes a source and receiver on the 

same probe and is intended to sample the wave speed of the material surrounding the tube. The 

numerous dark lines shown on the time record on the right side of Figure 7.13 represent arrivals 

of signal energy plotted on a vertical scale of depth vs. time on the horizontal axis. The 

anomalous lack of dark lines at the 5 to 6 m depth interval represents a delayed arrival time and 

weak signal between these depths, which may be indicative of a defect in the pile. 

The backscatter gamma test (see Figure 7.14), more commonly referred to as gamma-gamma 

logging, uses a small radioactive source on one end of the probe to emit gamma photons and a 

gamma ray detector on the other end. The photon count per unit of time can be calibrated to the 

grout/concrete density within a radius of about 100 mm (4 in.) around the tube. 

To be effective, the access tubes for CSL or backscatter gamma testing should be distributed 

evenly along the circumference around the reinforcing cage with a spacing of about 0.3 m (1 ft). 

Tubes should be placed inside the cage to avoid damage during installation. It is recommended 

that tubes used for CSL tests consist of Schedule 40 steel, because such tubes will remain bonded 

to the grout or concrete. Polyvinyl chloride (PVC) tubes do not ordinarily remain bonded to the 

grout or concrete beyond a few days after initial set, and debonding will render the CSL tests 

ineffective. PVC tubes must be used for backscatter gamma testing because the steel tubes block 

the gamma photons from penetrating into the surrounding concrete or grout. 

These downhole tests all require that the foundation contractor attach appropriate access tubing 

to the reinforcing steel prior to placing the steel in the grout column. While these tests are 

frequent with drilled shafts, downhole tests are more difficult to install in CFA piles (because the 

tubes must be pushed into the fluid grout/concrete). The tubing and instrumentation make 

downhole tests much more costly in proportion to the total cost of the pile when compared to 

sonic echo testing. The speed of testing is much slower than sonic echo, which adds to the final 

cost. 

186 
 

Figure 7.13: Downhole Single-Hole Sonic Logging (SSL) Concept 

Detector 

Source 

Figure 7.14: Gamma-Gamma Testing Via Downhole Tube 

187 
7.6 LOAD TESTING 

Load testing is a very important component for the effective use of CFA piles. Load tests are 

performed both as pre-production tests and as verification tests as part of the QA/QC of pile 

production (Figure 7.15). Axial compressive load tests are by far the most common; however, 

uplift and lateral load test can also be performed as part of a test program when evaluation of 

either load condition is important. As discussed in Section 7.3.5, both pre-production and 

verification load tests should be an integral part of transportation projects using CFA piles. 

A carefully planned and executed load test program can provide the following benefits: 

•	 Site-specific load test data provide verification of design parameters and increases 

reliability. This reduction in uncertainty may allow the use of lower design factors of 

safety employed in the ASD methodology. 

•	 The pile load testing program serves to establish the baseline parameters for 

construction of production piles, particularly with respect to target drilling penetration 

rate and pressure/volume relations during placement of grout/concrete. Other 

important parameters such as grout flow and necessary admixtures can be established 

during the test program. 

•	 The test results can be used to evaluate correlations of side and base resistance with 

site-specific soil parameters, and to revise or improve the design. 

The axial ultimate capacity of individual CFA piles are generally not larger than a few hundred 

tons. There are several options available in this load range for proof testing of production piles, 

such as RLT methods (e.g., Statnamic or Fundex systems) or DLT (e.g., drop hammer). Proof 

testing of CFA piles to confirm nominal axial resistance is generally not detrimental to the 

structural integrity or geotechnical performance of a sound pile; hence the tested pile may be 

used for in-service conditions. 

Details of axial load testing methods will not be repeated here, although a brief discussion of 

methods most appropriate for CFA piles is provided. An extensive discussion of axial, uplift, 

and lateral load testing methods and data interpretation is provided in the following manuals: 

• “Static Testing of Deep Foundations” (Kyfor et al., 1992) - FHWA-SA-91-042; 

•	 “Design and Construction of Driven Pile Foundations,” Volumes 1 and 2 (Hannigan et 

al., 2006) - NHI Course FHWA-NHI-132021; 

• “Micropile Design and Construction” (Sabatini et al., 2005) - FHWA NHI-05-039 and 

• “Drilled Shafts” (O’Neill and Reese, 1999) - FHWA-IF-99-025 

7.6.1 Considerations in Planning a CFA Pre-Production Test Pile Program 

The objectives of performing a load test program prior to the start of production pile construction 

are to: (a) provide measurements of site specific values of resistance; (b) correlate these values to 

construction methods; and (c) verify design assumptions. This is particularly important for 

188 
 

drilled displacement piles where the contractor may be using a proprietary system or tooling for 

installation. The baseline parameters for drilling rate and concrete or grout placement during the 

construction of successful test piles are thus established for production piles. For displacement 

piles, control parameters may also include specific target values of torque and downthrust forces. 

In a pre-production pile test program, it is important that test pile locations are selected which are 

representative of the dominant conditions across the project site. Subsurface information at the 

specific test pile locations is essential to interpret the results of the installation monitoring and 

load testing in a meaningful way. In cases of uniform soil and design load conditions, a single 

test pile may be suitable. In other cases, several test piles may be required to be installed at 

various locations on the project site. 

The axial compressive resistance of CFA piles is normally in a range such that conventional top 

down static load tests are easy to perform with reaction systems that can be assembled by most 

contractors. If RLT or DLT methods have been calibrated to local soil and geologic conditions, 

these alternative methods can offer advantages of speed and economy. On a large project with 

many piles to be installed, a single control static test supplemented by several RLTs or DLTs on 

both the control and piles can be a very effective means of achieving a maximum benefit at the 

least test cost. The additional control static test can provide the reliability of conventional static 

measurements and the RLT or DLT program can provide the coverage needed to rapidly evaluate 

a range of conditions that may be encountered. It is always important that a site-specific 

correlation between static tests and RLTs and/or DLTs be established regardless of project size. 

7.6.2 Proof Tests on Production Piles 

The relatively modest axial resistance of CFA piles and the availability of rapid and dynamic 

load test methods make proof load testing of production piles a viable option for QC/QA. Piles 

may be selected at random or piles of questionable quality can be chosen for proof testing. RLT 

and DLT methods are quite economical for loads of up to around 5 MN, (450 tons) (Figure 7.16). 

After RLT or DLT equipment is mobilized to the site, it is usually possible to efficiently test 

several piles each day. 

The use of proof tests on production piles can be planned to provide the increased reliability and 

lower design factor of safety (or higher design resistance factor) afforded by the inclusion of load 

testing in the project, and thus can result in significant cost savings. 

Axial load tests on production piles are not detrimental to the subsequent performance of the pile 

so long as the structural capacity of the pile has not been exceeded. Figure 7.17 illustrates the 

results of two cycles on the same pile, each of which achieved a geotechnical limit on the pile. 

The first load achieves a geotechnical limit according to the commonly used Davisson criterion. 

The second load cycle produces a load vs. deflection response that is actually stiffer than the first 

cycle. In general, the Davisson criterion will provide conservative results. This test result is 

typical of multiple loadings on a single pile, and the second load cycle is representative of the 

load deflection response of a pile after a static load test has been conducted. Two observations 

are made from these data: (a) a load test on a production pile does not adversely affect the ability 

of the pile to support subsequent loadings; and (b) multiple load tests on a CFA pile can result in 

189 
increased pile stiffness in subsequent load cycles. The second aspect can have implications 

when comparing RLT or DLT methods with a conventional static load test on the same pile, 

since the pile may provide a stiffer response compared to whichever test method is performed 

second. 

Figure 7.15: Static Load Test Setup on CFA Piles 

Figure 7.16: Proof Testing of Production Piles with Statnamic (RLT) Device 

190 
Load 

1st Load 

2nd Load 

Davisson Offset Line 

Deflection 

Figure 7.17: Effect of Multiple Load Cycles on a CFA Pile 

7.7 SUMMARY OF RECOMMENDED QC/QA PROCEDURES 

This section provides a summary of recommended QC/QA procedures for use on CFA pile 

projects and checklists for inspection of CFA piles. 

7.7.1 Prior to Construction 

The CFA pile inspector must be prepared and should have experience and knowledge of CFA 

pile construction techniques. Prior to construction the inspector should have and review the 

following: 

•	 Project plans and specifications; 

•	 Geotechnical report and/or other available subsurface information (often provided on 

the plans); 

•	 Contractor’s approved installation plan; 

•	 Details of load test program or pre-production test pile installations; 

•	 Details of required automated monitoring system and control parameters; 

•	 Details of grout or concrete mix design and sampling and testing requirements; and 

•	 Reinforcing details and methods for pile top finishing and cutoff levels. 

191 
7.7.2 On-Site Review of Contractor’s Equipment 

Upon arrival at the jobsite, the inspector should take the time to thoroughly review the 

contractor’s equipment for compliance with the plans and specifications and approved 

installation plan. This work includes: 

•	 Check-in with contractor to understand day’s planned work and confirm that party 

responsible for grout/concrete sampling is at site. 

•	 Document auger diameter and length, auger pitch, grout/concrete (each truck 

immediately when delivered), reinforcing type, and configuration, and centralizers. 

•	 Check calibration of grout/concrete volume monitoring equipment, and other 

measurement equipment for which calibration is required. Confirm that monitoring 

equipment is set to record at proper depth intervals as required. 

•	 Check equipment condition and tolerances. 

7.7.3 During Drilling 

•	 Confirm that pile location is within horizontal tolerances and pile plumbness is within 

the range specified. 

•	 Confirm plug placed at auger bit tip. 

•	 Confirm the location of the pile to be constructed, so that relevant subsurface 

conditions, pile construction requirements (i.e., pile number, embedment depth, cutoff, and batter, if required) can be quickly and accurately referenced. 

•	 Document auger verticality or specified batter, as applicable. Document cuttings and 

auger advance rate. Confirm for consistency with conditions disclosed in geotechnical 

report, pile test report, and load test report. 

•	 Confirm removal of excessive cuttings/spoil build-up around auger. 

•	 Monitor behavior of the pile and surrounding ground during construction of test pile 

foundations. Check for indications of ground subsidence or loss of fluid 

grout/concrete. 

7.7.4 During Grout/Concrete Placement 

•	 Document grout/concrete properties (batch time, temperature, additives, and flow) and 

those samples that have been obtained for strength testing at the intervals, per project 

specifications. 

•	 Document the pile grouting/concreting operation, including immediate start of 

placement and pumping of initial grout/concrete volume and pressure head, and auger 

withdrawal rates, per approved installation plan. Confirm (from automated monitoring 

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data and observations) that target minimum grout/concrete factor is attained along the 

length of the pile. Confirm for consistency with reported conditions disclosed in 

geotechnical report, test pile report, and load test report. 

•	 Document depth at which grout/concrete return is first observed. Confirm consistency 

with conditions disclosed in geotechnical report, test pile report, and load test report. 

•	 Should a discontinuity in grout/concrete return or other questionable conditions be 

observed, inform the contractor of the condition and note the conditions observed on 

pile logs or data sheets. In some cases, the contractor may re-drill the pile to the full 

length. Re-drilling the pile to less than the full length to restart the grouting 

/concreting operation is generally considered unacceptable. 

•	 Confirm continuous and steady auger pull, with slow positive auger rotation if 

approved in the installation plan, and grout/concrete pumping until auger tip comes out 

of the ground. Document total volume of grout/concrete pumped, and overall 

grout/concrete factor. Obtain pile records from automated monitoring equipment. 

•	 Confirm that the pile top is cleared of any debris or contaminated grout or concrete. 

7.7.5 During Reinforcement Placement and Pile Top Finishing 

•	 Document reinforcement installed in pile that is in accordance with specified design. 

•	 Document any installation difficulties, especially since they may be indicative of 

potential obstructions or undesired inclusions in the pile. In general, the most cost 

effective and time saving remedial measure is to re-drill and re-grout the pile if suspect 

conditions are observed. 

•	 Confirm that reinforcing is free of auger spoils or rust prior to insertion. 

•	 Confirm that reinforcing has specified extension above proposed cut-off elevation. 

•	 Confirm that the pile top finishing is performed in a manner consistent with the project 

requirements, including any forms above grade and tie-off details of the reinforcement. 

7.7.6 Post-Installation 

•	 Check for grout subsidence. 

•	 Inspect pile cut-off. 

•	 Ensure that any post-construction integrity testing or proof load testing is scheduled 

and performed in a timely manner and that any questionable or rejected piles are noted 

and the appropriate notification is provided to the owner agency and their engineer. 

Additional specific details for each of the items noted above are provided in the project 

specifications. Guide construction specifications are provided in Chapter 8, which may serve as 

a preliminary specification for state DOT engineers to use in developing a state-specific CFA 

pile specification. 

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CHAPTER 8 GUIDE CONSTRUCTION SPECIFICATIONS FOR 

CONTINUOUS FLIGHT AUGER (CFA) PILES 

Contractor Performance Based Specifications of CFA Piles 

English Units (Metric Units) 

(With Commentary) 

Commentary: Owner-controlled design specifications can vary in the amount of design 

performed by the Owner’s Design Engineer and the amount performed by the CFA Pile 

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/cap design, and pile layout for each footing/cap 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 CFA Pile 

Contractor designs the individual piles and pile cap connections and selects the CFA 

construction method and equipment. The CFA Pile Contractor prepares a preliminary CFA pile 

design and a firm cost proposal based on the Owner’s preliminary plans and specifications. 

Once the contract is awarded, the selected CFA Pile Contractor prepares detailed CFA pile 

design calculations and working drawings and submits them to the Engineer for review. 

8.1 DESCRIPTION 

This work shall consist of constructing CFA piles as shown on the contract plans and approved 

working drawings and as specified herein. The CFA Pile Contractor is responsible for furnishing 

all design, materials, products, accessories, tools, equipment, services, transportation, labor and 

supervision, and manufacturing techniques required for design, installation and testing of CFA 

piles and pile cap connections for this project. 

The CFA Pile Contractor shall design and install CFA piles, including selection of the CFA pile 

type, diameter, length, pile cap connection, and installation means and methods that will provide 

the load capacities indicated on the project plans, without damage to existing nearby structures. 

A minimum diameter will be specified and a minimum length may be specified. The CFA pile 

load capacities shall be verified by load testing as required, and the pile integrity will be verified 

by pile integrity tests as required. All piles must meet the test acceptance criteria specified 

herein. 

The imperative mood is used within this specification; for example, when it says, “submit three 

copies”, the CFA Pile Contractor shall submit three copies” is implied. 

194 
Sections of this specification are referred to in the text, for example, as “(8.)1.1” to facilitate 

locating them in this Chapter 8 and allow future renumbering them once the specification is 

modified according to the Owner’s needs. 

8.1.1 Definitions 

CFA Pile: any foundation that is made by rotating a hollow-stem auger into the ground to the 

specified pile depth. Grout or concrete is injected through the auger shaft under continuous 

positive pressure, as the auger is being withdrawn, in order to exert a positive upward pressure 

on the earth-filled auger flights as well as lateral pressure on the soil surrounding the placed 

grout or concrete column. Reinforcing steel, as specified, is inserted into the column of fluid 

grout or concrete following the completion of grout or concrete placement. CFA piles as defined 

herein include: a) traditional continuous flight auger piles; b) drilled displacement piles intended 

to install a cast-in-place pile with full displacement and minimal soil spoil; and, c) partial 

displacement piles which may displace some soil but not act as a full displacement pile. 

Commentary: Many contractors and equipment builders have patented various components of 

the drilling system for various types of CFA piles, most typically some part of the tooling. As 

defined within this specification, these various types of piles are all within the broader category 

of CFA pile; therefore, they would not be considered as “proprietary systems” for bidding 

purposes. All of the CFA pile systems are generally similar in installation techniques and 

performance. 

CFA Pile Contractor: the firm responsible for performing the CFA pile work. 

Design Engineer: the Licensed Professional Engineer that designs the CFA piles. The person 

must meet the experience requirements in Section (8.)1.6.2. 

Engineer: the Owner’s project engineer, project manager, or other representative. 

Inspector: the Owner’s field representative on the project site. 

Owner: agency responsible for the project. 

Plans: drawings provided by the Owner for bidding purposes. 

Project Manager: an employee of the CFA Pile Contractor supervising the work and that has a 

minimum of three years experience with CFA projects of similar size and scope. 

Working Draw ings: drawings submitted by the CFA Pile Contractor. This would include the 

detailed pile designs. 

8.1.2 Related Specifications 

Commentary: Engineer to specify all related specifications from the applicable standard 

specifications. 

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8.1.3 Reference 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 

otherwise indicated. 

AASHTO Standard Specification for Highway Bridges, current Edition, including current 

interim specifications. 

State Department of Transportation (DOT) Standard Specifications, current Edition, including 

interim specifications. 

Commentary: Engineer to note any additional publications to be referenced. 

8.1.4 Available Information 

Available information developed by the Owner, or the Owner’s duly authorized representative, 

include the following items: 

1.	 Plan Set(s) ____, Project No. _______, prepared by __________, dated __________. 

The plans include the preliminary CFA pile size and length developed for the project, 

as well as plan view, profile, and typical cross sections for the proposed CFA pile 

locations. 

Commentary: The Owner should provide preliminary design information for the 

Contractor as part of the bidding package. The complete list of items will vary according 

to project and local procedures, but will generally include: 

1.	 plans showing the pile design loadings, minimum pile diameter, minimum 

reinforcement, pile to footing/cap connection design, and pile layout for each 

footing/cap location. In some cases, the plans may include a minimum pile tip 

elevation. 

2.	 design criteria and requirements, such as minimum safety factors and 

maximum allowable vertical and horizontal displacements. 

Refer to Chapter 6 of FHWA Geotechnical Circular No. 8 “Augered Cast-in-Place and 

Continuous Flight Auger Piles” for detailed guidance on plan information to provide on 

the preliminary plans. 

2.	 Geotechnical Report No.(s)______, Project No. _____, prepared by _________, dated 

________, included or referenced in the bid documents, containing the results of 

exploratory borings, observation pits, or other site investigation data obtained in the 

vicinity of the proposed CFA pile locations. 

Commentary: The subsurface conditions expected can significantly impact the CFA Pile 

Contractor’s choice of procedures, methods, equipment, the bidding process, and contract 

196 
administration. A geotechnical investigation report should be included in the contract 

special provisions. This report provides information to bidders of the subsurface 

conditions and will reduce the potential for differing site conditions construction claims 

and disputes. By including the geotechnical investigation report in the contract special 

provisions, it becomes a legal part of the contract documents. 

8.1.5 Project Site Survey 

Before bidding the work, the CFA Pile Contractor shall review the available subsurface 

information and visit the project site to assess the site geometry, equipment access conditions, 

and locations of existing structures and above-ground facilities. 

The CFA Pile Contractor is responsible for field locating and verifying the locations of all 

utilities shown on the plans prior to starting the Work. The CFA Pile Contractor shall notify the 

Engineer of any utility locations different from those shown on the plans that may require 

relocation of foundation elements or modification to the structure design. 

Commentary: Many public owners have standard specifications or procedures for handling 

utilities on a project, so this section may not apply or can be modified to include reference to the 

applicable State DOT specification/procedure. As with any foundation system, the location of 

active and abandoned underground utilities can have a significant impact on the installation of 

CFA piles. 

Prior to the start of any CFA pile construction activity, the CFA Pile Contractor and the Engineer 

shall jointly inspect the site to observe and document the pre-construction condition of the site, 

existing structures, and utilities. 

8.1.6 CFA Pile Contractors Experience and Submittal of Experience 

Commentary: The quality of CFA piles is highly dependent upon the skill of the CFA Pile 

Contractor and the specific crew that is assigned to the project. It is essential that the CFA Pile 

Contractor is competent to perform the work at hand either through providing documentation of 

successful completion of prior projects of a similar nature to the project being bid, or by directly 

demonstrating his or her competence by installing a demonstration pile that does not contain 

defects and has been constructed to at least the diameter and depth shown on the plans. 

8.1.6.1 Experience Requirements 

Listed below are potential CFA Pile Contractors to design, furnish, and install CFA piles for the 

Owner, based on previous CFA Pile Contractor experience submittals verified and accepted by 

the Owner: 

1. Contractor Name, Mailing Address, Contact Name, Phone Number 

2. Contractor Name, Mailing Address, Contact Name, Phone Number 

3. Contractor Name, Mailing Address, Contact Name, Phone Number 

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If the CFA pile work is bid as a subcontract item to a prime contract, the Prime Contractor shall 

name the intended CFA Pile Contractor at least ______ calendar days prior to the beginning of 

the work for review. 

8.1.6.2 Experience Requirements and Submittal 

The CFA Pile Contractor shall be experienced in the construction and load testing of CFA piles 

and shall provide documentation of a minimum of three projects performed in the two-year 

period preceding the bid date in which CFA piles were installed successfully under subsurface 

and project conditions similar to those of the current project. The CFA Pile Contractor shall also 

provide documentation that the designated job site supervisor (foreman or crew chief) has had a 

minimum of three years of experience in supervision of the installation of CFA piles. Drill rig 

operators shall be documented to have a minimum of three years experience installing CFA 

piles. 

The CFA Pile Contractor shall assign a Project Manager to supervise the work that has a 

minimum of three years experience with CFA projects of similar size and scope. The CFA Pile 

Contractor shall not use consultants or manufacturers’ representatives to satisfy the Project 

Manager requirements of this section. This person may also be the Design Engineer if the 

Project Manager/Design Engineer is an employee of the CFA Pile Contractor. A Design 

Engineer that is a Consultant cannot be the Project Manager. 

The CFA piles shall be designed by the Design Engineer, a Professional Engineer licensed in the 

State of _________ with experience in the design of at least three successfully completed CFA 

pile projects over the past five years with CFA piles of similar capacity to those required for the 

project. The Design Engineer may be either an employee of the CFA Pile Contractor or a 

separate Consultant Design Engineer meeting the stated experience requirements. 

Five copies of the completed project reference list and personnel list shall be submitted by the 

CFA Pile Contractor at least ___ calendar days before the planned start of CFA pile construction. 

The project reference list shall include a brief project description with the project Owner’s name 

and current phone number and load test reports. The personnel list shall identify the CFA Pile 

Contractor, Project Manager, drill rig operators, and job site supervisor 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 CFA Pile Contractor’s qualifications 

within ___ calendar days after receipt of a complete submission. 

The work shall be performed by the personnel listed on the submittals. If personnel changes 

need to be made during the course of the project, work shall be suspended until the replacement 

personnel are approved by the Engineer. Additional time required due to incomplete submittals, 

unacceptable submittals, or obtaining approval of replacement personnel will not be cause for a 

time extension or delay claims. All costs associated with incomplete, replacement, or 

unacceptable submittals shall be borne by the CFA Pile Contractor. 

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8.1.7 CFA Pile Design Requirements 

The CFA piles shall be designed to meet the specified loading conditions as shown on the 

contract plans and approved working drawings. The piles shall be designed using the Service 

Load Design (SLD) procedures contained in Chapters 5 and 6 of FHWA Geotechnical Circular 

No. 8, “Augered Cast-in-Place and Continuous Flight Auger Piles”. 

The required geotechnical safety factors/strength factors for SLD shall be in accordance with the 

FHWA circular, unless otherwise specified. Estimated soil/rock design shear strength 

parameters, unit weights, applied foundation loadings, special corrosion protection requirements, 

known utility locations, easements, rights-of-way, and other applicable design criteria will be as 

shown or listed on the plans, other contract documents, or specified herein. Structural design of 

any individual CFA pile element not covered in the FHWA manual/circular shall be by the SLD 

method in conformance with appropriate articles of the most current Edition of the AASHTO 

Standard Specification for Highway Bridges (i.e., 17th Edition as of 2007), including current 

interim specifications. 

8.1.7.1 CFA Pile Design Submittals 

At least 60 calendar days before the planned start of CFA pile 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 

CFA piles. Verify the limits of the CFA pile structures and ground survey data before preparing 

the detailed working drawings. 

The working drawings and calculations shall be signed and sealed or stamped by the CFA Pile 

Contractor’s Design Engineer or by the consultant Design Engineer (if applicable), previously 

approved by the Engineer. If the CFA Pile Contractor uses a consultant Design Engineer to 

prepare the design, the CFA Pile Contractor shall have overall contractual responsibility for both 

the design and construction. 

Submit ___ sets of the working drawings with the initial submission. Drawing sheet size shall be 

____ by ____. One set will be returned with any indicated corrections. The Engineer will 

approve or reject the CFA Pile Contractor’s submittal within ____ calendar days after receipt of 

a complete submission. If revisions are necessary, make the necessary changes and resubmit 

____ revised sets. When the drawings are approved, furnish ___ sets and a Mylar sepia set of the 

approved drawings. The CFA Pile Contractor will not be allowed to begin CFA pile work until 

the submittal requirements are satisfied and found acceptable by 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. 

8.1.7.2 Design Calculations 

Design calculations shall include, but not be limited to, the following items: 

1. A written summary report which describes the overall CFA pile design. 

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2.	 Applicable code requirements and references. 

3.	 CFA pile structure critical design cross-section(s), including soil/rock strata, 

piezometric levels, and location, magnitude and direction of applied loads. 

4.	 Design criteria, including soil/rock shear strengths (friction angle and cohesion), unit 

weights, unit skin friction values, and unit end-bearing values. Any additional 

subsurface borings, laboratory work, or other subsurface data collected for the design 

shall also be included. 

5.	 Safety factors used in the design. 

6.	 Seismic design earthquake acceleration coefficient or other seismic design criteria 

applicable for the geographic area of the project. 

7.	 Design calculation sheets (both static and seismic) with the project number, CFA pile 

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. 

If applicable, requirements for items 2, 5, and 6 will be outlined in the bid package. 

8.1.7.3 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 CFA pile structure(s) identifying: 

a.	 A reference baseline datum. 

b.	 The offset from the construction centerline or baseline to the face of the CFA pile 

structure at all changes in horizontal alignment. 

c.	 Beginning and end station of CFA pile structures. 

d.	 CFA pile locations with center-to-center pile spacing. 

e.	 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. 

f.	 The centerline of any drainage structure or drainage pipe behind, passing through, 

or passing under the CFA pile structure. 

200 
g.	 Subsurface exploration locations shown on a plan view of the proposed CFA 

structure alignment with appropriate reference base lines to fix the locations of the 

explorations relative to the CFA structure. 

2.	 An elevation view of the CFA pile structure(s) identifying: 

a.	 CFA pile locations and elevations with vertical and horizontal spacing; and 

b.	 Existing and finished grade profiles both behind and in front of the CFA pile 

structure. 

3.	 General notes for constructing the CFA piles including construction sequencing or 

other special construction requirements. 

4.	 Horizontal and vertical curve data affecting the CFA pile structure and control points, 

including match lines or other details to relate CFA pile structure stationing to 

centerline stationing. 

5.	 A listing of the summary of quantities. 

6.	 CFA pile typical sections including spacing, diameter, reinforcing bar sizes, locations, 

and details; centralizers and spacers; and connection details to the substructure 

footing/pile cap. 

7.	 Typical details of verification and proof load test piles, including reaction systems. 

8.	 Details, dimensions, and schedules for all CFA piles and reinforcing steel. 

Commentary: Submittals procedures shall be coordinated with Owner procedures. 

evise the drawings when plan dimensions are changed due to field conditions or for other 

asons. Within ____ calendar days after completion of the work, submit as-built drawings to 

e Engineer. Provide revised design calculations signed by the approved Design Engineer for 

l design changes made during the construction of the CFA piles. 

1.8 Construction Submittals 

t least 60 calendar days before the planned start of CFA pile construction, submit complete 

nstruction submittals to the Engineer for review and comment. The Engineer will review and 

mment on the CFA Pile Contractor’s submittal within ____ calendar days after receipt of a 

mplete submission. If revisions are necessary, make the necessary changes and resubmit. The 

FA Pile Contractor will not be allowed to begin CFA pile work until the submittal requirements 

e satisfied and found acceptable by the Engineer. Changes or deviations from the approved 

bmittals must be re-submitted for approval. No adjustments in contract time or delay claims 

ill be allowed due to incomplete submittals. 

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8.1.8.1 Pile Installation Plan 

The CFA Pile Contractor shall use the Pile Installation Plan to demonstrate, to the satisfaction of 

the Engineer, the dependability of the equipment, techniques, and source of materials to be used 

on the project. Reference to successful completion of projects with similar pile sizes in similar 

soil conditions using the proposed equipment and procedures should be included. The 

components of the plan shall meet the requirements contained in this specification. This plan 

shall include, but not be limited to, the following items: 

1.	 List and sizes of proposed equipment, including drilling rigs, augers and other drilling 

tools, pumps for grout or concrete, mixing equipment, automated monitoring 

equipment, and similar equipment to be used in construction, including details of 

procedures for calibrating equipment as required; 

2.	 Step-by-step description of pile installation procedures; 

3.	 A plan of the sequence of pile installation; 

4.	 Target drilling and grouting parameters (along with acceptable ranges) for pile 

installation, including auger rotation speed, drilling penetration rates, torque, applied 

crowd pressures, grout pressures, and grout volume factors; 

5.	 Details of methods of reinforcement placement, including support for reinforcing 

cages at the top of the pile and methods for centering the cages within the grout or 

concrete column; 

6.	 Mix designs for all grout or concrete to be used on the project, including slump loss 

vs. time curves and strength development vs. time curves for mixes with fly ash 

and/or slag; 

7.	 Equipment and procedures for monitoring and recording auger rotation speed, auger 

penetration rates, auger depths, and crowd pressures during installation; 

8.	 Equipment and procedures for monitoring and recording grout or concrete pressures 

and volumes placed during installation; 

9.	 Contingency plans for equipment failures during drilling or grouting operations (grout 

pump, monitoring equipment, etc.); 

10. Procedures for protecting adjacent structures, on or off the right-of-way, that may be 

adversely affected by foundation construction operations, including a monitoring plan 

as required in Section 3.1; and 

11. Other required submittals shown on the plans or requested by the Engineer. 

202 
Commentary: A clearly written pile installation plan can be very effective in reducing 

misunderstandings between the Engineer and the CFA Pile Contractor and can form the 

basis for solving potential problems before they occur, thus keeping the project on 

schedule and minimizing claims. In reviewing the CFA Pile Contractor’s submittal, the 

key information regarding the equipment that should be scrutinized is: 

(1) the rated capacity and boom lengths of the drill rig; 

(2) the torque, rotational speed, and crowd capacity on the drilling machine; 

(3) the horsepower of the hydraulic power unit used to turn the auger; and 

(4) the positive displacement piston-ball valve pump, pump stroke displacements, engine 

horsepower and pump pressures of the grout pump to be used. 

Most CFA piling installed in the United States in the last 30 years has utilized cranemounted drilling equipment. Crane-mounted rigs have no means of applying crowd onto 

the auger, and thereby have limited ability to control the rate of penetration and the 

potential for soil mining, i.e., removal of excess soil during drilling. Crane-mounted rigs 

should be approved only for non-caving soil conditions after careful consideration of the 

amount of control the equipment provides on the applied downward pressure and 

penetration rate during drilling. Conversely, hydraulic rigs provide drilling control 

systems that allow the use of partial or full displacement piles, allowing more flexibility for 

the CFA Pile Contractor’s installation means and methods to achieve the desired pile 

capacity. The selection of equipment is ultimately the responsibility of the CFA Pile 

Contractor 

Stiff soils or large diameter piles (more than 18 inches [0.45 m]) require special 

consideration in sizing equipment. The minimum torque supplied should be 30,000 ft-lb 

(41 m-kN), and the equivalent crowd capacity should be at least 5,000 lb (22 kN). 

However, this minimum may not be sufficient in many circumstances. The Contractor’s 

plan for sequence of installation should preclude the installation of piles that are within six 

diameters of each other, center to center, prior to the time that the first pile installed is 

fully set. 

8.1.8.2 Conformance Testing Plan 

Along with the Pile Installation Plan, a specific plan for completing a testing program as outlined 

in the bid package shall be submitted by the CFA Pile Contractor to the Engineer for review. 

The program shall consist of pre-production static load tests, production static and/or rapid 

and/or dynamic load tests, and post-installation integrity tests in sufficient quantities to provide 

the data necessary to demonstrate that the installed piles meet the load and deflection criteria 

established in the project plans with an appropriate factor of safety. The complete installation 

process and equipment used during the pre-production test pile program should be used to install 

the production piles. 

203 
The pre-production test program establishes the baseline parameters for construction of 

production piles. Verification load tests and structural integrity tests during construction will be 

used to verify that the CFA Pile Contractor is producing acceptable piles. Pile testing methods 

and frequencies shall meet the requirements contained in Sections (8.)3.11 and (8.)3.12 of this 

specification and the appropriate sections of the State DOT Standard Specifications. 

The conformance testing program shall meet the requirements as indicated in the bid package 

and shall include a list of the automated measuring and recording equipment to be utilized during 

construction. The minimum requirements for automated measuring and recording equipment are 

contained in Section (8.)3.4 of this specification. The submitted list should include type of 

equipment, manufacturer, data to be collected, current calibration records, and sample data 

records. 

Sampling and testing of materials used on the project shall also be included in the conformance 

testing plan. The requirements for materials testing in the State DOT Standard Specifications 

shall be listed, as well as the requirements for grout or concrete testing included in Section (8.) 

3.2 of this specification. 

The Conformance Testing Plan will clearly indicate the QA/QC tasks to be performed by the 

CFA Pile Contractor or its representative, the Inspector, or both. 

Commentary: The intent of the Conformance Testing Program is to assure the Owner that the 

piles have been installed as designed by the CFA Pile Contractor and that they meet the required 

load performance criteria. The use of automated measuring and recording equipment provides a 

means of monitoring each pile for conformance to the installation criteria. 

8.1.9 Pre-Construction Meeting 

A pre-construction meeting will be scheduled by the Engineer and held prior to the start of CFA 

pile construction. The Engineer, prime Contractor, CFA Pile Contractor, Inspectors, excavation 

Contractor, and Geotechnical Instrumentation Specialist (if applicable) shall attend the meeting. 

Attendance is highly recommended. The pre-construction meeting will be conducted to clarify 

the construction requirements for the work, to coordinate the construction schedule activities and 

identify contractual relationships and delineation of responsibilities among the prime Contractor 

and various Subcontractors. Main aspects involving multiple subcontractors may include those 

pertaining with excavation for CFA pile structures, anticipated subsurface conditions, CFA pile 

installation and testing, CFA pile structure survey control, and site drainage control. 

8.2 MATERI ALS 

All materials shall conform to the pertinent item requirements in the relevant State DOT 

Standard Specifications, or as otherwise noted. 

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Portland cement (Types I, II, & III) Item ____ (Hydraulic Cement), ASTM C 150 

Water Item ____ (Portland Cement Concrete) AASHTO 

T 26 

Fine and coarse aggregate Item ____(Portland Cement Concrete), ASTM C 

33, ASTM C 87-90, ASTM C 227-90, ASTM C 

289-94, ASTM C 295-90, A ASTM C 586-92 

Mineral admixtures (Fly Ash) Item ____ (Concrete Admixtures) ASTM C 618 

Class C or F 

Water reducing admixtures Item ____ (Concrete Admixtures) ASTM C 494, 

ASTM C 1017 

Fluidifier (fluidizer) Item____ (Grout Admixtures) ASTM C 937, 

CRD-C 619 

Reinforcing steel Item ____ (Reinforcing Steel), ASTM A 615, 

ACI 315 

Grout flow testing (flow cone) ASTM C 939, CRD-611-94 

Grout cube samples ASTM C 109 

Grout cube testing ASTM C 109, ASTM C 942 

Concrete slump testing Item ____ (Portland Cement Concrete), ASTM 

C143 

Concrete cylinder samples Item ____ (Portland Cement Concrete), ASTM 

C31 

Concrete cylinder testing Item ____ (Portland Cement Concrete), ASTM C 

39 

Notes: 

1.	 Type III Portland cement shall not be used when the air temperature for the 12 hours 

following batching will exceed 60o F (15o C). 

2.	 Type B fly ash shall not be used in conjunction with Type II Portland cement. 

3.	 All admixtures must be approved by the __________, as specified in Item ___. 

Admixtures shall be stored in accordance with Item ___, Concrete Admixtures. 

4.	 Reinforcing steel item includes the requirements and the assemblies of reinforcing 

steel. 

Commentary: The appropriate sections of each State DOT Standard Specifications should 

be included under the materials section. A complete generic materials section cannot be 

provided herein considering the vast combinations of materials and control methods used 

by individual State DOTs. Some general guidance on grout and concrete is provided in 

Sections (8.)3.2 and (8.)3.3 of this specification. 

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8.3 CONSTRUCTION REQUIREMENTS 

8.3.1 Site Preparation and Protection of Adjacent Structures 

8.3.1.1 Site Preparation 

Muck, organics, soft clay, or other unsuitable materials encountered within 5 ft (1.5 m) of the 

ground surface, such material shall be removed or otherwise treated to prevent problems with 

pile top construction. Excavation of unsuitable surface material and backfilling shall be 

completed to the Engineer’s satisfaction, or as required in the contract documents, prior to the 

construction of CFA piles. Should more than 5 ft (1.5 m) of unsuitable surface material be 

encountered, the CFA Pile Contractor shall advise the Engineer immediately and proceed with 

work as directed by the Engineer. Should the CFA Pile Contractor suspect that any soils that are 

excavated are contaminated by hydrocarbons, refuse, or other environmentally hazardous 

material, he or she shall contact the Engineer immediately and proceed with work as directed by 

the Engineer. 

Commentary: Unsuitable materials should generally be removed to their full depth, or to a 

depth of 5 ft (1.5 m), whichever is less. The excavation is typically backfilled with soil having a 

plasticity index of 20 or less compacted to at least 95% of its maximum dry density, as specified 

by ASTM D 698 (AASHTO T 180), at within 2% of optimum moisture content. 

8.3.1.2 Protection of Adjacent Structures 

The CFA Pile Contractor shall be solely responsible for evaluating the need for, design of, and 

monitoring of measures to prevent damage to adjacent structures or underground utilities, on or 

off the right-of-way. These measures shall include, but are not limited to, selection of 

construction methods and procedures that will prevent over-excavation and excessive migration 

of grout through the ground, monitoring and controlling the vibrations from construction 

activities (including placement of casings, sheet piling, shoring and similar ancillary features), 

and protecting utilities. 

Structures located within a horizontal distance equal to the planned length of the pile shall be 

monitored for vertical and horizontal movement in a manner approved by the Engineer within an 

accuracy of 0.01 in. (0.3 mm). Monitoring of adjacent structures will be done by an independent 

party working for the CFA Pile Contractor and approved by the Engineer. A monitoring plan, 

including the locations of measurement points and the frequency of recording measurements 

shall be submitted to the Engineer for approval as part of the CFA Pile Installation Plan. 

Monitoring shall begin with a base-line measurement recorded no more than 10 calendar days 

prior to construction of the pile, any shoring, or similar ancillary features. In addition to 

monitoring for movement, the condition of the adjacent structure, including cracks and crack 

widths, before and after construction of the CFA piles, shall be documented by visual inspection, 

photographs, and/or video. Structures owned by Owner shall be monitored for movement but 

need not be monitored for condition unless called for on the plans. 

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As soon as any movements are detected in adjacent structures, the CFA Pile Contractor shall stop 

construction, notify the Engineer, and take any immediate remedial measures required to prevent 

damage to the adjacent structures. The CFA Pile Contractor and the Engineer shall then review 

the current installation procedures. If revisions to the installation procedures are deemed 

necessary, the CFA Pile Contractor shall submit a revised installation plan for approval by the 

Engineer before resuming work. 

Commentary: The installation of CFA piles can result in large settlement of the ground surface 

if the rate of rotation of the auger is high relative to its rate of penetration or over-rotation, 

especially in loose sandy soils. This action can promote settlement and damage to existing 

structures near the location of the pile installation. In some soils, the pumping of grout can 

result in the fracturing of the ground, the traveling of grout in the ground a considerable 

distance horizontally under pressure, which can lift the ground surface and structures (including 

buried conduits) founded nearby. Careful monitoring of the movements of adjacent structures 

and changes in the condition of such structures is necessary in order for the CFA Pile 

Contractor to know when their procedures are producing ground movements in order and when 

immediate corrective action needs to be taken during the pile installation. If a soil susceptible to 

densification is encountered, the penetration rate should be increased or the rate of rotation of 

auger be reduced. Condition surveys are needed for the evaluation of the effect of the 

construction process on the serviceability of adjacent structures by the Engineer. 

8.3.2 Grout or Concrete 

The grout or concrete property requirements listed to follow in this section shall be determined 

from samples taken during CFA pile construction as described in Section (8.)3.2.4. 

Commentary: CFA piles have traditionally been constructed in the United States with sandcement grout. Construction of CFA piles with concrete is now routinely accomplished in the 

United States and abroad, and has proven to produce acceptable piles when properly specified 

and constructed. The specifications herein allow for the use of either grout or concrete; 

however, once a mix design is established through the pile test program it should not be altered. 

As a guide for strength development, grout and concrete meeting these specifications typically 

attains 30 % and 70 % of their 28-day compressive strength after 3 and 7 days of curing, 

respectively. Both grout and concrete mixes may contain pozzolanic additives. The most 

commonly used is fly ash (ASTM C 618-94; however, finely ground silica flume and blast 

furnace slag (ASTM 989-94) can also be used. The use of pozzolanic additives results in lower 

permeability of the hardened concrete and tends to retard the set time of the cement paste, 

thereby increasing the time that the grout or concrete remains workable. As a consequence of 

providing a more workable mix, materials such as fly ash, silica flume, and/or slag will probably 

severely retard the early strength gain of the grout mix, typically until about 10 to 14 days of 

age. In all cases, the submitted mix design should include strength development vs. time 

information. 

Each DOT will likely have local mix designs that are preferred for CFA pile construction (or 

drilled shafts produced by the wet method), based on performance of local cements and 

207 
aggregates. Concrete mix design for CFA pile construction should be given special attention. 

Desirable properties are fluidity, compaction under self weight, resistance to segregation, and 

controlled set time. Specific guidance on slump and aggregate gradation are provided below. 

8.3.2.1 Mix Design – Grout 

The grout shall consist of a mixture of Portland cement fly ash, water, fine aggregate (sand), 

fluidifier, and if necessary, retarder, which shall be proportioned and mixed so that the grout will 

exhibit the following properties: 

1.	 All solids shall remain in suspension in the grout without excessive bleed-water. 

2.	 The grout shall be tested for fluid consistency (using a flow cone) in accordance with 

the modifications made to either ASTM C 939 or the U.S. Army Corps of Engineers 

specification CRD 611-94 (USACE, 1994), as described below, and shall be obtained 

as described in Section (8.)3.2.4. Either of these specifications is herein required to 

have the flow cone outlet modified from a 1⁄2 in. (12 mm) diameter outlet to a 3⁄4 in. 

(19 mm) diameter outlet. A range of acceptable fluid consistency (expressed as 

eff1ux time per standard volume as described in the cited specifications) shall be 

established, and must meet the approval of the Engineer. 

3.	 The grout shall not exhibit shrinkage in excess of 0.15 % in the vertical direction, as 

tested in accordance with ASTM C 1090, and shall be housed in a 100 % humidity 

room at a temperature of 68o F to 74o F (20o C to 23o C), or as otherwise specified by 

the Engineer. 

4.	 Grout samples recovered for strength testing, as described in Section (8.)3.2.4, shall 

exhibit a minimum compressive strength of ____ psi 28 days after casting, as required 

by the design. 

5.	 The submitted mix design shall include curves of viscosity loss versus time. In 

addition, grout shall be designed so as to maintain the range of acceptable fluid 

consistency for a period of at least 2 hours or longer, if required by the projectspecific pile installation plan. 

6.	 Strength development versus time curves/data shall be provided, with data for times 

beyond 28 days as required for mixes that include fly ash, silica flume, or slag. 

Commentary: The grouts used in CFA pile production are typically too thick to flow 

effectively from the standard 1⁄2 in. (12 mm) outlet. The flow cone specified by the U.S. 

Army Corps of Engineers (CRD 611-94) may be modified by simply taking out the 

removable 1⁄2 in. (12 mm) diameter orifice that extends out the bottom of the device to 

leave a 3⁄4 in. (19 mm) diameter opening, while a flow cone would need to be custom 

fabricated to the ASTM C 939 specification with the modified outlet diameter. Grouts 

acceptable for CFA pile construction typically have a fluid consistency represented by an 

eff1ux time of 10 to 25 seconds when tested in accordance with the modifications 

described herein. 

208 
Checking the grout flow is considered a quality control tool valued primarily for the 

purpose of quickly indicating whether the grout currently being tested will most likely 

conform with grout samples meeting the specified design requirements furnished 

previously on the project. Should any piles be found inadequate in subsequent testing, a 

record of grout flow may be valuable in identifying other suspect piles, which may then 

be subject to further testing at the discretion of the Engineer. 

8.3.2.2 Mix Design – Concrete 

The concrete shall consist of a mixture of Portland cement, fly ash, water, coarse aggregate, fine 

aggregate (sand), water reducers, and if necessary, retarder, which shall be proportioned and 

mixed so that the concrete will exhibit the following properties: 

1.	 All solids shall remain in suspension in the concrete mix without excessive bleedwater. 

2.	 Concrete samples recovered for slump testing as described in Section (8.)3.2.4, shall 

exhibit a slump of 8 in. ± 1 in (200 mm ± 25 mm) when tested in accordance with 

ASTM C 143. 

3.	 Concrete samples recovered for strength testing, as described in Section (8.)3.2.4, 

shall exhibit a compressive strength of ____ psi 28 days after casting, as required by 

the design. 

4.	 The submitted mix design shall include curves of slump loss versus time. 

5.	 Strength development versus time curves/data shall be provided for mixes that 

include fly ash, silica flume, or slag. 

Commentary: Concrete mix designs appropriate for drilled shafts constructed by the wet 

method are generally acceptable for use in CFA pile construction, with the notable 

exception that CFA pile construction may require a greater degree of workability. Greater 

workability is needed to allow for the concrete to be pumped through the delivery lines and 

auger, and subsequent insertion of the required reinforcing steel to planned elevation after 

placement of the concrete. Accordingly, the coarse aggregate for CFA pile construction is 

typically limited in size to no greater than 3⁄8 in. (9.5 mm). Consideration should be given 

to the benefit of well rounded aggregate (i.e., pea-gravel). 

Slump requirements are based on providing the necessary quality of workability for 

uniform and proper placement throughout the duration of CFA pile construction. A slump 

range of 8 in. ± 1 in. (200 mm ± 25 mm) is suggested. Sampling frequencies for slump 

measurement are recommended in Section (8.)3.2.4 

High workability is achieved with proper aggregate gradations, water-cement ratios and 

appropriate admixtures such as water reducing, with retarding admixtures, and air 

entraining agents. Angular crushed aggregates are harder to work than similar sized 

rounded aggregates. To insure against segregation, the sand/cement content should be 

high compared to the coarse aggregate content. Fly ash can be used to replace some of 

the Portland cement in many situations, but may result in slower strength development. 

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8.3.2.3 Field Operations 

1.	 All oil, rust inhibitors, residual drilling slurries and similar foreign materials shall be 

removed from holding tanks/hoppers, stirring devices, pumps and lines, and all other 

equipment in contact with the grout or concrete before use. 

2.	 All grout or concrete used shall be batched at a State approved facility, and delivered 

to the project site. The addition of water at the project site is permitted only with 

prior approval by the Engineer and only to the extent that the water-cementitious 

material ratio does not exceed the ratio of the approved design mix. 

3.	 If agitated continuously, the grout or concrete may be held in the ready mix truck for 

up to 2.5 hours if the air temperature is not greater than 68o F (20o C), or up to 2 hours 

if the air temperature is between 68o and 100o F (20o and 38o C) if other than Type III 

Portland cement is used. Grout or concrete shall not be placed if the air temperature 

exceeds 100o F (38o C) or is less than 39o F (4o C) unless approved procedures for hot 

(over 100o F [38o C]) or cold weather (less than 39o F [4o C]) placement are followed. 

Grout or concrete designed with retarders to extend the holding time or placement 

temperature range shall be placed in accordance with the mix design parameters. 

4.	 A screen with a mesh with openings no larger than 3⁄4 in. (19 mm) for grout, or 4 in. 

(100 mm) for concrete shall be used between the delivery point from a ready mix 

truck and the pump, to remove large particles or cement clumps that can clog the 

grout or concrete injection system. 

5.	 The grout or concrete pump shall be a positive displacement pump with a known 

volume per stroke that is capable of developing peak pressures of at least 350 psi 

(2,400 kPa) at the pump. The pump shall be sized appropriately to the pile size such 

that a smooth, continuous delivery of grout or concrete can be maintained while 

limiting the pressure variations (particularly the pressure drop) felt by the pile due to 

the pump strokes. The CFA Pile Contractor shall provide the Engineer with the value 

of the volume of grout or concrete delivered by each stroke of the pump and shall 

demonstrate to the Engineer that the actual volume delivered by each stroke of the 

pump is within 3% of the value provided. The volume per stroke shall be recalibrated 

when the Engineer suspects that the grout or concrete delivery performance has 

changed. 

6.	 Automatic measurements shall be made and recorded during the pile construction 

process as described in Section (8.)3.4 of this specification. All inspection records 

shall be made as described in Section (8.)3.10 of this specification. 

7.	 The minimum value of grout pressure at the pump outlet or at the top of the auger that 

is required on the approved working drawings or approved pile installation plan shall 

be maintained for all grout or concrete placement operations throughout the project. 

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8.3.2.4 Grout or Concrete Sampling and Testing 

Grout or concrete samples for strength testing shall be taken from the discharge at the delivery 

trucks prior to pumping. Concrete samples shall be cylinders 6 in. (150 mm) diameter by 12 in. 

(300-mm) high, or sized appropriately for maximum aggregate size according to ASTM C 39. 

Grout samples shall be 2 in. (50 mm) cubes and shall be subjected to a 10% increase in required 

compressive strength as compared to cylinder samples. 

The CFA Pile Contractor, Testing Agency, or qualified party specified in the contract documents 

shall make no less than six (6) such samples for each 50 yd3 (38 m3) of grout or concrete placed. 

No less than six (6) such samples shall be made per working day, or less than six (6) such 

samples for each mix of grout or concrete produced by the supplier. Concrete or grout cylinders 

(or alternatively cubes for grout) shall be cured and tested in accordance with the State DOT 

specifications. 

The samples will be tested by ______(Agency’s name) for unconfined compressive strength. As 

a minimum, two (2) samples shall be tested at seven days after sampling; two (2) samples shall 

be tested at 28 days after sampling; and two (2) samples will be held in reserve. Those samples 

tested at 28 days after casting shall exhibit a minimum compressive strength as specified in 

Section (8.)3.2.1 for grout or Section (8.)3.2.2 for concrete. 

A grout sample shall be obtained from every truck, and shall be tested for fluid consistency (flow 

cone) and temperature prior to discharging into the pump hopper. The grout sample shall exhibit 

the fluid consistency as specified in Section (8.)3.2.1. Alternatively, if a concrete mix is used, a 

concrete sample shall be obtained from every truck, and shall be tested for slump and 

temperature prior to discharging into the pump hopper. The concrete sample shall exhibit the 

slump as specified in Section (8.)3.2.2. Additional samples may be required at the discretion of 

the Engineer at any time during the grout or concrete placing process to ensure that consistent 

fluidity/slump is being achieved. 

Commentary: Often smaller sized cylinder samples of grout are used and are typically either 3 

in. (75 mm) diameter by 6 in. (150 mm) high, or 2 in. (50 mm) diameter by 4 in. (102 mm) high. 

Smaller sized cylinder samples for grout should only be permitted with prior approval by the 

Engineer. If the samples are cast using a method or sample different than that used for the mix 

design, a relationship between the compressive strengths obtained by the methods will need to be 

established. 

The type of and frequencies for grout or concrete testing listed in this section are recommended 

as a minimum requirement. The Engineer may choose to increase the type or frequency of 

testing in the project specifications or at any time during the construction of the CFA piles. For 

non-critical foundations, only the Engineer may choose to relax the frequency of grout and 

concrete sampling and testing. 

Some State DOTs have standard test procedures and/or frequencies that are not included in the 

specification when done by State personnel. In such cases, the State DOT should reference their 

testing manual/procedures and that the testing will be performed by State personnel. 

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8.3.3 Auger Equipment 

The auger flights shall be continuous from the top of the auger to the bottom tip of the cutting 

face of the auger, with no gaps or other breaks. Gaps in the flighting are allowed only where 

auger sections are joined and may not exceed 1 in. (25 mm). The length of any auger brought to 

the project site shall be such that the auger is capable of installing a pile to a depth that is 20% 

greater than the depth of the pile shown on the approved working drawings. The auger flighting 

shall be uniform in diameter throughout its length, and the outside diameter of the auger shall be 

at least 97% of the design diameter of the pile. Only single helix augers shall be used. The 

hollow stem of the auger shall be maintained in a clean condition throughout the construction 

operation. In order to facilitate inspection, the leads shall be clearly marked every 1 ft (0.3 m) 

along its length so that such marks are visible to the unaided eye from the ground. 

Commentary: The requirements contained in this section are a minimum requirement for CFA 

piles. The CFA Pile Contractor may propose to use alternative equipment subject to the 

approval of the Engineer through the Installation Plan submittal process. In general for CFA 

piles, continuous flight augers that continuously remove soil during drilling are the common type 

of auger or drilling tool used. Consideration of augers or drilling tools that provide full or 

partial displacement of the soil during drilling should also be made. 

The bottom of the auger flights and the cutting teeth attached thereto shall be constructed 

geometrically so that the bottom of the pile will be as flat as feasible. The grout or concrete 

injection port shall be fitted with a means of sealing it against ingress of water and soil during 

drilling. 

The auger shall be guided at the ground surface by a guide connected to the leads of the CFA 

piling rig. If the auger is over 40 ft (12 m) long, it shall also be guided by a guide to be located 

approximately half the length of the auger above the ground-surface guide. Where CFA piles are 

installed with hydraulic, fixed mast installation platforms, and the stem to which the auger is 

fixed has an outside diameter 10 in. (250 mm) or greater, a guide above the ground surface is not 

required. The leads that carry the rotary unit that power the auger should be restrained against 

rotation by an appropriate mechanism. 

The piling rig shall be capable of penetrating the ground without drawing surrounding soils 

laterally into the pile bore, as is described in Section 3.5. It shall be capable of installing a pile to 

a depth at least 20% greater than the depth of the piles shown on the approved working drawings. 

8.3.4 Automatic Measurement and Recording Equipment 

As a minimum, the following automatic measurements shall be made and recorded during the 

drilling operation: 

1. auger rotation; 

2. depth of the auger injection point; 

3. torque delivered to the auger; and 

4. crowd force (downward thrust on auger). 

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All measurements shall be referenced to (or plotted against) the depth of the auger injection 

point. This shall be accomplished with a rotational position indicator on the auger head system 

and an electronic position indicator on the crane line or boom holding the auger. Torque and 

thrust load cells shall be positioned on the auger head system. 

As a minimum, the following automatic measurements shall be made and recorded during the 

grouting or concreting operation: 

1. volume of grout or concrete; 

2. maximum and minimum grout or concrete pressure; 

3. auger rotation (if rotated); and, 

4. depth of the injection point. 

All measurements shall be referenced to (or plotted against) the depth of the auger injection 

point. This shall be accomplished with electronic flowmeters and electronic pressure transducers 

placed in the grout or concrete pressure line, an electronic position indicator on the crane line or 

boom holding the auger, and a rotational position indicator on the auger system. 

Calibration shall be made on all measuring and recording equipment at the beginning of the 

project that will demonstrate that the values indicated by the measuring and recording equipment 

are within 3% of the values indicated. Calibrations shall be performed in accordance with the 

equipment manufacturer’s specifications. All measuring and recording equipment shall also be 

recalibrated when the Engineer suspects that the drilling and grouting or concreting performance 

has changed. 

Commentary: Automated measuring and recording equipment provide real time evaluation of 

each pile on a project. Piles that have installation records out of specification or that otherwise 

appear abnormal can be selected for integrity tests or verification load tests to determine if they 

should be accepted or rejected. 

8.3.5 Drilling 

The CFA Pile Contractor shall perform the drilling required for the piling, through whatever 

materials are encountered, to the dimensions and elevations required by the CFA Pile 

Contractor’s design, as shown on the approved working drawings. Drilling shall not commence 

until sufficient supply of grout or concrete is present on the project site to complete the pile. The 

drilling parameters (auger rotation speed, penetration rates, crowd, torque, etc.) for the 

production piles shall be within the ranges established in the Pile Installation Plan, as verified by 

the pre-production testing program. The same procedures used to install the test piles shall be 

used to install production piles. 

The center of any pile shall be within 3 in. (75 mm) of the location shown on the approved 

working drawings in a horizontal plane (i.e., plan-view). The completed pile shall be plumb to 

within 2%, if vertical, or shall be installed to within 2% of its design batter, as determined by the 

213 
angle from the vertical, if planned as a batter pile. Any pile in violation of these tolerances will 

be subject to review by the Engineer and may be rejected or replaced at the CFA Pile 

Contractor’s expense. 

Adjacent piles within six diameters, center to center, of each other shall not be installed until it 

can be demonstrated by the CFA Pile Contractor that the grout or concrete in the first pile 

installed is fully set. The grout or concrete should have set enough such that the integrity of the 

existing pile will not be compromised if drilling the new pile causes mining of soil away from 

the existing pile. 

The auger shall not be extracted from the ground at any time during the construction of a pile in 

such a way that would result in an open unsupported borehole or inflow of water into the pile 

borehole. It should become necessary to raise the auger and subsequently re-insert the auger 

during the pile construction process, the depth of the pile shall be increased and/or other 

additional measures shall be required as directed by the Engineer. 

The auger shall be advanced into the ground at a continuous rate and at a rate of rotation that 

prevents excess spoil from being transported to the ground surface. The rate of penetration shall 

be established as a part of the test pile program. Automated monitoring equipment shall be used 

to verify this target rate of penetration is maintained during construction of production piles. 

Pile termination criteria, including refusal criteria, if applicable, will be established during the 

pre-production test pile program. If refusal is encountered before planned depth is achieved, 

rotation of the auger shall be stopped, and the CFA Pile Contractor shall inform the Engineer. 

The CFA Pile Contractor and Engineer shall evaluate the installation data and determine if the 

established termination criteria have been met, or if other action is required to complete the pile. 

If an obstruction is encountered and it does not allow the pile to be completed in the planned 

location, the CFA Pile Contractor shall notify the Engineer and the Design Engineer in order for 

the Engineer and Design Engineer to determine remedial action. 

Commentary: The penetration rate should generally be maintained such that the auger advances 

a depth equal to or greater than the pitch of the auger for every 1.5 to 2 revolutions for 

cohesionless soils, or 2 to 3 revolutions for cohesive soils. Loose cohesionless soils are more 

susceptible to mining by the auger flights, and generally call for the more stringent guideline. 

The intent of this provision is that the piles be constructed to a consistent standard as reflected in 

the results of the test pile program, and that soil mining be avoided. 

In general, refusal is defined as a rate of auger penetration of less than 1 ft/minute (0.3 

m/minute) with equipment that is appropriate for the project. If correlated with soil boring 

information, refusal may provide an indication that a strong layer has been reached, but should 

not be used as the sole criteria for setting pile tip levels for conventional CFA piles. Refusal 

criteria may be used to set pile tip levels for drilled displacement piles, based on the criteria 

established and verified to achieve capacity during the pile load testing program. 

214 
8.3.6 Placement of Grout or Concrete 

The placement of grout or concrete shall commence within 5 minutes after the auger has 

achieved the planned depth. Grout or concrete shall be pumped through the hollow-stem auger 

with sufficient pressure (as measured at the top of the auger) as the auger is withdrawn to 

completely form the pile and fill any soft or porous zones surrounding the pile. 

At the beginning of grout or concrete placement the sealing device (plug, or bottom cover plate 

at the tip of the auger) shall be removed by the application of grout or concrete pressure, or with 

a central reinforcing bar. As pumping begins, the auger shall be lifted from 6 to 12 in. (0.15 to 

0.3 m) to facilitate removal of the sealing device. Care shall be taken to ensure that the auger is 

lifted only within this specified range to initiate the flow of grout or concrete, and that water 

inflow and soil movement at or near the base of the auger are minimized. After withdrawing the 

auger to initiate the flow of grout or concrete, the tip of the auger should be re-inserted to at least 

the original depth. 

The technique and equipment used to initiate and maintain the grout or concrete flow shall be 

such that a pile of the full design cross-section is obtained from the maximum depth of boring to 

the final pile cut-off level. The grout or concrete shall be supplied to the pile at a rate during 

auger withdrawal that ensures that a continuous monolithic shaft of at least the full specified 

cross-section is formed, and is free from soil inclusions or any grout or concrete segregation. 

The auger shall be extracted at a smooth, steady rate while continuously pumping. If rotation of 

the auger occurs during auger extraction, it shall be positive, i.e. in the same direction as during 

drilling. 

Satisfactory coordination of auger withdrawal with pumping is indicated by maintaining a 

positive pressure in the grout at the auger tip, and a sufficient volume or pressure of grout or 

concrete to fill the pile (with a small oversupply of volume). Satisfactory coordination shall be 

verified using automated monitoring equipment. 

The volume of grout or concrete placed as a function of depth shall be measured and recorded at 

intervals not exceeding 2 ft (0.6 m) using automated monitoring equipment. The magnitude of 

minimum oversupply (or grout volume factor) appropriate for the site conditions shall be 

established during the pre –production test pile program and maintained during production pile 

construction. Inadequate volume pumped over a depth interval of 5 ft (1.5 m) is a basis for 

rejection of the pile. 

Commentary: Typical grout volume factors range from 1.15 to 1.2 (i.e., 15% to 20% 

oversupply). In general, a grout volume factor of 1.15 is considered to be a minimum value. 

Grout factors greater than 1.5 suggest that soil mining or other undesirable installation effects 

may be occurring. There may be some cases where grout factors greater than 1.5 are 

acceptable, particularly if integrity and proof tests indicate that the pile meets the performance 

requirements and if pre-production piles showed similar results. 

215 
The grout/concrete volume factor of the pile shall be within 7.5% of the target volume factor 

established in the Pile Installation Plan as modified by the results of the pre-production test pile 

program. Production piles installed outside of this range shall be considered unacceptable piles 

as listed in Section (8.)3.13. 

If placement of grout or concrete is suspended for any reason, such as equipment failure, the pile 

will need to be re-drilled. The pile may be re-drilled in the same location if the grout or concrete 

is still fluid enough for the drill rig to penetrate. If the concrete or grout has set, the pile will 

need to be re-drilled in a new location. The Pile Installation Plan and working drawings will 

need to be revised by the CFA Pile Contractor to reflect the changes and submitted to the 

Engineer for approval prior to re-drilling the pile. 

Commentary: During grouting, the auger should be pulled with either no rotation or slow 

continuous rotation in the direction of drilling. A static pull with no rotation can help maintain a 

static condition at the base of the auger against which the grout/concrete pressure acts. Some 

contractors prefer to slowly rotate the auger during withdrawal in order to minimize the risk of 

having the auger flight stick. In addition, some augers have an off-center discharge plug at the 

base and slow rotation may help to avoid concentrating the distribution of the grout and 

pressure to an off-center location within the hole. If rotation is used it must be very slow so that 

the auger does not tend to conduct the soil on the auger flights to the surface ahead of the auger. 

The intent of this provision is that the piles be constructed with grout/concrete volumes 

consistent with the standard as reflected in the results of the pre-production test pile program. 

The production piles should be installed at the same grout volume factor (within an acceptable 

range) that was used for the pre-production test pile installation. A pile which is not completed 

with adequate volume of grout or concrete may be re-drilled at the CFA Pile Contractor’s 

discretion, and this fact recorded on the pile record. The acceptance of a re-drilled pile is at the 

Engineer’s discretion. 

8.3.7 Pile Head Finishing and Protection 

Immediately upon completion of placement of the fluid grout or concrete, the CFA Pile 

Contractor shall remove all excess grout or concrete and spoil from the vicinity of the top of the 

excavation and place a suitable temporary device within the top of the excavation, extending 

both above and below the ground surface by at least 1 ft (0.3 m) to keep surface spoil from 

entering the grout or concrete column before it sets. Immediately upon placement of this 

temporary device, the CFA Pile Contractor shall remove any and all loose soil that has fallen into 

the grout or concrete column using the tools and methods contained in the approved Pile 

Installation Plan, and before the grout or concrete begins its initial set. The temporary device 

shall be removed without disturbing the natural soil surrounding the top of the pile once the grout 

or concrete has set. 

8.3.8 Reinforcing Steel Placement 

Any required reinforcing steel shall be placed as shown on the plans by lowering the steel into 

the grout or concrete column while it is in a fluid state. The reinforcing steel shall be free of oil, 

216 
soil, excessive rust or other deleterious material. The reinforcing steel shall be centered in the 

excavation by means of plastic or cementitious spacers placed at sufficient intervals along the 

pile and at sufficient intervals around the steel to keep the steel centered. Metallic spacers shall 

not be permitted. Centralizer types and spacing are subject to approval by the Engineer. If cages 

of reinforcing steel are called for on the approved working drawings, the longitudinal bars and 

lateral reinforcement (spiral or horizontal ties) shall be completely assembled and placed as a 

unit. Where spiral reinforcement is used, it shall be tied to the longitudinal bars at a spacing not 

to exceed 1 ft (0.3 m) unless otherwise shown on the plans. Welding of reinforcement is 

permitted only if weldable reinforcing steel is specified as part of the approved design. 

The reinforcing steel shall not be spliced except at locations that are shown on the plans, and the 

reinforcing steel shall be free of any permanent distortion, such as bars bent by improper pickup. 

If a pile is required by the Engineer to be lengthened after the steel has been cut and cages have 

been assembled, the schedule of reinforcing steel (both longitudinal and lateral) shall be 

extended to the required depth by splicing. Splices should be as close to the bottom of the 

reinforcing cage as possible. Splicing by welding shall not be permitted unless weldable 

reinforcing steel is specified as part of the approved design. 

The reinforcing steel shall be placed in the grout column immediately after screening the grout or 

concrete and before the grout or concrete begins to set. The steel may be lowered into the grout 

or concrete by gravity or pushed gently to final position by hand. The reinforcing steel shall not 

be vibrated, driven, or otherwise guided into position by mechanical means. 

The reinforcing steel shall be held in position at the ground surface within the fluid grout column 

by supports appropriate for the reinforcement used, which shall remain in place until the grout 

reaches its initial set, or 24 hours, whichever is longer. 

Commentary: If the soil profile contains considerable dry or moist sand, it is critical that the 

cage be placed as soon as possible after placement of grout or concrete, in less than 10 minutes 

if possible, because the grout or concrete will begin to set very quickly under such conditions. 

Steel spacers should not be permitted as they may greatly accelerate corrosion of the reinforcing 

steel, particularly above the ground water table. Centering guides made of steel, such as a wire 

“basket” or “football” tied at the base of single-rod reinforcement may be used. The time for 

initial set will vary according to mix design. Mixes with significant amounts of retarders or 

fluidifiers may require longer than 24 hours to reach initial set under certain conditions (cold 

weather, for example). The installation plan should include requirements for the duration of 

reinforcement support. 

8.3.9 Pile Cut-Off 

The CFA Pile Contractor shall cut off the tops of piles and square with the pile axis at the 

elevations indicated on the approved working drawings, by removing fresh grout or concrete 

from the top of the pile or by cutting off hardened grout or concrete down to the final cutoff 

point at any time after initial set has occurred. The finished top of pile shall be no more than 1 

in. (25 mm) below or 3 in. (75 mm) above the elevation shown on the approved working 

drawings. 

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8.3.10 Inspection and Records 

The CFA Pile Contractor shall maintain accurate records for each pile constructed. Similar 

records will be maintained by the Engineer. These records shall show: 

1.	 Pile location; 

2.	 Ground surface elevation (reference grade for pile length); 

3.	 Pile toe (bottom) depth and elevation; 

4.	 Elevation of top of grout or concrete; 

5.	 Pile length; 

6.	 Auger diameter; 

7.	 Details of the reinforcing steel (number, size, and grade of longitudinal bars, size and 

spacing of transverse steel; outside diameter and length of cage); 

8.	 Flowcone efflux time and volume of grout placed or slump and volume of concrete 

placed 

9.	 Theoretical volume of drilled hole (theoretical diameter = diameter of auger); 

10.	 Depth to which reinforcing steel was placed; 

11.	 Date/Time of beginning of drilling; 

12.	 Date/Time of completion of drilling; 

13.	 Date/Time grout or concrete was mixed; 

14.	 Date/Time ready-mix grout or concrete truck arrived at project site, and copies of all 

grout or concrete batch tickets used for the pile construction; 

15.	 Date/Time of beginning of grout or concrete pumping; 

16.	 Date/Time of completion of grout or concrete pumping; 

17.	 Date/Time of placement of reinforcing steel; 

18.	 Weather conditions, including air temperature, at time of grout or concrete placement; 

19.	 Identification of all grout or concrete samples taken from the pile; 

20.	 All other pertinent data relative to the pile installation; and 

21.	 All readings made by the automated measuring and recording equipment to include as 

a minimum: 

a.	 Auger rotation verses depth for every 2 ft (0.6 m) increment, or less, of pile 

advancement during the drilling process, and during placement of grout or 

concrete (if auger is rotated during this placement); 

b.	 Volume of grout or concrete placed versus depth of outlet orifice for every 2 ft 

(0.6 m) increment, or less, of pile placed; 

c.	 Average maximum and minimum pump stroke pressures at ground level for every 

2 ft (0.6 m) increment, or less, of pile placed; 

218 
d.	 Average maximum and minimum pump stroke pressure at or near the auger head 

for every 2 ft (0.6 m) increment, or less, of pile placed, if directed by the 

Engineer; and 

e.	 Additionally, the Engineer may also specify that torque and crowd force 

(downward thrust on auger) measurements be made for every 2 ft (0.6 m) 

increment, or less, of pile advancement during the drilling process. 

These data shall be provided to the Engineer within 24 hours of the completion of the pile. Data 

collected by automated measuring and recording equipment shall be provided in numerical or 

graphical form. 

8.3.11 Testing 

Any testing of CFA piles shall conform to the pertinent item requirements in the relevant State 

DOT’s Standard Specifications. If the relevant Standard Specifications do not refer to load 

testing for CFA piles specifically, the specifications for load testing of deep foundations may be 

used. 

Commentary: A discussion of testing programs and procedures is contained in Chapter 7 of the 

FHWA “Geotechnical Circular No. 8 – Augered Cast-in-Place and Continuous Flight Auger 

Piles”. The scope of the testing program for all structures will depend on many factors, 

including the anticipated loads and the quantity of piles to be installed on the project. For 

structures that are often referred to as “non-critical structures”, such as sound barrier walls, 

overhead signs, and light/signal pole foundations, the Engineer may not require the same 

frequency of testing as for bridges and other structures. For example, a qualified contractor that 

consistently demonstrates proper installation techniques may not need to perform a load test for 

a lightly loaded pile for a “non-critical” structure. Monitoring records during construction and 

post-construction integrity testing may provide sufficient confidence for the Owner that the piles 

will carry the design load. 

8.3.11.1 Pre-Production Testing 

Piles installed for pre-production testing (including any reaction piles required for static load 

testing) shall include all construction, monitoring, and inspection requirements of production 

piles. The results of the installation and testing will be used to: 

1.	 Establish target drilling penetration rate for the various subsurface conditions on the 

site; 

2.	 Establish pressure/volume relations during placement of grout/concrete. The grout 

factor ±7.5% calculated for the test pile(s) shall be used for the installation of the 

production piles; 

3.	 Establish target values for torque and downward thrust or crowd for displacement or 

partial displacement piles; 

4.	 Establish mix design parameters such as grout flow, necessary admixtures, etc; and 

219 
5.	 Evaluate design correlations of side and base resistance with the site specific soil 

parameters. Revision of the design by the CFA Pile Contractor may result from these 

tests, subject to approval by the Engineer. 

All of the parameters listed above that are established during the pre-production test pile program 

will be used to install the production piles. 

Commentary: In past practice, the pre-production test program was primarily a load test 

program which demonstrated that the contractor could properly install a test pile and achieve 

the desired load capacity of the pile. The intent of the pre-production testing program in this 

specification is to install test piles to establish and/or verify installation criteria as well as load 

capacity. The results of the pre-production test program will then be used during production 

pile installation to ensure that the CFA Pile Contractor is consistently installing acceptable piles 

(i.e. the production pile is the same as a test pile). 

Pre-production load tests will generally consist of a single or multiple static load tests, 

depending on the number of piles to be installed, the range of design pile capacities and the 

variation of subsurface conditions at the site. For very large projects, pre-production testing 

may include a single static load test supplemented with several piles tested by the rapid or 

dynamic load test methods outlined in Section (8.)3.11.2. Performing rapid or dynamic tests 

during the pre-production testing program will allow these methods to be calibrated against 

static load tests results prior to production pile installation. The CFA Pile Contractor and the 

Engineer will be able to best determine the appropriate quantity and level of pre-production 

testing based on the project conditions. 

Since a major advantage of CFA piles is speed of installation, the pre-production load test 

program may be performed concurrent to the start of production piles to reduce additional 

mobilization or delay costs. This may be sufficient for small to medium sized projects. The 

ability to modify the design based on the results of the load test may be limited in this case. 

8.3.11.2 Verification Load Testing 

Verification tests shall be performed on a minimum of 2% of production piles (and more as 

required by the Engineer) to demonstrate that the installed production piles meet the established 

load-deflection criteria. Verification tests can be performed using static load tests, rapid load 

tests (RLT), or dynamic load tests (DLT). Combinations of the various test methods may also be 

used as appropriate for the project. RLT and DLT test methods shall conform to the State DOT 

Standard Specifications or be otherwise approved by the Engineer. 

Commentary: A single pre-production test only demonstrates the performance of the test pile. 

Performing verification tests periodically throughout production pile installation will verify that 

the pile installation techniques continue to provide adequate pile capacities. The use of RLT 

(such as Statnamic TM or Fundex systems) or DLT (drop hammer) can often allow testing a large 

number of piles more efficiently, in terms of time and cost when compared to static load test 

methods. Calibrating the RLT or DLT tests with static load tests during the pre-production test 

program may reduce delays associated with analyzing the test data during pile production. 

220 
8.3.12 Integrity Testing 

Post-installation integrity tests shall be performed on a minimum of 20% of the production piles. 

Such tests include, but are not limited to, sonic echo tests, impulse-response tests, cross-hole 

sonic tests, and backscatter gamma tests. Specific integrity test requirements are outlined in the 

bid documents. Test methods shall conform to the State DOT Standard Specifications or be 

otherwise approved by the Engineer. 

The CFA Pile Contractor shall install access tubes (of a design that is acceptable to the Integrity 

Testing Firm) to accommodate those tests that require access to the interior of the CFA pile. 

These tubes shall be secured to the reinforcing steel and capped prior to placing the steel cage in 

the fluid grout. The piles that will include the access tubes shall be noted on the approved 

working drawings and in the test program. 

The CFA Pile Contractor shall engage an independent Consultant, acceptable to the Engineer, to 

perform integrity tests and to report the results, with interpretations, to the CFA Pile Contractor 

and the Engineer. 

Commentary: Post-installation integrity tests are valuable in establishing that a CFA Pile 

Contractor’s procedures are producing acceptable piles on any given project. The most reliable 

of the post-installation integrity tests for identifying anomalies within the pile are those that use 

down-tube instruments, such as the cross-hole sonic (CSL) test, single-hole sonic test (SST), the 

backscatter gamma test, and the fiber-optic television camera test. These tests all require that 

the CFA Pile Contractor attach appropriate access tubing to the reinforcing steel prior to 

placing the steel in the grout column. They also require interpretation, which should be 

performed by independent, experienced, and qualified specialty consultants. It is not always 

possible to determine whether an anomalous reading is a defect within the pile. The final 

decision on acceptability of the pile must be made by the Engineer, based on construction 

records, the post-installation integrity test expert’s report, and upon the Engineer’s analysis of 

the possible effect on foundation performance of the potential defect. 

In order to be effective, access tubes for sonic or backscatter gamma testing should be 

distributed evenly circumferentially around a reinforcing cage at a frequency of approximately 

one for every 1 ft (0.3 m) of cage diameter. It is advisable that tubes used for cross-hole sonic 

tests consist of Schedule 40 steel, because such tubes will remain bonded to the grout. Polyvinyl 

chloride (PVC) tubes do not ordinarily remain bonded to the grout beyond a few days after grout 

takes its initial set, and debonding will render the cross-hole sonic tests ineffective. PVC tubes 

should be used only for backscatter gamma testing unless cross-hole sonic tests will be 

performed within 72 hours of casting the grout. 

The necessary frequency of post-construction integrity testing should be outlined in the owner’s 

bid package. In situations when the Owner has little experience with CFA piles, a particularly 

difficult project is at hand, or the project or site conditions give reason to expect problems with 

pile integrity, integrity testing of more than 20% of production piles may be required. A typical 

reasonable approach for load-bearing piles is to subject the first 10 to 15 piles to be constructed 

to integrity tests to establish that the contractor’s construction practice at the site is adequate. 

221 
Thereafter, the frequency of such tests can be set to meet the 20% criteria, can be reduced, or 

perhaps eliminated if the construction records for the remaining production piles are similar to 

those of the initial piles that were subjected to integrity tests. 

8.3.13 Unacceptable Piles 

Unacceptable piles are defined as piles that do not meet the project performance criteria with 

regard to load carrying capacity and deflections. The following items constitute construction 

conditions would be considered a basis for pile rejection: 

1.	 Piles that are tested using post-installation integrity testing methods and are judged by 

the Engineer to be unacceptable. 

2.	 Piles subjected to a verification load test where the test indicates the load capacity of 

the pile does not meet the design load and deflection criteria with an appropriate 

factor of safety. 

3.	 Piles for which the data from the automated measuring and recording equipment, 

other recording methods, or the Inspector’s records indicate that a defective pile has 

been installed due to an inadequate penetration rates, grout/concrete volume factors or 

pressures, or other pile installation parameters that do not meet the criteria established 

by the pre-production test program. 

4.	 Piles out of position at the ground surface or not within the plumbness or batter limits 

defined in Section (8.)3.5. 

5.	 Piles in which the top of pile elevation is outside the limits shown on the approved 

working drawings and described in Section (8.)3.9. 

6.	 Piles in which the grout or concrete strength, and/or grout or concrete factor is less 

than as designed. 

7.	 Piles in which the reinforcing steel was not inserted as designed. 

8.	 Piles that exhibit any visual evidence of grout or concrete contamination, excessive 

settlement of grout/concrete, structural damage, or inadequate consolidation of 

grout/concrete (honeycombing). 

Unacceptable piles shall be replaced or repaired at the CFA Pile Contractor’s expense, as 

directed by the Engineer. 

Commentary: In addition to the above list, there may be incidents that cause a pile to be 

unacceptable, such as when lateral communication occurs between piles, or when excessively 

large grout takes occur. The action taken by the CFA Pile Contractor, Inspector, and Engineer 

will vary depending on the circumstances. The soil conditions, design load, and other design 

factors will need to be considered before the pile is rejected or the CFA Pile Contractor is 

allowed to repair or replace the pile. Options include, but are not limited to, abandoning the 

pile, switching from grout to concrete, or allow the pile to be grouted to the best of the CFA Pile 

Contractor’s ability and then re-drill the pile after the grout has had its initial set. Judgment on 

the part of the Engineer and the Design engineer will need to be exercised. 

222 
8.4 MEASUREMENT 

CFA pile foundations shall be measured as per pile. Pre-production testing will be measured as a 

lump sum. Integrity tests and verification load tests will be measured on a per pile basis. 

8.5 PAYMENT 

The work performed and materials furnished in accordance with this Item and measured as 

provided under Section (8.)4 (“Measurement”) will be paid for at the unit prices bid under the 

payment categories listed below. 

Payment categories: 

1.	 Per pile accepted by the Engineer. 

2.	 Per pile placed with access tubes for down-hole integrity testing accepted by the 

Engineer. 

3.	 Per pile for integrity testing on a production pile. 

4.	 Per pile for rapid load test on a production pile. 

5.	 Per pile for dynamic load test on a production pile. 

6.	 Lump sum for pre-production test program as approved by the Engineer. 

The quantities to be paid will be the quantities in each category shown on the approved working 

drawings and as accepted after installation by the Engineer, unless specific changes are required 

in writing by the Engineer. Unit prices that are bid will apply to the extension of any pile to a 

depth up to 120% of the depth for that pile that is shown on the approved working drawings 

when such an increase in depth is required by the Engineer. For such purposes, the length of the 

pile shall be measured between the top of the grout or concrete and the bottom of the pile. If 

increases in depth exceeding 120% of the depth shown on the working drawings are required by 

the Engineer, or if diameters other than those that are shown on the working drawings are 

required by the Engineer, the unit prices shall be renegotiated for those piles involved. 

223 
CHAPTER 9 REFERENCES 

AASHTO (2002). “Standard Specifications for Highway Bridges,” 17th Edition, American 

Association of State Highway and Transportation Officials, Washington, D.C. 

AASHTO (2006). “LRFD Bridge Design Specifications,” 4th Edition, American Association of 

State Highway and Transportation Officials, Washington, D.C. 

ACI (2004). “Building Code Requirements for Reinforced Concrete,” American Concrete 

Institute, Detroit, MI. 

API. (1993). “Recommended Practice for Planning, Designing and Constructing Fixed Offshore 

Platforms - Working Stress Design,” 20th Edition, American Petroleum Institute, Dallas, 

Texas, pp. 191. 

ASTM (2006). “Annual Book of ASTM Standards,” West Conshohocken, PA. 

Brown, D.A., Reese, L.C., and O’Neill, M.W. (1987). “Cyclic lateral loading of a large-scale pile 

group,” Journal of Geotechnical Engineering, ASCE, Vol. 113, No. 11, pp.1326–1343. 

Brown, D.A., Morrison, C. and Reese, L.C. (1988). “Lateral Load Behavior of a Pile Group in 

Sand,” Journal of Geotechnical Engineering, ASCE, Vol. 114, No. GT11, pp. 1261–1276. 

Brown, D.A. and Drew, C. (2000). “Axial Capacity of Augered Displacement Piles at Auburn 

University,” Geotechnical Special Publication No. 100, N. D. Dennis, R. Castelli, and 

M. W. O’Neill (Eds.), ASCE, August, pp. 397–403. 

Bridge Software Institute (2003). “FB-Pier” Version 3.0. University of Florida, Gainesville, FL. 

Bustamante, M., and Gianeselli, L. (1981). “Portance Réele et Portance Calculée des Pieux 

Isolés Sollicités Verticalement,” Revue Francaise de Geotéchnique, No. 16, Presses de l’ 

ENPC, France. 

Bustamante, M., and Gianeselli, L. (1982). “Pile Bearing Capacity by Means of Static 

Penetrometer CPT,” In Proceedings of the 2nd European Symposium on Penetration 

Testing. Amsterdam, pp. 493–500. 

Chin, F.K. (1970). “Estimation of the Ultimate Load of Piles not Carried to Failure,” 

Proceedings of the Second Southeast Asian Conference on Soil Engineering, Singapore, 

Vol. 1, pp. 81–90. 

Clemente, J.L.M., Davie, J.R., and Senapathy, H. (2000). “Design and Load Testing of 

Augercast Piles in Stiff Clay,” Geotechnical Special Publication No. 100, Ed. By N. D. 

Dennis, R. Castelli, and M. W. O’Neill (Eds.), ASCE, August, pp. 398–403. 

224 
Coleman, D.M. and Arcement, B.J. (2002). “Evaluation of Design Methods for Auger Cast Piles 

in Mixed Soil Conditions,” Proceedings of the International Deep Foundations Congress 

2002, February 14-16, 2002 Orlando, Florida; M.W. O’Neill and F.C. Townsend (Eds.), 

ASCE, pp. 1404–1420. 

Collin, J.G. (2004). “Column Supported Embankments - Technical Summary #7. Ground 

Improvement Methods”, FHWA NHI-04-001, October, Federal Highway Administration, 

Washington, D.C. 

Coyle H. M., and Castello, R. R. (1981). “New Design Correlations for Piles on Sand,” Journal 

of the Geotechnical Engineering Division, ASCE, Vol. 106 No. GT7, pp. 965–986. 

Decourt, L. (2003). “Behaviour of a CFA Pile in a Lateric Clay,” Proceedings of the 4th 

International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, BAP 

IV, Ghent, Belgium, pp. 301–308. 

DFI (2005). “Manual for Non Destructive Testing and Evaluation of Drilled Shafts”, Deep 

Foundations Institute, Chernauskas, L.E. (Ed.) Hawthorne, NJ. 

Douglas, D. J. (1983). “Discussion on Paper 17-22: Case Histories,” Proceeding, Conference on 

Piling and Ground Treatment, Institution of Civil Engineering, London, pp. 283. 

Fleming, W.G.K. (1995). “The Understanding of Continuous Flight Auger Piling, Its Monitoring 

and Control,” Proceedings, Institution of Civil Engineers Geotechnical Engineering, Vol. 

113, July, pp. 157–165. Discussion by R. Smyth-Osbourne and reply, Vol. 119, Oct., 1996, 

p. 237. 

Frizzi, R.P. and Meyer, M.E. (2000). “Augercast Piles: South Florida Experience,” Geotechnical 

Special Publication No. 100, N. D. Dennis, R. Castelli, and M. W. O’Neill (Eds.), ASCE, 

August, pp. 382–396. 

Garg, K.G. (1979). “Bored Pile Groups under Vertical Load in Sand,” Journal of the 

Geotechnical Engineering Division, ASCE, Vol. 105, No. GT8, pp. 939–956. 

Gupton, C. and Logan, T. (1984). “Design Guidelines for Drilled Shafts in Weak Rocks in South 

Florida,” Proceedings South Florida Annual ASCE Meeting, ASCE. 

Han, J. and Akins, K. (2002). “Case Studies of Geogrid-Reinforced and Pile-Supported Earth 

Structures on Weak Foundation Soils,” Proceedings of the International Deep Foundation 

Congress, Geotechnical Special Publication No. 116 - Deep Foundations 2002, 

M. W. O’Neill and F. C. Townsend (Eds.), ASCE, Orlando, FL, pp. 668–679. 

Hannigan, P.J., Goble, G.G., Likins, G.E., and Rausche, F., R.R. (2006). “Design and 

Construction of Driven Pile Foundations,” Volume I; NHI courses No. 132021 and 132022 

Reference Manual, April, 968 p. 

225 
Hetenyi, M. (1946). “Beams on Elastic Foundations,” University of Michigan Press, Ann Arbor, 

MI. 

Kaderabek, T. J., Reynolds, R. T. (1981). “Miami limestone foundation design and 

construction,” Journal of the Geotechnical Engineering Division, ASCE, Vol. 127 GT7, 

July, pp. 859–872. 

Kulhawy, F.H. (1984). “Limiting Tip and Side Resistance: Fact or Fallacy?,” Proceedings of the 

Symposium on the Analysis and Design of Pile Foundations. ASCE, San Francisco, CA, 

pp. 80–98. 

Kyfor, Zenon G., Schnere, Austars R. (1992). “Static Testing of Deep Foundations,” Report No. 

FHWA-SA-91-042, Federal Highway Administration, Washington, D.C. 

McVay, M., Armaghani, B, and Casper, R. (1994). “Design and Construction of Auger-Cast 

Piles in Florida,” Transportation Research Record 1447, Design and Construction of Auger 

Cast Piles, and Other Foundation Issues, Washington, pp. 10–18. 

McVay, M.C., Casper, R., and Shang, T. (1995). “Lateral Response of Three Row Groups in 

Loose to Dense Sands at 3D and 5D Pile Spacing,” ASCE, Journal of Geotechnical 

Engineering, ASCE, Vol. 121, No. 5, pp 436–441. 

Meyerhof, G.G. (1976). “Bearing Capacity and Settlement of Pile Foundations,” Journal of 

Geotechnical Engineering, ASCE, Vol. 102, GT3, pp. 195–228. 

Mindess, S., Young, J. F., and Darwin, D. (2003). “Concrete” 2nd Edition, Prentice Hall, Upper 

Saddle River, NJ, 644 p. 

Moss, R.E.S. (1997). “Cyclic Lateral Loading of Model Pile Groups in Clay Soil: Phase 2B,” 

Masters Thesis, Utah State University. 

Nataraja, M. S., and Cook, B. E. (1983). “Increase in SPT N-Values Due to Displacement Piles,” 

Journal of the Geotechnical Engineering Division, ASCE, Vol. 109, No. GT1, pp. 102–113. 

Neely, W. J. (1991) “Bearing Capacity of Auger-Cast Piles in Sand,” Journal of Geotechnical 

Engineering, ASCE, Vol. 117, No. 2, pp. 331–345. 

NeSmith, W.M. (2002). “Static Capacity Analysis of Augered, Pressure-Injected Displacement 

Piles,” Geotechnical Special Publication No. 116, M. W. O’Neill and F. C. Townsend 

(Eds.), ASCE, February, Vol. 1, pp. 1088–1097. 

O’Neill, M. W., Ata, A., Vipulanandan, C., and Yin, S. (2002). “Axial Performance of ACIP 

Piles in Texas Coastal Soils,” Geotechnical Special Publication No. 116, Ed. by M. W. 

O’Neill and F. C. Townsend (Eds.), ASCE, February, Vol. 1, pp. 1290–1304. 

226 
O’Neill, M. W., Vipulanandan, C., Ata, A., Tan, F. (1999). “Axial Performance of ContinuousFlight-Auger Piles for Bearing,” Final report to the Texas Department of Transportation, 

Report No. 7-3940-2, August, 254 p. 

O’Neill, M.W. and Reese, L.C. (1999). “Drilled Shafts: Construction Procedures and Design 

Methods,” FHWA Report No. IF-99-025, Federal Highway Administration, Washington, 

D.C. 

O’Neill, M.W., Vipulanandan, C., and Hassan, K. (2000). “Modeling of Laterally Loaded ACIP 

Piles in Overconsolidated Clay,” Geotechnical Special Publication No. 100, N. D. Dennis, 

R. Castelli, and M. W. O’Neill (Eds.), ASCE, August, pp. 382–396. 

Peck, R. B., Hanson, W. E., Thornbum, T. H. (1974). “Foundation Engineering”, 2nd Edition, 

Wiley & Sons, New York, NY. 

Ramos, H.R., Antorena, J.A., and McDaniel, G.T. (1994) “Correlations between the Standard 

Penetration Testing (SPT) and the Measured Shear Strength of Florida Natural Rock, in 

Proceedings FHWA International Conference on Design and Construction of Deep 

Foundations, Orlando, FL, pp. 699–711. 

Reese, L. C. (1986). “Behavior of Piles and Pile Groups Under Lateral Load”, Publication No. 

FHWA-RD-85-106, Federal Highway Administration, Washington, D.C. 

Reese, L. C., and O’Neill M. W. (1988). “Drilled Shaft: Construction Procedures and Design 

Methods,” FHWA-HI-88-042, Federal Highway Administration, Washington, D.C. 

Reese, L., Wang, S-T., Arrellaga, J.A., and Hendrix, J. (2006). “LPILE - A Program for the 

Analysis of Piles and Drilled Shafts Under Lateral Loads.” Version 5.0 Plus, ENSOFT, Inc., 

Houston, TX. 

Reese, L., Wang, S-T., Arrellaga, J.A., and Hendrix, J. (2006). “GROUP - A Program for the 

Analysis of a Group of Piles Subjected to Axial and Lateral Loading,” Version 7.0, 

ENSOFT, Inc., Houston, TX. 

Rizkallah, V. and Bruns, T. (1988). “Estimation of Pile Bearing Capacity of Cast-in-Place 

Screwed Piles,” Proceedings of the 3rd International Geotechnical Seminar on Deep 

Foundations on Bored and Auger Piles, BAP III, Ghent, Belgium, pp. 417–424. 

Rollins, K. M., Peterson, K. T., and Weaver, T. J. (1998). “Lateral load behavior of full-scale 

pile group in clay, “Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 

Vol. 124, No. 6, pp. 468.478. 

Ruesta, P.F., and Townsend, F.C. (1997). “Evaluation of laterally loaded pile group at Roosevelt 

Bridge,” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 123, No. 

12, pp. 1153–1161. 

227 
Sabatini, P.J., Tanyu, B., Armour, T., Groneck, P., and Keeley, J. (2005). “Micropile Design and 

Construction,” FHWA NHI-05-039; NHI Course 132078 Reference Manual, December, 436 p. 

Semeraro, M.A. (1982). “Evaluation of and Design Considerations for Drilled Shafts Socketed 

into Coral and Coquina Limestones,” MS Thesis, Massachusetts Institute of Technology, 

Dept. of Civil and Environmental Engineering. 

Senna R. S., Cintra, J. C. A., Rezende, M. E. B. (1993). “Load Distribution In Bored Pile 

Groups,” In Proceedings of the Second International Geotechnical Seminar on Deep 

Foundations on Bored and Auger Piles, Ghent, Belgium, Balkema, Rotterdam, pp. 151–154. 

Terzaghi, K. and Peck, R.B. (1967). “Soil Mechanics in Engineering Practice,” 2nd 

Edition, John Wiley & Sons, New York, NY. 

Texas Highway Department (1972). “Foundation Exploration and Design Manual,” Bridge 

Division, 2nd Edition, July. 

Tomlinson, M. J. (1957). “The Adhesion of Piles Driven in Clay Soils,” in Proceedings of the 

4th International Conference on Soil Mechanics and Foundation Engineering, Vol. 2, 1957, 

pp. 66–71, Butterworths Scientific Publications, Ltd. London, England. 

Tomlinson, M.J. (1994). “Pile Design and Construction Practice,” 4th Edition, E & FN Spon, 

Chapman and Hall, London, 411 p. 

U.S. Army Corps of Engineers. (1994) “Standard Test Method for Flow of Grout for PreplacedAggregate Concrete (Flow Cone Method) (ASTM C 939-94a),” CRD 611–94. 

Viggiani, C. (1993) “Further Experiences with Auger Piles in Naples Area,” Proceedings of the 

2nd International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, 

BAP II, Ghent, Belgium, pp. 445–458. 

Vipulanandan, C., Kim, M.G., and O’Neill, M.W. (2004). “Axial Performance of Continuous 

Flight Auger Piles for Bearing”, Project Report No. 7-3940-2, Texas Department of 

Transportation, 253 pp. 

Webb, D., Everts, H.J., de Boer, F., and Brons, K.F. (1994). “Bearing Capacity of Piles 

Influenced by Building Stages,” 13th International Conference on Soil Mechanics and 

Foundation Engineering, Vol. 2, p. 465, Balkema, Rotterdam. 

Wright, S.J. & Reese, L.C. (1979). “Design of Large Diameter Bored Piles,” Ground 

Engineering, Vol. 12, No. 8, pp. 17–51. 

Zelada, G. A., and Stephenson, R. W. (2000). “Design Methods for Auger CIP piles in 

Compression,” New Technological and Design Developments in Deep Foundations, ASCE 

Geotechnical Special Publication No. 100, N. D. Dennis, R. Castelli and M. W. O’Neill 

(Eds.), ASCE, August, pp. 418–432. 

228 
APPENDIX A COMPARISONS OF METHODS FOR ESTI MATING TH E 

STATIC AXIAL CAPACITY OF CFA PILES 

A.1 INTRODUCTION 

This appendix provides background documentation used to select the recommended method for 

computing the static axial capacity presented in Chapter 5, and to summarize alternative 

methods. The methods used for estimating the static axial capacity of continuous flight auger 

(CFA) piles include methods developed from evaluation of load tests conducted on CFA piles 

and methods developed for driven piles and drilled shafts. Most of the methods developed 

specifically for CFA piles are modifications of the methods developed originally for drilled 

shafts or driven piles, which are based on in-situ soil parameters. Results from four comparative 

studies, which were conducted to asses the effectiveness of several of these methods, are also 

presented. The recommendations made in Section 5.3 are based on the main findings of these 

comparative studies. 

The methods for estimating the static axial capacity of CFA piles are commonly separated for 

cohesive and cohesionless soils. In addition, the axial capacity has two components: the unit 

side shear capacity (fs) and the bearing unit capacity (qp). The ultimate shear capacity is obtained 

by integrating the fs values along the pile length. The ultimate bearing capacity is obtained by 

multiplying the qb by the pile tip cross sectional area. 

In cohesive soils, the static axial capacity of CFA piles is commonly estimated with correlations 

based on the undrained shear strength (Su) of the soil. The soil undrained shear strength is 

estimated in the filed using in-situ techniques (i.e., SPT or CPT) or in the laboratory (e.g., 

undrained triaxial tests on undisturbed samples). The ultimate side shear capacity is typically 

estimated using the “alpha method”, in which the factor α is dependant on Su. In general, ƒ s at a 

given depth is calculated as follows: 

ƒ s = α Su (Equation A-1)

The end-bearing unit capacity (qp) is typically estimated by a bearing capacity factor multiplied 

by Su. 

In cohesionless soils, the static axial capacity of CFA piles is commonly estimated following an 

effective stress approach for side shear and in-situ test parameters for the end-bearing resistance. 

The unit side shear capacity at a given depth is typically calculated as follows: 

ƒ s = β σv ' (Equation A-2)

where β is the beta factor and σv ′ is the vertical effective stress. With β = Ks tan δ, where Ks is 

the coefficient of lateral earth pressure and δ is the pile-to-soil friction angle. Beta factors and 

end-bearing capacity parameters are correlated with SPT-N values. 

A-1 
Silty soils that cannot be easily classified as cohesive or cohesionless require judgment to 

evaluate which method is more appropriate for selecting a resistance parameter. If the silty soil 

is expected to behave in an undrained manner, methods for cohesive soils should be used. 

Conversely, if the silty soil is expected to behave in a drained manner, methods for cohesionless 

soils should be used. 

Several methods exist that use correlations with in-situ test parameters to estimate side shear and 

end-bearing capacities in a variety of soil types. These methods are presented in the following 

sections. 

A.2 METHODS FOR AXIAL CAPACITY OF CFA PILES 

The methods presented are introduced in the chronological order they were published. 

A.2.1 Wright and Reese (1979) Method 

Wright and Reese (1979) developed a method for predicting the ultimate capacity of drilled 

shafts and CFA piles in sand. In this method, the average ultimate side shear resistance, fs ave, is 

calculated as: 

f s ave = σ' 

V ave Ks tan φ ≤ 0.15 MPa (≤ 1.6 tsf) (Equation A-3) 

Where σ’ v ave is the average vertical effective stress along the pile, Ks is the lateral earth pressure 

coefficient (assumed to be 1.1), and φ is the sand angle of internal friction. The value φ is a 

weighted average of the angle of internal friction of each sand layer along the pile length. 

The ultimate end-bearing resistance is calculated as: 

qp (MPa) = 0.064 N ≤ 3.8 (MPa) (Equation A-4a)

qp (tsf) = 0.67 N ≤ 40 (tsf) (Equation A-4b)

where N is the SPT-N value (blows/0.3 m [1 ft]) near the tip of the pile. 

A.2.2 Douglas (1983) Method 

Douglas (1983) developed a method for predicting the capacity of CFA piles based on full scale 

load test results of 28 CFA piles in sand in the UK and other European countries. The ultimate 

unite side shear resistance at a given depth is calculated as: 

fs = σ ' v Ko tanφ (Equation A-5)

Where σ’ v is the vertical effective stress, Ko is the lateral earth pressure coefficient (assumed to 

be 1.0), and φ is the sand angle of internal friction. The vertical effective stress is limited for 

depths greater than 6 or 10 pile diameters in loose and medium dense sands, respectively. 

A-2 
The ultimate capacity was defined occurring at a pile tip displacement of 30 mm (1.2 in.) 

although the bearing resistance was often observed to mobilize at displacements greater than 100 

mm (4 in.). The ultimate end-bearing resistance is calculated from the Dutch Cone point 

resistance (qc) as: 

q p = 0.25 qc (Equation A-6)

A.2.3 Rizkalla (1988) Method 

The Rizkalla (1988) method was developed in Germany to the axial capacity of CFA piles based 

on the CPT tip resistance (qc). Rizkalla (1988) based his methods on a database of load tests on 

CFA piles. The method appears to provide conservative predictions for high displacement screw 

piles. 

Cohesive Soils (0.025 ≤ Su≤ 0.2 MPa) 

The ultimate unit side shear in cohesive soils for a given depth is calculated as: 

fS (MPa) = 0.02 + 0.2 Su (MPa) (Equation A-7)

The ultimate unit end-bearing resistance, defined occurring at a pile tip displacement of 5% of 

the pile diameter, is calculated as: 

qp (MPa) = 6 Su (Equation A-8)

Su can be estimated from the CPT tip resistance (qc) as: 

q − σ S = c v

u NC (Equation A-9)

Where σv is the total vertical stress at the tip of the pile, and Nc is the cone factor, which ranges 

from 16 to 22. Alternatively, Su may be estimated conservatively from unconfined compressive 

strength (qu), with Su = 0.5 qu, an approach that is commonly used in many methods currently 

employed in Europe. 

Cohesionless Soils 

In cohesionless soils, the ultimate unit side shear at a given depth is calculated as: 

fS = 0.008 qc (MPa) (Equation A-10)

where qc is the CPT tip resistance. 

A-3 
In cohesionless soils, the ultimate unit end-bearing resistance is calculated as: 

qp (MPa) = 0.12 qc (MPa) + 0.1 for qc ≤ 25 MPa (Equation A-11) 

A.2.4 Neely (1991) Method 

Neely (1991) developed correlations for sandy soils using a database of load tests on 66 CFA 

piles performed by various researchers. In this method, the effective overburden stress is 

computed at the mid-depth of the overall pile length. Only one layer of sand is assumed in this 

method. The average ultimate unit side shear capacity is calculated as follows: 

' f = K	 p tanδ = β p 

' ≤ 1.4 tsf (Equation A-12) S s	 0 0 

ƒs = average ultimate unit side shear resistance along pile; 

β = factor (referred to as the skin friction factor in Neely’s method), which is a 

function of the pile length (see Figure A.1) and is limited to β ≥ 0.2; 

Ks	 horizontal earth pressure coefficient; 

po ’ average vertical effective stress along pile length; and 

δ		 angle of friction at the pile- soil interface. 

In this method, the ultimate unit end-bearing resistance for sandy soils is correlated to the SPT-N 

value near the pile tip. Neely (1991) used load test results from Roscoe (1983) and Van Den 

Elzen (1979) and equivalent SPT-N values, which were correlated with CPT values employing a 

the relationship developed by Robertson et al. (1983). The unit end-bearing capacity is 

calculated as follows: 

where: 

qp tsf (tsf) = 1.9 N ≤ 75 (Equation A-13)

where N is the SPT-N value. 

A.2.5 Viggiani (1993) Method 

Viggiani (1993) developed correlations for cohesionless soils based on load test results on CFA 

piles and CPT tip resistance, qc. The load tests and CPTs were performed near Naples, Italy, 

where soils are volcanic (mostly pyroclastic). The ultimate unit side shear at a given depth is 

calculated as: 

fS = α ⋅ qc	 

 (Equation A-14)

6.6 + 0.32 qc (MPa ) α = 

300 + 60 qc (MPa) With: 

In these cohesionless soils, the ultimate unit end-bearing resistance is calculated as: 

A-4 
qp (MPa) = qc( ave ) (Equation A-15)

where qc (ave) is the average CPT tip resistance calculated in the depth interval of 4 pile diameters 

above and 4 pile diameters below the pile tip. 

Factor β 

0 0.5 1 1.5 2 2.5 3 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

Pile Length (L) 

β = 0.2 

Figure A.1: β Factor vs. Pile Length (Neely, 1991) 

A.2.6 Decourt (1993) Method 

Decourt (1993) method was developed for CFA pile in residual soils (silt and silty soils) and was 

developed from load tests results. This method relies on the apparent shear resistance developed 

at the maximum torque required to twist a standard penetration test (SPT) split spoon sampler, 

after it has been driven into the bottom of the borehole. This method relies on the assumption 

that the influence of SPT dynamic penetration is eliminated during the subsequent twisting of the 

sampler in place. The ultimate unit side shear capacity for a given pile segment is assumed to be 

the same as the unit side shear developed during application of the maximum torque, or: 

fS = fS spoon) (during maximum torque of SPT (Equation A-16) 

A-5 
In these soils, the ultimate unit end-bearing resistance is calculated as: 

qp = 0 5. K' (MPa) N eq q c ≤ 25 (Equation A-17)

where K’ a factor dependent on soil type at the tip of the pile according to: 

 0.10 MPa (clays), 0.12 MPa (clayey silts), 0.14 MPa (sandy silts), 

 and 0.20 MPa (sands); and 

Neq average equivalent N value (blows/ft) from the SPT-torque test near the tip of the 

pile. It represents a correction factor and is Neq.= 0.83 T, where T is the torque in 

(kgf-m) measured in the SPT sampler. 

A.2.7 Clemente et al. (2000) Method 

Three CFA test piles were installed in clay soils that ranged from very stiff to hard at three sites 

in Louisiana, Mississippi, and Texas. Alpha values (α) were back-calculated from load test side 

shear data and compared with Su values. This relationship verified the common belief of a 

decreasing α with increasing Su, as shown below in Figure A.2. 

α value 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0 

LA site, Meyerhof (1986) 

LA site, FHWA (1988) 

MS site, Meyerhof (1986) w/ cutoff 

MS site, FHWA (1988) 

TX site, Meyerhof (1986) 

TX site, FHWA (1988) 

0 50 100 150 200 250 300 350 400 

Undrained Shear Strength, S (kPa) u 

Figure A.2: α vs. Undrained Shear Strength - Clayey Soils (Clemente et al., 2000) 

A-6 
A.2.8 Frizzi and Meyer (2000) Method 

Frizzi and Meyer (2000) published capacity relationships for CFA piles obtained from over 60 

load testes on drilled shafts and CFA piles in the Miami and Fort Thompson limestone 

formations found in South Florida (Broward and Miami-Dade Counties). Procedures for this 

method are detailed in Chapter 5.3. 

A.2.9 Zelada and Stephenson (2000) Method 

Zelada and Stephenson (2000) studied the results of 43 full-scale compression load tests, five of 

which were fully instrumented, and ten pull-out tests of CFA piles in sandy soils. They 

compared the adequacy of various capacity prediction methods. Results of the comparative 

study by Zelada and Stephenson are detailed in Section A.6.2. 

Their study recommended modifications to the β factor and unit tip values of the FHWA 1999 

method (O’Neill and Reese, 1999) to reflect their observations of decreased side shear and 

increased end-bearing in CFA piles when compared to those for drilled shafts. Their method 

estimates less side shear resistance than the FHWA method and thereby recommends a reduced β 

factor, only 0.8 of that of the FHWA. Figure A.3 shows the β factor from Zelada and 

Stephensons (2000) and from the FHWA 1999 method for comparison. The reduction in the β 

factor with respect to that of the FHWA method accounts for the reduced soil stress that tend to 

occur due to soil mining during CFA pile installation. This effect may be more pronounced in 

clean sands. As discussed in the main text of this document, this effect may be reduced or 

eliminated by preventing auger over-rotation relative to its penetration rate. 

Note that the β factor is also reduced for SPT-N values less than 15, as it is with the FHWA 1999 

method. In this method, the expression for β as a function of pile depth is: 

for N ≥ 15 bpf 

1 2 0 11 (ft) 0.5 β = − Z.. (Equation A-18a)

0 21 2 (m) 0.5 β = − Z.. (Equation A-18b)

for N < 15 bpf 

 

 

( 0 111 2 )(ft) 15 

0.5 Z.. N β = − (Equation A-18c)

( )(m)0 21 2 15 

0.5 Z.. N β = − (Equation A-18d)

The range of β in the Zelada and Stephenson (2000) method is 0.20 ≤ β ≤ 0.96, which takes into 

account the reduction factor of 0.8. 

In their analyses, the ultimate end-bearing resistance was defined at a pile tip displacement of 

10% of the pile diameter. The ultimate unit end-bearing resistance in this method, which is 

A-7 
based on test data from instrumented CFA load tests in cohesionless soils, is correlated to SPT-N 

values near the tip of the pile, as follows: 

qp tsf (tsf) = 1.7 N ≤ 75 (Equation A-19a)

qp MPa (MPa) = 0.16 N ≤ 7.2 (Equation A-19b)

Note that this correlation gives an ultimate end-bearing resistance that is 2.8 times greater than 

that estimated with the FHWA method for the same SPT-N value. Figure A.4 shows the 

recommended qp value as a function of SPT-N values and determined from instrumented CFA 

load tests. The correlation from the FHWA 1999 method for drilled shafts (i.e., “Reese & 

O’Neill”), the Meyerhof method for driven piles, and the Neely method (1991) for CFA piles are 

shown for comparison. 

 

Factor β 

0 0.5 1 1.5 2 2.5 3 3.5 

0 

Depth (m) 

5 

10 

15 

20 

25 

0.8 (1.5 - 0.244 z 0.5 [in m]) 

(R

1.5 - 0.244 z 0.5 [in m] 

eese and O'Neill, 1988) 

Data fro

Strain Gau

m 

ges 

Source: Zelada and Stephenson (2000) 

Figure A.3: β Factor vs. depth - Zelada and Stephenson (2000) and FHWA 1999 Methods 

A.2.10 Coleman and Arcement (2002) Method 

Coleman and Arcement (2002) compared the results of load tests conducted on 32 CFA piles in 

mixed soil conditions and evaluated the adequacy of various capacity prediction methods. Their 

study recommended modifications to the α-factor for cohesive soils and β factor for cohesionless 

A-8 
soils contained in the FHWA 1999 method. Results of the comparison study conducted by 

Colman and Arcement of several different commonly used methods are detailed in Section A.6.3 

of this Appendix and their recommended modifications to the α and β factors of the FHWA 1999 

method are included in Chapter 5.3. Coleman and Arcement did not propose any modifications 

/methods to estimate the end-bearing resistance. 

A.2.11 O’Neill et al. (2002) Method 

O’Neill et al. (2002) developed a method by analyzing a database on CFA piles data and data 

from the three fully instrumented load tests performed on CFA piles in geologically diverse sites 

of coastal Texas in 1999 (O’Neill et al., 1999). These sites are designated as “UH” (over 

consolidated clay), “Baytown” (mixed soil conditions), and “Rosenburg” (sands). In these three 

sites, the nominal diameter of the CFA piles was 0.46 m (18 in.) for all piles while the 

embedment depths were 15.2 m (50 ft), 15.2 m (50 ft), and 9.1 m (30 ft), respectively, for each of 

these sites. 

 

450 

400 

Unit Tip Resistance (tsf) 350 

300 

250 

200 

150 

100 

50 

0 

Average Unit Tip = 1.7 N 

Data from Measured Loads 

Meyerhof (Driven Piles) 

Neeley 

Reese and O'Neill 

0 20 40 60 80 100 

SPT - N value (bpf) 

Source: Zelada and Stephenson (2000) 

Figure A.4: Ultimate Unit End-Bearing Resistance vs. SPT-N values - Zelada and 

Stephenson (2000) and Other Methods 

Based on the load tests mentioned above, O’Neill et al. (2002) presented a normalized loadsettlement curve shown in Figure A.5, which may be suitable for use with CFA piles with similar 

aspect ratios and in similar geologic formations. Given the ultimate total load (Qt), Figure A.3 

A-9 
may be used to predict the total load (Q) at a given displacement ratio of pile displacement (w) to 

pile diameter (B). 

A.3 METHODS FOR AXIAL CAPACITY OF DRILLED SHAFTS APPLICABL E 

CFA PILES 

A.3.1 TxDOT Method (1972) 

Cohesive Soils 

For cohesive soils, this method (developed by Texas Department of Transportation, 1972) uses 

the undrained shear strength to estimate the side shear resistance and the blow count obtained 

from the TxDOT Dynamic Cone Penetrometer test to estimate the end-bearing resistance. 

Although the TxDOT Dynamic Cone Penetrometer is a relatively uncommon test, this method 

yielded good results for CFA piles in clays (O’Neill et al., 2002). Therefore, this method was 

recommended as an alternate way of predicting capacities in cohesive soils and the procedures 

are detailed in Section 5.3. 

Q/Qt 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 

0.1 

0.09 

0.08 

0.07 

0.06 

0.05 

0.04 

0.03 

0.02 

0.01 

0 

w/B 

Bounds 

Design Curve 

Figure A.5: Normalized Load-Settlement Relationship for Design of CFA Piles - Clay Soils 

of Texas Gulf Coast (O’Neill et al., 2002) 

A-10 
Cohesionless Soils 

For cohesionless soils, this method estimates the ultimate unit side-shear resistance using the 

blow count from a TxDOT Dynamic Cone Penetrometer (NTxDOT) according to the following 

Equation: 

⎛ N ⎞ f S (tsf) = 1.4 ⎜ TxDOT ⎟ ⎝ 80 ⎠ f ≤ 2.5 (tsf) with s (Equation A-20)

The ultimate end-bearing resistance in cohesionless soils is also determined using the blow count 

from the TxDOT Dynamic Cone Penetrometer (NTxDOT) as follows: 

N 

qp (tsf) = TxDOT

8.25	 (Equation A-21)

If the pile diameter is less than 0.6 m (24 in.), the ultimate end-bearing resistance is selected as 4 

tsf for cohesionless soils. 

A.3.2 FHWA 1999 Method 

The FHWA Method, originally proposed by Reese and O’Neill (1988) and latter modified by 

O’Neill and Reese (1999), has become perhaps the most recognized method for prediction of 

drilled shaft capacities, and has often been used to determine axial capacity of CFA piles. The 

comparison studies summarized in Section A.6 of this Appendix consistently show that FHWA 

method is reliable in estimating CFA pile capacities in both cohesive and cohesionless soils. 

This method is presented as the recommended method for estimating CFA pile capacity in both 

cohesive and cohesionless soils. Procedures for this method are presented in Section 5.3. 

A.4 METHODS FOR DRIVEN PILES APPLICABLE TO CFA PILES 

A.4.1 Coyle and Castello (1981) Method 

Cohesive Soils 

Coyle and Castello (1981) recommended the use of Tomlinson’s Method (1957) to obtain the 

average unit side shear capacity of the pile using Equation A-20: 

f Sa = α ⋅ S	 ua (Equation A-22)

where: Sua = average undrained shear strength along the pile length; and 

α = factor that varies from 0.2 to 1.0 and is a function of the average undrained 

shear strength along the pile length, as shown in Figure A.6. 

The ultimate unit end-bearing resistance in cohesive soils is calculated using the following: 

q p u = 9 ⋅ S (Equation A-23)

A-11 
Cohesionless Soil 

Coyle and Castello (1981) also presented estimates of the ultimate side shear and end-bearing 

capacities for driven piles in sand based on the sand angle of internal friction and the ratio of pile 

embedded depth (L) to pile diameter/width (D). 

In this method, the ultimate side shear resistance (i.e., maximum skin friction in the original 

method) can be determined from Figure A.7a, while the ultimate end-bearing resistance (i.e., 

maximum toe resistance in the original method) can be determined from Figure A.7b,. The 

ultimate end-bearing resistance was limited to 100 tsf for driven piles tipped into sand. 

Coyle and Castello (1981) also recommended that the angle of internal friction of the soil (φ) be 

obtained from Figure A.8, which presents the relationship between SPT N values and φ. Friction 

angles in this Figure are based on Peck et al. (1974). For the case of silty sands below the water 

table, and for SPT N values greater than 15, Coyle and Castello (1981) recommended that SPT N 

values be corrected according to the following expression: 

N’=15 + 0.5 (N - 15) (Equation A-24) 

The corrected N value (i.e., N’) can be utilized in the relationship between SPT N values and φ as 

well as the pile capacity design charts shown in Figure A.7. 

A.4.2 American Petroleum Institute (API) (1993) Method 

Cohesive Soils 

The ultimate unit side shear resistance for a pile segment in cohesive soils is calculated using an 

α factor as follows: 

f S u = α S (Equation A-25)

where: Su = undrained shear strength 

α = a function of Su and the vertical effective stress of the soil (as shown below) and 

ranges from 0.5 to 1.0 

α = 0.5/Ψ0.5, for Ψ < 1.0 

α = 0.5/Ψ0.25, for Ψ ≥ 1.0 

Where Ψ = Su/σv’, and σv ’= vertical effective stress of the soil at the depth of interest. 

For cohesive soils, the ultimate unit end-bearing resistance is calculated as follows: 

qp = 9 Su (Equation A-26)

A-12 
 

Figure A.6: α vs. Average Undrained Shear Strength along Pile Length (Coyle and 

Castello, 1981) 

Figure A.7. (a) Unit Side-Shear Capacity and (b) End-Bearing Capacity in Cohesionless 

Soils (Coyle and Castello, 1981) 

A-13 
Figure A.8. Relationship between SPT N Values and φ (Coyle and Castello, 1981) 

Cohesionless Soils 

The ultimate unit side shear resistance for a pile segment in cohesionless soils is calculated as 

follows: 

fS = K σ V 

' tan δ		 (Equation A-27)

where: K = horizontal earth pressure coefficient; 

σv’ = vertical effective stress of the pile segment 

δ = angle of friction at the pile - soil interface, which may be estimated from 

Table A.1 

The value for K in is assumed at: a) 0.8 for non-displacement piles and open-ended driven piles; 

and b) 1.0 for driven piles that have plugged. Therefore, assuming a K value of 1.0 would be 

most appropriate for CFA. Table A.1 lists limiting unit side shear resistance (i.e. skin friction), 

as well as typical values of soil-pile friction angles, which may be used if no other values are 

available. 

The ultimate unit end-bearing resistance in cohesionless soils is calculated as follow: 

qp = σ V ' Nq	 

 (Equation A-28)

where: σv’ = vertical effective stress of the pile segment; and 

Nq = bearing capacity factor. 

A-14 
The unit end-bearing resistance for cohesionless soils is limited in the Coyle and Castello (1981) 

and the API (1993) methods. For driven piles, the soil below the driven pile tip is compacted 

and highly stressed after driving. It is likely that the limiting unit end-bearing values for CFA is 

smaller because the effect of overstressing is lacking in CFA piles. 

Table A.1. Soil-Pile Friction Angle, Limiting Unit Side Shear Resistance, and Limiting 

End-bearing Values (API, 1993) 

Density Soil 

Description 

Soil-Pile 

Friction Angle 

δ (deg) 

Limiting Skin 

Friction, fs 

in kPa (kips/ft2) 

Bearing 

Capacity 

Factor, Nq 

Limiting Unit Endbearing Values, 

in MPa (kips/ft2

) 

Very Loose 

Loose 

Medium 

Sand 

Sand-Silt 

Silt 

15 47.8 (1.0) 8 1.9 (40) 

Loose 

Medium 

Dense 

Sand 

Sand-Silt 

Silt 

20 67,0 (1.4) 12 2.9 (60) 

Medium 

Dense 

Sand 

Sand-Silt 25 81.3 (1.7) 20 4.8 (100) 

Dense 

Very Dense 

Sand 

Sand-Silt 30 95.7 (2.0) 40 1.9 (200) 

Dense 

Very Dense 

Gravel 

Sand 35 114.8 (2.4) 50 1.9 (250) 

A.5 METHOD FOR DRILLED SHAFTS AND DRIVEN P ILES APP LICABLE TO 

CFA PILES 

Bustamonte and Gianeselli (1981, 1982) reported that the Laboratorie Des Ponts et Chausse 

(LPC) in France developed design procedures for use in the design of both driven piles and 

drilled shafts. This method is referred to as the LPC method. In this method, correlations were 

developed for cohesive and cohesionless soils based on CPT tip resistance measurements. While 

the original method is uses an average ultimate unit side shear resistance for the entire pile, the 

technique has also been applied to layered soils where the design charts are utilized for average 

CPT tip resistances measured at different depths along the pile length. The comparative studies 

summarized in Section A.6 of this Appendix show that this method is reliable in estimating 

capacities of CFA pile in both cohesive and cohesionless soils. This method is presented as an 

alternative for estimating CFA pile capacity in soils when CPT qc data is available. The 

procedures of this method are presented in Section 5.3. 

A-15 
 

A.6 COMPARISON OF DESIGN METHOD S FOR AXI AL CAPACITY OF CF A 

PILES 

Several studies have been conducted in the last few years, between 1994 and 2002, to compare 

load tests results on CFA piles to capacities predicted by various static analysis methods. These 

comparisons were made using existing load testing databases and, in some cases, were 

augmented with additional load test programs. The comparative studies report results according 

to soil type and for normal construction of CFA piles (i.e., drilled displacement piles were not 

considered in these studies). 

A.6.1 Comparison of Five Methods in Predominantly Sandy Soils (McVay et al., 1994) 

McVay et al. (1994) studied the results of 17 full-scale compression load tests and four pullout 

tests of CFA piles located at 21 different sites throughout Florida. The subsurface soils consisted 

of sandy soils in for 19 test piles, while clay was predominant in two test piles (both compression 

tests). The ultimate resistance was evaluated in their study at displacements defined by: (1) the 

Davisson Criteria; (2) a load corresponding to displacement equal to 2% of the pile diameter; and 

(3) load corresponding to displacement equivalent to five percent of the pile diameter. 

Five methods were evaluated: Wright and Reese (1979), Neely (1991), LPC (1981), original 

FHWA (Reese and O’Neill, 1988); and Coyle and Castello (1981). In the comparison, the mean 

and standard deviations of the ratio of the measured (Qt meas) to predicted (Qt pred) resistances 

developed in the McVay et al. (1994) study. These quantities are presented in Table A.2. The 

study concluded that all methods provided reasonably accurate estimates of total capacity when 

failure was defined as 5% of the pile diameter displacement. The results for the 5% criteria are 

illustrated in Figure A.9. This study concluded that the original FHWA method (Reese and 

O’Neill, 1988) for drilled shafts provided the best prediction for ultimate total pile capacity in 

sandy soils and this is followed closely by the Wright and Reese Method (1979) for CFA piles in 

sand. 

A.6.2 Comparison of Eight Methods in Predominantly S andy Soils ( Zelada and 

Stephenson, 2000) 

Zelada and Stephenson (2000) studied the results of 43 full-scale compression load tests and ten 

pullout tests of CFA piles located at 28 sites locations in the United States and Europe. 

Subsurface soils ranged from medium dense to dense, silty to fine sands. Installed piles that had 

more than 25 percent of clay along their length were not included in this study. 

The ultimate resistance was defined at displacements of 5 to 10% of the pile diameter. The pile 

diameters ranged from 0.3 to 0.6 m (12 to 24 in.), with the majority within 0.40 to 0.45 m (16 to 

18 in.) diameter range. The pile lengths ranged from 7.5 to 21 m (25 to 70 ft), with the majority 

between 9 and 12 m (30 and 40 ft). All piles were constructed with sand-cement grout, except 

those reported by Roscoe (1983), which were constructed using concrete. 

Eight methods for static capacity were evaluated using this database: Viggiani (1993), Reese and 

O’Neill (1988), LPC (1981), Wright and Reese (1979), Rizkalla (1988), Coyle and Castello 

A-16 
Pile No. Wright Neely LPC FHWA Coyle 

Davisson 2% Dia 5% Dia Davisson 2% Dia 5% Dia Davisson 2% Dia 5% Dia Davisson 2% Dia 5% Dia Davisson 2% Dia 5% Dia 

1 1.71 1.64 1.14 2.15 2.06 1.43 3.00 2.87 2.00 2.00 1.91 1.33 2.50 2.39 1.67 

2 1.30 1.56 1.01 1.82 2.18 1.42 2.01 2.40 1.56 1.49 1.78 1.16 3.33 3.98 2.59 

3 0.92 0.95 0.95 0.95 0.99 0.98 1.11 1.15 1.14 0.99 1.03 1.02 1.43 1.49 1.47 

4 0.81 0.87 0.70 0.86 0.92 0.75 1.47 1.58 1.28 0.94 1.02 0.82 0.79 0.86 0.69 

5 1.55 1.72 1.03 2.54 2.82 1.69 2.30 2.55 1.53 1.64 1.82 1.09 3.14 3.49 2.09 

6 0.77 0.87 0.64 1.69 1.90 1.41 1.15 1.29 0.96 0.89 1.00 0.74 1.32 1.48 1.09 

7 1.04 1.14 0.75 1.72 1.89 1.24 1.52 1.67 1.09 1.18 1.29 0.85 2.23 2.45 1.60 

8 3.10 3.54 1.98 1.51 1.72 0.96 3.49 3.99 2.24 3.16 3.61 2.02 2.44 2.79 1.50 

9 1.01 0.93 0.71 1.66 1.52 1.15 1.83 1.68 1.28 1.30 1.19 0.90 2.73 2.50 1.90 

10 1.06 1.25 0.94 0.69 0.81 0.61 1.42 1.67 1.25 1.16 1.36 1.02 1.24 1.45 1.09 

11 1.19 1.52 1.04 1.18 1.50 1.03 1.21 1.54 1.06 1.19 1.51 1.04 1.75 2.23 1.50 

12 1.24 1.02 1.00 1.43 1.17 1.15 1.25 1.02 1.01 1.32 1.09 1.07 1.10 0.90 0.80 

13 0.66 1.05 0.66 1.28 2.05 1.28 1.06 1.69 1.06 0.86 1.38 0.86 1.70 2.72 1.70 

14 1.13 1.13 1.13 0.97 0.97 0.97 1.41 1.41 1.41 1.06 1.06 1.06 1.51 1.51 1.51 

15 1.46 1.41 0.95 2.19 2.13 1.43 1.99 1.93 1.29 1.46 1.42 0.95 1.77 1.72 1.10 

16 0.89 1.27 0.80 0.87 1.24 0.78 1.07 1.52 0.96 0.79 1.12 0.71 1.13 1.61 1.00 

17 0.75 0.96 0.68 1.38 1.77 1.25 1.08 1.39 0.99 0.87 1.12 0.79 1.59 2.04 1.40 

18 1.46 1.90 1.02 1.99 2.57 1.39 1.84 2.38 1.29 2.00 2.59 1.40 3.68 4.76 2.50 

19 1.26 1.26 0.84 1.18 1.18 0.79 2.03 2.03 1.36 1.58 1.58 1.05 1.34 1.34 0.80 

20 N.A. N.A. N.A. N.A. N.A. N.A. 1.18 1.25 1.15 0.98 1.03 0.95 0.92 0.97 0.80 

21 N.A. N.A. N.A. N.A. N.A. N.A. 1.40 1.40 1.02 1.42 1.42 1.03 1.18 1.18 0.80 

 

i Mean 

St Dev 

1.23 1.37 0.95 1.48 1.65 1.14 1.66 1.83 1.28 1.35 1.49 1.04 1.85 2.09 1.40 

0.52 0.59 0.29 0.50 0.56 0.28 0.63 0.68 0.32 0.53 0.61 0.28 0.81 1.01 0.50 

ii Mean 

St Dev. 

1.10 1.24 0.89 1.49 1.70 1.19 1.46 1.64 1.18 1.21 1.36 0.98 1.87 2.14 1.40 

0.26 0.30 0.16 0.50 0.58 0.27 0.38 0.43 0.19 0.31 0.39 0.16 0.93 1.05 0.50 

i. includes both compression and tension piles 

ii. includes compression piles only 

N.A. - not applicable 

(1981), Douglas (1983), and Neely (1991). The results of this evaluation for the 5 and 10% of 

pile diameter as displacement criteria are shown in Table A.3. A summary of results for all tests 

(both compression and tension) at a pile displacement of 10% of the respective pile diameter is 

provided in Figure A.10. The Reese and O’Neill (1988) method for drilled shafts provided the 

best correlation for ultimate total pile capacity in these sandy soils, regardless whether the 5 or 

10% of the pile diameter displacement failure criteria was used. 

Table A.2. Total Resistance - Results from Five Methods (McVay et al., 1994) 

Ratio of Predicted to Measured Capacities 

The accuracy of the eight methods for a given pile diameter was also evaluated. The results from 

the Zelada and Stephenson (2000) study are presented in Table A.4. These results indicate that, 

in most cases, the accuracy of the method increased with increasing pile diameter and there was 

a tendency for better correlation with higher pile length-to-pile diameter ratios. Similar to the 

findings in the McVay et al. (1994) study, the original FHWA method for drilled shafts provided 

the best estimate of ultimate total pile capacity, regardless of pile diameter. 

Results comparing side shear resistance from Zelada and Stephenson (2000) are provided in 

Table A.5. Again, according to this study, the Reese and O’Neill (1988) method for drilled 

shafts provides the best correlation for side shear resistance in these sandy soils, with the LPC 

(1981) and the Wright and Reese (1979) methods also giving reasonably accurate results. 

Results comparing end-bearing unit resistances from the Zelada and Stephenson (2000) study are 

provided in Table A.6. The comparison indicates that the Viggiani (1993) method overestimated 

the end-bearing resistance by approximately 50 percent at displacements of 5 and 10% of the pile 

A-17 
diameter. The Neely (1991) method generally provided the best predictions, slightly 

overestimating and underestimating the end-bearing resistance at displacements of 5 and 10%, 

respectively. The Coyle and Castello (1981) method overestimated the end-bearing resistance, 

but the estimates from this method are close to measured values for a displacement of 10% of 

pile diameter. The remaining five methods underestimated the end-bearing resistance by more 

than a factor of two, with the exception that the Douglas (1983) method at 5% of the pile 

diameter. 

A.6.3 Comparison of Four Methods in Mixe d Soil Conditions (Coleman and Arcement, 

2002) 

Coleman and Arcement (2002) studied the results of compression load tests conducted on 32 

auger-cast piles in mixed soil conditions and performed in accordance with ASTM D 1143. 

These load tests were conducted at 19 different sites throughout Mississippi and Louisiana 

during the period of 1985 to 2001. 

Several methods for defining CFA failure were considered. It was concluded that while 

displacements of 5% of the pile diameter was a suitable criterion for large diameter shafts, 

displacements of 10% of the pile diameter was more appropriate for smaller diameter shafts such 

as those diameters typical for CFA piles. Therefore, Coleman and Arcement (2002) defined 

ultimate failure occurs at displacements of 10% of the pile diameter or at the plunging failure, 

whichever occurred first. In the event that the load was not increased to a level sufficient to 

cause plunging failure or displacements of ten percent of the pile diameter, the final load 

obtained was considered ultimate. The pile diameters ranged from 0.36 to 0.6 m (14 to 24 in.) 

and the pile lengths ranged from 6.1 to 32 m (20 to 105 ft). 

Four design methods were evaluated: API (1993), Neely (1991), Coyle and Castello (1981) and 

FHWA 1999 methods. The results for these design methods are provided in Figure A.11. The 

API method (1993) gave the best correlation for ultimate total pile capacity in mixed soil 

conditions and was slightly conservative (i.e., the average ratio of the measured to predicted 

capacity was 1.03). However, when considering the sites with sandy profiles only, the Neely 

method (1991) was slightly unconservative (i.e., the average ratio of the measured to predicted 

capacity was 0.93) and it gave the smallest standard deviation. The FHWA 1999 method (i.e., 

equivalent to Reese and O’Neill, 1988) was the most conservative and showed a relatively small 

standard deviation. The Coyle and Castello method (1981) was slightly unconservative and had 

the highest standard deviation. 

Based on this comparison, Coleman and Arcement (2002) recommended a modified FHWA 

1999 method because it is widely used and employs factors of side shear resistance (i.e., α and β

factors) that can easily be modified. Coleman and Arcement reported that the FHWA 1999 

method, although conservative, generally appeared reasonable for predicting the end-bearing 

component for cohesionless soils. Coleman and Arcement did not make recommendations for 

modifications to the end-bearing resistance provided by the FHWA method, as they believed 

there was insufficient data to formulate such modifications. 

A-18 
Measured Load (MN) Measured Load (MN) 

0 1 2 0 1 2 

300 300 

Predicted Load (tons) Predicted Load (tons) Predicted Load (tons) 

Predicted Load (MN) Predicted Load (MN) Predicted Load (MN) 

Predicted Load (tons) Predicted Load (tons) 

a) Wright 

and Reese 2

b) Neely 

Predicted Load (MN) Predicted Load (MN) 

2 

200 200 

1 1 100 100 

0 0 0 0 

0 100 200 300 0 100 200 300 

Measured Load (tons) Measured Load (tons) 

Measured Load (MN) Measured Load (MN) 

0 1 2 0 1 2 

300 300 

c) LPC d) FHWA 

2 

1 

2 

200 

100 

200 

1 100 

0 0 0 0 

0 100 200 300 0 100 200 300 

Measured Load (tons) Measured Load (tons) 

Measured Load (MN) 

0 1 2 

300 

e) Coyle 

2 

200 

100 1 

0 0 

0 100 200 300 

Measured Load (tons) 

Figure A.9. Summary of Total Resistance – Results from Five Methods (McVay et al., 

1994) 

A-19 
Stephenson, 2000) 

Table A.3. Total Resistance - Results from Eight Methods (Zelada and Stephenson, 2000) 

Q ult Measured / Q ult Predicted Ratios + Standard Deviations 

(Coefficients of Variation) 

Qult 

Method 

Wright 

& Reese Viggiani Neely Coyle & Castello 

Reese & 

O’Neill Douglas LPC Rizkallah 

Comp. 

Tests 

Only 

5% 

PD 

1.19 ± 

0.33 

0.54 ± 

0.22 

1.09 ± 

0.41 

1.00 ± 

0.43 

1.10 ± 

0.26 

1.59 ± 

0.45 

1.24 ± 

0.40 

1.45 ± 

0.56 

10% 

PD 

1.25 ± 

0.47 

0.64 ± 

0.30 

1.31 ± 

0.54 

1.25 ± 

0.52 

1.19 ± 

0.38 

1.72 ± 

0.70 

1.45 ± 

0.55 

1.72 ± 

0.75 

Tens. 

Tests 

Only 

5% 

PD 

1.20 ± 

0.57 

0.74 ± 

0.25 

1.73 ± 

0.74 

1.54 ± 

0.72 

1.00 ± 

0.42 

1.93 ± 

0.63 

0.91 ± 

0.29 

1.12 ± 

0.56 

10% 

PD 

0.96 ± 

0.26 

0.86 ± 

0.31 

1.76 ± 

1.12 

1.94 ± 

0.72 

0.82 ± 

0.25 

1.66 ± 

0.54 

0.94 ± 

0.36 

1.49 ± 

0.57 

All 

Tests 

Only 

5% 

PD 

1.19 ± 

0.38 

(0.32) 

0.58 ± 

0.24 

(0.41) 

1.21 ± 

0.54 

(0.45) 

1.10 ± 

0.54 

(0.42) 

1.08 ± 

0.30 

(0.28) 

1.65 ± 

0.50 

(0.30) 

1.17 ± 

0.40 

(0.34) 

1.39 ± 

0.57 

(0.41) 

10% 

PD 

1.21 ± 

0.45 

(0.38) 

0.67 ± 

0.30 

(0.45) 

1.38 ± 

0.65 

(0.47) 

1.36 ± 

0.59 

(0.44) 

1.13 ± 

0.38 

(0.34) 

1.71 ± 

0.67 

(0.39) 

1.37 ± 

0.55 

(0.40) 

1.69 ± 

0.72 

(0.43) 

Unconservative Conservative 

Wright and Reese (1979)
 

Viggiani (1993)
 

Neely (1991)
 

Coyle and Castello (1981)
 

Reese and O'Neill (1988)
 

Douglas (1983)
 

LPC (1981)
 

Rizkalla (1988)
 

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 

Qt meas. / Qt pred. 

Figure A.10. Summary of Total Resistance - Results from Eight Methods (Zelada and 

A-20 
 

Table A.4. Total Resistances - Results with from Eight Methods (Zelada and Stephenson, 

2000) 

Ratios of Qult measured/Qult predicted + Standard Deviations 

(Coefficients of Variation) 

Diam. 

(in.) 

Qult 

displ. 

criteria 

Wright 

and 

Reese 

Viggiani Neely 

Coyle 

and 

Castello 

Reese 

and 

O’Neill 

Douglas LPC Rizkallah 

14 

5% 

PD 

1.30 + 

0.42 

0.58 + 

0.21 

1.21 

+ 

0.47 

0.92 + 

0.38 

1.15 + 

0.31 

1.83 + 

0.50 

1.20 + 

0.43 

1.34 + 

0.62 

10% 

PD 

1.46 + 

0.39 

0.74 + 

0.23 

1.36 

+ 

0.38 

1.29 + 

0.34 

1.29 + 

0.31 

2.05 + 

0.47 

1.64 + 

0.37 

1.96 + 

0.51 

16 

5% 

PD 

1.10 + 

0.32 

0.58 + 

0.21 

1.25 

+ 

0.60 

1.31 + 

0.61 

1.01 + 

0.29 

1.48 + 

0.41 

1.10+ 

0.34 

1.38 + 

0.50 

10% 

PD 

1.10 + 

0.32 

0.62 + 

0.31 

1.30 

+ 

0.74 

1.36 + 

0.69 

0.99 + 

0.28 

1.50 + 

0.47 

1.07+ 

0.39 

1.43 + 

0.57 

18 

5% 

PD 

1.08 + 

0.26 

0.61 + 

0.34 

1.27 

+ 

0.83 

1.27 + 

0.62 

1.02 + 

0.30 

1.54 + 

0.63 

1.41+ 

0.56 

1.68 + 

0.71 

10% 

PD 

24 

5% 

PD 

10% 

PD 

1.12 + 

0.32 

0.41 + 

0.07 

0.79 

+ 

0.19 

0.73 + 

0.22 

1.03 + 

0.30 

1.34 + 

0.35 

0.96+ 

0.17 

1.08 + 

0.30 

* A minimum of three pile tests per diameter category were required for this statistical analysis. 

Note: Qult: Ultimate Total Pile Resistance, PD: Pile Displacement as a % of Pile Diameter 

Table A.5. Side Shear Resistance - Results from Eight Methods (Source: Zelada and 

Stephenson, 2000) 

Qult measured /Qult predicted Ratios + Standard Deviations 

Wright 

and 

Reese 

Viggiani Neely 

Coyle 

and 

Castello 

Reese 

and 

O’Neill 

Douglas LPC Rizkallah 

1.09 + 

0.57 

0.83 + 

0.42 

1.50 + 

0.78 

1.94 + 

1.20 

0.92 + 

0.41 

1.81 + 

0.41 

1.05 + 

0.51 

1.39 + 

0.78 

A-21 
 

Table A.6. End-Bearing Resistance–Results from Eight Methods (Zelada and Stephenson, 2000)
	

Qult 

Method 

Wright 

& Reese Viggiani Neely Coyle & 

Castello 

Reese & 

O’Neill Douglas LPC Rizkallah 

5% PD 2.35 ± 

2.40 

0.43 ± 

0.44 

0.87 ± 

0.88 

0.73 ± 

0.71 

2.47 ± 

2.43 

1.62 ± 

1.59 

2.70 ± 

2.66 

3.01 ± 

2.84 

10% PD 3.05 ± 

2.51 

0.56 ± 

0.46 

1.11 ± 

0.92 

0.98 ± 

0.71 

3.26 ± 

2.57 

2.14 ± 

1.69 

3.57 ± 

2.81 

4.01 ± 

2.98 

Note: Qult: Ultimate Total Pile Resistance, PD: Pile Displacement as a % of Pile Diameter. 

O’Neill et al. (1999) studied the results of 43 load tests performed on CFA piles in coastal Texas. 

Their study was for mixed soil conditions. Because the available data from CFA piles for sands 

in coastal Texas were limited, their study was augmented with the database developed by McVay 

et al (1994) from load tests performed on CFA piles in Florida sands. In addition, three CFA test 

piles were instrumented and load tested in geologically diverse sites in coastal Texas (O’Neill et 

al., 2002). These sites were designated as “UH” (over consolidated clay), “Baytown” (mixed 

soil conditions), and “Rosenburg” (sands). These three sites had CFA piles with a nominal 

diameter of 0.46 m (18 in.) and had embedment depths of 15.2, 15.2, and 9.1 m (50, 50, and 

30 ft), respectively. 

A.6.4 Comparison of Seven Methods - Sandy and Clay Soils (O’Neill et al., 1999) 

To investigate the effect of CFA construction on the earth pressure at a given depth, an effective 

stress cell was placed near the surface at each of the three instrumented CFA piles to monitor the 

changes in lateral earth pressure during drilling and grouting. Figure A.14 shows the test 

arrangement and the measured horizontal earth pressures during a typical installation. The 

increase and the subsequent drop of horizontal earth pressure from the in situ value as the auger 

tip moves is part of the cell location during the drilling process. The horizontal earth pressure 

then increased again during grouting to a residual 20 kPa (0.21 tsf) above the in situ value; 

however, the residual increase in lateral earth pressure at completion was small compared to the 

approximately 1,500 kPa (15 tsf) of grout pressure that was maintained during auger extraction. 

As part of this study, seven methods were evaluated against this database to evaluate their 

effectiveness in predicting the CFA capacities. These methods include: Wright and Reese 

(1979), Neely (1991), TxDOT (1972), FHWA 1999 (O’Neill and Reese, 1999), Coyle and 

Castello (1981), API method (1993), and LPC method (1981). Additionally, O’Neill et al. 

(2002) later published a normalized load-settlement curve suitable for design of similar diameter, 

single CFA piles in the geologic formations of the Texas Gulf Coast (as is presented in Section 

A.2.11 of this Appendix). In their investigation of load-settlement response, O’Neill et al. 

(2002) reported that although predictions were generally good, they may have been an artifact of 

compensating errors in the prediction of the side shear resistance. The measured side shear 

resistances were generally larger than those predicted for the surficial layer to depths of 

approximately 4 m (13 ft) but they were generally smaller than the values predicted for deeper 

strata. 

A-22 
For clay soils, the LPC (1981) and the TxDOT (1972) methods gave the closest correlation for 

ultimate total pile capacity. Their predictions produced average ratios of the measured to 

measured capacity of 0.98 and 0.86, and had standard deviations of this ratio of 0.35 and 0.33, 

respectively. The remaining three methods compared similarly, with the FHWA 1999 method 

being the most conservative (average ratio of the measured to predicted capacity of 1.52, and a 

standard deviation of this ratio 0.56). The results with the LPC (1981) and the FHWA methods 

are illustrated in Figure A.15 (a) and (b), respectively. Predicted Capacity/Measu

red Capacity

2 

1.75 

1.5 

1.25 

1 

0.75 

0.5 

0.25 

0 

1.49 

1.2 

1.29 1.34 

0.97 

1.07 1.07 

0.89 

0.8 

0.57 

0.65 0.65 

FHWA API Neely Coyle 

Design Method 

Figure A.11. Summary of Total Resistance - Results from Four Methods (Coleman and 

Arcement, 2002) 

For sandy soils, the LPC (1981) and FHWA 1999 method s gave the best correlation for ultimate 

total pile capacity; both methods produced an average measured to predicted capacity ratio of 

1.02 and had standard deviations of this ratio of 0.34 and 0.27, respectively. The results of the 

LPC (1981) and the FHWA methods are illustrated in Figure A.15 (c) and (d), respectively. 

A comparison of various prediction methods of total capacity for cohesive soils is presented in 

Figure A.16. In this Figure, the mean and standard deviation of the ratio of the measured total 

capacity to the predicted total capacity is presented for the various methods. The comparison 

study conducted by O’Neill et al. (1999) is the only study with profiles consisting of entirely 

cohesive soils. The results for mixed soil conditions from the O’Neill et al. (1999) and Coleman 

and Arcement (2002) studies are also shown in Figure A.16. 

A-23 
The results from O’Neill et al. (1999) show that the best method for cohesive soils is the LPC 

method (1981), followed by the TxDOT (1972) method. However, the LPC Method (1981) 

requires CPT soundings while the TxDOT (1972) method requires a Dynamic Cone 

Penetrometer (uncommon to most regions of the U.S.). The remaining three methods all appear 

to have the same trend, with the FHWA 1999 method being the most conservative. The Coyle 

and Castello (1981) method generally has the average ratio of measured to predicted total 

capacity closest to 1.0, but also has the lowest mean of this ratio (i.e., it is most unconservative) 

for mixed soil conditions (Coleman and Arcement, 2002). In all three methods, the most 

conservative predictions of total capacity occur for clay soils and mixed soil conditions. 

0 

500 

1000 

1500 

2000 

2500 

3000 

3500 

4000 

Measured Capacity (kN) 

0 500 1000 1500 2000 2500 3000 3500 4000 

Predicted Capacity (kN) 

Figure A.12. Total Capacity - Results From FHWA 1999 Method (Coleman and Arcement, 

2002) 

3500 

Measured Capacity (kN) 3000 

2500 

2000 

1500 

1000 

500 

0 

0 500 1000 1500 2000 2500 3000 3500 

Predicted Capacity (kN) 

Figure A.13. Total Capacity Results - Coleman and Arcement (2002) Method 

A-24 
A.6.5 Summary of Comparison Study Results for Cohesive Soils 

Figure A.14: Effective Lateral Earth Pressure near a CFA Pile during Construction 

(O’Neill et al., 2002) 

A.6.6 Summary of Comparison Study Results for Cohesionless Soils 

A comparison of the mean and range of the measured-to-predicted total capacity ratios for 

cohesionless soils using various prediction methods is presented in Figure A.17. The mean and 

the standard deviation of this ratio are presented. The results for mixed soil conditions from 

Coleman and Arcement (2002) are also presented. 

The FHWA 1999 method consistently provides the most accurate method for cohesionless soils 

in all comparison studies. O’Neill et al. (1999) for sands and Coleman and Arcement (2002) for 

mixed soils report good average mean ratios for the API method (1993), but also a greater 

standard deviation than for the FHWA 1999 method. McVay et al. (1994), Zelada and 

Stephenson (2000), and O’Neill et al. (1999) also found that the Wright and Reese (1979) and 

LPC (1981) methods provide good results; however, the LPC (1981) method may be 

occasionally unconservative. 

The FHWA 1999 method requires SPT borings for estimating the end-bearing resistance and the 

pile depth for the side shear component. The LPC Method (1981) requires CPT soundings for 

estimating both components of resistance. The Wright and Reese (1979) and API (1993) 

methods require estimation of the lateral earth pressure coefficient (K). The Wright and Reese 

(1979) method requires the internal soil friction angle (φ) and the API (1993) method requires 

the pile-to-soil interface friction angle (δ). 

A-25 
)

4000 )4000 

 (kN

a) LPC Method for Clayey Soil N

3500 k

b) FHWA Method for Clayey Soil 

 (

3500 

ce

ec

n

3000 n3000 

a

a

st

2500 

sist2500 

ise

2000 e2000 

ted R1500 Mean: 1.02 

d R

1500 Mean: 1.52 

1000 St. Dev. : 0.33 

et

1000 St. Dev. : 0.60 

ic

COV: 0.32 c

COV: 0.39 

Pred

500 

edi

500 

0 

Pr

0 

0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 

Measured Resistance (kN) Measured Resistance (kN) 

)

4000 )

N

N

4000 

k(

d) FHWA Method for Mixed Soil 

 (k

3500 c) LPC Method for Sandy Soil 3500 

ce

e 

3000 c3000 

2500 

istan

n

2500 a

s

sist

e

2000 e2000 

d R

1500 Mean: 0.98 

et

ed R

1500 Mean: 0.98 

1000 St. Dev. : 0.34 

ict

1000 St. Dev. : 0.27 

ic

COV: 0.34 COV: 0.28 

Pred

500 

ed

500 

0 

Pr

0 

0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 

Measured Resistance (kN) Measured Resistance (kN) 

Source: O’Neill et al. (2002) 

Figure A.15. Total Resistance - Results from Four Methods 

The study by Zelada and Stephenson (2000) for cohesionless soils concluded that the FHWA 

1999 method had the best correlation for the side shear capacity, although this method is 

somewhat unconservative. This study concluded that the FHWA method was conservative for 

end-bearing resistance. Zelada and Stephenson (2000) recommended modifications to the 

FHWA 1999 method to reflect the tendency for CFA piles to exhibit less side shear and greater 

end-bearing resistance in cohesionless soils than that predicted with the FHWA 1999 method. 

The side shear capacity predicted was reduced by a factor of 0.8, and the end-bearing resistance 

was increased by a factor of 2.8. 

Coleman and Arcement (2002) recommended modifications to the β factor of the FHWA 1999 

method for side shear estimation in cohesionless soils (either sandy or silty soils). This was done 

to reflect the tendency for CFA piles to exhibit greater side shear resistance than the values 

predicted near the surface and less side shear resistance than that predicted at greater depths. 

A-26 
 

 

 

 

 

 

 

0 

0.2 

0.4 

0.6 

0.8 

1 

1.2 

1.4 

1.6 

1.8 

2 

2.2 

TxDOT Method (1972)

FHWA Method (1988)

Coyle and Castello (1981)

API Method (1993)

LPC Method (1981) 

Measured Total Capacity / Predicted Total Capacity

Drilled Shaft's 

& Driven Pile's 

Driven Pile's Drilled Shaft's 

Basis for M ethods

M ethods E valuated 

CONSERVATIVE UN-CONSERVATIVE

 Predominant Soil Type Study Ultimate Capacity Defined 

at Displacem ents of 

 Mixed Soils Colem an and Arcem ent (2002) - 10 % of the Pile Diam eter

 Mixed Soils

 Clay Soils 

O'Neill et al. (1999) - 5 % of the Pile Diam eter 

Figure A.16. Comparison of Study Results - Axial Capacity in Cohesive Soils 

A-27 
 

 

 

 

 

 

 

 

 

Measured Total Capacity / Predicted Total Capacity 

2.2 

2 

1.8 

1.6 

1.4 

1.2 

1 

0.8 

0.6 

0.4 

0.2 

0 

Wright and Reese (1979)

Douglas Method (1983)

Rizkalla (1988) 

Neely (1991) 

Viggiani Method (1993)

FHWA Method (1988) 

Coyle and Castello (1981)

API Method (1993)

LPC Method (1981) 

Sandy Soils 

Sandy Soils 

Mixed Soils 

Sandy Soils 

ACIP's Drilled Shaft's 

& Driven Pile's 

Drilled Shaft's Driven Pile's 

Basis for Methods 

McVay et al (1994) - 5 % of the Pile Diameter

 Zelada and Stephenson (2000) - 5 % of the Pile Diameter

 Coleman and Arcement (2002) - 10 % of the Pile Diameter 

O'Neill et al. (1999) - 5 % of the Pile Diameter 

Methods Evaluated 

CONSERVATIVE UN-CONSERVATIVE 

Predominant Soil Type Study Ultimate Capacity Defined 

at Displacements of 

Figure A.17: Comparison of Study Results – Axial Capacity in Cohesionless Soils 

A-28 
APPENDIX B. EXAMPLE PRO BLEMS: SPREADSHEET S OLUTIONS FOR 

AXIAL CAPACITY OF SINGLE CFA PILES WITH DEPTH 

B.1 CONVENTIONAL CFA PILE IN COHESIVE SOIL 

Problem Statement 

Conventional CFA piles, 18 inches in nominal diameter, are being considered for use to provide 

support for a highway interchange in a coastal plains area. A subsurface investigation 

performed, as described in the Chapter 6 example problem (Section 6.7.4, Part A), provided 

information necessary to develop the generalized soil profile at the pier location as was shown in 

Figure 5.32. The bottom of the proposed pile cap is at a depth of 4 ft. An allowable stress 

design (ASD) is to be used with a safety factor of 2.0, as detailed in Chapter 6 (Section 6.7.4 Part 

D). Note that a safety factor of 2.0 is used, as full-scale load testing will be implemented to 

verify (or modify if necessary) the pile capacity estimates. Details of the safety factor selection 

criteria (ASD) will be presented subsequently in Chapter 6. Loading of the bridge and the 

proposed foundation layout has determined the axial loads to the individual CFA pile (as detailed 

in Section 6.7.4 Part E). For an allowable pile capacity of 130 kips, what pile embedment depth 

should be specified in accordance with ASD? 

Spreadsheet Solution 

The following section presents a spreadsheet solution for the ultimate static axial resistance and 

the allowable static axial resistance with depth of a single CFA pile in accordance with ASD. 

Note that a hand calculation of resistance at a pile depth of 60 ft is presented in Section 5.8.1. 

The recommended method, as detailed in Section 5.3.1.1, for estimating the ultimate resistance 

of a single CFA pile in cohesive soil was used. 

The calculations for an ASD approach are presented in Table B.1. The calculations will be 

detailed column by column in the section to follow. A graphical presentation of the estimated 

resistances in accordance with ASD is provided as Figure B.1. It can be seen in this figure that a 

CFA pile minimum embedment depth of 69 ft is required to provide the specified minimum total 

allowable resistance of 130 kips, with a safety factor of 2.0 applied to the ultimate resistance. 

The following list details the calculations in Table B.1 (column-by-column) 

A. Pile Embedment Depth (L) – increments of 1 ft (∆L) have been chosen for the 

spreadsheet solution with depth, as it is convenient and customary to provide a required 

embedment depth, in whole feet (ft). Note that the first whole ft increment with an 

allowable capacity greater than the required 130 kips should be specified. 

B. Undrained Shear Strength (Su) – provided from the subsurface investigation (from 

Section 6.7.4, Part A), as was shown in Figure 5.32 at the pier location. The top soil 

layer (soft clay) was idealized as having constant Su with depth, while the bottom soil 

layer (medium to stiff clay) was idealized as having values of Su that increased linearly 

with depth. Note that the values of Su for the bottom soil layer are linearly interpolated 

from the depth at the mid-point of each of the pile segments. 

B-1
 
Table B.1. ASD Example Calculations for 18-inch Diameter - CFA pile in Cohesive Soils
	

B-2
 
Table B.1. (continued) 

B-3
 
5 

CFA Pile Embedment Depth (ft) 

Resistance (kips) 

0 50 100 150 200 250 300
 

0 

10
 

15
 

20
 

25
 

30
 

35
 

40
 

45
 

50
 

55
 

60
 

65
 

70
 

75
 

80
 

Allowable Total Resistance (RT(Allow)) 

Minimum 

Required Pile 

Embedment 

Depth (Lmin) 

Allowable End Bearing RB(Allow) Ultimate End Bearing RB 

Allowable Side Shear RS(Allow) Ultimate Side Shear RS 

Allowable Total RT(Allow) Ultimate Total RT 

CFA Pile 

with an 18-inch 

Nominal Diameter 

Top Soil Layer 

(Soft Clay) 

Bottom Soil Layer 

(Medium to Stiff Clay) 

Figure B.1. ASD Example for CFA Pile in Cohesive Soils 

B-4
 
C. Alpha Factor (α) – because the ratio of the undrained shear strength to standard 

atmospheric pressure is less than 1.5 (Su/Pa ≤ 1.5), the alpha factor (α) is constant at 0.55. 

Note that for Su/Pa > 1.5, α would need to be reduced as detailed in Section 5.3.1.1. 

D. Ultimate Unit Side Shear (fS) – the product of columns “C” and “B” (fS = α · Su). 

E. Ultimate Side Shear for Pile Segment (∆RS) – the product of column “D” and the 

peripheral area of the pile segment (∆RS = fS A(peripheral) = fS π D(diameter) ∆L). 

F.	 Ultimate Side Shear (RS) – the sum of the pile segment ultimate side shear values (Σ ∆RS) 

to the pile embedment depth with the following contributions discounted: The top 5 ft 

(shaded section in Column “F”), and the bottom section of pile equal in length to one pile 

diameter (1.5 ft for this example). Discounting of sections at the top and bottom of pile is 

detailed in Section 5.3.1.1. Note that if an evaluation of the depth of seasonal moisture 

change were to reveal a depth in excess of 5 ft, then this larger depth would be discounted 

from contributing to the side shear resistance. 

G. The Safety Factor (SF) – given in problem statement as 2.0. 

H. The Allowable Side Shear Resistance (RS(Allow)) - column “F” divided by column “G”. 

I.	 Average Undrained Shear Strength Below the Pile Tip (Su(ave,2-D)) – the average of 

column “B” from the pile tip to a depth of 2 pile diameters below the pile tip (in this 

example 3 ft). This is as recommended in Section 5.3.1.1; solutions for the depth of 

influence of end-bearing typically range from as shallow as 2 diameters above the tip and 

as deep as 3 to 4 diameters below the tip. 

J.	 Bearing Capacity Factor (N *

c ) – linearly interpolated from the undrained shear strength 

(Su) of each soil layer from the values listed in Table B.1, because modulus data (ES) was 

not obtained in the site investigation. Note that the bearing capacity factor has been 

further reduced for embedment depths less than 3 pile diameters (L < 3 D(diameter)) as 

detailed in Section 5.3.1.1 (shown as shaded section of column “J” in Table 5.3). 

K. Ultimate Unit End-Bearing (qp) – the product of columns “J” and “I” (qp = Nc*

 Su (ave,2-D)). 

L. Ultimate End-Bearing (RB) – the product of column “K” and the cross-sectional area of 

the pile (RB = q π/4) ·D 2

p A(cross-section) = qp ( (diameter) ). 

M. The Safety Factor (SF) – given in problem statement as 2.0. Note that a safety factor of 

2.0 is used, as full-scale load testing will be implemented to verify (or modify if 

necessary) the pile capacity estimates. 

B-5
 
N. The Allowable End-Bearing Resistance (RB(Allow)) – Column “L” divided by column “M”. 

O. Ultimate Total Resistance (RT) – sum of columns “F” and “L” (RT = RS + RB). 

P.	 The Allowable Total Resistance (RT(Allow)) – sum of columns “H” and “N”. Note this 

could be calculated as the product of column “O” and the Safety Factor, as only an 

overall safety factor was specified. 

B.2 CONVENTIONAL CFA AND DRILLED DISPLACEMENT PILES IN 

COHESIONLESS SOILS 

Problem Statement 

Both conventional CFA piles and drilled displacement piles, either of which have a nominal 

diameter of 18 inches, are being considered for use to provide support for a bridge over a small 

stream within a flood plain. A subsurface investigation performed provided information to 

develop the generalized soil profile at the pier location, as was shown in Figure 5.33, in terms of 

SPT-N values, soil descriptions, and unit weights. While the pier location is usually accessible 

by track mounted equipment, extreme high tides have been known to bring the water level up to 

that of the site. The hydraulic engineer for the project has indicated that potential scour exists at 

the pier to a depth of 6 ft. The bottom of the proposed pile cap is also proposed at a depth of 6 ft. 

An allowable stress design (ASD) may be used with a safety factor of 2.5. Note that details of 

the safety factor selection criteria (ASD) were presented in Chapter 6. Loading of the bridge and 

the proposed foundation layout has determined an allowable total capacity of 170 kips per pile 

(in accordance with ASD). What minimum pile embedment depth for both pile types should be 

specified in accordance with ASD. 

Spreadsheet Solution 

The recommended method for estimating the ultimate resistance of a single CFA pile in 

cohesionless soil was used as detailed in Section 5.3.2.1, and the recommended method for 

estimating the ultimate resistance of a single drilled displacement pile in cohesionless soil was 

used as detailed in Section 5.4.2. The calculations for the conventional CFA pile are presented 

in Table B.2., while the calculations for the drilled displacement pile are presented in Table B.3. 

All calculations will be detailed column by column in the section to follow. 

For the conventional CFA pile, a graphical presentation of the estimated resistances in 

accordance with ASD is provided as Figure B.2 for the conventional CFA pile, and as Figure B.3 

for the drilled displacement pile. It can be seen in these figures that the specified minimum total 

allowable resistance of 170 kips, with a safety factor of 2.5, may be provided by a conventional 

CFA pile minimum embedment depth of 62 ft, while a drilled displacement pile minimum 

embedment depth of only 37 ft is required. Note from the borings near the pier location (Figure 

5.33) that a depth of 37 ft corresponds to the transition from soil layer 2 (Silty Fine Sand) to the 

more competent soil layer 3 (Shelly Sand). Prudence suggests that the embedment depth should 

B-6
 
be extended a couple of feet to ensure that the pile is tipped into this more competent soil layer in 

order to take advantage of the associated greater end-bearing development. 

Figure B.4 presents the ultimate resistances of both the conventional CFA pile and the drilled 

displacement pile with depth to illustrate the capacity advantage that can be realized with a 

drilled displacement technique in cohesionless soils. For this example, the drilled displacement 

piles provide a total resistance of approximately 3.5 times (on the average) the total resistance 

provided by the CFA pile at any given depth. 

The following list details the CFA pile calculations in Table B.2 (column-by-column) 

A.	 SPT-N Values – from the subsurface investigation, as was shown in Figure 5.33. 

B. Depth of SPT-N Values – from the subsurface investigation, as was shown in Figure 5.33. 

C. Pile Embedment Depth (L) – increments (∆L) have been chosen for the spreadsheet 

solution such that the division between pile sections lies midway between the reported 

SPT-N values with depth. The pile was segmented in this way mainly for ease in 

illustrating the recommended method for estimating the end-bearing resistance with SPTN values. However, minor differences in SPT-N values obtained within a soil layer type 

may very well be an artifact of testing inconsistencies as much as soil variation, and even 

if attributable to soil variation construction of the CFA pile may tend to average out these 

effects. Alternatively, either simple averages of similar soil types and strengths or a 

linear fit of the strengths with depth (perhaps from multiple borings) are routinely 

performed and easily accommodated. 

D. Depth to Mid-Point of Pile Segment (L(mid)) – midpoint between pile tip elevation and pile 

tip elevation from previous segment. 

E. Length of Pile Segment (∆L) – difference between pile tip elevation and pile tip elevation 

from previous segment. 

F.	 Vertical Effective Stress at Mid-Point of Pile Segment (σv’) – total vertical stress minus 

hydrostatic pressure. Further, the solution in this example has assumed a worst case 

“bed” scour where the top 6 ft has been discounted (shown as shaded areas in columns 

“F” and “G”) in calculating both the effective stress distribution and beta factor (β) with 

depth. Note that if the scour was anticipated to be only “localized”, the top 6 ft need not 

be discounted in calculating the effective stress distribution and beta factor (β). 

G. Beta Factor (β) – determined as a function of pile embedment depth (L) in accordance 

with Section 5.3.2.1. Note that the β factor for the first and second pile segments were 

subject to the limitation of 1.2, and the eighth through tenth pile segments were reduced 

by the ratio of N/15 as these SPT-N values were less than 15 (all shown as shaded areas 

of Column “G”). None of the pile segments were subjected to the lower limit of β ≥ 0.25. 

B-7
 
Table B.2. ASD Example Calculations for 18-inch Diameter CFA Pile in Cohesionless S

B-8
Table B.3. ASD Example Calculations for 18-inch Diameter Drilled Displacement Pile in Cohesi

B-9
CFA Pile Embedment Depth (ft) 

Resistance (kips) 

0 100 200 300 400 500
 

0 

5
 

10
 

15
 

20
 

25
 

30
 

35
 

40
 

45
 

50
 

55
 

60
 

65
 

70
 

Allowable Total Resistance (RT(Allow)) = 170 kips 

Minimum 

Required Pile 

Embedment 

Depth (Lmin) 

Allowable End Bearing RB(Allow) Ultimate End Bearing RB 

Allowable Side Shear RS(Allow) Ultimate Side Shear RS 

Allowable Total RT(Allow) Ultimate Total RT 

Conventional CFA Pile 

with an 18-inch 

Nominal Diameter 

Light Brown 

Fine Sand (SP) 

Greenish-Gray 

Silty Fine Sand (SM) 

Greyish-White 

Shelly Sand (SW) 

Figure B.2: ASD Example for CFA Pile in Cohesionless Soils 

B-10
 
Resistance (kips) 

0 100 200 300 400 500 600 700 800 900 1000 Allowable Total Resistance (RT(Allow)) = 170 kips 

Minimum 

Required Pile 

Embedment 

Depth (Lmin) 

0 

5 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

CFA Pile Embedment Depth (ft) 

Drilled Displacement Pile 

with an 18-inch 

Nominal Diameter 

Light Brown 

Fine Sand (SP) 

Greenish-Gray 

Silty Fine Sand (SM) 

Greyish-White 

Shelly Sand (SW) 

Allowable End Bearing RB(Allow) Ultimate End Bearing RB 

Allowable Side Shear RS(Allow) Ultimate Side Shear RS 

Allowable Total RT(Allow) Ultimate Total RT 

Figure B.3: ASD Example for Drilled Displacement Pile in Cohesionless Soils 

B-11 
 

t

Ultimate Resistance (kips) 

0 100 200 300 400 500 600 700 800 900 1000 

0 

5 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

CFA Pile Embedment Depth (ft) 

Comparison of Ultimate Resistances 

CFA Pile and Drilled Displacement 

Pile both with an 18-inch Nominal 

Di 

Light Brown 

Fine Sand (SP) 

Greenish-Gray 

Silty Fine Sand (SM) 

Greyish-White 

Shelly Sand (SW) 

CFA Pile Drilled Displacement Pile 

Ultimate End Bearing RB Ultimate End Bearing RB 

Ultimate Side Shear RS Ultimate Side Shear RS 

Ultimate Total RT Ultimate Total RT 

Figure B.4: Comparison of Ultimate Resistances of 18 inch Diameter CFA Pile and 

Drilled Displacement Pile for Cohesionless Soil Example
	

B-12
 
H. Ultimate Unit Side Shear (fS) – the product of columns “G” and “F” (fS = β · σv’), 

note that none of the pile segments exceeded the limit of 2 tsf. 

I.	 Ultimate Side Shear for Pile Segment (∆RS) – the product of column “H” and the 

peripheral area of the pile segment (∆RS = fS · Aperipheral = fS π ·Ddiameter · ∆L). 

J.	 Ultimate Side Shear (RS) – the sum of the pile segment ultimate side shear values 

(Σ ∆RS) to the pile embedment depth. 

K. The Safety Factor (SF) – given in problem statement as 2.5. 

L. The Allowable Side Shear Resistance (RS(Allow)) - column “F” divided by column 

“G”. 

M. Average SPT-N Value Below Pile Tip (N(ave)) – the average of column “A” from 

the pile tip to a depth of 2 to 4 pile diameters below the pile tip (in this example 4 

to 8 ft), depending upon the frequency of SPT-N values with depth and soil 

layering. Note that the 14th and 15th pile segments have N(ave) > 75 (shown as 

shaded areas of column “M), and the resulting qp has been limited as described for 

column “O”. 

N. Intentionally left Blank – for easy comparison of example calculations of CFA 

piles (Table B.2) to drilled displacement piles (Table B.3). 

O. Ultimate Unit End-Bearing (qp) – columns “M” multiplied by 0.6 (qp = 0.6 N(ave)) 

to get q units to ksf. Note that the 14th

p in tsf, and multiplied by 2 to convert and 

15th pile segments have been subject to the upper limit of 90 ksf (shown as shaded 

areas of column “O”). 

P.	 Ultimate End-Bearing (RB) – the product of column “O” and the cross-sectional 

area of the pile (R 2

B = qp · A(cross-section) = qp · (π/4) · D(diameter) ). 

Q. The Safety Factor (SF) – given in problem statement as 2.5. 

R. The Allowable End-Bearing Resistance (RB(Allow)) – Column “P” divided by 

column “Q”. 

S.	 Ultimate Total Resistance (RT) – sum of columns “J” and “P” (RT = RS + RB). 

T. The Allowable Total Resistance (RT(Allow)) – sum of columns “L” and “R”. Note 

this could be calculated as the product of column “S” and the safety factor, as 

only an overall safety factor was specified. 

B-13
 
The following list details the drilled displacement pile calculations in Table B.3 (columnby-column) 

The calculations for the static axial capacity of the single drilled displacement pile differs 

from that for the CFA pile only in the estimation of the ultimate unit side shear and 

ultimate unit end-bearing resistances. Thus details for the drilled displacement pile 

calculations (column-by-column) are as described above for the CFA pile, with the 

following exceptions noted to follow. 

A. Unit Side Shear Constant (Ws) – as specified by the recommended method 

detailed in Section 5.4.2. Ws = 0 ksf for the top two layers (Well rounded, and 

poorly graded material), and Ws = 1 ksf (0.5 tsf) for the bottom layer (angular, and 

well graded). 

B. Ultimate Unit Side Shear (fS) – as specified by the recommended method detailed 

in Section 5.4.2., (0.05·N· (2 ksf / 1 tsf) + Ws), where SPT-N is from Column “A” 

and Ws is from Column “G”. Note that the 12th through the 17th pile segments 

exceeded the limit of 4.4 ksf (2.2 tsf), and thus were set to this limiting value 

(shown as shaded areas of column “H”). 

C. Average SPT-N Value Below Pile Tip (N(ave)) – the average of column “A” from 

the pile tip to a depth of approximately 4 pile diameters above and below the pile 

tip (in this example 4 to 8 ft), depending upon the frequency of SPT-N values with 

depth and soil layering. Note that the 12th through 15th pile segments have 

N(ave) > 50 (shown as shaded areas of column “M”), and the resulting qp will be 

limited in column “O”. 

D. Unit End-Bearing Constant (WT) – as specified by the recommended method 

detailed in Section 5.4.2. Ws = 0 ksf for the top two layers (Well rounded, and 

poorly graded material), and Ws = 28 ksf (14 tsf) for the bottom layer (angular, 

and well graded). 

E. Ultimate Unit End-Bearing (fS) – as specified by the recommended method 

detailed in Section 5.4.2., (1.9·N(ave) (2 ksf / 1 tsf) + WT), where N(ave) is from 

Column “M” and Ws is from Column “N”. Note that the 11th through the 15th pile 

segments exceeded the limit of 178 ksf (89 tsf), and thus were set to this limiting 

value (shown as shaded areas of column “O”). 

B-14