U. S. Department of Transportation Publication No. FHWA-NHI-10-025 

Federal Highway Administration	 FHWA GEC 011 – Volume II 

November 2009 

NHI Courses No. 132042 and 132043 

Design and Construction of 

Mechanically Stabilized Earth Walls 

and Reinforced Soil Slopes – Volume II 

Developed following:
 

AASHTO LRFD Bridge Design and AASHTO LRFD Bridge Construction 

Specifications, 4th Edition, 2007, Specifications, 2nd Edition, 2004, with 

with 2008 and 2009 Interims. 2006, 2007, 2008, and 2009 Interims.
 
NOTICE

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

accuracy of the data presented herein. The contents do not necessarily reflect policy of the 

Department of Transportation. This report does not constitute a standard, specification, or 

regulation. The United States Government does not endorse products or manufacturers. Trade 

or manufacturer's names appear herein only because they are considered essential to the object of 

this document. 
 

Technical Report Documentation Page 

1. REPORT NO. 2. GOVERNMENT 3. RECIPIENT'S CATALOG NO. 

ACCESSION NO. 

FHWA-NHI-10-025 FHWA GEC 011-Vol II 

4. TITLE AND SUBTITLE 5. REPORT DATE 

November 2009 

Design of Mechanically Stabilized Earth Walls 

and Reinforced Soil Slopes – Volume II 6. PERFORMING ORGANIZATION CODE 

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

Ryan R. Berg, P.E.; Barry R. Christopher, 

Ph.D., P.E. and Naresh C. Samtani, Ph.D., P.E. 

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

Ryan R. Berg & Associates, Inc. 11. CONTRACT OR GRANT NO. 

2190 Leyland Alcove DTFH61-06-D-00019/T-06-001 

Woodbury, MN 55125 

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

National Highway Institute 

Federal Highway Administration 14. SPONSORING AGENCY CODE 

U.S. Department of Transportation 

Washington, D.C. 

15. SUPPLEMENTARY NOTES 

FHWA Technical Consultants: Rich Barrows, P.E., Silas Nichols, P.E., and Daniel Alzamora, P.E. 

Technical Consultant: James G. Collin, Ph.D., P.E. 

16. ABSTRACT 

 This manual is the reference text used for the FHWA NHI courses No. 132042 and 132043 

on Mechanically Stabilized Earth Walls and Reinforced Soil Slopes and reflects current 

practice for the design, construction and monitoring of these structures. This manual was 

prepared to enable the engineer to identify and evaluate potential applications of MSE walls 

and RSS as an alternative to other construction methods and as a means to solve construction 

problems. The scope is sufficiently broad to be of value for specifications specialists, 

construction and contracting personnel responsible for construction inspection, development 

of material specifications and contracting methods. With the aid of this text, the engineer 

should be able to properly select, design, specify, monitor and contract for the construction of 

MSE walls and RSS embankments. 

 The MSE wall design within this manual is based upon Load and Resistance Factor Design 

(LRFD) procedures. This manual is a revision (to LRFD) and an update to the FHWA NHI00-043 manual (which was based upon allowable stress design (ASD) procedures). 

17. KEY WORDS 18. DISTRIBUTION STATEMENT 

Design, Load and Resistance Factor Design No restrictions. (LRFD), analysis, performance criteria, 

Mechanically Stabilized Earth (MSE) Walls, 

Reinforced Soil Slopes (RSS), soil reinforcement, 

geosynthetics, specifications, contracting methods 

19. SECURITY CLASSIF. 20. SECURITY CLASSIF. 21. NO. OF PAGES 22 

Unclassified Unclassified 378 
 

 

 

 

 

 

 

SI CONVERSION FACTORS 

APPROXIMATE CONVERSIONS FROM SI UNITS 

Symbol When You Know Multiply By To Find Symbol 

LENGTH 

mm 

m 

m 

km 

millimeters 

meters 

meters 

kilometers 

0.039 

3.28 

1.09 

0.621 

inches 

feet 

yards 

miles 

in 

ft 

yd 

mi 

AREA 

mm2 

m

2 

m

2 

ha 

km2 

square millimeters 

square meters 

square meters 

hectares 

square kilometers 

0.0016 

10.764 

1.195 

2.47 

0.386 

square inches 

square feet 

square yards 

acres 

square miles 

in2 

ft2 

yd2 

ac 

mi2 

VOLUME 

ml 

l 

m3 

m3 

millimeters 

liters 

cubic meters 

cubic meters 

0.034 

0.264 

35.71 

1.307 

fluid ounces 

gallons 

cubic feet 

cubic yards 

fl oz 

gal 

ft3 

yd3 

MASS 

g 

kg 

grams 

kilograms 

0.035 

2.202 

ounces 

pounds 

oz 

lb 

TEMPERATURE 

°C Celsius 1.8 C + 32 Fahrenheit °F 

kN/m3 

WEIGHT DENSITY 

kilonewton / cubic m 6.36 poundforce / cubic foot pcf 

FORCE and PRESSURE or STRESS 

N 

kN 

kPa 

kPa 

newtons 

kilonewtons 

kilopascals 

kilopascals 

0.225 

225 

0.145 

20.9 

poundforce 

poundforce 

poundforce / sq in. 

poundforce / sq ft 

lbf 

lbf 

psi 

psf 
PREFACE
 

Engineers and specialty material suppliers have been designing reinforced soil structures for 

the past 35 years. Currently, many state DOTs are transitioning their design of substructures 

from Allowable Stress Design (ASD) to Load and Resistance Factor Design (LRFD) 

procedures. 

This manual is based upon LRFD for MSE wall structures. It has been updated from the 

2001 FHWA NHI-00-043 manual. In addition to revision of the wall design to LRFD 

procedures, expanded discussion on wall detailing and general updates throughout the 

manual are provided. The primary purpose of this manual is to support educational programs 

conducted by FHWA for transportation agencies. 

A second purpose of equal importance is to serve as the FHWA standard reference for 

highway projects involving MSE wall and reinforced soil structures. 

This Mechanically Stabilized Earth Walls (MSE) and Reinforced Soil Slopes (RSS), Design 

and Construction Guidelines Manual which is an update of the current FHWA NHI-00-043, 

has evolved from the following AASHTO and FHWA references: 

C AASHTO LRFD Bridge Design Specifications, 4th Edition, 2007, with 2008 and 2009 

Interim Revisions. 

C Earth Retaining Structures, by B.F. Tanyu, P.J. Sabatini, and R.R. Berg, FHWA-NHI-07­

071 (2008). 

C AASHTO LRFD Bridge Construction Specifications, 2nd Edition, 2004, with 2006 

Interim Revisions. 

C Geosynthetic Design and Construction Guidelines, by R.D. Holtz, B.R. Christopher, and 

R.R. Berg, FHWA HI-07-092 (2008). 

C Guidelines for Design, Specification, and Contracting of Geosynthetic Mechanically 

Stabilized Earth Slopes on Firm Foundations, by R.R. Berg, FHWA-SA-93-025, January 

1993. 

C Reinforced Soil Structures - Volume I, Design and Construction Guidelines - Volume II, 

Summary of Research and Systems Information, by B.R. Christopher, S.A. Gill, J.P. 

Giroud, J.K. Mitchell, F. Schlosser, and J. Dunnicliff, FHWA RD 89-043 (1990). 

C Design and Construction Monitoring of Mechanically Stabilized Earth Structures, by 

J.A. DiMaggio, FHWA, (1994). 

C AASHTO Bridge T-15 Technical Committee unpublished working drafts for the update 

of Section 11.0 of the AASHTO LRFD Bridge Design Specifications. 

FHWA NHI-10-025 

MSE Walls and RSS – Vol II iii	 November 2009 
The authors recognize the efforts and contributions of Messrs. Richard Barrows, P.E., Silas 

Nichols, P.E., and Daniel Alzamora P.E. who were the FHWA Technical Consultants for this 

work. 

The authors also recognize the contributions of the other Technical Consultants on this 

project. They are: 

C Tony Allen, P.E. of Washington DOT 

C Christopher Benda, P.E. of Vermont DOT 

C James Brennan, P.E. of Kansas DOT 

C James Collin, Ph.D., P.E. of The Collin Group 

C Jerry DiMaggio, P.E. of the National Academy of Sciences 

C Kenneth L. Fishman, Ph.D., P.E. of Earth Reinforcement Testing, Inc. 

C Kathryn Griswell, P.E. of CALTRANS 

C John Guido, P.E. of Ohio DOT 

C Dan Johnston, P.E. of South Dakota DOT 

C Dov Leshchinsky, Ph.D. of the University of Delaware 

C Michael Simac, P.E. of Earth Improvement Technologies, Inc. 

C James L. Withiam, Ph.D., P.E. of D’Appolonia Engineers 

And the authors acknowledge the contributions of the following industry associations: 

C Association of Metallically Stabilized Earth (AMSE) 

C Geosynthetic Materials Association (GMA) 

C National Concrete Masonry Association (NCMA) 

A special acknowledgement of Mr. Jerry A. DiMaggio, P.E. who was the FHWA Technical 

Consultant for most of the above referenced publications. Mr. DiMaggio's guidance and 

input to this and the previous works has been invaluable. 

Lastly, the authors wish to acknowledge the extensive work of the late Victor Elias, P.E. for 

his vital contributions and significant effort as Lead Author in preparing the earlier two 

(1997, 2001) versions of this manual, and as the author of the earlier companion manuals on 

corrosion/degradation of soil reinforcements. Mr. Elias was instrumental in the introduction 

and implementation of reinforced soil technology in the U.S., as a Vice President for The 

Reinforced Earth Company from 1974 to 1985. He was instrumental in research, refinement 

of design methods, and standards of practice and codes for MSE walls, as a Consultant from 

1985 until 2006. 

FHWA NHI-10-025 

MSE Walls and RSS – Vol II iv November 2009 
 

TABLE OF CONTENTS – Volume II
 

CHAPTER 8 REINFORCED (STEEPENED) SOIL SLOPES PROJECT EVALUATION ..... 8-1 

8.1 INTRODUCTION ............................................................................................... 8-1 

8.2 REINFORCED SOIL SLOPE SYSTEMS .......................................................... 8-1 

8.2.1 Types of Systems ..................................................................................... 8-1 

8.2.2 Construction Materials ............................................................................. 8-2 

8.3 DESIGN APPROACH ........................................................................................ 8-2 

8.3.1 Use Considerations .................................................................................. 8-2 

8.3.2 Design of Reinforcement for Compaction Aid ........................................ 8-4 

8.3.3 Design of Reinforcement for Steepening Slopes and Slope Repair ........ 8-4 

8.3.4 Computer-Assisted Design ...................................................................... 8-6 

8.3.5 Evaluation of External Stability .............................................................. 8-8 

8.4 CONSTRUCTION SEQUENCE ...................................................................... 8-11 

8.5 TREATMENT OF OUTWARD FACE............................................................. 8-15 

8.5.1 Grass Type Vegetation........................................................................... 8-15 

8.5.2 Soil Bioengineering (Woody Vegetation) ............................................. 8-16 

8.5.3 Armored ................................................................................................. 8-19 

8.6 DESIGN DETAILS ........................................................................................... 8-20 

8.6.1 Guardrail and Traffic Barriers ............................................................... 8-20 

8.6.2 Drainage Considerations ........................................................................ 8-20 

8.6.3 Obstructions ........................................................................................... 8-21 

8.7 CASE HISTORIES ............................................................................................ 8-21 

8.7.1 The Dickey Lake Roadway Grade Improvement Project ...................... 8-21 

8.7.2 Salmon-Lost Trail Roadway Widening Project ..................................... 8-24 

8.7.3 Cannon Creek Alternate Embankment Construction Project ................ 8-26 

8.7.4 Pennsylvania SR 54 Roadway Repair Project ....................................... 8-27 

8.7.5 Massachusetts Turnpike - Use of Soil Bioengineering .......................... 8-29 

8.7.6 242-foot High 1H:1V Reinforced Soil Slope for Airport Runway 

Extension................................................................................................ 8-32 

8.8 STANDARD RSS DESIGNS ............................................................................ 8-34 

CHAPTER 9 DESIGN OF REINFORCED SOIL SLOPES ....................................................... 9-1 

9.1 INTRODUCTION ............................................................................................... 9-1 

9.2 REINFORCED SLOPE DESIGN GUIDELINES............................................... 9-3 

9.2.1 Step 1 - Establish the geometric, loading, and performance 

requirements for design............................................................................ 9-3 

9.2.2 Step 2 - Determine the engineering properties of the in-situ soils........... 9-3 

9.2.3 Step 3 - Determine the properties of reinforced fill and, if different, the 

retained fill............................................................................................... 9-5 

9.2.4 Step 4 - Evaluate design parameters for the reinforcement ..................... 9-5 

9.2.5 Step 5 - Check unreinforced stability....................................................... 9-5 

9.2.6 Step 6 - Design reinforcement to provide a stable slope ......................... 9-7 

9.2.7 Step 7 - Check external stability ............................................................ 9-16 

9.2.8 Step 8 - Seismic stability........................................................................ 9-18 

9.2.9 Step 9 - Evaluate requirements for subsurface and surface water runoff 

control .................................................................................................... 9-19

FHWA NHI-10-025	 Table of Contents 

MSE Walls and RSS – Vol II v November 2009 
 

9.3 COMPUTER ASSISTED DESIGN .................................................................. 9-23 

9.4 PROJECT COST ESTIMATES ........................................................................ 9-24 

 CHAPTER 10 CONTRACTING METHODS AND SPECIFICATIONS
 

FOR MSE WALLS AND SLOPES............................................................................... 10-1 

10.1 POLICY DEVELOPMENT............................................................................... 10-2 

10.2 SYSTEM OR COMPONENT APPROVALS ................................................... 10-2 

10.3 DESIGN AND PERFORMANCE CRITERIA ................................................. 10-5 

10.4 AGENCY OR SUPPLIER DESIGN ................................................................. 10-5 

10.4.1 Plan and Elevation Sheets...................................................................... 10-6 

10.4.2 Facing/Panel Details ............................................................................ 10-7 

10.4.3 Drainage Facilities/Special Details........................................................ 10-7 

10.4.4 Design Computations............................................................................. 10-7 

10.4.5 Geotechnical Report............................................................................... 10-7 

10.4.6 Construction Specifications ................................................................... 10-8 

10.5 END RESULT DESIGN APPROACH ............................................................. 10-8 

10.5.1 Geometric Requirements ....................................................................... 10-9 

10.5.2 Geotechnical Requirements ................................................................... 10-9 

10.5.3 Structural and Design Requirements ..................................................... 10-9 

10.5.4 Performance Requirements .................................................................. 10-10 

10.6 STANDARD DESIGNS .................................................................................. 10-10 

10.6.1 MSEW Standard Designs .................................................................... 10-10 

10.6.2 RSS Standard Designs ......................................................................... 10-12 

10.7 REVIEW AND APPROVALS........................................................................ 10-13 

10.8 CONSTRUCTION SPECIFICATIONS AND SPECIAL PROVISIONS FOR 

MSEW AND RSS CONSTRUCTION ............................................................ 10-14 

10.9 EXAMPLE SPECIFICATION FOR MSE WALLS ....................................... 10-15 

10.10 CONSTRUCTION SPECIFICATIONS FOR REINFORCED 

SLOPE SYSTEMS ...................................................................................... 10-41 

10.10.1 Specification Guidelines For RSS Construction (Agency Design) 10-42 

10.10.2 Specification for Erosion Control Mat or Blanket......................... 10-46 

10.10.3 Specification for Geosynthetic Drainage Composite..................... 10-48 

10.10.4 Specification Guidelines for Geosynthetic Reinforced Soil 

 Slope Systems ................................................................................ 10-52 

CHAPTER 11 FIELD INSPECTION AND PERFORMANCE MONITORING..................... 11-1 

11.1 PRECONSTRUCTION REVIEWS................................................................... 11-1 

11.1.1 Plans and Specifications ........................................................................ 11-3 

11.1.2 Review of Site Conditions and Foundation Requirements .................... 11-3 

11.2 PREFABRICATED MATERIALS INSPECTION ......................................... 11-11 

11.2.1 Precast Concrete Elements................................................................... 11-11 

11.2.2 Reinforcing Elements........................................................................... 11-13 

11.2.3 Facing Joint Materials.......................................................................... 11-15 

11.2.4 Reinforced Backfill .............................................................................. 11-15 

11.3 CONSTRUCTION CONTROL ....................................................................... 11-16 

11.3.1 Leveling Pad ........................................................................................ 11-16 

11.3.2 Erection of Facing Elements ................................................................ 11-16 

FHWA NHI-10-025	 Table of Contents 

MSE Walls and RSS – Vol II vi	 November 2009 
11.3.3 Reinforced Fill Placement, Compaction .............................................. 11-22 

11.3.4 Placement of Reinforcing Elements..................................................... 11-25 

11.3.5 Placement of Subsequent Facing Courses (Segmental Facings) ......... 11-26 

11.4 PERFORMANCE MONITORING PROGRAMS .......................................... 11-35 

11.4.1 Purpose of Monitoring Program .......................................................... 11-35 

11.4.2 Limited Monitoring Program ............................................................... 11-36 

11.4.3 Comprehensive Monitoring Program .................................................. 11-37 

11.4.4 Program Implementation ..................................................................... 11-37 

11.4.5 Data Interpretation ............................................................................... 11-40 

REFERENCES ............................................................................................................................R-1 

APPENDICES 

APPENDIX A LRFD LOAD COMBINATIONS AND LOAD FACTORS, AND LOAD 

FACTOR FOR PERMANENT LOADS ....................................................................... A-1 

APPENDIX B DETERMINATION OF PULLOUT RESISTANCE FACTORS .................B-1 

B.1 EMPIRICAL PROCEDURES TO DETERMINE F*

 AND α .......................B-1 

B.2 EXPERIMENTAL PROCEDURES TO DETERMINE F* AND α .............B-2 

B.3 CONNECTION RESISTANCE AND STRENGTH OF PARTIAL AND 

FULL FRICTION SEGMENTAL BLOCK/REINFORCEMENT FACING 

CONNECTIONS ...........................................................................................B-5 

B.4 CONNECTION RESISTANCE DEFINED WITH

 SHORT-TERM TESTING .........................................................................B-12 

B.5 REFERENCES ............................................................................................B-15 

APPENDIX C TYPICAL DIMENSIONS OF STEEL REINFORCEMENTS .....................C-1 

APPENDIX D DETERMINATION OF CREEP STRENGTH REDUCTION FACTOR ... D-1 

D.1 BACKGROUND .......................................................................................... D-1 

D.2 STEP-BY-STEP PROCEDURES FOR EXTRAPOLATING STRESS 

RUPTURE DATA -- CONVENTIONAL METHOD .................................. D-5 

D.3 STEP-BY-STEP PROCEDURES FOR EXTRAPOLATING STRESS 

RUPTURE DATA -- STEPPED ISOTHERMAL METHOD (SIM) ......... D-10 

D.4 DETERMINATION OF RFCR .................................................................... D-13 

D.5 USE OF CREEP DATA FROM "SIMILAR" PRODUCTS AND 

EVALUATION OF PRODUCT LINES .................................................... D-14 

D.6 CREEP EXTRAPOLATION EXAMPLES USING STRESS

 RUPTURE DATA .......................................................................................E-16 

D.6.1 Stress Rupture Extrapolation Example ............................................E-16 

D.7 REFERENCES ............................................................................................E-20 

FHWA NHI-10-025	 Table of Contents 

MSE Walls and RSS – Vol II vii November 2009 
APPENDIX E EXAMPLE CALCULATIONS 

E.1 MBW Unit Faced MSE Wall with Broken Back Sloping Fill and Live 

Load Surcharge, Reinforced with Geogrid ................................................. E.1-1 

E.2 Bearing Check for Sloping Toe Conditions, with and without Water ........ E.2-1 

E.3 Segmental Precast Panel MSE Wall with Sloping Backfill Surcharge, 

Reinforced with Steel Strips .......................................................................E.3-1 

E.4 Segmental Precast Panel MSE Wall with Level Backfill and Live Load 

Surcharge, Reinforced with Steel Bar Mats................................................E.4-1 

E.5 True Bridge Abutment with Segmental Precast Panel MSE Wall, 

Reinforced with Steel Strips .......................................................................E.5-1 

E.6 Traffic Barrier Impact Loading on Top of an MSE Wall ...........................E.6-1 

E.7 Seismic Loading . . . ., Psuedo-Static Analysis........................................... E.7-1 

E.8 Reinforced Soil Slope Design -- Road Widening .......................................E.8-1 

E.9 Reinforced Soil Slope Design -- High Slope for New Road Construction . E.9-1 

E.10 Reinforced Soil Slope Design -- Facing Stability Calculation .................E.10-1 

APPENDIX F OTHER DESIGN PROCEDURES AND ANALSIS MODELS 

F.1 ASD Procedure and the Simplified Method ..................................................F-2 

F.2 Coherent Gravity Method ..............................................................................F-3 

F.3 National Concrete Masonry Association Procedure ......................................F-5 

F.4 GRS ......................................................................................................F-5 

F.5 FHWA Structural Stiffness Method............................................................... F-7 

F.6 K-Stiffness Method ........................................................................................F-8 

F.7 Deep Patch ...................................................................................................F-11 

FHWA NHI-10-025	 Table of Contents 

MSE Walls and RSS – Vol II viii November 2009 
LIST OF TABLES – Volume II
 

Table 8-1. RSS Slope Facing Options (after Collin, 1996)................................................. 8-14 

Table 9-1. Estimated Project Costs. .................................................................................... 9-25 

Table 11-1. Outline of MSE/RSS Field Inspection Checklist. .............................................. 11-2 

Table 11-2. Checklist for Drawing Review........................................................................... 11-5 

Table 11-3. Checklist for Specification Compliance. ........................................................... 11-7 

Table 11-4. Out-of-Tolerance Conditions and Possible Causes.......................................... 11-30 

Table 11-5. Checklist for Construction. .............................................................................. 11-32 

Table 11-6. Possible Instruments for Monitoring Reinforced Soil Structures. ................... 11-38 

FHWA NHI-10-025 Table of Contents 

MSE Walls and RSS – Vol II ix November 2009 
 

FHWA NHI-10-025 Table of Contents
 

MSE Walls and RSS – Vol II x November 2009
 
 

LIST OF FIGURES – Volume II 

Figure 8-1. Failure modes for RSSs including internal failure within the reinforced soil 

zone, external failure entirely outside the reinforced soil zone, and compound 

failure starting behind and passing through the reinforced soil zone .......... .... 8-3 

Figure 8-2. Modified limit equilibrium analysis for reinforced slope design......................... 8-5 

Figure 8-3. External failure modes for reinforced soil slopes. ............................................... 8-9 

Figure 8-4. Construction of reinforced soil slopes. .............................................................. 8-12 

Figure 8-5. Welded wire mesh detail for temporary (during construction) or permanent 

face support........................................................................................................ 8-15 

Figure 8-6. Components of a vegetated reinforced slope (VRSS) system ........................... 8-17 

Figure 8-7. Dickey Lake site. ............................................................................................... 8-23 

Figure 8-8. Salmon Lost Trail site. ....................................................................................... 8-25 

Figure 8-9. Cannon Creek project. ....................................................................................... 8-26 

Figure 8-10. Pennsylvania SR54. ........................................................................................... 8-28 

Figure 8-11. Massachusetts Turnpike during construction, immediately after construction 

and after the second growing season. ................................................................ 8-31 

Figure 8-12. Reinforced soil slope for runway extension at Yeager Airport, Charleston, 

West Virginia..................................................................................................... 8-33 

Figure 8-13. Example of standard RSS design. ...................................................................... 8-36 

Figure 9-1. Flow chart of steps for reinforced soil slope design. ........................................... 9-2 

Figure 9-2. Requirements for design of reinforced soil slopes............................................... 9-4 

Figure 9-3. Critical zone defined by rotational and sliding surface that meet the required 

safety factor.......................................................................................................... 9-6 

Figure 9-4. Rotational shear approach to determine required strength of reinforcement....... 9-8 

Figure 9-5. Chart solution for determining the reinforcement strength requirements.......... 9-10 

Figure 9-6. Reinforcement spacing considerations for high slopes...................................... 9-11 

Figure 9-7. Developing reinforcement lengths. .................................................................... 9-14 

Figure 9-8. Failure through the foundation........................................................................... 9-17 

Figure 9-9. Seismic stability analysis. .................................................................................. 9-19 

Figure 9-10. Subsurface drainage considerations. .................................................................. 9-20 

Figure 11-1. Casting yard for precast facing elements. ........................................................ 11-12 

Figure 11-2. Inspect reinforcing elements: top photo shows a variety of reinforcements 

including metallic strips, welded wire mesh, and geosynthetics and bottom 

photo shows reinforcement length painted on geogrid reinforcement............. 11-14 

Figure 11-3. Leveling pads: a) leveling the concrete, b) completed pad, and c) placing the 

facing elements on the leveling pad. ................................................................ 11-17 

Figure 11-4. Checking facing element batter and alignment................................................ 11-18 

Figure 11-5. Full height facing panels require special alignment care. ................................ 11-19 

Figure 11-6. Setting first row of precast facing elements..................................................... 11-21 

Figure 11-7. Placement of reinforced fill. ............................................................................ 11-23 

Figure 11-8. Compaction equipment showing: a) large equipment permitted away from 

face; and b) lightweight equipment within 3 ft (1 m) of the face. ................... 11-24 

Figure 11-9. Facing connection examples ............................................................................ 11-27 

Figure 11-10. Geotextile joint cover and neoprene pads. ....................................................... 11-29 

FHWA NHI-10-025 Table of Contents 

MSE Walls and RSS – Vol II xi November 2009 
FHWA NHI-10-025 Table of Contents
 

MSE Walls and RSS – Vol II xii November 2009
 
TABLE OF CONTENTS – Volume I
 

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

1.1 OBJECTIVES...................................................................................................... 1-1 

1.1.1 Scope ...................................................................................................... 1-1 

1.1.2 Source Documents ................................................................................... 1-2 

1.1.3 Terminology............................................................................................. 1-3 

1.2 HISTORICAL DEVELOPMENT ....................................................................... 1-4 

1.3 LOAD AND RESISTANCE FACTOR DESIGN (LRFD) ............................... 1-12 

CHAPTER 2 SYSTEMS AND PROJECT EVALUATION ....................................................... 2-1 

2.1 APPLICATIONS ................................................................................................. 2-1 

2.1.1 MSE Walls ............................................................................................... 2-1 

2.1.2 Reinforced Soil Slopes............................................................................. 2-4 

2.2 ADVANTAGES AND POTENTIAL DISADVANTAGES............................... 2-6 

2.2.1 Advantages of Mechanically Stabilized Earth (MSE) Walls................... 2-6 

2.2.2 Advantages of Reinforced Soil Slopes (RSS).......................................... 2-6 

2.2.3 Potential Disadvantages ........................................................................... 2-7 

2.3 RELATIVE COSTS............................................................................................. 2-7 

2.4 DESCRIPTION OF MSE/RSS SYSTEMS....................................................... 2-10 

2.4.1 Systems Differentiation ......................................................................... 2-10 

2.4.2 Types of Systems ................................................................................... 2-11 

2.4.3 Facing Systems ...................................................................................... 2-12 

2.4.4 Reinforcement Types ............................................................................. 2-16 

2.4.5 Reinforced Fill Materials ....................................................................... 2-17 

2.4.6 Appurtenant Materials of Construction ................................................. 2-18 

2.5 CONSTRUCTION SEQUENCE ....................................................................... 2-18 

2.5.1 Construction of MSEW systems with precast facings ........................... 2-18 

2.5.2 Construction of MSE systems with Flexible Facings ............................ 2-24 

2.5.3 RSS Construction................................................................................... 2-28 

2.6 SITE EVALUATION ........................................................................................ 2-28 

2.6.1 Site Exploration ..................................................................................... 2-28 

2.6.2 Field Reconnaissance ............................................................................. 2-30 

2.6.3 Subsurface Exploration .......................................................................... 2-30 

2.6.4 Laboratory Testing ................................................................................. 2-32 

2.6.5 Foundation Soils .................................................................................... 2-33 

2.7 PROJECT EVALUATION................................................................................ 2-34 

2.7.1 Structure Selection Factors .................................................................... 2-34 

2.7.2 Geologic and Topographic Conditions .................................................. 2-35 

2.7.3 Environmental Conditions ..................................................................... 2-36 

2.7.4 Size and Nature of Structure.................................................................. 2-37 

2.7.5 Aesthetics............................................................................................... 2-38 

2.7.6 Questionable Applications ..................................................................... 2-38 

2.8 ESTABLISHMENT OF PROJECT CRITERIA ............................................... 2-38 

2.8.1 Alternates ............................................................................................... 2-39 

2.8.2 Facing Considerations............................................................................ 2-39 

FHWA NHI-10-025 Table of Contents 

MSE Walls and RSS – Vol II xiii November 2009 
 

2.8.3 Performance Criteria .............................................................................. 2-40 

2.8.4 Design Life............................................................................................. 2-46 

2.9 PROPRIETARY ASPECTS .............................................................................. 2-46 

2.10 CASE HISTORIES -- MSE WALLS ................................................................ 2-47 

2.10.1 Mn/DOT Crosstown Project MSE Walls............................................... 2-47 

2.10.2 Veterans Memorial Overpass True Abutment MSE Walls.................... 2-49 

2.10.3 SEATAC Runway Extension Wall ........................................................ 2-50 

2.10.4 Guanella Pass Roadway Reconstruction................................................ 2-51 

CHAPTER 3 SOIL REINFORCEMENT PRINCIPLES 

AND SYSTEM DESIGN PROPERTIES ........................................................................ 3-1 

3.1 OVERVIEW ........................................................................................................ 3-1 

3.2 ESTABLISHMENT OF ENGINEERING PROPERTIES BASED ON SITE 

EXPLORATION AND TESTING ...................................................................... 3-2 

3.2.1 Reinforced Fill Soil .................................................................................. 3-2 

3.2.2 Retained Backfill and Natural Retained Soil ........................................... 3-8 

3.2.3 Electrochemical Properties ...................................................................... 3-9 

3.3 REINFORCED SOIL CONCEPTS ................................................................... 3-10 

3.3.1 Stress Transfer Mechanisms .................................................................. 3-10 

3.3.2 Mode of Reinforcement Action ............................................................. 3-12 

3.3.3 Geometric Characteristics ...................................................................... 3-12 

3.4 SOIL REINFORCEMENT INTERACTION USING NORMALIZED 

CONCEPTS ....................................................................................................... 3-13 

3.4.1 Evaluation of Pullout Performance ........................................................ 3-13 

3.4.2 Estimate of the Reinforcement Pullout Capacity in MSE Structures .... 3-16 

3.4.3 Interface Shear ....................................................................................... 3-21 

3.5 ESTABLISHMENT OF STRUCTURAL DESIGN PROPERTIES ................. 3-22 

3.5.1 Strength Properties of Steel Reinforcements ......................................... 3-22 

3.5.2 Strength Properties of Geosynthetic Reinforcement.............................. 3-28 

3.5.2.a Ultimate Tensile Strength, Tult ................................................... 3-31 

3.5.2.b Installation Damage Reduction Factor, RFID ............................. 3-31 

3.5.2.c Creep Reduction Factor, RFCR ................................................... 3-32 

3.5.2.d Durability Reduction Factor, RFD.............................................. 3-33 

3.5.2.e Durability Reduction Factor, RFD, at Wall Face Unit ............... 3-38 

3.5.2.f LRFD Geosynthetic Resistance Factor, .................................. 3-38 

3.5.2.g Preliminary Design Reduction Factor, RF ................................. 3-39 

3.5.2.h Serviceability Limit State .......................................................... 3-40 

3.6 FACING MATERIALS ..................................................................................... 3-41 

3.6.1 Precast Concrete Panels ......................................................................... 3-41 

3.6.1.a Segmental Panels ....................................................................... 3-41 

3.6.1.b Full-Height Panels ..................................................................... 3-42 

3.6.2 Modular Block Wall (MBW) Units ....................................................... 3-43 

3.6.3 Welded Wire Mesh Facing .................................................................... 3-46 

3.6.4 Geosynthetic Wrap-Around Facing ....................................................... 3-47 

3.6.5 Other Facings ......................................................................................... 3-47 

3.6.6 Two-Stage Facings................................................................................. 3-50 

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CHAPTER 4 DESIGN OF MSE WALLS .................................................................................. 4-1 

4.1 DESIGN METHODOLOGY AND ANALYSIS METHODS ............................ 4-1 

4.1.1 Load and Resistance Factor Design (LRFD) Platform ............................ 4-1 

4.1.2 Analysis Methods..................................................................................... 4-2 

4.2 LOADS AND LOAD COMBINATIONS ........................................................... 4-3 

4.3 DESIGN OF MSE WALLS USING LRFD METHODOLOGY ........................ 4-6 

4.3.1 Design Steps............................................................................................. 4-7 

4.4 MSE WALLS DESIGN GUIDELINES .............................................................. 4-9 

4.4.1 Step 1 - Establish Project Requirements .................................................. 4-9 

4.4.2 Step 2 - Establish Project Parameters ...................................................... 4-9 

4.4.3 Step 3 - Estimate Wall Embedment Depth & Reinforcement Length ... 4-10 

4.4.4 Step 4 - Define Nominal Loads ............................................................. 4-11 

4.4.5 Step 5 - Summarize Load Combinations, Load Factors, and Resistance 

Factors ................................................................................................... 4-17 

4.4.6 Step 6 - Evaluate External Stability....................................................... 4-18 

4.4.6.a Evaluate Sliding Stability .......................................................... 4-19 

4.4.6.b Evaluate Eccentricity ................................................................. 4-22 

4.4.6.c Evaluate Bearing on Foundation................................................ 4-26 

4.4.6.d Settlement Estimate ................................................................... 4-31 

4.4.7 Step 7 - Evaluate Internal Stability ........................................................ 4-31 

4.4.7.a Select Type of Reinforcement ................................................... 4-32 

4.4.7.b Define Critical Slip Surface ....................................................... 4-33 

4.4.7.c Define Unfactored Loads ........................................................... 4-35 

4.4.7.d Establish Vertical Layout of Soil Reinforcements..................... 4-38 

4.4.7.e Calculate Factored Tensile Forces in Reinforcements............... 4-39 

4.4.7.f Calculate Soil Reinforcement Resistance .................................. 4-47 

4.4.7.g Select Grade of &/or Number of Elements at Each Level ......... 4-49 

4.4.7.h Internal Stability with Respect to Pullout Failure...................... 4-49 

4.4.7.i Check Connection Strength ....................................................... 4-52 

4.4.7.j Lateral Movements .................................................................... 4-57 

4.4.7.k Vertical Movement and Bearing Pads ....................................... 4-57 

4.4.8 Step 8 - Design of Facing Elements....................................................... 4-58 

4.4.8.a Design of Concrete, Steel, and Timber Facings ........................ 4-58 

4.4.8.b Design of Flexible Wall Facings................................................ 4-59 

4.4.9 Step 9 - Assess Overall Stability............................................................ 4-59 

4.4.10 Step 10 - Assess Compound Stability .................................................... 4-61 

4.4.11 Step 11 - Wall Drainage Systems .......................................................... 4-65 

4.11.a Surface Drainage........................................................................ 4-65 

4.11.b Surface Water Runoff ................................................................ 4-65 

4.11.c Scour .......................................................................................... 4-65 

4.5 TEMPORARY WALLS .................................................................................... 4-66 

4.6 DESIGN CHECKLIST ...................................................................................... 4-66 

4.7 COMPUTER-AIDED DESIGN ........................................................................ 4-80 

4.8 VENDOR........................................................................................................... 4-80 

4.9 STANDARD MSEW DESIGNS ....................................................................... 4-80 

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CHAPTER 5 MSE WALL DESIGN DETAILS ......................................................................... 5-1 

5.1 TOP OF WALL ELEMENTS ............................................................................. 5-1 

5.1.1 Copings .................................................................................................... 5-1 

5.1.2 Traffic Barriers......................................................................................... 5-4 

5.1.3 Parapets.................................................................................................... 5-4 

5.1.4 Post and Beam Barriers............................................................................ 5-4 

5.1.5 Drainage Related to Top of Wall Elements ............................................. 5-6 

5.2 BOTTOM OF WALL ELEMENTS .................................................................... 5-6 

5.3 DRAINAGE......................................................................................................... 5-8 

5.3.1 Internal Drainage Systems ....................................................................... 5-9 

5.3.2 External Drainage .................................................................................. 5-17 

5.3.3 Filtration and Drainage System Component Requirements................... 5-24 

5.3.4 Maintenance of Drainage....................................................................... 5-34 

5.4 INTERNAL DETAILS ...................................................................................... 5-35 

5.4.1 Contact Between Dissimilar Metals....................................................... 5-35 

5.4.2 Vertical Obstructions in Reinforced Soil Mass ..................................... 5-35 

5.4.3 Horizontal Obstructions in Reinforced Soil Mass ................................. 5-42 

5.4.4 Wall Face Penetrations .......................................................................... 5-44 

5.4.5 Slip Joints............................................................................................... 5-46 

5.4.6 Wall Curves ........................................................................................... 5-47 

5.4.7 Wall Corners .......................................................................................... 5-51 

5.4.8 Two-Stage Facing .................................................................................. 5-52 

5.5 WALL INITIATIONS AND TERMINATIONS .............................................. 5-54 

5.6 AESTHETICS.................................................................................................... 5-56 

CHAPTER 6 DESIGN OF MSE WALLS WITH COMPLEX GEOMETRICS ........................ 6-1 

6.1 BRIDGE ABUTMENTS ..................................................................................... 6-3 

6.1.1 MSEW Abutments on Spread Footings ................................................... 6-3 

6.1.2 MSEW Abutments on Stub Footings Supported by Deep Foundations 

through Reinforced Wall Fill ................................................................... 6-6 

6.1.3 Alternative Configuration of MSE Walls at Bridge Abutments ............ 6-10 

6.1.4 Protection of MSE Wall at Abutments .................................................. 6-11 

6.2 SUPERIMPOSED (TIERED) MSE WALLS.................................................... 6-13 

6.2.1 2-Tier Superimposed Wall ..................................................................... 6-13 

6.2.2 Superimposed Walls with More than 2-Tiers ........................................ 6-15 

6.3 WALLS WITH UNEVEN REINFORCEMENT LENGTHS ........................... 6-16 

6.4 BACK-TO-BACK (BBMSE) WALLS ............................................................. 6-17 

6.5 SHORED MSE WALLS FOR STEEP TERRAINS AND LOW VOLUME 

ROADS.............................................................................................................. 6-19 

6.6 STABLE FEATURE MSE (SFMSE) WALLS ................................................. 6-26 

CHAPTER 7 DESIGN OF MSE WALLS FOR EXTREME EVENTS...................................... 7-1 

7.1 SEISMIC EVENTS ............................................................................................. 7-1 

7.1.1 External Stability ..................................................................................... 7-1 

7.1.2 Internal Stability....................................................................................... 7-9 

7.1.2.a Tensile Failure ........................................................................... 7-11 

7.1.2.b Pullout Failure............................................................................ 7-12 

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7.1.3 Facing Reinforcement Connections ....................................................... 7-13 

7.2 VEHICULAR IMPACT EVENTS .................................................................... 7-14 

7.2.1 Traffic Barriers....................................................................................... 7-15 

7.2.2 Post and Beam Railings ......................................................................... 7-17 

7.3 FLOODS AND SCOUR .................................................................................... 7-18 

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FHWA NHI-10-025 Table of Contents
 

MSE Walls and RSS – Vol II xviii November 2009
 
 

LIST OF TABLES – Volume I
 

Table 1-1. Summary of Reinforcement and Face Details for MSE Wall Systems. .............. 1-7 

Table 1-2. Representative List of Geogrid and Geotextile Reinforcement Manufacturers 

and Suppliers...................................................................................................... 1-11 

Table 2-1. Typical Minimum Length of Reinforcement ..................................................... 2-43 

Table 2-2. Minimum MSEW Embedment Depths .............................................................. 2-43 

Table 2-3. Relationship Between Joint Width and Limiting Differential 

Settlements for MSE Precast Panels .................................................................. 2-46 

Table 3-1. MSE Wall Select Granular Reinforced Fill Requirements .................................. 3-3 

Table 3-2. RSS Granular Reinforced Fill Requirements....................................................... 3-6 

Table 3-3. Recommended Limits of Electrochemical Properties for Reinforced Fills with 

Steel Reinforcement ............................................................................................. 3-9 

Table 3-4. Recommended Limits of Electrochemical Properties for Reinforced Fills with 

Geosynthetic Reinforcements ............................................................................ 3-10 

Table 3-5. Basic Aspects of Reinforcement Pullout Performance in Granular 

and Cohesive Soils of Low Plasticity ................................................................ 3-15 

Table 3-6. Summary of Pullout Capacity Design Parameters. ............................................ 3-17 

Table 3-7. Minimum Galvanization Thickness by Steel Thickness.................................... 3-26 

Table 3-8. Steel Corrosion Rates for Mildly Corrosive Reinforced Fill ............................. 3-26 

Table 3-9. Installation Damage Reduction Factors. ............................................................ 3-32 

Table 3-10. Anticipated Resistance of Polymers to Specific Environments......................... 3-34 

Table 3-11. Durability (Aging) Reduction Factors for PET. ................................................ 3-36 

Table 3-12. Minimum Requirements for use of Default Durability Reduction Factors 

(RFD) for Primary Geosynthetic Reinforcement................................................ 3-37 

Table 3-13. Minimum Requirements for use of Preliminary Design Reduction Factor (RF) 

for Primary Geosynthetic Reinforcement. ......................................................... 3-40 

Table 3-14. Additional MBW Cold Weather Requirements Recommended by 

 Mn/DOT (2008). ................................................................................................ 3-45

Table 4-1. Typical MSE Wall Load Combinations and Load Factors (after Table 3.4.1-1, 

AASHTO, 2007) ................................................................................................. 4-4 

Table 4-2. Typical MSE Wall Load Factors for Permanent Loads, γp (after Table 3.4.1-2, 

AASHTO, 2007) ................................................................................................. 4-4 

Table 4-3. Basic LRFD Design Steps for MSE Walls .......................................................... 4-8 

Table 4-4. Equivalent Height of Soil, heq, for Traffic Loading on Abutments ........................... 

Perpendicular to Traffic (Table 3.11.6.4-1, AASHTO {2007}) ....................... 4-17 

Table 4-5. External Stability Resistance Factors for MSE Walls (Table 11.5.6-1, 

 AASHTO {2007}) ............................................................................................ 4-19

Table 4-6. Bearing Resistance Factors (Table 10.6.3.1.2a-1, AASHTO {2007}) ............. 4-29 

Table 4-7. Resistance Factors for Tensile and Pullout Resistance for MSE Walls (after 

Table 11.5.6-1, AASHTO (2007........................................................................ 4-48 

Table 4-8. Example MBW Faced MSE Wall Standard Design (Minnesota DOT, 2008) .. 4-82 

FHWA NHI-10-025 Table of Contents 

MSE Walls and RSS – Vol II xix November 2009 
 

Table 5-1. Values of B for Various Cu Values for Soils with less than 50% Passing the 

No. 200 Sieve ..................................................................................................... 5-27 

Table 5-2. Values of B and AOS for Soils with more than 50% Passing the No. 200 Sieve 

Based on Type of Geotextile ............................................................................... 5-27 

Table 5-3. Geotextile Survivability Requirements (AASHTO M 288, 2006) ................... 5-29 

Table 5-4. Recommended Minimum Properties for General Geomembrane Installation 

Survivability (after Koerner, 1998) ................................................................... 5-33 

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LIST OF FIGURES – Volume I 

Figure 1-1. Generic cross section of an MSE structure. ......................................................... 1-4 

Figure 1-2. Generic cross sections of reinforced soil slope structures, reinforcements used 

to: (a) increase stability of a slope; and (b) provide improved compaction and 

surficial stability at edge of a slopes. ................................................................... 1-5 

Figure 2-1. Representative MSE applications (a) retaining wall; (b) access ramp; (c) 

waterfront structure; and (d) bridge abutment. .................................................... 2-2 

Figure 2-2. MSE walls to support temporary bridge abutment roadway embankment .......... 2-3 

Figure 2-3. MSE wall used to temporarily support a permanent roadway embankment for 

phased construction.............................................................................................. 2-3 

Figure 2-4. Application of reinforced soil slopes. .................................................................. 2-5 

Figure 2-5. Cost evaluation of reinforced soil slopes. .......................................................... 2-10 

Figure 2-6. Example MSE wall surface treatments. ............................................................. 2-13 

Figure 2-7. Examples of commercially available MBW units (NCMA, 1997).................... 2-14 

Figure 2-8. Erection of precast panels. ................................................................................. 2-21 

Figure 2-9. Fill spreading and reinforcement connection..................................................... 2-22 

Figure 2-10. Compaction of reinforced wall fill..................................................................... 2-23 

Figure 2-11. Lift construction sequence for geosynthetic faced MSE walls. ......................... 2-25 

Figure 2-12. Typical geosynthetic face construction detail. ................................................... 2-26 

Figure 2-13. Types of geosynthetic reinforced soil wall facing (after Wu, 1994) ................. 2-27 

Figure 2-14. Reinforced slope construction: (a) geogrid and fill placement; (b) soil filled 

erosion control mat placement; and (c) finished, vegetated 1:1 slope ............... 2-29 

Figure 2-15. Empirical curve for estimating probable anticipated lateral displacement 

during construction for MSE walls (after FHWA 89-043 {Christopher et al., 

1990}) .............................................................................................................. 2-41 

Figure 2-16. MSE wall embedment depth requirements, (a) level toe condition and (b)
 

benched slope toe condition............................................................................... 2-44 

Figure 2-17. MSE wall construction on Mn/DOT Crosstown Project, 2008. ........................ 2-48 

Figure 2-18. Veterans Memorial Overpass............................................................................. 2-49 

Figure 2-19. MSE true bridge abutment ................................................................................. 2-49 

Figure 2-20. Typical cross section, VMO project .................................................................. 2-50 

Figure 2-21. SeaTac Airport runway extension MSE wall..................................................... 2-51 

Figure 2-22. Guanella Pass wire-faced wall........................................................................... 2-52 

Figure 2-23. Guanella Pass architectural concrete faced wall ................................................ 2-52 

Figure 3-1. Examples of reinforced fill zone extension beyond the reinforced zone. ............ 3-8 

Figure 3-2. Stress transfer mechanisms for soil reinforcement. ........................................... 3-11 

Figure 3-3. Coverage ratio.................................................................................................... 3-13 

Figure 3-4. Definition of grid dimensions for calculating pullout capacity ......................... 3-18 

Figure 3-5. Parameters for metal reinforcement strength calculations showing (a) steel 

strips and (b) metallic grids and bar mats .......................................................... 3-24 

Figure 3-6. Long-term geosynthetic reinforcement strength concepts ................................. 3-29 

Figure 3-7. Large, wet-cast concrete face unit with reinforcement placed between units. .. 3-48 

Figure 3-8. Large, wet-cast concrete face unit with embedded reinforcement connectors. . 3-49 

Figure 3-9. Geocell face unit with vegetation. ..................................................................... 3-49 

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Figure 4-1. External stability load factors for simple walls.................................................... 4-5 

Figure 4-2. External analysis: nominal earth pressures; horizontal backslope with traffic 

surcharge (after AASHTO, 2007) ..................................................................... 4-12 

Figure 4-3. External analysis: earth pressure; sloping backfill case (after AASHTO, 

2007). ................................................................................................................ 4-13 

Figure 4-4. External analysis: earth pressure; broken backslope case (after AASHTO, 

2007) ................................................................................................................ 4-14 

Figure 4-5. Notation for Coulomb active earth pressures used with wall batters, , greater 

than 100 (after AASHTO, 2007)..................................................................... 4-16 

Figure 4-6. Potential external failure mechanisms for a MSE wall...................................... 4-18 

Figure 4-7. Calculation of eccentricity and vertical stress for bearing check, for horizontal 

backslope with traffic surcharge condition ........................................................ 4-24 

Figure 4-8. Calculation of eccentricity and vertical stress for bearing check, for sloping
 

backslope condition ........................................................................................... 4-25 

Figure 4-9. Location of potential failure surface for internal stability design of MSE Walls 

(a) inextensible reinforcements and (b) extensible reinforcements ................... 4-34 

Figure 4-10. Variation of the coefficient of lateral stress ratio (K/Ka) with depth in a MSE 

wall (Elias and Christopher, 1997; AASHTO, 2002; after AASHTO, 2007) .. 4-37 

Figure 4-11. Calculation of vertical stress for sloping backfill conditions for internal 

stability............................................................................................................... 4-38 

Figure 4-12. Distribution of stress from concentrated vertical load for internal and external 

stability calculations........................................................................................... 4-44 

Figure 4-13. Distribution of stresses from concentrated horizontal loads.............................. 4-45 

Figure 4-14. Reinforcement load contributory height ............................................................ 4-46 

Figure 4-15. Nominal vertical stress at the reinforcement level in the resistant zone, 

beneath a sloping backfill .................................................................................. 4-50 

Figure 4-16. Bodkin connection detail (looking at cross section of segmental panel face .... 4-53 

Figure 4-17. Determination of hinge height for modular concrete block faced MSE walls 

(NMCA, 1997) .................................................................................................. 4-56 

Figure 4-18. Typical geometries where MSE wall compound stability is of concern: steep 

and tall backslope on top of the wall; tiered walls; slope at the toe of the wall; 

and water at toe of the slope .............................................................................. 4-64 

Figure 4-19. Example of standard MSEW design. (Minnesota DOT, 2008) ....................... 4-83 

Figure 5-1. Example copings for MSE walls.......................................................................... 5-2 

Figure 5-2. Example traffic barrier for MSE walls. (a) Barrier behind coping, (b) barrier 

on top of panels, (c) barrier on top of modular block units ................................. 5-5 

Figure 5-3. Leveling pads, (a) Common size, b) Step detail for precast panel facing units, 

(c) Step detail for modular block facing units ..................................................... 5-7 

Figure 5-4. Potential sources and flowpaths of water........................................................... 5-10 

Figure 5-5. Example layout of filter at joints between segmental precast facing units ........ 5-11 

Figure 5-6. Layout of drainage fabric and drainage fill at the face for modular block units. 

(Collin et al., 2002) ............................................................................................ 5-12 

Figure 5-7. Example layout of geotextile filter near the face for welded wire facing units . 5-13 

Figure 5-8. Example drainage blanket detail behind the retained backfill ........................... 5-14 

Figure 5-9. Example drainage detail using a geocomposite sheet drain............................... 5-15 

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MSE Walls and RSS – Vol II xxii November 2009 
Figure 5-10. Example drainage detail using a blanket drain with chimney drain (Collin et 

al., 2002) ............................................................................................................ 5-16 

Figure 5-14. Example detail for wall that may experience inundation................................... 5-17 

Figure 5-12. Example MSE wall overflow sill at top of wall................................................. 5-19 

Figure 5-13. Example drainage swale near top of wall. ((b) Collin et al., 2002) ................... 5-20 

Figure 5-14. (a) Example geomembrane barrier details, (b) Installation of geomembrane 

deicing salt runoff barrier, (c) Geomembrane installation around manhole 

penetration.......................................................................................................... 5-22 

Figure 5-15. Example of undesirable water seepage through pavement due to deficient 

grades (Collin et al., 2002)................................................................................. 5-23 

Figure 5-16. Example of surface flow erosion at the bottom of an MSE wall ....................... 5-24 

Figure 5-17. Examples of avoiding a vertical obstruction without severing soil 

reinforcements.................................................................................................... 5-37 

Figure 5-18. Vertical obstructions in reinforced soil mass with segmental precast facing
 

units ................................................................................................................ 5-39 

Figure 5-19. Example of a structural frame around vertical obstruction (a) with segmental 

precast facing - note that vertically adjacent layers of reinforcement to be 

separated by a minimum of 3-in. (75 mm) of wall fill, (b)-(c) with modular 

block face – note corner detail ........................................................................... 5-40 

Figure 5-20. Example details of reinforcements around vertical obstructions in reinforced 

soil mass with modular block units.................................................................... 5-41 

Figure 5-21. Navigating horizontal obstruction in MSE walls with inextensible 

reinforcements.................................................................................................... 5-43 

Figure 5-22. Navigating horizontal obstruction in MSE walls with extensible 

 reinforcement ..................................................................................................... 5-43

Figure 5-23. Example of backup panels for large horizontal obstructions ............................. 5-44 

Figure 5-24. Example pipe penetrations through segmental precast panel facing units ........ 5-45 

Figure 5-25. Example pipe penetration through modular block facing units ......................... 5-46 

Figure 5-26. Example slip joints for segmental precast panel facings ................................... 5-48 

Figure 5-27. Example slip joint for modular block wall facings ............................................ 5-49 

Figure 5-28. Example layout of geogrid reinforcement for walls with curves....................... 5-50 

Figure 5-29. Example corner details....................................................................................... 5-51 

Figure 5-30. Conceptual connection details for a 2-stage facing system ............................... 5-53 

Figure 5-31. Common joint details between segmental precast panel facing units and CIP 

structures............................................................................................................ 5-55 

Figure 5-32. Common joint between modular block facing units and CIP structures ........... 5-55 

Figure 5-33. Example of MSE wall aesthetics ....................................................................... 5-58 

Figure 5-34. Examples of cast-in-place abutment to MSE wall panel transitions.................. 5-59 

Figure 6-1. Types of complex MSE structures ....................................................................... 6-2 

Figure 6-2. Geometry definition, location of critical failure surface and variation of Kr and 

F* parameters for analysis of a MSEW abutment on spread footing ................. 6-4 

Figure 6-3. Details of a typical pile supported MSE abutment .............................................. 6-7 

Figure 6-4. Geometry definition and typical supplemental lateral pressure distribution 

from deep foundation on MSE wall face ............................................................. 6-9 

Figure 6-5. Example of use of a geosynthetic wrapped face wall behind an integral 

abutment............................................................................................................. 6-12 

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Figure 6-6. Example abutment seat detail ............................................................................ 6-12 

Figure 6-7. Design rules for a 2-tier superimposed MSE wall system ................................. 6-14 

Figure 6-8. Dimensioning of MSE wall with uneven reinforcement lengths ....................... 6-17 

Figure 6-9. Back–to–back MSE walls.................................................................................. 6-18 

Figure 6-10. Generic cross-section of a shored MSE (SMSE) wall system for steep terrains 

(Morrison et al., 2006) ....................................................................................... 6-19 

Figure 6-11. Minimum recommended geometry of a shored MSE wall system in steep 

terrains, (a) with extension of upper two rows of reinforcement, and (b) with 

the upper two rows connected to the shoring wall (Morrison et al., 2006) ....... 6-21 

Figure 6-12. Location of potential failure surface for internal stability design of shored 

MSE walls (a) extensible reinforcements, (b) inextensible reinforcements 

(Morrison et al., 2006) ....................................................................................... 6-23 

Figure 6-13. Distribution of stress from concentrated vertical load for internal and external 

stability calculations (Morrison et al., 2006) ..................................................... 6-23 

Figure 6-14. Computation for TMAX and evaluation of pullout resistance (after Morrison et 

al., 2006) ............................................................................................................ 6-25 

Figure 6-15. Example global stability and compound failure surfaces (Morrison et al., 

2006) ................................................................................................................ 6-26 

Figure 6-16. Minimum recommended geometry of a stable feature MSE (SFMSE) wall 

system ................................................................................................................ 6-28 

Figure 7-1. Definition of heights for seismic analyses ..................................................................7-3 

Figure 7-2. Use of a slope stability approach to compute seismic earth pressure........................7-6 

Figure 7-3. Procedure for determination of ky (Anderson et al., 2008) ........................................7-7 

Figure 7-4. Boundary between WUS and CEUS (Anderson et al. 2008) ...................................7-8 

Figure 7-5. Seismic internal stability of a MSE wall............................................................ 7-10 

Figure 7-6. Comparison of static and dynamic impact force with 1-inch (25 mm) 

maximum displacement (Bligh et al., 2009) ...................................................... 7-15 

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MSE Walls and RSS – Vol II xxiv November 2009 
 

CHAPTER 8 

REINFORCED SOIL SLOPES PROJECT EVALUATION
 

 

8.1 INTRODUCTION 

Where right of way is available and the cost of a MSE wall is high, a steepened slope should 

be considered. In this chapter the background and design requirements for evaluating a 

reinforced soil slope (RSS) alternative are reviewed. Step-by-step design procedures are 

presented in Chapter 9. Section 8.2 reviews the types of systems and the materials of 

construction. Section 8.3 provides a discussion of the internal stability design approach for 

use of reinforcement as compaction aids, steepening slopes and slope repair. Computer 

assisted design programs are also reviewed. The section concludes with a discussion of 

external stability requirements. Section 8.4 reviews the construction sequence. Section 8.5 

covers treatment of the outward face of the slope to prevent erosion. Section 8.6 covers 

design details of appurtenant features including traffic barrier and drainage considerations. 

Finally, section 8.7 presents several case histories to demonstrate potential cost savings. 

8.2 REINFORCED SOIL SLOPE SYSTEMS 

8.2.1 Types of Systems 

Reinforced soil systems consist of planar reinforcements arranged in nearly horizontal planes 

in the reinforced fill to resist outward movement of the reinforced fill mass. Facing 

treatments ranging from vegetation to flexible armor systems are applied to prevent 

unraveling and sloughing of the face. These systems are generic in nature and can 

incorporate any of a variety of reinforcements and facing systems. Design assistance is often 

available through many of the reinforcement suppliers, which often have proprietary 

computer programs. 

This manual does not cover reinforcing the base section of an embankment for construction 

over soft soils, which is a different type reinforcement application. The user is referred to the 

FHWA Geosynthetics Design and Construction Guidelines (Holtz et al., 2008) for that 

application. An extension of this application is to lengthen reinforcement at the base of the 

embankment to improve the global stability of a reinforced soil slope. This application will 

be covered; however, steepening a slope significantly increases the potential for bearing 

capacity failure over soft soils and extensive geotechnical exploration along with rigorous 

analysis is required. 

FHWA NHI-10-025 8 – Reinforced Soil Slopes 

MSE Walls and RSS – Vol II 8 – 1 November 2009
 
 

An alternate slope reinforcement technique, the “Deep Patch” method, is used for stabilizing 

and potentially repairing roadway fill slopes on secondary roads where removal and 

replacement are not feasible (e.g., in mountainous terrain). In this method, reinforcements 

(typically geogrids) are placed in the upper portion of the slope to essentially tie it back. An 

empirical design approach has been developed by the U.S. Department of Agriculture 

(USDA) Forest Service technology in partnership with FHWA Federal Lands Highway 

(Musser and Denning, 2005). The method is not explicitly included in the design sections of 

Chapters 8 and 9 as this approach is often considered as a temporary repair method to retard 

the movement of a slope until a more permanent solution can be implemented; however, a 

brief description of the method is included in Appendix F. 

8.2.2 Construction Materials 

Reinforcement types. Reinforced soil slopes can be constructed with any of the 

reinforcements described in Chapter 2. While discrete strip type reinforcing elements can be 

used, a majority of the systems are constructed with continuous sheets of geosynthetics (i.e., 

geotextiles or geogrids) or wire mesh. Small, discrete micro reinforcing elements such as 

fibers, yarns, and microgrids located very close to each other have also been used. However, 

the design is based on more conventional unreinforced designs with cohesion added by the 

reinforcement (which is not covered in this manual). 

Reinforced Fill Requirements. Reinforced fill requirements for reinforced soil slopes are 

discussed in Chapter 3. Because a flexible facing (e.g. wrapped facing) is normally used, 

minor face distortion that may occur due to reinforced fill settlement, freezing and thawing, 

or wetting and drying can be tolerated. Thus, lower quality reinforced fill than recommended 

for MSE walls can be used. The recommended reinforced fill is limited to low-plasticity, 

granular material (i.e., PI ≤ 20 and ≤ 50 percent finer than a No. 200 US sieve {0.075 mm}). 

However, with good drainage, careful evaluation of soil and soil-reinforcement interaction 

characteristics, field construction control, and performance monitoring (see Chapter 11), 

most indigenous soil can be considered. 

8.3 DESIGN APPROACH 

8.3.1 Application Considerations 

As reviewed in Chapter 2, there are two main purposes for using reinforcement in slopes: 

 Improved stability for steepened slopes and slope repair. 

 Compaction aids, for support of construction equipment and improved face stability. 

FHWA NHI-10-025 8 – Reinforced Soil Slopes 

MSE Walls and RSS – Vol II 8 – 2 November 2009
 
 

The design of reinforcement for safe, steep slopes requires a rigorous analysis. The design of 

reinforcement for this application is critical, as failure of the reinforcement would result in 

failure of the slope. 

The overall design requirements for reinforced slopes are similar to those for unreinforced 

slopes: A limit equilibrium, allowable stress approach is used and the factor of safety must 

be adequate for both the short-term and long-term conditions and for all possible modes of 

failure. LRFD methods have not been fully developed for either unreinforced or reinforced 

slopes and are thus not included in this manual. 

As illustrated in Figure 8-1, there are three failure modes for reinforced slopes: 

 Internal, where the failure plane passes through the reinforcing elements. 

 External, where the failure surface passes behind and underneath the reinforced zone. 

 Compound, where the failure surface passes behind and through the reinforced soil 

zone. 

In some cases, the calculated stability safety factor can be approximately equal in two or all 

three modes, if the reinforcement strengths, lengths and vertical spacings are optimized (Berg 

et al., 1989). 

FHWA NHI-10-025 8 – Reinforced Soil Slopes 

MSE Walls and RSS – Vol II 8 – 3 November 2009
 

Figure 8-1.	 Failure modes for reinforced soil slopes including internal failure within the 

reinforced soil zone, external failure entirely outside the reinforced soil zone, and 

compound failure starting behind and passing through the reinforced soil zone. 
 

8.3.2 Design of Reinforcement for Compaction Aid 

For the use of geosynthetics as compaction aids, the design is relatively simple. Assuming 

the slope is safe without reinforcement, no reinforcement design is required. Place any 

geotextile or geogrid that will survive construction at every lift or every other lift of 

compacted soil in a continuous plane along the edge of the slope. Only narrow strips, about 

4 to 6 ft (1.2 to 1.8 m) in width, at 8 to 18 in. (200 to 500 mm) vertical spacing are required. 

Where the slope angle approaches the angle of repose of the soil, it is recommended that a 

face stability analysis be performed using the method presented in the reinforcement design 

section of Chapter 9. Where reinforcement is required by analysis, the narrow strip 

reinforcement may be considered as secondary reinforcement used to improve compaction 

and stabilize the slope face between primary reinforcing layers. 

8.3.3 Design of Reinforcement for Steepening Slopes and Slope Repair 

For steepened reinforced slopes (face inclination up to 70 degrees) and slope repair, design is 

based on modified versions of the classical limit equilibrium slope stability methods as 

shown in Figure 8-2: 

 Circular or wedge-type potential failure surface is assumed. 

 The relationship between driving and resisting forces or moments determines the slope 

factor of safety. 

 Reinforcement layers intersecting the potential failure surface are assumed to increase 

the resisting force or moment based on their tensile capacity and orientation. (Usually, 

the shear and bending strengths of stiff reinforcements are not taken into account.) 

 The tensile capacity of a reinforcement layer is taken as the minimum of its allowable 

pullout resistance behind (or in front of) the potential failure surface and its long-term 

allowable design strength, Tal. 

As shown in Figure 8-1, a wide variety of potential failure surfaces must be considered, 

including deep-seated surfaces through or behind the reinforced zone. For the internal 

analysis, the critical slope stability factor of safety is taken from the internal unreinforced 

failure surface requiring the maximum reinforcement. This is the failure surface with the 

largest unbalanced driving moment to resisting moment and not the surface with the 

minimum calculated unreinforced factor of safety. This failure surface is equivalent to the 

critical reinforced failure surface with the lowest factor of safety. Detailed design of 

reinforced zone is performed by determining the factor of safety with successively modified 

reinforcement layouts until the target factor of safety is achieved. External and compound 

stability of the reinforced zone are then evaluated. 

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Figure 8-2. Modified limit equilibrium analysis for reinforced slope design. 

For slope repair applications, it is also very important to identify the cause of the original 

failure to make sure that the new reinforced soil slope will not have the same problems. If a 

water table or erratic water flows exist, particular attention has to be paid to drainage. In 

natural soils, it is also necessary to identify any weak seams that might affect stability. 

The method presented in this manual uses any conventional slope stability computer program 

and the steps necessary to manually calculate the reinforcement requirements for almost any 

condition. Figure 8-2 shows the conventional rotational slip surface method used in the 

analysis. Fairly complex conditions can be accommodated depending on the analytical 

method used (e.g., Modified Bishop, Spencer). The computer program ReSSA (ADAMA, 

2001) was developed by the FHWA to specifically perform this analysis. 

The rotational slip surface approach is used for slopes up to 70 degrees, although technically 

it is a valid method for evaluating even steeper slopes. Slopes steeper than 70 degrees are 

defined as walls and lateral earth pressure procedures in Chapter 4 apply. 

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The assumed orientation of the reinforcement tensile force influences the calculated slope 

safety factor. In a conservative approach, the deformability of the reinforcements is not 

taken into account, and thus, the tensile forces per unit width of reinforcement Tr are assumed 

to always be in the horizontal direction of the reinforcements. When close to failure, 

however, the reinforcements may elongate along the failure surface, and an inclination from 

the horizontal can be considered. 

The above reinforcement orientations represent a simplifying assumption considering the 

reinforcement is not incorporated directly into the analysis of the slope. If a more rigorous 

evaluation is performed in which the vertical and horizontal components of the tension forces 

are included in the equations of equilibrium, then it can be shown that an increase in normal 

stress will occur for reinforcements with an orientation other than tangential to the failure 

surface (Wright and Duncan, 1990). In effect, this increase in normal stress will result in 

practically the same reinforcement influence on the safety factor whether it is assumed to act 

tangentially or horizontally. Although these equilibrium considerations may indicate that the 

horizontal assumption is conservative for discontinuous strip reinforcements, it should be 

recognized that the stress distribution near the point of intersection of the reinforcement and 

the failure surface is complicated. The conclusion concerning an increase in normal stress 

should only be considered for continuous and closely spaced reinforcements: it is 

questionable and should not be applied to reinforced slopes with widely spaced and/or 

discrete, strip type reinforcements. 

Tensile force direction is, therefore, dependent on the extensibility and continuity of the 

reinforcements used, and the following inclination is suggested: 

 Discrete, strip reinforcements: T parallel to the reinforcements. 

 Continuous, sheet reinforcements: T tangent to the sliding surface. 

8.3.4 Computer-Assisted Design 

The ideal method for reinforced slope design is to use a conventional slope stability computer 

program that has been modified to account for the stabilizing effect of reinforcement. Such 

programs should account for reinforcement strength and pullout capacity, compute reinforced 

and unreinforced safety factors automatically, and have some searching routine to help locate 

critical surfaces. The method may also include the confinement effects of the reinforcement 

on the shear strength of the soil in the vicinity of the reinforcement. 

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A number of reinforced slope programs are commercially available, several of which follow 

the design approach detailed in Chapter 9 of this manual. As previously indicated the 

development of program ReSSA was initially sponsored by the FHWA. ReSSA implicitly 

contains the design approach in this manual, noted as the FHWA Bishop Method in the 

program’s rotational stability analysis section, and contains the previous version of this 

manual in the help screens. ReSSA also provides alternate methods of analysis and the help 

screens describe those methods in detail including a theoretical discussion of the approaches. 

FHWA does not exclude the use of other methods of analysis, especially those which are 

more comprehensive. However, the user must have a fundamental understanding of which 

design method(s) are being used and how the algorithms incorporate the reinforcement into 

the stability analysis, with some programs using simplifying assumptions, while others apply 

comprehensive formulation and correspondingly complicated computations. Appropriate 

factors of safety must then be applied to account for uncertainties of the analytical method 

and the geotechnical and reinforcement materials. 

Some of the less sophisticated programs do not design the reinforcement but allow for an 

evaluation of a given reinforcement layout. An iterative approach then follows to optimize 

either the reinforcement strength or layout. Many of these programs are limited to simple 

soil profiles and, in some cases, simple reinforcement layouts. Also, external stability 

evaluation may be limited to specific soil and reinforcement conditions and a single mode of 

failure. In some cases, these programs are reinforcement-specific. 

With computerized analyses, the actual factor of safety value (FS) is dependent upon how the 

specific program accounts for the reinforcement tension in the moment equilibrium equation. 

The method of analysis in Chapter 9 and in FHWA Bishop method in ReSSa, as well as 

many others, assume the reinforcement force as contributing to the resisting moment, i.e.: 

FS R

D 

SR 

M 

 T RM  (8-1) 

 where, FSR = the required stability factor of safety 

MR = resisting moment provided by the strength of the soil 

MD = driving moment about the center of the failure circle 

 TS = sum of tensile force per unit width of reinforcement (considering 

rupture and pullout) in all reinforcement layers intersecting the 

failure surface 

 R = the moment arm of TS about the center of failure circle as shown 

in Figure 8-2 

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With this assumption, FSR is applied to both the soil and the reinforcement as part of the 

analysis. As a result, the stability with respect to breakage of the reinforcement requires that 

the allowable reinforcement strength Tal from Chapter 3, equation 3-12 must be greater than 

or equal to the required maximum design tension Tmax for each reinforcement layer. 

Some computer programs use an assumption that the reinforcement force is a negative 

driving component, thus the FS is computed as: 

 MR FS  (8-2) M D  TS R 

With this assumption, the stability factor of safety is not applied to TS. Therefore, the 

allowable design strength Tal should be computed as the ultimate tensile strength TULT 

divided by the required safety factor (i.e., target stability factor of safety) along with the 

appropriate reduction factors RF in equation 8-12; i.e., Tal = TULT / (FSR RF). This provides 

an equivalent factor of safety to equation 8-1, which is appropriate to account for uncertainty 

in material strengths and reduction factors. The method used to develop design charts should 

likewise be carefully evaluated to determine FS used to obtain the allowable reinforcement 

strength. 

8.3.5 Evaluation of External Stability 

The external stability of reinforced soil slopes depends on the ability of the reinforced zone 

to act as a stable block and withstand all external loads without failure. Failure possibilities 

as shown in Figure 8-3 include wedge and block type sliding, deep-seated overall instability, 

local bearing capacity failure at the toe (lateral squeeze type failure), as well as excessive 

settlement from both short- and long-term conditions. 

The reinforced zone must be sufficiently wide at any level to resist wedge and block type 

sliding. To evaluate sliding stability, a wedge type failure surface defined by the limits of the 

reinforcement can be analyzed using the conventional sliding block method of analysis as 

detailed in the FHWA Soils and Foundations Workshop Reference Manual, (Samtani and 

Nowatzki, 2006). The computer program ReSSA incorporates wedge analysis of the 

reinforced system, using force equilibrium to analyze sliding both beyond and through the 

reinforced section. 

Conventional soil mechanics stability methods should also be used to evaluate the global 

stability of the reinforced soil zone. Both rotational and wedge type failure surfaces 

extending behind and below the structure should be considered. Care should be taken to 

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identify any weak soil layers in the retained fill and natural soils behind and/or foundation 

soil below the reinforced soil zone. Evaluation of potential seepage forces is especially 

critical for global stability analysis. Compound failure surfaces initiating externally and 

passing through or between reinforcement sections should also be evaluated, especially for 

complex slope or soil conditions. Extending the lengths of lower level reinforcements may 

improve the overall global stability, however, special considerations for the orientation of the 

reinforcement in the analysis must be considered based on the foundation conditions, as 

detailed in Chapter 9. 

FHWA NHI-10-025 8 – Reinforced Soil Slopes 

MSE Walls and RSS – Vol II 8 – 9 November 2009 

Figure 8-3. External failure modes for reinforced soil slopes. 
 

Evaluation of deep-seated failure does not automatically check for bearing capacity of the 

foundation or failure at the toe of the slope. High lateral stress in a confined soft stratum 

beneath the embankment could lead to a lateral squeeze type failure. The shear forces 

developed under the embankment should be compared to the corresponding shear strength of 

the soil. Approaches discussed by Jurgenson (1934), Silvestri (1983), and Bonaparte et al. 

(1987), and Holtz et al. (2008) are appropriate. The approach by Silvestri is demonstrated in 

example problem E.10 in Appendix E. 

Settlement should be evaluated for both total and differential movement. While settlement of 

the reinforced slope is not of concern, adjacent structures or structures supported by the slope 

may not tolerate such movements. Differential movements can also affect decisions on 

facing elements as discussed in Section 8.4. 

In areas subject to potential seismic activity, a simple pseudo-static type analysis should be 

performed using a seismic coefficient obtained from Division 1A of the AASHTO Standard 

Specifications for Highway Bridges (AASHTO, 2002), AASHTO LRFD Bridge Design 

Specifications (AASHTO, 2007) or using local practice. Reinforced slopes are flexible 

systems and, unless used for bridge abutments, they are not laterally restrained. For free 

standing abutments that can tolerate lateral displacement of up to 10A in., Division 1A – 

Seismic Design, Article 6.4.3 Abutments (AASHTO, 2002) and Appendix A11.1.1.2 

(AASHTO, 2007) both imply that a seismic design acceleration Am = A/2 and a 

corresponding horizontal seismic coefficient Kh =A/2 can be used for seismic design. 

Appropriately a seismic design acceleration of A/2 is recommended for reinforced soil 

slopes, unless the slope supports structures that cannot tolerate such movements. 

If any of the external stability safety factors are less than the required factor of safety, the 

following foundation improvement options could be considered: 

 Excavate and replace soft soil. 

 Flatten the slope. 

 Construct a berm at the toe of the slope to provide an equivalent flattened slope. The 

berm could be placed as a surcharge at the toe and removed after consolidation of the 

soil has occurred. 

 Stage construct the slope to allow time for consolidation of the foundation soils. 

 Embed the slope below grade (> 3 ft), or construct a shear key at the toe of the slope 

(evaluate based on active-passive resistance). 

 Use ground improvement techniques (e.g., wick drains, stone columns, etc.) 

Additional information on ground improvement techniques can be found in the FHWA 

Ground Improvement Methods reference manuals NHI-06-019 and NHI-06-020 (Elias et al., 

2006). 

FHWA NHI-10-025 8 – Reinforced Soil Slopes 

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8.4 CONSTRUCTION SEQUENCE 

As the reinforcement layers are easily incorporated between the compacted lifts of fill, 

construction of reinforced slopes is very similar to normal slope construction. The elements 

of construction consist of simply: 

1. Placing the soil 

2. Placing the reinforcement 

3. Constructing the face 

The following is the usual construction sequence as shown in Figure 8-4: 

 Site Preparation 

- Clear and grub site. 

- Remove all slide debris (for slope reinstatement projects). 

- Prepare a level subgrade for placement of the first level of reinforcement. 

- Proof-roll subgrade at the base of the slope with a roller or rubber-tired 

vehicle. 

- Observe and approve foundation prior to fill placement. 

- Place drainage features (e.g., basedrain and/or backdrain) as required. 

 Reinforcing Layer Placement 

- Reinforcement should be placed with the principal strength direction 

perpendicular to the face of the slope. 

- Secure reinforcement with retaining pins to prevent movement during fill 

placement. 

- A minimum overlap of 6 in. (150 mm) is recommended along the edges 

perpendicular to the slope for wrapped face structures. Alternatively with grid 

reinforcement, the edges may be clipped or tied together. When 

reinforcements are not required for face support, no overlap is required and 

edges should be butted. 

 Reinforced fill Placement 

- Place fill to the required lift thickness on the reinforcement using a front end 

loader or dozer operating on previously placed fill or natural ground. 

- Maintain a minimum of 6 in. (150 mm) of fill between the reinforcement and 

the wheels or tracks of construction equipment. 

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Figure 8-4. Construction of reinforced soil slopes. 

FHWA NHI-10-025 8 – Reinforced Soil Slopes 

MSE Walls and RSS – Vol II 8 – 12 November 2009 
 

- Compact with a vibratory roller or plate type compactor for granular materials 

or a rubber-tired or smooth drum roller for cohesive materials. 

- When placing and compacting the reinforced fill material, care should be 

taken to avoid any deformation or movement of the reinforcement. 

- Use lightweight compaction equipment near the slope face with welded wire 

mesh systems to help maintain face alignment. 

 Compaction Control 

- Provide close control on the water content and density of the reinforced fill. It 

should be compacted to at least 95 percent of the standard AASHTO T99 

maximum density within 2 percent of optimum moisture. 

- If the reinforced fill is a coarse aggregate, then a relative density or a method 

type compaction specification should be used. 

 Face Construction 

- Slope facing requirements will depend on soil type, slope angle and the 

reinforcement spacing as shown in Table 8-1. 

If slope facing is required to prevent sloughing (i.e., slope angle β is greater than soil) 

or erosion, several options are available. Sufficient reinforcement lengths could be 

provided for wrapped faced structures. A face wrap may not be required for slopes 

up to about 1H:1V as indicated in Figure 8-4. In this case, the reinforcements 

(primary and secondary) can be simply extended to the face. For this option, a facing 

treatment as detailed under Section 8.5 Treatment of Outward Face, should be applied 

at sufficient intervals during construction to prevent face erosion. For wrapped or no 

wrap construction, the reinforcement should be maintained at close spacing (i.e., 

every lift or every other lift but no greater than 16 in. {400 mm}). For armored, hard 

faced systems the maximum spacing should be no greater than 32 in. (800 mm). A 

positive frictional or mechanical connection should be provided between the 

reinforcement and armored type facing systems. 

The following procedures are recommended for wrapping the face. 

- Turn up reinforcement at the face of the slope and return the reinforcement a 

minimum of 3 ft (1 m) into the embankment below the next reinforcement 

layer (see Figure 8-4). 

- For steep slopes, formwork may be required to support the face during 

construction, improving compaction at the face and providing a smoother face 

finish. Welded wire mesh is often used as a face form (see Figure 8-5). The 

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welded wire face is left in place with ungalvanized used for temporary support 

and galvanized wire used for permanent support. 

For grid reinforcements, a fine mesh screen or geotextile may be required at 

the face to retain reinforced fill materials. 

Slopes steeper than approximately 1:1 typically require facing support during 

construction. Exact slope angles will vary with soil types, i.e., amount of cohesion. 

Removable facing supports (e.g., wooden forms) or left-in-place welded wire mesh 

forms are typically used. Facing support may also serve as permanent or temporary 

erosion protection, depending on the requirements of the slope. 

 Additional Reinforcing Materials and Retained Backfill Placement 

If drainage layers are required, they should be constructed directly behind or on the 

sides of the reinforced section. 

Table 8-1. RSS slope facing options (after Collin, 1996). 

Slope Face Angle and 

Soil Type 

Type of Facing 

When Geosynthetic is not Wrapped at Face When Geosynthetic is Wrapped at Face 

Vegetated Face1

 Hard Facing2 Vegetated Face1 Hard Facing2 

> 50o 

(> ~0.9H:1V) 

All Soil Types 

Not Recommended Gabions Sod, 

Permanent Erosion 

Blanket w/ seed 

Wire Baskets,3 

Stone, 

Shotcrete 

35o

 to 50o 

(~ 1.4H:1V to 0.9H:1V) 

Clean Sands (SP)4 

Rounded Gravel (GP) 

Not Recommended Gabions, 

Soil-Cement 

Sod, 

Permanent Erosion 

Blanket w/ seed 

Wire Baskets,3 

Stone, 

Shotcrete 

35o

 to 50o 

(~ 1.4H:1V to 0.9H:1V) 

Silts (ML) 

Sandy Silts (ML) 

Soil Bio reinforcement, 

Drainage 

Composites5 

Gabions, 

Soil-Cement, 

Stone Veneer 

Sod, 

Permanent Erosion 

Blanket w/ seed 

Wire Baskets,3 

Stone, 

Shotcrete 

35o

 to 50o 

(~ 1.4H:1V to 0.9H:1V) 

Silty Sands (SM) 

Clayey Sands (SC) 

Well graded sands and 

gravels (SW & GW) 

Temporary 

Erosion Blanket 

w/ Seed or Sod, 

Permanent 

Erosion Mat 

w/ Seed or Sod 

Hard Facing, 

Not Needed 

Geosynthetic 

Wrap Not 

Needed 

Geosynthetic 

Wrap Not 

Needed 

25o

 to 35o 

(~ 2H:1V to 1.4H:1V) 

All Soil Types 

Temporary 

Erosion Blanket 

w/ Seed or Sod, 

Permanent Erosion Mat 

w/ Seed or Sod 

Hard Facing 

Not Needed 

Geosynthetic 

Wrap Not 

Needed 

Geosynthetic 

Wrap Not 

Needed 

Notes: 1. Vertical spacing of reinforcement (primary/secondary) shall be no greater than 16 in. (400 mm) with 

primary reinforcements spaced no greater than 32 in. (800 mm) when secondary reinforcement is used. 

2. Vertical spacing of primary reinforcement shall be no greater than 32 in. (800 mm). 

3. 18 in. (450 mm) high wire baskets are recommended. 

4. Unified Soil Classification 

5. Geosynthetic or natural horizontal drainage layers to intercept and drain the saturated soil at the face of 

the slope. 

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SEEDED TOPSOIL 

A) 

B) 

AASHTO M288 Class 2 

Geotextile Filter 

Reinforcement 

Figure 8-5. Example of welded wire mesh detail for temporary (during construction) or 

permanent face support showing a) smooth inclined face, and b) stepped face. 

8.5 TREATMENT OF OUTWARD FACE 

8.5.1 Grass Type Vegetation 

Stability of a slope can be threatened by erosion due to surface water runoff. Erosion control 

and revegetation measures must, therefore, be an integral part of all reinforced slope system 

designs and specifications. If not otherwise protected, reinforced slopes should be vegetated 

after construction to prevent or minimize erosion due to rainfall and runoff on the face. 

Vegetation requirements will vary by geographic and climatic conditions and are, therefore, 

project specific. 

For the unwrapped face (the soil surface exposed), erosion control measures are necessary to 

prevent raveling and sloughing of the face. A wrapped face helps reduce erosion problems; 

however, treatments are still required on the face to shade geosynthetic soil reinforcement 

and prevent ultraviolet light exposure that will degrade the geosynthetic over time. In either 

case, conventional vegetated facing treatments generally rely on low growth, grass type 

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vegetation with more costly flexible armor occasionally used where vegetation cannot be 

established. Due to the steep grades that can be achieved with reinforced soil slopes, it can 

be difficult to establish and maintain grass type vegetative cover. The steepness of the grade 

limits the amount of water absorbed by the soil before runoff occurs. Although root 

penetration should not affect the reinforcement, the reinforcement may restrict root growth, 

depending on the reinforcement type. This can have an adverse influence on the growth of 

some plants. Grass is also frequently ineffective where slopes are impacted by waterways. 

A synthetic (permanent) erosion control mat is normally used to improve the performance of 

grass cover. This mat must also be stabilized against ultra-violet light and should be inert to 

naturally occurring soil-born chemicals and bacteria. The erosion control mat serves to: 1) 

protect the bare soil face against erosion until the vegetation is established; 2) assist in 

reducing runoff velocity for increased water absorption by the soil, thus promoting long-term 

survival of the vegetative cover; and 3) reinforce the surficial root system of the vegetative 

cover. 

Once vegetation is established on the face, it must be protected to ensure long-term survival. 

Maintenance issues, such as mowing (if applicable), must also be carefully considered. The 

shorter, weaker root structure of most grasses may not provide adequate reinforcement and 

erosion protection. Grass is highly susceptible to fire, which can also destroy the synthetic 

erosion control mat. Downdrag from snow loads or upland slides may also strip matting and 

vegetation off the slope face. The low erosion tolerance combined with other factors 

previously mentioned creates a need to evaluate revegetation measures as an integral part of 

the design. Slope face protection should not be left to the construction contractor or vendor's 

discretion. Guidance should be obtained from maintenance and regional landscaping groups 

in the selection of the most appropriate low maintenance vegetation. 

8.5.2 Soil Bioengineering (Woody Vegetation) 

An alternative to low growth, grass type vegetation is the use of soil bioengineering methods 

to establish hardier, woody type vegetation in the face of the slope (Sotir and Christopher, 

2000). Soil bioengineering uses living vegetation purposely arranged and imbedded in the 

ground to prevent shallow mass movement and surficial erosion. However, the use of soil 

bioengineering in itself is limited to stable slope masses. Combining this highly erosive 

system with geosynthetic reinforcement produces a very durable, low maintenance structure 

with exceptional aesthetic and environmental qualities. 

Appropriately applied, soil bioengineering offers a cost-effective and attractive approach for 

stabilizing slopes against erosion and shallow mass movement, capitalizing on the benefits 

and advantages that vegetation offers. The value of vegetation in civil engineering and the 

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role woody vegetation plays in the stabilization of slopes has gained considerable recognition 

in recent years (Gray and Sotir, 1995). Woody vegetation improves the hydrology and 

mechanical stability of slopes through root reinforcement and surface protection. The use of 

deeply-installed and rooted woody plant materials, purposely arranged and imbedded during 

slope construction offers: 

 Immediate erosion control for slopes; stream, and shoreline. 

 Improved face stability through mechanical reinforcement by roots. 

 Reduced maintenance costs, with less need to return to revegetate or cut grass. 

 Modification of soil moisture regimes through improved drainage and depletion of 

soil moisture and increase of soil suction by root uptake and transpiration. 

 Enhanced wildlife habitat and ecological diversity. 

 Improved aesthetic quality and naturalization. 

The biological and mechanical elements must be analyzed and designed to work together in 

an integrated and complementary manner to achieve the required project goals. In addition 

to using engineering principles to analyze and design the slope stabilization systems, plant 

science and horticulture are needed to select and establish the appropriate vegetation for root 

reinforcement, erosion control, aesthetics and the environment. Numerous areas of expertise 

must integrate to provide the knowledge and awareness required for success. RSS systems 

require knowledge of the mechanisms involving mass and surficial stability of slopes. 

Likewise when the vegetative aspects are appropriate to serve as reinforcements and drains, 

an understanding of the hydraulic and mechanical effects of slope vegetation is necessary. 

Figure 8-6 shows a cross section of the components of a vegetated reinforced slope (VRSS) 

system. The design details for face construction include vegetation selection, placement, and 

development as well as several agronomic and geotechnical design issues (Sotir and 

Christopher, 2000). 

FHWA NHI-10-025 8 – Reinforced Soil Slopes 

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Figure 8-6. Components of a 

vegetated reinforced slope 

(VRSS) system. 
 

 Vegetation Selection 

The vegetation used in the VRSS system is typically in the form of live woody branch 

cuttings from species that root adventitiously or from bare root and/or container 

plants. Plant materials may be selected for a variety of tolerances including: drought, 

salt, flooding, fire, deposition, and shade. They may be chosen for their 

environmental wildlife value, water cleansing capabilities, flower, branch and leaf 

color or fruits. Other interests for selection may include size, form, rate of growth 

rooting characteristics and ease of propagation. Time of year for construction of a 

VRSS system also plays a critical roll in plant selection. 

 Vegetation Placement 

The decision to use native, naturalized or ornamental species is also an important 

consideration. The plant materials are placed on the frontal section of the formed 

terraces. Typically 6 to 12 in. (150 to 300 mm) protrude beyond the constructed 

terrace edge or finished face, and 1.5 to 10 ft (0.5 to 3 m) of the live branch cuttings 

(when used) are embedded in the reinforced fill behind, or as in the case of rooted 

plants, are placed 1 to 3 ft (0.3 to 1 m) into the reinforced fill. The process of plant 

installation is best and least expensive when it occurs simultaneously with the 

conventional construction activities, but may be incorporated later if necessary. 

 Vegetation Development 

Typically soil bioengineering VRSS systems offer immediate results from the surface 

erosion control structural/mechanical and hydraulic perspectives. Over time, 

(generally within the first year) they develop substantial top and root growth further 

enhancing those benefits, as well as providing aesthetic and environmental values. 

 Design Issues 

There are several agronomic and geotechnical design issues that must be considered, 

especially in relation to selection of geosynthetic reinforcement and type of 

vegetation. Considerations include root and top growth potential. The root growth 

potential consideration is important when face reinforcement enhancement is 

required. This will require a review of the vertical spacing based on the anticipated 

root growth for the specific type of plant. In addition to spacing, the type of 

reinforcements is also important. Open-mesh geogrid-type reinforcements, for 

example, are excellent as the roots will grow through the grid and further "knit" the 

system together. On the other hand, geocomposites, providing both reinforcement and 

lateral drainage, offer enhanced water and oxygen opportunities for the healthy 

development of the woody vegetation. Dependent upon the species selected, aspect, 

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MSE Walls and RSS – Vol II 8 – 18 November 2009
 
 

climatic conditions, soils, etc., dense woody vegetation can provide ultraviolet light 

protection within the first growing season and maintain the cover thereafter. 

In arid regions, geosynthetics that will promote moisture movement into the slope 

such as non-woven geotextiles or geocomposites may be preferred. Likewise, the 

need for water and nutrients in the slope to sustain and promote vegetative growth 

must be balanced against the desire to remove water so as to reduce hydrostatic 

pressures. Plants can be installed to promote drainage toward geosynthetic drainage 

net composites placed at the back of the reinforced soil section. 

Organic matter is not required; however, a medium that provides nourishment for 

plant growth and development is necessary. As mentioned earlier, the agronomic 

needs must be balanced with the geotechnical requirements, but these are typically 

compatible. For both, a well-drained reinforced fill is needed. The plants also 

require sufficient fines to provide moisture and nutrients. While this may be a 

limitation, under most circumstances, some slight modifications in the specifications 

to allow for some non-plastic fines in the reinforced fill in the selected frontal zone 

offers a simple solution to this problem. 

While many plants can be installed throughout the year, the most cost effective, 

highest rate of survival and best overall performance and function occurs when 

construction is planned around the dormant season for the plants, or just prior to the 

rainy season. This may require some specific construction coordination in relation to 

the placement of fill, and in some cases could preclude the use of a VRSS structure. 

8.5.3 Armored 

A permanent facing such as gunite or emulsified asphalt may be applied to a geosynthetic 

reinforcement RSS slope face to provide long-term ultra-violet protection, if the geosynthetic 

UV resistance is not adequate for the life of the structure. Galvanized welded wire mesh 

reinforcement or facing or gabions may also be used to facilitate face construction and 

provide permanent facing systems. 

 Other armored facing elements may include riprap, stone veneer, articulating modular 

units, or fabric-formed concrete. 

 Structural elements. 

Structural facing elements (see MSE walls) may also be used, especially if discrete 

reinforcing elements such as metallic strips are used. These facing elements may include 

prefabricated concrete slabs, modular precast blocks, or precast slabs. 

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8.6 DESIGN DETAILS 

As with MSE wall projects, certain design details must often be considered that are not 

directly connected with internal or external stability evaluation. These important details 

include: 

 Guardrail and traffic barriers. 

 Drainage considerations. 

 Obstructions. 

8.6.1 Guardrail and Traffic Barriers 

Guardrails are usually necessary for steeper highway embankment slopes. Guardrail posts 

usually can be installed in their standard manner (i.e. drilling or driving) through 

geosynthetic reinforcements. Special wedge shaped shoes can be used to facilitate 

installation. This does not significantly impair the overall strength of the geosynthetic and no 

adjustments in the design are required. Alternatively, post or concrete form tubes at post 

locations can be installed during construction. Either this procedure or cantilever type 

guardrail systems are generally used for metallic reinforcement. 

Impact traffic load on barriers constructed at the face of a reinforced soil slope is designed on 

the same basis as an unreinforced slope. The traffic barrier may be designed to resist the 

overturning moment in accordance with Article 2.7 in Division I of AASHTO Standard 

Specifications for Highway Bridges (AASHTO, 2002), Section 13 of AASHTO LRFD 

Bridge Design Specifications (AASHTO, 2007) or as addressed in the 2006 AASHTO 

Roadside Design Guide, and will be covered in detail in Chapter 9. 

8.6.2 Drainage Considerations 

Uncontrolled subsurface water seepage can decrease stability of slopes and could ultimately 

result in slope failure. 

 Hydrostatic forces on the back of the reinforced zone will decrease stability against 

sliding failure. 

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 Uncontrolled seepage into the reinforced zone will increase the weight of the 

reinforced mass and may decrease the shear strength of the soil, thus decreasing 

stability. 

 Seepage through the reinforced zone can reduce pullout capacity of the reinforcement 

at the face and increase soil weight, creating erosion and sloughing problems. 

As a precaution, drainage features should be included unless detailed analysis proves that 

drainage is not required. Drains are typically placed at the rear of the reinforced soil zone to 

control subsurface water seepage as detailed in Chapter 9. Surface runoff should also be 

diverted at the top of the slope to prevent it from flowing over the face. 

8.6.3 Obstructions 

If encountered in a design, guidance provided in Chapters 5 should be considered. 

8.7 CASE HISTORIES 

The following case histories are presented to provide representative examples of costeffective, successful reinforced slope projects. In several cases, instrumentation was used to 

confirm the performance of the structure. All project information was obtained from the 

indicated references which, in most cases, contain additional details. 

8.7.1 The Dickey Lake Roadway Grade Improvement Project 

(Yarger and Barnes,1993) 

Dickey Lake is located in northern Montana approximately 25 miles (40 km) south of the 

Canadian border. Reconstruction of a portion of U.S. 93 around the shore of Dickey Lake 

required the use of an earth-retention system to maintain grade and alignment. The fill soils 

available in the area consist primarily of glacial till. Groundwater is active in the area. A 

slope stability factor of safety criteria of 1.5 was established for the embankments. A global 

stability analysis of reinforced concrete retaining walls to support the proposed embankment 

indicated a safety factor that was less than required. Analysis of a reinforced soil wall or 

slope indicated higher factors of safety. Based on an evaluation of several reinforcement 

systems, a decision was made to use a reinforced slope for construction of the embankment. 

The Montana Department of Transportation (MDT) decided that the embankment would not 

be designed “in-house,” due to their limited experience with this type of structure. 

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Proposals were solicited from a variety of suppliers, who were required to design the 

embankment. An outside consultant, experienced in geosynthetic reinforcement design, was 

retained to review all submittals. Plans and specifications for the geosynthetic reinforced 

embankments(s) were developed by MDT, with the plans indicating the desired finished 

geometry. The slopes generally ranged from 30 to 60 ft (9 to 18.3 m) in height. Face angles 

varied from 1.5H:1V to 0.84H:1V with the typical angle being 1H:1V. The chosen supplier 

provided a design that utilized both uniaxially and biaxially oriented geogrids. The resulting 

design called for primary reinforcing geogrids 15 to 60 ft (4.6 to 18.3 m) long and spaced 2 

to 4 ft (0.6 to 1.2 m) vertically throughout the reinforced embankment. The ultimate strength 

of the primary reinforcement was on the order of 6850 lb/ft (100 kN/m). The length of 

primary reinforcement was partially dictated by global stability concerns. In addition, 

intermediate reinforcement consisting of lower strength, biaxial geogrids was provided in 

lengths of 5 ft (1.5 m) with a vertical spacing of 1 ft (0.3 m) at the face of slopes 1H:1V or 

flatter. Erosion protection on the 1H:1V or flatter sections was accomplished by using an 

organic erosion blanket. Steeper sections (maximum 0.84H:1V) used L-shaped, welded wire 

forms with a biaxial grid wrap behind the wire. A design evaluation of this project is 

presented in Chapter 9. 

The design also incorporated subsurface drainage. This drainage was judged to be 

particularly important due to springs or seeps present along the backslope of the 

embankment. The design incorporated geocomposite prefabricated drains placed along the 

backslope, draining into a French drain at the toe of the backslope. Laterals extending under 

the embankment were used to "daylight" the French drain. 

The project was constructed in 1989 at a cost of approximately $17/ft2

 ($180/m2) of vertical 

face and has been periodically monitored by visual inspection and slope inclinometers. 

Project photos are shown in Figure 8-7. To date, the embankment performance has been 

satisfactory with no major problems observed. Some minor problems have been reported 

with respect to the erosion control measures and some minor differential movement in one of 

the lower sections of the embankment. 

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Figure 8-7. Dickey Lake site. 

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MSE Walls and RSS – Vol II 8 – 23 November 2009
 
 

8.7.2 Salmon-Lost Trail Roadway Widening Project 

(Zornberg et al., 1995) 

As part of a highway widening project in Idaho, the FHWA Western Federal Lands Highway 

Division designed and supervised the construction of a 565 ft long, 50 ft high (172 m long, 

15.3 m high) permanent geosynthetic-reinforced slope to compare its performance with 

retaining structures along the same alignment. Widening of the original road was achieved by 

turning the original 2H:1V unreinforced slope into a 1H:1V reinforced slope. Aesthetics was 

an important consideration in the selection of the retaining structures along scenic Highway 93, 

which has been recognized by articles in National Geographic. A vegetated facing was, 

therefore, used for the reinforced slope section. On-site soil consisting of decomposed granite 

was used as the reinforced fill. An important factor in the design was to deal with water 

seepage from existing slope. Geotextile reinforcements with an in-plane transmissivity were 

selected to evaluate the potential of modifying the seepage regime in the slope. 

The geotextile-reinforced slope was designed in accordance with the guidelines presented in 

Chapters 8 and 9 of this manual. The final design consisted of two reinforced zones with a 

constant reinforcing spacing of 1 ft (0.3 m). The reinforcement in the lower zone had an 

ultimate tensile strength of 6,850 lb/ft (100 kN/m), and the reinforcement in the upper zone had 

a reinforcement strength of 1,370 lb/ft (20 kN/m). The reinforcement strength was reduced 

based on partial reduction factors which are reviewed in Chapter 3. Field tests were used to 

reduce the reduction factor for construction damage from the assumed value of 2.0 to the test 

value of 1.1 at a substantial savings to the project (40 percent reduction in reinforcement). 

The construction was completed in 1993 (see Figure 8-8 for project photos). The structure was 

constructed as an experimental features project and was instrumented with inclinometers 

within the reinforced zone, extensometers on the reinforcement, and piezometers within and at 

the back of the reinforced section. Survey monitoring was also performed during construction. 

Total lateral displacements recorded during construction were on the order of 0.1 to 0.2 percent 

of the height of the slope, with maximum strains in the reinforcement measured at only 0.2 

percent. Post construction movement has not been observed within the accuracy of the 

instruments. These measurements indicate the excellent performance of the structure as well 

as the conservative nature of the design. Long-term monitoring is continuing. 

The steepened slope was constructed at a faster rate and proved more economical than the 

other retaining structures constructed along the same alignment. The constructed cost of the 

reinforced slope section was on the order of $15/ft2

 ($160/m2) of vertical face. Metallic grid 

reinforced MSE wall costs in other areas of the site were on the order of $22/ft2 ($240/m2) of 

vertical face for similar or lower heights. 

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Figure 8-8. Salmon Lost Trail site. 

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MSE Walls and RSS – Vol II 8 – 25 November 2009 
 

8.7.3 Cannon Creek Alternate Embankment Construction Project 

(Hayden et al., 1991) 

A large embankment was planned to carry Arkansas State Highway 16 over Cannon Creek. 

The proposed 100,000 yd3 (77,000 m3) embankment had a maximum height of 75 ft (23 m) 

and was to be constructed with on-site clay soils and 2H:1V side slopes (with questionable 

stability). A cast-in-place concrete box culvert was first constructed to carry the creek under 

the embankment. Embankment construction commenced but was halted quickly when 

several small slope failures occurred. It then became apparent that the embankment fill could 

not be safely constructed at 2H:1V. 

With the box culvert in place, there were two options for continuation of embankment 

construction. A gravelly soil could be used for embankment fill, or the on-site soil could be 

used with geosynthetic reinforcement. Both options were bid as alternatives and the 

geosynthetic option was selected for construction (see Figure 8-9). The reinforcement used 

was a high-density polyethylene geogrid with a reported wide-width strength of 6850 lb/ft 

(100 kN/m). The geogrid reinforcement option was estimated to be $200,000 less expensive 

than the gravelly soil fill option. 

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MSE Walls and RSS – Vol II 8 – 26 November 2009
 

Figure 8-9. Cannon Creek project. 
 

8.7.4 Pennsylvania SR 54 Roadway Repair Project 

(Wayne and Wilcosky, 1995) 

During the winter of 1993 - 1994, a sinkhole formed in a section of State Route 54 in 

Pennsylvania. Further investigation revealed that an abandoned railroad tunnel had 

collapsed. The traditional repair would have involved the removal and replacement of the 50 

ft (15 m) high embankment. The native soil, a sandy clay, was deemed an unsuitable 

reinforced fill due to its wet nature and potential stability and settlement problems with the 

embankment. Imported granular fill to replace the native soil was estimated to be $21/yd3 

($16/m3). Due to the high cost of replacement materials, the Pennsylvania Department of 

Transportation decided to use geosynthetics to provide drainage of the native soil and 

reinforce the side slopes. A polypropylene needlepunched nonwoven geotextile was selected 

to allow for pore pressure dissipation of the native soil during compaction, thus accelerating 

consolidation settlement and improving its strength. Field tests were used to confirm pore 

pressure response. 

With the geotextile placed at a compacted lift spacing of 1 ft (0.3 m), full pore pressure 

dissipation was achieved within approximately 4 days as compared with a minimum 

dissipation (approximately 25 percent) without the geosynthetic during the same time period. 

By placing the geotextile at 1 ft (0.3 m) lift intervals, the effective drainage path was reduced 

from the full height of the slope of 50 ft (15 m) to 0.5 ft (0.15 m) or by a factor of over 100. 

This meant that consolidation of the embankment would essentially be completed by the end 

of construction as opposed to waiting almost a year for completion of the settlement without 

the geosynthetic. 

The geotextile, with an ultimate strength of 1100 lb/ft (16 kN/m) and placed at every lift 12 

in. (0.3 m), also provided sufficient reinforcement to safely construct 1.5H:1V side slopes. 

Piezometers at the base and middle of the slope during construction confirmed the test pad 

results. Deformations of the geotextile in the side slope were also monitored and found to be 

less than the precision of the gages (± 1 percent strain). Project photos are shown in Figure 

8-10 along with the measurements of pore pressure dissipation during construction. 

The contractor was paid on a time and material basis with the geotextile purchased by the 

agency and provided to the contractor for installation. The cost of the geotextile was 

approximately $1/yd2

 ($1.2/m2). In-place costs of the geotextile, along with the on-site fill 

averaged just over $3/yd3 ($4/m3) for a total cost of $70,000, resulting in a savings of 

approximately $200,000 over the select-fill alternative. Additional savings resulted from not 

having to remove the on-site soils from the project site. 

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MSE Walls and RSS – Vol II 8 – 27 November 2009
 
 

Figure 8-10. Pennsylvania SR54. 

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 PORE PRESSURE READINGS DURING CONSTRUCTION
 

-1 0 

0 

10 

20 

30 

40 

50 

60 

70 

80 

0 2 0 4 0 60 8 0 

T im e (d ays ) 

Po re Pressu re (kPa) 

1 kPa = 0.145 lb/ft2, 1 m = 3.28 ft 

Figure 8-10. Pennsylvania SR54 continued. 

8.7.5 Massachusetts Turnpike - Use of Soil Bioengineering (Sotir et al., 1998; Sotir and 

Stulgis,1999) 

The Massachusetts Turnpike in Charlton, Massachusetts is an example where a vegetated 

reinforced slope (VRSS) system was used to construct 1H:4V slopes to replace unstable 

1.5H:1V slopes along a 500 ft (150 m) section of the Turnpike. This slope eroded for a 

number of years. The erosion was widening and threatening to move back into private 

property beyond the right-of-way. Eventually, the increased maintenance to clean up the 

sloughed material, the visual scar on the landscape and the threat of private property loss 

prompted the Turnpike Authority to seek a solution. The combined soil bioengineering and 

geosynthetic reinforcement approach was adopted to meet the narrow right-of-way 

requirement, assist in controlling internal drainage, and reconstruct an aesthetically pleasing 

and environmentally sound system that would blend into the natural landscape. The 10 to 60 

ft (3 to 18 m) high 1H:4V slope was stabilized with layers of primary and secondary 

geogrids, erosion control blankets, brushlayers in the frontal geogrid wrapped portion of the 

face, and additional soil bioengineering treatments above the constructed slope. 

 

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The design was essentially the same as the soil bioengineering cross section shown in Figure 

8-6. The primary geogrid was designed to provide global, internal and compound stability to 

the slope. This grid extends approximately 20 ft (6.1 m) from the face to the back of the 

slope. The vertical spacing of the primary geogrid is 2 ft (0.6 m) and 4 ft (1.2 m), 

respectively, over the lower and upper halves of the slope. The face wrap extends 

approximately 3 ft (0.9 m) into the slope at the bottom of each vertical lift and 5 ft (1.5 m) at 

the top to form 3 ft (0.9 m) thick earthen terraces. Brushlayers consisting of 8 to 10 ft (2.4 m 

to 3 m) long willow (Salix sp.) and dogwood (Cornus sp.) live cut branches were placed on 

each constructed wrapped section at a vertical spacing of 1 ft (0.9 m), extending back to 

approximately the mid point of the slope. The branches and geogrids were sloped back to 

promote drainage to backdrains placed in the slopes while providing moisture for the plants. 

Live fascine bundles (see Figure 8-11) were installed above the reinforced slope in a 3H:1V 

cut section to prevent surface erosion and assist in revegetating that portion of the slope. 

The backdrain system consisted of 3.3 ft (1 m) wide geocomposite panels spaced 15 ft (4.6 

m) on center. Design of the panels and spacing was based on the anticipated groundwater 

flow and surface infiltration conditions. The panels connect into a 1 ft (0.3 m) thick crushedstone drainage layer at the base of the slope, which extends the full length and width of the 

slope. The reinforced fill soils consisted of granular borrow, ordinary borrow, 50/50 mix of 

ordinary granular fill and specified fill. The first three materials constitute the structurally 

competent core while the specified fill was placed at the face to provide a media amenable to 

plant growth. The specified fill consisted of fertilizers and a blend of four parts ordinary 

borrow to one part organic loam by volume and was used in the front 10 ft (3 m) of each lift 

for the installed brushlayers to optimize the growing conditions. This was a modification 

from the normal geotechnical specification to accommodate the soil bioengineering. 

The VRSS slope was constructed in the winter/spring of 1995/96 at a cost of US $25/ft2 

($270/m2) of vertical face. After the fourth growing season, the vegetated slope face was 

evaluated and found to perform as intended, initially protecting the surface from erosion 

while providing a pleasing aesthetic look (see Figure 8-11). Natural invasion from the 

surrounding plant community occurred, causing the system to blend into the naturally 

wooded scenic setting of the area and meeting the long-term aesthetic and ecological goals. 

Lessons Learned: In the future on similar projects, the use of more rooted plants rather than 

all live cut branches is recommended to provide greater diversity and to improve construction 

efficiency. Reducing the height of the wrapped earth terraces would allow for the vegetation 

to be more evenly distributed with less densities, and possibly using a preformed wire form 

in the front. These items would all reduce construction costs by improving efficiency. 

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MSE Walls and RSS – Vol II 8 – 30 November 2009
 
 

Figure 8-11. Massachusetts Turnpike during construction, immediately after construction 

and the after the second growing season. 

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MSE Walls and RSS – Vol II 8 – 31 November 2009 
 

8.7.6 242 ft (74 m) High 1H:1V Reinforced Soil Slope for Airport Runway Extension 

(Lostumbo, 2009) 

The tallest reinforced soil slope in North America as of this writing was constructed to 

extend the runway at Yeager Airport in Charleston, WV. Yeager Airport was constructed in 

the 1940’s atop mountainous terrain. Due to the mountainous conditions, the ground surface 

around the airport slopes down steeply over 300 ft (91 m) to the surrounding Elk and 

Kanawha Rivers, roadways, churches, houses and other structures. In order to meet recent 

FAA Safety Standards, updates to the airport runways required extending Runway 5 

approximately 500 ft (150 m) to create an emergency stopping apron for airplanes. 

Construction options for extending the runway past the existing hillside included evaluation 

of bridge structures, retaining walls and reinforced slopes. Engineering evaluation indicated 

the reinforced slope provided the most cost effective and easiest constructed option. In 

addition, the vegetated facing of the completed slope will provide a structure that will blend 

into the surrounding green hills of Charleston, WV. The final design was a 242 ft (74 m) 

high, 1H:1V reinforced steepened slope (RSS). 

The design utilized polyester woven geogrid reinforcements with long term design strengths 

Tal of 2,970 lb/ft (43.4 kN/m), 3720 lb/ft (54.4 kN/m) and 3860 lb/ft (56.4 kN/m) as the 

primary reinforcement. The vertical spacing of the primary reinforcement was 1.5 ft (460 

mm) in the lower portion of the slope and 3 ft (900 m) in the upper portion. The design 

embedment length of the primary reinforcement in the taller section of the slope ranged from 

175 feet (53 m) at the bottom to 145 ft (44 m) at the top. The design also incorporated a 

geosynthetic drainage composite for drainage behind the reinforced zone along the back of 

the excavation to intercept and drain seepage water from the existing mountain side away 

from the reinforced zone. A geosynthetic erosion control mat was installed on the face of the 

slope at 2 ft (0.6 m) vertical intervals, with 3 foot (0.9 m)embedded into the slope face and 

2.5 ft (0.76 m) down the face for facial stability and erosion protection. An open mesh 

biaxial geosynthetic specifically designed as a face wrap material was also used in the slope 

face. 

The RSS allowed for an economical solution and less complicated construction than the 

other, traditional methods that were considered. The reinforced slope was successfully 

completed and is performing as expected. The structure allowed the airport to meet recent 

FAA Safety Standards while creating an engineered structure that blends into the scenic 

green hills of Charleston, WV. 

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MSE Walls and RSS – Vol II 8 – 32 November 2009
 
 

 a) Early construction at the bottom of the slope. b) Slope face during construction. 

c) Aerial photo of slope during construction, approximately d) Slope shortly after completion with early vegetation growth 

80% complete. 

Figure 8-12. Reinforced soil slope for runway extension at Yeager Airport, Charleston, 

West Virginia. 

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MSE Walls and RSS – Vol II 8 – 33 November 2009
 

8.8 STANDARD RSS DESIGNS
 

RSS structures are customarily designed on a project-specific basis. Most agencies use a 

line-and-grade contracting approach, thus the contractor selected RSS vendor provides the 

detailed design after contract bid and award. This approach works well. However, in 

addition to agencies performing project specific designs, standard designs can be developed 

and implemented by an agency for RSS structures. 

Use of standard designs for RSS structures offers the following advantages over a line-andgrade approach: 

C Agency is more responsible for design details and integrating slope design with other 

components. 

C Pre-evaluation and approval of materials and material combinations, as opposed to 

evaluating contractor submittal post bid. 

C Economy of agency design versus vendor design/stamping of small reinforced slopes. 

C Agency makes design decisions versus vendors making design decisions. 

C More equitable bid environment as agency is responsible for design details, and vendors 

are not making varying assumptions. 

C Filters out substandard work, systems and designs with associated approved product lists. 

The Minnesota Department of Transportation (Mn/DOT) developed and implemented (inhouse) standardized RSS designs (Berg, 2000). The use of these standard designs are limited 

by geometric, subsurface and economic constraints. Structures outside of these constraints 

should be designed on a project-specific basis. The general approach used in developing 

these standards could be followed by other agencies to develop their own, agency-specific 

standard designs. 

Standardized designs require generic designs and generic materials. Generic designs require 

definition of slope geometry and surcharge loads, soil reinforcement strength, structure 

height limit, and slope facing treatment. As an example, the Mn/DOT standard designs 

address two geometric and surcharge loadings, two reinforced soil fills, and can be used for 

slopes up to 26.2 ft (8 m) in height. Three reinforcement long-term strengths, Tal, of 700, 

1050 and 1400 lb/ft (10, 15 and 20 kN/m) are used in the standard designs, although a 

structure must use the same reinforcement throughout its height and length. 

Generic material properties used definitions of shear strength and unit weight of the 

reinforced fill, retained backfill and foundation soils applicable to the agency’s specifications 

and regional geology. Definition of generic material properties requires the development of 

approved product lists for soil reinforcements and face erosion control materials. A standard 

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MSE Walls and RSS – Vol II 8 – 34 November 2009
 
 

face treatment is provided, however, it is footnoted with Develop site specific 

recommendations for highly shaded areas, highly visible urban applications, or in sensitive 

areas. 

An example design cross section and reinforcement layout table from the Mn/DOT standard 

designs is presented in Figure 8-13. Note that the Mn/DOT standard designs are not directly 

applicable to, nor should they be used by, other agencies. 

FHWA NHI-10-025 8 – Reinforced Soil Slopes 

MSE Walls and RSS – Vol II 8 – 35 November 2009
 
 

Figure 8-13. Example of standard RSS design (Mn/DOT, 2008). 

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MSE Walls and RSS – Vol II 8 – 36 November 2009 
 

CHAPTER 9 

DESIGN OF REINFORCED SOIL SLOPES
 

9.1 INTRODUCTION 

This chapter provides step-by-step procedures for the design of reinforced soil slopes. Design 

and analysis of existing design using a computer program is also presented. The design 

approach principally assumes that the slope is to be constructed on a stable foundation. 

Recommendations for deep seated failure analysis are included. The user is referred to 

standard soil mechanics texts and FHWA Geosynthetics Design and Construction Guidelines 

(Holtz et al., 2008) in cases where the stability of the foundation is at issue. 

As indicated in Chapter 8, there are several approaches to the design of reinforced steepened 

slopes. The method presented in this chapter uses the classic rotational, limit equilibrium slope 

stability method as shown in Figure 8-2. As for the unreinforced case, a circular arc failure 

surface (not location) is assumed for the reinforced slope. This geometry provides a simple 

means of directly increasing the resistance to failure from the inclusion of reinforcement, is 

directly adaptable to most available conventional slope stability computer programs, and 

agrees well with experimental results. 

The reinforcement is represented by a concentrated force within the soil mass that intersects 

the potential failure surface. By adding the failure resistance provided by this force to the 

resistance already provided by the soil, a factor of safety equal to the rotational stability safety 

factor is inherently applied to the reinforcement. The tensile capacity of a reinforcement layer 

is taken as the minimum of its allowable pullout resistance behind the potential failure surface 

or its long-term allowable design strength. The slope stability factor of safety is taken from the 

critical surface requiring the maximum amount of reinforcement. Final design is performed by 

distributing the reinforcement over the height of the slope and evaluating the external stability 

of the reinforced section. 

The suitability of this design approach has been verified through extensive experimental 

evaluation by the FHWA including numerical analysis, centrifuge models, and full scale 

instrumented structures and found to be somewhat conservative. A chart solution developed 

for simplistic structures is provided as a check for the results. The method for evaluating a 

given reinforced soil profile is also presented. The flow chart in Figure 9-1 shows the steps 

required for design of reinforced soil slopes. 

FHWA NHI-10-025 9 – Design of Reinforced Soil Slopes 

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Establish the geometric, loading, and performance requirements for design 

Determine engineering properties of the in-situ soils 

Determine properties of available fill 

Evaluate design parameters for the reinforcement 

 allowable reinforcement strength 

 durability criteria 

 soil-reinforcement interaction 

Check unreinforced stability of the slope 

Design reinforcement to provide stable slope 

 strength 

 spacing 

 length 

Extensible Inextensible 

Check external stability 

Sliding Deep Seated 

Global 

Local Bearing 

Capacity Settlement Seismic 

Evaluate requirements for subsurface and surface water control 

Develop specifications and contract documents 

Figure 9-1. Flow chart of steps for reinforced soil slope design. 

FHWA NHI-10-025 9 – Design of Reinforced Soil Slopes 

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9.2 REINFORCED SLOPE DESIGN GUIDELINES 

The design steps outlined in the flow chart are as follows: 

9.2.1 Step 1. Establish the geometric, loading, and performance requirements for design. 

a. Geometric and loading requirements (see Figure 9-2). 

 Slope height, H 

 Slope angle, θ

 External (surcharge) loads: 

- Surcharge load, q 

- Temporary live load, ∆q 

- Design seismic acceleration, Am (See Division 1A, AASHTO Standard 

Specifications for Highway Bridges {AASHTO, 2002} or AASHTO LRFD Bridge 

Design Specifications {AASHTO, 2007}). 

	 Traffic Barrier 

- See article 2.7 of AASHTO Standard Specifications for Highway Bridges 

(AASHTO, 2002), Section 13 of AASHTO LRFD Bridge Design Specifications 

(AASHTO, 2007), and AASHTO Roadside Design Guide (AASHTO, 2006). 

b. Performance requirements. 

 External stability and settlement 

- Sliding: F.S. ≥ 1.3 

- Deep seated (overall stability): F.S. ≥ 1.3 

- Local bearing failure (lateral squeeze): F.S. ≥ 1.3 

- Dynamic loading: F.S. ≥ 1.1 

- Settlement-post construction magnitude and time rate based on project requirements 

 Compound failure: F.S. ≥ 1.3 

 Internal slope stability: F.S. ≥ 1.3 

9.2.2 Step 2. Determine the engineering properties of the in-situ soils. 

(see recommendations in Chapter 2, Section 2.6 and Chapter 3, Section 3.2.2) 

 The foundation and retained soil (i.e., soil beneath and behind reinforced zone) profiles. 

 Strength parameters cu and u, or c ́ and  ́ for each soil layer. 

 Unit weights γwet and γdry. 

 Consolidation parameters (Cc, Cr, cv and σ ́ p). 

 Location of the groundwater table dw, and piezometric surfaces. 

 For failure repair, identify location of previous failure surface and cause of failure. 

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Notations: 

H = slope height 

 = slope angle 

Tal = allowable strength of reinforcement 

L = length of reinforcement 

Sv = vertical spacing of reinforcement 

q = surcharge load 

q = temporary live load 

Ao = ground acceleration coefficient 

Am = design seismic acceleration 

dw = depth to ground water table in slope 

dwf = depth to ground water table in foundation 

cu and u or cand  = strength parameters for each soil layer 

wet and dry = unit weights for each soil layer 

Cc, Cr, cv and p = consolidation parameters for each soil layer 

Figure 9-2. Requirements for design of reinforced soil slopes. 

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9.2.3	 Step 3. Determine the properties of reinforced fill and, if different, the retained 

backfill. (see recommendations in Chapter 3, Section 3.2) 

 Gradation and plasticity index 

 Compaction characteristics based on 95% AASHTO T-99, γd and ±2% of optimum 

moisture, wopt 

	 Compacted lift thickness 

	 Shear strength parameters, cu, u or c ́, and  ́ 

	 Electro chemical properties of reinforced fill 

- For geosynthetic reinforcement: pH 

- For steel reinforcement: pH, resistivity, chlorides, sulfates, and organic content 

9.2.4 Step 4. Evaluate design parameters for the reinforcement. (see recommendations 

in Chapter 3, Section 3.5.) 

	 Allowable geosynthetic strength (Eq. 3-12), Tal = ultimate strength (TULT) ÷ reduction 

factor (RF) for creep, installation damage and durability: 

For granular reinforced fill meeting the recommended gradation in Chapter 3, and 

electrochemical properties in Chapter 3, RF = 7 may be conservatively used for 

preliminary design and for routine, noncritical structures where the minimum test 

requirements outlined in Table 3-12 are satisfied. Remember, there is a significant 

cost advantage in obtaining lower RF from test data supplied by the manufacture 

and/or from agency evaluation! 

	 Allowable steel strength (Eq. 3-11), Tal = Fy Ac / b, where Ac is the area of the steel 

adjusted for corrosion. Note: Soils with higher fines are often more corrosive and 

Table 3-3 property requirements must be carefully checked for the reinforced fill. 

	 Pullout Resistance: (See recommendations in Chapter 3 and Appendix B) 

- Use F.S. = 1.5 for granular soils 

- Use F.S. = 2 for cohesive soils 

- Minimum anchorage length, Le, = 3 ft (1 m) 

9.2.5 Step 5. Check unreinforced stability. 

 (see discussion in Chapter 8) 

a. Evaluate unreinforced stability to determine: if reinforcement is required; critical nature 

of the design (i.e., unreinforced F.S. ≤ or ≥ 1); potential deep-seated failure problems; 

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and the extent of the reinforced zone. Perform a stability analysis using conventional 

stability methods (see FHWA Soils and Foundations Workshop Reference Manual 

{Samtani and Nowatzki, 2006}) to determine safety factors and driving moments for 

potential failure surfaces. 

	 Use both circular-arc and sliding-wedge methods, and consider failure through the 

toe, through the face (at several elevations), and deep-seated below the toe. 

(A number of stability analysis computer programs are available for rapid evaluation, 

e.g., FHWA sponsored programs including ReSSA and the STABL family of programs 

developed at Purdue University including the current version, STABL4M. In all cases, 

a few calculations should be made by hand to be sure the computer program is giving 

reasonable results.) 

b. Determine the size of the critical zone to be reinforced. 

 Examine the full range of potential failure surfaces found to have: 

Unreinforced safety factor, FSU ≤ Required safety factor, FSR. 

 Plot all of these surfaces on the cross-section of the slope. 

 The surfaces that just meet the required safety factor roughly envelope the limits of 

the critical zone to be reinforced as shown in Figure 9-3. 

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Figure 9-3. Critical zone defined by rotational and sliding surfaces that meets the required 

safety factor. 
 

c. Critical failure surfaces extending below the toe of the slope are indications of deep 

foundation and edge bearing capacity problems that must be addressed prior to 

completing the design. Where foundation problems are indicated, a more extensive 

foundation analysis is warranted, and foundation improvement measures should be 

considered as discussed in Chapter 8. 

9.2.6 Step 6. Design reinforcement to provide a stable slope. 

 (see Figure 9-4, and discussion in Chapter 8.) 

a. Calculate the total reinforcement tension per unit width of slope TS required to obtain 

the required factor of safety FSR for each potential failure surface inside the critical 

zone in step 5 that extends through or below the toe of the slope using the following: 

where: 

 TS = the sum of the required tensile force per unit width of reinforcement 

(considering rupture and pullout) in all reinforcement layers 

intersecting the failure surface 

MD = driving moment about the center of the failure circle 

D = the moment arm of TS about the center of failure circle 

 = radius of circle R for continuous, sheet type extensible 

reinforcement (i.e., assumed to act tangentially to the circle) 

 = radius of circle R for continuous, sheet type inextensible 

reinforcement (e.g., wire mesh reinforcement) to account for normal 

stress increase on adjacent soil 

 = vertical distance, Y, to the centroid of TS for discrete element, strip 

type reinforcement. Assume H/3 above slope base for preliminary 

calculations (i.e. assumed to act in a horizontal plane intersecting the 

failure surface at H/3 above the slope base) 

 FSU = unreinforced slope safety factor 

FSR = target minimum slope factor of safety which is applied to both the soil 

and reinforcement 

TS-MAX = the largest TS calculated and establishes the total design tension 

	 Note: the minimum unreinforced safety factor usually does not control the 

location of TS-MAX; the most critical surface is the surface requiring the 

greatest amount of reinforcement strength. 

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M T	  FS FS  D

S R U (9-1) D 
 

Figure 9-4. Rotational shear approach to determine required strength of reinforcement. 

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b. Determine the total design tension per unit width of slope, TS-MAX, using the charts in 

Figure 9-5 and compare with TS-MAX from step 6a. If significantly different, check the 

validity of the charts based on the limiting assumptions listed in the figure and recheck 

calculations in steps 5 and equation 9-1. 

	 Figure 9-5 is provided for a quick check of computer-generated results. The figure 

presents a simplified method based on a two-part wedge type failure surface and is 

limited by the assumptions noted on the figure. 

Note that Figure 9-5 is not intended to be a single design tool. Other design charts 

available from the literature could also be used (e.g., Ruegger, 1986; Leshchinsky 

and Boedeker, 1989; Jewell, 1990). As indicated in Chapter 8, several computer 

programs are also available for analyzing a slope with given reinforcement and can 

be used as a check. Judgment in selection of other appropriate design methods (i.e., 

most conservative or experience) is required. 

c. Determine the distribution of reinforcement: 

 

	 For low slopes (H ≤ 20 ft {6 m}) assume a uniform reinforcement distribution and 

use TS-MAX to determine spacing or the required tension TMAX requirements for each 

reinforcement layer. 

	 For high slopes (H > 20 ft {6 m}), either a uniform reinforcement distribution may 

be used (preferable) or the slope may be divided into two (top and bottom) or three 

(top, middle, and bottom) reinforcement zones of equal height using a factored 

TS-MAX in each zone for spacing or design tension requirements (see Figure 9-6). 

The total required tension in each zone is found from: 

For 1 zone: 

 Use TS-MAX
 

 

For 2 zones: 

TBottom = 3/4 TS-MAX (9-2) 

TTop = 1/4 TS-MAX (9-3) 

 For 3 zones: 

TBottom S-MAX

TMiddle = 1/3 TS-MAX (9-5)

TTop = 1/6 TS-MAX (9-6)

 = 1/2 T (9-4)

The force is assumed to be uniformly distributed over the entire zone. 

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CHART PROCEDURE: 

1) Determine force coefficient K from figure above, where r = friction angle of reinforced fill: 

 tan  1 r f  tan 

  

 FRR	  

2) Determine: 

TS-MAX = 0.5 K γr (H’)2 

where: H' = H + q/γr 

q = a uniform load 

3) Determine the required reinforcement length at the top LT and bottom LB of the slope from the 

figure above. 

LIMITING ASSUMPTIONS 

● Extensible reinforcement 

●	 Slopes constructed with uniform, cohesionless soil, c = 0) 

●	 No pore pressures within slope 

●	 Competent, level foundation soils 

●	 No seismic forces 

●	 Uniform surcharge not greater than 0.2 γr H 

●	 Relatively high soil/reinforcement interface friction angle, sg = 0.9 r (may not be appropriate for some 

geosynthetics) 

Figure 9-5. Chart solution for determining the reinforcement strength requirements 

(after Schmertmann et. al., 1987). NOTE: Charts © The Tensar Corporation 

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32 in. (800 mm) 

4 ft (1,2 m) 16 in. (400 mm) 

4 ft (1,2 m) 

Figure 9-6. Reinforcement spacing considerations for high slopes. 

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d. Determine reinforcement vertical spacing Sv or the maximum design tension TMAX 

requirements for each reinforcement layer. 

	 For each zone, calculate TMAX for each reinforcing layer in that zone based on an 

assumed Sv or, if the allowable reinforcement strength is known, calculate the 

minimum vertical spacing and number of reinforcing layers N required for each 

zone based on: 

Tzone Sv Tzone Tmax    Tal Rc (9-7) Hzone N 

where: 

Rc = coverage ratio of the reinforcement which equals the width of 

the reinforcement b divided by the horizontal spacing Sh

 Sv = vertical spacing of reinforcement in meters; multiples of 

compacted layer thickness for ease of construction 

Tzone = maximum reinforcement tension required for each zone 

 = TS-MAX for low slopes (H< 6m) 

Tal = Tult /RF (see Chapter 3 and equation 3-12) 

Hzone = height of zone 

 = Ttop, Tmiddle, and TBottom for high slopes (H > 20 ft {6 m}) 

N = number of reinforcement layers 

	 Use short 4 to 6.5 ft (1.2 to 2 m) lengths of intermediate reinforcement layers to 

maintain a maximum vertical spacing of 16 in. (400 mm) or less for face stability 

and compaction quality (see Figure 9-6b). 

- For slopes flatter than 1H:1V, closer spaced reinforcements (i.e., every lift or 

every other lift, but no greater than 16 in. {400 mm}) preclude having to wrap 

the face in well graded soils (e.g., sandy gravel and silty and clayey sands). 

Wrapped faces are required for steeper slopes and uniformly graded soils to 

prevent face sloughing. Alternative vertical spacings could be used to prevent 

face sloughing, but in these cases a face stability analysis should be performed 

either using the method presented in this chapter or by evaluating the face as an 

infinite slope using (Collin, 1996): 

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2	 2 c'H  γ	  γ H z cos βtanφ'  F cosβsinβ  sin βtanφ g w	 g F.S. 	 (9-8)

γ g H z cosβsinβ

 

where: c = effective cohesion 

  = effective friction angle 

 γg = saturated unit weight of soil 

 γw = unit weight of water 

 z = vertical depth to failure plane defined by the depth of saturation 

 H = vertical slope height 

 β = slope angle 

 Fg = summation of geosynthetic resisting force 

- Intermediate reinforcement should be placed in continuous layers and needs not 

be as strong as the primary reinforcement, but it must be strong enough to 

survive construction (e.g. minimum survivability requirements for geotextiles in 

road stabilization applications in AASHTO M-288, 2006) and provide localized 

tensile reinforcement to the surficial soils. 

- If the interface friction angle of the intermediate reinforcement ρsr (from ASTM 

D 5321 or estimated as discussed in Chapter 3, Section 3.4.3) is less than that of 

the primary reinforcement ρr, then ρsr should be used in the analysis for the 

portion of the failure surface intersecting the reinforced soil zone. 

e. To ensure that the rule-of-thumb reinforcement force distribution is adequate for critical 

or complex structures, recalculate TS using equation 9-1 to determine potential failure 

above each layer of primary reinforcement. 

f. 	 Determine the reinforcement lengths required: 

	 The embedment length Le of each reinforcement layer beyond the most critical 

sliding surface (i.e., circle found for TS-MAX) must be sufficient to provide adequate 

pullout resistance based on: 

 T FS

L  max (9-9) e F * ασ' v Rc C 

where F*, α , Rc, C and σ́v are defined in Chapter 3, Section 3.4. 

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	 Minimum value of Le is 3 ft (1 m). For cohesive soils, check Le for both short- and 

long-term pullout conditions, when using the semi empirical equations in Chapter 3 

to obtain F*. 

For long-term design, use r with cr = 0 

For short-term evaluation, conservatively use r with cr = 0 from consolidated 

undrained triaxial or direct shear tests or run pullout tests 

	 Plot the reinforcement lengths as obtained from the pullout evaluation on a slope 

cross section containing the rough limits of the critical zone determined in step 5 

(see Figure 9-7). 

- The length required for sliding stability at the base will generally control the 

length of the lower reinforcement levels. 

- Lower layer lengths must extend at least to the limits of the critical zone as 

shown in Figure 9-7. Longer reinforcements may be required to resolve deep 

seated failure problems (see step 7). 

- Upper levels of reinforcement may not be required to extend to the limits of the 

critical zone, provided sufficient reinforcement exists in the lower levels to 

provide the FSR for all circles within the critical zone as shown in Figure 9-7. 

	 Check that the sum of the reinforcement forces passing through each failure surface 

is greater than Ts required for that surface. 

- Only count reinforcement that extends 3 ft (1 m) beyond the surface to account 

for pullout resistance. 

- If the available reinforcement force is not sufficient, increase the length of 

reinforcement not passing through the surface or increase the strength of lowerlevel reinforcement. 

	 Simplify the layout by lengthening some reinforcement layers to create two or three 

sections of equal reinforcement length for ease of construction and inspection. 

	 Reinforcement layers do not generally need to extend to the limits of the critical 

zone, except for the lowest levels of each reinforcement section. 

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	 Check the length obtained using chart b in Figure 9-5. Note: Le is already included 

in the total length, Lt and LB from chart B. 

g. Check design lengths of complex designs. 

	 When checking a design that has zones of different reinforcement length, lower 

zones may be over reinforced to provide reduced lengths of upper reinforcement 

levels. 

	 In evaluating the length requirements for such cases, the pullout stability for the 

reinforcement must be carefully checked in each zone for the critical surfaces 

exiting at the base of each length zone. 

Le from pullout  4 ft (1.2 m) 

Figure 9-7. Developing reinforcement lengths. 

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9.2.7 Step 7. Check external stability. (see discussion in Chapter 8.) 

 Sliding resistance (Figure 9-8) 

- Evaluate the width of the reinforced soil zone at any level to resist sliding along 

the reinforcement. Use a two-part wedge type failure surface defined by the 

limits of the reinforcement (the length of the reinforcement at the depth of 

evaluation defined in step 5). The analysis can best be performed using a 

computerized method which takes into account all soil strata and interface 

friction values. If the computer program does not account for the presents of 

reinforcement, the back of the failure surface should be angled at 45 + /2 or 

parallel to the back of the reinforced zone, whichever is flatter (i.e., the wedge 

should not pass through layers of reinforcement to avoid an overly conservative 

analysis). The frictional resistance provided by the weakest layer, either the 

reinforced soil, the foundation soil or the soil-reinforcement interface, should be 

used in the analysis. 

A simple analysis using Figure 9-5b can be performed as a quick check, but 

should not be used for the primary analysis due to the limiting assumptions 

noted on the figure. The method also assumes that the reinforcement layers are 

truncated along a plane parallel to the slope face, which may or may not be the 

case. The analysis was based on a two-part wedge model to predict LB 

assuming that the reinforcement interface is the weakest plane. A reduction is 

applied to the interface friction angle, sg = 0.9 r, which may not be appropriate 

for some geosynthetics. The frictional resistance provided by the weakest layer 

in contact with the geosynthetic, either the reinforced soil or the foundation soil, 

should be used in the analysis. 

	 Deep seated global stability (Figure 9-8a). 

- Evaluate potential deep-seated failure surfaces behind the reinforced soil zone 

to provide: 

M R F.S.   1.3 minimum (9-14) MD 

Note: F.S.  1.3 is recommended as a minimum and that value should be 

increased based on the criticality of the slope (e.g., slopes beneath bridge 

abutments and major roadways) and/or confidence in geotechnical conditions 

(e.g., soil properties and location of groundwater). 

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The analysis performed in step 5 should provide the factor of safety for failure 

surfaces behind the reinforced soil zone. However, as a check, classical 

rotational slope stability methods such as simplified Bishop, Morgenstern and 

Price, Spencer, or others may be used (see FHWA’s Ground Improvement 

Manuals, FHWA NHI-06-019 and FHWA NHI-06-020 {Elias et al., 2006}). 

Appropriate computer programs also may be used. 

Figure 9-8. Failure through the foundation. 

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	 Local bearing failure at the toe (lateral squeeze) (Figure 9-8b). 

- If a weak soil layer exists beneath the embankment to a limited depth DS which 

is less than the width of the slope b', the factor of safety against failure by 

squeezing may be calculated from (Silvestri, 1983): 

2c 4.14c u u FSsqueezing    1.3 (9-15)

γ Ds tanθ H γ

where: 

 θ = angle of slope 

 γ = unit weight of soil in slope 

Ds = depth of soft soil beneath slope base of the embankment 

 H = height of slope 

cu = undrained shear strength of soft soil beneath slope 

Caution is advised and rigorous analysis (e.g., numerical modeling) should be 

performed when FS < 2. This approach is somewhat conservative as it does not 

provide any influence from the reinforcement. When the depth of the soft layer, DS, 

is greater than the slope base width, b', general slope stability will govern design. 

	 Foundation settlement. 

- Determine the magnitude and rate of total and differential foundation 

settlements using classical geotechnical engineering procedures (see FHWA 

Soils and Foundations Workshop Reference Manual, {Samtani and Nowatzki, 

2006}). 

9.2.8 Step 8. Seismic stability. 

	 Dynamic stability (Figure 9-9). 

- Perform a pseudo-static type analysis using a seismic ground coefficient A, 

obtained from local building code and a design seismic acceleration Am equal to 

Am = A/2. Reinforced soil slopes are clearly yielding type structures, more so 

than walls. As such, Am can be taken as A/2 as allowed by AASHTO in 

Division 1A-Seismic Design, 6.4.3 Abutments (AASHTO, 2002) and Appendix 

A11.1.1.2 (AASHTO, 2007) 

F.S. dynamic ≥ 1.1 

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In the pseudo-static method, seismic stability is determined by adding a horizontal 

and/or vertical force at the centroid of each slice to the moment equilibrium 

equation (see Figure 9-9). The additional force is equal to the seismic coefficient 

times the total weight of the sliding mass. It is assumed that this force has no 

influence on the normal force and resisting moment, so that only the driving 

moment is affected. The liquefaction potential of the foundation soil should also be 

evaluated. 

9.2.9 Step 9. Evaluate requirements for subsurface and surface water runoff control. 

	 Subsurface water control. 

- Design of subsurface water drainage features should address flow rate, 

filtration, placement, and outlet details. 

- Drains are typically placed at the rear of the reinforced zone as shown in Figure 

9-10. Geocomposite drainage systems or conventional granular blanket and 

trench drains could be used (see Chapter 5). 

Figure 9-9. Seismic stability analysis. 

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0.2 ft (0.6 m) TYP 

0.2 ft (0.6 m) TYP 

Figure 9-10. Subsurface drainage considerations. 

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- Lateral spacing of outlets is dictated by site geometry, estimated flow, and 

existing agency standards. Outlet design should address long-term performance 

and maintenance requirements. 

- Geosynthetic drainage composites can be used in subsurface water drainage 

design. Drainage composites should be designed with consideration of: 

o Geotextile filtration/clogging 

o Long-term compressive strength of polymeric core 

o Reduction of flow capacity due to intrusion of geotextile into the core 

o Long-term inflow/outflow capacity 

Procedures for checking geotextile permeability and filtration/clogging criteria 

were presented in FHWA Geosynthetic Design and Construction Guidelines 

(Holtz et al., 2008). Long-term compressive stress and eccentric loadings on the 

core of a geocomposite should be considered during design and selection. 

Though not yet addressed in standardized test methods or standards of practice, 

the following criteria are suggested for addressing core compression. The 

design pressure on a geocomposite core should be limited to either: 

o the maximum pressure sustained on the core in a test of 10,000 hours 

minimum duration 

o the crushing pressure of a core, as defined with a quick loading test, 

divided by a factor of safety of 5 

Note that crushing pressure can only be defined for some core types. For cases 

where a crushing pressure cannot be defined, suitability should be based on the 

maximum load resulting in a residual thickness of the core adequate to provide 

the required flow after 10,000 hours, or the maximum load resulting in a 

residual thickness of the core adequate to provide the required flow as defined 

with the quick loading test divided by a factor of safety of 5. 

Intrusion of the geotextiles into the core and long-term outflow capacity should 

be measured with a sustained transmissivity test. The ASTM D4716 test 

procedure Constant Head Hydraulic Transmissivity of Geotextiles and 

Geotextile Related Products, should be followed. The test procedure should be 

modified for sustained testing and for use of sand sub-stratum and super-stratum 

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in lieu of closed cell foam rubber. Load should be maintained for 100 hours or 

until equilibrium is reached, whichever is greater. 

- Slope stability analyses should account for interface shear strength along a 

geocomposite drain. The geocomposite/soil interface will most likely have a 

friction value that is lower than that of the soil. Thus, a potential failure surface 

may be induced along the interface. 

- Geotextile reinforcements (primary and intermediate layers) must be more 

permeable than the reinforced fill material to prevent a hydraulic build up above 

the geotextile layers during precipitation. 

Special emphasis on the design and construction of subsurface drainage 

features is recommended for structures where drainage is critical for 

maintaining slope stability. Redundancy in the drainage system is also 

recommended for these cases. 

	 Surface water runoff. 

- Surface water runoff should be collected above the reinforced slope and 

channeled or piped below the base of the slope. Standard Agency drainage 

details should be utilized. 

- Wrapped faces and/or intermediate layers of secondary reinforcement may be 

required at the face of reinforced slopes to prevent local sloughing. Guidance is 

provided in Chapter 8 and Table 8-1. Intermediate layers of reinforcement help 

achieve compaction at the face, thus increasing soil shear strength and erosion 

resistance. These layers also act as reinforcement against shallow or sloughing 

types of slope failures. Intermediate reinforcement is typically placed on each 

or every other soil lift, except at lifts where primary structural reinforcement is 

placed. Intermediate reinforcement also is placed horizontally, adjacent to 

primary reinforcement, and at the same elevation as the primary reinforcement 

when primary reinforcement is placed at less than 100 percent coverage in plan 

view. The intermediate reinforcement should extend 4 to 6.5 ft (1.2 to 2 m) 

back into the fill from the face. 

- Select a long-term facing system to prevent or minimize erosion due to rainfall 

and runoff on the face. 

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- Calculate flow-induced tractive shear stress on the face of the reinforced slope 

by: 

 λ = d · γW · s (9-16)

where: 

 λ	 = tractive shear stress, psf (kPa) 

 d = depth of water flow, ft (m) 

 γw 	 = unit weight of water, lbs/ft3

 (kN/m3) 

 s = the vertical to horizontal angle of slope face, ft/ft (m/m) 

For λ < 2 psf (100 Pa), consider vegetation with temporary or permanent 

erosion control mat 

For λ > 2 psf (100 Pa), consider vegetation with permanent erosion control mat 

or other armor type systems (e.g., riprap, gunite, prefab modular units, fabricformed concrete, etc.) 

- Select vegetation based on local horticultural and agronomic considerations and 

maintenance. 

- Select a synthetic (permanent) erosion control mat that is stabilized against 

ultra-violet light and is inert to naturally occurring soil-born chemicals and 

bacteria. Erosion control mats and blankets vary widely in type, cost, and, more 

importantly, applicability to project conditions. Slope protection should not 

be left to the construction contractor or vendor's discretion. Guideline 

material specifications for synthetic permanent erosion control mats are 

provided in Chapter 10. 

9.3 COMPUTER ASSISTED DESIGN 

An alternative to reinforcement design (step 6 in the previous section) is to develop a trial 

layout of reinforcement and analyze the reinforced slope with a computer program such as the 

FHWA ReSSA program. Layout includes number, length, design strength, and vertical 

distribution of the geosynthetic reinforcement. The charts presented in Figure 9-5 provide a 

method for generating a preliminary layout. Note that these charts were developed with the 

specific assumptions noted on the figure. 

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Analyze the reinforced soil slope with the trial geosynthetic reinforcement layouts. The most 

economical reinforcement layout must provide the minimum required stability safety 

factors for internal, external, and compound failure planes. A contour plot of lowest safety 

factor values about the trial failure circle centroids is recommended to map and locate the 

minimum safety factor values for the three modes of failure. 

The method of analysis in section 9.2 assumes that the reinforcing force contributed to the 

resisting moment and thus inherently applies the required factor of safety to the reinforcement. 

However, some computer programs (and design charts) are based on the assumption that the 

reinforcement force reduces the driving moment with the stability factor of safety FS 

calculated as: 

 M R FS  (9-17) M D  Ts D 

With this assumption, the stability factory of safety is not applied to the reinforcement. For 

such computations and any other methods not applying a factor of safety to the reinforcement, 

the allowable strength of the reinforcement Tal must be divided by a required minimum factor 

of safety FSR = 1.3 to provide an equivalent material uncertainty. 

External stability analysis as was previously shown in step 7 will include an evaluation of local 

bearing capacity, foundation settlement, and dynamic stability. 

9.4 PROJECT COST ESTIMATES 

Cost estimates for reinforced slope systems are generally per square foot of vertical face. 

Table 9-1 can be used to develop a cost estimate. As an example, the following provides a cost 

estimate for the 6.5 ft (5 m) high reinforced slope design Example E.8. Considering the 12 

layers of reinforcement at a length of 16 ft (4.9 m), the reinforced section would require a total 

reinforcement of 192 ft2

 per ft (60 m2 per meter) length of embankment or 12 ft2 per vertical ft 

of height (12 m2

 per vertical meter of height). Adding 10 to 15 percent for overlaps and 

overages results in an anticipated reinforcement quantity of 13.5 ft2

 per ft (13.5 m2 per meter 

embankment height). Based on the cost information from suppliers, reinforcement with an 

allowable strength Ta ≥ 280 lb/ft (4.14 kN/m) would cost on the order of $0.10 to 0.15/ft2 

($1.00 to $1.50/m2

). Assuming $0.05 ft2 ($0.50 m2) for handling and placement, the in-place 

cost of reinforcement would be approximately $2.50/ft2

 ($25/m2) of vertical embankment face. 

Approximately 24.6 yd3

 (18.8 m3) of additional fill would be required for the reinforced 

section per foot (per meter) of embankment length. Using a typical in-place cost for locally 

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available fill with some hauling of $6 yd3

 ($8/m3) (about $4 per 1000 kg), $2.80/ft2 ($30/m2) 

will be added to the cost. In addition, overexcavation and backfill of existing embankment 

material will be required to allow for placement of the reinforcement. Assuming $1.50/yd3 

($2/m3

) for overexcavation and replacement will add approximately $0.40/ft2 ($4/m2) of 

vertical face. The erosion protection for the face would also add a cost of $0.50 ft2

 ($5/m2) of 

vertical face plus seeding and mulching. Thus, the total estimated cost for this option would be 

on the order of $6/ft2

 ($64/m2) of vertical embankment face. Alternative facing systems such 

as soil bioengineered treatment and/or the use of wire baskets for face would each add 

approximately $2 to $3/ft2

 ($20 to $30/m2) to the construction costs, but reduction in long-term 

maintenance will most likely offset these costs. 

Table 9-1. Estimated Project Costs. 

Item Total Volume Unit Cost Extension per Vertical 

square foot (meter) 

Reinforced fill 

(in place) 

yd3

 (m3) 

Overexcavation yd3

 (m3 

Reinforcement 

(in place) 

yd2 (m2) 

Facing system 

Support 

Vegetation 

Permanent 

erosion control mat 

yd2

 (m2) 

yd2

 (m2) 

Alternate facing 

systems ft2

 (m2) 

Groundwater control 

system ft2

 (m2) 

Guardrail ft (m) 

Total ------- ---------

Unit cost per vertical 

ft2

 (m2) 

Note Slope Dimensions: Height H = 

 Length L = 

Face Surface Area, A 

Reinforcement Area = Lreinforcement * Number of Layers 

FHWA NHI-10-025 

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9 – Design of Reinforced Soil Slopes 

November 2009 
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CHAPTER 10 

CONTRACTING METHODS AND SPECIFICATIONS 

FOR MSE WALLS AND SLOPES 

From its introduction in the early 1970s, it is estimated that the total construction value of 

MSE walls is in excess of $2 billion. This estimate does not include reinforced slope 

construction, for which estimates are not available. 

Since the early 1980s, hundreds of millions of dollars have been saved on our Nation's 

highways by bidding alternates for selection of earth retaining structures. During that time, 

the number of available MSE systems or components have increased, and some design and 

construction problem areas that have been identified. These include misapplication of wall 

technology; poor specifications; lack of specification enforcement; inequitable bidding 

procedures; poor construction techniques; inadequate inspection; and inconsistent selection, 

review, and acceptance practices on the part of public agencies. Although the actual causes 

of each particular problem are unique, Agency procedures that address the design and 

construction of earth retaining systems Can, when well formulated and enforced, minimize 

such problems; or when not well formulated or enforced, can contribute to such problems. 

MSE wall and RSS systems are contracted using two different approaches: 

C Agency or material supplier designs with system components, drainage details, erosion 

measures, and construction execution explicitly specified in the contracting documents; 

or 

C Performance or end-result approach using approved or generic systems or components, 

with lines and grades noted on the drawings and geometric and design criteria specified. 

In this case, a project-specific design review and detail plan submittal occurs in 

conjunction with working drawing submittal. 

Some user agencies prefer one approach to the other or a mixed use of approaches developed 

based upon criticality of a particular structure. Both contracting approaches are valid if 

properly implemented. Each approach has advantages and disadvantages. 

This chapter will outline the necessary elements of each contracting procedure, the approval 

process, and current material and construction specifications. 

While this chapter specifically addresses the need for formal policy and procedures for 

MSE and RSS structures, the recommendations and need for uniformity of practice 

applies to all types of retaining structures. 

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10.1 POLICY DEVELOPMENT 

It is desirable that each Agency develop a formal policy with respect to design and 

contracting of MSE wall and RSS systems. 

The general objectives of such a policy are to: 

C Obtain uniformity within the Agency.
 

C Establish standard policies and procedures for design technical review and acceptance of 

MSEW and RSS systems or components. 

C Establish a policy for the review/acceptance of new retaining wall and reinforced slope 

systems and or components. 

C Delineate responsibility in house for the preparation of plans, design review and 

construction control. 

C Delineate design responsibility for plans prepared by consultants and material suppliers. 

C Develop design and performance criteria standards to be used on all projects. 

C Develop and or update material and construction specifications to be used on all projects. 

C Establish contracting procedures by weighing the advantages/disadvantages of 

prescriptive or end-result methods. 

10.2 SYSTEM OR COMPONENT APPROVALS 

The recent expiration of most process or material patents associated with MSE systems has 

led to introduction by numerous suppliers of a variety of complete systems or components
 

that are applicable for use. Alternatively, it opens the possibility of Agency-generic designs 

that may incorporate proprietary and generic elements. 

Approval of systems or components is a highly desirable feature of any policy for reinforced 

soil systems prior to their inclusion during the design phase, or as part of a value engineering 

alternate. 

For the purpose of prior approval, it is desirable that the supplier submit data that 

satisfactorily addresses the following items as a minimum:
 

C System development or component and year it was commercialized. 

C Systems or component supplier organizational structure, specifically engineering and 

construction support staff. 

C Limitations and disadvantages of system or component. 

C Prior list of users including contact persons, addresses and telephone numbers. 

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C Sample material and construction control specifications showing material type, quality, 

certifications, field testing, acceptance and rejection criteria and placement procedures. 

C A documented field construction manual describing in detail, with illustrations as 

necessary, the step-by-step construction sequence and the contractor’s quality control 

plan. 

C Detailed design calculations for typical applications in conformance with current practice 

or AASHTO, whenever applicable. 

C Typical unit costs, supported by data from actual projects. 

C Independent performance evaluations of a typical project by a professional engineer. 

The development, submittal, and approval of such a technical package provides a complete 

bench-mark for comparison with systems that have been in successful use and a standard 

when checking project-specific designs. 

Some vendor wall systems have been reviewed, and others are currently being reviewed, 

under the HITEC program (see Section 1.2). The HITEC program is still available within 

the American Society of Civil Engineers (ASCE) organization. Wall system suppliers are 

encouraged to conduct an independent review of newly developed components and/or 

systems related to materials, design, construction, performance, and quality assurance for use 

be DOTs in their system approval process. 

For the purpose of review and approval of geosynthetics (systems or components) used for 

reinforcement applications, the manufacturer/supplier submittal must satisfactorily address 

the following items that are related to the establishment of a long-term allowable tensile 

strength used in design: 

C Laboratory test results documenting creep performance over a range of load levels for 

minimum duration of 10,000 hr. in accordance with ASTM D5262. 

C Laboratory test results and methodology for extrapolation of creep data for 75- and 100- 

year design life as described in Appendix D. 

C Laboratory test results documenting ultimate strength in accordance with ASTM D4595 

for geotextiles or ASTM D6637 for geogrids. Tests to be conducted at a strain rate of 10 

percent per minute. 

C Laboratory test results and extrapolation techniques, documenting the hydrolysis 

resistance of polyester (PET), oxidative resistance of polypropylene (PP) and high 

density polyethylene (HDPE), and stress cracking resistance of HDPE for all components 

of geosynthetic and values for partial factor of safety for aging degradation calculated for 

a 75- and 100-year design life. Recommended methods are outlined in FHWA RD 97­

144 (Elias et al., 1999). 

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C Field and laboratory test results along with literature review documenting reduction 

factor values for installation damage as a function of backfill gradation. 

C For projects where a potential for biological degradation exists, laboratory test results and 

extrapolation techniques, documenting biological resistance of all material components of 

the geosynthetic and values for a reduction factor for biological degradation. 

C Laboratory test results documenting joint (seams and connections) strength (ASTM 

D4884 and GRI:GG2). 

C Laboratory tests documenting pullout interaction coefficients for various soil types or 

site-specific soils in accordance with ASTM D6706. 

C Laboratory tests documenting direct sliding coefficients for various soil types or project 

specific soils in accordance with ASTM D5321. 

C Manufacturing quality control program and data indicating minimum test requirements, 

test methods, test frequency, and lot size for each product. Further minimum 

conformance requirements as proscribed by the manufacturer shall be indicated. The 

following is a minimum list of conformance criteria required for approval: 

Minimum Conformance 

Test Test Procedure Requirement 

Wide Width Tensile (geotextiles) ASTM D4595 To be provided by 

Specific Gravity (HDPE only) ASTM D1505 material supplier or 

Melt Flow index (PP & HDPE) ASTM D1238 specialty company 

Intrinsic Viscosity (PET only) ASTM D4603 

Carboxyl End Group (PET only) ASTM D2455 

Single Rib Tensile (geogrids) ASTM D6637 

C The primary resin used in manufacturing shall be identified as to its ASTM type, class, 

grade, and category. 

For HDPE resin type, class, grade and category in accordance with ASTM D1248 shall 

be identified. For example type III, class A, grade E5, category 5. 

For PP resins, group, class and grade in accordance with ASTM D4101 shall be 

identified. For example group 1, class 1, grade 4. 

For PET resins minimum production intrinsic viscosity (ASTM4603) and maximum 

carboxyl end groups (ASTM D2455) shall be identified. 

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For all products the minimum UV resistance as measured by ASTM D4355 shall be 

identified. 

Prior approval should be based on Agency evaluations with respect on the following: 

C The conformance of the design method and construction specifications to current Agency 

requirements for MSE walls and RSS slopes and any deviations to current engineering 

practice. For reinforced slope systems, conformance to current geotechnical practice. 

C Past experience in construction and performance of the proposed system. 

C The adequacy of the data in support of nominal long-term strength (Tal) for geosynthetic 

reinforcements. 

C The adequacy of the QA/QC plan for the manufacture of geosynthetic reinforcements. 

10.3 DESIGN AND PERFORMANCE CRITERIA 

It is highly desirable that each Agency formalize its design and performance criteria as part 

of a design manual that may be incorporated in the Bridge Design Manual under Retaining 

Structures for MSE walls and/or a Highway Design Manual for reinforced slope structures. 

This would ensure that all designs whether Agency/Consultant or Supplier prepared, are 

based on equal, sound principles. 

The design manual may adopt current AASHTO LRFD Bridge Design Specifications (2007) 

Section 11.10 Mechanically Stabilized Earth Walls, or methods outlined in this manual as a 

primary basis for design and performance criteria and list under appropriate sections any 

deviations, additions and clarification to this practice that are relevant to each particular 

Agency, based on its experience. Construction material specifications for MSE walls may be 

modeled on Section 7 of current AASHTO LRFD Bridge Construction Specifications (2004), 

Earth Retaining Systems, or the complete specifications contained in this chapter. 

With respect to reinforced slope design, the performance criteria should be developed based 

on data outlined in Chapter 9. Material and construction specifications for RSS are provided 

in this chapter as well as for drainage and erosion control materials usually required for such 

construction. 

10.4 AGENCY OR SUPPLIER DESIGN 

This contracting approach includes the development of a detailed set of MSE wall or RSS 

slope plans and material specifications in the bidding documents. 

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The advantage of this approach is that the complete design, details, and material 

specifications can be developed and reviewed over a much longer design period. This 

approach further empowers Agency engineers to examine more options during design but 

requires an engineering staff trained in MSE and RSS technology. This trained staff is also a 

valuable asset during construction, when questions arise or design modifications are required. 

The disadvantage is that for alternate bids, additional sets of designs and plans must be 

processed, although only one will be constructed. A further disadvantage is that newer 

systems or components may not be considered during the design stage. 

The fully detailed plans shall include but not be limited to, the following items: 

10.4.1 Plan and Elevation Sheets 

C Plan view to reflect the horizontal alignment and offset from the horizontal control line to 

the face of wall or slope. Beginning and end stations for the reinforced soil construction 

and transition areas, and all utilities, signs, lights, etc. that affect the construction should 

be shown. 

C For MBW unit faced walls, the plan view should show alignment baseline, limits of 

bottom of wall alignment and limits of top of wall alignment, as alignments vary with the 

batter of MBW system actually supplied. 

C Elevation views indicating elevations at top and bottom of walls or slopes, beginning and 

end stations, horizontal and vertical break points, location and elevation of copings and 

barriers, and whole station points. Location and elevation of final ground line shall be 

indicated. 

C Length, size, and type of soil reinforcement and where changes in length or type occur 

shall be shown. 

C Panel and MBW unit layout and the designation of the type or module, the elevation of 

the top of leveling pad and footings, the distance along the face of the wall to all steps in 

the footings and leveling pads. 

C Internal drainage alignment, elevation, and method of passing reinforcements around 

such structures. 

C Any general notes required for construction. 

C Cross sections showing limits of construction, fill requirements, and excavation limits. 

Mean high water level, design high water level, and drawdown conditions shall be shown 

where applicable. 

C Limits and extent of reinforced soil volume. 

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C All construction constraints, such as staged construction, vertical clearance, right-of-way 

limits, etc. 

C Payment limits and quantities. 

10.4.2 Facing/Panel Details 

C Facing details for erosion control for reinforced slopes and all details for facing modules, 

showing all dimensions necessary to construct the element, reinforcing steel, and the 

location of reinforcing attachment devices embedded in the panels. 

C All details of the architectural treatment or surface finishes. 

10.4.3 Drainage Facilities/Special Details 

C All details for construction around drainage facilities, overhead sign footings, and 

abutments. 

C All details for connection to traffic barriers, copings, parapets, noise walls, and attached 

lighting. 

C All details for temporary support including slope face support where warranted. 

C All details for wall initiation and termination, and any transitions. 

10.4.4 Design Computations 

The plans shall be supported by detailed computations for internal and external stability and 

life expectancy for the reinforcement. 

For plans prepared by material suppliers, the Owner and/or their consultant normally 

determine deep seated global stability. The Owner must define responsibility for compound 

stability analysis, when applicable. 

10.4.5 Geotechnical Report 

The plans shall be prepared based on a geotechnical report that details the following: 

C Engineering properties of the foundation soils including shear strength and consolidation 

parameters used to establish settlement and stability potential for the proposed 

construction. Maximum bearing pressures must be established for MSE wall 

construction. 

C Engineering properties of the reinforced soil including shear strength parameters (φ, c) 

compaction criteria, gradation, and electrochemical limits. 

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C Engineering properties of the fill or in-situ soil behind the reinforced soil mass, including 

shear strength parameters (φ, c) and compaction criteria. 

C Groundwater or free water conditions and required drainage schemes if required. 

10.4.6 Construction Specifications 

Construction and material specifications for the applicable system or component as detailed 

later in this chapter, which include testing requirements for all materials used. 

10.5 END RESULT DESIGN APPROACH 

Under this approach, often referred as "line and grade" or "two line drawing," the Agency 

prepares drawings of the geometric requirements for the structure or reinforced slope and 

material specifications for the components or systems that may be used. The components or 

systems that are permitted are specified or are from a pre-approved list maintained by the 

Agency, from its prequalification process. 

The end-result approach, with sound specifications and prequalification of suppliers and 

materials, offers several benefits. Trained and experienced staff performs design of the MSE 

structure. The prequalified material components (facing, reinforcement, and miscellaneous) 

have been successfully and routinely used together, which may not be the case for in-house 

design with generic specifications for components. Also, the system specification approach 

lessens engineering costs and manpower for an Agency and transfers some of the project's 

design cost to construction. 

The disadvantage is that Agency engineers may not fully understand the technology at first 

and, therefore may not be fully qualified to review and approve construction modifications. 

Newer systems may not be considered due to the lack of confidence of Agency personnel to 

review and accept these systems. In addition, complex phasing and special details are not 

addressed until after the contract has been awarded. 

The bid quantities are obtained from specified pay limits denoted on the "line and grade" 

drawings and can be bid on a lump-sum or unit-price basis. The basis for detailed designs to 

be submitted after contract award are contained either as complete special provisions or by 

reference to AASHTO or Agency manuals, as a special provision. 

Plans, furnished as part of the contract documents, contain the geometric, geotechnical and 

design-specific information listed below. 

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10.5.1 Geometric Requirements 

C Plan and elevation of the areas to be retained, including beginning and end stations. 

C For MBW unit faced walls, the plan view should show alignment baseline, limits of 

bottom of wall alignment and limits of top of wall alignment, as alignments vary with the 

batter of MBW system actually supplied. 

C Typical cross section that indicates face batter, pay limits, drainage requirements, 

excavation limits, etc. 

C Elevation view of each structure showing original ground line, minimum foundation 

level, finished grade at ground surface, and top of wall or slope line. 

C Location of utilities, signs, etc., and the loads imposed by each such appurtenance, if any. 

C Construction constraints such as staged construction, right-of-way, construction 

easements, etc. 

C Mean high water level, design high water level, and drawdown conditions where 

applicable. 

10.5.2 Geotechnical Requirements 

They are the same as in Section 8.4 except that the design responsibility is clearly delineated 

as to areas of contractor/supplier and Agency responsibility. 

Typically, the Agency would assume design responsibility for developing global stability, 

bearing resistance and settlement analyses, as they would be the same regardless of the 

system used. The contractor/supplier would assume responsibility for both internal and local 

external stability for the designed structures. 

10.5.3 Structural and Design Requirements 

C Reference to specific governing sections of the Agency design manual (materials, 

structural, hydraulic and geotechnical), construction specifications and special provisions. 

If none is available for MSE walls, refer to current AASHTO, both Division I, Design 

and Division II, Specifications. 

C Magnitude, location, and direction of external loads due to bridges, overhead signs and 

lights, and traffic surcharges. 

C Limits and requirements of drainage features beneath, behind, above, or through the 

reinforced soil structure. 

C Slope erosion protection requirements for reinforced slopes. 

C Size and architectural treatment of concrete panels for MSE walls. 

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10.5.4 Performance Requirements 

C Tolerable movement of the structure both horizontal and vertical. 

C Tolerable face panel movement. 

C Monitoring and measurement requirements. 

10.6 STANDARD DESIGNS 

The development and use of standard MSEW and RSS designs are discussed in Sections 4.8 

and 8.8, respectively. With standard design, the Agency has certain responsibilities in 

preparation of the project plans and the vendor has certain responsibilities. For the example 

standard designs (Berg, 2000), the following Agency responsibilities are noted on the 

standard plans. 

10.6.1 MSEW Standard Designs 

Agency Responsibilities: 

In addition to the standard sheets, plan and front elevation views of the modular block 

retaining walls shall be included in the plans. The plan view must show alignment baseline, 

limits of bottom of wall alignment, and limits of top of wall alignment as alignments vary 

with batter of wall system supplied. The front elevation must identify bottom and top of wall 

elevations, existing grades, and finished grades. 

If the wall is curved, show the radius at the bottom and the top of each wall segment and the 

P.C. and P.T. station points off of baseline and limits of bottom and top of wall alignment. 

Reference adjacent pavement elevations (including superelevations, as applicable). 

Reference standard plates and provide details for traffic barriers, curb and gutter, handrails 

and fencing as required by project conditions. See AASHTO and Agency design manuals, 

standard plates and details for requirements. 

Surface drainage patterns shall be shown in the plan view. Provide dimensions for width and 

depth of the drainage swale as well as the type of impervious liner material. Surface water 

runoff should be collected above and diverted around wall face. 

Detail lines and grades of the internal drainage collection pipe. Detail or note the destination 

of internal wall drains as well as the method of termination (daylight end of pipe or 

connection into hydraulic structure). 

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Soft soils and/or high water conditions may not be suitable for application of standard 

designs and may require a project specific design. 

Standard design charts are not applicable to: 

C Project/sites where foundation soils shear strength and/or bearing capacity do not meet or 

exceed values used in the development of standard design charts. 

C Projects with a large (Agency defined) quantity of face area where project specific 

designs are recommended. 

C Where slopes in front of wall are steeper than 1:3. 

C Where maximum wall height exceeds 32 ft (7.0 m). 

C Where walls are tiered. 

C Walls with soundwalls. 

Contractor Responsibilities: 

Approved combinations of modular block unit and soil reinforcement products list with 

MBW reinforcement class noted are held and maintained by the Agency. Only approved 

product combinations may be used in standard designs. 

Provide detailed drawings for construction containing: 

C Elevation view with reinforcement placement requirements, wall facing layout, and 

geometric information. Top of wall may extend up to 4 inches (100 mm) above plan top 

of wall elevation. 

C Plan view with bottom and top of wall alignment, and plan limits of wall alignment. 

C Cross sections detailing batter, reinforcement, vertical spacing. Reinforcement lengths. 

Subsurface drainage, surface drainage, and water runoff collection above wall. 

C Reinforcement layouts reinforcement shall be placed at 100% coverage ratio. 

Reinforcement elevations shall be consistent across length of wall structure. 

C Note block, reinforcement, and fill placement methods and requirements. 

C Detail all wall fill penetrations and wall face penetrations. Detail reinforcement and/or 

wall facing unit placement around penetrations. 

C Details that are specific to vendor products and their interaction with other project 

components. 

C List information on approved combination of MBW unit and geosynthetic reinforcement, 

including Agency classification code, nominal block width, properties for field 

identification, and installation instructions. 

C Details of cap units and installation/fastening instructions for the caps. Cap units shall be 

set in a bed of adhesive designed to withstand moisture and temperature extremes, remain 

flexible, and shall be specifically formulated for bonding masonry to masonry. 

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C Certification by professional engineer that the construction layout meets the requirements 

of plans and Agency MSEW standards. Deviation from standard design tables by value 

engineering submittal only. 

10.6.2 RSS Standard Designs 

Agency Responsibilities: 

Review by Turf and Erosion Prevention Unit and the Office of Environmental Services (or 

similar), shall be performed for all RSS applications. Turf establishment and maintenance 

items, hydroseeding over erosion control blanket, use of turf reinforcement mat in 

channelized flow areas, modification of seed mix, turf maintenance contract items, in 

addition to the details contained on these drawings, should be evaluated on a project basis. 

In addition to the standard sheets, typical cross sections of the soil slopes shall be included in 

the plans as well as including soil slopes on the project cross sections. 

Detail transition of RSS to adjacent slopes or structures. 

Reference standard plates and provide details for traffic barriers, curb and cutter, handrails 

and fencing as required by project conditions. See AASHTO and Agency design manuals, 

standard plates, and details for requirements. 

Detail lines and grades of the internal drainage collection pipe. Detail or note the destination 

of internal drains as well as the method of termination (daylight end of pipe or connection 

into adjacent hydraulic structure). 

Surface drainage patterns shall be shown in the plan view. Surface water runoff should be 

collected above and diverted around slope face. 

Define reinforced soil slope angle and define construction limits on the plan view based on 

this angle. Standard slope angles are 45 and 70 degrees. 

Soft soils and/or high water conditions (defined as groundwater within a depth equal to the 

slope height H) may not be suitable for application of standard designs and requires special 

consideration by the Agency. 

Standard designs are not applicable for projects with large quantity (Agency defined) of 

vertical face area where project specific designs are recommended. 

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Designs based on level backfill, zero toe slope and traffic surcharge. Slopes above or below 

the oversteepened reinforced slope are not suitable for application of standard designs and 

require special consideration by the Agency. 

Refer to Case 1A and 1B for soil slopes between l:2 (26.5°) and 45° maximum. Use Case 2 

for soil slopes greater than 45° and up to 70° maximum. 

Geotechnical investigation shall be performed for all RSS applications. 

Agency Responsibilities: 

Approved soil reinforcement products list, with type noted, and approved erosion control 

products list, are held and maintained by the Agency. Only approved products may be used 

in standard designs. 

Provide detailed drawings for construction, containing: 

C Elevation view with reinforcement placement requirements, soil slope layout and 

geometric information. 

C Cross sections detailing slope face angle, reinforcement vertical spacing, reinforcement 

lengths, subsurface drainage, surface drainage, and slope face erosion protection. 

C Detail all reinforced fill penetrations and face penetrations. Detail reinforcement and 

erosion protection placement around penetrations. 

C List information on approved geosynthetic reinforcement, including Agency 

classification code, properties for field identification and installation directions. List 

product and installation information on welded wire mesh facing forms if utilized. 

C Certification by Professional Engineer that construction layout meets the requirements of 

plans and Agency RSS standards. Deviation from standard design tables by value 

engineering submittal only. 

10.7 REVIEW AND APPROVALS 

Where Agency design is based on a supplier’s plans, it should be approved for incorporation 

in the contract documents following a rigorous evaluation by Agency structural and 

geotechnical engineers. The following is a checklist of items requiring review: 

C Conformance to the project line and grade. 

C Conformance of the design calculations to Agency standards or codes such as current 

AASHTO with respect to design methods, allowable bearing capacity, allowable tensile 

strength, connection design, pullout parameters, surcharge loads, and factors of safety. 

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C Development of design details at obstructions such as drainage structures or other 

appurtenances, traffic barriers, cast-in-place junctions, etc. 

C Facing details and architectural treatment. 

For end result contracting methods, the special provisions should contain a requirement that 

complete design drawings and calculations be submitted within 60 days of contract award for 

Agency review. 

The review process should be similar to the supplier design outlined above and be conducted 

by the Agency's structural and geotechnical engineers. 

10.8 CONSTRUCTION SPECIFICATIONS AND SPECIAL PROVISIONS FOR 

MSE WALL AND RSS CONSTRUCTION 

A successful reinforced soil project will require sound, well-prepared material and 

construction specifications to communicate project requirements as well as construction 

guidance to both the contractor and inspection personnel. Poorly prepared specifications 

often result in disputes between the contractor and owner representatives. 

A frequently occurring problem with MSE systems is the application of different or unequal 

construction specifications for similar MSE systems. Users are encouraged to utilize a single 

unified specification that applies to all systems, regardless of the contracting method used. 

The construction and material requirements for MSE systems are sufficiently well developed 

and understood to allow for unified material specifications and common construction 

methods. 

Guide construction and material specifications are presented in this chapter for the following 

types of construction: 

C Section 10.9 – Example specification for MSE walls with segmental precast concrete,
 

WWM, or MBW facings and steel (grid or strip) or geosynthetic reinforcements. 

C Section 10.10 – Example specifications for RSS systems. 

These guide specifications should serve as the technical basis for Agency developed standard 

specifications for these items. Local experience and practice should be incorporated as 

applicable. EDIT NOTE: Some key items that may be edited based upon local experience 

and/or practice are noted with a text box insert and discussion. The contractor should be 

required to submit a quality control plan detailing measurements and documentation that will 

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be maintained during construction to assure consistency in meeting specification 

requirement. 

10.9 EXAMPLE SPECIFICATION FOR MECHANICALLY STABILIZED EARTH 

(MSE) WALLS 

The following specification addresses MSE walls reinforced with galvanized steel or 

geosynthetics, and faced with precast segmental panels, welded wire mesh (WWM), or 

masonry modular block wall (MBW) units. This example specification has been modified 

from the Arizona DOT (2009) LRFD MSE Wall specification. It is consistent with the 

design checklist in Chapter 4 and with recommendations with in this manual, but in some 

cases may extend beyond these recommendations. Sections to be filled in are shown as: 

________ or with an example value noted, e.g. 30 days. 

MECHANICALLY STABILIZED EARTH (MSE) WALLS 

1 Description: 

1.01 General: 

The work under this section consists of designing, furnishing all materials and constructing 

Mechanically Stabilized Earth (MSE) retaining walls in accordance with these specifications and in 

compliance with the lines and grades, dimensions and details shown on the project plans and as 

directed by the Engineer. 

The contractor shall provide the MSE wall designer with a complete set of project plans and 

specifications and shall ensure that the wall design is compatible with all other project features that 

can impact the design and construction of the wall. The following terms are used in this specification 

for identification of various entities for which the contractor shall be fully responsible: 

Term Entity 

Wall Manufacturer The entity contractually retained by the contractor to provide materials and 

construction services for an accepted MSE wall system as identified in 

Subsection 1.03. 

Wall Designer The entity contractually retained by the contractor to provide design of an 

accepted MSE wall system as identified in Subsection 1.03. The wall 

designer may be a representative of the wall manufacturer. 

1.02 Certifications: 

(A) Certification of Design Parameters: 

See Subsection 2.01 herein specified. 

(B) Certification of Materials: 

See Subsections 3.04, 3.07 and 3.10 herein specified. 

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1.03 Accepted Systems: 

The contractor shall select one of the appropriate __DOT pre-approved earth retaining systems to be 

constructed for the MSE walls designated on the plans. 

Pre-approved systems are listed under category “Proprietary Retaining Walls” in the Approved 

Products List (APL). Copies of the most current version of the APL are available on the Internet at 

____________________. 

The features of the system furnished, including design and configuration of precast elements, 

fasteners, connections, soil reinforcements, joint fillers, geotextile filter, and other necessary 

components, shall be those that have been pre-approved. 

Heights and lengths of earth retaining walls may vary from, but shall not be less than, those shown on 

the plans. The height and length to be used for any system shall be the minimum for that system that 

will effectively retain the earth behind the wall for the loading conditions and the contours, profile, or 

slope lines shown on the plans, or on the approved working drawings, and in accordance with all 

relevant internal and external stability design criteria, but not more than the pre-approved height for 

the particular MSE wall system selected. 

1.04 Manufacturer’s Field Representative: 

The manufacturer’s field representative performing the work described in this specification shall 

have, in the past three years, successfully installed at least four MSE retaining walls of heights, 

lengths and complexity similar to those shown on the plans and meeting the tolerances specified 

herein. The manufacturer’s field representative may make field changes subject to the approval of the 

Engineer. Any such changes shall be documented in writing within 24 hours of the approved 

changes. This written document shall be sealed by the manufacturer’s design engineer, who is 

registered as a Civil Engineer in the State . 

1.05 MSE Pre-Activity Meeting: 

A pre-activity meeting will be scheduled prior to commencement of MSE wall construction activity. 

As a minimum, this meeting shall be attended by the Engineer, contractor (including wall 

construction crew chiefs), the MSE wall sub-contractor, MSE wall manufacturer’s and MSE Wall 

designer’s representatives. No wall construction activity shall be performed until the contractor’s 

final submittals have been approved as having satisfactorily resolved all review comments and the 

pre-activity meeting has been held. 

1.06 Wall Aesthetics: 

Wall aesthetics shall be as specified in the project plans and special provisions. 

2 Submittals (Working Drawings and Design): 

2.01 Submittals: 

The submittals required shall include working drawings, construction procedures, supporting design 

calculations, verification of experience, and a transmittal letter. The transmittal letter shall only list 

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the documents included in the submittal. No technical information shall be included in the 

transmittal letter. 

Working drawings and calculations shall be sealed by an engineer, who is registered as a Civil 

Engineer in the State. The MSE wall designer/supplier shall document on the working drawings all 

assumptions made in the design. The following statement shall be included near the P.E. seal on the 

first sheet of the working drawings: “All design assumptions are validated through notes or details on 

these drawings.” 

Six complete sets of working drawings, design calculations and MSE supplier’s construction 

procedures modified as necessary by the contractor and Wall Designer for site-specific conditions 

shall be submitted to the Engineer for review. The Engineer shall have 30 calendar days after 

receiving the six complete sets to finish a review. The revised package shall be resubmitted to the 

Engineer for review. The Engineer shall have 15 calendar days to complete this review. This review 

process shall be repeated until the entire submittal is accepted by the Engineer. 

The Department assumes no responsibility for errors or omissions in the working drawings. 

Acceptance of the final working drawings submitted by the contractor shall not relieve the contractor 

of any responsibility under the contract for the successful completion of the work. 

Construction of the wall shall not commence until the contractor receives a written Notification To 

Proceed (NTP) from the Engineer. The NTP will be issued once the complete wall package 

(drawings, calculations and construction procedures) is approved. Fabrication of any of the wall 

components before the NTP shall be at the sole risk of the contractor. 

2.02 Working Drawings: 

The contractor shall submit complete working drawings and specifications for each installation of the 

system in accordance with the requirements of Subsection _____ as modified herein. 

Working drawings shall include the following at a minimum: 

(1) Layout of the wall including plan and elevation views; 

(2) All design parameters and assumptions including design life; 

(3) Existing ground elevations and utilities impacted by the wall, and those that should be field 

verified by the contractor, for each location; 

(4) Complete details of all elements and component parts required for the proper construction of 

the system at each location and any required accommodations for drainage systems, 

foundation subgrades or other facilities shown on the contract documents; 

(5) The working drawing submittal shall clearly detail any special design requirements. These 

special design requirements may include, but are not limited to; structural frames to place 

reinforcements around obstructions such as deep foundations and storm drain crossings, 

drainage systems, placement sequence of drainage and unit core fill with respect to reinforced 

(structure) fill behind a wall face using modular block facing units, guardrail post installation, 

scour protection, foundation subgrade modification, all corner details (acute, obtuse and 90 

degrees), slip joints, joint details of MSE walls with other cast-in-place structures, wedges, 

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shims and other devices such as clamps and bracing to establish and maintain vertical and 

horizontal wall facing alignments; 

(6) A complete listing of components and materials specifications; and 

(7) Other site-specific or project specific information required by the contract. 

2.03 MSE Wall Design: 

(A) General: 

The working drawings shall be supplemented with all design calculations for the particular 

installation as required herein. Installations that deviate from the pre-approved design shall be 

accompanied by supporting stability (internal; external; and global/overall and/or compound if 

required in the project documents) calculations of the proposed structure as well as supporting 

calculations for all special details not contained in the pre-approved design. The MSE wall 

designer/supplier shall note all deviations of the proposed wall design from the pre-approved design. 

The proposed design shall satisfy the design parameters shown on the project plans and listed in these 

specifications, and comply with the design requirements of the following document: 

 FHWA NHI-10-024 Vol I and NHI-10-025 Vol II, “Design of MSE Walls and Reinforced 

Slopes,” (Berg et al., 2009). 

 AASHTO (2007),”AASHTO LRFD Bridge Design Specifications,” 4th Edition, including 2008 

and 2009 Interims. 

All references to AASHTO (2007) shall mean to include the latest interims. 

Maximum reinforcement loads shall be calculated using the “Simplified Method” as presented in 

AASHTO (2007) and as per the requirements specified herein. No other design method will be 

allowed. EDIT NOTE: The 2008 Interims states that the Simplified Method or the Coherent Gravity 

Method may be used. Agencies should specify what method(s) are acceptable and not leave as a 

contractor option. 

Sample analyses and hand-calculations shall be submitted to verify the output from software used by 

the MSE wall designer. Sample analyses and hand-calculations shall be required for complex walls 

having geometries and loading conditions that are not readily amenable to computer analysis. Failure 

modes, including circular, non-circular, and multi-part wedge, shall be analyzed for deep-seated 

global stability and compound stability to verify the most critical failure case. EDIT NOTE: Agency 

must specify who – the Agency or the contractor/wall vendor – is responsible for global and for 

compound stability analyses. If the contractor/wall supplier is responsible, subsurface data in 

sufficient detail to perform the analyses must be provided by the Agency to the contractor/wall 

supplier. See Chapter 4 for additional discussion. 

Unless otherwise specified in the contract, all structures shall be designed to conform to the 

requirements shown in Table 1 and other requirements specified herein. 

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TABLE 1 

DESIGN PARAMETERS 

Description Limit State Value Note* 

1. Design Life All limit states 75 Years 

2. Effective (Drained) Friction Angle 

a. Retained Backfill All limit states 32o

 min

 b. Reinforced Backfill All limit states 34o

 to max 40o 1 

3. Length of soil reinforcement, B All limit states 0.7H min or 8-ft 

whichever is more 2 

4. Limiting eccentricity Strength (all) B/4 (soil), 3/8B (rock) 

Service I B/6 (soil), B/4 (rock) 

5. Coefficient of Sliding Friction Strength (all) tan[min(r, f, i)] 3 

6. Resistance factors 

a. Sliding Strength (all) 1.0 4 

b. Bearing Strength (all) 0.65 5 

c. Overall (slope) stability 

I. Deep Seated Stability Service I 0.65 6 

II. Compound Stability Service I 0.65 6 

d. Pullout resistance 

I. Static Strength (all) 0.90 7 

II. Combined static/earthquake Strength (all) 1.20 7 

e. Tensile resistance of metallic 

reinforcements and connectors 

I. Static 

- Strip reinforcement 

 - Grid reinforcement 

Strength (all) 

Strength (all) 

0.75 

0.65 

8 

8,9 

II. Combined static/earthquake 

- Strip reinforcement 

 - Grid reinforcement 

Strength (all) 

Strength (all) 

1.00 

0.85 

8 

8,9 

f. Tensile resistance of geosynthetic 

reinforcements and connectors 

I. Static Strength (all) 0.90 

II. Combined static/earthquake Strength (all) 1.20 

* Refer to Table 1.1 for notes. 

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TABLE 1.1 

NOTES FOR TABLE 1 

# Note 

1 A minimum friction angle of 34 degrees shall be substantiated by laboratory tests discussed in 

Subsection 3.05(D). If the measured friction angle in laboratory tests as per Subsection 

3.05(D) is greater than 40-degrees then the friction angle in the analysis shall be limited to 40­

degrees. 

2 H is the design height of the wall and is defined as the difference in elevation between from 

the finished grade at the tope of wall and the top of leveling pad. The top of the leveling pad 

shall always be below the minimum embedment reference line as indicated on the plans for 

that location. The length of the soil reinforcement, B, is measured from the backface of the 

wall facing unit. In case of grid type reinforcements the length of the soil reinforcement is 

measured from the backface of the wall to the last full transverse member. For modular block 

facing units, the total length of the reinforcement, BT, as measured from the front face of the 

wall is the length B as defined above plus the width of the modular block unit (the horizontal 

dimension of the block unit measured perpendicular to the wall face). 

3 r= friction angle of reinforced wall fill; f = friction angle of foundation soil; i = friction 

angle of the interface between reinforcement and soil for cases of sheet reinforcement such as 

geotextiles. All friction angles are effective (drained) friction angles. Refer to Geotechnical 

Report for friction angle of foundation soil. 

4 Passive resistance shall not be considered in evaluation of sliding resistance. 

5 For all limit states, the design loading for the MSE retaining wall system shall not exceed the 

factored general and local bearing resistances specified in the Geotechnical Report(s). 

6 For earthquake loading condition, a resistance factor of 0.90 shall be used. 

7 Live load due to vehicular traffic shall be included in the computations to determine the 

maximum tensile forces in reinforcement layers, but shall be neglected in the computations for 

pullout resistance. EDIT NOTE: Agency should specify whether or not to include live load 

in tensile force calculations for pullout check, see Chapter 4 for discussion. Intensity of live 

load shall be considered as a uniform surcharge using the equivalent height of soil in 

accordance with Section Article 3.11.6.4 of AASHTO (2007). 

8 Apply to gross cross-section less sacrificial area. For sections with holes, reduce gross area in 

accordance with Article 6.8.3 of AASHTO (2007) and apply to net section less sacrificial 

area. 

9 Applies to grid reinforcements connected to a rigid facing element, e.g., a concrete panel or 

block. For grid reinforcements connected to a flexible facing mat or which are continuous 

with the facing mat, use the resistance factor for strip reinforcements. 

10 Unless otherwise specified, all resistance factors shall be taken as 1.0 when investigating an 

extreme event limit state. 

(B) Subsurface Drainage Systems: 

Walls shall be provided with subsurface drainage measures as shown on the project plans and 

specifications. As a minimum, an underdrain system shall be provided for leading subsurface and 

surface water away from the backfill and outside the limits of the wall. Geocomposite drains, if used 

for subsurface drainage, shall be in accordance with Subsection ____ and _____ of the specifications. 

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(C) Obstructions in Backfill: 

(1) General: 

Where obstructions, such as deep foundations or storm drains crossings, are located in the 

reinforced backfill zone, cutting of reinforcements to avoid obstructions shall not be permitted. A 

minimum offset of one diameter but not less than three (3) feet shall be maintained between the 

face of any pipe crossings and the back face of retaining wall panels. A minimum clearance of 

three (3) feet shall be maintained between the face of any other obstruction and the back face of 

retaining wall panels. 

(2) Horizontal Deflection of Reinforcements: 

In the horizontal plane at a reinforcing level, a deviation up to fifteen (15) degrees from the 

normal to the face of the wall may be allowed for strip reinforcement and bolted connection. This 

deviation is herein referred to as the splay angle. Grid reinforcements may not be splayed, unless 

connection has been specifically fabricated to accommodate a splay and connection detail has 

been approved by the Agency. If used, the splay in grid reinforcement is limited to fifteen (15) 

degrees. For obstructions that cannot be accommodated with splayed reinforcement, structural 

frames and connections shall be required, and shall be designed in accordance with Section 10 

(“Steel Structures”) of AASHTO (2007) for the maximum tension in the reinforcements. The 

structural frame design shall be such that bending moments are not generated in the soil 

reinforcement or the connection at the wall face. The design, along with supporting calculations, 

shall be included in the working drawings. 

(3) Vertical Deflection of Reinforcements: 

Vertical deflection of the reinforcement to avoid obstructions such as utilities along the wall face 

shall be limited to a maximum of 15 degrees from normal to face of wall. Bends in the 

reinforcement shall be smooth and gradual to ensure that galvanization remains intact. 

(D) Hydrostatic Pressures: 

As determined by the Engineer and/or as noted on the plans, for walls potentially subject to 

inundation, such as those located adjacent to rivers, canals, detention basins or retention basins, a 

minimum hydrostatic pressure equal to three (3) feet shall be applied at the high-water level for the 

design flood event. Effective unit weights shall be used in the calculations for internal and external 

stability beginning at levels just below the equivalent surface of the pressure head line. Where the 

wall is influenced by water fluctuations, the wall shall be designed for rapid drawdown conditions 

which could result in differential hydrostatic pressure greater than three (3) feet. As an alternative to 

designing for rapid drawdown conditions, Size 57 coarse aggregate, as specified in AASHTO M 43, 

shall be provided as reinforced wall fill for the full length of the wall and to the maximum height of 

submergence of the wall. Separation geotextile, as specified in Subsection ____, shall be provided at 

the interface of the Size 57 coarse aggregate and reinforced wall fill above it, and at the interface of 

the retained backfill behind it. Adjoining sections of separation geotextile shall be overlapped by a 

minimum of 12 inches. 

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(E) Acute Angle Corners: 

Wall corners with an included angle of less than 70 degrees shall be designed for bin-type lateral 

pressures for the extent of the wall where the full length of the reinforcement cannot be installed 

without encountering a wall face. Acute angle corner structures shall not be stand-alone separate 

structures. Computations shall be provided that demonstrate deformation compatibility between the 

acute angle corner structure and the rest of the MSE wall. Full-height vertical slip joints shall be 

provided at the acute angle corner and after the last column of panels where full length of the 

reinforcements can be placed. The soil reinforcement attached to the slip joints shall be oriented 

perpendicular to the slip joint panels and shall be the full design length. Special connection and 

compaction details shall be provided on the working drawings. 

(F) Spacing of Metallic Reinforcement for Flexible Face Wall Systems: 

For permanent walls, vertical and horizontal spacing of metallic reinforcements for flexible face 

(welded wire or similar) wall systems shall not exceed 18 inches. The stiffness of the facing and 

spacing of reinforcements shall be such that the maximum local deformation between soil 

reinforcement layers shall be limited to less than 11⁄2 inches. EDIT NOTE: Recommended limitation 

range, see Chapter 3, is 1 to 2 inches. Agency should specify specific value. Facing elements shall 

not yield in bending and tension. 

For temporary walls, i.e., walls with up to 36 months service life, the contractor may adjust the 

stiffness of the facing and spacing of the reinforcements such that the local deformation between the 

reinforcement is within the elastic range in bending and tension, and the overall geometry meets the 

line and grade requirements for the temporary walls. 

(G) Soil Reinforcement for Modular Block Wall Systems: 

The soil reinforcement lengths and percent coverage at a given reinforcement level shall be in 

accordance with the plans. All soil reinforcement shall be positively connected to the modular block 

facing units that is capable of resisting 100% of the maximum tension in the soil reinforcements at 

any level within the wall. Detailed documentation for connection strength shall be submitted as noted 

in Subsection 3.10. The vertical spacing of the soil reinforcement for walls with modular block 

facing units shall be as follows: 

1. The first (bottom) layer of soil reinforcement shall be no further than 16 inches above the top 

of the leveling pad. 

2. The last (top) layer of soil reinforcement shall be no further than 20 inches on the average 

below the top of the uppermost MBW unit. 

3. The maximum vertical spacing between layers of adjacent soil reinforcement shall not exceed 

32 inches. For walls deriving any part of their connection capacity by friction the maximum 

vertical spacing of the reinforcement should be limited to two times the block depth (front 

face to back face) to assure construction and long-term stability. The top row of 

reinforcement should be one-half the vertical spacing. 

(H) Initial Batter of Wall: 

The initial batter of the wall, both during construction and upon completion, shall be within the 

vertical and horizontal alignment tolerances included in this specification. The initial batter of the 

wall at the start of construction and the means and methods necessary to achieve the batter shall be 

provided on the working drawings. Subject to Engineer’s approval, the initial batter may be modified 

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at the start of construction by the manufacturer’s field representative based on the evaluation of the 

backfill material selected by the contractor. Any such changes shall be documented in writing within 

24 hours of the approved changes. This written document shall be sealed by the manufacturer’s 

design engineer who is registered as a Civil Engineer in the state. Details of the wedges or shims or 

other devices, such as clamps and external bracing used to achieve or maintain the wall batter, shall 

be as shown on the working drawings and/or accompanying construction manual. Permanent shims 

shall comply with the design life criteria, and shall maintain the design stress levels required for the 

walls. 

3 Material Requirements: 

3.01 Precast Concrete Elements: 

Precast concrete elements shall conform to the requirements for precast minor structures in Sections 

___ and ____. The concrete shall be Class __ with minimum design strength of 4,000 pounds per 

square inch. The mix design shall conform to the requirements of Subsection 3.02. 

Prior to casting, all embedded components shall be set in place to the dimensions and tolerances 

designated in the plans and specifications. Rustication for wall aesthetics shall be in accordance with 

project plans, special provisions, and applicable requirements of Sections ___, ___, ___ and ___. 

(A) Concrete Testing and Inspection: 

Precast concrete elements shall be subjected to compressive strength testing in accordance with 

Subsection ___, and inspected for dimensional tolerances and surface conditions in accordance with 

Subsections ____ and ____ respectively. Panels delivered to the site without the Agency acceptance 

stamp will be rejected. 

(B) Casting: 

Precast concrete face panels shall be cast on a horizontal surface with the front face of the panel at the 

bottom of the form. Connection hardware shall be set in the rear face. The concrete in each precast 

concrete panel shall be placed without interruption and shall be consolidated by deploying an 

approved vibrator, supplemented by such hand tamping as may be necessary to force the concrete into 

the corner of the forms, and to eliminate the formation of stone pockets or cleavage planes. Form 

release agents as specified in Subsection _____ shall be used on all form faces for all casting 

operations. 

The contractor shall advise the Engineer of the starting date for concrete panel casting at least 14 

calendar days prior to beginning the operation if the casting operation is within the State, or 21 

calendar days if the casting operation is outside the State. 

(C) Finish: 

(1) Non-Exposed Surfaces: 

Rear faces of precast concrete panels shall receive a Class 1 finish in accordance with Subsection 

____. 

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 (2) Exposed Surfaces: 

The type of finish required on exposed surfaces shall be as shown in the plans. 

(a) Exposed Aggregate Finish: 

(1) Prior to placing concrete, a set retardant shall be applied to the casting forms in 

accordance with the manufacturer’s instructions. 

(2) After removal from the forms and after the concrete has set sufficiently to prevent its 

dislodging, the aggregate shall be exposed by a combination of brushing and washing 

with clear water. The depth of exposure shall be between 3⁄8 inch and 1⁄2 inch. 

(3) An acrylic resin sealer consisting of 80 percent thinner and 20 percent acrylic solids 

by weight shall be applied to the exposed aggregate surface at a rate of one (1) gallon 

per 250 square feet. 

 (b) Concrete Panel Finish: 

 Concrete panel finish shall be in accordance with Subsection ____. 

(D) Tolerances: 

Precast concrete elements shall comply with Subsection ____ and ____. Connection device 

placement shall be within ± 1 inch of the dimensions shown on the drawings. Panel squareness as 

determined by the difference between the two diagonals shall not exceed 1⁄2 inch. 

(E) Identification and Markings: 

The date of manufacture, the production lot number, and the piece mark shall be inscribed on a nonexposed surface of each element. 

(F) Handling, Storage and Shipping: 

All panels shall be handled, stored, and shipped in such a manner to eliminate the dangers of 

chipping, discoloration, cracks, fractures, and excessive bending stresses. Panels in storage shall be 

supported in firm blocking to protect panel connection devices and the exposed exterior finish. 

Storing and shipping shall be in accordance with the manufacturer’s recommendations. 

(G) Compressive Strength: 

Precast concrete elements shall not be shipped or placed in the wall until a compressive strength of 

3,400 pounds per square inch has been attained. The facing elements shall be cast on a flat and level 

area and shall be fully supported until a compressive strength of 1,000 pounds per square inch has 

been attained. 

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(H) Precast Concrete Panel Joints: 

(1) General: 

Where the wall wraps around an inside corner, a corner block panel shall be provided with flange 

extensions that will allow for differential movement without exposing the panel joints. The back 

face of vertical and horizontal joints shall be covered with geotextile filter. Joint filler, bearing 

pads, and geotextile filter shall be as recommended by the wall manufacturer and shall meet the 

requirements shown on the approved working drawings. 

If required, as indicated on the plans, flexible open-cell polyurethane foam strips shall be used for 

filler for vertical joints between panels, and in horizontal joints where pads are used. 

All joints between panels on the back side of the wall shall be covered with a geotextile meeting 

the requirements for filtration applications as specified by AASHTO M 288. The minimum 

width shall be one (1) foot. 

(2) Bearing Pads: 

All horizontal and diagonal joints between panels shall include bearing pads. Bearing pads shall 

meet or exceed the following material requirements: 

	 Preformed EPDM (Ethylene Propylene Diene Monomer) rubber pads conforming to 

ASTM D 2000 Grade 2, Type A, Class A with a Durometer Hardness of 70. 

	 Preformed HDPE (High Density Polyethylene) pads with a minimum density of 0.946 

grams per cubic centimeter in accordance with ASTM D 1505. 

The stiffness (axial and lateral), size, and number of bearing pads shall be determined such that 

the final joint opening shall be 3⁄4+1/8 inch unless otherwise shown on the plans. The MSE wall 

designer shall submit substantiating calculations verifying the stiffness (axial and lateral), size, 

and number of bearing pads assuming, as a minimum, a vertical loading at a given joint equal to 2 

times the weight of facing panels directly above that level. As part of the substantiating 

calculations, the MSE wall designer shall submit results of certified laboratory tests in the form of 

vertical load-vertical strain and vertical load-lateral strain curves for the specific bearing pads 

proposed by the MSE wall designer. The vertical load-vertical strain curve should extend beyond 

the first yield point of the proposed bearing pad. 

3.02 Steel Components: 

Steel components shall conform to the applicable requirements of Sections ___ and ___. 

(A) Galvanization: 

Soil reinforcement steel shall be hot-dip galvanized in accordance with AASHTO M 111 (ASTM 

A123). Connection hardware steel can be galvanized by hot-dipping or other means, provided the 

method satisfies the requirements of AASHTO M 111 (ASTM A123). A minimum galvanization 

coating of 2.0 oz/ft2

 (605 g/m2) or 3.4 mils (85 μm) thickness is required. Soil reinforcement steel 

shall be adequately supported while lifting and placing such that the galvanization remains intact. 

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Steel members with damaged (peeled) galvanization shall be repaired according to ASTM A780 and 

as specified in approved working drawings, at no additional cost to the Agency. 

(B) Metallic Reinforcing Strips and Tie Strips: 

Reinforcing strips shall be hot-rolled from bars to the required shape and dimensions. The strips’ 

physical and mechanical properties shall conform to the requirements of ASTM A572, Grade 65 

minimum. 

Tie strips shall be shop fabricated of hot-rolled steel conforming to the requirements of ASTM 

A1101, Grade 50 minimum. The minimum bending radius of the tie strips shall be 3⁄8 inch. 

Galvanization shall be applied after the strips are fabricated, inclusive of punch holes for bolts as 

shown on approved drawings. 

(C) Metallic Reinforcing Mesh: 

Reinforcing mesh shall be shop fabricated of cold-drawn steel wire conforming to the requirements of 

AASHTO M 32, and shall be welded into the finished mesh fabric in accordance with AASHTO M 

55. Galvanization shall be applied after the mesh is fabricated. A minimum galvanization coating of 

2.0 oz/ft2

 (605 g/m2) or 3.4 mils (85 μm) thickness is required. 

(D) Connector Pins: 

Connector pins and mat bars shall be fabricated and connected to the soil reinforcement mats as 

shown in the approved working drawings. Connector bars shall be fabricated of cold drawn steel wire 

conforming to the requirements of AASHTO M 32. 

(E) Welded Wire Fabric: 

All welded wire fabric shall conform to the requirements of AASHTO M 32, AASHTO M 55, and the 

approved working drawings. Welded wire fabric shall be galvanized in conformance with the 

requirements of ASTM A123. 

(F) Fasteners: 

Connection hardware shall conform to the requirements shown in the approved working drawings. 

Connection hardware shall be cast in the precast concrete panels such that all connectors are in 

alignment and able to transfer full and even load to the soil reinforcement. Once the reinforcement is 

connected to the panel, the amount of slack shall not exceed 1⁄8 inch between the connector and the 

reinforcement during field installation. Fasteners shall be galvanized and conform to the 

requirements of AASHTO M 164 or equivalent. 

3.03 Geosynthetic Reinforcement: 

Geosynthetic soil reinforcement shall be limited to geogrids listed on the Agency’s Approved 

Products List (APL). The geogrid shall be a regular network of integrally connected polymer tensile 

elements, with aperture geometry sufficient to permit significant mechanical interlock with the 

surrounding soil. Geogrid structure shall be dimensionally stable and able to retain its geometry 

under manufacture, transport and installation. 

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The nominal long-term tensile design strength (Tal) of specific geosynthetic material shall meet or 

exceed the Agency’s APL. 

3.04 Certificate of Analysis for Soil Reinforcements: 

The contractor shall furnish the Engineer with a Certificate of Analysis conforming to the 

requirements of Subsection ____ for all materials. 

For geosynthetics, the Certificate of Analysis shall verify that the supplied geosynthetic is the type 

approved by the Engineer and as measured in full accordance with all test methods and standards 

specified herein. The manufacturer’s certificate shall state that the furnished geosynthetic meets the 

requirements of the specifications, as evaluated by the manufacturer’s quality control program. In 

case of dispute over validity of values, the Engineer can require the contractor to supply test data 

from an Agency-approved laboratory to support the certified values submitted, at no additional cost to 

the Department. 

For metallic wall reinforcement, a mill test report containing the ultimate tensile strength for the soil 

reinforcement shall be included in the certification. For metallic wall reinforcement, a mill test report 

containing the galvanization coverage shall be included in the certification. For metallic mesh wall 

reinforcement, a mill test report containing the ultimate weld strength for the soil reinforcement shall 

be included in the certification. 

3.05 Reinforced Wall Fill Material: 

(A) General: 

Reinforced wall fill material shall be free of shale, organic matter, mica, gypsum, smectite, 

montmorillonite, or other soft poor durability particles. No salvaged material, such as asphaltic 

concrete millings or Portland Cement Concrete rubble, etc., will be allowed. 

(B) Soundness: 

The reinforced backfill material shall have a soundness loss of 30 percent or less when tested in 

accordance with AASHTO T 104 using a magnesium sulfate solution with a test duration of four 

cycles. Alternatively, the material shall have a soundness loss of 15 percent or less when tested in 

accordance with AASHTO T 104 using a sodium sulfate solution with a test duration of five cycles. 

(C) Gradation and Plasticity Index: 

Gradations will be determined per AASTHO T 27 and shall be in accordance with Table 2, unless 

otherwise specified. The reinforced backfill shall be well-graded in accordance with the Unified Soil 

Classification System (USCS) in ASTM D2487. Furthermore, the reinforced wall fill shall not be 

gap-graded. 

Plasticity Index (PI), as determined in accordance with AASHTO T 90, shall not exceed six. 

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Table 2 

BACKFILL GRADATION REQUIREMENTS 

Sieve Size Percent Passing 

4 inch (Note 1) 100 

No. 40 0-60 

No. 200 0-15 

Note 1: Maximum particle size shall be limited to 3⁄4 inch for geosynthetics and epoxy- or PVCcoated reinforcements unless the contractor provides tests, acceptable to the Engineer, that have 

evaluated the extent of construction damage anticipated for the specific fill material and 

reinforcement combination. Construction damage testing shall be performed in accordance with the 

requirements of Chapter 5 of Publication No. FHWA NHI-09-087, dated 2009 

(“Corrosion/Degradation of Soil Reinforcements for Mechanically Stabilized Earth Walls and 

Reinforced Soil Slopes.”) 

(D) Internal Friction Angle Requirement: 

The reinforced wall fill material shall exhibit an effective (drained) angle of internal friction of not 

less than 34 degrees, as determined in accordance with AASHTO T 236. 

The test shall be run on the portion finer than the No. 10 sieve. The sample shall be compacted at 

optimum moisture content to 95 percent of the maximum dry density, as determined in accordance 

with the requirements of AASHTO T 99. The sample shall be tested at the compacted condition 

without addition of water. No direct shear testing will be required when 80 percent or more of the 

material is larger than 3⁄4 inch. 

(E) Electrochemical Requirements: 

The reinforced backfill material shall meet the electrochemical requirements of Table 3 when metallic 

soil reinforcement is used and Table 4 when geosynthetic soil reinforcement is used. For all soil 

reinforcements, the organic content of backfill shall be less than one (1) percent, determined in 

accordance with AASHTO T-267. 

Table 3 

ELECTROCHEMICAL REQUIREMENTS FOR METALLIC REINFORCEMENTS 

Characteristic Requirement Test Method 

pH 5.0 to 10.0 AASHTO T-289 

Resistivity, min. 3,000 ohm-cm AASHTO T-288 

Chlorides, max. 100 ppm ASTM D4327 

Sulfates, max. 200 ppm ASTM D4327 

* If the resistivity is greater or equal to 5,000 ohm-cm, the chloride and sulfate requirements may be 

waived. 

Table4 

ELECTROCHEMICAL REQUIREMENTS FOR GEOSYNTHETIC REINFORCEMENTS 

Base Polymer Property Requirement Test Method 

Polyolefin (PP and HDPE)* pH > 3 AASHTO T-289 

Polyester pH > 3 and < 9 AASHTO T-289 

* PP: Polypropylene and HDPE: High Density Polyethylene. 

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(F) Rock Reinforced Wall Fill: 

Material that is composed primarily of rock fragments (material having less than 25 percent passing a 

3⁄4-inch sieve) shall be considered to be a rock fill. The maximum particle size shall not exceed the 

limits listed in Table 2. Such material shall meet all the other requirements of Subsection 3.05(B) and 

Subsection 3.05(E). When such material is used, a very high survivability separation geotexitle, 

meeting the minimum requirements for filtration applications specified in AASHTO M 288 and 

Subsection ____, shall encapsulate the rock backfill to within three (3) feet below the wall coping. 

Adjoining sections of separation fabric shall be overlapped by a minimum of 12 inches. Additionally, 

the upper three (3) feet of backfill shall contain no stones greater than three (3) inches in their greatest 

dimension, and shall be composed of material not considered to be rock backfill, as defined herein. 

(G) Limits of Reinforced Wall Fill: 

For all walls, except back-to-back walls, the reinforced backfill shall extend to at least one (1) foot 

beyond the free end of the reinforcement. EDIT to Agency practice/requirements. For back-to-back 

walls wherein the free ends of the reinforcement of the two walls are spaced apart less than or equal 

to one-half the design height of the taller wall, reinforced wall fill shall be used for the space between 

the free ends of the reinforcements as well. The design height of the wall is defined as the difference 

in elevation between finished grade at top of wall and the top of leveling pad. The top of the leveling 

pad shall always be below the minimum embedment reference line as indicated on the plans for the 

location under consideration. 

3.06 Retained Backfill Material: 

(A) General: 

Backfill behind the limits of the reinforced backfill shall be considered as retained backfill for a 

distance equal to 50 percent of the design height of the MSE wall or as shown on the plans, except for 

back-to-back MSE walls as described in Subsection 3.05(G) above. The retained backfill shall be 

free of shale, mica, gypsum, smectite, montmorillonite or other soft particles of poor durability. The 

retained backfill shall meet the soundness criteria as described in Subsection 3.05(B). 

The percent fines (the fraction passing No. 200 sieve) shall be less than 50 as determined in 

accordance with ____ Test Method, and the Liquid Limit (LL) and the Plasticity Index (PI) shall be 

less than 40 and 20, respectively, as determined in accordance with AASHTO T-90. 

Material that is composed primarily of rock fragments (material having less than 25 percent passing a 

3⁄4-inch sieve), shall be considered to be a rock backfill and the requirements of Subsection 3.05(F) 

shall apply. 

(B) Internal Friction Angle Requirement: 

Unless otherwise noted on the plans, the retained backfill material shall exhibit an effective (drained) 

angle of internal friction of not less than degrees as determined by AASHTO T 236. EDIT insert 

Agency value consistent with material specification. 

The test shall be run on the portion finer than the No. 10 sieve. The sample shall be compacted at 

optimum moisture content and to 95 percent of maximum dry density, as determined in accordance 

with AASHTO T 99 (Proctor) test OR AASHTO T 180 (Modified Proctor) test. EDIT NOTE: 

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Specify test method consistent with compaction specification. The sample shall be tested at the 

compacted condition without addition of water. 

No direct shear testing will be required when 80 percent or more of the material is larger than 3⁄4 inch. 

3.07 Certificate of Analysis for Reinforced Wall Fill and Retained Backfill Materials 

At least three weeks prior to construction of the MSE wall, the contractor shall furnish the Engineer 

with an 80-pound representative sample of each of the backfill material and a Certificate of Analysis 

conforming to the requirements of Subsection 106.05 certifying that the backfill materials comply 

with the requirements specified herein. During construction the reinforced and retained backfill shall 

be sampled and tested by the Contractor for acceptance and quality control testing in accordance with 

the requirements stated in Table 929-5 and Table 929-6, respectively. A new sample and Certificate 

of Analysis shall be provided any time the reinforced and retained backfill material changes as noted 

in Table 929-5 and 929-6, respectively. 

Table 5 

Sampling Frequency for Reinforced Backfill Material 

Test Frequency 

Gradation (AASHTO T 26), 

Plasticity Index (AASHTO T 90) 

One per 2,000 CY 

At job site 

Resistivity, pH, Organic Content, Chlorides, Sulfates (Table 929-3) One per 2,000 CY 

At job site 

Internal friction angle (AASHTO T 236) 

Proctor density and Optimum Moisture by AASHTO T 99 OR AASHTO T 

180 EDIT NOTE: Specify one, consistent with compaction specification. 

Test pad section (Subsection 4.06(B)) 

One per material 

change and change 

in source* 

* The gradation and plasticity tests performed at the frequency noted in Table 5 shall be used to 

determine the Unified Soil Classification System (USCS) designation as per ASTM D 2487. New 

tests shall be required with each change in USCS designation including change in dual symbol 

designations (example: SW-SM, SW-SC, etc.). All requirements of Subsection 3.05 shall be 

satisfied. New tests shall also be required for each new source regardless of whether the USCS 

designation changes or not. 

Table 6 

Sampling Frequency for Retained Backfill Material 

Test Frequency 

Gradation (AASHTO T 27), 

Plasticity Index (AASHTO T 90) 

One per 5,000 CY 

At job site 

Internal friction angle (AASHTO T 236) 

Proctor density and Optimum Moisture by AASHTO T 99 OR AASHTO T 

180 EDIT NOTE: Specify one, consistent with compaction specification. 

One per material 

change and change 

in source* 

* The gradation and plasticity tests performed at the frequency noted in Table 6 shall be used to 

determine the Unified Soil Classification System (USCS) designation as per ASTM D2487. New 

tests shall be required with each change in USCS designation including change in dual symbol 

designations (example: SW-SM, SW-SC, etc.). All requirements of Subsection 3.06 shall be 

satisfied. New tests shall also be required for each new source regardless of whether the USCS 

designation changes or not. 

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3.08 Cast-in-Place Concrete: 

Cast-in-place concrete shall conform to the requirements of Sections ___ and ___. Unless otherwise 

approved, all cast-in-place concrete shall be Class __ with a minimum compressive strength of 4,000 

pounds per square inch. 

3.09 Modular Block (Segmental) Facing Units: 

This section covers dry-cast hollow and solid concrete masonry structural retaining wall units, 

machine made from Portland cement, water, and suitable mineral aggregates. The units are intended 

for use as facing units in the construction of mortarless, modular block walls (MBW) also known as 

segmental retaining walls (SRW). Metallic or geosynthetic reinforcement specified in Section 3.02 and 

3.03, respectively, may be used as soil reinforcement in the reinforced (structure) wall fill zone. 

(A) Casting: 

Cementitious material in the modular block facing unit shall be Portland cement conforming to the 

requirements of ASTM C 150. If fly ash is used it shall not exceed 20% by weight of the total cement 

content and shall conform to ASTM C 618. Aggregates used in concrete blocks shall conform to 

ASTM C 33 for normal weight concrete aggregate. Efflorescence control agent shall be used in 

concrete mix design to prevent efflorescence on the block. 

The contractor shall advise the Engineer of the starting date for concrete panel casting at least 14 

calendar days prior to beginning the operation if the casting operation is within the State, or 21 

calendar days if the casting operation is outside the State. 

(B) Physical Requirements: 

At the time of delivery to the work site, the modular block facing units shall conform to the following 

physical requirements: 

1) Minimum required compressive strength of 4,000 psi (average 3 coupons) 

2) Minimum required compressive strength of 3,500 psi (individual coupon) 

3) Minimum oven dry unit weight of 125 pcf 

4) Maximum water absorption of 5 % after 24 hours 

5) Maximum number of blocks per lot of 2,000. Tests on blocks shall be submitted at the 

frequency of one set per lot. 

Acceptance of the concrete block, with respect to compressive strength, water absorption and unit 

weight, will be determined on a lot basis. The lot shall be randomly sampled and tested in accordance 

with ASTM C140. As no additional expense to the Department, the manufacturer shall perform the 

tests at an Agency approved laboratory and submit the results to the Engineer for approval. 

Compressive strength test specimens shall be cored or shall conform to the saw-cut coupon provisions 

of ASTM C 140. Block lots represented by test coupons that do not reach an average compressive 

strength of 4,000 psi will be rejected. 

(C) Freeze-Thaw Durability: 

In areas where repeated freezing and thawing under saturated conditions occur, the units shall be 

tested to demonstrate freeze-thaw durability in accordance with Test Method ASTM C1262. Freezethaw durability shall be based on tests from five specimens made with the same materials, concrete 

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mix design, manufacturing process, and curing method, conducted not more than 18 months prior to 

delivery. Specimens used for absorption testing shall not subsequently be used for freeze-thaw 

testing. Specimens shall comply with either or both of the following acceptance criteria depending on 

the severity of the project location as determined by the Department: 

1) The weight loss of four out of five specimens at the conclusion of 150 cycles shall not exceed 

1% of its initial weight when tested in water. 

2) The weight loss of each of four out of the five test specimens at the conclusion of 50 cycles 

shall not exceed 1.5% of its initial mass when tested in a saline (3% sodium chloride by 

weight) solution. 

(D) Tolerances for Modular Block Dimensions: 

Modular blocks shall be manufactured within the following tolerances: 

1) The length and width of each individual block shall be within  1⁄8 inch of the specified 

dimension. Hollow units shall have a minimum wall thickness of 11⁄4 inches. 

2) The height of each individual block shall be within  1/16 inch of the specified dimension. 

3) When a broken (split) face finish is required, the dimension of the front face shall be within 

1.0 inch of the theoretical dimension of the unit. 

(E) Finish and Appearance: 

Units that indicate imperfect molding, honeycomb or open texture concrete and color variation on 

front face of block due to excess form oil or other reasons shall be rejected. All units shall be visually 

efflorescence free. All units shall be sound and free of cracks or other defects that would interfere 

with the proper placing of the unit or significantly impair the strength or permanence of the 

construction. Minor cracks (e.g. no greater than 1/50 inch in width and no longer than 25% of the 

unit height) incidental to the usual method of manufacture or minor chipping resulting from shipment 

and delivery, are not grounds for rejection. 

The exposed faces shall be free of chips, cracks or other imperfections when viewed from a distance 

of 30 feet under diffused lighting. Up to five (5) percent of a shipment may contain slight cracks or 

small chips not larger than 1.0 inch. 

Color and finish shall be as shown on the plans and shall be erected with a running bond 

configuration. 

(F) Pins: 

If pins are required to align modular block facing units, they shall consist of a non-degrading polymer 

or hot-dipped galvanized steel and be made for the express use with the modular block units supplied. 

Connecting pins shall be capable of holding the geogrid in the proper design position during 

backfilling. 

(G) Cap Units and Adhesive: 

The cap unit connection to the block unit immediately under it shall be of a positive interlocking type 

and not frictional. Cap units shall be cast to or attached to the top of modular block facing units in 

strict accordance with the requirements of the manufacturer of the blocks and the adhesive. The 

surface of the block units under the cap units shall be clear of all debris and standing water before the 

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approved adhesive is placed. Contractor shall provide a written 10-year warranty, acceptable to 

Owner, that the integrity of the materials used to attach the cap blocks will preclude separation and 

displacement of the cap blocks for the warranty period. 

(H) Unit (Core) Fill: 

Unit (core) fill is defined as free-draining, coarse grained material that is placed within the empty 

cores of the modular block facing units. Unit (core) fill shall be a well graded crushed stone or 

granular fill meeting the gradation shown in Table 7. Gradation for unit fill shall be tested at the 

frequency of 1 test per 50 yd3

 at the job site and for every change in the material source. 

Table 7 

Gradation for Unit (Core) Fill 

U.S. Sieve Size Percent Passing 

11⁄2-inch 100 

1-inch 75-100 

3⁄4-inch 50-75 

No. 4 0-60 

No. 40 0-50 

No. 200 0-5 

(I) Gravel Fill: 

A minimum width of 1-ft of gravel fill should be provided behind solid (non-hollow) modular block 

units. A minimum volume of 1-ft3

/ft2 of drainage fill shall be provided. Gravel fill shall meet the 

requirements of the unit (core) fill. A suitable geotextile fabric between the gravel fill and reinforced 

wall fill shall be used to meet the filtration requirements if the gravel fill does not meet the filtration 

criteria. The selection of a suitable geotextile for filtration purposes shall be supported by design 

computations taking in to account the actual gradations of the gravel fill and the reinforced wall fill to 

be used on the project. Gradation for gravel fill shall be tested at the frequency of 1 test per 50 yd3

 at 

the job site and for every change in the material source. 

3.10 Certificate of Analysis for Modular Block Connection 

For modular block facing units, a certification shall be provided with detailed calculations according 

to AASHTO (2007) and the results of laboratory test results performed in accordance with Section 

C.3 in Appendix B of FHWA NHI-10-025, dated 2009 (“Mechanically Stabilized Earth Walls and 

Reinforced Soil Slopes – Volume II”). Such certification shall demonstrate that all connections, 

including block-to-reinforcement and block-to-block connections, and all related components meet or 

exceed the current AASHTO 75 year design life requirements and are capable of resisting 100% of 

the maximum tension in the soil reinforcements at any level within the wall. Long-term connection 

testing for extensible reinforcements is also required. The effect of wall batter and normal pressures 

representative of the full range of wall configurations and heights shall be incorporated in the tests. 

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4 Construction Requirements: 

4.01 Excavation: 

The contractor shall ensure that temporary slopes are safe during the period of wall construction, and 

shall adhere to all applicable local, state and federal regulations. During construction of the MSE 

walls, the contractor shall design, construct, maintain and, when called for, remove temporary 

excavation support systems (shoring). Temporary excavation support systems may be left in place if 

approved by the Engineer. The back slope of the excavation shall be benched. Where shoring is 

required, the contractor shall submit the shoring design, and a plan outlining construction and 

removal procedures, to the Engineer for review and approval prior to proceeding with the work. 

Shoring plans shall be prepared and submitted as part of the working drawings, as specified in 

Subsection ____ and shall bear the seal and signature of a licensed Professional Civil or Structural 

Engineer, registered in the State. All shoring design shall include appropriate input and review by a 

geotechnical engineer. 

4.02 Foundation Preparation: 

(A) General: 

In the absence of specific ground improvement requirements in the plans and special provisions, the 

following applies: 

The foundation for the reinforced wall fill and retained backfill shall be graded level for the entire 

area of the base of such backfills, plus an additional 12 inches on all sides, or to the limits shown in 

the plans. 

If soil reinforcement components are to be positioned on native soil, the top one (1) foot of native soil 

shall meet the requirements of the reinforced backfill material specified in Subsection 3.05. 

If soil reinforcement components are to be positioned on native rock mass, the rock mass shall be 

classified as at least Class II rock mass in accordance with Section 10 of 4th Edition of AASHTO 

(2007) Bridge Specifications. Otherwise the top foot of native rock mass on which the MSE structure 

is to be constructed shall be scarified and compacted to a dry density not less than 100 percent of 

maximum dry density as determined in accordance with AASHTO T 99 OR AASHTO T 180 . EDIT 

NOTE: Specify one method, consistent with compaction specification. 

(B) Proof-Rolling: 

The contractor shall perform proof-rolling to evaluate the stability and uniformity of the subgrades on 

which the MSE structure will be constructed. Proof rolling shall be performed on the entire areas at 

the following locations: 

1. At the bottom of the overexcavation and recompaction zones, if specified on the plans. 

2. At the bottom of the overexcavation and replacement zones, if specified on the plans. 

3. At the base of all walls. 

4. At the top of native soil layers that have been scarified, moisture-conditioned, and 

recompacted (if different from the bottom of the overexcavation and recompaction zones, 

or overexcavation and replacement zones). 

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Proof-rolling shall be done immediately after subgrade compaction while the moisture content of the 

subgrade soil is near optimum, or at the moisture content that was used to achieve the required 

compaction. 

If proof-rolling is performed after installation of pipe underdrains, the proof-roller shall not be used 

within 11⁄2 feet of the underdrains. 

Proof-rolling shall be performed with a pneumatic-tired tandem axle roller with at least three wheels 

on each axle, a gross weight of 25 tons (50 kips), a minimum tire pressure of 75 pounds per square 

inch, and a minimum rolling width of 75 inches. A Caterpillar PS-300B (or PF-300B), IngersollRand PT-240R, BOMAG BW24R, Dynapac CP271, or equipment with equivalent capabilities shall 

be used for proof-rolling. 

Proof-rolling equipment shall be operated at a speed between 1.5 and 3 miles per hour, or slower as 

required by the Engineer to permit measurements of the deformations, ruts and/or pumping. 

Proof-rolling shall be carried out in two directions at right angles to each other with no more than 24 

inches between tire tracks of adjacent passes. The contractor shall operate the proof-roller in a pattern 

that readily allows for the recording of deformation data and complete coverage of the subgrade. 

The following actions shall be taken based on the results of the proof-rolling activity: 

1. Rutting less than 1⁄4-inch – The grade is acceptable. 

2. Rutting greater than 1⁄4-inch and less than 11⁄2 inches – The grade shall be scarified and recompacted. 

3. Rutting greater than 11⁄2 inches – The compacted area shall be removed and reconstructed. 

4. Pumping (deformation that rebounds, or materials that are squeezed out of a wheel’s path) 

greater than one(1) inch – The area shall be remediated as directed by the Engineer. 

The contractor shall be responsible for maintaining the condition of the approved proof-rolled soils 

throughout the duration of the retaining wall construction. Wall construction shall not commence 

until the foundation has been approved by the Engineer. 

4.03 Concrete Leveling Pad: 

Leveling pads shall be constructed of unreinforced concrete as shown on the working drawings. 

Gravel leveling pads shall not be allowed. As a minimum, the concrete for leveling pads shall meet 

the requirements of Section __. The elevation of the top of leveling pad shall be within 1⁄8 inch from 

the design elevation when measured by a straightedge over any 10-foot run of the leveling pad. 

The minimum width of the leveling pad shall be the width of the facing unit plus 8-inches. The 

centerline of the leveling pad shall be within 1 inch from design location. When the facing units are 

centered on the leveling pad, the leveling pad shall extend approximately 4-inches beyond the limits 

of the facing unit as measured in the direction perpendicular to the face of the wall. 

Cast-in-place leveling pads shall be cured for a minimum of 24 hours before placement of wall facing 

units. A geotextile shall be applied over the back of the area of any openings between the facing units 

and leveling pad steps. The geotextile shall extend a minimum of six (6) inches beyond the edges of 

the opening. The opening shall be filled with concrete, conforming to Section ___, or shall be 

concurrently backfilled on both sides with soil.. 

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4.04 Subsurface Drainage: 

Prior to wall erection, the contractor shall install a subsurface drainage system as shown on the 

working drawings. 

4.05 Wall Erection: 

(A) General: 

Walls shall be erected in accordance with the manufacturer’s written instructions. The contractor 

shall be responsible for ensuring that a field representative from the manufacturer is available at the 

site during construction of the initial 10-foot height of the full length of wall, and as called upon 

thereafter by the Engineer, to assist the contractor and Engineer at no additional cost to the Agency. 

All temporary construction aids (e.g., wedges, clamps, etc.) shall be in accordance with the 

manufacturer’s recommendations. 

(B) Placement Tolerances for Walls with Precast Facing: 

For walls with rigid facing, such as precast concrete panels, the panels shall be placed such that their 

final position is vertical or battered as shown on the working drawings. As wall fill material is 

placed, the panels shall be maintained in the correct vertical alignment by means of temporary 

wedges, clamps, or bracing as recommended by the manufacturer. A minimum of two, but not more 

than three, rows of panel wedges shall remain in place at all times during wall erection. Wedges shall 

be removed from lower rows as panel erection progresses, so as to prevent chipping or cracking of 

concrete panels. The contractor shall repair any damage to erected concrete panels as directed by the 

Engineer and to the Engineer’s satisfaction. No external wedges in front of the wall shall remain in 

place when the wall is complete. 

Erection of walls with panel facing shall be in accordance with the following tolerances: 

	 Vertical and horizontal alignment of the wall face shall not vary by more than 3⁄4 inch when 

measured along a 10-foot straightedge. 

	 The overall vertical tolerance (plumbness) of the finished wall shall not exceed 1⁄2 inch per 10 

feet of wall height. Negative (outward leaning) batter is not acceptable. 

	 The maximum permissible out of plane offset at any panel joint shall not exceed 3⁄8 inch. 

	 The final horizontal and vertical joint gaps between adjacent facing panel units shall be 

within 1⁄8 inch and 1⁄4 inch, respectively, of the design final joint opening per the approved 

calculations required in Subsection 3.01(H). 

Wall sections not conforming to these tolerances shall be reconstructed at no additional cost to the 

Department. 

(C) Placement Tolerances for Permanent Walls with Flexible Facing: 

Erection of permanent walls with flexible facing (such as welded wire mesh) shall be in accordance 

with the following tolerances: 

	 Vertical and horizontal alignment of the wall face shall not vary by more than two (2) inches 

when measured along a 10-foot straightedge, or as shown in the plans and specifications. 

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 The overall vertical tolerance (plumbness) of the wall shall not exceed one (1) inch per 10 

feet of wall height. Negative (outward leaning) batter is not acceptable. 

 The offset limit between consecutive rows of facing shall not exceed one (1) inch from 

planned offset. 

Wall sections not conforming to these tolerances shall be reconstructed at no additional cost to the 

Department. 

(D) Placement Tolerances for Modular Block Units: 

Erection of walls with Modular Block Units shall be as per the following requirements: 

Vertical and horizontal alignment of the wall face shall not vary by more than 3⁄4-inch when 

measured along a 10-feet straightedge. 

Overall vertical tolerance (plumbness) of the wall shall not exceed 11⁄4-inch per 10-ft of wall 

height from the final wall batter. Negative (outward leaning) batter is not acceptable. 

The first row of units shall be level from unit-to-unit and from front-to-back. Use the tail of 

the units for alignment and measurement. 

All units shall be laid snugly together and parallel to the straight or curved line of the wall 

face. 

Unless otherwise noted, all blocks shall be dry-stacked and placed with each block evenly 

spanning the joint in the row below (running bond). Shimming or grinding shall control the 

elevations of any two adjacent blocks within 1/16 inch. 

The top of blocks shall be checked with a minimum length of 3-feet long straight edge bubble 

level. Any high points identified by the straight edge shall be ground flat. Block front to 

back tilting shall be checked frequently, however correction by shimming shall be done no 

later than 3 completed courses. 

Wall sections not conforming to these tolerances shall be reconstructed at no additional cost to the 

Department. 

(E) Placement of Metallic Reinforcement Elements: 

Metallic reinforcement elements shall be placed normal (perpendicular) to the face of the wall, unless 

otherwise shown on the approved plans. All reinforcement shall be structurally connected to the wall 

face. 

At each level of the soil reinforcement, the reinforced wall fill material shall be roughly leveled and 

compacted before placing the next layer of reinforcement. The reinforcement shall bear uniformly on 

the compacted reinforced soil from the connection to the wall to the free end of the reinforcing 

elements. The reinforcement placement elevation shall be at the connection elevation to two (2) 

inches higher than the connection elevation. 

Where overlapping of reinforcing may occur, such as at corners, reinforcing connections to panels 

shall be adjusted to maintain at least three (3) inches of vertical separation between overlapping 

reinforcement. 

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(F) Placement of Geotextile: 

All joints between precast concrete panels shall be covered with geotextile on the backside of the 

wall. Adhesive shall be applied to panels only. Adhesive shall not be applied to geotextile fabric or 

within two (2) inches of a joint. The contractor shall provide geotextile having a minimum width of 

12 inches, and shall overlap fabric a minimum of four (4) inches. For modular block walls, the 

placement of the geotextile fabric shall be in accordance with the plans. 

(G) Joint Pads and Fillers: 

The contractor shall install joint pads and fillers as shown on the working drawings. 

(H) Placement of Geosynthetic Reinforcement: 

Geosynthetic reinforcement shall be installed in accordance with the manufacturer’s site-specific wall 

erection instructions. 

Geosynthetic reinforcement shall be placed in continuous longitudinal rolls in the direction of the 

main reinforcement. Joints parallel to the wall shall not be permitted, except as shown on the 

working drawings. 

Reinforcement coverage shall be 100 percent of embedment area unless otherwise shown in the 

working drawings. Adjacent sections of geosynthetic reinforcement need not be overlapped except 

when exposed in a wrap-around face system, at which time the reinforcement rolls shall be 

overlapped or mechanically connected per the manufacturer’s requirements. 

Geosynthetic reinforcement shall be placed to lay flat and pulled tight prior to backfilling. After a 

layer of geosynthetic reinforcement has been placed, suitable means, such as pins or small piles of 

soil, shall be used to hold the geosynthetic reinforcement in position until the subsequent soil layer 

can be placed. 

During construction, the surface of the fill shall be kept approximately horizontal. Geosynthetic 

reinforcement shall be placed directly on the compacted horizontal fill surface. The reinforcement 

shall bear uniformly on the compacted reinforced soil from the connection to the wall to the free end 

of the reinforcing elements. The reinforcement placement elevation shall be at the connection 

elevation to two (2) inches higher than the connection elevation. 

4.06 Reinforced Wall Fill Placement: 

(A) General: 

Reinforced wall fill placement shall closely follow erection of each course of facing panels. Backfill 

shall be placed in such a manner to avoid damage or disturbance of the wall materials, misalignment 

of facing panels, or damage to soil reinforcement or facing members. The contractor shall place 

backfill to the level of the connection and in such a manner as to ensure that no voids exist directly 

beneath reinforcing elements. 

For walls with modular block facing units, the backfill shall not be advanced more than the height of 

a modular block unit until the drainage fill, core fill and all fill in all openings within the blocks at 

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that level have been placed. The filled units shall be swept clean of all debris before installing the 

next level of units and/or placing the geogrid materials. 

For walls with flexible facing with gabion style facing, the rock near the wall face shall be handplaced in accordance with the recommendations of the wall manufacturer. 

The maximum lift thickness before compaction shall not exceed ten (10) inches. EDIT NOTE: Insert 

Agency maximum lift height. The contractor shall decrease this lift thickness, if necessary, to obtain 

the specified density. 

For geosynthetic reinforcements, the fill shall be spread by moving the machinery parallel to or away 

from the wall facing and in such a manner that the geogrid remains taut. Construction equipment 

shall not operate directly on the geogrid. A minimum fill thickness of six (6) inches over the geogrid 

shall be required prior to operation of vehicles. Sudden braking and sharp turning shall be avoided. 

For metallic reinforcements, the fill shall be spread by moving the machinery parallel to or away from 

the wall facing and in such a manner that the steel reinforcement remains normal to the face of the 

wall. Construction equipment shall not operate directly on the steel reinforcement. A minimum fill 

thickness of three (3) inches over the steel reinforcement shall be required prior to operation of 

vehicles. Sudden braking and sharp turning shall be avoided. 

Wall materials which are damaged during backfill placement shall be removed and replaced by the 

contractor, at no additional cost to the Department. The contractor may submit alternative corrective 

procedures to the Engineer for consideration. Proposed alternative corrective procedures shall have 

the concurrence of the MSE wall supplier and designer, in writing, prior to submission to the 

Engineer for consideration. All corrective actions shall be at no additional cost to the Department. 

(B) Compaction: 

Reinforced wall fill shall be compacted to 95 percent of the maximum dry density as determined in 

accordance with the requirements of AASHTO T 99 OR AASHTO T 180. EDIT NOTE: Specify 

one method, consistent with compaction specification. 

Retained backfill shall be compacted to 95 percent of the maximum dry density as determined in 

accordance with the requirements of AASHTO T 99 (Standard Proctor) OR AASHTO T 180 

(Modified Proctor). EDIT NOTE: Specify one method, consistent with compaction specification. 

Backfill shall be compacted using a static-weighted or vibratory roller. Sheeps-foot or grid-type 

rollers shall not be used for compacting material within the limits of the soil reinforcement. The 

contractor shall take soil density tests, in accordance with _______________, to ensure compliance 

with the specified compaction requirements. Soil density tests shall be taken at intervals of not less 

than one for every 2000 cubic yards, with a minimum of one test per lift. Compaction tests shall be 

taken at locations determined by the Engineer. 

The backfill density requirement within three (3) feet of the wall facing shall be 90 percent of 

maximum dry density as determined by AASHTO T 99 (Standard Proctor) OR AASHTO T 180 

(Modified Proctor). EDIT NOTE: Specify one method, consistent with compaction specification.. 

Compaction within three (3) feet of the wall shall be achieved by a minimum number of passes of a 

lightweight mechanical tamper or roller system. The minimum number of passes and rolling pattern 

shall be determined, prior to construction of the wall, by constructing a test pad section. The 

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minimum dimensions of the test pad shall be five (5) feet wide, 15 feet long, and three (3) feet final 

depth. 

Compaction in the test pad section shall be performed as follows: 

 Maximum lift thickness before compaction shall be eight (8) inches. 

 Minimum one density test per lift. 

Only those methods used to establish compaction compliance in the test pad section shall be used for 

production work. Any change in the material as per Table 5 or the approved equipment shall require 

the contractor to conduct a new test pad section and obtain re-approval by the Engineer of the 

minimum number of passes and rolling pattern. No measurement or payment will be made for test 

pad sections. 

(C) Moisture Control: 

The moisture content of the backfill material prior to and during compaction shall be uniformly 

dispersed throughout each layer. Backfill materials shall have a placement moisture content three (3) 

percent less than or equal to optimum moisture content, as determined in accordance with the 

requirements of AASHTO T 99 (Standard Proctor) OR AASHTO T 180 (Modified Proctor). EDIT 

NOTE: Specify one method, consistent with compaction specification. for the reinforced wall fill, 

and AASHTO T 99 (Standard Proctor) OR AASHTO T 180 for (Modified Proctor). EDIT NOTE: 

Specify one method, consistent with compaction specification. the retained backfill. Backfill material 

with a placement moisture content in excess of optimum shall be removed and reworked until the 

moisture content is uniform and acceptable throughout the entire lift. 

(D) Protection of the Work: 

The contractor shall not allow surface runoff from adjacent areas to enter the wall construction site at 

any time during construction operations. In addition, at the end of each day’s operation, the 

contractor shall slope the last lift of backfill away from the wall facing so that runoff is directed away 

from the structure. If the subgrade is damaged due to water or otherwise, such that it does not meet 

the requirements of Subsection 4.02, then as directed by the Engineer, the contractor shall rework and 

repair the damaged subgrade at no additional expense to the Department. The criteria in Subsection 

4.02 shall be used to judge the adequacy of the repair. Rework and repair shall extend to a depth 

where undamaged work is encountered. 

5 Method of Measurement: 

Mechanically Stabilized Earth (MSE) retaining walls will be measured by the square foot of 

completed wall. The vertical height will be taken as the difference in elevation measured from the 

top of wall to the top of the leveling pad. OR The pay area will be taken as the wall panel area 

supplied. EDIT NOTE: Specify one or the other option. 

6 Basis of Payment: 

The accepted quantities of Mechanically Stabilized Earth (MSE) retaining walls, measured as 

provided above, will be paid for at the contract unit price per square foot of wall, complete in place. 

Such price shall include full compensation for furnishing all designs, design revisions, associated 

working drawings, engineering calculations, labor, materials EDIT NOTE: may or may not include 

reinforced wall fill, see below, tools, equipment, and incidentals. Such price shall also include 

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provision of manufacturer’s field representative, and all work involved in constructing the retaining 

walls, including foundation preparation, proof-rolling, footings, drainage features, wall facing, slip 

joints, concrete or shotcrete caps and aprons, rustication, paint or stain, grout, tendons, cables, 

anchors, fabric, and all hardware and reinforcing steel, complete in place as shown on the plans and 

as specified herein. 

No separate measurement or payment will be made for excavation, reinforced wall fill, and retained 

backfill associated with retaining walls, the cost of such work being considered as included in the 

price paid for the MSE retaining wall. EDIT NOTE: Reinforced wall fill is a separate pay item for 

some Agencies, and is listed as such. 

No separate measurement or payment will be made for the design, construction, or removal of 

temporary excavation support systems (shoring), or associated geotechnical review, the cost of such 

work being considered as included in the price paid for the MSE retaining wall. 

10.10 CONSTRUCTION SPECIFICATIONS FOR REINFORCED SLOPE 

SYSTEMS 

The availability of many different geosynthetic reinforcement materials as well as drainage 

and erosion control products requires consideration of different alternatives prior to 

preparation of contract documents so contractors are given an opportunity to bid using 

feasible, cost-effective materials. Any proprietary material should undergo an Agency 

review prior to inclusion as either an alternate offered during design (in-house) or 

construction (value engineering or end result) phase. 

It is highly recommended that each Agency develop documented procedures for: 

C Review and approval of geosynthetic soil reinforcing materials. 

C Review and approval of drainage composite materials. 

C Review and approval of erosion control materials. 

C Review and approval of geosynthetic reinforced slope systems and suppliers. 

C In-house design and performance criteria for reinforced slopes. 

The following guidelines are recommended as the basis for specifications or special 

provisions for the furnishing and construction of reinforced soil slopes on the basis of pre 

approved reinforcement materials. Specification guidelines are presented for each of the 

following topics: 

1. Specification Guidelines for RSS Construction (Agency design). 

2. Specifications for Erosion Control Mat or Blanket. 

3. Specifications for Geosynthetic Drainage Composite. 

4. Specification Guidelines for Proprietary Geosynthetic RSS Systems. 

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10.10.1 Specification Guidelines For RSS Construction (Agency Design) 

Description 

Work shall consist of furnishing and placing geosynthetic soil reinforcement for construction of 

reinforced soil slopes. 

Geosynthetic Reinforcement Material 

The specific geosynthetic reinforcement material and supplier shall be pre approved by the Agency as 

outlined in the Agency's reinforced soil slope policy. 

The geosynthetic reinforcement shall consist of a geogrid or a geotextile that can develop sufficient 

mechanical interlock with the surrounding soil or rock. The geosynthetic reinforcement structure shall 

be dimensionally stable and able to retain its geometry under construction stresses and shall have high 

resistance to damage during construction, ultraviolet degradation, and all forms of chemical and 

biological degradation encountered in the soil being reinforced. 

The geosynthetics shall have a Nominal Long-Term Strength (Tal) and Pullout Resistance, for the soil 

type(s) indicated, as listed in Table S1 for geotextiles and/or Table S2 for geogrids. 

The Contractor shall submit a manufacturer's certification that the geosynthetics supplied meet the 

respective index criteria set when the geosynthetic was approved by the Agency, measured in full 

accordance with all test methods and standards specified. In case of dispute over validity of values, 

the Engineer can require the Contractor to supply test data from an Agency approved laboratory to 

support the certified values submitted, the Contractor’s cost. 

Quality Assurance/Index Properties: Testing procedures for measuring design properties require 

elaborate equipment, tedious set up procedures and long durations for testing. These tests are 

inappropriate for quality assurance (QA) testing of geosynthetic reinforcements received on site. In 

lieu of these tests for design properties, a series of index criteria may be established for QA testing. 

These index criteria include mechanical and geometric properties that directly impact the design 

strength and soil interaction behavior of geosynthetics. It is likely each family of products will 

have varying index properties and QC/QA test procedures. QA testing should measure the 

respective index criteria set when the geosynthetic was approved by the Agency. Minimum average 

roll values, per ASTM D 4759, shall be used for conformance. 

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Table S-1. Required Geotextile Reinforcement Properties. 

Geotextile(1) Ultimate Strength (TULT) 

ASTM D4595(2) 

Nominal 

Long-Term 

Strength(3) 

(Tal) 

For use with 

these Fills(4) 

A GW-GM 

A SW-SM-SC 

B GW-GM 

B SW-SM-SC 

NOTES: 

1. For geotextiles, minimum permeability > ___ cm/s > reinforced soil permeability. 

Minimum survivability properties – Class 1 per AASHTO M-288 specification. 

2. Based on minimum average roll values (MARV) (lb/ft {kN/m}). 

3. Nominal long-term strength (Tal) based on (lb/ft {kN/m}) 

D ID CR

ULT 

al RFRFRF 

T T 

  

where RFCR is developed from creep tests performed in accordance with ASTM 

D5262, RFID obtained from site installation damage testing and RFD from 

hydrolysis or oxidative degradation testing extrapolated to 75 or 100 year design 

life. For default reduction factors, include the durability requirements in Table 3­

12 as additional reinforcement property requirements. 

4. Unified Soil Classification. 

Table S-2. Required Geogrid Properties. 

Geosynthetic(1) 

Ultimate Strength (TULT) 

ASTM D6637(2) 

Nominal 

Long-Term 

Strength(3) 

(Tal) 

For use with 

these Fills(4) 

A GW-GM 

A SW-SM-SC 

B GW-GM 

B SW-SM-SC 

NOTES: 

1. For geotextiles, minimum permeability > ___ cm/s > reinforced soil permeability. 

Minimum survivability properties – Class 1 per AASHTO M-288 specification. 

2. Based on minimum average roll values (MARV) (kN/m). Use D6637 for 

geogrids. 

3. Nominal long-term strength (Tal) based on (lb/ft {kN/m}) 

D ID CR

ULT 

al RFRFRF 

T T 

  

where RFCR is developed from creep tests performed in accordance with ASTM 

D5262, RFID obtained from site installation damage testing and RFD from 

hydrolysis or oxidative degradation testing extrapolated to 75 or 100 year design 

life. For default reduction factors, include the durability requirements in Table 3­

12 as additional reinforcement property requirements. 

4. Unified Soil Classification. 

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Construction 

Delivery, Storage, and Handling - Follow requirements set forth under materials specifications for 

geosynthetic reinforcement, drainage composite, and geosynthetic erosion mat. 

Site Excavation - All areas immediately beneath the installation area for the geosynthetic 

reinforcement shall be properly prepared as detailed on the plans, specified elsewhere within the 

specifications, or directed by the Engineer. Subgrade surface shall be level, free from deleterious 

materials, loose, or otherwise unsuitable soils. Prior to placement of geosynthetic reinforcement, 

subgrade shall be proof-rolled to provide a uniform and firm surface. Any soft areas, as determined 

by the Owner's Engineer, shall be excavated and replaced with suitable compacted soils. The 

foundation surface shall be inspected and approved by the Owner's Geotechnical Engineer prior to fill 

placement. Benching the backcut into competent soil shall be performed as shown on the plans or as 

directed, in a manner that ensures stability. 

Geosynthetic Placement - The geosynthetic reinforcement shall be installed in accordance with the 

manufacturer's recommendations, unless otherwise modified by these specifications. The 

geosynthetic reinforcement shall be placed within the layers of the compacted soil as shown on the 

plans or as directed. 

C The geosynthetic reinforcement shall be placed in continuous longitudinal strips in the 

direction of main reinforcement. Joints in the design strength direction (perpendicular to the 

slope) shall not be permitted with geotextile or geogrid, except as indicated on the drawings. 

C Horizontal coverage of less than 100 percent shall not be allowed unless specifically detailed 

in the construction drawings. In the case of 100% coverage in plan view adjacent strips need 

not be overlapped. 

C Adjacent rolls of geosynthetic reinforcement shall be overlapped or mechanically connected 

where exposed in a wrap-around face system, as applicable. 

C Place only that amount of geosynthetic reinforcement required for immediately pending work 

to prevent undue damage. After a layer of geosynthetic reinforcement has been placed, the 

next succeeding layer of soil shall be placed and compacted as appropriate. After the 

specified soil layer has been placed, the next geosynthetic reinforcement layer shall be 

installed. The process shall be repeated for each subsequent layer of geosynthetic 

reinforcement and soil. 

C Geosynthetic reinforcement shall be placed to lay flat and pulled tight prior to backfilling. 

After a layer of geosynthetic reinforcement has been placed, suitable means, such as pins or 

small piles of soil, shall be used to hold the geosynthetic reinforcement in position until the 

subsequent soil layer can be placed. Under no circumstances shall a track-type vehicle be 

allowed on the geosynthetic reinforcement before at least 6 in. (150 mm) of soil has been 

placed. Sudden braking and sharp turning – sufficient to displace fill – shall be avoided. 

C During construction, the surface of the fill should be kept approximately horizontal. 

Geosynthetic reinforcement shall be placed directly on the compacted horizontal fill surface. 

Geosynthetic reinforcements are to be placed within 3 in. (75 mm) of the design elevations 

and extend the length as shown on the elevation view unless otherwise directed by the 

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Owner's Engineer. Correct orientation of the geosynthetic reinforcement shall be verified by 

the Contractor. 

Fill Placement - Fill shall be compacted as specified by project specifications or to at least 95 percent 

of the maximum density determined in accordance with AASHTO T-99, whichever is greater. 

C Density testing shall be made every 500 yd3

 (420 m3) of soil placement or as otherwise 

specified by the Owner's Engineer or contract documents. 

C Backfill shall be placed, spread, and compacted in such a manner to minimize the 

development of wrinkles and/or displacement of the geosynthetic reinforcement. 

C Fill shall be placed in 12-inch (300 mm) maximum lift thickness where heavy compaction 

equipment is to be used, and 6-inch (150 mm) maximum uncompacted lift thickness where 

hand operated equipment is used. 

C Backfill shall be graded away from the slope crest and rolled at the end of each work day to 

prevent ponding of water on surface of the reinforced soil mass. 

C Tracked construction equipment shall not be operated directly upon the geosynthetic 

reinforcement. A minimum fill thickness of 6-in. (150 mm) is required prior to operation of 

tracked vehicles over the geosynthetic reinforcement. Turning of tracked vehicles should be 

kept to a minimum to prevent tracks from displacing the fill and the geosynthetic 

reinforcement. 

C If approved by the Engineer, rubber-tired equipment may pass over the geosynthetic 

reinforcement at speeds of less than 25 mph (16 km/h). Sudden braking and sharp turning 

shall be avoided. 

Erosion Control Material Installation. See Erosion Control Material Specification for installation 

notes. 

Geosynthetic Drainage Composite. See Geocomposite Drainage Composite Material Specification 

for installation notes. 

Final Slope Geometry Verification. Contractor shall confirm that as-built slope geometries conform 

to approximate geometries shown on construction drawings. 

Method of Measurement 

Measurement of geosynthetic reinforcement is on a square yard (meter) basis and will be computed 

on the total area of geosynthetic reinforcement shown on the construction drawings, exclusive of the 

area of geosynthetics used in any overlaps. Overlaps are an incidental item. 

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Basis of Payment 

The accepted quantities of geosynthetic reinforcement by Type will be paid for per square yard 

(meter) in-place. 

Payment will be made under: 

Pay Item Pay Unit 

Geogrid Soil Reinforcement – Type A Square yard (meter) 

Geogrid Soil Reinforcement – Type B square yard (meter) 

Or 

Geotextile Soil Reinforcement – Type A square yard (meter) 

Geotextile Soil Reinforcement – Type B square yard (meter) 

10.10.2 Specification for Erosion Control Mat or Blanket 

Description 

Work shall consist of furnishing and placing a synthetic erosion control mat and/or degradable 

erosion control blanket for slope face protection and lining of runoff channels for use in construction 

of reinforced soil slopes as shown on the plans or as specified by the Engineer. 

Materials 

(1) Erosion Control 

The specific erosion control material and supplier shall be prequalified by the Agency prior to 

use. 

Prequalification procedures and a current list of prequalified materials may be obtained by 

writing to the Agency. A 1 ft by 1 ft (0.3 m by 0.3 m) sample of the material may be required by 

the Engineer in order to verify prequalification. 

The soil erosion control mat shall be a Class __ material and be one (1) of the following types as 

shown on the plans: 

(i) Type __. Long-term duration (Longer than 2 Years) 

 Shear Stress (td) > 2 psf (95 Pa) to < 5 psf (240 Pa) 

 Prequalified Type __ products are: 

 ______________ ______________ 

 ______________ ______________ 

(ii) Type __. Long-term duration (Longer than 2 Years) 

 Shear Stress (td) greater than or equal to 5 psf (240 Pa) 

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 Prequalified Type __ products are: 

 ______________ ______________

 ______________ ______________
 

Certification. The Contractor shall submit a manufacturer's certification that the erosion 

mat/blanket supplied meets the property criteria specified when the material was approved by the 

Agency. The manufacturer's certification shall include a submittal package of documented test 

results that confirm the property values. In case of dispute over validity of property values, the 

Engineer can require the Contractor to supply property test data from an approved laboratory to 

support the certified values submitted. Minimum average roll values, per ASTM D4759, shall be 

used for conformance. 

(2) Staples. 

Staples for anchoring the soil erosion control mat shall be U-shaped, made of 1/8 in. (3 mm) or 

large diameter steel wire, or other approved material, have a width of 1 to 2 in. (25 to 50 mm), 

and a length of not less than 18 in. (450 mm) for the face of RSS, and not less than 12 in. (300 

mm) for runoff channels. 

Construction Methods 

(1) General. 

The soil erosion control mat shall conform to the class and type shown on the plans. The 

Contractor has the option of selecting an approved soil erosion control mat conforming to the 

class and type shown on the plans, and according to the current approved material list. 

(2) Installation. 

The soil erosion control mat, whether installed as slope protection or as flexible channel liner in 

accordance with the approved materials list, shall be placed within 24 hours after seeding or 

sodding operations have been completed, or as approved by the Engineer. Prior to placing the 

mat, the area to be covered shall be relatively free of all rocks or clods over 1-1⁄2 inches (38 mm) 

in maximum dimension and all sticks or other foreign material which will prevent the close 

contact of the mat with the soil. The area shall be smooth and free of ruts or depressions exist for 

any reason, the Contractor shall be required to rework the soil until it is smooth and to reseed or 

resod the area at the Contractor’s expense. 

Installation and anchorage of the soil erosion control mat shall be in accordance with the project 

construction drawings unless otherwise specified in the contract or directed by the Engineer. 

The erosion control material shall be placed and anchored on a smooth graded, firm surface 

approved by the Engineer. Anchoring terminal ends of the erosion control material shall be 

accomplished through use of key trenches. The material in the trenches shall be anchored to the 

soil with staples on maximum 20 in. (0.5 m) centers. 

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Erosion control material shall be anchored, overlapped, and otherwise constructed to ensure 

performance until vegetation is well established. Pins shall be as designated on the construction 

drawings, with a maximum spacing of 4 ft. (1.25 m) recommended. 

Soil Filling. If noted on the construction drawings, the erosion control mat shall be filled with a 

fine grained topsoil, as recommended by the manufacturer. Soil shall be lightly raked or brushed 

on/into the mat to fill mat thickness or to a maximum depth of 1 in. (25 mm). 

Method of Measurement 

Measurement of erosion mat and erosion blanket material is on a square meter basis and will be 

computed on the projected slope face area from defined plan lines, exclusive of the area of material 

used in any overlaps, or from payment lines established in writing by the Engineer. Overlaps, 

anchors, checks, terminals or junction slots, and wire staples or wood stakes are incidental items. 

Quantities of erosion control material as shown on the plans may be increased or decreased at the 

direction of the Engineer based on construction procedures and actual site conditions. Such variations 

in quantity will not be considered as alterations in the details of construction or a change in the 

character of work. 

Basis of Payment 

The accepted quantities of erosion control material will be paid for per square meter in place. 

Payment will be made under: 

Pay Item Pay Unit 

Geosynthetic (Permanent) Erosion Control Mat square yard (meter) 

 

 and/or 

Degradable (Temporary) Erosion Control Blanket square yard (meter) 

10.10.3 Specification for Geosynthetic Drainage Composite 

Description 

Work shall consist of furnishing and placing a geosynthetic drainage system as a subsurface drainage 

media for reinforced soil slopes. 

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Drainage Composite Materials 

The specific drainage composite material and supplier shall be preapproved by the Agency. 

The geocomposite drain shall be: 

[ insert approved materials that meet the project requirements. Geocomposites 

should be designed on a project specific basis. Design criteria for flow capacity, 

filtration, and permeability are summarized in the FHWA Geosynthetic, Design and 

Construction Guidelines (Holtz et al., 2008). ] 

OR 

The geocomposite drain shall be a composite construction consisting of a supporting structure or 

drainage core material surrounded by a geotextile. The geotextile shall encapsulate the drainage core 

and prevent random soil intrusion into the drainage structure. The drainage core material shall consist 

of a three dimensional polymeric material with a structure that permits flow along the core laterally. 

The core structure shall also be constructed to permit flow regardless of the water inlet surface. The 

drainage core shall provide support to the geotextile. The core and fabric shall meet the minimum 

property requirements listed in Table S3. 

A geotextile flap shall be provided along all drainage core edges. This flap shall be of sufficient 

width for sealing the geotextile to the adjacent drainage structure edge to prevent soil intrusion into 

the structure during and after installation. The geotextile shall cover the full length of the core. 

The geocomposite core shall be furnished with an approved method of constructing and connecting 

with outlet pipes or weepholes as shown on the plans. Any fittings shall allow entry of water from 

the core but prevent intrusion of backfill material into the core material. 

Certification and Acceptance. The Contractor shall submit a manufacturer's certification that the 

geosynthetic drainage composite supplied meets the design properties and respective index criteria 

measured in full accordance with all test methods and standards specified. The manufacturer's 

certification shall include a submittal package of documented test results that confirm the design 

values. In case of dispute over validity of design values, the Engineer can require the Contractor to 

supply design property test data from an approved laboratory, to support the certified values 

submitted. Minimum average roll values, per ASTM D4759, shall be used for conformance. 

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Table S3. Minimum Physical Property Criteria For 

Geosynthetic Drainage Composites In Reinforced Soil Slopes 

PROPERTY TEST METHOD VALUE1 

Composite:

ASTM D4716 ft2 Flow Capacity /s/ unit width (min) 2 

Geotextile:

 AOS3 ASTM D4751 ___ Max. Diameter (mm) 

 Permeability4

 ASTM D44915 ______ cm/s 

Trapezoidal Tear 

CLASS 26 

CLASS 37 

ASTM D4533 

56 lb (250 N) 

40 lb (180 N) 

 Grab Strength 

CLASS 26

 CLASS 37 

ASTM D4632 

160 lb (700 N) 

110 lb (500 N) 

Puncture 

CLASS 26

 CLASS 37 

ASTM D6241 

310 lb (1375 N) 

40 lb (180 N) 

Notes: 

1. Values are minimum unless noted otherwise. Use value in weaker principal direction, as applicable. All 

numeric values represent minimum average roll values. 

2. The flow capacity requirements for the project shall be determined with consideration of design flow rate, 

compressive load on the drainage material, and slope of drainage composite installation. 

3. Both a maximum and a minimum AOS may be specified. Sometimes a minimum diameter is used as a 

criterion for improved clogging resistance. See FHWA Geosynthetic Design and Construction Guidelines 

(Holtz et al., 2008) for further information. 

4. Permeability is project specific. A nominal coefficient of permeability may be determined by multiplying 

permittivity value by nominal thickness. The k value of the geotextile should be greater than the k value of 

the soil. 

5. Standard Test Methods for Water Permeability (hydraulic conductivity) of Geotextiles by Permittivity. 

6. CLASS 2 geotextiles are recommended where construction conditions are unknown or where sharp angular 

aggregate is used and a heavy degree of compaction (95% AASHTO T99) is specified. 

7. CLASS 3 geotextiles (from AASHTO M-288) may be used with smooth graded surfaces having no sharp 

angular projections, no sharp aggregate is used, and compaction requirements are light (<95% AASHTO 

T99). 

Construction 

Delivery, Storage, and Handling. The Contractor shall check the geosynthetic drainage composite 

upon delivery to ensure that the proper material has been received. During all periods of shipment 

and storage, the geosynthetic drainage composite shall be protected from temperatures greater than 

140o

 F (60o C), mud, dirt, and debris. Follow manufacturer's recommendations in regards to 

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MSE Walls and RSS – Vol II 10 - 50 November 2009 
 

 

 

protection from direct sunlight. At the time of installation, the geosynthetic drainage composite shall 

be rejected if it has defects, tears, punctures, flaws, deterioration, or damage incurred during 

manufacture, transportation, or storage. If approved by the Engineer, torn or punctured sections may 

be removed or repaired. Any geosynthetic drainage composite damaged during storage of installation 

shall be replaced by the Contractor at no additional cost to the Owner. 

Placement. The soil surface against which the geosynthetic drainage composite is to be placed shall 

be free of debris and inordinate irregularities that will prevent intimate contact between the soil 

surface and the drain. 

Seams. Edge seams shall be formed by utilizing the flap of geotextile extending from the 

geocomposite's edge and lapping over the top of the geotextile of the adjacent course. The geotextile 

flap shall be securely fastened to the adjacent fabric by means of plastic tape or non-water-soluble 

construction adhesive, as recommended by the supplier. Where vertical splices are necessary at the 

end of a geocomposite roll or panel, a 8-inch (200-mm)-wide continuous strip of geotextile may be 

placed, centered over the seam and continuously fastened on both sides with plastic tape or non water 

soluble construction adhesive. As an alternative, rolls of geocomposite drain material may be joined 

together by turning back the geotextile at the roll edges and interlocking the cuspidations 

approximately 2 in. (50 mm). For overlapping in this manner, the geotextile shall be lapped over and 

tightly taped beyond the seam with tape or adhesive. Interlocking of the core shall always be made 

with the upstream edge on top in the direction of water flow. To prevent soil intrusion, all exposed 

edges of the geocomposite drainage core shall be covered by tucking the geotextile flap over and 

behind the core edge. Alternatively, a 1 ft (300 mm) wide strip of geotextile may be used in the same 

manner, fastening it to the exposed fabric 8 in. (200 mm) in from the edge and fold the remaining 

flap over the core edge. 

Repairs. Should the geocomposite be damaged during installation by tearing or puncturing, the 

damaged section shall be cut out and replaced completely or repaired by placing a piece of geotextile 

that is large enough to cover the damaged area and provide a sufficient overlap on all sides to fasten. 

Soil Fill Placement. Structural backfill shall be placed immediately over the geocomposite drain. 

Care shall be taken during the backfill operation not to damage the geotextile surface of the drain. 

Care shall also be taken to avoid excessive settlement of the backfill material. The geocomposite 

drain, once installed, shall not be exposed for more than seven days prior to backfilling. 

Method of Measurement 

Measurement of geosynthetic drainage composite is on a square meter basis and will be computed on 

the total area of geosynthetic drainage composite shown on the construction drawings, exclusive of 

the area of drainage composite used in any overlaps. Overlaps, connections, and outlets are incidental 

items. 

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MSE Walls and RSS – Vol II 10 - 51 November 2009
 
 

 

Quantities of drainage composite material as shown on the plans may be increased or decreased at the 

direction of the Engineer based on construction procedures and actual site conditions. Such variations 

in quantity will not be considered as alterations in the details of construction or a change in the 

character of work. 

Basis of Payment 

The accepted quantities of drainage composite material will be paid for per square meter in place. 

Payment will be made under: 

Pay Item Pay Unit 

 

 Geosynthetic Drainage Composite square yard (meter) 

10.10.4 Specification Guidelines for Geosynthetic Reinforced Soil Slope Systems 

Description 

Work shall consist of design, furnishing materials, and construction of geosynthetic reinforced soil 

slope structure. Supply of geosynthetic reinforcement, drainage composite, and erosion control 

materials, and site assistance are all to be furnished by the slope system supplier. 

Reinforced Slope System 

Acceptable Suppliers - The following suppliers can provide Agency approved system: 

(1) 

(2) 

(3) 

Materials. Only geosynthetic reinforcement, drainage composite, and erosion mat materials approved 

by the contracting Agency prior to project advertisement shall be utilized in the slope construction. 

Geogrid Soil Reinforcement, Geotextile Soil Reinforcement, Drainage Composite, and Geosynthetic 

Erosion Mat materials are specified under respective material specifications. 

Design Submittal. The Contractor shall submit six sets of detailed design calculations, construction 

drawings, and shop drawings for approval within 30 days of authorization to proceed and at least 60 

days prior to the beginning of reinforced slope construction. The calculations and drawings shall be 

prepared and sealed by a Professional Engineer, licensed in the State. Submittal shall conform to 

Agency requirements for RSS. 

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MSE Walls and RSS – Vol II 10 - 52 November 2009
 
 

 

 

 

Material Submittals. The Contractor shall submit six sets of manufacturer's certification that indicate 

the geosynthetic soil reinforcement, drainage composite, and geosynthetic erosion mat meet the 

requirements set forth in the respective material specifications, for approval at least 60 days prior to 

start of RSS. 

Construction 

(Should follow the specifications details in this chapter) 

Method of Measurement 

Measurement of geosynthetic RSS Systems is on a vertical square foot basis. 

Payment shall include reinforced slope design and supply and installation of geosynthetic soil 

reinforcement, reinforced soil fill, drainage composite, and geosynthetic erosion mat. Excavation of 

any unsuitable materials and replacement with select fill, as directed by the Engineer shall be paid 

under a separate pay item. 

Quantities of reinforced soil slope system as shown on the plans may be increased or decreased at the 

direction of the Engineer based on construction procedures and actual site conditions. 

Basis of Payment 

The accepted quantities of geosynthetic RSS system will be paid for per vertical square foot (meter) 

in place. 

Payment will be made under: 

Pay Item Pay Unit 

Geosynthetic RSS System Vertical square foot (meter) 

FHWA NHI-10-025 10 – Contracting Methods
 

MSE Walls and RSS – Vol II 10 - 53 November 2009
 
 

 

FHWA NHI-10-025 10 – Contracting Methods
 

MSE Walls and RSS – Vol II 10 - 54 November 2009
 
 

CHAPTER 11 

FIELD INSPECTION AND PERFORMANCE MONITORING
 

Construction of MSE and RSS systems is relatively simple and rapid. The construction 

sequence consists mainly of preparing the subgrade, placing and compacting backfill in 

normal lift operations, laying the reinforcing layer into position, and installing the facing 

elements (tensioning of the reinforcement may also be required) or outward facing for RSS 

slopes. Special skills or equipment are usually not required, and locally available labor can 

be used, however, experienced crews can provide higher production rates. Most material 

suppliers provide training for construction of their systems. The outline of a checklist 

showing general requirements for monitoring and inspecting MSE and RSS systems is 

provided in Table 11-1. The table should be expanded by the agency to include detailed 

requirements based on the agencies specifications and the specific project plans and 

specification requirements. Examples of detailed checklists for specific sections are provided 

later in this chapter. 

There are some special construction considerations that the designer, construction personnel, 

and inspection team need to be aware of so that potential performance problems can be 

avoided. These considerations relate to the type of system to be constructed, to specific site 

conditions, the backfill material used and facing requirements. The following sections 

review items relating to: 

C Section 11.1 - preconstruction reviews. 

C Section 11.2 - prefabricated materials inspection. 

C Section 11.3 - construction control. 

C Section 11.4 - performance monitoring programs. 

11.1 PRECONSTRUCTION REVIEWS 

Prior to erection of the structure, personnel responsible for observing the field construction of 

the retaining structure must become thoroughly familiar with the following items: 

C Plans and specifications. 

C Site conditions relevant to construction requirements. 

C Material requirements. 

C Construction sequences for the specific reinforcement system. 

FHWA NHI-10-025 11 – Field Inspection 

MSE Walls and RSS – Vol II 11 – 1 November 2009
 
 

Table 11-1. Outline of MSE/RSS Field Inspection Checklist Requirements. 

□ 1.	 Read the specifications and become familiar with:

 - material requirements 

- construction procedures 

- soil compaction procedures 

- alignment tolerances 

- acceptance/rejection criteria 

□ 2.	 Review the construction plans and become familiar with:

 - construction sequence 

- corrosion protection requirements
 

- special placement to reduce damage 

- soil compaction restrictions 

- details for drainage requirements 

- details for utility construction 

- construction of slope face 

- contractor's documents 

□ 	 3. Review material requirements and approval submittals. 

Review construction sequence for the reinforcement system. 

□ 4. Check site conditions and foundation requirements. Observe: 

- preparation of foundations 

- leveling pad construction (check level and alignment)

 - site accessibility 

- limits of excavation

 - construction dewatering 

- drainage features; seeps, adjacent streams, lakes, etc. 

□ 	 5. On site, check reinforcements and prefabricated units. Perform inspection of prefabricated 

elements (i.e. casting yard) as required. Reject precast facing elements if: 

- compressive strength < specification requirements 

- molding defects (e.g., bent molds)

 - honey-combing 

- severe cracking, chipping or spalling 

- color of finish variation 

- tolerance control 

- misaligned connections
 

□ 6. Check reinforcement labels to verify whether they match certification documents. 

□ 	 7. Observe materials in batch of reinforcements to make sure they are the same. Observe 

reinforcements for flaws and nonuniformity. 

□ 	 8. Obtain test samples according to specification requirements from randomly selected 

reinforcements. 

□ 	 9. Observe construction to see that the contractor complies with specification requirements for 

installation. 

□ 10. If possible, check reinforcements after aggregate or riprap placement for possible damage. This 

can be done either by constructing a trial installation, or by removing a small section of 

aggregate or riprap and observing the reinforcement after placement and compaction of the 

aggregate, at the beginning of the project. If damage has occurred, contact the design engineer. 

□ 11. Check all reinforcement and prefabricated facing units against the initial approved shipment 

and collect additional test samples. 

□ 12. Monitor facing alignment: 

- adjacent facing panel joints 

- precast face panels 

- modular block walls

 - wrapped face walls 

- line and grade 

FHWA NHI-10-025 11 – Field Inspection 

MSE Walls and RSS – Vol II 11 – 2 November 2009
 
 

11.1.1 Plans and Specifications 

Specification requirements for MSE and RSS are reviewed in Chapter 10. The owner's field 

representatives should carefully read the specification requirements for the specific type of 

system to be constructed, with special attention given to material requirements, construction 

procedures, soil compaction procedures, alignment tolerances, and acceptance/rejection 

criteria. Plans should be reviewed. Unique and complex project details should be identified 

and reviewed with the designer and contractor, if possible. Special attention should be given 

to material handling and storage, the construction sequence, corrosion protection 

requirements for metallic reinforcement and UV protection for geosynthetics, special 

placement requirements to reduce construction damage of reinforcement, soil compaction 

restrictions, details for drainage requirements and utility construction, and construction of the 

outward slope. The contractor's documents should be checked to make sure that the latest 

issue of the approved plans, specifications, and contract documents are being used. 

A checklist for review of MSE structures drawings is presented in Table 11-2 (FHWA NHI08-094 and 095). A checklist for review of MSE specifications is presented in Table 11-3 

(FHWA NHI-08-094/095). 

11.1.2 Review of Site Conditions and Foundation Requirements 

The site conditions should be reviewed to determine if there will be any special construction 

procedures required for preparation of the foundations, site accessibility, excavation for 

obtaining the required reinforcement length, and construction dewatering and other drainage 

features. 

Foundation preparation involves the removal of unsuitable materials from the area to be 

occupied by the retaining structure including all organic matter, vegetation, and slide debris, 

if any. This is most important in the facing area to reduce facing system movements and, 

therefore, to aid in maintaining facing alignment along the length of the structure. The field 

personnel should review the borings to determine the anticipated extent of the removal 

required. 

Where construction of reinforced fill will require a side slope cut, a temporary earth support 

system may be required to maintain stability. The contractor's method and design should be 

reviewed with respect to safety and the influence of its performance on adjacent structures. 

Caution is also advised for excavation of utilities or removal of temporary bracing or 

sheeting in front of the completed MSE structures. Loss of ground from these activities 

could result in settlement and lateral displacement of the retaining structure. 

FHWA NHI-10-025 11 – Field Inspection 

MSE Walls and RSS – Vol II 11 – 3 November 2009
 
 

The groundwater level found in the site investigation should be reviewed along with levels of 

any nearby bodies of water that might affect drainage requirements. Slopes into which a cut 

is to be made should be carefully observed, especially following periods of precipitation, for 

any signs of seeping water (often missed in borings). Construction dewatering operations 

should be required for any excavations performed below the water table to prevent a 

reduction in shear strength due to hydrostatic water pressure. 

MSE/RSS structures should be designed to permit drainage of any seepage or trapped 

groundwater in the retained soil. If water levels intersect the structure, it is also likely that a 

drainage structure behind and beneath the wall will be required. Surface water infiltration 

into the retained fill and reinforced fill should be minimized by providing an impermeable 

cap and adequate slopes to nearby surface drain pipes or paved ditches with outlets to storm 

sewers or to natural drains. 

Internal drainage of the reinforced fill can be attained by use of a free-draining granular 

material that is free of fines (material passing No. 200 {0.075 mm} sieve should be less than 

5 percent). Because of its high permeability, this type of fill will prevent retention of any 

water in the soil fill as long as a drainage outlet is available. Details are generally provided 

for drainage to the base of the fill as shown on Figures 5-6, 5-9 and 5-10, to avert water from 

exiting through the face of the wall, which could cause erosion and/or face stains. The drains 

will, of course, require suitable outlets for discharge of seepage away from the reinforced soil 

structure. Care should be taken to avoid creating planes of weakness within the structure 

with drainage layers. 

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MSE Walls and RSS – Vol II 11 – 4 November 2009
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 11-2. Checklist for Drawing Review. (after FHWA NHI-08-094/095) 

YES NO NA 

1.0 DOCUMENTS 

1.1 Have you thoroughly reviewed the design drawings? 

1.2 Is there a set of all project drawings in the field trailer? 

1.3 Has the contractor submitted shop drawings? 

1.4 Have the shop drawings been approved by the designer and/or construction 

division manager? 

2.0 LAYOUT 

2.1 Have you located the horizontal and vertical control points? 

2.2 Do you know where the MSEW/RSS begins and ends? 

2.3 Have you identified any locations of existing utilities, signs, piles, lights that 

affect the proposed construction? 

2.4 Have you identified the elevations/ grade at top and at bottom of 

MSEWs/RSSs? 

2.5 Have you identified the existing and finished grades? 

2.6 Do you know where the construction limits are? 

2.7 Have you identified how the site will be accessed and any provisions for 

material storage? 

2.8 Is phased construction involved? 

3.0 FOUNDATION PREPARATION 

3.1 Are any special foundation treatments required? 

3.2 Is the foundation stepped? 

3.3 Is concrete leveling pad and the required elevation(s) shown on the drawings? 

3.4 Is shoring required? 

4.0 DRAINAGE 

4.1 Have you located the details for drainage? 

4.2 When must the drainage provisions be installed? 

4.3 Where does the drainage system outlet and does it allow for positive drainage? 

4.4 Are geotextile filters required? 

4.5 Is a drainage barrier (geomembrane) required for this project? 

5.0 FACING 

5.1 Have you identified the facing type, shape, size, and architectural finishing? 

5.2 Are there different types, colors, or sized facing units on the job? 

5.3 How do the facing units fit together? 

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YES NO NA 

5.4 Do you understand any corner/curve details? 

5.5 Do you understand bracing, bearing pads, wedging and shimming 

requirements? 

5.6 Is the facing battered? 

5.7 Are geotextile filters required for wall joints and is the placement shown on the 

drawings including overlaps and termination at the base and toe of the wall. 

6.0 REINFORCING 

6.1 What type of reinforcement is used in this project? 

6.2 Can you determine the length, location and type of reinforcement throughout 

the length and height of the wall or slope? 

6.3 Do you understand how the reinforcing connects to the facing? 

6.4 Have you identified any details for avoiding obstructions when placing 

reinforcement? 

6.5 Are cross sections showing reinforcement location? Are cross sections 

shown for each stationing and major elevation change? 

7.0 BACKFILL 

7.1 Are different types of fill required in different locations in the wall? 

8.0 ANCILLARY ITEMS 

8.1 Is there any coping specified in the drawings? 

8.2 Is there any traffic barrier or guard rail specified in the drawings? 

8.3 Have you considered interfaces with CIP structures? 

8.4 Do you understand the details for joints at or connections to CIP structures? 

8.5 Are any of the following involved in this project? 

8.5.1 Catch Basins/Drop Inlets 

8.5.2 Culverts/Pipes? 

8.5.3 Piles/Drilled Shafts? 

8.5.4 Utilities and other obstructions? 

8.6 Have you identified and do you understand any special detail to 

accommodate these obstructions? 

8.7 Do you know who is responsible for installation of each ancillary item? 

8.8 Are diversion ditches, collection ditches, or slope drains shown on the 

drawings? 

8.9 Is a permanent or temporary erosion control blanket required? 

8.10 Do you understand any erosion control details? 

FHWA NHI-10-025 11 – Field Inspection 

MSE Walls and RSS – Vol II 11 – 6 November 2009
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 11-3. Checklist for Specification Compliance. (after FHWA NHI-08-094/095) 

YES NO NA 

1.0 DOCUMENTS 

1.1 Have you thoroughly reviewed the specifications? 

1.2 Is there a set of specifications in the field trailer? 

1.3 Are standard specifications or special provisions required in addition to 

the project specifications? Do you have a copy? 

2.0 PRE-CONSTRUCTION QUALIFYING OF MATERIAL SOURCES / 

SUPPLIERS 

2.1 Has the Contractor submitted pre-construction qualification test results 

(showing that it meets the gradation, density, electrochemical, and other 

soil-property requirements) for:

 2.1.1 Reinforced soil

 2.1.2 Retained soil

 2.1.3 Facing soil (if applicable)

 2.1.4 Drainage aggregate 

2.1.4 Graded granular filters (if applicable) 

2.2 Has the Contractor or Manufacturer submitted pre-construction 

qualification test results and/or Certificate of Compliance demonstrating 

that the facing materials comply with the applicable sections of the 

specifications including: 

2.2.1 Facing unit and connections 

2.2.2 Horizontal facing joint bearing pads 

2.2.3 Geotextile filter for facing joint 

2.3 Has the Contractor or Manufacturer submitted pre-construction 

qualification test results and/or Certificate of Compliance demonstrating 

that the reinforcing materials comply with the applicable sections of the 

specifications? 

2.4 Has the Contractor or Manufacturer submitted pre-construction 

qualification test results and/or Certificate of Compliance demonstrating 

that the drainage materials comply with the applicable sections of the 

specifications including: 

2.2.1 Geotextile filters (e.g., Type, AOS, permittivity, strength) 

2.2.2 Prefabricated Drains (i.e., geotextile filter and core) 

2.2.3 Drainage Pipe (material, type, ASTM designation and schedule 

2.4 Has approval of the soil sources been officially granted for: 

2.4.1 Reinforced soil 

2.4.2 Retained soil 

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YES NO NA

 2.4.3 Facing soil 

2.4.4 Drainage aggregate 

2.5 Has approval of the facing material sources been officially granted 

2.6 Has approval of the reinforcing material sources been officially granted? 

3.0 FOUNDATION PREPARATION 

3.1 Has temporary shoring been designed and approved? 

4.0 DRAINAGE 

4.1 Is the Contractor or Manufacturer submitting QC test results at the specified 

frequency demonstrating that the drainage materials comply with the 

applicable sections of the specifications? 

4.2 Do the drainage materials delivered to the site correspond to the approved 

shop drawings? 

4.3 Do the identification labeling/markings on the geotextile filters and/or 

prefabricated drainage materials delivered to the site correspond to the preconstruction and QC submittals (date of manufacturing, lot number, roll 

numbers, etc.)? 

4.4 Have the drainage materials been inspected for damage due to transport, 

handling, or storage activities? 

4.5 Are the drainage materials properly stored to prevent damage, exposure to 

UV light, contamination? 

4.6 If any drainage materials were found damaged, have they been set aside, 

rejected, or repaired in accordance with the specifications? 

4.7 Has QA sampling of the drainage materials been performed at the required 

frequency? 

4.8 Does the QA lab know exactly which tests to run and the required test 

parameters? 

4.9 Do the QA test results for the drainage materials meet the specified 

property values? 

5.0 FACING 

5.1 Is the Contractor or Manufacturer submitting QC test results at the specified 

frequency demonstrating that the facing materials comply with the 

applicable sections of the specifications? 

5.2 Do the facing components delivered to the site correspond to the approved 

shop drawings including: 

5.2.1 Facing unit (shape, dimensions, reinforcement connections, overall 

quantity)? 

5.2.2 Horizontal facing joint bearing pads (material type, hardness, 

modulus) 

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YES NO NA 

5.2.3 Geotextile filter for facing joint (type, AOS, permittivity, strength) 

5.3 Do the identification labeling/markings on the facing units and components 

delivered to the site correspond to the pre-construction qualification and 

QC submittals (date of manufacturing, batch number, lot number, etc.)? 

5.4 Have the facing units and components been inspected for damage due to 

transport, handling, or storage activities? 

5.5 Are the facing units and components properly stored to prevent damage? 

5.6 If any facing units and components were found damaged, have they been 

rejected or repaired in accordance with the specifications? 

5.7 Has QA sampling of the facing units and component materials been 

performed at the required frequency? 

5.8 Does the QA lab know exactly which tests to run and the required test 

parameters? 

5.9 Do the QA test results for the facing unit and component materials meet the 

specified property values? 

6.0 REINFORCING 

6.1 Is the Contractor or Manufacturer submitting QC test results at the 

specified frequency demonstrating that the reinforcing materials comply 

with the applicable sections of the specifications? 

6.2 Do the reinforcing materials delivered to the site correspond to the 

approved shop drawings (strength, dimensions, overall quantity)? 

6.3 Do the identification labeling/markings on the reinforcing materials 

delivered to the site correspond to the pre-construction and QC submittals 

(date of manufacturing, lot number, roll numbers, etc.)? 

6.4 Have the reinforcing materials been inspected for damage due to 

transport, handling, or storage activities? 

6.5 Are the reinforcing materials properly stored to prevent damage, exposure 

to UV light, or corrosion? 

6.6 If any reinforcing materials were found damaged, have they been set 

aside, rejected, or repaired in accordance with the specifications? 

6.7 Has QA sampling of the reinforcing materials been performed at the 

required frequency? 

6.8 Does the QA lab know exactly which tests to run and the required test 

parameters? 

6.9 If pullout or interface shear testing is required, does the QA lab have 

enough of the applicable soil and the compaction criteria (in addition to 

the reinforcing materials)? 

6.10 Do the QA test results for the reinforcing materials meet the specified 

property values? 

FHWA NHI-10-025 11 – Field Inspection 

MSE Walls and RSS – Vol II 11 – 9 November 2009
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

YES NO NA 

7.0 BACKFILL 

7.1 Is the Contractor submitting QC test results at the specified frequency for:

 7.1.1 Reinforced soil 

7.1.2 Retained soil 

7.1.3 Facing soil 

7.2 Does the QA lab know exactly which tests to run and the required test 

parameters? 

7.3 Do the QA test results for the various materials meet the specified 

property values: 

7.3.1 Reinforced Soil 

7.3.2 Retained Soil 

7.3.3 Facing Soil 

8.0 ANCILLARY ITEMS 

8.1 Do any ancillary materials delivered to the site correspond to the 

approved shop drawings (prefabricated copings, cap blocks and 

attachment glue, if required, catch basins, pipe, guardrail, etc.)? 

8.2 Do the identification labeling/markings on the ancillary materials 

delivered to the site correspond to the QC submittals (date of 

manufacturing, batch number, etc.)? 

8.3 Have the ancillary materials been inspected for damage due to transport, 

handling, or storage activities? 

8.4 Are the ancillary materials properly stored to prevent damage? 

8.5 If any ancillary materials were found damaged, have they been set aside, 

rejected, or repaired in accordance with the specifications? 

8.6 Have all requirements to sample/test any aspect of the work product after 

assembly, installation, compaction been met? 

FHWA NHI-10-025 11 – Field Inspection 

MSE Walls and RSS – Vol II 11 – 10 November 2009
 
 

 

 

 

 

 

 

11.2 PREFABRICATED MATERIALS INSPECTION 

Material components should be examined at the casting yard (for systems with precast 

elements) and on site. Typical casting operations are shown on Figure 11-1. Material 

acceptance should be based on a combination of material testing, certification, and visual 

observations. 

When delivered to the project site, the inspector should carefully inspect all material (precast 

facing elements, reinforcing elements, bearing pads, facing joint materials, and reinforced 

backfill). On site, all system components should be satisfactorily stored and handled to avoid 

damage. The material supplier's construction manual should contain additional information 

on this matter. 

11.2.1. Precast Concrete Elements 

At the casting yard, the inspector should assure the facing elements are being fabricated in 

accordance with the agency's standard specifications. For example, precast concrete facing
 

panels should be cast on a flat surface. Clevis loop embeds, tie strips, and other connection
 

devices must not contact or be attached to the facing element reinforcing steel. Curing 

should follow required procedures and requirements (e.g., temperature, cover, moisture, etc.). 

Facing elements delivered to the project site should be examined prior to erection. Panels
 

should be rejected on the basis of the following deficiencies or defects: 

C Insufficient compressive strength. 

C Mold defects (e.g., bent molds). 

C Honey-combing. 

C Severe cracking, chipping, or spalling. 

C Significant variation in color of finish. 

C Out-of-tolerance dimensions. 

C Misalignment of connection devices. 

The following maximum facing element dimension tolerances are usually specified for 

precast concrete: 

C Overall dimensions: 1/2-inch (13 mm) 

C Connection device locations: 1-inch (25 mm) 

C Clevis loop embeds: 1/8-inch (3 mm) horizontal alignment 

C Element squareness: 1/2-inch (13 mm) difference between diagonals 

C Surface finish: 1/8-inch in 5 ft (2 mm in 1 m) (smooth surface) 

C Surface finish: 5/16-inch in 5 ft (5 mm in 1 m) (textured surface) 

FHWA NHI-10-025 11 – Field Inspection 

MSE Walls and RSS – Vol II 11 – 11 November 2009
 
 

Figure 11-1. Casting yard for precast facing elements. 

FHWA NHI-10-025 11 – Field Inspection 

MSE Walls and RSS – Vol II 11 – 12 November 2009 
 

In cases where repair to damaged facing elements is possible, it should be accomplished to 

the satisfaction of the engineer. 

For drycast modular blocks, it is essential that compressive strengths and water absorption be 

carefully checked on a lot basis. The following dimensional tolerances are usually specified: 

C Overall dimensions: ± 1/8-inch (3.2 mm) 

C Height of each block: ± 1/16-inch (1.6 mm) 

11.2.2 Reinforcing Elements 

Reinforcing elements (strips, mesh, sheets) should arrive at the project site securely bundled 

or packaged to avoid damage (see Figure 11-2). These materials are available in a variety of 

types, configurations, and sizes (gauge, length, product styles), and even a simple structure 

may have different reinforcement elements at different locations. The inspector should 

verify that the material is properly identified and check the specified designation (AASHTO, 

ASTM, or agency specifications). Grid reinforcement should be checked for wire diameter, 

length, width, and spacing of longitudinal and transverse members. For strip reinforcements, 

the length and thickness should be checked. 

Material verification is especially important for geotextiles and geogrids where many product 

styles look similar but have different properties. In addition to the above measurements, 

geogrids or geotextile samples should be weighed in the field to compare the mass per unit 

area with the manufacturer’s identification value. Samples should also be sent to the 

laboratory for verification testing. Color coding of roll ends can be helpful, especially in 

complex configurations to prevent improper installations. Where more than one style will be 

used, the roll ends could be painted and when reinforcements are cut to length, the lengths 

could be painted on the material as shown in Figure 11-2. 

Galvanization (application thickness 2 oz/ft2 {610 g/m2}), epoxy coatings (thickness 16 mils 

{0.41 mm}) or other coatings, should be verified by certification or agency conducted tests 

and checked for defects. Geosynthetic reinforcements should be properly packaged and 

protective wraps should be maintained during shipping and handling to protect the material 

from UV (e.g., sunlight) exposure. 

Storage areas should meet both specifications and manufacturer’s storage requirements. 

Materials should be stored off the ground to protect reinforcement from mud, dirt, and debris. 

Geosynthetic reinforcements should not be exposed to temperatures greater than 140o F 

(60oC) and manufacturer's recommendations should be followed in regards to UV protection 

from direct sunlight. 

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Figure 11-2. Inspect reinforcing elements: top photo shows a variety of reinforcements 

including metallic strips, welded wire mesh, and geosynthetics and bottom photo 

shows reinforcement length painted on geogrid reinforcement. 

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At the time of installation, the reinforcement should be rejected if it has defects, flaws, 

deterioration, or damage incurred during manufacture, transportation, or storage. Metal 

reinforcements should not contain bent, cut or repaired (e.g., welded or bent and 

straightened) sections without approval of the MSE wall or RSS design engineer of record. 

Geosynthetics should not contain tears, cuts or punctures and should be replaced or repaired 

at the direction of the design engineer. 

11.2.3 Facing Joint Materials 

Bearing pads (HDPE, EPDM, PVC and neoprene), joint filler and joint cover (e.g., 

geotextiles) should be properly packaged to minimize damage in unloading and handling. 

For example, polymer filler material and geotextiles, as previously indicated, must be 

protected from sunlight during storage. 

Although these items are often considered as miscellaneous materials, it is important for the 

inspector to recognize that use of the wrong material or its incorrect placement can result in 

significant structure distress. Properties of these materials must be checked, either based on 

laboratory tests submitted by the supplier or preapproval (e.g., from a qualified products list), 

for conformance with specification requirements. Samples should be sent to the laboratory 

for verification testing. 

11.2.4 Reinforced Backfill 

The backfill in MSE/RSS structures is the key element in satisfactory performance. Both use 

of the appropriate material and its correct placement are important considerations. 

Reinforced backfill is normally specified to meet certain gradation, plasticity, soundness, and 

electrochemical requirements. Depending on the type of contract, tests to ensure compliance 

may be performed by either the contractor or the owner. The tests conducted prior to 

construction and periodically during construction for quality assurance form the basis for 

approval. During construction these tests include gradation and plasticity index testing at the 

rate required in the agency’s or project-specific specifications (e.g., typically one test per 

2000 yd3 (1500 m3

) of material placed on large projects) and whenever the appearance and 

behavior of the backfill changes noticeably. 

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11.3 CONSTRUCTION CONTROL 

Each of the steps in the sequential construction of MSE and RSS systems is controlled by 

certain method requirements and tolerances. Construction manuals for proprietary MSE 

systems should be obtained from the contractor to provide guidance during construction 

monitoring and inspection. A detailed description of general construction requirements for 

MSE walls follows with requirements that apply to RSS systems noted. 

11.3.1 Leveling Pad 

A concrete leveling pad should have minimum dimensions in conformance with the plans 

and specifications (typically 6 inches {150 mm} thick by the panel width plus 8 in. {200 

mm} wide). The concrete compressive strength should also meet minimum specification 

requirements. Curing of cast-in-place pads should follow the requirements in the 

specifications (e.g., typically a minimum of 12 to 24 hours before facing units are placed). 

Careful inspection of the leveling pad to assure correct line, grade, and offset is important. A 

vertical tolerance of 1⁄8-inch (3 mm) to the design elevation is recommended. If the leveling 

pad is not at the correct elevation, the wall will likely be difficult to construct and the 

leveling pad elevation should be corrected. An improperly placed leveling pad can result in 

subsequent facing unit misalignment, cracking, and spalling. Full height precast facing 

elements may require a larger leveling pad to maintain alignment and provide temporary 

foundation support. Gravel pads of suitable dimensions may be used with modular block 

walls used for landscaping type applications. Typical installations are shown on Figure 11-3. 

11.3.2 Erection of Facing Elements 

Precast facing panels are purposely set at a slight backward batter (toward the reinforced fill) 

in order to assure correct final vertical alignment after backfill placement as shown on Figure 

11-4. Minor outward movement of the facing elements from wall fill placement and 

compaction cannot be avoided and is expected as the interaction between the reinforcement 

and reinforced backfill occurs. Typical backward batter for segmental precast panels is 1⁄2-in. 

in 4 ft (20 mm per meter) of panel height with steel reinforcements. Modular block units are 

typically stacked with an offset 1⁄2 to 1 in. to account for horizontal movements. 

Full height precast panels as shown on Figure 11-5 are more susceptible cracking during 

backfilling and misalignment difficulties than segmental panels. When using full-height 

panels, the construction procedure should be carefully controlled to maintain tolerances. 

Special construction procedures such as additional bracing and larger face panel batter may 

be necessary. 

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(a) (b) 

(c) 

 Figure 11-3. Concrete leveling pad showing: a) leveling the concrete, b) completed 

pad, and c) placing the facing elements on the leveling pad. 

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Figure 11-4. Checking facing element batter and alignment. 

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MSE Walls and RSS – Vol II 11 – 18 November 2009 
 

Figure 11-5. Full height facing panels require special alignment care. 

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First Row of Facing Elements. Setting the first row of facing elements is a key detail as 

shown in Figure 11-6. Construction should always begin adjacent to any existing structure 

and proceed toward the open end of the wall. The facing units should be set directly on the 

concrete leveling pad. Horizontal joint material or shims generally should not be permitted 

between the first course of panels and the leveling pad unless specifications specifically 

allow for and provide detail requirements (e.g., material type, properties, maximum thickness 

(e.g., 1/16-inch, 1/8-inch) and other dimensional requirements) for such materials. 

Temporary wood wedges may be used between the first course of concrete panels and the 

leveling pad to set panel batter, but they must be removed during subsequent construction. 

Some additional important details are: 

C The first row of segmental panels must be braced until the bottom several layer(s) of 

reinforcements has been backfilled. Adjacent panels should be clamped together to 

prevent individual panel displacement. 

C After setting and battering the first row of panels or placing the first row of modular 

blocks, horizontal alignment should be visually checked (i.e., with survey instruments or 

with a string-line). 

C When using full-height panels, initial bracing and clamping are even more critical 

because misalignments are difficult to correct as construction continues. 

C Most MSE systems use a variety of panel sizes to best fit the wall envelope. Special 

panels or modular block types may also be used to accommodate aesthetic treatments 

design requirements (geometric shape, size, color, finish, connection points). The facing 

element types must be checked to make sure that they are installed exactly as shown on 

the plans. 

C A geotextile filter should be placed over the back of the area of any openings between the 

facing units and the leveling pad. The geotextile should extend a minimum of 6-in. (150 

mm) beyond the edges of the openings. For large openings > than 1 in. (25 mm) in width 

(such as where stepped leveling pads are required or wall drain outlets are placed over the 

leveling pad), the openings should either be filled in with concrete or the section should 

be concurrently backfilled on both sides of the facing unit with soil. 

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Figure 11-6. Setting first row of precast facing elements. 

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11.3.3 Reinforced Fill Placement, Compaction 

Moisture and density control is imperative for construction of MSE and RSS systems. Even 

when using high-quality granular materials, problems can occur if compaction control is not 

exercised. Reinforced wall fill material should be placed and compacted at or within 2 

percent dry of the optimum moisture content. If the reinforced fill is free draining with less 

than 5 percent passing a No. 200 (0.075 mm) U.S. Sieve, water content of the fill may be 

within ±3 percentage points of the optimum. Placement moisture content can have a 

significant effect on reinforcement-soil interaction. Moisture content wet of optimum makes 

it increasingly difficult to maintain an acceptable facing alignment, especially if the fines 

content is high. Moisture contents that are too dry may not achieve required density and 

could result in significant settlement during periods of precipitation (i.e., due to bulking). 

A density of 95 percent of T-99 maximum value or 90 percent of T-180 is typically 

recommended for retaining walls and slopes, and 100 percent of T-99 or 95% of T-180 is 

usually recommended for abutments and walls or slopes supporting structural foundations. 

A procedural specification is preferable where a significant percentage of coarse material, 

generally 30 percent or greater retained on the 3⁄4-inch (19 mm) sieve, prevents the use of the 

AASHTO T-99 or T-180 test methods. In this situation, typically four to five passes with 

conventional vibratory roller compaction equipment is adequate to attain the maximum 

practical density. The actual requirements should be determined based on a test section as 

discussed in Chapter 3, Section 3.2.1. 

Reinforced backfill should be dumped onto or parallel to the rear and middle of the 

reinforcements and bladed toward and away from the front face as shown on Figure 11-7. At 

no time should any construction equipment be in direct contact with the reinforcements 

because the reinforcements can be damaged. Soil layers should be compacted up to 2 in. 

(50 mm) above but no less than even with the elevation of each level of reinforcement 

connections prior to placing that layer of reinforcing elements. 

Compaction Equipment - With the exception of the 3-foot (1-m) zone directly behind the 

facing elements or slope face, large, smooth-drum, vibratory rollers should be used to obtain 

the desired compaction as shown on Figure 11-8a. Sheepsfoot and grid type rollers should 

not be permitted because of possible damage to the reinforcements. When compacting 

uniform medium to fine sands (in excess of 60 percent passing a No. 40 sieve) use a smoothdrum static roller or lightweight (walk behind) vibratory roller, especially for the last pass. 

The use of large vibratory compaction equipment with this type of backfill material will 

make wall alignment control difficult and actually may loosen the upper surface of the soil. 

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Figure 11-7. Placement of reinforced fill. 

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Figure 11-8.	 Compaction equipment showing: a) large equipment permitted away 

from face; and b) lightweight equipment within 3 ft (1 m) of the face. 

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Within 3 ft (1 m) of the wall or slope face, use small single or double drum, walk-behind 

vibratory rollers or vibratory plate compactors as shown in Figure 11-8b. Placement of the 

reinforced backfill near the front should not lag behind the remainder of the structure by 

more than one lift. Poor fill placement and compaction in this area has in some cases 

resulted in facing movement and/or downdrag on reinforcements, which increases connection 

stresses. Within this 3 ft (1 m) zone, quality control should be maintained by a method 

specification such as four passes of a light, walk-behind vibratory plate or drum compactor. 

Test pads should be constructed to determine the actual number of passes and lift thickness 

required to achieve compaction requirements with the compaction equipment to be used. 

Higher quality fill is sometimes used in this zone so that the desired properties can be 

achieved with less compactive effort. Excessive compactive effort or use of too heavy 

equipment near the wall face could result in excessive face unit movement (segmental panels 

and modular blocks) or structural damage (full-height, precast panels), and overstressing of 

reinforcement layers. For welded wire wall facing systems, caution must be exercised such 

that struts do not become dislodged during placement of backfill and compaction, which 

could jeopardize the wall face integrity. 

Inconsistent compaction and undercompaction caused by insufficient compactive effort or 

allowing the contractor to "compact" backfill with trucks and dozers will lead to gross 

misalignments and settlement problems and should not be permitted. Flooding of the backfill 

to facilitate compaction should also not be permitted. Compaction control testing of the 

reinforced backfill should be performed on a regular basis during the entire construction 

project. A minimum frequency of one test within the reinforced soil zone per lift for every 

150 ft (45 m) of wall is recommended. 

11.3.4 Placement of Reinforcing Elements 

Reinforcing elements for MSE and RSS systems should be installed in strict compliance with 

spacing and length requirements shown on the plans. Reinforcements should generally be 

placed perpendicular to the back of the facing panel. In specific situations (e.g., abutments 

and curved walls) it may be permissible to skew the reinforcements from their design 

location in either the horizontal or vertical direction. Skewing should not exceed the limits 

defined in the specifications and overlapping layers of reinforcements should be separated by 

3-in. (75-mm) minimum thickness of fill. 

Curved walls create special considerations with MSE panel and reinforcement details. 

Different placement procedures are generally required for convex and concave curves. For 

reinforced fill systems with precast panels or modular blocks, joints will either be further 

closed or opened by nominal facing movements that normally occur during construction. 

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Special considerations also arise when constructing MSE/RSS structures around deep 

foundation elements or drainage structures. For deep foundations either drive piles prior to 

face construction or use hollow sleeves at proposed pile locations during reinforced fill 

erection. The latter method is generally preferred. Predrilling for pile installation through 

the reinforced soil structure between reinforcements is risky and should be avoided. 

Reinforcement skew to avoid obstructions must be within specification tolerances and in no 

case should reinforcements be cut or excessively bent. 

Connections. Each MSE system has a unique facing connection detail. Several types of 

connections are shown on Figure 11-9. Connections are manufacturer specific and must be 

made in accordance with the approved drawings. For example on Reinforced Earth 

structures bolts are inverted between tie strips making a connection that acts in shear (i.e., 

double shear on the connector). Nuts are securely tightened with hand tools. 

Flexible reinforcements, such as geotextiles and geogrids, usually require pretensioning to 

remove any slack in the reinforcement and in the connection to the facing unit. The tension 

is then maintained by staking or by placing fill during tensioning. Tensioning and staking 

will reduce subsequent horizontal movements of the panel as the wall fill is placed. 

11.3.5 Placement of Subsequent Facing Courses (Segmental Facings) 

Throughout construction of segmental panel walls, facing panels should only be set at grade. 

Placement of a panel on top of one not completely backfilled should not be permitted. 

Alignment Tolerances. The key to a satisfactory end product is maintaining reasonable 

horizontal and vertical alignments during construction. Generally, the degree of difficulty in 

maintaining vertical and horizontal alignment increases as the vertical distance between 

reinforcement layers increases. The following alignment tolerances are recommended: 

C Adjacent facing panel joint gaps (all reinforcements): 3⁄4-inch ± 1⁄4-inch (19 mm ± 6 mm) 

C Precast face panel (all reinforcements): 1/2-inch per 10 ft (6 mm per m) (horizontal and 

vertical directions) 

C Wrapped face walls and slopes (e.g., welded wire or geosynthetic facing): 2-inch per 10 

ft (15 mm per m) (horizontal and vertical directions) 

C Wrapped face walls and slopes (e.g., welded wire or geosynthetic facing) overall vertical: 

1-inch per 10 ft (8 mm per m) 

C Wrapped face walls and slopes (e.g., welded wire or geosynthetic facing) bulging: 1 to 2 

inches (25 to 50 mm) maximum 

C Reinforcement placement elevations: 1-inch (25 mm) of connection elevation 

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Figure 11-9. Facing connection examples. 

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Failure to attain these tolerances when following suggested construction practices indicates 

that changes in the contractor's procedures are necessary. These might include changes in 

reinforced backfill placement and compaction techniques, construction equipment, and 

facing panel batter. 

Facing elements that are out of alignment should not be pushed or pulled into place because 

this may damage the panels and reinforcements and, hence, weaken the system. Appropriate 

measures to correct an alignment problem are the removal of reinforced fill and reinforcing 

elements, followed by the resetting of the panels. Decisions to reject structure sections that 

are out of alignment should be made expediently because panel resetting and reinforced fill 

handling are time consuming and expensive. “Post erection" deformations may be an 

indication of foundation, drainage (i.e., if after a heavy rain). or retained soil problems and 

should be evaluated immediately by qualified geotechnical specialists. 

All material suppliers use bearing pads (HDPE, EPDM, PVC or neoprene are typically used) 

on horizontal joints between segmental facing panels to keep the panel joints open. The 

thickness of the bearing pads is based on the amount of anticipated short term and long term 

settlement. Pads that are two thin could result in cracking and spalling of panels due to point 

stresses and excessively large panel joint openings may result in an unattractive end product. 

Filter materials (usually geotextiles) are used to prevent erosion of fill through the facing 

joints while allowing water to pass. These materials should be installed in strict accordance 

with the plans and specifications, especially with regard to type of material, thickness of 

bearing pads, opening characteristics of geosynthetics, and quantity. Geotextile joint covers 

and bearing pads are shown on Figure 11-10. 

Wooden wedges shown on Figure 11-6 placed during erection to aid in alignment should 

remain in place until the third layer of segmental panels are set, at which time the bottom 

layer of wedges should be removed. Each succeeding layer of wedges should be removed as 

the succeeding panel layer is placed. When the wall is completed, all temporary wedges 

should be removed. 

At the completion of each day's work, the contractor should grade the wall fill away from the 

face and lightly compact the surface to reduce the infiltration of surface water from 

precipitation. At the beginning of the next day's work, the contractor should scarify the 

backfill surface, especially backfills containing fines, to prevent shear planes from 

developing between lifts. 

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(a) 

(b) 

Figure 11-10. Joint materials: a) geotextile joint cover, and b) EPDM bearing pads. 

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A summary of several out-of-tolerance conditions and their possible causes is presented in 

Table 11-4. 

Table 11-4. Out-of-Tolerance Conditions and Possible Causes. 

MSEW structures are to be erected in strict compliance with the structural and aesthetic 

requirements of the plans, specifications, and contract documents. The desired results can 

generally be achieved through the use of quality materials, correct construction/erection 

procedures, and proper inspection. However, there may be occasions when dimensional tolerances 

and/or aesthetic limits are exceeded. Corrective measures should quickly be taken to bring the 

work within acceptable limits. Presented below are several out-of-tolerance conditions and their 

possible causes. 

CONDITION	 POSSIBLE CAUSE 

1. Distress in wall: 1. a. Foundation (subgrade) material too 

a. Differential settlement or low spot in 

wall. (Cause 1. a & b apply)	 

b. Overall wall leaning beyond vertical 

alignment tolerance. (Cause 1 a&b) 

 

b. 

soft or wet for proper bearing.

Fill material of poor quality or not 

properly compacted. 

c. Spalling, chipping, or cracking of 

facing units (Cause 1 a – e apply) 

(e.g., from panel to panel contact or 

differential movement of modular 

c. 

d. 

Inadequate spacing in horizontal

and vertical joints 

Use of improper bearing pads 

block facing units). e. Stones or concrete pieces between 

facing units (e.g. units not clean or 

used to level face units) 

2. First panel course difficult (impossible) 2. a. Leveling pad not level. 

to set and/or maintain level. 

3. Wall out of vertical alignment tolerance 3. a. Panel not battered sufficiently. 

(plumbness), or leaning out. b. Oversized compaction equipment 

working within 3 ft (1 m) of wall 

facing panels. 

 c. Backfill material placed wet of 

optimum moisture content. Backfill 

contains excessive fine materials 

(beyond the specifications for percent 

of materials passing a No. 200 sieve). 

 d. Backfill material pushed against back 

of facing panel before being placed 

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and compacted above reinforcing 

elements. 

e. Excessive compaction of uniform, 

medium-fine sand (more than 60 

percent passing a No. 40 sieve). 

f. Backfill material dumped close to free 

end of reinforcing elements, then 

spread toward wall face, causing 

displacement of reinforcements and 

pushing panel out. 

g. Shoulder wedges not seated securely. 

h. Shoulder clamps not tight. 

i. Slack in reinforcement to facing 

connections. 

j. Inconsistent tensioning of 

geosynthetic reinforcement to facing. 

k. Localized over-compaction adjacent 

to MBW unit. 

4. Wall out of vertical alignment tolerance 

(plumbness) or leaning in. 

4. a. Excessive batter set in panels or offset 

in modular block units for select 

granular backfill material being used. 

b. Inadequate compaction of backfill. 

c. Possible bearing capacity failure. 

5. Wall out of horizontal alignment 

tolerance, or bulging. 

5. a. See Causes 3c, 3d, 3e, 3j, 3k. Backfill 

saturated by heavy rain or improper 

grading of backfill after each day's 

operations. 

6. Panels do not fit properly in their 

intended locations. 

6. a. Panels are not level. Differential 

settlement (see Cause 1). 

b. Panel cast beyond tolerances. 

7. Large variations in movement of 

adjacent panels. 

7. a. 

b. 

Backfill material not uniform. 

Backfill compaction not uniform. 

c. Inconsistent setting of facing panels 

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Table 11-5. Checklist for Construction. (after FHWA NHI-08-094/095) 

YES NO NA 

1.0 DOCUMENTS AND PLANS 

1.1 Has the Contractor furnished a copy of the installation plans or instructions 

from the MSEW or RSS supplier as required by the Specifications? 

1.2 Have the installation plans or instructions been approved by the Designer 

and/or Construction Division Manager? 

1.3 Have stockpile and staging areas been discussed and approved? 

1.4 Have access routes and temporary haul roads been discussed and 

approved? 

2.0 LAYOUT 

2.1 Has the contractor staked out sufficient horizontal and vertical control 

points, including points required for stepped foundations? 

2.2 Has the contractor accounted for wall batter when staking the base of the 

wall? 

2.3 Have drainage features and all utilities been located and marked? 

2.4 Have Erosion & Sedimentation Controls been installed? 

3.0 FOUNDATION PREPARATION 

3.1 Has the MSEW or RSS foundation area been excavated to the proper 

elevation? 

3.2 Has the foundation subgrade been inspected (e.g., proof rolled) as required 

by the specifications? 

3.3 Has all soft or loose material been compacted or unsuitable materials (e.g., 

wet soil, organics) been removed and replaced? 

3.4 Has the leveling-pad (if applicable) area been properly excavated and set to 

the proper vertical and horizontal alignment? 

3.5 Has the leveling pad (if applicable) cured for the specified time (typically 

at least 12 hours) before the Contractor sets any facing panels? 

4.0 DRAINAGE 

4.1 Is the drainage being installed in the correct location? 

4.2 Are drainage aggregates being kept free of fine materials? 

4.3 Are all holes, rips and punctures in geotextiles being repaired in 

accordance with the specifications? 

4.4 Are composite drain materials being placed with the proper side to the 

seepage face? 

4.5 Do all collection and outlet pipes have a positive slope? 

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YES NO NA 

5.0 FACING 

5.1 Is the first row of facing panels (when applicable) properly placed? Do 

they have proper spacing, bracing, batter, and do they have the wood 

spacers installed? 

5.2 Is the Contractor using the correct facing unit (correct size, shape, color, 

and with the proper number of connections) for the applicable location and 

elevation? 

5.3 Is a geotextile filter being properly placed over joints in the facing panels? 

5.4 Are the lower tiers of facing baskets (when applicable) properly placed? 

Are they setback correctly to result in the designed slope angle? Are the 

struts spaced correctly? 

5.5 Have secondary reinforcing layers (e.g., biaxial geogrid) and vegetated 

matting (where applicable) been properly placed? Are they setback 

correctly to result in the designed slope angle? 

5.6 Is the vertical elevation and horizontal alignment being checked 

periodically and adjusted as needed? 

5.7 Is the contractor removing the wooden wedges as per the specifications? 

(Typically removed as soon as soon as erection and backfilling the panel 

above the wedged panel is completed.) 

5.8 Is the spacing between individual facing units (or for RSS and wrapped face 

walls, overlap of reinforcement) in accordance with the specifications? 

6.0 REINFORCING 

6.1 Is the reinforcement being properly connected (connections tight and all of 

the slack in the reinforcing layers removed) 

6.2 Is the reinforcement in the proper alignment? 

6.3 Is the reinforcement the right type? 

6.4 Is the reinforcement the correct length? 

6.5 Is the reinforcement being placed at the correct spacing and location? 

6.6 Is the fill being brought up to 2” above the soil reinforcement elevation 

before the reinforcement is connected? 

6.7 Is construction equipment being kept from operating directly on the 

reinforcement (i.e., until adequate soil cover is placed over the 

reinforcement)? 

7.0 BACKFILL 

7.1 At the end of each day's operation is the Contractor grading the upper 

surface of reinforced and retained soil to ensure runoff of storm water 

away from the MSEW or RSS face or provide a positive means of 

controlling runoff away from the construction area? 

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YES NO NA 

7.2 Where applicable, has the Contractor backfilled in front of the MSEW or 

RSS? 

7.3 Is the Contractor placing the reinforced soil in lifts that are thin enough to 

ensure good compaction, but thick enough not to damage the 

reinforcement? 

7.4 If the Contractor is using water to adjust the moisture of the reinforced, 

retained, or facing soil, does it meet the requirements set forth in the 

specifications? 

7.5 Is the reinforced soil being placed to prevent damage to the reinforcement? 

7.6 Are the lifts being spread to prevent excessive tension or excess slack in 

the reinforcement? 

7.7 Is the fill being compacted using the correct equipment and in the correct 

pattern? 

7.8 Is the soil moisture content within the specified range? 

7.9 Is the soil compaction (dry density) within the specified range? 

7.10 Is large compaction equipment being kept at least 3’ from the face? 

8.0 ANCILLARY ITEMS AND FINISHED PRODUCT 

8.1 Could installation of ancillary components (e.g., catch basins, storm-water 

piping, guardrail) affect the reinforcing or facing components already 

installed? 

8.2 Have ancillary items been installed in accordance with the drawings and 

specifications? 

8.3 Are ancillary items being installed at the proper locations? 

8.4 Are diversion ditches, collection ditches, or slope drains installed in 

accordance with the drawings and specifications? 

8.5 Is permanent or temporary erosion control blanket installed at the required 

locations and using the details shown on the drawings? 

8.6 Are there any visible signs of MSEW or RSS tilting, bulging, or 

deflecting? 

8.7 Has the vertical and horizontal alignment been confirmed by survey? 

8.8 Is there a need to confirm the vertical or horizontal alignment at a future 

time to evaluate whether movement is occurring? 

8.9 Are there any signs of distress to the facing components (e.g., fracturing or 

spalling of concrete panels, bowing of wire baskets, etc)? 

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11.4 PERFORMANCE MONITORING PROGRAMS 

Since MSE wall and RSS technologies are well established, the need for monitoring 

programs should be limited to cases in which new features or materials have been 

incorporated in the design, substantial post construction settlements are anticipated and/or 

construction rates require control, where degradation/corrosion rates of reinforcements are to 

monitored (e.g., to allow use of marginal fills), or for asset management. 

Degradation/Corrosion monitoring schemes are fully outlines in the companion Corrosion/ 

Degradation document. 

11.4.1 Purpose of Monitoring Program 

The first step in planning a monitoring program is to define the purpose of the measurements. 

Every instrument on a project should be selected and placed to assist in answering a specific 

question. 

If there is no question, there should be no instrumentation. Both the questions that need to
 

be answered and the clear purpose of the instrumentation in answering those questions 

should be established. The most significant parameters of interest should be selected, with 

care taken to identify secondary parameters that should be measured if they may influence 

primary parameters. 

Important parameters that may be considered include: 

C Horizontal movements of the face (for MSEW structures). 

C Vertical movements of the surface of the overall structure. 

C Local movements or deterioration of the facing elements. 

C Drainage behavior of the backfill. 

C Performance of any structure supported by the reinforced soil, such as approach slabs for 

bridge abutments or footings. 

C Horizontal movements within the overall structure. 

C Vertical movements within the overall structure. 

C Lateral earth pressure at the back of facing elements. 

C Vertical stress distribution at the base of the structure. 

C Stresses in the reinforcement, with special attention to the magnitude and location of the 

maximum stress. 

C Stress distribution in the reinforcement due to surcharge loads. 

C Relationship between settlement and stress-strain distribution. 

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C Stress relaxation in the reinforcement with time. 

C Aging condition of reinforcement such as metal losses due to corrosion or degradation of 

polymeric reinforcements. 

C Pore pressure response below structure. 

C Temperature which often is a cause of real changes in other parameters, and also may 

affect instrument readings. 

C Rainfall which often is a cause of real changes in other parameters. 

C Barometric pressure, which may affect readings of earth pressure and pore pressure 

measuring instruments. 

The characteristics of the subsurface, backfill material, reinforcement, and facing elements in 

relation to their effects on the behavior of the structure must be assessed prior to developing 

the instrumentation program. It should be remembered that foundation settlement will affect 

stress distribution within the structure. Also, the stiffness of the reinforcement will affect the 

anticipated lateral stress conditions within the retained soil mass. 

11.4.2 Limited Monitoring Program 

Limited observations and monitoring that should be performed on practically all structures 

will typically include: 

C Horizontal and vertical movements of the face (for MSEW structures). 

C Vertical movements of the surface of the overall structure. 

C Local movements or deterioration of the facing elements. 

C Performance of any structure supported by the reinforced soil, such as approach slabs for 

bridge abutments or footings. 

Horizontal and vertical movements can be monitored by surveying methods, using suitable 

measuring points on the retaining wall facing elements or on the pavement or surface of the 

retained soil. Permanent benchmarks are required for vertical control. For horizontal 

control, one horizontal control station should be provided at each end of the structure. 

The maximum lateral movement of the wall face during construction is anticipated to be on 

the order of H/250 for inextensible reinforcement and H/75 for extensible reinforcement. 

Tilting due to differential lateral movement from the bottom to the top of the wall would be 

anticipated to be less than 1⁄4-inch per 5 ft (4 mm per m) of wall height for either system. 

Post-construction horizontal movements are anticipated to be very small. Post construction 

vertical movements should be estimated from foundation settlement analyses, and 

measurements of actual foundation settlement during and after construction should be made. 

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11.4.3 Comprehensive Monitoring Program 

Comprehensive studies involve monitoring of surface behavior as well as internal behavior of 

the reinforced soil. A comprehensive program may involve the measurement of nearly all of 

the parameters enumerated above and the prediction of the magnitude of each parameter at 

working stress to establish the range of accuracy for each instrument. 

Whenever measurements are made for construction control or safety purposes, or when used 

to support less conservative designs, a predetermination of warning levels should be made. 

An action plan must be established, including notification of key personnel and design 

alternatives so that remedial action can be discussed or implemented at any time. 

A comprehensive program may involve all or some of the following key purposes: 

C Deflection monitoring to establish gross structure performance and as an indicator of the 

location and magnitude of potential local distress to be more fully investigated. 

C Structural performance monitoring to primarily establish tensile stress levels in the 

reinforcement and or connections. A second type of structural performance monitoring 

would measure or establish degradation rates of the reinforcements. 

C Pullout resistance proof testing to establish the level of pullout resistance within a 

reinforced mass as a function of depth and elongation. 

The possible instruments for monitoring are outlined in Table 11-6. 

11.4.4 Program Implementation 

Selection of instrument locations involves three steps. First, sections containing unique 

design features are identified. For example, sections with surcharge or sections with the 

highest stress. Appropriate instrumentation is located at these sections. Second, a selection 

is made of cross sections where predicted behavior is considered representative of behavior 

as a whole. These cross sections are then regarded as primary instrumented sections, and 

instruments are located to provide comprehensive performance data. There should be at least 

two "primary instrumented sections." Third, because the selection of representative zones 

may not be representative of all points in the structure, simple instrumentation should be 

installed at a number of "secondary instrumented sections" to serve as indices of comparative 

behavior. For example, surveying the face of the wall in secondary cross sections would 

examine whether comprehensive survey and inclinometer measurements at primary sections 

are representative of the behavior of the wall. 

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Table 11-6. Possible Instruments for Monitoring Reinforced Soil Structures. 

PARAMETERS POSSIBLE INSTRUMENTS 

Horizontal movements of face Visual observation 

Surveying methods 

Horizontal control stations 

Tiltmeters 

Vertical movements of overall structure Visual observation 

Surveying methods 

Benchmarks 

Tiltmeters 

Local movements or deterioration of facing 

elements 

Visual observation 

Crack gauges 

Drainage behavior of backfill Visual observation at outflow points 

Open standpipe piezometers 

Horizontal movements within overall structure Surveying methods 

Horizontal control stations 

Probe extensometers 

Fixed embankment extensometers 

Inclinometers 

Tiltmeters 

Vertical movements within overall structure Surveying methods 

Benchmarks 

Probe extensometers 

Horizontal inclinometers 

Liquid level gauges 

Performance of structure supported by reinforced 

soil 

Numerous possible instruments (depends on 

details of structure) 

Lateral earth pressure at the back of facing 

elements 

Earth pressure cells 

Strain gauges at connections 

Load cells at connections 

Stress distribution at base of structure Earth pressure cells 

Stress in reinforcement Resistance strain gauges 

Induction coil gauges 

Hydraulic strain gauges 

Vibrating wire strain gauges 

Multiple telltales 

Stress distribution in reinforcement due to 

surcharge loads 

Same instruments as for stress in reinforcement 

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PARAMETERS POSSIBLE INSTRUMENTS 

Relationship between settlement and stress-strain 

distribution 

Same instruments as for: 

C vertical movements of surface of overall 

C 

structure 

vertical movements within mass of overall 

structure 

C stress in reinforcement 

Earth pressure cells 

Stress relaxation in reinforcement Same instruments as for stress in reinforcement 

Total stress within backfill and at back of 

reinforced wall section 

Earth pressure cells 

Pore pressure response below structures Open standpipe piezometers 

Pneumatic piezometers 

Vibrating wire piezometers 

Temperature Ambient temperature record 

Thermocouples 

Thermistors 

Resistance temperature devices 

Frost gauges 

Rainfall Rainfall gauge 

Barometric pressure Barometric pressure gauge 

Access to instrumentation locations and considerations for survivability during construction 

are also important. Locations should be selected, when possible, to provide cross checks 

between instrument types. For example, when multipoint extensometers (multiple telltales) 

are installed on reinforcement to provide indications of global (macro) strains, and strain 

gauges are installed to monitor local (micro) strains, strain gauges should be located midway 

between adjacent extensometer attachment points. 

Most instruments measure conditions at a point. In most cases, however, parameters are of 

interest over an entire section of the structure. Therefore, a large number of measurement 

points may be required to evaluate such parameters as distribution of stresses in the 

reinforcement and stress levels below the retaining structure. For example, accurate location 

of the locus of the maximum stress in the reinforced soil mass will require a significant 

number of gauge points, usually spaced on the order of 1-foot (300 mm) apart in the critical 

zone. Reduction in the number of gauge points will make interpretation difficult, if not 

impossible, and may compromise the objectives of the program. 

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In preparing the installation plan, consideration should be given to the compatibility of the 

installation schedule and the construction schedule. If possible, the construction contractor 

should be consulted concerning details that might affect his operation or schedule. 

Step-by-step installation procedures should be prepared well in advance of scheduled 

installation dates for installing all instruments. Detailed guidelines for choosing instrument 

types, locations and installation procedures are given in FHWA RD 89-043 (Christopher et 

al., 1989) and FHWA HI-98-034 (Dunnicliff, 1998). 

11.4.5 Data Interpretation 

Monitoring programs have failed because the data generated was never used. If there is a 

clear sense of purpose for a monitoring program, the method of data interpretation will be 

guided by that sense of purpose. Without a purpose, there can be no interpretation. 

When collecting data during the construction phase, communication channels between design 

and field personnel should remain open so that discussions can be held between design 

engineers who planned the monitoring program and field engineers who provide the data. 

Early data interpretation steps should have already been taken, including evaluation of data, 

to determine reading correctness and also to detect changes requiring immediate action. The 

essence of subsequent data interpretation steps is to correlate the instrument readings with 

other factors (cause and effect relationships) and to study the deviation of the readings from 

the predicted behavior. 

After each set of data has been interpreted, conclusions should be reported in the form of an 

interim monitoring report and submitted to personnel responsible for implementation of 

action. The report should include updated summary plots, a brief commentary that draws 

attention to all significant changes that have occurred in the measured parameters since the 

previous interim monitoring report, probable causes of these changes, and recommended 

action. 

A final report is often prepared to document key aspects of the monitoring program and to 

support any remedial actions. The report also forms a valuable bank of experience and 

should be distributed to the owner and design consultant so that any lessons may be 

incorporated into subsequent designs. 

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MSE Walls and RSS – Vol II 11 – 40 November 2009
 
 

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NCMA (2009). Design Manual for Segmental Retaining Walls, National Concrete Masonry 

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FHWA NHI-10-025 References 

MSE Walls and RSS – Vol II R – 12 November 2009
 
 

 

APPENDIX A 

LRFD LOAD NOTATION, 

LOAD COMBINATIONS, AND LOAD FACTORS 

FHWA NHI-10-025 Appendix A – LRFD Factors & Nomenclature 

MSE Walls and RSS – Vol II A –1 November 2009
 
 

 

A.1 LOAD NOTATION 

From AASHTO 3.3.2, the following notation is used for permanent and transient loads and 

forces. 

Permanent Loads 

CR = Force effects due to creep 

DD = Downdrag force 

DC = Dead load of structural components and nonstructural attachments 

DW = Dead load of wearing surfaces and utilities 

EH = Horizontal earth loads 

EL = Miscellaneous locked-in force effects resulting from the construction 

process, including jacking apart cantilevers in segmental construction 

ES = Earth surcharge load 

EV = Vertical pressure from dead load of earth fill 

PS = Secondary forces from post-tensioning 

SH = Force effects due shrinkage 

 

Transient Loads 

BR = Vehicular braking force 

CE = Vehicular centrifugal force 

CT = Vehicular collision force 

CV = Vessel collision force 

EQ = Earthquake load 

FR = Friction load 

IC = Ice load 

IM = Vehicular dynamic load allowance 

LL = Vehicular live load 

LS = Live load surcharge 

PL = Pedestrian live load 

SE = Force effect due to settlement 

TG = Force effect due to temperature gradient 

TU = Force effect due to uniform temperature 

WA = Water load and stream pressure 

WL = Wind on live load 

WS = Wind load on structure 

FHWA NHI-10-025 Appendix A – LRFD Factors & Nomenclature 

MSE Walls and RSS – Vol II A –2 November 2009 
 

 

 

 

 

 

 

A.2 LOAD COMBINATIONS 

Load combinations and load factors from AASHTO 3.4, Table 3.4.1-1 are listed below. 

Load Combinations and Load Factors (Table 3.4.1-1, AASHTO, 2007) 

Load 

Combination 

Limit State 

DC 

DD 

DW 

EH 

EV 

ES 

EL 

PS 

CR 

SH 

LL 

IM 

CE 

BR 

PL 

LS WA WS WL FR TU TG SE 

Use One of These at a Time 

EQ IC CT CV 

STRENGTH I 

(unless noted) 

γp 1.75 1.00 – – 1.00 0.50/1.20 γTG γSE – – – – 

STRENGTH II γp 1.35 1.00 – – 1.00 0.50/1.20 γTG γSE – – – – 

STRENGTH III γp – 1.00 1.40 – 1.00 0.50/1.20 γTG γSE – – – – 

STRENGTH IV γp – 1.00 – – 1.00 0.50/1.20 – – – – – – 

STRENGTH V γp 1.35 1.00 0.40 1.0 1.00 0.50/1.20 γTG γSE – – – – 

EXTREME 

EVENT I 

γp γEQ 1.00 – – 1.00 – – – 1.00 – – – 

EXTREME 

EVENT II 

γp 0.50 1.00 – – 1.00 – – – – 1.00 1.00 1.00 

SERVICE I 1.00 1.00 1.00 0.30 1.0 1.00 1.00/1.20 γTG γSE – – – – 

SERVICE II 1.00 1.30 1.00 – – 1.00 1.00/1.20 – – – – – – 

SERVICE III 1.00 0.80 1.00 – – 1.00 1.00/1.20 γTG γSE – – – – 

SERVICE IV 1.00 – 1.00 0.70 – 1.00 1.00/1.20 – 1.0 – – – 

FATIGUE – LL, 

IM & CE ONLY 

– 0.75 – – – – – – – – – – – 

FHWA NHI-10-025 Appendix A – LRFD Factors & Nomenclature 

MSE Walls and RSS – Vol II A –3 November 2009
 
 

 

A.3 LOAD FACTORS FOR PERMANENT LOADS 

Load factors for permanent loads, from AASHTO 3.4, Table 3.4.1-2 are listed below. 

Load Factors for Permanent Loads, γp (Table 3.4.1-2, AASHTO, 2007) 

Type of Load, Foundation Type, and 

Method Used to Calculate Downdrag 

Load Factor 

Maximum Minimum 

DC: Component and Attachments 

DC: Strength IV only 

1.25 

1.50 

0.90 

0.90 

DD: Downdrag Piles, α Tomlinson Method 

Piles, Method 

Drilled shafts, O’Neill and Reese (1999) Method 

1.4 

1.05 

1.25 

0.25 

0.30 

0.35 

DW: Wearing Surfaces and Utilities 1.50 0.65 

EH: Horizontal Earth Pressure 

 Active 

 At-Rest 

 AEP for anchored walls 

1.50 

1.35 

1.35 

0.90 

0.90 

N/A 

EL: Locked-in Construction Stresses 1.00 1.00 

EV: Vertical Earth Pressure 

 Overall Stability 

 Retaining Walls and Abutments 

 Rigid Buried Structure 

 Rigid Frames 

 Flexible Buried Structures other than Metal Box Culverts 

 Flexible Metal Box Culverts 

1.00 

1.35 

1.30 

1.35 

1.95 

1.50 

N/A 

1.00 

0.90 

0.90 

0.90 

0.90 

ES: Earth Surcharge 1.50 0.75 

FHWA NHI-10-025 Appendix A – LRFD Factors & Nomenclature 

MSE Walls and RSS – Vol II A –4 November 2009
 
APPENDIX B 

DETERMINATION OF PULLOUT RESISTANCE FACTORS and 

MBW UNIT – GEOSYNTHETIC CONNECTION STRENGTH 

Pullout resistance of soil reinforcement is defined by the ultimate pullout resistance required 

to cause outward sliding of the reinforcement through the soil. Reinforcement specific data 

has been developed and is presented in Chapter 3. The empirical data uses different 

interaction parameters, and it is therefore difficult to compare the pullout performance of 

different reinforcements. 

The method for determining reinforcement pullout presented herein, consists of the 

normalized approach recommended in the FHWA manual FHWA-RD-89-043 (Christopher 

et al., 1990). The pullout resistance, F* is a function of both frictional and passive resistance, 

depending on the specific reinforcement type. The scale effect correction factor, α, is a 

function of the nonlinearity in the pullout load - mobilized reinforcement length relationship 

observed in pullout tests. Inextensible reinforcements usually have little, if any nonlinearity 

in this relationship, resulting in α equal to 1.0, whereas extensible reinforcements can exhibit 

substantial nonlinearity due to a decreasing shear displacement over the length of the 

reinforcement, resulting in an α of less than 1.0. 

Both F* and α must be determined through product specific tests, or empirically/theoretically 

using the procedures provided herein and in Section 3.3, in particular Table 5. It should be 

noted that the empirical procedures provided in this appendix for the determination of F* 

reduce, for the most part, to the equations currently provided in 2007 AASHTO for pullout 

design. 

The pullout resistance of partial/full friction facing/reinforcement connections is defined as 

the load required to cause sliding of the reinforcement relative to the facing blocks or 

reinforcement rupture at the facing connection, whichever occurs first. 

B.1 EMPIRICAL PROCEDURES TO DETERMINE F*

 AND α

Pullout resistance can be estimated empirically/theoretically using the method provided in 

Chapter 3. F* using this method, is calculated as follows: 

F*

 = Frictional Resistance + Passive Resistance 

= Tan ρ + Fq αβ
 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–1 November 2009
 
where Tan ρ is an apparent friction coefficient for the specific reinforcement, ρ is the soilreinforcement interface friction angle, Fq is the embedment (or surcharge) bearing capacity 

factor, and αβ is a structural geometric factor for passive resistance. The determination of 

each of these parameters is provided in Table 5, Chapter 3, with α estimated analytically 

using direct shear test data and the "t-z" method used in the design of friction piles. 

However, since some test data is required and the analytical method is complex, it is better to 

obtain α directly from pullout test data or use conservative default values for α. If pullout 

test data is not available, a default value of 1.0 can be used for α for inextensible 

reinforcements and a default value of 0.6 to 0.8 can be used for extensible reinforcements. 

B.2EXPERIMENTAL PROCEDURES TO DETERMINE F* AND α

Two types of tests are used to obtain pullout resistance parameters: the direct shear test, and 

the pullout test. The direct shear test is useful for obtaining the peak or residual interface 

friction angle between the soil and the reinforcement material. ASTM D-5321 should be 

used for this purpose. In this case, F*

 would be equal to tan ρ * peak. F can be obtained directly 

from this test for sheet and strip type reinforcements. However, the value for α must be 

assumed or analytically derived, as α cannot be determined directly from direct shear tests. 

A pullout test can also be used to obtain pullout parameters for these types of soil 

reinforcement. A pullout test must be used to obtain pullout parameters for bar mat and grid 

type reinforcements, and to obtain values for α for all types of reinforcements. In general, 

the pullout test is preferred over the direct shear test for obtaining pullout parameters for all 

soil reinforcement types. It is recommended that ASTM D6706 test procedure using the 

controlled strain rate method be used. For long-term interaction coefficients, the constant 

stress (creep) method can be used. For extensible reinforcements, it is recommended that 

specimen deformation be measured at several locations along the length of the specimen 

(e.g., three to four points) in addition to the deformation at the front of the specimen. For all 

reinforcement materials, it is recommended that the specimen tested for pullout have a 

minimum embedded length of 24 inches (600 mm). Additional guidance is provided herein 

regarding interpretation of pullout test results. 

For geogrids, the grid joint, or junction strength, must be adequate to allow the passive 

resistance on the transverse ribs to develop without failure of the grid joint throughout the 

design life of the structure. To account for this, F*

 for geogrids should be determined using 

one of the following approaches: 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–2 November 2009
 
C Using quick effective stress pullout tests (i.e., constant rate of displacement method for 

short-term loading condition per ASTM D6706) and creep testing (per ASTM D5262) of 

the geogrid with clamping and loading through-the-junction. 

C Using quick effective stress pullout tests (i.e., constant rate of displacement method for 

short-term loading condition per ASTM D6706), but with the geogrid transverse ribs 

severed. 

C Using quick effective stress pullout tests (i.e., constant rate of displacement method for 

short-term loading condition per ASTM D6706) if the summation of the shear strengths 

of the joints occurring in a 1 ft. (300 mm) length of grid sample is equal to or greater than 

the ultimate strength of the grid element to which they are attached. If this joint strength 

criteria is used, grid joint shear strength should be measured in accordance with 

GRI:GG2 (GRI, 1988). 

C Conduct long-term effective stress pullout tests of the entire geogrid structure in 

accordance with the constant stress (creep) method of ASTM D6706. 

For pullout tests, a normalized pullout versus mobilized reinforcement length curve should 

be established as shown in Figure B-1. Different mobilized lengths can be obtained by 

instrumenting the reinforcement specimen. Strain or deformation measuring devices such as 

wire extensometers attached to the reinforcement surface at various points back from the 

grips should be used for this purpose. A section of the reinforcement is considered to be 

mobilized when the deformation measuring device indicates movement at its end. Note that 

the displacement versus mobilized length plot (uppermost plot in figure) represents a single 

confining pressure. Tests must be run at several confining pressures to develop the Pr versus 

σvLp plot (middle plot in figure). The value of Pr selected at each confining pressure to be 

plotted versus σvLp is the lessor of either the maximum value of Pr (i.e., maximum 

sustainable load), the load which causes rupture of the specimen, or the value of Pr obtained 

at a predefined maximum deflection measured at either the front or the back of the specimen. 

Note that Pr is measured in terms of load per unit reinforcement width. 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–3 November 2009
 
Figure B-1 Experimental procedure to determine F* and α for soil reinforcement using 

pullout test. 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–4 November 2009
 
It is recommended that for inextensible reinforcements, a maximum deflection of 3⁄4-inch (20 

mm) measured at the front of the specimen be used to select Pr if the maximum value for Pr 

or rupture of the specimen does not occur first. For extensible reinforcements, it is 

recommended that a maximum deflection of 15 mm (5/8-inch) measured at the back of the 

specimen be used to select Pr if the maximum value for Pr or rupture of the specimen does 

not occur first. Note that it is acceptable, as an alternative, to define Pr for inextensible 

reinforcements based on a maximum deflection of 5/8-inch (15 mm) measured at the back of 

the specimen as is recommended for extensible reinforcements. 

F* and F* 

peak m are determined from the pullout data as shown in Figure B-1. The method 

provided in this figure is known as the corrected area method (Bonczkiewicz et. al., 1988). 

The determination of α is also illustrated in Figure B-1. Typical values of F*

 and α for 

various types of reinforcements are provided by Christopher (1993). 

Note that the conceptualized curves provided in Figure B-1 represent a relatively extensible 

material. For inextensible materials, the deflection at the front of the specimen will be nearly 

equal to the deflection at the back of the specimen, making the curves in the uppermost plot 

in the figure nearly horizontal. Therefore, whether the deflection criteria to determine Pr for 

inextensible reinforcements is applied at the front of the specimen or at the back of the 

specimen makes little difference. For extensible materials, the deflection at the front of the 

specimen can be considerably greater than the deflection at the back of the specimen. The 

goal of the deflection criteria is to establish when pullout occurs, not to establish some 

arbitrary serviceability criteria. For extensible materials, the pullout test does not model well 

the reinforcement deflections which occur in full scale structures. Therefore, just because 

relatively large deflections occur at the front of an extensible reinforcement material in a 

pullout test when applying the deflection criteria to the back of the specimen does not mean 

that unacceptable deflections will occur in the full scale structure. 

B.3 CONNECTION RESISTANCE AND STRENGTH OF PARTIAL AND FULL 

FRICTION SEGMENTAL BLOCK/REINFORCEMENT FACING 

CONNECTIONS 

For reinforcement connected to the facing through embedment between facing elements 

using a partial or full friction connection (e.g., segmental concrete block faced walls), the 

connection strength can be determined directly through long-term testing of the connection to 

failure. The test set up should be in general accordance with ASTM D6638 with the 

modifications as described in the interim Long-Term Connection Strength Testing Protocol 

described below. Extrapolation of test data should be conducted in general accordance with 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–5 November 2009
 
Appendix D. Tests should be conducted at a confining stress that is greater than or equal to 

the highest confining stress considered for the wall system, and as necessary at additional 

confining stresses below that level to determine behavior for the full range of confining 

stresses anticipated. 

Regardless of the mode of failure extrapolation of the time to failure envelope must be 

determined. Once the failure envelope has been determined, a direct comparison between the 

short-term ultimate strength of the connection and the creep rupture envelope for the 

geosynthetic reinforcement in isolation can be accomplished to determine RFCR. The 

connection strength obtained from the failure envelope must also be reduced by the durability 

reduction factor RFD. This reduction factor should be based on the durability of the 

reinforcement or the connector, whichever is failing in the test. 

If it is determined that the connectors failed during the connection test and not the 

geosynthetic, the durability of the connector, not the geosynthetic, should be used to 

determine the reduction factors for the long-term connection strength in this case. If the 

connectors between blocks are intended to be used for maintaining block alignment during 

wall construction and are not intended for long-term connection shear capacity, the alignment 

connectors should be removed before assessing the connection capacity for the selected 

block-geosynthetic combination. If the pins or other connection devices are to be relied upon 

for long-term capacity, the durability of the connector material must be established. 

The connection strength reduction factor resulting from long term testing, CRcr, is evaluated 

as follows: 

CR crc

cr  (B-1) T lot 

T

where Tcrc is the extrapolated ( 75 - 100 year) connection test strength and Tlot is the ultimate 

wide width tensile strength (ASTM D4595) for the reinforcement material lot used for 

connection strength testing. 

The connection strength reduction factor resulting from quick tests, CRult, is evaluated as 

follows: 

T CR ultconn

ult  (B-2) Tlot 

where Tultconn is the peak connection load at each normal load. 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–6 November 2009
 
Testing Protocol 

Objective: Determine the sustained load capacity of the connection between a modular block 

wall (MBW) facing element and a geosynthetic reinforcing material. 

Method: Construct a test apparatus of full-scale MBW units and geosynthetic reinforcing 

material in a laboratory. Perform a series of tests at different normal loads (confining 

pressures) to model different wall heights, varying the applied load from 95 percent of the 

peak connection capacity determined from the quick connection test (SRWU-1) to 50 percent 

of the peak connection capacity. Measure and record the deflections and time to pullout or 

rupture of the connection. 

Procedure: 

1. Determine index properties of the geosynthetic reinforcing roll being tested: 

a. Wide width tensile strength (ASTM D4595) 

Note: it is preferable to perform the D4595 test on the roll sample being tested and to 

perform the test in the same apparatus being used for the long-term connection 

testing. This will help remove uncertainty in the test results from using different lots 

of the geosynthetic reinforcement material and from comparing test results from 

different test equipment. 

b. Creep rupture envelope for geosynthetic: develop a rupture envelope for the 

specific geosynthetic being tested based on creep rupture tests, Appendix D, using 

the same longitudinal strip of reinforcement. 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–7 November 2009 

 

Creep Load (as a % of the

Ultimate Strength) 

Material Creep Rupture Envelope 

TULT 

75-year life 

1 

Elapsed Time (Hours) 

Figure B-2 Creep Rupture Envelope for Geosynthetic Reinforcement 
2. Determine short-term (quick test) connection properties of the MBW unit/geosynthetic 

reinforcement combination, per ASTM D6638, as modified below. 

a. Construct a test setup in general accordance with the ASTM D6638 test method with 

the following revisions: 

i. Testing shall be carried out on a single width block specimen. Setup shall 

consist of two MBW units at the base with one MBW unit centered over the 

two base units. 

ii. Geosynthetic reinforcement width shall be as close as possible to the length of 

the MBW unit (for geogrids this is dependent on the transverse aperture). In 

no case shall the geosynthetic be wider than the length of the MBW unit. 

iii.	 Geosynthetic specimen shall have sufficient length to cover the interface 

surface as specified by the user. The specimen must be trimmed to provide 

sufficient anchorage at the geosynthetic loading clamp and a free length 

between the back of the MBW units and loading clamp ranging from a 

minimum of 8 in. to a maximum of 24 in. (203 to 610 mm). The same free 

length used for the short-term test shall be used for the long-term test. The 

same longitudinal strip of reinforcement shall be used for all short-term and 

long-term connection tests. 

iv. The temperature in the test space, especially close to the gage length of the 

specimen shall be maintained within ± 2° C (±4° F) of the targeted value. 

v. Where granular infill is required in the connection, half units may be used to 

provide confinement for the granular fill on each side of the single top unit. 

Granular fill may or may not be used in the short-term and long-term test as 

desired. Whichever condition (with or without infill) is selected for the shortterm tests shall be the same for the long-term tests. Where granular infill is 

not required as part of the connection, the single unit may be used. 

vi.	 Normal load shall be applied to the top of the MBW unit to provide the 

desired confining pressure by a mechanism capable of maintaining the desired 

load for a period of not less than one year. (It has been observed that under 

rapid loading some blocks may rotate and short-term instantaneous high 

normal loads can result if the vertical loading system does not have the 

mechanical compliance necessary to dilate. Tests shall be run for a period of 

1,000 hours, however the apparatus should be capable of sustaining loads for 

longer periods if determined later during the test.) 

vii.	 Tension loads shall be applied to the reinforcing member in a direction 

parallel to the connection interface, and in the plane of the connection 

interface. (The mechanism for applying the tensile loads shall be capable of 

sustaining an applied load for periods of not less than one-year.) 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–8 November 2009
 
b. Perform a series of quick tests in accordance with ASTM D6638, as modified above, 

on the MBW unit/ geosynthetic reinforcement combination at different normal loads 

to establish the Tultconn/Normal Load connection curve. 

3. Determine the normal and tensile load levels for sustained load testing on the MBW 

unit/geosynthetic reinforcement combination. 

a. The highest normal load for the sustained load test may not exceed point A (Figure B3) when the Tultconn/Normal load curve is bilinear or multilinear or point B (Figure B3) when the slope of the curve is linear. Tultconn is defined as the ultimate connection 

strength determined from ASTM D6638. Additional normal loads may be evaluated 

to determine the long-term connection strength as a function of normal load. 

b. From the connection strength verses displacement curve (Figure B-4) for the quick 

test, using the normal load determined in step A, determine the applied tensions loads 

for a range of percentages of the Peak Connection Capacity (e.g., 95, 90, 85, 80,75, 

66 and 50 percent of Peak Connection capacity). The tensile loads should be selected 

to define the connection rupture curve for 1000 hours. 

4. Perform sustained load testing on the MBW unit/geosynthetic reinforcement combination 

at the normal and tensile load levels determined from step 3 using the same test apparatus 

used to determine the short-term connection properties. A different test apparatus may be 

used to perform the long-term tests as long as a correlation is made between the two test 

machines. Unless otherwise agreed upon, a minimum of four normal load levels shall be 

used to develop the connection rupture curve. 

a. Assemble the MBW unit/geosynthetic reinforcement test as done in step 3, and 

apply the normal load desired to the top MBW unit. 

b. Apply the full load (e.g., 95, 90, 85, and 80 percent of Tultconn) tensile load rapidly 

and smoothly to the specimen, preferably at a strain rate of 10 ± 3%/min. Record 

the total time for loading. 

c. Measure the extension/deflection of the connection, at the back of the MBW unit 

in accordance with the following approximate time schedule: 1, 2, 6, 10, 30 min, 

and 1, 2, 5, 10, 30, 100, 200, 500 and 1,000 hrs (Note: shorter reading times may 

be required). 

Record the time to failure of the connection. 

d. Repeat steps A through C for the other normal load levels recording the loads and 

time to failure. 

5. Presentation of data. 

a. Plot the results of the creep rupture test on a log time plot extrapolated to a 

minimum of 75 years, per Appendix D. The extrapolated load is the (75 - 100 

year) connection load, Tcrc 

b. On the same graph, plot the time to failure for the results of the sustained load 

tests on the reinforcement itself from Step 1. 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–9 November 2009
 
c. From the data plot, extrapolate to 75 years (670,000 hrs), per Appendix D. 

d. All deviations from the connection test setup from the actual connection used for 

construction shall be noted in the test report. 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–10 November 2009
 

 

Peak Connection Load 

Tultconn 

Tultconn 

A (example 1 connection – where

 curve becomes horizontal) 

B (example 2 connection – 

 where curve is linear) 

Normal Load (kN) 

Figure B-3 Connection Strength verses Normal Load 
 

 

Connection Load 

Tultconnn 

T95 

T90 

T85 

T80 

Displacement (mm) 

Figure B-4 Connection Strength verses Displacement 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–11 November 2009
 
 

 

B.4CONNECTION RESISTANCE DEFINED WITH SHORT-TERM TESTING 

B.4.1 Protocol 

As discussed in Section 4.4.7.i, the long-term connection strength reduction factor to account 

for reduced ultimate strength resulting from the connection, CRcr, may be obtained from 

long-term or short-term tests. as described below. 

Short-term (i.e., quick) ultimate strength tests, per ASTM D6638, are used to define an 

ultimate connection strength, Tultconn, at a specified confining pressure. Tests should be 

performed in accordance with ASTM D6638, Determining Connection Strength Between 

Geosynthetic Reinforcement and Segmental Concrete Units (Modular Concrete Blocks). 

With short-term testing, CRcr, is defined as follows: 

Tultconn CRcr 	 (4-43) RF T cr lot 

RFcr is the geosynthetic creep reduction factor (see Chapter 3), and Tlot is the ultimate wide 

width tensile strength of the reinforcement material roll/lot used for the connection strength 

testing. 

The raw data from short-term connection strength laboratory testing should not be used for 

design. The wall designer (and/or system supplier) should evaluate the data and define the 

nominal long-term connection strength, Talc. Steps for this data reduction are summarized 

and discussed below. 

Step 1: Separate laboratory test data by failure mode – pullout and rupture 

The laboratory data is separated by observed failure mode – pullout or 

rupture. Note that observed pullout may be more of a combination of pullout 

and rupture versus a clearly defined pullout. 

Step 2: Replot data and develop equations for ultimate connection strength, Tultconn 

Data should be plotted and Tultconn defined as a function of normal load or 

normal pressure. Tultconn is defined in one or two straight-line segments on the 

plot. Data points for the two different failure modes should be plotted as 

separate lines. 

Step 3: Evaluate data with consideration of other tests 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–12 November 2009
 
 

Evaluate data with consideration of data from testing of different grade(s) of 

reinforcement with same MBW unit. Replot data and develop equations, as 

appropriate. Trends in data between different tests should be rational. 

Step 4: Determine short-term ultimate connection strength reduction factor, CRu 

CRu is the short-term ultimate connection strength reduction factor defined as 

follows: 

 Tultconn CRu  (B-3) Tlot 

Step 5: Determine reinforcement creep reduction factor, RFCR 

The creep reduction factor for the geosynthetic reinforcement was previously 

defined (see Chapter 3 and Appendix D). 

Step 6: Determine long-term connection strength, CRcr 

CRcr, the long-term ultimate connection strength reduction factor (based upon 

short-term testing) is defined as follows: 

 CRu CRcr  (B-4) RFCR 

 

Note that the creep reduction factor is applied to short-term ultimate 

connection strength regardless of observed failure mode (i.e., rupture or 

pullout). 

Step 7: Determine nominal long-term connection strength, Talc 

Use equation 4-41 to determine Talc. 

The nominal long-term connection strength, Talc developed by frictional 

and/or structural means, determined as follows: 

 T ult cr CR

Talc 	 (4-41) RFD 

 

 

where: 

Talc = nominal long-term reinforcement/facing connection 

strength per unit reinforcement width at a specified 

confining pressure 

Tult = ultimate tensile strength of the geosynthetic soil 

reinforcement, defined as the minimum average roll value 

(MARV) 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–13 November 2009
 
 RFD = reduction factor to account for chemical and 

biological degradation 

 CRcr = long-term connection strength reduction factor to 

account for reduced ultimate strength resulting 

from the connection 

Step 8: Define limits of applicability of the defined Talc 

The nominal long-term connection strength equation defined is applicable to 

the test conditions utilized. The limits of the testing program normal loading 

should be stated with Talc. Extrapolation of the connection strength equation 

should not be extended significantly above or below this normal loading 

range. 

 

B.4.2 Example Calculation 

An example problem is presented within to demonstrate the analysis of laboratory connection 

strength data of modular block wall (MBW) units and geosynthetic reinforcements. Data is 

analyzed to determine the nominal strength envelope to use in design. This example is for a 

large MBW unit where one grade of a geogrid was tested, and all failure occurred by rupture 

of the reinforcement. (Fictional MBW unit and geosynthetic manufacturer names are used 

within.) 

Table B-1. Summary of steps for data reduction of MBW connection strength, with 

short-term (quick) test data. 

Step Item 

1 Separate laboratory test data by failure mode – pullout and rupture 

2 Replot data and develop equations for ultimate connection strength, Tultconn 

3 Evaluate data with consideration of data from testing of different grade(s) of 

reinforcement with same MBW unit. Replot data and develop equations, as 

appropriate. 

4 Determine short-term ultimate connection strength reduction factor, CRu 

5 Determine reinforcement creep reduction factor, RFCR 

6 Determine long-term connection strength, CRcr 

7 Determine nominal long-term connection strength, Talc 

8 Define limits of applicability (i.e., limits of testing program normal loading) 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–14 November 2009
Laboratory Report 

The following information was provided in the two laboratory test reports (a report for each 

grade of geogrid used). 

AA MBW Unit and Grade II, Type XX Geogrid” 

Apparatus and General 

Test Procedure: per ASTM D6638 

Large Modular Block Unit: AA 

42 in. wide (toe to heel), 18 in. high, 48 in. long 

Weight  2,200 lbs per unit 

Geogrid: Grade II, Type XX 

Tult-MARV = 4,300 lb/ft (reported by manufacturer) 

Lot and roll numbers provided 

TLOT = 4,730 lb/ft 

Connection Test Results:	 Tensile loads at peak capacity 

Tensile loads at 3⁄4-inch displacement 

7 normal loads 

Two tests at one normal load 

Data – see table below 

Recommended design curve and equation presented 

Connection Test Notes: All tests ended in geogrid rupture after large deformation. 

Evidence of slippage of the geogrid within the MBW unitgeogrid interface in all tests. 

Amount of slippage diminished with increased normal 

loading. 

The actual design capacity envelope could be lower than 

presented if the quality of construction in the field is less 

than that adopted in this controlled laboratory 

investigation. 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–15 November 2009
 
FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–16 November 2009

Test Number

Normal Load 

(lb/ft) 

Approximate 

Wall Height (ft) 

Tensile Capacity 

(lb/ft) at 3⁄4-inch 

Displacement 

Peak Tensile 

Capacity (lb/ft) 

1 816 2.4 557 1073

2 1665 4.9 659 1431

3 2498 7.3 620 1259

4 2509 7.3 669 1445

5 2509 7.3 688 1293

6 3353 9.8 641 1390

7 4219 12.4 667 1582

8 5074 14.9 859 1637

Peak connection capacity, Tultconn = 1068 + N tan 6 in (lb/ft of geogrid) and N in lb/ft of wall 

length 

Evaluate Data

Step 1. Separate data by failure mode – pullout and rupture. 

 All data for this MBW unit and soil reinforcement is rupture failure. 

Step 2. Replot raw data and check equation for Tultconn. 

 Equation provided in report checks. Tultconn = 1068 + N tan 6 in (lb/ft) and N in lb/ft 

Step 3. Evaluate data with consideration of data from different grade of soil 

reinforcement. 

There is no additional test data with similar products to compare this data to. 

Step 4. Determine CRu

The short-term connection strength reduction factor is: 

T CRu  ultconn

Tlot

Tlot is the ultimate tensile strength of the material used in the connection testing. The was 

laboratory test report listed a Tlot = 4,730 lb/ft. 

Step 5. Determine the creep reduction factor, RFCR 

The agency had previously evaluated the long-term (i.e., nominal) strength of the 

Grade II, Type XX geogrid. The agency evaluation used a creep reduction factor 

equal to 1.9, which was based upon an evaluation of the data supplied by the 

manufacturer. 
 

Step 6. Determine CRcr 

Short-term connection strength testing was used. Therefore, the long-term connection 

strength reduction factor to account for reduced ultimate strength resulting from the 

connection, using Equation 4-43, is equal to: 

T 1068  N tan6 1068  N tan6

ultconn CRcr    RFcr Tlot 1.9  1.10 Tult MARV  2.09 Tult MARV  

Step 7. Determine Talc 

The nominal long-term reinforcement/facing connection strength per unit 

reinforcement width at a specified normal load, N, using Equation 4-41, is equal to: 

1068  N tan6

ult MARV

Talc  

Tult  CRcr  

T  

2.09 TultMARV   444  0.044 N

RFD 1.15 

 

where Talc is in terms of lb/ft width of reinforcement and N is in terms of lb/ft width 

of wall facing length. 

The laboratory test data and the nominal long-term connection strength lines are 

presented in Figure B-5. 

Step 8. Define limits of applicability 

The nominal long-term connection strength equation defined is applicable to the test 

conditions utilized. The limits of the testing program normal loading should be stated 

with Talc. Extrapolation of the connection strength equation should not be extended 

significantly above or below this normal loading range. 

As noted in the laboratory test report (see data table under Laboratory Report) the 

limits of this test program are approximate wall heights of 2.4 to 14.9 ft. 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–17 November 2009
 
AA MBW Unit - Type XX, Grade II Ge ogrid
 

Conne ction Rupture Stre ngth
 

Ultimate Connection Strength (lb/ft

1800 

1600 

1400 

1200 

1000 

800 

600 

400 

200 

0 

y = 0.1132x + 1068.2 

y = 0.044x + 444 

0 1000 2000 3000 4000 5000 6000 

Normal Pre s sure (lb/ft) 

Test Data Design Line Linear (Test Data) Linear (Design Line) 

Figure B-5. Laboratory test data and the nominal long-term connection strength lines for 

AA MBW unit and Type XX, Grade II geogrid. 

Practical Considerations 

 The nominal long-term connection strength should be compared that of other soil 

reinforcements with this MBW unit and to other MBW units with this soil reinforcement, 

as a check for reasonableness. 

 The laboratory test reports presented “design connection strength” lines. These were 

based on ultimate strength reduced by a factor of safety equal to 1.5 and a 3/4 –inch 

displacement criteria. These “design connection strength” lines are for a design standard 

that is different from AASHTO, and therefore should not be used fro transportation 

works. Data should be evaluated in accordance with AASHTO/FHWA criteria, as 

detailed within this example. 

FHWA NHI-10-025 Appendix B – Pullout & Connection Strengths 

MSE Walls and RSS – Vol II B–18 November 2009
 
 

 

APPENDIX C 

STEEL SOIL REINFORCEMENTS 

Linear Strip Reinforcements 

Type Dimensions Fy/Fu 

Vertical 

Spacing 

Horizontal 

Spacing 

Steel Strips 

(ribbed) 

5/32 in. thick by 2 in. wide 

(4 mm thick by 50 mm wide) 

65/75 ksi 

(450/520 MPa) 

30 in. 

(750 mm) 

Varies, but typically 

12 to 30in, 

(300 to 750 mm) 

Welded Wire 

Wire 

Designation 

Wire 

Area 

Wire 

Diameter 

Wire 

Area 

Wire 

Diameter 

in2 in. mm2 mm 

W3.5 0.035 0.211 22.6 5.4 Fy/Fu 65/80 ksi (450/550 MPa) 

W4 0.040 0.226 25.8 5.7 Longitudinal 

Wire Spacing 

Typically 6 in. (150 mm) 

W4.5* 0.045 0.239 29.0 6.0 

W5 0.050 0.252 32.3 6.4 Transverse 

Wire Spacing 

Typically varies 9 to 24 in. 

W7 0.070 0.298 45.2 7.6 (230 to 600 mm) 

W9.5 0.095 0.348 61.3 8.8 Mat Spacing: 

For welded wire faced walls, vertically 12, 18 or 24 in. 

(300, 450, or 600 mm) and continuous horizontally. 

For precast concrete faced walls, vertically 24 to 30 in. 

(600 to 750 mm), horizontally 3.6 to 4 ft. (1.1 to 1.2 m) 

wide mats spaced at 6.2 ft (1.9 m) center-to-center or 

continuous 

W11 0.110 0.374 71.0 9.5 

W12 0.120 0.391 77.4 9.9 

W14 0.140 0.422 90.3 10.7 

W16 0.160 0.451 103 11.5 

W20 0.200 0.505 129 12.8 

*Typical min. size for permanent walls 

Bar Mats 

Wire 

Designation 

Wire 

Area 

Wire 

Diameter 

Wire 

Area 

Wire 

Diameter 

in2 in. mm2 mm 

W8 0.080 0.319 51.6 8.1 

Fy/Fu 65/75 ksi (450/520 MPa) 

Longitudinal 

Wire Spacing 

Typically 6 in. (150 mm) with 

4 to 7 longitudinal bars per 

mat 

W11 0.110 0.374 71.0 9.5 Transverse 

Wire Spacing 

Typically varies 6 to 24 in. 

(150 to 600 mm) 

W15 0.150 0.437 96.8 11.1 

Mat Spacing: 

Mat Spacing: 

Typically 30 in. (750 mm) vertically and 5 ft (1.5 

m) center-to-center horizontally 

W20 0.200 0.505 129 12.8 

Specific wall manufacturers may be able to provide a much wider range of reinforcement 

configurations depending on the design needs. 

FHWA NHI-10-025 Appendix C – Steel Reinforcements 

MSE Walls and RSS – Vol II C –1 November 2009 
 

 

 

FHWA NHI-10-025 Appendix C – Steel Reinforcements
 

MSE Walls and RSS – Vol II C –2 November 2009
 
 

 

APPENDIX D 

DETERMINATION OF CREEP STRENGTH REDUCTION FACTOR, RFCR AND 

DETERMINATION LONG-TERM ALLOWABLE STRENGTH, Tal
 

(after WSDOT Standard Practice T 925, Standard Practice for Determination 

of Long-Term Strength for Geosynthetic Reinforcement)
 

D.1 BACKGROUND 

The effect of long-term load/stress on geosynthetic reinforcement strength and deformation 

characteristics should be determined from the results of product specific, controlled, longterm laboratory creep tests conducted for a range of load levels and durations in accordance 

with ASTM D5262 adequate for extrapolation purposed to the desired design life, carried out 

to rupture when possible. Creep testing in accordance with ASTM D5262, but carried out to 

rupture where feasible, is described herein as the “conventional method.” A limited number 

of conventional creep tests may be supplemented and extended to longer creep rupture times 

using ASTM D6992 (Stepped Isothermal Method, or SIM) as described in this appendix. 

Specimens should be tested in the direction in which the load will be applied in use. Test 

results should be extrapolated to the required structure design life. Based on the extrapolated 

test results, the following is to be determined: 

• For ultimate limit state design, the highest load level, designated T1, which precludes 

both ductile and brittle creep rupture within the required lifetime. 

• For the limit state design, creep test results should be extrapolated to the required 

design life and design site temperature in general accordance with the procedures 

outlined in this Appendix. 

C In both cases, unless otherwise specified or mutually agreed upon by the geosynthetic 

supplier, the testing laboratory, and the owner, a baseline testing temperature of 68o F 

(20o C) shall be used for this testing. Higher test temperatures shall be considered as 

elevated temperatures to be used for the purpose of time extrapolation. ASTM D5262 

requires that the testing temperature be maintained at +3.6o

 F (2o C). For some polymers, 

this degree of variance could significantly affect the accuracy of the shift factors and 

extrapolations determined in accordance with this appendix. For polymers that are 

relatively sensitive to temperature variations, this issue should be considered when 

extrapolating creep data using time-temperature superposition techniques, or minimized 

by using a tighter temperature tolerance. 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –1 November 2009
 
 

 

 

• The creep reduction factor, RFCR, is determined by comparing the long-term creep 

strength, T1, to the ultimate tensile strength (ASTM D4595 for geotextiles, ASTM 

D6637 for geogrids) of the sample tested for creep. The sample tested for ultimate 

strength should be taken from the same lot, and preferably the same roll, of material 

that is used for the creep testing. For ultimate limit state design, the strength 

reduction factor to prevent long-term creep rupture is determined as follows: 

Tultlot RFCR  (D-1) Tl 

where, Tultlot is the average lot specific ultimate tensile strength (ASTM D4595) for 

the lot of material used for the creep testing. 

At present, creep tests are conducted in-isolation (ASTM D5262) rather than confined in-soil 

(e.g., FHWA RD-97-143, Elias et al., 1998), even though in-isolation creep tests tend to 

overpredict creep strains and underpredict the true creep strength when used in a structure. 

Note that the procedures provided in this appendix are for in-isolation creep rupture testing. 

Considering that typical design lives for permanent MSE structures are 75 years or more, 

extrapolation of creep data is required. No standardized method of geosynthetic creep data 

modeling and extrapolation exists at present, though a number of extrapolation and creep 

modeling methods have been reported in the literature (Findley et al., 1976; Wilding and 

Ward, 1978; Wilding and Ward, 1981, Takaku, 1981; McGown et al., 1984; Andrawes et al., 

1986; Murray and McGown, 1988; Bush, 1990; Popelar et al., 1991; Helwany and Wu, 

1992). Many of the methods discussed in the literature are quite involved and 

mathematically complex. Therefore, rather than attempting to develop mathematical models 

which also have physical significance to characterize and extrapolate creep, as is often the 

case in the literature (for example, using Rate Process Theory to develop rheological models 

of the material), a simplified visual/graphical approach will be taken. This does not mean 

that the more complex mathematical modeling techniques cannot be used to extrapolate creep 

of geosynthetics; they are simply not outlined in this appendix. 

The determination of T1 can be accomplished through the use of stress rupture data. Rupture 

data is necessary to determine the creep reduction factor for ultimate limit state conditions.. 

Stress rupture test results, if properly accelerated and extrapolated can be used to investigate 

the effects of stress cracking and the potential for a ductile to brittle transition to occur. 

Since the primary focus of creep evaluation in current practice is at rupture, only 

extrapolation of stress rupture data will be explained in this appendix. Creep strain data can 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –2 November 2009
 
 

 

be used to estimate T1, provided that the creep strain data is not extrapolated beyond the 

estimated long-term rupture strain. The use of rupture data, and not strain data, is 

recommended. Therefore, no guidance is provided regarding extrapolation of creep strain 

data to determine T1. 

Single ribs for geogrids, or yarns or narrow width specimens for woven geotextiles may be 

used for creep testing for ultimate limit state design provided that it can be shown through a 

limited creep testing program (conducted as described in Section D.5) that the rupture 

behavior and envelope for the single ribs, yarns, or narrow width specimens are the same as 

that for the full product, with product width as defined in ASTM D5262. This comparison 

must demonstrate that there is no statistical difference between the full width product creep 

rupture regression line and the single rib, yarn, or narrow width specimen regression line at a 

time of 1,000 hours using a student-t distribution at a confidence level of 0.10 (see Equation 

D.3-1). 

Considering that typical design lives for permanent MSE structures are 75 years or more, 

extrapolation of creep data will be required. Current practice allows creep data to be 

extrapolated up to one log cycle of time beyond the available data without some form of 

accelerated creep testing, or possibly other corroborating evidence (Jewell and Greenwood, 

1988; GRI, 1990). Based on this, unless one is prepared to obtain 7 to 10 years of creep data, 

temperature accelerated creep data, or possibly other corroborating evidence, must be 

obtained. 

It is well known that temperature accelerates many chemical and physical processes in a 

predictable manner. In the case of creep, this means that the creep strains under a given 

applied load at a relatively high temperature and relatively short times will be approximately 

the same as the creep strains observed under the same applied load at a relatively low 

temperature and relatively long times. Temperature affects time to rupture at a given load in 

a similar manner. This means that the time to a given creep strain or to rupture measured at 

an elevated temperature can be made equivalent to the time expected to reach a given creep 

strain or to rupture at in-situ temperature through the use of a time shift factor. 

The ability to accelerate creep with temperature for polyolefins such as polypropylene (PP) 

or high density polyethylene (HDPE) has been relatively well defined (Takaku, 1981; Bush, 

1990; Popelar et al., 1991). Also for polyolefins, there is some risk that a "knee" in the stress 

rupture envelope due to a ductile to brittle transition could occur at some time beyond the 

available data (Popelar et al., 1991). Therefore, temperature accelerated creep data is 

strongly recommended for polyolefins. However, in practice, a ductile to brittle transition for 

polyolefin geosynthetic reinforcement products has so far not been observed, likely due to 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –3 November 2009
 
 

 

the highly oriented nature of polymer resulting from the processing necessary to make fibers 

and ribs. In general, the degree of orientation of the polymer is an important factor regarding 

the potential for ductile to brittle transitions. 

For polyester (PET) geosynthetics, available evidence indicates that temperature can also be 

used to accelerate PET creep, based on data provided by den Hoedt et al., (1994) and others. 

However, the creep rupture envelopes for PET geosynthetics tend to be flatter than polyolefin 

creep rupture envelopes, and accurate determination of time-shift factors can be difficult for 

PET geosynthetics because of this. This may require greater accuracy in the PET stress 

rupture data than would be required for polyolefin geosynthetics to perform accurate 

extrapolations using elevated temperature data. This should be considered if using elevated 

temperature data to extrapolate PET stress rupture data. Note that a "knee" in the stress 

rupture envelope of PET does not appear to be likely based on the available data and the 

molecular structure of polyester. 

If elevated temperature is used to obtain accelerated creep data, it is recommended that 

minimum increments of 10o

 C be used to select temperatures for elevated temperature creep 

testing. The highest temperature tested, however, should be below any transitions for the 

polymer in question. If one uses test temperatures below 70 to75o

 C for polypropylene (PP), 

high density polyethylene (HDPE), and PET geosynthetics, significant polymer transitions 

will be avoided. If higher temperatures must be used, the effect of any transitions on the 

creep behavior should be carefully evaluated. One should also keep in mind that at these 

high temperatures, significant chemical interactions with the surrounding environment are 

possible, necessitating that somewhat lower temperatures or appropriate environmental 

controls be used. These chemical interactions are likely to cause the creep test results to be 

conservative. Therefore, from the user's point of view, potential for chemical interactions is 

not detrimental to the validity of the data for predicting creep limits. However, exposure to 

temperatures near the upper end of these ranges could affect the stress-strain behavior of the 

material due to loss of molecular orientation, or possibly other effects that are not the result 

of chemical degradation. Therefore, care needs to be exercised when interpreting results from 

tests performed at temperatures near the maximum test temperature indicated above. In 

general, if the stiffness of the material after exposure to the environment is significantly 

different from that of the virgin material, the stress-strain properties, and possibly the 

strength, of the material may have been affected by the exposure temperature in addition to 

the chemical environment. If the stiffness has been affected, the cause of the stiffness change 

should be thoroughly investigated to determine whether or not the change in stiffness is 

partially or fully due to the effect of temperature, or alternatively not use the data obtained at 

and above the temperature where the stiffness was affected. 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –4 November 2009
 
 

 

Unless otherwise specified or required by site-specific temperature data, an effective design 

temperature of 20o C (Tamb) should be assumed. 

A number of extrapolation and creep modeling methods have been reported in the literature 

(Findley et al., 1976; Wilding and Ward, 1978; Wilding and Ward, 1981; Takaku, 1981; 

McGown et al., 1984; Andrawes et al., 1986; Murray and McGown, 1988; Bush, 1990; 

Popelar et al., 1991; Helwany and Wu, 1992). Many of the methods discussed in the 

literature are quite involved and mathematically complex. 

Two creep extrapolation techniques are provided herein for creep rupture evaluation: the 

conventional method, which utilizes a simplified visual/graphical approach, temperature 

acceleration of creep, regression techniques, and statistical extrapolation, and the Stepped 

Isothermal Method (SIM). This does not mean that the more complex mathematical 

modeling techniques cannot be used to extrapolate creep of geosynthetics; they are simply 

not explained herein. These two techniques are described in more detail as follows: 

D.2 STEP-BY-STEP PROCEDURES FOR EXTRAPOLATING STRESS 

RUPTURE DATA – CONVENTIONAL METHOD 

Step 1: Plot the creep rupture data as log time to rupture versus log load level or versus load 

level, as shown in Figure D.2-1. Do this for each temperature in which creep rupture data is 

available. The plotting method that provides the best and most consistent fit of the data 

should be used. In general, 12 to 18 data points (i.e., combined from all temperature levels 

tested to produce the envelope for a given product, with a minimum of 4 data points at each 

temperature) are required to establish a rupture envelope (Jewell and Greenwood, 1988; 

ASTM D5262. 2007). The data points should be evenly distributed through each log cycle of 

time. Rupture points with a time to rupture of less than 5 hours should in general not be 

used, unless it can be shown that these shorter duration points are consistent with the rest of 

the envelope (i.e., they do not contribute to non-linearity of the envelope). As a guide: 

C three of the test results should have rupture times (not shifted by temperature 

acceleration) of 10 to 100 hours, 

C four of the test results should have rupture times between 100 and 1,000 hours, and 

C four of the test results should have rupture times of 1,000 to 10,000 hours, with at least 

one additional test result having a rupture time of approximately 10,000 hours (1.14 

years) or more. 

It is recommended that creep strain be measured as well as time to rupture, since the creep 

strain data may assist with conventional time-temperature shifting and in identifying any 

change in behavior that could invalidate extrapolation of the results. 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –5 November 2009
 
 

 

0

20

40

60

80

100

Load Level, P (%)

T1

T3

T2

T1 < T2 < T3

aT2 aT3

0 

20 

40 

60 

80 

100 

Load Level, P (%) 

T1 

T3 

T2 

T1 < T2 < T3 

aT2 aT3 

1 10 100 1,000 10,000 100,000 1,000,000 

Time to Rupture, t (hrs) 

Figure D.2-1 Typical stress rupture data for geosynthetics and the determination of shift 

factors for time-temperature superposition. 

It is acceptable to establish rupture points for times of 10,000 hours or more by assuming that 

specimens subjected to a given load level which have not yet ruptured to be near a state of 

rupture. Therefore, the time to rupture for those particular specimens would be assumed 

equal to the time the load has been in place. Note that this is likely to produce conservative 

results. 

Step 2: Extrapolate the creep rupture data. Elevated temperature creep rupture data can be 

used to extrapolate the rupture envelope at the design temperature through the use of a time 

shift factor, aT. If the rupture envelope is approximately linear as illustrated in Figure D.2-1, 

the single time shift factor aT will be adequate to perform the time-temperature superposition. 

This time-temperature superposition procedure assumes that the creep-rupture curves at all 

temperatures are linear on a semi-logarithmic or double logarithmic scale and parallel. It has 

been found empirically that the curves for PET are semi-logarithmic and approximately 

parallel, or double logarithmic and approximately parallel in the case of HDPE and PP. It 

should be pointed out that the theory of Zhurkov (1965), which assumes that the fracture 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –6 November 2009
 
 

 

process is activated thermally with the additional effect of applied stress, predicts that the 

creep-rupture characteristics should be straight when plotted on a double logarithmic 

diagram, and that their gradients should be stress-dependent. 

Use of a single time shift factor to shift all the creep rupture data at a given temperature, 

termed “block shifting,” assumes that the shift factor aT is not highly stress level dependent 

and that the envelopes at all temperatures are parallel, allowing an average value of aT to be 

used for all of the rupture points at a given temperature. While research reported in the 

literature indicates that aT may be somewhat stress level dependent and that the curves at all 

temperatures are not completely parallel, this assumption tends to result in a more 

conservative assessment of the creep reduction factor RFCR (Thornton and Baker, 2002). 

The time to rupture for the elevated temperature rupture data is shifted in accordance with the 

following equation: 

t  (t ) (a ) (D.2-1) amb elev T 

where, tamb is the predicted time at in-situ temperature to reach rupture under the specified 

load, telev is the measured time at elevated temperature to reach a rupture under the specified 

load, and aT is the time shift factor. aT can be approximately estimated using a 

visual/graphical approach as illustrated in Figures D.2-1 and D.2-2. The preferred approach, 

however, is to use a computer spreadsheet optimization program to select the best shift 

factors for each constant temperature block of data to produce the highest R2 value for the 

combined creep rupture envelope to produce the result in Figure D.2-2. 

Note that incomplete tests may be included, with the test duration replacing the time to 

rupture, but should be listed as such in the reported results, provided that the test duration, 

after time shifting, is 10,000 hours or more. The rule for incomplete tests is as follows. The 

regression should be performed with and without the incomplete tests included. If the 

incomplete test results in an increase in the creep limit, keep the incomplete tests in the 

regression, but if not, do not include them in the regression, in both cases for incomplete tests 

that are 10,000 hours in duration after time shifting or more. Record the duration of the 

longest test which has ended in rupture, or the duration of the longest incomplete test whose 

duration exceeds its predicted time to failure: this duration is denoted as tmax. 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –7 November 2009
 
 

 

0

20

40

60

80

100

Load Level, P (%)

T1

T3

T2

T1 < T2 < T3

aT2 aT3

td

Pd

tmax

0 

20 

40 

60 

80 

100 

Load Level, P (%) 

T1 

T3 

T2 

T1 < T2 < T3 

aT2 aT3 

td 

Pd 

tmax 

1 10 100 1,000 10,000 100,000 1,000,000 

Time to Rupture, t (hrs) 

Figure D.2-2. Extrapolation of Stress Rupture Data and the Determination of the Creep 

Limit Load. 

It is preferred that creep rupture data be extrapolated statistically beyond the elevated 

temperature time shifted data using regression analysis (i.e., curve fitting) up to a maximum 

of one log cycle of time for all geosynthetic polymers (greater extrapolation using only 

statistical methods is feasible, but uncertainty in the result increases substantially and must be 

taken into account). Therefore, adequate elevated temperature data should be obtained to 

limit the amount of statistical extrapolation required. 

Also note that there may be situations where extrapolation to create a creep rupture envelope 

at a lower temperature than was tested is necessary. Situations where this may occur include 

the need to elevate the ambient temperature to have greater control regarding the temperature 

variations during the creep testing (i.e., ambient laboratory temperature may vary too much), 

or for sites where the effective design temperature is significantly lower than the “standard” 

reference temperature used for creep testing (e.g., northern or high elevation climates). In 

such cases, it is feasible to use lower bound shift factors based on previous creep testing 

experience to allow the creep rupture envelope to be shifted to the lower temperature, as shift 

factors for the materials typically used for geosynthetic reinforcement are reasonably 

consistent. Based on previous creep testing experience and data reported in the literature 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –8 November 2009
 
 

 

(Chow and Van Laeken, 1991; Thornton et al., 1998a; Thornton, et al., 1998b; Lothspeich 

and Thornton, 2000; Takemura 1959; Bush, 1990; Popelar et al., 1990; Wrigley et al., 2000; 

Takaku 1981; Thornton and Baker, 2002), shift factors for HDPE and PP geosynthetics are 

typically in the range of 0.05 to 0.18 decades (i.e., log cycles of time) per 1o C increase in 

temperature (i.e., a 10o C increase would result in a time shift factor of 12 to 15) and 0.05 to 

0.12 decades per 1o

 C increase in temperature for PET geosynthetics. It is recommended that 

if shifting the creep rupture envelope to temperatures below the available data is necessary, 

that a shift factor of 0.05 decades per 1o C increase in temperature for PP, HDPE, and PET be 

used. This default shift factor should not be used to shift the creep rupture data more than 

10o

 C. 

Step 3: Once the creep data has been extrapolated, determine the design, lot specific, creep 

limit load by taking the load level at the desired design life directly from the extrapolated 

stress rupture envelope as shown in Figure D.2-2. If statistical extrapolation beyond the time 

shifted stress rupture envelopes (PP or HDPE), or beyond the actual data if temperature 

accelerated creep data is not available, is necessary to reach the specified design life, the 

calculated creep load T1 should be reduced by an extrapolation uncertainty factor as follows: 

where Pcl is the creep limit load taken directly from the extrapolated stress rupture envelope, 

and "x" is the number of log cycles of time the rupture envelope must be extrapolated beyond 

the actual or time shifted data, and is equal to log td – log tmax as illustrated in Figure D.2-2. 

The factor (1.2)x-1 is the extrapolation uncertainty factor. If extrapolating beyond the actual 

or time shifted data less than one log cycle, set “x-1” equal to “0”. This extrapolation 

uncertainty factor only applies to statistical extrapolation beyond the actual or time shifted 

data using regression analysis and assumes that a “knee” in the rupture envelope beyond the 

actual or time shifted data does not occur. 

Note that a condition on the extrapolation is that there is no evidence or reason to believe that 

the rupture behavior will change over the desired design life. It should be checked that at 

long durations, and at elevated temperatures if used: 

 There is no apparent change in the gradient of the creep-rupture curve 

 There is no evidence of disproportionately lower strains to failure 

 There is no significant change in the appearance of the fracture surface. 

Any evidence of such changes, particularly in accelerated tests, should lead to the exclusion 

of any reading where either the gradient, strain at failure or appearance of the failure is 

different to those in the test with the longest failure duration. Particular attention is drawn to 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –9 November 2009
 

P T  cl

l 1 (D.2-2)   1.2 x
 

 

the behavior of unoriented thermoplastics under sustained load, where a transition in 

behavior is observed in long-term creep-rupture testing (i.e., the so called “ductile to brittle 

transition – Popelar et al., 1991). The effect of this transition is that the gradient of the creeprupture curve becomes steeper at the so-called “knee” such that long-term failures occur at 

much shorter lifetimes than would otherwise be predicted. The strain at failure is greatly 

reduced and the appearance of the fracture surface changes from ductile to semi-brittle. If 

this is observed, any extrapolation should assume that the “knee” will occur. For the method 

of extrapolation reference should be made to ISO/FDIS 9080 (2001), ASTM D5262 (2007), 

and Popelar et al., (1991). 

This extrapolation uncertainty factor also assumes that the data quality is good, data scatter is 

reasonable, and that approximately 12 to 18 data points which are well distributed (see Step 1 

for a definition of well distributed) defines the stress rupture envelope for the product. If 

these assumptions are not true for the data in question, this uncertainty factor should be 

increased. The uncertainty factor may also need to be adjusted if a method other than the one 

presented in detail herein is used for extrapolation. This will depend on how well that method 

compares to the method provided in this appendix. This extrapolation uncertainty factor 

should be increased to as much as (1.4)x

 if there is the potential for a "knee" in the stress 

rupture envelope to occur beyond the actual or time shift data, or if the data quality, scatter, 

or amount is inadequate. Furthermore, if the data quantity or over the time scale is 

inadequate, it may be necessary to begin applying the extrapolation uncertainty factor before 

the end of the time shifted data. 

Note that based on experience, the R2 value for the composite (i.e., time shifted) creep 

rupture envelope should be approximately 0.8 to 0.9 or higher to be confident that Equation 

B.2-3 will adequately address the extrapolation uncertainty. If the R2

 value is less than 

approximately 0.6 to 0.7, extrapolation uncertainty is likely to be unacceptably high, and 

additional testing and investigation should be performed. In general, such low R2 values are 

typically the result of data that is too bunched up, unusually high specimen-to-specimen 

variability, or possibly poor testing technique. 

D.3 PROCEDURES FOR EXTRAPOLATING CREEP RUPTURE DATA – 

STEPPED ISOTHERMAL METHOD (SIM) 

An alternative creep strain/rupture analysis and extrapolation approach that has recently 

become available for geosynthetics is the Stepped Isothermal Method (SIM) proposed, 

illustrated, and investigated by Thornton et al. (1997), Thornton et al. (1998a), Thornton et 

al. (1998b), and Thornton and Baker (2000). SIM has been applied successfully to PET 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –10 November 2009
 
 

 

geogrids and PP geotextiles. SIM utilizes an approach similar to the Williams-Landell-Ferry, 

or WLF, approach to creep extrapolation (Ferry, 1980), where master creep curves for a 

given material are produced from a series of short-term tests (i.e., creep test durations on the 

order of a few hours) on the same specimen over a wide range of temperatures (i.e., while the 

load on the specimen is held constant, the temperature is increased in steps). The sections of 

creep curve at the individual temperatures are shifted in time and combined to form a 

continuous prediction of the creep strain at the starting temperature. 

Though the general principles of this method have been in use for many years in the polymer 

industry (Ferry, 1980), it has been only recently that this approach has been used for 

geosynthetics. Though this approach was initially developed to extrapolate creep strain data, 

it has been adapted to produce stress rupture data by taking the specimen to rupture once the 

highest test temperature is reached. In effect, through time shifting of the creep strain data 

obtained prior to rupture, the rupture point obtained has an equivalent shifted time that is 

several orders of magnitude greater than the actual test time, which could be on the order of 

only a few days. 

The method is conducted in accordance with ASTM D6992. Key issues are the very short 

test time used for this method, potential use of temperatures that are well above transitions in 

the geosynthetic material, and its complexity. Key technical advantages of the method, 

however, include more accurate determination of time shift factors, since the same specimen 

is used at the same load level at all of the temperatures (the “conventional” method must deal 

with the effect of specimen to specimen variability when determining the shift factors), and 

that time shift factors between temperatures are determined at the same load level, 

eliminating the effect of load level in the determination of the shift factors (in the 

“conventional” method, the shift factors used are in fact an average value for a wide range of 

loads). 

SIM can be considered for use in generating and extrapolating geosynthetic creep and creep 

rupture data provided this method is shown to produce results which are consistent with the 

“conventional” extrapolation techniques recommended in this appendix. To this end, creeprupture testing shall be conducted using conventional tests (ASTM D5262) and SIM tests 

(ASTM D6992). At least six SIM rupture tests and six conventional rupture tests and shall 

be conducted on one of the products in the product line being evaluated. Of the six SIM 

rupture tests, four shall have rupture times (shifted as appropriate) between 100 and 2000 

hours and two shall have rupture times greater than 2000 hours. All of the conventional 

creep rupture points shall be obtained at the reference temperature (i.e., not temperature 

shifted). Creep rupture plots shall be constructed, regression lines computed and the log 

times to rupture determined at a load level that corresponds to 1,000 hours and 50,000 hours 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –11 November 2009
 
 

 

on the conventional creep rupture envelope, for the two data sets. The log time to rupture for 

the SIM regression at this load level shall be within the upper and lower 90% confidence 

limits of the mean conventional regressed rupture time at the same load level using Student’s 

t test. 

The following minimum creep rupture data points are recommended where conventional and 

SIM data points are used in combination: 

C 4 conventional rupture and 4 SIM rupture data points between 100 and 2,000 hours 

(after shifting) 

C 2 conventional and 2 SIM rupture data points between 2,000 and ~10,000 hours 

(after shifting), with 

o 1 conventional rupture data point at ~10,000 hours or greater with 1 SIM 

rupture data point at ~10,000 hours or greater (after shifting); OR 

o 2 conventional rupture data points at ~10,000 hours or greater without SIM 

data point at ~10,000 hours or greater (after shifting) 

The confidence limit for the regression performed for the conventional creep rupture data is 

given by (Wadsworth, 1998): 



and 

   

where: 

log tL = lower and upper bound confidence limit. The + or – term in Equation B.2-1 

results in the lower and upper bound confidence limits, respectively. 

treg = time corresponding to the load level from the conventional creep rupture 

envelope at which the comparison between the two envelopes will be made 

(e.g., at 1,000 and 50,000 hrs after time shifting) 

t,n-2 = value of the t distribution determined from applicable Student t table (or 

from the Microsoft EXCEL function TINV(,n-2)) at  = 0.10 and n-2 

degrees of freedom (this corresponds to the 90% two-sided prediction limit). 

n = the number of rupture or allowable run-out points in the original test sample 

(i.e., the conventional creep rupture data) 

	 

logt L 

2  1 P  P logt 

reg  t

  ,n2 

n P  	  i P  2 	 (D.3-1) 



2  Pi  P  2 

 logt

logti  log i  logt  t  	 

 2 (D.3-2) P 

  i  P

n  2 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –12 November 2009
 
 

 

 P = load level obtained at treg from the regression line developed from the 

conventional creep rupture testing 

P = the mean rupture load level for the original test sample (i.e., all rupture or runout points used in the regression to establish the conventional creep rupture 

envelope) 

Pi = the rupture load level of the i’th point for the rupture points used in the 

regression for establishing the conventional creep rupture envelope 

log t = the mean of the log of rupture time for the original test sample (i.e., all rupture 

or run-out points used in the regression to establish the conventional creep 

rupture envelope) 

ti = the rupture time of the i’th point for the rupture points used in the regression 

for establishing the conventional creep rupture envelope 

Once log tL, both upper and lower bound, has been determined at the specified load level, 

compare these values to the log rupture time (i.e., log tSIM) obtained for the SIM creep rupture 

envelope test at the specified load level (e.g., 1,000 and 50,000 hours). The value of log tSIM 

at the two specified load levels must be between the upper and lower bound confidence limits 

(log tL). If this requirement is not met, perform two additional SIM tests at each load level P 

for the specified treg where this comparison was made and develop a new SIM creep rupture 

envelope using all of the SIM data. If for the revised SIM regression envelope resulting from 

these additional tests this criterion is still not met, perform adequate additional conventional 

creep rupture testing to establish the complete rupture envelope for the product in accordance 

with this appendix). 

If the criterion provided above is met, the SIM testing shall be considered to be consistent 

with the conventional data, and SIM may be used in combination with the conventional data 

to meet the requirements of Section D.2 regarding the number of rupture points and their 

distribution in time and maximum duration. Therefore, the combined data can be used to 

create the creep rupture envelope as shown in Figure D.2-2. In that figure, the SIM data shall 

be considered to already be time shifted. Equation D.2-3 is then used to determine Tl. 

D.4 DETERMINATION OF RFCR 

Step 4: The creep reduction factor, RFCR, is determined by comparing the long-term creep 

strength, T1, to the ultimate tensile strength (ASTM D4595 or ASTM D6637) of the sample 

tested for creep (Tlot). The sample tested for ultimate tensile strength should be taken from 

the same lot, and preferably the same roll, of material that is used for the creep testing. For 

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MSE Walls and RSS – Vol II D –13 November 2009
 

 

ultimate limit state design, the strength reduction factor to prevent long-term creep rupture is 

determined as follows: 

where, Tultlot is the average lot specific ultimate tensile strength (ASTM D4595 or ASTM 

D6637) for the lot of material used for the creep testing. Note that this creep reduction factor 

takes extrapolation uncertainty into account, but does not take into account variability in the 

strength of the material. Material strength variability is taken into account when RFCR, along 

with RFID and RFD, are applied to Tult to determine the long-term allowable tensile strength, 

as Tult is a minimum average roll value. The minimum average roll value is essentially the 

value that is two standard deviations below the average value. 

D.5 USE OF CREEP DATA FROM "SIMILAR" PRODUCTS and EVALUATION 

OF PRODUCT LINES 

Long-term creep data obtained from tests performed on older product lines, or other products 

within the same product line, may be applied to new product lines, or a similar product 

within the same product line, if one or both of the following conditions are met: 

C The chemical and physical characteristics of tested products and proposed products are 

shown to be similar. Research data, though not necessarily developed by the product 

manufacturer, should be provided which shows that the minor differences between the 

tested and the untested products will result in equal or greater creep resistance for the 

untested products. 

C A limited testing program is conducted on the new or similar product in question and 

compared with the results of the previously conducted full testing program. 

For polyolefins, similarity could be judged based on molecular weight and structure of the 

main polymer (i.e., is the polymer branched or crosslinked, is it a homopolymer or a blend, 

percent crystallinity, etc.?), percentage of material reprocessed, tenacity of the fibers and 

processing history, and polymer additives used (i.e., type and quantity of antioxidants or 

other additives used). For polyesters and polyamides, similarity could be judged based on 

molecular weight or intrinsic viscosity of the main polymer, carboxyl end group content, 

percent crystallinity, or other molecular structure variables, tenacity of the fibers and 

processing history, percentage of material reprocessed or recycled, and polymer additives 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –14 November 2009
 

T

RFCR	  ultlot (D.4-1) Tl 
 

 

used (e.g., pigments, etc.). The untested products should also have a similar macrostructure 

(i.e., woven, nonwoven, extruded grid, needlepunched, yarn structure, etc.) and fiber 

dimensions (e.g., thickness) relative to the tested products. It should be noted that percent 

crystallinity is not a controlled property and there is presently no indication of what an 

acceptable value for percent crystallinity should be. 

For creep evaluation of a similar product not part of the original product line, this limited 

testing program should include creep tests taken to at least 1,000 to 2,000 hours in length 

before time shifting if using the “conventional” creep testing approach, with adequate 

elevated temperature data to permit extrapolation to 50,000 hours or more. If it has been 

verified that SIM can be used, in accordance with Section D.3, durations after time shifting 

due to elevated temperature up to a minimum of 50,000 hours are required. A minimum of 4 

data points per temperature level tested should be obtained to determine time shift factors and 

to establish the envelope for the similar product. These limited creep test results must show 

that the performance of the similar product is equal to or better than the performance of the 

product previously tested. This comparison must demonstrate that there is no statistical 

difference between the old product regression line and the regression line obtained for the 

similar product at a time of 2,000 hours (not temperature accelerated) and 50,000 hours (after 

time shifting) using a student-t distribution at a confidence level of 0.10 (see Equation D.3­

1). If no statistical difference is observed, the results from the full testing program on the 

older or similar product could be used for the new/similar product. If this is not the case, then 

a full testing and evaluation program for the similar product should be conducted. 

Similarly, for extension of the creep data obtained on one product in the product line (i.e., the 

primary product tested, which is typically a product in the middle of the range of products in 

the product line) to the entire product line as defined herein, a limited creep testing program 

must be conducted on at least two additional products in the product line. The combination 

of the three or more products must span the full range of the product line in terms of weight 

and/or strength. The limited test program described in the preceding paragraph should be 

applied to each additional product in the product line. The loads obtained for the data in each 

envelope should then be normalized by the lot specific ultimate tensile strength, Tlot. All 

three envelopes should plot on top of one another, once normalized in this manner, and the 

two additional product envelopes should be located within the confidence limits for the 

product with the more fully developed creep rupture envelope (i.e., the “primary” product) as 

described above for “similar” products. If this is the case, then the creep reduction factor for 

the product line shall be the lesser of the reduction factor obtained for the product with the 

fully developed rupture envelope and the envelope of all three products combined, and 

normalization using the ultimate tensile strength shall be considered acceptably accurate. 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –15 November 2009
 
 

 

If this is not the case, then the creep rupture envelopes for the other two products, plus 

enough other products within the product line, to establish the trend in RFCR as a function of 

product weight or ultimate tensile strength, so that the RFCR for the other products within the 

product line can be accurately interpolated. Furthermore, Tal must be determined in 

accordance with the following: 

Note that normalization using the ultimate lot specific tensile strength may not be completely 

accurate for some geosynthetic products regarding characterization of creep rupture behavior, 

and other normalization techniques may be needed (Wrigley et al., 1999). In such cases, 

individual creep reduction factors for each product in the product line may need to be 

established through fully developed creep rupture envelopes for representative products 

obtained at the low, middle, and high strength end of the product series. Once the creep 

limited strength, Pcl and the creep reduction factors are established for each product, in this 

case, product variability must still be taken into account. In such cases, Tal must be the lesser 

of the determination from Equation 1 and the following determination: 

where, 

P95 = the tensile strength determined from the 95% lower bound prediction limit for 

the creep rupture envelope at the specified design life (see Equations 4 and 5 in 

“Quality Assurance (QA) Criteria for Comparison to Initial Product 

Acceptance Test Results”) 

D.6 CREEP EXTRAPOLATION EXAMPLES USING STRESS RUPTURE DATA 

A creep extrapolation example using stress rupture data is provided. The example uses 

hypothetical stress rupture data, which is possible for PET geosynthetics, to illustrate the 

simplest extrapolation case. 

D.6.1 Stress Rupture Extrapolation Example 

The following example utilizes hypothetical stress rupture data for a PET geosynthetic. The 

data provided in this example is for illustration purposes only. 

Given: A PET geosynthetic proposed for use as soil reinforcement in a geosynthetic MSE 

wall. A design life of 1,000,000 hours is desired. The manufacturer of the geogrid has 

provided stress rupture data at one temperature for use in establishing the creep limit for the 

material. The stress rupture data came from the same lot of material as was used for the wide 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –16 November 2009
 

P 

T  95 

al RFID  RFD
 

 

width load-strain tests. The wide width ultimate strength data for the lot is as provided in 

Figure D.6-1. The stress rupture data is provided in Figure D.6-2. 

Find: The long-term creep strength, T1, at a design life of 1,000,000 hours and a design 

temperature of 20o C, and the design reduction factor for creep, RFCR using the stress rupture 

data. 

Solution: The step-by-step procedures provided for stress rupture data extrapolation will be 

followed. Step 1 has already been accomplished (Figure D.6-2). 

Step 2: Extrapolate the stress rupture data. Use regression analysis to establish the best fit 

line through the stress rupture data. Extend the best fit line to 1,000,000 hours as shown in 

Figure D.6-2. 

Step 3: Determine the design, lot specific, creep limit load from the stress rupture envelope 

provided in Figure D.6-2. The load taken directly from the rupture envelope at 1,000,000 

hours is 63.4 kN/m. This value has been extrapolated 1.68 log cycles beyond the available 

data. Using Equation D.4, 

1.68  1 Tl  63.4 kN/m / 1.2  56.0 kN/m 

Step 4: The strength reduction factor to prevent long-term creep rupture RFCR is determined 

as follows (see Equation D.1): 

Tultlot RFCR  Tl 

where, Tutlot is the average lot specific ultimate tensile strength for the lot material used for 

creep testing. From Figure D.6-1, Tutlot is 110 kN/m. Therefore, 

RFCR  110 kN/m / 56.0 kN/m  2.0 

In summary, using rupture based creep extrapolation, T1 = 56.0 kN/m, and RFCR = 2.0 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –17 November 2009
 
 

 

Figure D.6-1 Wide width load-strain data for PET geosynthetic at 20 C. 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –18 November 2009
 
 

 

Figure D.6-2 Stress rupture data for PET geosynthetic at 20 C. 

D.7 RECOMMENDED PROCEDURES TO DETERMINE Tal 

(after WSDOT Standard Practice T 925, Standard Practice for Determination of Long-Term 

Strength for Geosynthetic Reinforcement) 

The AASHTO LRFD Bridge Design Specifications provide minimum requirements for the 

assessment of Tal for use in the design of geosynthetic reinforced soil structures. A 

framework for the use of installation damage, creep, and durability test data that can be 

obtained from available ASTM, ISO, and GRI test standards to determine RFID, RFCR, and 

RFD is presented below. This protocol should be used to establish values of RFID, RFCR, and 

RFD that are not project or site specific, that can applied to the typical situations a given 

agency or owner will face. These reduction factors could then be applied to most design 

situations. Using this approach, a generalized step-by-step procedure to determine these 

reduction factors is as follows: 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –19 November 2009
 
 

 

1. Characterize the typical environment to which the geosynthetic reinforcement will be 

exposed during installation and throughout its life. Key environmental parameters to 

be considered include the soil gradation and its angularity above and below the 

geosynthetic layers (RFID), likely backfill placement procedures (RFID), in-soil 

“average” site temperature to be used for design (RFCR and RFD), backfill pH range 

likely to be present (RFD), potential exposure to sunlight, in particular UV light, and 

special soil conditions that may affect aging, such as summarized in Table 3-9 (RFD). 

“Average” site temperature to be used for design is defined as the temperature which 

is halfway between the average yearly air temperature and normal daily air 

temperature for the highest month at the site. This site temperature definition is 

considered to be a conservative estimation of the average effective temperature in the 

soil. Note that at the connection between the soil reinforcement and the facing 

elements, the temperature could be significantly higher than this, especially if the 

facing has a southern exposure. 

2. To determine RFCR, conduct laboratory creep tests as described previously, using the 

“average” site temperature as the baseline test temperature. For those located in the 

northern tier of states within the USA, in most cases, it is sufficiently accurate, and a 

little conservative, to use a default baseline temperature of 20o C. For those located 

in the southern reaches of the U.S., where “average” in-soil temperatures could 

approach 30o

 C or higher, a higher baseline temperature should be used. Using the 

creep test results and time-temperature superposition to shift elevated temperature 

creep data to the baseline temperature timescale (see following section), create a 

creep rupture envelope for the baseline temperature, making sure that the rupture 

envelope extends out to the desired design life (typically 75 years). If necessary, 

extrapolate the envelope to the design life beyond the time shifted data using 

regression analysis techniques. 

3. To determine RFD, conduct the index durability tests described previously and as 

summarized in Table 3-11, provided that the environment to which the geosynthetic 

will be exposed during its life (i.e., step 1 above) is within the boundaries of 

conditions to which the index test results are applicable. These environment 

boundaries are as follows: 

	 Granular soils (sands, gravels) used in the reinforced volume. 

	 pH as determined by AASHTO T289 ranging from 4.5 < pH < 9 for 

permanent applications and 3 < pH < 10 for temporary applications 

	 Site temperature < 85o F (30o C) for permanent applications and < 95o F (35o 

C) for temporary applications 

	 Maximum backfill particle size of 3⁄4-inch (19 mm), unless full scale 

installation damage tests conducted in accordance with ASTM D5818 are 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –20 November 2009
 
 

 

 

available and indicate that RFID for the site backfill soil and geosynthetic 

combination is less than 1.7, and 

 Soil organic content, as determined by AASHTO T267 for material finer than 

the 0.0787 in. (No. 10) sieve < 1 percent. 

Site conditions not within these boundaries should be considered to be aggressive 

with regard to the determination of RF. If the test results meet the established criteria 

to consider the geosynthetic adequately durable, a default value for RFD as specified 

herein may be used. If the index test results do not meet the specified criteria, or if 

the anticipated environment is likely to be outside the boundaries applicable to the 

index tests, long-term durability tests such as described by Elias et al. (2009) should 

be considered to determine RFD directly. 

4. To determine RFID, field expose samples of the geosynthetic to three or more 

different fill materials that encompass the range of soil conditions likely to be 

encountered. For state agencies, the selection of backfill gradations could be tied to 

the standard backfill materials used for reinforced walls and slopes by the agency. 

Once the samples exposed to installation stresses are tested to determine tensile 

strength loss for each backfill condition, the tensile strength loss and RFID could be 

plotted as a function of a key gradation parameter, such as the d50 size, to enable 

selection of RFID for the specific backfill gradation being considered. 

The four step approach provided above is also applicable to specifically target the 

determination of these reduction factors to a specific site environment. The most common 

adaptation for targeting a site specific condition is to conduct installation damage tests using 

the actual backfill material to be used in the reinforced soil structure. The value of RFID 

derived from that site specific testing is then used with the values of RFCR and RFD 

determined as described in the above four step process. Site specific determination of RFCR, 

primarily in consideration of a site specific baseline temperature, can also be accomplished, 

provided that adequate creep data is available to establish a rupture envelope for the site 

specific baseline temperature (assuming that site specific temperature is significantly 

different from the baseline temperature used for the available creep test data). If inadequate 

creep rupture data is available to accomplish that, it is generally cost and time prohibitive to 

conduct a new suite of creep tests targeted to the site specific temperature as a baseline. 

Also, determination of RFD for site specific conditions is time and cost prohibitive and is 

rarely done, as such testing typically takes one to two years or more to complete. 

Once the reduction factors are determined, then Tal can be determined in accordance with 

Equation 3-12 and used to design the geosynthetic structure (see Chapter 4). 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –21 November 2009
 
 

 

FHWA NHI-10-025 Appendix D – Geosynthetic Creep Factor
 

MSE Walls and RSS – Vol II D –22 November 2009
 
 

APPENDIX E 

EXAMPLE CALCULATIONS 

This appendix presents ten example problems that illustrate the application of the various 

equations and principles for design of MSE walls and slopes discussed in Chapters 2 to 8. 

The ten example problems were chosen to encompass a variety of geometries, soil 

reinforcements, and loading conditions. The first seven examples are for MSE walls, and 

the final three examples are for reinforced soil slopes (RSS). A summary of the example 

problems is included in Table E0. 

Table E0 

Summary of Example Problems
 

No. Problem Description 

 MSE Walls 

E1 Modular Block Wall (MBW) Faced MSE wall with broken back sloping fill and live 

load surcharge, reinforced with geogrids 

E2 Bearing check for sloping toe conditions, with and without high groundwater 

E3 Segmental precast panel MSE wall with sloping backfill surcharge, reinforced with 

steel strips 

E4 Segmental precast panel MSE wall with level backfill and live load surcharge, 

reinforced with steel bar mats 

E5 Bridge abutment with spread footing on top of a segmental precast panel faced MSE 

wall with steel strips 

E6 Example E4 with traffic barrier impact loading 

E7 Example E4 with seismic loading 

RSS 

E8 Road widening 

E9 High slope for new road construction 

E10 Facing stability calculation 

MSE Wall Examples: 

While using LRFD methodology care has to be taken in using the correct load factors and 

load combinations. There are several different ways in which the computations using LRFD 

can be performed. As noted in Chapter 4, for simple problem geometries the critical loading 

conditions can be readily identified while for complex geometries this may not be possible 

because the critical load effects due to various combinations of maximum and minimum 

loads may not be clear without performing all the intermediate computations for various load 

FHWA NHI-10-025 Appendix E – Example Calculations 

MSE Walls and RSS – Vol II E –1 November 2009
 
 

 

factors. Therefore, the MSE wall example problems in this appendix have been solved in the 

following two formats: 

Format A: In this format designs are developed based on critical load combinations that 

are readily identifiable based on the problem geometry. This format is used in 

Example E1. 

Format B: In this format, the computations for load effects are first performed using 

maximum load factors and minimum load factors. Then, using the values 

computed for maximum and minimum load combinations, the critical load 

effects are obtained by suitably combining the maximum and minimum loads. 

This format is used in Examples E2, E3 and E4. 

Format B involves more computations than Format A. However, in the LRFD context, 

Format B is essential while evaluating MSE walls with complex geometries such as those 

discussed in Chapter 6. This is because the critical combination of various loads may not be 

readily apparent until the complex system of surcharges on and within the MSE walls are 

analyzed with applicable maximum and minimum load factors. 

Rather than introduce the more comprehensive Format B in Example E5 which addresses a 

case of complex geometry, a conscious attempt was made to first introduce Format B with 

respect to relatively simpler geometries. Thus, Example E3 and E4 have been solved with 

Format B. Example E3 is similar to Example E1 in the sense that they both include sloping 

backfill. Thus, the reader can develop a good feel for the design using both formats. Then, 

in Example E5 it will become evident that Format B represents a more logical way of 

handling complex geometries. 

Format B also permits easier incorporation of extreme events such as vehicular impact and 

seismic events as demonstrated in Examples E6 and E7, respectively. Format B will also 

provide a more adaptable solution scheme in the event that load factors are modified and/or 

additional recommendations are developed for load combinations in future versions of 

AASHTO. 

FHWA NHI-10-025 Appendix E – Example Calculations 

MSE Walls and RSS – Vol II E –2 November 2009
 
 

EXAMPLE E1 

MBW UNIT FACED, MSE WALL WITH BROKEN BACKSLOPE AND 

LIVE LOAD SURCHARGE, REINFORCED WITH GEOGRIDS 

 

E1-1 INTRODUCTION 

This example problem demonstrates the analysis of an MSE wall with a broken backslope 

and live load traffic surcharge. The MSE wall is faced with modular block wall (MBW) 

units and has geogrid soil reinforcements. The MSE wall configuration to be analyzed is 

shown in Figure E.1-1. 

This MSE wall is (assumed to be) a “simple” structure and, therefore, is analyzed with the 

load factors that typically control external stability analyses (see Figure 4-1). The design 

steps used in these calculations follow the basic design steps presented in Table 4-3, of 

which, the primary steps are presented in Table E1-1. Each of the steps and sub-steps are 

sequential. Therefore, if the design is revised at any step or sub-step the previous 

computations need to be re-examined. Each step and sub-step follow. 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 1 November 2009
 

Figure E.1-1 Configuration of example problem E1. 
 

Table E.1-1. Primary Design/Analysis Steps 

Step 1. Establish Project Requirements 

Step 2. Establish Project Parameters 

Step 3. Estimate Wall Embedment Depth, Design 

Height(s), and Reinforcement Length 

Step 4 Define unfactored loads 

Step 5 Summarize Load Combinations, Load Factors, 

and Resistance Factors 

Step 6. Evaluate External Stability 

Step 7. Evaluate Internal Stability 

Step 8. Design of Facing Elements 

Step 9. Assess Overall Global Stability 

Step 10. Assess Compound Stability 

Step 11. Design Wall Drainage Systems 

Step 1. Establish Project Requirements 

C Geometry 

o Exposed wall height above finished grade, He = 18 ft 

o MBW unit facing, with 3 batter 

o 2H:1V broken backslope, 9 feet high 

o Level toe slope 

C Loading Conditions 

o Broken back slope 

o Traffic surcharge 

o No loads from adjacent structures 

o No seismic 

o No traffic barrier impact 

C Performance Criteria 

o Design code – AASHTO/FHWA LRFD 

o Maximum tolerable differential settlement = 1/200 

o Design life = 100 years 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 2 November 2009
 
 

Step 2. Establish Project Parameters 

C Subsurface conditions 

o Foundation soil, 'f = 30°, f = 125 pcf 

o Factored Bearing resistance of foundation soil 

 For service limit consideration, qnf-ser = 7.50 ksf for 1-inch of total settlement 

 For strength limit consideration, qnf-str = 10.50 ksf 

No groundwater influence 

C Reinforced wall fill, 'r = 34°, r = 125 pcf, pH = 7.3, maximum size 3⁄4-inch 

C Retained backfill, 'b = 30°, b = 125 pcf 

 

Step 3. Estimate Wall Embedment Depth and Reinforcement Length 

 

The minimum embedment depth = H/20 for walls with horizontal ground in front of wall, see 

Table 2-1; i.e., 0.9 ft for exposed wall height of 18 ft. Therefore, use minimum embedment 

depth of 2.0 ft. Thus, design height of the wall, H = 20 ft. 

Due to the 2H:1V backslope and traffic surcharge on the retained backfill, the initial length 

of reinforcement is assumed to be 0.9H or 18 ft. This length will be verified as part of the 

design process. 

Step 4 – Define Unfactored Loads 

The primary sources of external loading on an MSE wall are the earth pressure from the 

retained backfill behind the reinforced zone and any surcharge loadings above the reinforced 

zone. The 3 batter is a near vertical face, therefore assume a vertical face and that the MSE 

wall acts as a rigid body with earth pressures developed on a vertical pressure plane at the 

back end of the reinforcements. Estimate the earth pressures on wall for the broken 

backslope condition as shown in Figure 4-4 (reproduced below) and with Equations 4-2 and 

4-3. 

From figure: 

 H = 20.0 ft 

 2H = 40.0 ft 

 Height of slope = 9 ft 

 Therefore, angle I = arctan (9/40) = 12.7

 Slope crest is at the end of the reinforcement length, therefore, h = 20 + 9 = 29 ft 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 3 November 2009
 
 

Figure 4-4. External analysis: earth pressure; broken backslope case (after AASHTO, 

2007). 

Using Eq. 4-3, and  = I ,  = I,  for vertical and near vertical wall face, and b = 30

 

  ' ' sin ( +  ) sin ( -  )  

2  sin30  12.7 sin30  12.7 

2 

 = 1 + b b   1    2.133 

 sin ( -  ) sin ( +  ) 

  sin90  12.7sin90  12.7  

The external lateral pressure coefficient, Kab, using Eq. 4-2, is equal to: 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 4 November 2009
 

 

 

2 '	 2 sin ( + b ) sin 90  30 Kab = 2  2	  0.360

 sin	  sin ( -  ) 2.133 sin 90 sin 90    12.7 
 

Traffic Load 

The traffic load is on the level surface of the retained backfill. For external stability, traffic 

load for walls parallel to traffic have an equivalent height of soil, heq equal to 2.0 ft. 

Unfactored Loads:

 F1 = 1⁄2  1⁄2 (125 pcf) (29 ft)2

b h2

 Kab = (0.360) = 18.92 k/lft 

FH1 = F1 cos I = 18.92 k/lft (cos 12.7) = 18.46 k/lft 

FV1 = F1 sin I = 18.92 k/lft (sin 12.7) = 4.16 k/lft 

 q = 2.0 ft (125 pcf) = 250 psf 

F2 = q h Kab = 250 psf (29 ft) (0.360) = 2.61 k/lft 

FH2 = F2 cos I = 2.61 k/lft (cos 12.7) = 2.55 k/lft 

FV2 = F2 sin I = 2.61 k/lft (sin 12.7) = 0.57 k/lft 

V1 = r H L = 125 pcf (20 ft) (18 ft) = 45.00 k/lft 

V2 = 1⁄2 r L (h – H) = 1⁄2 (125 pcf) (18 ft) (29 ft – 20 ft) = 10.12 k/lft 

Step 5. Summarize Load Combinations, Load Factors, and Resistance Factors 

The design requires checking Strength I and Service I limit states. This is a simple wall. 

Note that examination of only the critical loading combination, as described in Section 4.2, is 

sufficient for simple walls. Load factors typically used for MSE walls are listed in Tables 4­

1 and 4-2. Load factors applicable to this problem are listed in Table E1-5.1. 

Table E1-5.1. Summary of applicable load factors 

Load Combination Load Factors 

EV ES EH 

Strength I (maximum) 1.35 1.50 1.50 

Strength I (minimum) 1.00 0.75 0.90 

Service I 1.00 1.00 1.00 

Resistance factors for external stability and for internal stability are summarized in Table E1­

5.2, see Tables 4-6 and 4-8 for more detail and AASHTO reference. 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 5 November 2009
 
 

Table E1-5.2. Summary of applicable resistance factors for evaluation of resistances 

Item Resistance Factor 

Sliding of MSE wall on foundation soil s = 1.00 

Bearing resistance b = 0.65 

Tensile resistance and connectors for 

geosynthetic reinforcement – static t = 0.90 

Pullout resistance – static p = 0.90 

Step 6. Evaluate External Stability 

The external stability is a function of the various forces and moments that are shown in 

Figure E1-2. In the LRFD context the forces and moments need to be categorized into 

various load types. For this example problem, the primary load types are soil loads (EV, EH 

and ES). 

6.1 Evaluate Sliding Stability 

This is a simple wall and, therefore, which load factor – minimum or maximum – is readily 

identified, see Figure E1.6-1 below (or Figure 4-1) for load factors for sliding and 

eccentricity checks. 

E.1.6-1 Typical load factors for sliding stability and eccentricity check. 

 

 

The factored resistance against failure by sliding (RR) can be estimated with Eq. 4-4: 

RR =  R

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 6 November 2009
 
 

1) Calculate nominal thrust, per unit width, acting on the back of the reinforced zone. From 

Step 4: 

FH1 = 18.46 k/lft 

FH2 = 2.55 k/lft 

2) Calculate the nominal and the factored horizontal driving forces. For a broken back slope 

and uniform live load surcharge, use Equations 4-9, 4-10, and 4-11 to calculate the 

factored driving force. Use the maximum load factors of EH = 1.50 and LS = 1.75 in 

these equations because it creates the maximum driving force effect for the sliding limit 

state. 

Pd  γEH FH1  γLS FH2 

P	  γ F   F  1.50 18.46  1.75 2.55  27.69  4.46  32.15 k/lft d EH H1 LS 2 

3) Assume that the critical sliding failure is along the foundation soil. Thus, the frictional 

property is tan ' f. Since this is a sheet type of reinforcement, sliding should also be 

checked at the elevation of the first layer of soil reinforcement (and applicable height). 

  tan f

  tan 30  0.577 

4) Calculate the nominal components of resisting force and the factored resisting force per 

unit length of wall. The minimum EV load factor (= 1.00) is used because it results in 

minimum resistance for the sliding limit state. The maximum EH and LS load factors are 

used to stay consistent with factors used to calculate the driving forces. The factored 

resistance, Rr, is equal to: 

R	 r  [ γEV 1 2 EH V1 LS V2 (V  V )  γ (F )   (F )]  μ

Rr	  1.00 (45.00  10.12 k/lft)  1.50 (4.16 k/lft)  1.75 (0.57)(0.577) 

Rr	  (55.12  6.24  1.00) (0.577)  36.0 k/lft 

5) Compare factored sliding resistance, Rr, to the factored driving force, Pd, to check that 

resistance is greater. If the CDR < 1.0, increase the reinforcement length, L, and repeat 

the calculations. The sliding capacity demand ratio is: 

R 36.0 k/lft CDR  r   1.12 O.K. S Pd 32.15 k/lft 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 7 November 2009
 
 

6.2 Eccentricity Limit Check 

The system of forces for checking the eccentricity at the base of the wall is shown on Figure 

E1.6-2. The weight and width of the wall facing is neglected in the calculations. 

Sum the factored moments about the centerline of the wall zone, with the loads as previously 

defined and moment arms as shown in Figure E1.6-1. This is a simple wall and, therefore, 

which load factor – minimum or maximum – is readily identified, see Figure 4-1, and are the 

same as used for the sliding check. 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 8 November 2009
 

Figure E1.6-2 Forces for eccentricity check. 

 M  M 

e  O 

V 

R 

 F 9.67 ft   F 14.5 ft   V 0   V 3 ft   F   F 9 ft EH-MAX H1 LS H2 EVMIN 1 EVMIN 2 EH-MAX V1 LS V2 e   EV-MIN 1 EV V   MIN 2 EH V   MAX V1 LS V2 F   F
 

1.50 18.46 9.67 ft   1.752.5514.5 ft  1.0045.000  1.0010.123 ft  1.504.16  1.750.579 ft e  1.0045.00  1.0010.12  1.504.16  1.750.57 

267.8 k - ft  64.70 k - ft  0  30.36 k - ft  65.14 k - ft 237.00 k - ft 

e    3.80 ft

45.00 k  10.12 k  6.24 k  1.00 k 62.36 k 

Check that e < L/4: 

L 18   4.5 ft e  3.80  4.50 ft O.K.

4 4 

6.3 Evaluate Bearing on Foundation 

This step, 6.3, requires a different computation of the eccentricity value computed in Step 6.2 

because different, i.e., maximum in lieu of minimum, load factor(s) are used. This is a 

simple wall and, therefore, which load factor – minimum or maximum – is readily identified, 

see Figure E1.6-3 below (or Figure 4-1) for load factors for bearing check. 

E.1.6-1 Typical load factors for bearing check. 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 9 November 2009
 
 

1) Calculate the eccentricity, eB, of the resulting force at the base of the wall. The e value 

from the eccentricity check, Step 6.a, cannot be used, calculate eB with factored loads. 

The maximum load factors for EH and EV are used to be consistent with the computation 

for v (below) where maximum load factors results in the maximum vertical stress. 

 EH-MAX FH1 9.67 ft   LS FH2 14.5 ft   EV MAX V1 0   EVMAX V2 3 ft   EH-MAX FV1   LS FV2 9 ft eB   EV-MAX 1 EV V   MAX 2 EH V   MAX V1 LS V2 F   F

1.50 18.46 9.67 ft   1.752.5514.5 ft  1.3545.000  1.3510.123 ft  1.504.16  1.750.579 ft eB  1.3545.00  1.3510.12  1.504.16  1.750.57 

267.8 k - ft  64.70 k - ft  0  41.00 k - ft  65.14 k - ft 226.36 k - ft 

eB 	   2.77 ft

60.75 k  13.66 k  6.24 k  1.00 k	 81.65 k 

2) Calculate the factored vertical stress V-F at the base assuming Meyerhof-type 

distribution. Maintain consistency with loads and load factors used in the eccentricity 

calculation and corresponding bearing stress calculation. 

V

σ V	  

L  2eB 

For this wall with a broken backslope and traffic surcharge the factored bearing stress is: 

γEV-MAX 1 EV-MAX 2 EH-MAX V1 LS V2 V  γ V  γ F  γ F

q V-F	  L  2eB 

81.65 k/lft

qV-F 	  6.55 ksf

18ft  22.77 ft 

3) Determine the nominal bearing resistance, qn, see Eq. 4-22. 

The nominal bearing resistance for strength limit state was provided. qn-str = 10.50 ksf 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 10 November 2009
 
 

4) Compute the factored bearing resistance, qR. The resistance factor, , for MSE walls is 

equal to 0.65 (see Table E1-5.2). The factored bearing resistance (qR or qnf-str) was given 

in Step 2 as equal to 10.50 ksf. (see Eq. 4-23) as: 

qR =  qn 

qR = 10.50 ksf 

5) Compare the factored bearing resistance, qR, to the factored bearing stress, V-F, to check 

that the resistance is greater. 

q 10.50 ksf CDRS  R   1.60 O.K.

 V-F 6.55 ksf 

6.4 Settlement Estimate 

Settlement is evaluated at Service I Limit State. From Step 2, the estimated settlement under 

a bearing stress of 7.50 ksf is 1.00 in. The bearing stress for Service I limit state is ___ ksf. 

Therefore, the settlement will be less than 1.00 in. 

Step 7 EVALUATE INTERNAL STABILITY 

7.1 Select Type of Soil Reinforcement 

Geogrid soil reinforcement will be used. Three grades, or strengths, of geogrid may be used. 

The grades and ultimate tensile strengths of these geogrids are summarized in Table E1-7.1. 

Table E1-7.1. Geogrid grades and strengths. 

Name (Grade): GG-I GG-II GG-III 

Ultimate Tensile Strength (lb/ft): 6,000 9,000 12,000 

7.2 Define Critical Slip Surface 

The critical failure surface is approximately linear in the case of extensible, geogrid 

reinforcements (see Figure E1-7-1), and passes through the toe of the wall. 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 11 November 2009
 
Figure E.7-1.	 Location of failure surface for internal stability of MSE walls and extensible 

reinforcements (from Figure 4-9. 

 

7.3 Define Unfactored Loads 

The relationship between the type of the reinforcement and the overburden stress is shown in 

Figure 4-10. The Kr/Ka ratio extensible (e.g., geogrid) reinforcement is a constant, and is 

equal to 1.0. 

The lateral earth pressure coefficient Kr is determined by applying a multiplier to the active 

earth pressure coefficient. The active earth pressure coefficient is determined using a 

Coulomb earth pressure relationship, assuming no wall friction and a β angle equal to zero 

(i.e., equivalent to the Rankine earth pressure coefficient, see Eq. 4-25). With a reinforced 

fill friction angle of 34, the active lateral earth pressure coefficient is: 

' 	  2  r 2   K 34  a  tan  45   tan  45   0.283 2  2    

Therefore, 

 Kr  K  K K r a    0.283  1.0  0.283  a  

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 12 November 2009
 
The stress, 2, due to a sloping backfill on top of an MSE wall can be determined as shown 

in Figure 4-11. An equivalent soil height, S, is computed based upon the slope geometry. 

The value of S should not exceed the slope height for broken back sloping fills. A 

reinforcement length of 0.7H is used to compute the sloping backfill stress, 2, on the soil 

reinforcement, as a greater length would only have minimal effect on the reinforcement. The 

vertical stress is equal to the product equivalent soil height and the reinforced fill unit weight, 

and is uniformly applied across the top of the MSE zone. 

The equivalent uniform height of soil, Seq, is equal to: 

1 1  Seq   20.7H tanβ   20.7 20 ft tan 26.6  3.51 ft 

7.4 Establish Vertical Layout of Soil Reinforcements 

The MBW units are 8 inches tall. The geogrid soil reinforcement spacing is listed in Table 

E1-7.5. The upper layer of geogrid will be 8 inches below top of wall, and the bottom layer 

of geogrid will be 8 inches above the leveling pad. The grade of geogrid to use at each 

elevation will be determined by strength and connection requirements. 

7.5 Calculate Factored Tensile Forces in the Reinforcement Layers 

The factored horizontal stress, H, at any depth Z below the top of wall is equal to (after 

equation 4-29): 

σH = Kr [r (Z + Seq) γEV-MAX] 

The maximum tension TMAX in each reinforcement layer per unit width of wall based on the 

vertical spacing Sv (see Eq. 4-32a) is: 

T MAX H v  σ S

The term Sv is equal to the vertical reinforcement spacing for a layer where vertically 

adjacent reinforcements are equally spaced from the layer under consideration. In this case, 

H, calculated at the level of the reinforcement, is at the center of the contributory height. 

The contributory height is defined as the midpoint between vertically adjacent reinforcement 

elevations, except for the top and bottom layers reinforcement. For the top and bottom layers 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 13 November 2009
 
 

 

 

 

 

of reinforcement, Sv is the distance from top or bottom of wall, respectively, to the midpoint 

between the first and second layer (from top or bottom of wall, respectively) of 

reinforcement. Sv distances are illustrated in Figure 4-14. 

The factored horizontal stress, vertical spacing, and maximum tension for all layers are 

summarized in Table E1-7.5. Example calculation, for layer #3 follows. 

 For all layers: Kr = 0.283 r = 125 pcf 

Seq = 3.51 ft EV-MAX = 1.35 

For Layer #3: Z = 4.67 ft SV = 2.0 ft 

σH = Kr [r (Z + Seq) γEV-MAX] = 0.283 [125 pcf (4.67 + 3.51 ft) (1.35)] = 391 lb/ft2 

TMAX H V

For Layer #1: Z = 0.67 ft SV = 1.67 ft 

 SV-Top = 0 ft SV-Bottom = 1.67 ft ZAve = 0.835 ft 

 =  S = 391 lb/ft2 (2.0 ft) = 781 lb/lft 

σH = Kr [r (ZAVE + Seq) γEV-MAX] = 0.283 [125 pcf (0.835 + 3.51 ft) (1.35)] = 207 lb/ft2 

TMAX = H SV = 207 lb/ft2 (1.67 ft) = 346 lb/lft 

Table E1-7.2 Maximum Tension in Geogrid Layers. 

Layer 

# 

Z 

(ft) 

SV 

(ft) 

H 

(lb/ft2) 

TMAX 

(lb/lft) 

1 0.67 1.67 115 346 

2 2.67 2.0 203 590 

3 4.67 2.0 298 781 

4 6.67 2.0 394 972 

5 8.67 2.0 489 1163 

6 10.67 2.0 585 1354 

7 12.67 2.0 681 1545 

8 14.67 2.0 776 1736 

9 16.67 2.0 872 1927 

10 18.67 1.33 951 1366 

11 19.33 1.0 1006 1091 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 14 November 2009
 
 

7.6 Calculate Soil Reinforcement Resistance 

The nominal geosynthetic reinforcement strength, Tal, per Eq. 3-12, is equal to: 

T T ult ult T al   RF RF ID CR D RF RF

The procedure and discussion on definition of nominal long-term reinforcement design 

strength (Tal), for both steel and geosynthetic reinforcements, are presented in Section 3.5 of 

this manual. 

The factored soil resistance is the product of the nominal long-term strength and applicable 

resistance factor, . The resistance factors for tensile rupture of MSE wall soil 

reinforcements are summarized in Table 4-8. The resistance factor for geosynthetic 

reinforcement is 0.90. The factored soil reinforcement tensile resistance, Tr, is (per Eq. 4-33) 

equal to: 

Tr =  Tal 

The strength reduction factors, nominal resistance, and factored resistance for the three 

grades of geogrids are summarized in Table E1-7.3. 

Table E1-7.3 Geogrid Nominal and Factored Resistance. 

Geogrid: GG-I GG-II GG-III 

Tult (lb/ft) 3,000 6,000 9,000 

Creep, RFCR 1.85 1.85 1.85 

Durability, RFD 1.15 1.15 1.15 

Installation, RFID 1.3 1.3 1.2 

Tal (lb/ft) 1,085 2,169 3,525 

Tr 976 1,952 3,173 

7.7 Select Grade of and/or Number of Soil Reinforcement Elements at Each Level 

The soil reinforcement vertical layout, the factored tensile force at each reinforcement level, 

and the factored soil reinforcement resistance were defined in the previous three steps. 

Suitable grades (strength) of reinforcement for the defined vertical reinforcement layout is 

summarized in Table E1-7.4. The CRD for each layer is also listed. 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic 

MSE Walls and RSS – Vol II E1 – 15 November 2009 
 

 

 

 

Check this layout for pullout and connection resistance. Adjust layout if/as necessary. 

Table E1-7.4 Geogrid Nominal and Factored Resistance. 

Layer 

# 

Z 

(ft) 

SV 

(ft) 

TMAX 

(lb/lft) 

Geogrid 

CDR Grade Tr 

(lb/ft) 

1 0.67 1.67 346 GG-I 976 2.82 

2 2.67 2.0 590 GG-I 976 1.65 

3 4.67 2.0 781 GG-I 976 1.25 

4 6.67 2.0 972 GG-I 976 1.00 

5 8.67 2.0 1163 GG-II 1,952 1.68 

6 10.67 2.0 1354 GG-II 1,952 1.44 

7 12.67 2.0 1545 GG-II 1,952 1.26 

8 14.67 2.0 1736 GG-II 1,952 1.12 

9 16.67 2.0 1927 GG-II 1,952 1.01 

10 18.67 1.33 1366 GG-II 1,952 1.43 

11 19.33 1.0 1091 GG-II 1,952 1.79 

7.8 Internal Stability with Respect to Pullout Failure 

Therefore, the required embedment length in the resistance zone (i.e., beyond the potential 

failure surface) can be determined from (Eq. 4-36): 

 TMAX L   3 ft 1 m e  F *  v CRc 

where: 

Le = Length of embedment in the resisting zone 

TMAX = Maximum reinforcement tension 

  = Resistance factor for soil reinforcement pullout, = 0.90 

F* = Pullout resistance factor, = 0.45 for these geogrids 

 α = Scale correction factor, = 0.8 for these geogrids 

σv = Average (see Figure E.7-2), nominal (i.e., unfactored) vertical stress at 

the reinforcement level in the resistant zone 

C = 2 for geogrid type reinforcement 

Rc = Coverage ratio, = 1.0 for geogrid and 100% coverage 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 16 November 2009
 
Figure E.7-2. Nominal vertical stress at the reinforcement level in the resistant zone, 

beneath a sloping backfill (also presented as Figure 4-15). 

 

Table E1-7.5 Pullout Check. 

Layer 

# 

Z 

(ft) 

La 

(ft) 

Available 

Le 

(ft) 

TMAX 

(lb/lft) 

ZP 

(ft) 

Required 

Le 

(ft) 

CDR 

1 0.67 10.28 7.72 346 7.74 0.55 14.0 

2 2.67 9.22 8.78 590 9.47 0.77 11.4 

3 4.67 8.16 9.84 781 11.21 0.86 11.4 

4 6.67 7.09 10.91 972 12.94 0.93 11.8 

5 8.67 6.03 11.97 1163 14.68 0.98 12.2 

6 10.67 4.96 13.04 1354 16.41 1.02 12.8 

7 12.67 3.90 14.10 1545 18.14 1.05 13.4 

8 14.67 2.84 15.16 1736 19.88 1.08 14.1 

9 16.67 1.77 16.23 1927 21.61 1.10 14.7 

10 18.67 0.71 17.29 1366 23.35 0.72 23.9 

11 19.33 0.36 17.64 1091 23.92 0.56 31.1 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 17 November 2009
 
 

 

 

 

7.9 Check Connection Strength 

The connection of the reinforcements with the facing, should be designed for TMAX for all 

limit states. The resistance factors () for the connectors is the same as for the reinforcement 

strength, i.e.,  = 0.90 for geogrids. 

The nominal long-term connection strengths, Talc, based upon laboratory connection tests 

between these MBW units and geogrids, as a function of geogrid grade and normal pressure, 

are summarized in Table E1-7.6. 

Table E1-7.6 Connection Strength Check. 

Layer 

# 

Geogrid 

Grade 

Talc 

A 

(lb/ft) 

alc 

(lb/ft) 

TMAX 

(lb/lft) CDR 

1 GG-I 533 480 346 1.39 

2 GG-I 733 660 590 1.12 

3 GG-I 933 840 781 1.08 

4 GG-I 1133 1020 972 1.05 

5 GG-II 1333 1200 1163 1.03 

6 GG-II 1533 1380 1354 1.02 

7 GG-II 1733 1560 1545 1.01 

8 GG-II 1933 1740 1736 1.00 

9 GG-II 2150 1935 1927 1.00 

10 GG-II 2450 2205 

1952B 1366 1.43 

11 GG-II 2550 2295 

1952B 1091 1.79 

Notes: 

A. Talc values previously established when Agency placed this system on its 

approved wall systems list. 

B. The Tr value limits factored connection strength. 

7.10 Lateral Movements 

The magnitude of lateral displacement depends on fill placement techniques, compaction 

effects, reinforcement extensibility, reinforcement length, reinforcement-to-facing 

connection details, and details of the wall facing. A rough estimate of probable lateral 

displacements of simple MSE walls that may occur during construction can be estimated 

based on empirical correlations (see Figure 2-15). It is assumed that experience with this 

type of MBW unit facing and wall fill material have demonstrated lateral movements are 

within acceptable limits. 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 18 November 2009
 
7.11 Vertical Movement and Bearing Pads 

Bearing pads are generally not used with MBW unit facings, and are not used with this 

example problem. The wall height is 20 feet, and is below the recommended maximum 

height of 32 ft without bearing pads (see 3.6.1). 

Calculation of the external settlement was reviewed in Step 6.4. The reinforced wall fill is a 

well graded, granular soil and, therefore, the internal movement will be negligible with good 

compaction control during construction. 

Step 8. Design of Facing Elements 

Facing elements are designed to resist the horizontal forces developed in Step 7. With the 

modular concrete facing blocks (MBW), the maximum spacing between reinforcement layers 

should be limited to twice the front to back width, i.e., 24 in. The maximum depth of facing 

below the bottom reinforcement layer is 8 in., and is less than the MBW unit depth. The top 

row of reinforcement is 8 in. below top of wall, and is less than 1.5 the block depth. 

Sufficient inter-unit shear capacity exceeds the factored horizontal earth pressure at the 

facing. 

Step 9. Assess Overall/Global Stability 

This design step is performed to check the overall, or global, stability of the wall. Overall 

stability is determined using rotational or wedge analyses, as appropriate, to examine 

potential failure planes passing behind and under the reinforced zone. Analyses can be 

performed using a classical slope stability analysis method with standard slope stability 

computer programs. This step is not detailed in this example calculation, see Chapter 9. 

 

Step 10. Assess Compound Stability 

This design step is performed to check potential compound failure planes passing through the 

reinforced soil zone. Compound stability is determined using rotational or wedge analyses, 

as appropriate, performed with computer programs that directly incorporate reinforcement 

elements in the analyses. This step is not detailed in this example calculation, see Chapter 9. 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 19 November 2009
 
 

Step 11. Wall Drainage Systems 

Subsurface and surface drainage are important aspects in the design and specifying of MSE 

walls. The Agency should detail and specify drainage requirements for vendor designed 

walls. Furthermore, the Agency should coordinate the drainage design and detailing (e.g., 

outlets) within its own designers and with the vendor. This step is not detailed in this 

example calculation, see Chapter 5. 

FHWA NHI-10-025 Example E1 – Broken Backslope & Traffic
 

MSE Walls and RSS – Vol II E1 – 20 November 2009
 
 

EXAMPLE E2 

BEARING CHECK FOR EXAMPLE E1 MSE WALL 

WITHOUT and WITH HIGH GROUNDWATER, 

and WITH A SLOPING TOE
 

 

E2-1 INTRODUCTION 

This example problem demonstrates the strength limit state bearing resistance analyses of an 

MSE wall with various foundation conditions. A flat bearing surface with and without a high 

groundwater condition, and a sloping toe without groundwater are examined. The MSE wall 

configuration to be analyzed is shown in Figure E.2-1 (and in Figure E.1-1). 

This MSE wall is (assumed to be) a “simple” structure and, therefore, is analyzed with the 

load factors that typically control external stability analyses (see Figure 4-1). The design 

steps used in these calculations follow the basic design steps presented in Table 4-3, of 

which, the primary steps are presented in Table E1-1. Each of the steps and sub-steps are 

sequential. Therefore, if the design is revised at any step or sub-step the previous 

computations need to be re-examined. Each step and sub-step follow. 

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 1 November 2009
 

Figure E.2-1 Configuration of example problem E1. 
 

Table E.2-1. Primary Design/Analysis Steps 

Step 1. Establish Project Requirements 

Step 2. Establish Project Parameters 

Step 3. Estimate Wall Embedment Depth, Design 

Height(s), and Reinforcement Length 

Step 4 Define unfactored loads 

Step 5 Summarize Load Combinations, Load Factors, 

and Resistance Factors 

Step 6. Evaluate External Stability 

Step 7. Evaluate Internal Stability 

Step 8. Design of Facing Elements 

Step 9. Assess Overall Global Stability 

Step 10. Assess Compound Stability 

Step 11. Design Wall Drainage Systems 

See Example E1 for Steps 1 – 11. 

However, for these computations, bearing resistances are computed (for several cases) in lieu 

of defined bearing resistances. 

Step 2. Establish Project Parameters 

C Foundation soil, 'f = 30°, f = 125 pcf 

C Factored bearing resistance of foundation soil 

o For service limit consideration, qnf-ser = 7.5 ksf for 1-inch of total settlement 

o For strength limit consideration, qnf-str – is to be determined 

C Reinforced wall fill, 'r = 34°, r = 125 pcf, pH = 7.3, maximum size 3⁄4-inch 

C Retained backfill, 'b = 30°, b = 125 pcf 

From Example E1: 

Step 4. Define Unfactored Loads 

Traffic Load 

The traffic load is on the level surface of the retained backfill. For external stability, traffic 

load for walls parallel to traffic and more than 1-ft behind the backface of the MSE wall is 

represented by an equivalent height of soil, heq equal to 2.0 ft. 

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 2 November 2009
 
 

Unfactored Loads:

 F1 = 1⁄2 b h2 Kab = 1⁄2 (125 pcf) (29 ft)2 (0.360) = 18,922 lb/lft = 18.92 k/lft 

FH1 = F1 cos I = 18.92 k/lft (cos 12.7) = 18.46 k/lft 

FV1 = F1 sin I = 18.92 k/lft (sin 12.7) = 4.16 k/lft 

 q = 2.0 ft (125 pcf) = 250 psf 

F2 = q h Kab = 250 psf (29 ft) (0.360) = 2,610 lb/lft = 2.61 k/lft 

FH2 = F2 cos I = 2.61 k/lft (cos 12.7) = 2.55 k/lft 

FV2 = F2 sin I = 2.61 k/lft (sin 12.7) = 0.57 k/lft 

V1 = r H L = 125 pcf (20 ft) (18 ft) = 45,000 lb/lft = 45.0 k/lft 

V2 = 1⁄2 r L (h – H) = 1⁄2 (125 pcf) (18 ft) (29ft – 20ft) = 10,125 lb/lft = 10.12 k/lft 

Step 5. Summarize Load Combinations, Load Factors, and Resistance Factors 

The design requires checking Strength I limit state. This is a simple wall. Note that 

examination of only the critical loading combination, as described in Section 4.2, is sufficient 

for simple walls. Load factors typically used for MSE walls are listed in Tables 4-1 and 4-2. 

Load factors applicable to this problem are listed in Table E2-5.1. Bearing resistance factor 

for MSE walls is listed in Table E2-5.2 

Table E2-5.1. Summary of applicable load factors 

Load Combination Load Factors 

EV ES EH 

Strength I (maximum) 1.35 1.50 1.50 

Strength I (minimum) 1.00 0.75 0.90 

Table E2-5.2. Bearing resistance factor 

Item Resistance Factor 

Bearing resistance b = 0.65 

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 3 November 2009
 
 

Step 6. Evaluate Bearing on Foundation 

This step, 6.3, requires a different computation of the eccentricity value computed in Step 6.2 

because different, i.e., maximum in lieu of minimum, load factor(s) are used. This is a 

simple wall and, therefore, which load factor – minimum or maximum – is readily identified 

for load factors for bearing check. 

2) Calculate the factored vertical stress V-F at the base assuming Meyerhof-type 

distribution. Maintain consistency with loads and load factors used in the eccentricity 

calculation and corresponding bearing stress calculation. 

 

V

σ	 V  L  2eB 

For this wall with a broken backslope and traffic surcharge the factored bearing stress is 

(see Example E1): 

γEV-MAX 1 EV-MAX 2 EH-MAX V1 LS V2 V  γ V  γ F  γ F

qV-F  L  2eB 

81.65 k/lft

qV-F 	  6.55 ksf

18ft  22.77 ft 

 

E2-1 CALCULATIONS 

It is not obvious whether the strength or the service (i.e., settlement) limit state controls. 

Therefore, check both. 

2) (cont.) 

Calculate e for service limit state: 

F	 9.67 ft  F 14.5 ft  V 0  V 3 ft  F  F 9 ft H1 H2 1 2 V1 V2 e b-ser  V1 2 V1 V2 	  V  F  F

18.46 9.67 ft   2.55 14.5 ft   45.000  10.123 ft  4.16  0.579 ft e b-ser  45.00  10.12  4.16  0.57 

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 4 November 2009
 
 

178.51 k - ft  36.98 k - ft  0  30.36 k - ft  42.57 k - ft 142.55 k - ft 

e 	   2.38 ft b-ser 59.85 k	 59.85 k 

Calculate service limit state bearing stress: 

 

1.00(45k/lft)  1.00(10.12k/lft)  (1.00)4.16 k/lft 59.85 k/lft q 	   4.52 ksf vservice 18 ft  2(2.38 ft)	 13.24 ft 

The bearing stress of 4.52 ksf is less than the stated 7.5 ksf for a 1-inch total settlement. 

Therefore, less than 1-inch of settlement is anticipated and service limit state is O.K. 

Note: See FHWA Soils and Foundations reference manual, FHWA NHI-06-089 

(Samtani and Nowatzki, 2006) for settlement analysis and bearing pressure versus 

settlement plotting procedures. 

3) Determine the nominal bearing resistance, qn, see Eq. 4-22. 

The nominal bearing resistance for strength I (max) limit state, with N from Table 4-6, 

for  ́ f = 30o is: 

qn  cf Nc  0.5 L' γf Nγ  0 Nc  0.5 (12.46ft) (125 pcf) (22.4)  17.44 ksf 

where L ́ = 18 ft – 2 (2.77 ft) = 12.46 ft 

4) Compute the factored bearing resistance, qR. The resistance factor, , for MSE walls is 

equal to 0.65 (see Table E2-5.2). The factored bearing resistance (qR) is given (see Eq. 4­

23) as: 

qR =  qn 

For strength limit state: 

qR = 0.65 (17.44 ksf) = 11.34 ksf 

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 5 November 2009
 
 

 

5) Compare the factored bearing resistance, qR, to the factored bearing stress, V-F, to check 

that the resistance is greater. 

For strength limit state: 

q

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 6 November 2009
 

R 11.34 ksf CDR    1.73 O.K. Strength  V-F 6.55 ksf 
 

E2-2 CALCULATIONS WITH GROUNDWATER NEAR SURFACE 

Compute Strength I (max) limit state bearing resistance and CDR assuming groundwater is 

12 ft below the ground surface, as illustrated in Figure E.2-2. 

Figure E.2-2. Bearing groundwater influence terms for spread footing 

 (Note: Bf = L ́ for MSE wall design). 

With groundwater consideration, and no cohesion, the nominal bearing resistance (see Eq. 4­

22 and AASHTO 10.6.3.1.2a-1) is equal to: 

q n  0.5 L' γf N Cγ w 

 

The term Cw is defined in Table 10.6.3.1.2a-2 (AASHTO, 2007): 

Coefficient Cw for Various Groundwater Depths 

(after AASHTO Table 10.6.3.1.2a-2) 

Dw Cw 

0.0 0.5 

Df 0.5 

> 1.5 L' + Df 1.0 

Note: Interpolate between the values shown for 

intermediate positions of the groundwater table. 

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 7 November 2009
 
 

Calculations: 

Given: Moist unit weight, m = 125 lb/ft3 

 Dw = 12 ft 

The buoyant unit weight should be used to compute the overburden pressure if the 

groundwater table is located with the potential failure zone. 

1.5 L  Df  1.5 18 ft  22.77 ft  2 ft  20.69 ft 

At Dw = Df = 2.0 ft Cw = 0.5 

At Dw = 1.5 L' + Df = 20.7 ft Cw = 1.0 

Interpolating to Dw = 12 ft 

 12 ft  2 ft  Cw  0.5  0.5      0.77

 20.69 ft  2 ft  

The nominal bearing resistance for strength limit state, with Cw = 0.77, moist unit weight ' 

= 125 pcf, and N from Table 4-6, is: 

q n  0.5 L' γf N γ C w  0.5 (12.46ft) (125 pcf) (22.4) (0.77)  13,432 psf  13.43 ksf

The factored strength limit state bearing resistance is: 

qR = 0.65 (13.43 ksf) = 8.73 ksf 

The capacity to demand ratio is: 

q CDR R 8.73 ksf

Strength    1.33 O.K.

 V-F 6.55 ksf 

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 8 November 2009
 
 

 

 

 

 

E2-3 CALCULATIONS WITH TOE SLOPE AND WITHOUT GROUNDWATER 

Compute Strength I (max) limit state bearing resistance and CDR assuming with sloping toe 

and no groundwater, as illustrated in Figure E.2-3, and with the following geometry: 

B = L – 2 eB = 12.46 ft 

b = 4 ft 

Df = assume = 0 

I = 18.4o (3H:1V) 

Figure E.2-3. Bearing sloping toe terms. 

For footings bearing near a slope the term N is replaced by Nq (AASHTO 10.6.3.1.2c). The 

Nq term is taken from AASTHO Figure 10.6.3.1.2c-2. The nominal bearing resistance, for a 

foundation soil with no cohesion, is equal to: 

qn  0.5 L' γf Nγq 

From AASTHO Figure 10.6.3.1.2c-2 an Nq value equal to approximately 18 is found for f 

= 30o, b/B = 0.32, and  = 18.4o. 

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 9 November 2009
 
The nominal bearing resistance for strength limit state with Nq = 20 is: 

qn  0.5 L' γf Nγq  0.5 (12.46 ft) (125 pcf) (18)  14,017 psf  14.02 ksf 

The factored strength limit state bearing resistance is: 

qR = 0.65 (14.02 ksf) = 9.11 ksf 

The capacity to demand ratio is: 

q 9.11 ksf R CDR    1.39 O.K. Strength  V-F 6.55 ksf 

FHWA NHI-10-025 Example E2 – Bearing Resistance 

MSE Walls and RSS – Vol II E2 – 10 November 2009
 
 

 

EXAMPLE E3 

SEGMENTAL PRECAST PANEL MSE WALL WITH SLOPING BACKFILL 

SURCHARGE 

E3-1 INTRODUCTION 

This example problem demonstrates the analysis of a MSE wall with a sloping backfill 

surcharge. The MSE wall is assumed to include a segmental precast panel face with ribbed 

steel strip reinforcements. The MSE wall configuration to be analyzed is shown in Figure 

E3-1. The analysis is based on various principles that were discussed in Chapter 4. Table 

E3-1 presents a summary of steps involved in the analysis. Each of the steps and sub-steps is 

sequential and if the design is revised at any step or sub-step then all the previous 

computations need to be re-visited. Each of the steps and the sub-steps in Table E3-1 is 

explained in detail herein. 

Table E3-1. Summary of steps in analysis of MSE wall with sloping backfill 

Step Item 

1 Establish project requirements 

2 Establish project parameters 

3 Estimate wall embedment depth and length of reinforcement 

4 Estimate unfactored loads 

5 Summarize applicable load and resistance factors 

6 Evaluate external stability of MSE wall 

6.1 Evaluation of sliding resistance 

6.2 Evaluation of limiting eccentricity 

6.3 Evaluation of bearing resistance 

6.4 Settlement analysis 

7 Evaluate internal stability of MSE wall 

7.1 Estimate critical failure surface, variation of Kr and F* for internal stability 

7.2 Establish vertical layout of soil reinforcements 

7.3 Calculate horizontal stress and maximum tension at each reinforcement level 

7.4 Establish nominal and factored long-term tensile resistance of soil reinforcement 

7.5 Establish nominal and factored pullout resistance of soil reinforcement 

7.6 Establish number of soil reinforcing strips at each level of reinforcement 

8 Design of facing elements 

9 Check overall and compound stability at the service limit state. 

10 Design wall drainage system 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 1 November 2009
 
 

 

2 

1 

Reinforced backfill 

'r, γr

H He

L d 

Retained backfill 

(above the behind 

the reinforced 

backfill) 

'f, γf 

Leveling Foundation Soil 

Pad 'fd, γfd 

Figure E3-1. Configuration showing various parameters for analysis of a MSE wall with 

sloping backfill (not-to-scale). 

STEP 1. ESTABLISH PROJECT REQUIREMENTS 

	 Exposed wall height, He = 28 ft 

	 Length of wall = 850 ft 

	 Design life = 75 years 

	 Precast panel units: 5 ft wide x 5 ft tall x 0.5 ft thick 

	 Type of reinforcement: Grade 65 (Fy = 65 ksi), 1.969 in. x 0.157 in. (50 mm wide x 4 

mm) thick galvanized steel ribbed strips with zinc coating of 3.386 mils (86 m). 

	 No seismic considerations 

STEP 2. EVALUATE PROJECT PARAMETERS 

	 Reinforced backfill, 'r = 34°, r = 125 pcf, coefficient of uniformity, Cu = 7.0 and 

meeting the AASHTO (2007) requirements for electrochemical properties 

	 Retained backfill, 'f = 30°, f = 125 pcf 

	 Foundation soil, 'fd = 30°, fd = 125 pcf 

 Factored Bearing resistance of foundation soil 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 2 November 2009
 
 

 

o For service limit consideration, qnf-ser = 7.50 ksf for 1-inch of total settlement 

o For strength limit consideration, qnf-str = 10.50 ksf 

Note: the above bearing resistance values are assumed values for the purpose of this 

example problem. In actual designs, the geotechnical engineer should develop 

appropriate project and wall specific values. 

STEP 3. ESTIMATE DEPTH OF EMBEDMENT AND LENGTH OF 

REINFORCEMENT 

Based on Table C.11.10.2.2.-1 of AASHTO (2007), the minimum embedment depth = H/20 

for walls with horizontal ground in front of wall, i.e., 1.4 ft for exposed wall height of 28 ft. 

For this design, assume embedment, d = 2.0 ft. Thus, design height of the wall, H = He + d = 

28 ft + 2.0 ft = 30 ft. 

Due to the 2H:1V backslope, the initial length of reinforcement is assumed to be 0.8H or 24 

ft. This length will be verified as part of the design process. The length of the reinforcement 

is assumed to be constant throughout the height to limit differential settlements across the 

reinforced zone because differential settlements could overstress the reinforcements. 

STEP 4. ESTIMATE UNFACTORED LOADS 

Tables E3-4.1 and E3-4.2 present the equations for unfactored loads and moment arms about 

Point A shown in Figure E3-2. The moments are a product of the respective forces and 

moment arms. Each force is assigned a designation representing the applicable load type as 

per Tables 3.4.1-1 and 3.4.1-2 of AASHTO (2007). 

To compute the numerical values of various forces and moments, the parameters provided in 

Step 2 are used. Using the values of the various friction angles, the coefficients of lateral 

earth pressure for the retained fill is computed as follows: 

Coefficient of active earth pressure per Eq. 3.11.5.3-1 of AASHTO (2007) is 

2   

where per Eq. 3.11.5.3-2 of AASHTO (2007) the various parameters in above equation are as 

follows: 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 3 November 2009
 

sin  f Ka 

 2 sin sin( ) 
 

 

 sin(  ) sin(  ) 

2 

f f   1  sin( ) sin()  

 = friction angle between fill and wall taken as specified 

 = angle (nominal) of fill to horizontal 

 = angle of back face of wall to horizontal 

'f = effective angle of internal friction of retained backfill 

For the case of level backfill with vertical backface,  =  = 0° and  = 90°, the coefficient of 

active earth pressure is given as follows: 

Ka = (1-sin' f)/(1+sin' f) 

For this example problem, compute the coefficient of active earth pressure for the retained 

fill, Kaf, using  = 26.56° (for the 2:1 backslope), vertical backface,  = 90°, and  =  as 

follows 

2  o o o  sin(30  26.56o ) sin(30  26.56 )  (0.834)(0.060) 

2 

  1   1 1.563

o o o o  sin(90  26.56 ) sin(90  26.56 )   (0.894)(0.894) 

  

2 2 o o sin  

f  sin (90  30 ) 0.750 K    0.537 2 o 2 o o af 

sin sin( ) 1.563(sin 90 ) [ sin(90  26.56 )] (1.563)(1.0)(0.894) 

For the example problem, Tables E3-4.3 and E3-4.4 summarize the numerical values 

unfactored forces and moments, respectively, based on the equations, various dimensions and 

values of lateral earth pressure coefficients presented above. Refer to Figure E3-2 for 

notations of various forces. 

The unfactored forces and moments in Tables E3-4.3 and E3-4.4 form the basis of all 

computations in this example problem. The unfactored forces and moments should be 

multiplied by the appropriate load factors based on the load types identified in the second 

column of the Tables E3-4.1 and E3-4.2 to perform the analysis for various load 

combinations such as Strength I, Service I, etc. 

The load factors for various load types relevant to this example problem are discussed in Step 

5. 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 4 November 2009
 
 

 

 A 

(2/3)L

 L/2 FTV

 FTH 

(a) 

(b) 

Figure E3-2. Legend for computation of forces and moments (a) for external stability 

analysis, (b) for internal stability analysis (not-to-scale). 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 5 November 2009
 
 

 

Table E3-4.1. Equations of computing unfactored vertical forces and moments 

Vertical Force LRFD Moment arm (Length units) 

(Force/length units) Load Type @ Point A 

V1=(γr)(H)(L) EV L/2 

V2= (L)(L tan ))( 2 

1 

   f 

 



 EV (2/3)L 

FTV = (1/2)(γr)(h2

)(Kaf)(sin) EH L 

Note: h = H + Ltan

Table E3-4.2. Equations of computing unfactored horizontal forces and moments 

Horizontal Force 

(Force/length units) 

LRFD 

Load Type 

Moment arm (Length units) 

@ Point A 

FTH = (1/2)(γr)(h2)(Kaf)(cos) EH h/3 

Note: h = H + Ltan
 

For this example problem, tan = 0.5, and h = 30 ft + 24 ft (0.5) = 42.00 ft. 

Table E3-4.3. Unfactored vertical forces and moments 

Force Value 

k/ft 

Moment 

Arm @ 

Point A, ft 

Moment 

Moment at 

Point A, 

k-ft/ft 

V1 = 90.00 12.00 MV1 = 1080.00 

V2 = 18.00 16.00 MV2 = 288.00 

FTV = 26.48 24.00 MFTV = 635.44 

Table E3-4.4. Unfactored horizontal forces and moments 

Force Value 

k/ft 

Moment 

Arm @ 

Point A, ft 

Moment 

Moment at 

Point A, 

k-ft/ft 

FTH = 52.95 14.00 MFTH = 741.35 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 6 November 2009
 
 

 

STEP 5. SUMMARIZE APPLICABLE LOAD AND RESISTANCE FACTORS 

Table E3-5.1 summarizes the load factors for the various LRFD load type shown in second 

column of Tables E3-4.1 and E3-4.2. Throughout the computations in this example 

problem, the forces and moments in Tables E3-4.1 and E3-4.2 should be multiplied by 

appropriate load factors. For example, if computations are being done for Strength I 

(maximum) load combination, the forces and moments corresponding to load V2 should be 

multiplied by 1.35 which is associated with load type EV assigned to load V2. 

Table E3-5.1. Summary of applicable load factors 

Load Combination 

Load Factors 

(after AASHTO, 2007 Tables 3.4.1-1 and 3.4.1-2) 

EV EH 

Strength I (maximum) 1.35 1.50 

Strength I (minimum) 1.00 0.90 

Service I 1.00 1.00 

For computation of factored resistances during evaluation of strength limits states, 

appropriate resistance factors have to be used. Table E3-5.2 summarizes the applicable 

resistance factors. For service limit state, all resistance factors are equal to 1.0. 

Table E3-5.2. Summary of applicable resistance factors for evaluation of resistances 

Item Resistance 

Factors 

AASHTO (2007) 

Reference 

Sliding of MSE wall on foundation soil s = 1.00 Table 11.5.6-1 

Bearing resistance b = 0.65 Table 11.5.6-1 

Tensile resistance (for steel strips) t = 0.75 Table 11.5.6-1 

Pullout resistance p = 0.90 Table 11.5.6-1 

STEP 6. EVALUATE EXTERNAL STABILITY OF MSE WALL 

The external stability of MSE wall is a function of the various forces and moments that are 

shown in Figure E3-2a. In the LRFD context the forces and moments need to be categorized 

into various load types. For this example problem, the primary load types are soil loads (EV 

and EH). 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 7 November 2009
 
 

 

6.1 Sliding Resistance at Base of MSE Wall 

The purpose of these computations is to evaluate the sliding resistance at the base of the MSE 

wall. Since the computations are related to sliding resistance, the beneficial contribution of 

live load to resisting forces and moments is neglected. The computations for sliding 

resistance at the base of the MSE wall are illustrated in Table E3-6.1. Note that sliding 

resistance is a strength limit state check and therefore service limit state calculations are not 

performed. Since the friction angle of foundation soil, fd, is less than the friction angle for 

reinforced soil, r, the sliding check will be performed using fd. The critical values based on 

max/min result in the extreme force effect and govern the sliding mode of failure. The 

resistance to load ratio, CDR, based on critical values of max/min is 1.07 indicating that the 

choice of 24 ft long reinforcement is justified because lesser length would result in CDR < 

1.0 which is not acceptable. 

Table E3-6.1. Computations for evaluation of sliding resistance of MSE wall 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Lateral load on the MSE wall, Hm = FTH k/ft 79.43 47.66 N/A 

Vertical load at base of MSE wall, VA1 = V1+V2 k/ft 145.80 108.00 N/A 

Vertical load at base of MSE wall, VA2 = FTV k/ft 39.72 23.83 N/A 

Total vertical load at base of MSE wall, VA=VA1+VA2 k/ft 185.52 131.83 N/A 

Nominal sliding resistance at base of MSE wall, VNm1 

= tan('fd)( V1+V2) k/ft 84.18 62.35 N/A 

Nominal sliding resistance at base of MSE wall, VNm2 

= tan('fd)( FTV) k/ft 22.93 13.76 N/A 

Nominal sliding resistance at base of MSE wall, VNm 

= VNm1+VNm2 

k/ft 107.11 76.11 N/A 

Factored sliding resistance at base of MSE wall, VFm1= 

s*VNm1 

k/ft 84.18 62.35 N/A 

Factored sliding resistance at base of MSE wall, VFm2= 

s*VNm2 

k/ft 22.93 13.76 N/A 

Factored sliding resistance at base of MSE wall, VFm= 

VFm1+VFm2 

k/ft 107.11 76.11 N/A 

Is VFm > Hm? - Yes Yes N/A 

Capacity:Demand Ratio (CDR) = VFm:Hm dim 1.35 1.60 N/A 

CRITICAL VALUES BASED ON MAX/MIN 

Minimum VF (VFmin) k/ft 85.28* 

Maximum Hm (Hmmax) k/ft 79.43 

Is VFmin > Hmmax? - Yes 

Capacity:Demand Ratio (CDR) = VFmin:Hmmax dim 1.07 

Note: *85.28 = 62.35+22.93. This is to maintain consistency between the total inclined 

lateral force and its components. 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 8 November 2009 
 

 

6.2 Limiting Eccentricity at Base of MSE Wall 

The purpose of these computations is to evaluate the limiting eccentricity at the base of the 

MSE wall. Since the computations are related to limiting eccentricity, the beneficial 

contribution of live load to resisting forces and moments is neglected. The computations for 

limiting eccentricity at the base of the MSE wall are illustrated in Table E3-6.2. Limiting 

eccentricity is a strength limit state check and therefore service limit state calculations are not 

performed. The critical values based on max/min result in the extreme force effect and 

govern the limiting eccentricity mode of failure. 

Table E3-6.2. Computations for evaluation of limiting eccentricity for MSE wall 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Vertical load at base of MSE wall, VA1 = V1+V2 k/ft 145.80 108.00 N/A 

Vertical load at base of MSE wall, VA2 = FTV k/ft 39.72 23.83 N/A 

Total vertical load at base of MSE wall, 

VA=VA1+VA2 

k/ft 185.52 131.83 N/A 

Resisting moments about Point A = MRA1 

=MV1+MV2 

k-ft/ft 1846.80 1368.00 N/A 

Resisting moments about Point A = MRA2 = MFTV k-ft/ft 953.17 571.90 N/A 

Total resisting moment @ Point A, 

MRA=MRA1+MRA2 

k-ft/ft 2799.97 1939.90 N/A 

Overturning moments about Point A = MOA = MFTH k-ft/ft 1112.03 667.22 N/A 

Net moment at Point A, MA = MRA - MOA k-ft/ft 1687.94 1272.68 N/A 

Location of the resultant force on base of MSE wall 

from Point A, a = (MRA - MOA)/VA 

ft 9.10 9.65 N/A 

Eccentricity at base of MSE wall, eL = L/2 – a ft 2.90 2.35 N/A 

Limiting eccentricity, e = L/4 for strength limit state ft 6.00 6.00 N/A 

Is the resultant within limiting value of eL? - Yes Yes N/A 

Calculated eL/L - 0.12 0.10 N/A 

CRITICAL VALUES BASED ON MAX/MIN 

Overturning moments about Point A, MOA-C k-ft/ft 1112.03 

Resisting moments about Point A, MRA-C k-ft/ft 2321.17* 

Net moment about Point A, MA-C = MRA-C - MOA-C k-ft/ft 1209.14 

Vertical force, VA-C k/ft 147.72** 

Location of resultant from Point A, anl = MA-C/VA-C ft 8.19 

Eccentricity from center of wall base, eL=0.5*L - anl ft 3.81 

Limiting eccentricity, e = L/4 ft 6.00 

Is the limiting eccentricity criteria satisfied? - Yes 

Effective width of base of MSE wall, B' = L-2eL ft 16.37 

Calculated eL/L - 0.16 

Notes: * 2321.17 = 1368.00 + 953.17; **147.72 = 108.00+39.72. This is to maintain 

consistency between the total inclined lateral force and its components. 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 9 November 2009 
 

 

6.3 Bearing Resistance at base of MSE Wall 

The bearing stress at the base of the MSE wall can be computed as follows: 

V

v  L  2eL 

where ΣV = R = V1+V2+FTV is the resultant of vertical forces and the load eccentricity eL is 

calculated by principles of statics using appropriate loads and moments with the applicable 

load factors. 

In LRFD, σv is compared with the factored bearing resistance when computed for strength 

limit state and used for settlement analysis when computed for service limit state. The 

various computations for evaluation of bearing resistance are presented in Table E3-6.3. The 

Strength I (max) load combination results in the extreme force effect in terms of maximum 

bearing stress and therefore governs the bearing resistance mode of failure. The Service I 

load combination is evaluated to compute the bearing stress for settlement analysis. Since 

the CDR ≈ 1.0 for Strength I (max) and Service I load combinations, shorter reinforcement 

lengths are not recommended. 

6.4 Settlement Analysis 

Settlement is evaluated at Service I Limit State. From Step 2, the estimated settlement under 

a bearing stress of 7.50 ksf is 1.00 in. From Table E3-6.3, the bearing stress for Service I 

limit state is 7.16 ksf. Therefore, the settlement will be less than 1.00 in. 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 10 November 2009
 
 

 

Table E3-6.3. Computations for evaluation of bearing resistance for MSE wall 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Vertical load at base of MSE wall, VAb1 = V1+V2 k/ft 145.80 108.00 108.00 

Vertical load at base of MSE wall, VAb2 = FTV k/ft 39.72 23.83 26.48 

Total vertical load at base of MSE wall, ΣV = R = 

VAb1+VAb2 

k/ft 185.52 131.83 134.48 

Resisting moments about Point A, MRA1 

=MV1+MV2 

k-ft/ft 1846.80 1368.00 1368.00 

Resisting moments about Point A, MRA2 = MFTV k-ft/ft 953.17 571.90 635.44 

Total resisting moment @ Point A, 

MRA=MRA1+MRA2 

k-ft/ft 2799.97 1939.90 2003.44 

Overturning moments @ Point A, MOA = MFTH k-ft/ft 1112.03 667.22 741.35 

Net moment at Point A, MA = MRA - MOA k-ft/ft 1687.94 1272.68 1262.09 

Location of the resultant force on base of MSE wall 

from Point A, a = (MRA - MOA)/VA 

ft 9.10 9.65 9.39 

Eccentricity at base of MSE wall, eL = 0.5*L – a ft 2.90 2.35 2.61 

Limiting eccentricity, e = L/4 for strength limit states 

and e= L/6 for service limit state ft 6.00 6.00 4.00 

Is the resultant within limiting value of e? - Yes Yes Yes 

Effective width of base of MSE wall, B' = L-2eL ft 18.20 19.31 18.77 

Bearing stress due to MSE wall =ΣV/(L-2eL) = v ksf 10.19 6.83 7.16 

Factored bearing resistance, (qnf-str for strength) or 

(qnf-ser for service) (given) ksf 10.50 10.50 7.50 

Is factored bearing stress less than the factored 

bearing resistance? - Yes Yes Yes 

Capacity:Demand Ratio (CDR) = qnf:σv dim 1.03 1.54 1.05 

CRITICAL VALUES BASED ON MAX/MIN 

Overturning moments about Point A, MOA-C k-ft/ft 1112.03 

Resisting moments about Point A, MRA-C k-ft/ft 2321.17* 

Net moment about Point A, MA-C = MRA-C - MOA-C k-ft/ft 1209.14 

Vertical force, ΣVC k/ft 147.72** 

Location of resultant from Point A, a = MA-C/ ΣVC ft 8.19 

Eccentricity from center of wall, eL = 0.5*L – a ft 3.81 

Limiting eccentricity, e = L/4 ft 6.00 

Is the limiting eccentricity criteria satisfied? - Yes 

Effective width of base of MSE wall, B' = L-2eL ft 16.37 

Bearing stress, ΣVC / (L-2eL) = v-c ksf 9.02*** 

Factored bearing resistance, qnf-str (given) ksf 10.50 

Is bearing stress < factored bearing resistance? dim Yes 

Capacity:Demand Ratio (CDR) = qnf-str:σv-c dim 1.16 

Notes: * 2321.17 = 1368.00 + 953.17; **147.72 = 108.00+39.72; ***9.02=147.72/16.37. 

This is to maintain consistency between the total inclined lateral force and its components. 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 11 November 2009 
 

STEP 7: EVALUATE INTERNAL STABILITY ANALYSIS OF MSE WALL
 

7.1 Estimate critical failure surface, variation of Kr and F* for internal stability 

For the case of inextensible steel ribbed strips, the profile of the critical failure surface, the 

variation of internal lateral horizontal stress coefficient, Kr, and the variation of the pullout 

resistance factor, F*, are as shown in Figure E3-5 wherein other definitions such as 

measurement of depths Z and Zp as well as heights H and H1 are also shown. It should be 

noted that the variation of Kr and F* are with respect to depth Z that is measured from the top 

of the reinforced soil zone. For the computation of Kr, the value of Ka is based on the angle 

of internal friction of the reinforced backfill, r, and the assumption that the backslope angle 

 = 0; thus, Ka = tan2

(45° - 34°/2) = 0.283. Hence, the value of Kr varies from 1.7(0.283) = 

0.481 at Z = 0 ft to 1.2(0.283) = 0.340 at Z = 20 ft. For steel strips, F*=1.2+log10Cu. Using 

Cu = 7.0 as given in Step 2, F*= 1.2+log10(7.0) = 2.045 > 2.000. Therefore, use F*=2.000. 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 12 November 2009
 

 

0.3H1 

Z 

Zp 

Kr F* 

Z=0 1.7 Ka 

1.2 Ka 

2.000 

tan (1) 

= 0.675 

Z=20 ft 

Zp 

Z=0 

Z=20 ft 

H 

(tan )(0.3H) H  H1= H + H

10.3tan

Zp at start of resistant zone, Zp-s= Z + Latan

Zp at end of resistant zone, Zp-e= Z + Ltan

Use average Zp over the resistance zone, Zp-ave, for computing pullout resistance 

Zp-ave = Z + 0.5(Latan + Ltan) = Z + 0.5 tan (La + L) 

Ka is computed assuming that the backslope angle is zero, i.e., = 0 per Article 

C11.10.6.2.1 of AASHTO (2007) 

Figure E3-5. Geometry definition, location of critical failure surface and variation of Kr and 

F* parameters for steel ribbed strips. 
 

 

7.2 Establish vertical layout of soil reinforcements 

Using the definition of depth Z as shown in Figure E3-5 the following vertical layout of the 

soil reinforcements is chosen. 

 

Z = 1.25 ft, 3.75 ft, 6.25 ft, 8.75 ft, 11.25 ft, 13.75 ft, 16.25 ft, 18.75 ft, 21.25 ft, 23.75 ft, 

26.25 ft, and 28.75 ft. 

The above layout leads to 12 levels of reinforcements. The vertical spacing was chosen 

based on a typical vertical spacing, Sv, of approximately 2.5 ft that is commonly used in the 

industry for steel ribbed strip reinforcement. The vertical spacing near the top and bottom of 

the walls are locally adjusted as necessary to fit the height of the wall. 

For internal stability computations, each layer of reinforcement is assigned a tributary area, 

Atrib as follows 

Atrib = (wp)(Svt) 

where and wp is the panel width of the precast facing element and Svt is the vertical tributary 

spacing of the reinforcements based on the location of the reinforcements above and below 

the level of the reinforcement under consideration. The computation of Svt is summarized in 

Table E4-7.1 wherein S  

vt  Z  Z . Note that wp = 5.00 ft per Step 2. 

Table E3-7.1. Summary of computations for Svt 

Level Z (ft) Z (ft) Z (ft) Svt (ft) 

1 1.25 0 1.25+0.5(3.75–1.25)=2.50 2.50 

2 3.75 3.75-0.5(3.75–1.25)=2.50 3.75+0.5(6.25-3.75)=5.00 2.50 

3 6.25 6.25-0.5(6.25-3.75)=5.00 6.25+0.5(8.75-6.25)=7.50 2.50 

4 8.75 8.75-0.5(8.75-6.25)=7.50 8.75+0.5(11.25-8.75)=10.00 2.50 

5 11.25 11.25-0.5(11.25-8.75)=10.00 11.25+0.5(13.75-11.25)=12.50 2.50 

6 13.75 13.75-0.5(13.75-11.25)=12.50 13.75+0.5(16.25-13.75)=15.00 2.50 

7 16.25 16.25-0.5(16.25-13.75)=15.00 16.25+0.5(18.75-16.25)=17.50 2.50 

8 18.75 18.76-0.5(18.75-16.25)=17.50 18.75+0.5(21.25-18.75)=20.00 2.50 

9 21.25 21.25-0.5(21.25-18.75)=20.00 21.25+0.5(23.75-21.25)=22.50 2.50 

10 23.75 23.75-0.5(23.75-21.25)=22.50 23.75+0.5(26.25-23.75)=25.00 2.50 

11 26.25 26.25-0.5(26.25-23.75)=25.00 26.25+0.5(28.75-26.25)=27.50 2.50 

12 28.75 28.75-0.5(28.75-26.25)=27.50 30.00 2.50 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 13 November 2009
 
 

7.3 Calculate horizontal stress and maximum tension at each reinforcement level 

The horizontal spacing of the reinforcements is based on the maximum tension (Tmax) at each 

level of reinforcements which requires computation of the horizontal stress, σH, at each 

reinforcement level. The reinforcement tensile and pullout resistances are then compared 

with Tmax and an appropriate reinforcement pattern is adopted. This section demonstrates the 

calculation of horizontal stress, σH, and maximum tension, Tmax. 

The horizontal stress, σH, at any depth within the MSE wall is based on only the soil load as 

summarized in Table E3-7.2. 

σH = σH-soil + σH-surcharge 

Table E3-7.2. Summary of load components leading to horizontal stress 

Load Component Load Type Horizontal Stress 

Soil load from reinforced mass, σv-soil EV σH-soil = [Krσv-soil]γP-EV 

Surcharge load due to backslope, σ2 EV σH-surcharge = [Krσ2]γP-EV 

Using the unit weight of the reinforced soil mass and heights Z and S as shown in Figure E3­

2b , the equation for horizontal stress at any depth Z within the MSE wall can be written as 

follows (also see Chapter 4): 

σH 	 = Kr (r Z) γP-EV + Kr (r S) γP-EV = Kr [r (Z + S) γP-EV] 

Once the horizontal stress is computed at any given level of reinforcement, the maximum 

tension, Tmax, is computed as follows: 

Tmax = (σH)(Atrib) 

where Atrib is the tributary area for the soil reinforcement at a given level as discussed in 

Section 7.2 

The computations for Tmax are illustrated at z = 8.75 ft which is Level 4 in the assumed 

vertical layout of reinforcement. Assume Strength I (max) load combination for illustration 

purposes and use appropriate load factors from Table E3-5.1. 

	 At Z = 8.75 ft, the following depths are computed 

Z = 7.50 ft (from Table E3-7.1) 

Z = 10.00 ft (from Table E3-7.1) 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 14 November 2009
 
 

	 Obtain Kr by linear interpolation between 1.7Ka = 0.481 at Z = 0.00 ft and 1.2Ka = 

0.340 at Z = 20.00 ft as follows: 

At Z = 7.50 ft, Kr(Z-)= 0.340 + (20.00 ft – 7.50 ft)(0.481-0.340)/20.00 ft = 0.428 

At  Z = 10.00 ft, Kr(Z+)= 0.340 + (20.00 ft – 10.00 ft)(0.481-0.340)/20.00 ft = 0.411 

	 Compute σH-soil = [Kr σv-soil]γP-EV as follows: 

γP-EV = 1.35 from Table E3-5.1 

At Z = 7.50 ft, 

v-soil(Z-) = (0.125 kcf)(7.50 ft) = 0.94 ksf 

σH-soil(Z-) = [Kr(Zp-)σv-soil(z-)]γP-EV = (0.428)(0.94 ksf)(1.35) = 0.54 ksf 

At Z = 10.00 ft, 

v-soil(Z+) = (0.125 kcf)(10.00 ft) = 1.25 ksf 

σH-soil(Z+) = [Kr(Zp+)σv-soil(z+)]γP-EV = (0.411)(1.25 ksf)(1.35) = 0.69 ksf 

σH-soil = 0.5(0.54 ksf + 0.69 ksf) = 0.62 ksf 

	 Compute σH-surcharge = [Kr σ2]γP-EV as follows: 

σ2 = (1/2)(0.7Htan)(f) (from Figure E3-2b) 

σ2 = (1/2)(0.7*30 ft)[tan (26.56°)](0.125 kcf) = 0.656 ksf 

γP-EV = 1.35 from Table E3-5.1 

At Z = 7.50 ft, 

σH-surcharge = [Kr(Z-) σ2]γP-EV = (0.428)(0.656 ksf)(1.35) = 0.38 ksf 

At z

 = 10.00 ft and Z

p = 15.29 ft,

σH-surcharge = [Kr(Z+) σ2]γP-ES = (0.411)(0.656 ksf)(1.35) = 0.36 ksf 

σH-surcharge = 0.5(0.38 ksf + 0.36 ksf) = 0.37 ksf 

	 Compute σH = σH-soil + σH-surcharge as follows: 

σH = 0.62 ksf + 0.37 ksf = 0.99 ksf 

	 Based on Table E3-7.1, the vertical tributary spacing at Level 4 is Svt = 2.50 ft 

	 The panel width, wp, is 5.00 ft (given in Step 1) 

	 The tributary area, Atrib, is computed as follows: 

Atrib = (2.50 ft)(5.00 ft) = 12.50 ft2 

 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 15 November 2009
 
 

 

	 The maximum tension at Level 4 is computed as follows: 

Tmax = (σh)(Atrib) = (0.99 ksf)(12.50 ft2

) = 12.37 k for panel of 5-ft width 

Using similar computations, the various quantities can be developed at other levels of 

reinforcements and load combinations. 

7.4 Establish nominal and factored long-term tensile resistance of soil reinforcement 

The nominal tensile resistance of galvanized steel ribbed strip soil reinforcement is based on 

the design life and estimated loss of steel over the design life during corrosion. 

As per Step 1, the soil reinforcement for this example is assumed to be Grade 65 (Fy = 65 

ksi), 1.969 in. x 0.157 in. (50 mm wide x 4 mm) thick galvanized steel ribbed strips with zinc 

coating of 3.386 mils (86 m). As per Step 2, the reinforced backfill meets the AASHTO 

(2007) requirements for electrochemical properties. For this reinforced backfill, the basis for 

calculating the thickness losses due to corrosion is as follows per Article 11.10.6.4.2a of 

AASHTO (2007): 

Zinc loss = 0.58 mil for first 2 years and 0.16 mil per year thereafter 

Steel loss = 0.47 mil/year/side 

Based on the above corrosion rates, the following can be calculated: 

Life of zinc coating (galvanization) = 2 years + (3.386 – 2*0.58)/0.16 ≈ 16 years 

As per Step 1, the design life is 75 years. The base carbon steel will lose thickness for 75 

years – 16 years = 59 years at a rate of 0.47 mil/year/side. Therefore, the anticipated 

thickness loss is calculated as follows: 

ER = (0.47 mil/year/side) (59 years) (2 sides) = 55.46 mils = 0.055 in., and 

EC = 0.157 in. – 0.055 in. = 0.102 in. 

Based on a 1.969 wide strip, the cross-sectional area at the end of 75 years will be equal to 

(1.969 in.) (0.102 in.) = 0.200 in2 

. 

For Grade 65 steel with Fy = 65 ksi, the nominal tensile resistance at end of 75 year design 

life will be Tn = 65 ksi (0.200 in2

) = 13.00 k/strip. Using the resistance factor, t = 0.75 as 

listed in Table E3-5.2, the factored tensile resistance, Tr = 13.00 k/strip (0.75) = 9.75 k/strip. 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 16 November 2009
 
 

7.5 Establish nominal and factored pullout resistance of soil reinforcement 

The nominal pullout resistance, Pr, of galvanized steel ribbed strip soil reinforcement is based 

on various parameters in the following equation: 

Pr = (F*)(2b)(Le)[(σv)(γP-EV)] 

For this example problem, the following parameters are constant at levels of reinforcements: 

b = 1.969 in. = 0.164 ft 

 = 1.0 for inextensible reinforcement per Table 11.10.6.3.2-1 of AASHTO (2007) 

The computations for Pr are illustrated at z = 8.75 ft which is Level 4 as measured from top 

of the wall. Assume Strength I (max) load combination for illustration purposes and use 

appropriate load factors from Table E3-5.1. 

	 Compute effective (resisting) length, Le, as follows: 

Since Z < H1/2, active length La = 0.3(H1) and Le = L – La = L – 0.3(H1) 

H1= H + H = 30.00 ft + 5.29 ft = 35.29 ft 

Active length, La = 0.3(35.29 ft) = 10.59 ft 

Effective (resisting) length, Le = 24.00 ft – 10.59 ft = 13.41 ft 

	 Compute (σv)(γP-EV) 

As per Figure E3-2b, σv = r(Zp-ave) 

Zp-ave = Z+0.5 tan (La + L) = 8.75 ft + 0.5[tan(26.56°)](10.59 ft + 24.00 ft) = 17.40 ft 

Per Article 11.10.6.3.2 of AASHTO (2007), use unfactored vertical stress for pullout 

resistance. Thus, 

γP-EV = 1.00 

σv(γP-EV) = (0.125 kcf)(17.40 ft) (1.00) = 2.175 ksf 

	 Obtain F* at Z =8.75 ft 

Obtain F* by linear interpolation between 2.000 at Z = 0 and 0.675 at Z = 20.00 ft as 

follows: 

F* = 0.675 + (20.00 ft – 8.75 ft)(2.000 – 0.675)/20 ft = 1.420 

	 Compute nominal pullout resistance as follows: 

Pr = (F*)(2)(b)(Le)[(σv-soil)(γP-EV)] 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 17 November 2009
 

H1= H + H 

(tan)(0.3H) (0.5)(0.3x 30ft) H	   5.29ft 

10.3tan 10.3(0.5) 
 

Pr = (1.0)(1.420)(2)(0.164 ft)(13.41 ft)(2.175 ksf) = 13.58 k/strip 

	 Compute factored pullout resistance as follows: 

Prr = Pr = (0.90)(13.58 k/strip) = 12.23 k/strip 

Using similar computations, the various quantities can be developed at other levels of 

reinforcements and load combinations. 

7.6 Establish number of soil reinforcing strips at each level of reinforcement 

Based on Tmax, Tr and Prr, the number of strip reinforcements at any given level of 

reinforcements can be computed as follows: 

 Based on tensile resistance considerations, the number of strip reinforcements, Nt, is 

computed as follows: 

Nt = Tmax/Tr 

 Based on pullout resistance considerations, the number of strip reinforcements, Np, is 

computed as follows: 

Np = Tmax/Prr 

Using the Level 4 reinforcement at Z = 8.75 ft, the number of strip reinforcements can be 

computed as follows: 

 Tmax = 13.13 k for panel of 5-ft width, Tr = 9.75 k/strip, Prr = 12.23 k/strip 

 Nt = Tmax/Tr = (13.13 k for panel of 5 ft width)/(9.75 k/strip) = 1.35 strips for panel of 

5-ft width 

 Np = Tmax/Prr = (13.13 k for panel of 5 ft width)/(12.23 k/strip) = 1.07 strips for panel 

of 5-ft width 

 Since Nt > Np, tension breakage is the governing criteria and therefore the governing 

value, Ng, is 1.35. Round up to select 2 strips at Level 4 for each panel of 5 ft width. 

The computations in Sections 7.4 to 7.6 are repeated at each level of reinforcement. Table 

E3-7.3 presents the computations at all levels of reinforcement for Strength I (max) load 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 18 November 2009
 
 

 

combination. The last column of Table E3-7.3 provides horizontal spacing of the reinforcing 

strips which is obtained by dividing the panel width, wp, by the governing number of strips, 

Ng. Similar computations can be performed for Strength I (min) and Service I load 

combination but they will not govern the design because the load factors for these two load 

combinations are less than those for Strength I (max) load combination. The facing design 

(Step 8) may necessitate more reinforcement per level. 

Note to users: All the long-form step-by-step calculations illustrated in Step 8 were based on 

hand-calculations in which numbers were rounded to the third or fourth significant digit as 

appropriate in each step. Table E3-7.3 was generated using a spreadsheet in which numbers 

at all calculation steps were not rounded. Thus, the end result in Table E3-7.3 may be 

somewhat different when compared to long-form hand calculations. However, the difference 

should be less than 0.2 in most cases. 

Table E3-7.3. Summary of internal stability computations for Strength I (max) load 

combination 

Level 

Z 

ft 

Zp-ave 

dim 

H

ksf 

Tmax

k/5 ft 

wide 

panel 

F* 

dim 

Le 

ft 

p(Pr) 

k/strip 

s(Tn) 

k/strip 

Np 

-

Nt 

-

Ng 

-

Sh 

ft 

1 1.25 9.90 0.52 6.46 1.917 13.41 9.40 9.75 0.7 0.7 2 2.50 

2 3.75 12.40 0.69 8.63 1.751 13.41 10.76 9.75 0.8 0.9 2 2.50 

3 6.25 14.90 0.85 10.58 1.586 13.41 11.70 9.75 0.9 1.1 2 2.50 

4 8.75 17.40 0.99 12.35 1.420 13.41 12.23 9.75 1.0 1.3 2 2.50 

5 11.25 19.90 1.12 13.96 1.254 13.41 12.36 9.75 1.1 1.4 2 2.50 

6 13.75 22.19 1.23 15.40 1.089 14.25 12.70 9.75 1.2 1.6 2 2.50 

7 16.25 24.31 1.33 16.59 0.923 15.75 13.05 9.75 1.3 1.7 2 2.50 

8 18.75 26.44 1.41 17.60 0.757 17.25 12.76 9.75 1.4 1.8 2 2.50 

9 21.25 28.56 1.52 18.98 0.675 18.75 13.33 9.75 1.4 1.9 3 1.67 

10 23.75 30.69 1.66 20.77 0.675 20.25 15.50 9.75 1.3 2.1 3 1.67 

11 26.25 32.81 1.81 22.56 0.675 21.75 17.79 9.75 1.3 2.3 3 1.67 

12 28.75 34.94 1.95 24.36 0.675 23.25 20.24 9.75 1.2 2.5 3 1.67 

Note 1: Based on pullout and tension breakage considerations only 1 strip is required at Level 1 and 2. 

However, a minimum 2 strips at a horizontal spacing not exceeding 2.5 ft should be provided as per the 

criteria in Chapter 4. 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 19 November 2009
 
 

STEP 8:	 DESIGN OF FACING ELEMENTS 

The precast facing elements must be designed as structural elements with appropriate 

connection strength as discussed in Chapter 4. Depending on the design of the facing panel, 

the number of strips at each level may have to be increased. 

STEP 9:	 CHECK OVERALL AND COMPOUND STABILITY AT SERVICE LIMIT 

STATE 

From Step 2, it is given that the foundation soil is dense clayey sand that has f = 30°, f = 

125 pcf. Furthermore, the ground in front of the wall is horizontal and the foundation soil 

has no water table. Therefore, based on observation, overall stability is adequate. For actual 

projects, overall stability should be investigated at the Service I load combination and a 

resistance factor of 0.65. 

STEP 10: DESIGN WALL DRAINAGE SYSTEMS 

Drains are detailed on construction drawings. For a MSE wall with sloping backfill, the 

drainage system for the MSE wall must be carefully integrated with the other hillside drain 

systems as appropriate. 

FHWA NHI-10-025 Example E3 – Sloping backfill surcharge 

MSE Walls and RSS – Vol II E3 – 20 November 2009
 
 

 

EXAMPLE E4 

SEGMENTAL PRECAST PANEL MSE WALL WITH LEVEL BACKFILL AND 

LIVE LOAD SURCHARGE 

E4-1 INTRODUCTION 

This example problem demonstrates the analysis of a MSE wall with a level backfill and live 

load surcharge. The MSE wall is assumed to include a segmental precast panel face with 

steel grid (bar mat) reinforcements. The MSE wall configuration to be analyzed is shown in 

Figure E4-1. The analysis is based on various principles that were discussed in Chapter 4. 

Table E4-1 presents a summary of steps involved in the analysis. Each of the steps and substeps is sequential and if the design is revised at any step or sub-step then all the previous 

computations need to be re-visited. Each of the steps and the sub-steps in Table E4-1 is 

explained in detail herein. Practical considerations are presented in Section E4-2 after the 

illustration of the step-by-step procedures. 

Table E4-1. Summary of steps in analysis of MSE wall with level backfill and live 

load surcharge 

Step Item 

1 Establish project requirements 

2 Establish project parameters 

3 Estimate wall embedment depth and length of reinforcement 

4 Estimate unfactored loads 

5 Summarize applicable load and resistance factors 

6 Evaluate external stability of MSE wall 

6.1 Evaluation of sliding resistance 

6.2 Evaluation of limiting eccentricity 

6.3 Evaluation of bearing resistance 

6.4 Settlement analysis 

7 Evaluate internal stability of MSE wall 

7.1 Estimate critical failure surface, variation of Kr and F* for internal stability 

7.2 Establish vertical layout of soil reinforcements 

7.3 Calculate horizontal stress and maximum tension at each reinforcement level 

7.4 Establish nominal and factored long-term tensile resistance of soil reinforcement 

7.5 Establish nominal and factored pullout resistance of soil reinforcement 

7.6 Establish number of soil reinforcing elements at each level of reinforcement 

8 Design of facing elements 

9 Check overall and compound stability at the service limit state. 

10 Design wall drainage system 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 1 November 2009
 
 

 

Traffic Surcharge 

Reinforced backfill 

'r, γr

H He

L d 

Retained backfill 

'f, γf 

Roadway 

Surface 

Leveling Foundation Soil 

Pad 'fd, γfd 

Figure E4-1. Configuration showing various parameters for analysis of a MSE wall with 

level backfill and live load surcharge (not-to-scale). 

STEP 1. ESTABLISH PROJECT REQUIREMENTS 

 Exposed wall height, He = 23.64 ft 

 Length of wall = 850 ft 

 Design life = 75 years 

 Precast panel units: 5 ft wide x 5 ft tall x 0.5 ft thick 

 Type of reinforcement: Grade 65 (Fy = 65 ksi), steel bar mat with W15 and W11 wires. 

Assume wires to be galvanized with zinc coating of 3.386 mils (86 m). 

 No seismic considerations 

STEP 2. EVALUATE PROJECT PARAMETERS 

 Reinforced backfill, 'r = 34°, r = 125 pcf, coefficient of uniformity, Cu = 7.0 and 

meeting the AASHTO (2007) requirements for electrochemical properties 

 Retained backfill, 'f = 30°, f = 125 pcf 

 Foundation soil, dense clayey sand with 'fd = 30°, fd = 125 pcf 

 Factored Bearing resistance of foundation soil 

o For service limit consideration, qnf-ser = 7.50 ksf for 1-inch of total settlement 

o For strength limit consideration, qnf-str = 10.50 ksf 

 Live load surcharge, heq = 2 ft of soil per Table 3.11.6.4-2 of AASHTO (2007) 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 2 November 2009
 
 

 

STEP 3. ESTIMATE DEPTH OF EMBEDMENT AND LENGTH OF 

REINFORCEMENT 

Based on Table C.11.10.2.2.-1 of AASHTO (2007), the minimum embedment depth = H/20 

for walls with horizontal ground in front of wall, i.e., 1.2 ft for exposed wall height of 23.64 

ft. For this design, assume embedment, d = 2.0 ft. Thus, design height of the wall, H = He + 

d = 23.64 ft + 2.0 ft = 25.64 ft. 

Due to the level backfill, the minimum initial length of reinforcement is assumed to be 0.7H 

or 18 ft. This length will be verified as part of the design process. The length of the 

reinforcement is assumed to be constant throughout the height to limit differential settlements 

across the reinforced zone because differential settlements could overstress the 

reinforcements. 

STEP 4. ESTIMATE UNFACTORED LOADS 

Tables E4-4.1 and E4-4.2 present the equations for unfactored loads and moment arms about 

Point A shown in Figure E4-2. The moments are a product of the respective forces and 

moment arms. Each force is assigned a designation representing the applicable load type as 

per Tables 3.4.1-1 and 3.4.1-2 of AASHTO (2007). 

To compute the numerical values of various forces and moments, the parameters provided in 

Step 2 are used. Using the values of the various friction angles, the coefficients of lateral 

earth pressure are as follows: 

Kar = (1 - sin34°)/(1 + sin34°) = 0.283 

Kaf = (1 - sin30°)/(1 + sin30°) = 0.333 

For the example problem, Tables E4-4.3 and E4-4.4 summarize the numerical values 

unfactored forces and moments, respectively, based on the equations, various dimensions and 

values of lateral earth pressure coefficients presented above. Refer to Figure E4-2 for 

notations of various forces. 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 3 November 2009
 
 

 

A 

 (a) 

(b) 

Figure E4-2. Legend for computation of forces and moments (not-to-scale). 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 4 November 2009
 
 

 

The unfactored forces and moments in Tables E4-4.3 and E4-4.4 form the basis of all 

computations in this example problem. The unfactored forces and moments should be 

multiplied by the appropriate load factors based on the load types identified in the second 

column of the Tables E4-4.1 and E4-4.2 to perform the analysis for various load 

combinations such as Strength I, Service I, etc. 

The load factors for various load types relevant to this example problem are discussed in Step 

5. 

Table E4-4.1. Equations of computing unfactored vertical forces and moments 

Vertical Force 

(Force/length units) 

LRFD 

Load Type 

Moment arm 

(Length units) 

@ Point A 

V1 = (γr)(H)(L) EV L/2 

VS = (γf)(heq)(L) = (q)L LL L/2 

Note: heq is the equivalent height of soil such that q = (γf)(heq) 

Table E4-4.2. Equations of computing unfactored horizontal forces and moments 

Horizontal Force 

(Force/length) 

LRFD 

Load Type 

Moment arm 

(Length units) 

@ Point A 

F1 = 1⁄2(Kaf)(γf)H2

 EH H/3 

F2 = (Kaf)[(γf)(heq)](H) LL H/2 

Table E4-4.3. Unfactored vertical forces and moments 

Force Value 

k/ft 

Moment 

Arm @ 

Point A, ft 

Moment 

Moment at 

Point A, 

k-ft/ft 

V1 = 57.69 9.00 MV1 = 519.21 

Vs = 4.50 9.00 MVs = 40.50 

Note: Vs is based on heq of 2 ft per Table 3.11.6.4-1 of 

AASHTO (2007). 

Table E4-4.4. Unfactored horizontal forces and moments 

Force Value 

k/ft 

Moment 

Arm @ 

Point A, ft 

Moment 

Moment at 

Point A, 

k-ft/ft 

F1 = 13.68 8.55 MF1 = 116.94 

F2 = 2.13 12.82 MF2 = 27.36 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 5 November 2009
 
 

 

STEP 5. SUMMARIZE APPLICABLE LOAD AND RESISTANCE FACTORS 

Table E4-5.1 summarizes the load factors for the various LRFD load type shown in second 

column of Tables E4-4.1 and E4-4.2. Throughout the computations in this example 

problem, the forces and moments in Tables E4-4.1 and E4-4.2 should be multiplied by 

appropriate load factors. For example, if computations are being done for Strength I 

(maximum) load combination, the forces and moments corresponding to load V1 should be 

multiplied by 1.35 which is associated with load type EV assigned to load V1. 

Table E4-5.1. Summary of applicable load factors 

Load Combination 

Load Factors 

(after AASHTO, 2007 Tables 3.4.1-1 and 3.4.1-2) 

EV EH LL 

Strength I (maximum) 1.35 1.50 1.75 

Strength I (minimum) 1.00 0.90 1.75 

Service I 1.00 1.00 1.00 

For computation of factored resistances during evaluation of strength limits states, 

appropriate resistance factors have to be used. Table E4-5.2 summarizes the applicable 

resistance factors. For service limit state, all resistance factors are equal to 1.0. 

Table E4-5.2. Summary of applicable resistance factors for evaluation of resistances 

Item Resistance 

Factors 

AASHTO (2007) 

Reference 

Sliding of MSE wall on foundation soil s = 1.00 Table 11.5.6-1 

Bearing resistance b = 0.65 Table 11.5.6-1 

Tensile resistance (for steel bar mats) t = 0.65 Table 11.5.6-1 

Pullout resistance p = 0.90 Table 11.5.6-1 

STEP 6. EVALUATE EXTERNAL STABILITY OF MSE WALL 

The external stability of MSE wall is a function of the various forces and moments shown in 

Figure E4-2. In the LRFD context the forces and moments need to be categorized into 

various load types. The primary load types for this example problem are soil loads (EV, EH) 

and live load (LL). 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 6 November 2009
 
 

 

6.1 Sliding Resistance at Base of MSE Wall 

The purpose of these computations is to evaluate the sliding resistance at the base of the MSE 

wall. Since the computations are related to sliding resistance, the beneficial contribution of 

live load to resisting forces and moments is neglected. The computations for sliding 

resistance at the base of the MSE wall are illustrated in Table E4-6.1. Note that sliding 

resistance is a strength limit state check and therefore service limit state calculations are not 

performed. Since the friction angle of foundation soil, 'fd, is less than the friction angle for 

reinforced soil, 'r, the sliding check will be performed using 'fd. The critical values based 

on max/min result in the extreme force effect and govern the sliding mode of failure. 

Table E4-6.1. Computations for evaluation of sliding resistance of MSE wall 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Lateral load on the MSE wall, Hm = F1+F2 k/ft 24.26 16.05 NA 

Vertical load at base of MSE wall without LL 

surcharge = V1 

k/ft 77.88 57.69 NA 

Nominal sliding resistance at base of MSE wall, VNm 

= tan('fd)(V1) k/ft 44.96 33.31 NA 

Sliding resistance at base of MSE wall, VFm= s*VNm k/ft 44.96 33.31 NA 

Is VFm > Hm? - Yes Yes NA 

Capacity:Demand Ratio (CDR) = VFm:Hm dim 1.85 2.08 NA 

CRITICAL VALUES BASED ON MAX/MIN 

Minimum VFm (VFmmin) k/ft 33.31 

Maximum Hm (Hmmax) k/ft 24.26 

Is VFmmin > Hmmax? - Yes 

Capacity:Demand Ratio (CDR) = VFmmin:Hmmax dim 1.37 

6.2 Limiting Eccentricity at Base of MSE Wall 

The purpose of these computations is to evaluate the limiting eccentricity at the base of the 

MSE wall. Since the computations are related to limiting eccentricity, the beneficial 

contribution of live load to resisting forces and moments is neglected. The computations for 

limiting eccentricity at the base of the MSE wall are illustrated in Table E4-6.2. Limiting 

eccentricity is a strength limit state check and therefore service limit state calculations are not 

performed. The critical values based on max/min result in the extreme force effect and 

govern the limiting eccentricity mode of failure. 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 7 November 2009
 
 

 

 

Table E4-6.2. Computations for evaluation of limiting eccentricity for MSE wall 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Total vertical load at base of MSE wall without LL, 

VA = V1 

k/ft 77.88 57.69 N/A 

Resisting moments about Point A without LL 

surcharge= MRA = MV1 

k-ft/ft 700.93 519.21 N/A 

Overturning moments about Point A = MOA = 

MF1+MF2 

k-ft/ft 223.30 153.13 N/A 

Net moment about Point A = MA = MRA – MOA k-ft/ft 477.64 366.08 N/A 

Location of the resultant force on base of MSE wall 

from Point A, a = MA/VA 

ft 6.13 6.35 N/A 

Eccentricity at base of MSE wall, eL = L/2 – a ft 2.87 2.65 N/A 

Limiting eccentricity, e = L/4 for strength limit state ft 4.50 4.50 N/A 

Is the resultant within limiting value of e? - Yes Yes N/A 

Calculated eL/L - 0.16 0.15 N/A 

CRITICAL VALUES BASED ON MAX/MIN 

Overturning moments about Point A, MOA-C k-ft/ft 223.30 

Resisting moments about Point A, MRA-C k-ft/ft 519.21* 

Net moment about Point A, MA-C = MRA-C - MOA-C k-ft/ft 295.91 

Vertical force, VA-C k/ft 57.69* 

Location of resultant from Point A, anl = MA-C/VA-C ft 5.13 

Eccentricity from center of wall base, eL=0.5*L - anl ft 3.87 

Limiting eccentricity, e = L/4 ft 4.50 

Is the limiting eccentricity criteria satisfied? - Yes 

Effective width of base of MSE wall, B' = L-2eL ft 10.26 

Calculated eL/L - 0.22 

Note: *519.21 and 57.69 are consistent values based on the mass of reinforced soil block 

6.3 Bearing Resistance at base of MSE Wall 

For bearing resistance computations, the effect of live load is included since it creates larger 

bearing stresses. The bearing stress at the base of the MSE wall can be computed as follows: 

V

v 

L 2eL 

where ΣV = R = V1 + VS is the resultant of vertical forces and the load eccentricity eL is 

calculated by principles of statics using appropriate loads and moments with the applicable 

load factors. 

In LRFD, σv is compared with the factored bearing resistance when computed for strength 

limit state and used for settlement analysis when computed for service limit state. The 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 8 November 2009
 
 

 

 

 

various computations for evaluation of bearing resistance are presented in Table E4-6.3. The 

Strength I (max) load combination results in the extreme force effect in terms of maximum 

bearing stress and therefore governs the bearing resistance mode of failure. The Service I 

load combination is evaluated to compute the bearing stress for settlement analysis. 

Table E4-6.3. Computations for evaluation of bearing resistance for MSE wall 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Vertical load at base of MSE wall including LL on 

top, ΣV = R = V1 + VS 

k/ft 85.76 65.57 62.19 

Resisting moments @ Point A on the MSE wall, 

MRA = MV1+MVS 

k-ft/ft 771.81 590.09 559.71 

Overturning moments @ Point A on the MSE wall, 

MOA = MF1+MF2 

k-ft/ft 223.30 153.13 144.30 

Net moment at Point A, MA = MRA - MOA k-ft/ft 548.51 436.95 415.41 

Location of Resultant from Point A, a = MA/ΣV ft 6.40 6.66 6.68 

Eccentricity from center of wall base, eL = 0.5*L – a ft 2.60 2.34 2.32 

Limiting eccentricity, e = L/4 for strength limit states 

and e= L/6 for service limit state ft 4.50 4.50 3.00 

Is the resultant within limiting value of eL? - Yes Yes Yes 

Effective width of base of MSE wall, B' = L-2eL ft 12.79 13.33 13.36 

Bearing stress due to MSE wall =ΣV/(L-2eL) = v ksf 6.70 4.92 4.66 

Bearing resistance, (qnf-str for strength) or (qnf-ser for 

service) (given) ksf 10.50 10.50 7.50 

Is bearing stress less than the bearing resistance? - Yes Yes Yes 

Capacity:Demand Ratio (CDR) = qnf:σv dim 1.57 2.13 1.61 

CRITICAL VALUES BASED ON MAX/MIN 

Resisting moments about Point A, MRA-C k-ft/ft 590.09* 

Overturning moments about Point A, MOA-C k-ft/ft 223.30 

Net moment about Point A, MA-C = MRA-C - MOA-C k-ft/ft 366.79 

Vertical force, ΣVC k/ft 65.57* 

Location of resultant from Point A, a = MA-C/ΣVC ft 5.59 

Eccentricity from center of wall base, eL = 0.5*L – a ft 3.41 

Limiting eccentricity, e = L/4 ft 4.50 

Is the limiting eccentricity criteria satisfied? - Yes 

Effective width of base of MSE wall, B' = L-2eL ft 11.19 

Bearing stress, ΣVC / (L-2eL) = v-c ksf 5.86 

Bearing resistance, qnf-str (given) ksf 10.50 

Is bearing stress < bearing resistance? dim Yes 

Capacity:Demand Ratio (CDR) = qnf-str:σv-c dim 1.79 

Note: *590.09 and 65.57 are consistent values based on the mass of reinforced soil block 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 9 November 2009
 
 

6.4 Settlement Analysis 

Settlement is evaluated at Service I Limit State. From Step 2, the estimated settlement under 

a bearing stress of 7.50 ksf is 1.00 in. From Table E1-6.3, the bearing stress for Service I 

limit state is 4.66 ksf. Therefore, the settlement will be less than 1.00 in. 

STEP 7: EVALUATE INTERNAL STABILITY ANALYSIS OF MSE WALL 

7.1 Estimate critical failure surface, variation of Kr and F* for internal stability 

For the case of inextensible steel bar mats, the profile of the critical failure surface, the 

variation of internal lateral horizontal stress coefficient, Kr, and the variation of the pullout 

resistance factor, F*, are as shown in Figure E4-5 wherein other definitions such as 

measurement of depth, Z, and height, H, are also shown. It should be noted that the variation 

of Kr and F* are with respect to depth Z that is measured from top of the reinforced soil zone. 

The value of Ka is based on the angle of internal friction of the reinforced backfill, r, which 

is equal to Ka = 0.283 calculated in Step 4. Thus, the value of Kr varies from 2.5(0.283) = 

0.707 at Z=0 to 1.2(0.283) = 0.340 at Z =20 ft. The value of F* is a function of the 

transverse wire configuration and is calculated later. 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 10 November 2009
 

2.5 Ka Kr 20(t/St) F*

Z=0 Z=0

Z 

Z=20 ft 1.2 Ka Z=20 ft 10(t/St)

z z 

Note: In this example problem, the backfill is level, i.e., =0. Therefore, the Kr and 

F* profiles start at Z = 0 where Z is the depth below the top of the reinforced soil 

zone as shown in the figure. 

Figure E4-5. Geometry definition, location of critical failure surface and variation of Kr and 

F* parameters for steel bar mats. 
 

 

7.2 Establish vertical layout of soil reinforcements 

Using the definition of depth Z as shown in Figure E4-5 the following vertical layout of the 

soil reinforcements is chosen. 

 

Z = 1.87 ft, 4.37 ft, 6.87 ft, 9.37 ft, 11.87 ft, 14.37 ft, 16.87 ft, 19.37 ft, 21.87 ft, and 24.37 ft 

The above layout leads to 10 levels of reinforcements. The vertical spacing was chosen 

based on a typical vertical spacing, Sv, of approximately 2.5 ft that is commonly used in the 

industry for steel grid (bar mat) reinforcement. The vertical spacing near the top and bottom 

of the walls are locally adjusted as necessary to fit the height of the wall. 

For internal stability computations, each layer of reinforcement is assigned a tributary area, 

Atrib as follows 

Atrib = (wp)(Svt) 

where wp is the panel width of the precast facing element and Svt is the vertical tributary 

spacing of the reinforcements based on the location of the reinforcements above and below 

the level of the reinforcement under consideration. The computation of Svt is summarized in 

Table E4-7.1 wherein S  vt  z

  z . Note that wp = 5.00 ft per Step 1. 

Table E4-7.1. Summary of computations for Svt 

Level Z (ft) Z (ft) Z (ft) Svt (ft) 

1 1.87 0 1.87+0.5(4.37–1.87)=3.12 3.12 

2 4.37 4.37-0.5(4.37–1.87)=3.12 4.37+0.5(6.87-4.37)=5.62 2.50 

3 6.87 6.87-0.5(6.87-4.37)=5.62 6.87+0.5(9.37-6.87)=8.12 2.50 

4 9.37 9.37-0.5(9.37-6.87)=8.12 9.37+0.5(11.87-9.37)=10.62 2.50 

5 11.87 11.87-0.5(11.87-9.37)=10.62 11.87+0.5(14.37-11.87)=13.12 2.50 

6 14.37 14.37-0.5(14.37-11.87)=13.12 14.37+0.5(16.87-14.37)=15.62 2.50 

7 16.87 16.87-0.5(16.87-14.37)=15.62 16.87+0.5(19.37-16.87)=18.12 2.50 

8 19.37 19.37-0.5(19.37-16.87)=18.12 19.37+0.5(21.87-19.37)=20.62 2.50 

9 21.87 21.87-0.5(21.87-19.37)=20.62 21.87+0.5(24.37-21.87)=23.12 2.50 

10 24.37 24.37-0.5(24.37-21.87)=23.12 25.64 2.52 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 11 November 2009
 
 

7.3 Calculate horizontal stress and maximum tension at each reinforcement level 

The horizontal spacing of the reinforcements is based on the maximum tension (Tmax) at each 

level of reinforcements which requires computation of the horizontal stress, σH, at each 

reinforcement level. The reinforcement tensile and pullout resistances are then compared 

with Tmax and an appropriate reinforcement pattern is adopted. This section demonstrates the 

calculation of horizontal stress, σH, and maximum tension, Tmax. 

The horizontal stress, σH, at any depth within the MSE wall is based on only the soil load as 

summarized in Table E4-7.2. 

σH = σH-soil + σH-surcharge 

Table E4-7.2. Summary of load components leading to horizontal stress 

Load Component Load Type Horizontal Stress 

Soil load from reinforced mass, σv-soil EV σH-soil = [Krσv-soil]γP-EV 

Surcharge traffic live load, q EV σH-surcharge = [Krq]γP-EV 

Using the unit weight of the reinforced soil mass and heights Z and heq, the equation for 

horizontal stress at any depth Z within the MSE wall can be written as follows (also see 

Chapter 4): 

σH 	 = Kr (r Z) γP-EV + Kr (r heq) γP-EV = Kr [r (Z + heq) γP-EV] 

Once the horizontal stress is computed at any given level of reinforcement, the maximum 

tension, Tmax, is computed as follows: 

Tmax = (σH)(Atrib) 

where Atrib is the tributary area for the soil reinforcement at a given level as discussed in 

Section 7.2. 

The computations for Tmax are illustrated at zo = 9.37 ft which is Level 4 in the assumed 

vertical layout of reinforcement. Assume Strength I (max) load combination for illustration 

purposes and use appropriate load factors from Table E4-5.1. 

	 At Z = 9.37 ft, the following depths are computed 

Z = 8.12 ft (from Table E4-7.1) 

Z = 10.62 ft (from Table E4-7.1) 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 12 November 2009
 
 

 

	 Obtain Kr by linear interpolation between 1.7Ka = 0.707 at Z = 0 and 1.2Ka = 0.340 at 

Z = 20.00 ft as follows: 

At Z = 8.12 ft, Kr(z-)= 0.340 + (20.00 ft – 8.12 ft)(0.707-0.340)/20.00 ft = 0.558 

At Z = 10.62 ft, Kr(z+)= 0.340 + (20.00 ft – 10.62 ft)(0.707-0.340)/20.00 ft = 0.512 

	 Compute σH-soil = [kr σv-soil]γP-EV as follows: 

γP-EV = 1.35 from Table E4-5.1 

At Z = 8.12 ft, 

v-soil(Z-) = (0.125 kcf)(8.12 ft) = 1.02 ksf 

σH-soil(Z-) = [Kr(z-)σv-soil(z-)]γP-EV = (0.558)(1.02 ksf)(1.35) = 0.76 ksf 

At Z = 10.62 ft, 

v-soil(Z+) = (0.125 kcf)(10.62 ft) = 1.33 ksf 

σH-soil(Z+) = [Kr(z+)σv-soil(z+)]γP-EV = (0.512)(1.33 ksf)(1.35) = 0.92 ksf 

σH-soil = 0.5(0.76 ksf + 0.92 ksf) = 0.84 ksf 

	 Compute σH-surcharge = [Kr q] γP-EV as follows: 

γP-EV = 1.35 from Table E4-5.1 

q = (γf)(heq) = (0.125 kcf)(2.00 ft) = 0.25 ksf 

At Z = 8.12 ft, σH-surcharge(Z-) = [Kr(Z-) q] γP-EV = (0.558)(0.25 ksf)(1.35) = 0.19 ksf 

At Z = 10.62 ft, σH-surcharge(Z+) = [Kr(Z+) q] γP-EV = (0.512)(0.25 ksf)(1.35) = 0.17 ksf 

σH-surcharge = 0.5(0.19 ksf + 0.17 ksf) = 0.18 ksf 

	 Compute σH = σH-soil + σH-surcharge as follows: 

σH = 0.84 ksf + 0.18 ksf = 1.02 ksf 

	 Based on Table E4-7.1, the vertical tributary spacing at Level 4 is Svt = 2.50 ft 

	 The panel width, wp, is 5.00 ft (given in Step 1) 

	 The tributary area, Atrib, is computed as follows: 

Atrib = (2.50 ft)(5.00 ft) = 12.50 ft2 

	 The maximum tension at Level 4 is computed as follows: 

Tmax = (σh)(Atrib) = (1.02 ksf)(12.50 ft2

) = 12.75 k/panel of 5-ft width 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 13 November 2009
 
 

Using similar computations, the various quantities can be developed at other levels of 

reinforcements and load combinations. 

7.4 Establish nominal and factored long-term tensile resistance of soil reinforcement 

The nominal tensile resistance of galvanized steel bar mat soil reinforcement is based on the 

design life and estimated loss of steel over the design life during corrosion. 

The nominal diameters, D, of W15 and W11 wires are as follows: 

For W15 wires, D = 0.437 in. = 11.10 mm = 11,100 m 

For W11 wires, D = 0.374 in. = 9.50 mm = 9,500 m 

As per Step 2, the reinforced backfill meets the AASHTO (2007) requirements for 

electrochemical properties. For this reinforced backfill, the basis for calculating the 

thickness losses due to corrosion is as follows per Article 11.10.6.4.2a of AASHTO (2007): 

Zinc loss = 0.58 mil for first 2 years and 0.16 mil per year thereafter 

Steel loss = 0.16 mil/year/side 

Based on the above corrosion rates, the following can be calculated: 

Life of zinc coating (galvanization) = 2 years + (3.386 – 2*0.58)/0.16 ≈ 16 years 

As per Step 1, the design life is 75 years. The base carbon steel will lose thickness for 75 

years – 16 years = 59 years at a rate of 0.47 mil/year/side. Therefore, the anticipated 

diameter and area after 75 years for W15 and W11 is calculated as follows: 

For W15 wires 

D75 = 0.437 in. – (0.47 mil/year/side) (59 years) (2 sides)/1000 = 0.437 in. – 0.056 in. 

D75 = 0.381 in. 

Based on a 0.381 in. diameter wire, the cross-sectional area at the end of 75 years will be 

equal to ()(0.381 in.)2

/4 = 0.1142 in2/wire 

For W11 wires 

D75 = 0.374 in. – (0.47 mil/year/side) (59 years) (2 sides) = 0.374 in. – 0.056 in. 

D75 = 0.318 in. 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 14 November 2009
 
 

Based on a 0.318 in. diameter wire, the cross-sectional area at the end of 75 years will be 

equal to ()(0.318 in.)2

/4 = 0.0795 in2/wire 

For Grade 65 steel with Fy = 65 ksi, the nominal tensile resistance, Tn, and factored tensile 

resistance, Tr, for the W15 and W11 wires will be as follows: 

For W15 wires 

Tn = 65 ksi (0.1142 in2

) = 7.42 k/wire. 

Using the resistance factor, t = 0.65 as listed in Table E4-5.2, the factored tensile resistance, 

Tr = 7.42 k/wire (0.65) = 4.82 k/wire. 

For W11 wires 

Tn = 65 ksi (0.0795 in2

) = 5.17 k/wire. 

Using the resistance factor, t = 0.65 as listed in Table E4-5.2, the factored tensile resistance, 

Tr = 5.14 k/wire (0.65) = 3.36 k/wire. 

7.5 Establish nominal and factored pullout resistance of soil reinforcement 

The nominal pullout resistance, Pr, of galvanized steel bar mat (grid) reinforcement is based 

on various parameters in the following equation: 

Pr = (F*)(2b)(Le)[(σv-soil)(γP-EV)] 

In the above equation, the contribution of live load is not included as per Figure E4-2b. 

Since the steel bar mat has welded connections, it can be considered inextensible with  = 1. 

Assume a W11 transverse wire which has a nominal diameter of 0.374 in. The transverse 

spacing of transverse wires, St, is varied depending on the level of reinforcement to optimize 

the design from an economical perspective. For this example problem, assume that the 

spacing of the transverse wires, St = 6 in., 12 in. and 18 in. Based on these spacing, the value 

of t/St is as follows: 

For, St = 6 in., t/St = 0.374 in./6 in. = 0.0623 

For, St = 12 in., t/St = 0.374 in./12 in. = 0.0312 

For, St = 18 in., t/St = 0.374 in./18 in. = 0.0208 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 15 November 2009
 
 

Based on the value of t/St, the F* parameter varies from 20(t/St) at z = 0 ft to 10(t/St) at z ≥

20 ft and greater as shown in Figure E4-5. For the three value of t/St the variation of F* is as 

follows: 

For t/St = 0.0623, F* = 1.2460 at Z = 0 ft and F* = 0.623 at Z ≥ 20 ft 

For t/St = 0.0312, F* = 0.623 at Z = 0 ft and F* = 0.312 at Z ≥ 20 ft 

For t/St = 0.0208, F* = 0.416 at Z = 0 ft and F* = 0.208 at Z ≥ 20 ft 

Assume bar mat width, b = 1 ft for computing pullout resistance on a per foot width basis. 

The actual bar mat width will be computed based on comparison of the pullout resistance 

with Tmax. 

For this example problem, assume the layout of longitudinal and transverse wires as shown 

in Table E4-7.3. The number of longitudinal wires and thus the width of the bar mats will be 

determined in Section 7.6. 

Table E4-7.3. Assumed bar mat configuration for internal stability analysis 

Level Longitudinal wire Transverse wire Spacing of transverse wires, St 

1 to 4 W11 W11 6 in. 

5 to 7 W15 W11 12 in. 

8 to 10 W15 W11 18 in. 

The computations for Pr are illustrated at z = 9.37 ft which is Level 4 as measured from top 

of the wall. Assume Strength I (max) load combination for illustration purposes and use 

appropriate load factors from Table E4-5.1. 

	 Obtain F* at z = 9.37 ft by linear interpolation between 1.2460 at Z = 0 and 0.623 at 

Z = 20 ft as follows: 

F* = 0.623 + (20.00 ft – 9.37 ft)(1.246 – 0.623)/20 ft = 0.955 

	 Compute effective length Le as follows: 

Since Z < H/2, Le = L – 0.3(H) 

Le = 18 ft – 0.3(25.64 ft) = 10.31 ft 

	 Compute (σv-soil)(γP-EV) 

Per Article 11.10.6.3.2 of AASHTO (2007), use unfactored vertical stress for pullout 

resistance. Thus, 

γP-EV = 1.00 

(σv-soil)(γP-EV) = (0.125 kcf)(9.37 ft)(1.00) = 1.171 ksf 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 16 November 2009
 
 

	 Compute nominal pullout resistance as follows: 

Pr = (F*)(2b)(Le)[(σv-soil)(γP-EV)] 

Pr = (1.0)(0.955)(2)(1.00 ft)(10.31 ft)(1.171 ksf) = 23.06 k/ft 

	 Compute factored pullout resistance as follows: 

Prr = Pr = (0.90)(23.06 k/ft) = 20.75 k/ft 

Using similar computations, the various quantities can be developed at other levels of 

reinforcements and load combinations. 

7.6 Establish number of longitudinal wires at each level of reinforcement 

Based on Tmax, Tr and Prr, the number of longitudinal wires at any given level of 

reinforcements can be computed as follows: 

 Assume spacing of the longitudinal wires, Sl = 6 in. = 0.5 ft 

 Based on tensile resistance considerations, the number of longitudinal, Nt, is 

computed as follows: 

Nt = Tmax/Tr 

 Based on pullout resistance considerations, the number of longitudinal wires, Np, is 

computed as follows: 

Np = 1 + (Tmax/Prr)/(Sl) 

Using the Level 4 reinforcement at Z = 9.37 ft, the number of W11 longitudinal wires for 5 ft 

wide panel can be computed as follows: 

 Tmax = 12.75 k/panel of 5 ft width, Tr = 3.36 k/wire, Prr = 20.75 k/ft 

 Nt = Tmax/Tr = (12.75 k/panel of 5 ft width)/(3.36 k/wire) = 3.8 longitudinal 

wires/panel of 5 ft width 

 Np = 1 + (Tmax/Prr)/(Sl) = 1 + [(12.75 k/panel of 5 ft width)/(20.75 k/ft)]/(0.5 ft) = 2.2 

longitudinal wires/panel 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 17 November 2009
 
 

	 Since Nt > Np, tension breakage is the governing criteria and therefore the governing 

value, Ng, is 3.8. Select 4 longitudinal wires at Level 4 for each panel of 5 ft width. 

Thus, the steel bar mat configuration at Level 4 is 4W11 + W11x0.5' which means a bar mat 

with 4 W11 longitudinal wires spaced at 0.5 ft on centers with W11 transverse wires spaced 

at 0.5 ft on centers. 

The computations in Sections 7.4 to 7.6 are repeated at each level of reinforcement. Table 

E4-7.4 presents the computations at all levels of reinforcement for Strength I (max) load 

combination. Similar computations can be performed for Strength I (min) and Service I load 

combination but they will not govern the design because the load factors for these two load 

combinations are less than those for Strength I (max) load combination. 

Note to users: All the long-form step-by-step calculations illustrated in Step 7 were based on 

hand-calculations in which numbers were rounded to the third or fourth significant digit as 

appropriate in each step. Table E4-7.4 was generated using a spreadsheet in which numbers 

at all calculation steps were not rounded. Thus, the end result in Table E4-7.4 may be 

somewhat different when compared to long-form hand calculations. However, the difference 

should be less than 0.2 in most cases. 

Table E4-7.4. Summary of internal stability computations for Strength I (max) load 

combination 

Level 

Z 

ft 

H

ksf 

Tmax

k/5 ft 

wide 

panel 

F* 

dim 

Le 

ft 

p(Pr) 

k/ft 

s(Tn) 

k/wire 

Np 

-

Nt 

-

Ng 

-

Bar Mat 

-

1 1.87 0.40 6.25 1.188 10.31 5.16 3.38 3.4 1.9 4 4W11+W11x0.5' 

2 4.37 0.67 8.36 1.110 10.31 11.25 3.38 2.5 2.5 3 3W11+W11x0.5' 

3 6.87 0.86 10.80 1.033 10.31 16.47 3.38 2.3 3.2 4 4W11+W11x0.5' 

4 9.37 1.02 12.77 0.955 10.31 20.75 3.38 2.2 3.8 4 4W11+W11x0.5' 

5 11.87 1.14 14.26 0.438 10.31 12.06 4.84 3.4 2.9 4 4W15+W11x1' 

6 14.37 1.22 15.23 0.399 11.24 14.50 4.84 3.1 3.1 4 4W15+W11x1' 

7 16.87 1.26 15.71 0.360 12.74 17.41 4.84 2.8 3.2 4 4W15+W11x1' 

8 19.37 1.28 16.03 0.214 14.24 13.27 4.84 3.4 3.3 4 4W15+W11x1.5' 

9 21.87 1.37 17.10 0.208 15.74 16.12 4.84 3.1 3.5 4 4W15+W11x1.5' 

10 24.37 1.51 19.05 0.208 17.24 19.66 4.84 2.9 3.9 4 4W15+W11x1.5' 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 18 November 2009
 
 

STEP 8:	 DESIGN OF FACING ELEMENTS 

The precast facing elements must be designed as structural elements with appropriate 

connection strength as discussed in Chapter 4. 

STEP 9:	 CHECK OVERALL AND COMPOUND STABILITY AT SERVICE LIMIT 

STATE 

From Step 2, it is given that the foundation soil is dense clayey sand that has fd = 30°, fd = 

125 pcf. Furthermore, the ground in front of the wall is horizontal and the foundation soil 

has no water table. Therefore, based on observation, overall stability is adequate. For actual 

projects, overall stability should be investigated at the Service I load combination and a 

resistance factor of 0.65. 

STEP 10: DESIGN WALL DRAINAGE SYSTESM 

See Chapter 5 for wall drainage considerations. 

E4-2 PRACTICAL CONSIDERATIONS 

Following is a general list of practical considerations from a geotechnical and structural 

viewpoint: 

 Attempt should be made to not vary the bar mat configuration too much because that 

increases the possibility of inadvertent mixing of bar mats and use of wrong bar mat at a 

given level. 

FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 19 November 2009
 
FHWA NHI-10-025 Example E4 – Level backfill with LL 

MSE Walls and RSS – Vol II E4 – 20 November 2009
 
 

EXAMPLE PROBLEM E5 

BRIDGE ABUTMENT SUPPORTED ON SPREAD FOOTING ON TOP OF AN MSE 

WALL WITH SEGMENTAL PRECAST PANEL FACING 

E5-1 INTRODUCTION 

This example problem demonstrates the analysis of a bridge abutment supported on a spread 

footing on top of an MSE wall with segmental precast panel facing. A typical configuration 

of such a bridge abutment is shown in Figure E5-1. The analysis of a true bridge abutment is 

based on various principles that were discussed in Chapters 4 and 5. Table E5-1 presents a 

summary of steps involved in the analysis of a bridge abutment supported on spread footing. 

Each of the steps and sub-steps is sequential and if the design is revised at any step or substep then all the previous computations need to be re-visited. Each of the steps and the substeps in Table E5-1 is explained in detail herein. Practical considerations for implementation 

of a true abutment system are presented in Section E5-2 after the illustration of the step-bystep procedures. 

NOTE: A bridge abutment is a complex structure and should be analyzed very 

carefully since the performance of the bridge and its approach system will be 

affected. This example problem presents a typical case that may not be 

representative of all possible configurations, e.g., skewed bridge abutment, 

integral abutments, extensible reinforcements or other features may require 

additional considerations. The example problem is presented herein to 

demonstrate the formulation of various equations in the LRFD context for 

complex geometries. The formulations may have to be modified for projectspecific bridge abutment configurations. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 1 November 2009
 
 

Table E5-1. Summary of steps in analysis of a true bridge abutment 

Step Item 

1 Establish project requirements 

2 Establish project parameters 

3 Estimate wall embedment depth and length of reinforcement 

4 Estimate unfactored loads 

5 Summarize applicable load and resistance factors 

6 Evaluate external stability of spread footing 

6.1 Evaluation of limiting eccentricity 

6.2 Evaluation of sliding resistance 

6.3 Evaluation of bearing resistance 

7 Evaluate external stability of MSE wall 

7.1 Evaluation of limiting eccentricity 

7.2 Evaluation of sliding resistance 

7.3 Evaluation of bearing resistance 

7.4 Settlement analysis 

8 Evaluate internal stability of MSE wall 

8.1 Estimate critical failure surface, variation of Kr and F* for internal stability 

8.2 Establish vertical layout of soil reinforcements 

8.3 Calculate horizontal stress and maximum tension at each reinforcement level 

8.4 Establish nominal and factored long-term tensile resistance of soil reinforcement 

8.5 Establish nominal and factored pullout resistance of soil reinforcement 

8.6 Establish number of soil reinforcing strips at each level of reinforcement 

9 Design of facing elements 

10 Check overall and compound stability at the service limit state. 

11 Design wall drainage system 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 2 November 2009
 
 

cf bf

 b1 b2 b3 b4 b5 Joint 

F2 

DL 

LL

 h2

 h 

h3

 h1 

Reinforced backfill 

'1, γ1

H Ha

L 

Bridge Approach 

d 

Retained backfill 

'3, γ3 

Spread footing backfill above Plane XY 

'2, γ2 

Bridge Superstructure 

Bearing 

Pad 

Leveling Pad 

X Y 

Foundation Soil 

'fd, γfd

 H' 

Figure E5-1. Configuration showing various parameters for analysis of a bridge abutment 

supported on spread footing on top of an MSE wall (not-to-scale). 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 3 November 2009
 
 

STEP 1. ESTABLISH PROJECT REQUIREMENTS 

 Abutment wall height, Ha = 23 ft (measured from finished ground to bottom of spread 

footing as shown in Figure E5-1) 

 Length of wall at abutment = 120 ft 

 Design life = 100 years (since the abutment application is considered critical) 

 Precast panel units: 10 ft wide x 5 ft tall x 0.5 ft thick 

 Type of reinforcement: Grade 65 (Fy = 65 ksi), 1.969 in. x 0.157 in. (50 mm wide x 4 

mm) thick galvanized steel ribbed strips with zinc coating of 3.386 mils (86 m). 

 Cast-in-place spread footing 

 No approach slab (therefore, consider live load) 

STEP 2. EVALUATE PROJECT PARAMETERS 

Figure E5-1 shows the typical configuration of a true bridge abutment. 

Bridge loading parameters (see Figure E5-1): 

 Nominal (unfactored) Dead Load reaction, DL = 10.60 k/ft 

 Nominal (unfactored) Live Load reaction, LL = 5.70 k/ft 

 Nominal (unfactored) lateral friction force, F2, at the bearing level = 0.82 k/ft 

Spread footing configuration (see Figure E5-1): 

 Footing base width, bf = 10.75 ft with the following values 

o b1= 1.50 ft, b2= 1.50 ft, b3= 1.50 ft, b4= 1.00 ft, b5= 5.25 ft 

 Distance between toe of footing and backface of MSE panels, cf = 0.5 ft 

 Height of footing, h = 10.35 ft with the following values 

o h1 = 1.50 ft, h2 = 3.85 ft, h3 = 5.00 ft 

 Bearing pad height, hb = 0.08 ft included in h3 dimension 

Soil Properties (see Figure E5-1): 

 Reinforced backfill, '1 = 34°, 1 = 125 pcf, coefficient of uniformity, Cu = 7.0 and 

meeting the AASHTO (2007) requirements for electrochemical properties 

 Random backfill behind spread footing, '2 = 34°, 2 = 125 pcf 

 Retained backfill, '3 = 30°, 3 = 125 pcf 

Other relevant parameters: 

 Spread footing concrete, c = 150 pcf 

 Foundation soil, 'fd = 30°, fd = 120 pcf, clayey sand with no water table 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 4 November 2009
 
 

	 Factored Bearing resistance of foundation soil 

o For service limit consideration, qnf-ser = 7.0 ksf for 1-inch of total settlement 

o For strength limit consideration, qnf-str = 15.0 ksf 

	 Factored Bearing resistance of MSE wall (for use in analysis of spread footing on top 

of MSE wall) 

o For service limit considerations, qnm-ser = 4.0 ksf for < 1⁄2-inch settlement 

o For strength limit considerations, qnm-str = 7.0 ksf 

 Live load on bridge approach, heq = 2-ft of soil per Table 3.11.6.4-1 of AASHTO 

(2007) 

 No seismic considerations. 

STEP 3. ESTIMATE DEPTH OF EMBEDMENT AND LENGTH OF 

REINFORCEMENT 

Based on Table C.11.10.2.2.-1 of AASHTO (2007), the minimum embedment depth = H/10 

for abutment walls with horizontal ground in front of wall, i.e., 2.3 ft for abutment height of 

23 ft. For this design, assume embedment, d = 2.5 ft. Thus, design height of the wall, H = Ha 

+ d = 23 ft + 2.5 ft = 25.5 ft. 

Due to the large surcharges the length of the reinforcements for bridge abutment applications 

will be longer than the minimum value of 0.7H for walls with level backfill without 

surcharge(s). A good starting point for length of reinforcements for bridge abutment 

applications is assuming them to be approximately 1.0H rounded to the nearest higher 

number. Since in this case H=25.5 ft, the length of reinforcement for this example problem 

is assumed to be 26 ft. This length will be verified as part of the design process. The length 

of the reinforcement is assumed to be constant throughout the height to limit differential 

settlements across the reinforced zone because differential settlements could overstress the 

reinforcements. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 5 November 2009
 
 

STEP 4. ESTIMATE UNFACTORED LOADS 

Tables E5-4.1 and E5-4.2 present the equations for unfactored loads and moment arms about 

Points A and B shown in Figure E5-2. The moments are a product of the respective forces 

and moment arms. Each force is assigned a designation representing the applicable load type 

as per Tables 3.4.1-1 and 3.4.1-2 of AASHTO (2007). 

To compute the numerical values of various forces and moments, the parameters provided in 

Step 2 are used. Using the values of the various friction angles, the coefficients of lateral 

earth pressure are as follows: 

Ka1 = (1 - sin34°)/(1 + sin34°) = 0.283 

Ka2 = (1 - sin34°)/(1 + sin34°) = 0.283 

Ka3 = (1 - sin30°)/(1 + sin30°) = 0.333 

For the example problem, Tables E5-4.3 and E5-4.4 summarize the numerical values of 

unfactored forces and moments, respectively, based on the equations, various dimensions and 

values of lateral earth pressure coefficients presented above. Refer to Figure E5-2 for 

notations of various forces. The height of equivalent soil surcharge to represent live load, 

heq, will be different for analysis of footing and MSE wall block since the height of the 

footing is less than 20 ft. In subsequent computations, the notation heqF is used for heq for 

analysis of footing versus heqM for analysis of MSE block. In this example problem, the 

height of the footing, h, is 10.35 ft. Based on Table 3.11.6.4-1 of AASHTO (2007), heqF = 

2.96 ft. For analysis of MSE wall, heqM = 2 ft since the height of MSE wall, H, is greater 

than 20 ft. 

The unfactored forces and moments in Tables E5-4.3 and E5-4.4 form the basis of all 

computations in this example problem. The unfactored forces and moments should be 

multiplied by the appropriate load factors based on the load types identified in the second 

column of the Tables E5-4.1 and E5-4.2 to perform the analysis for various load 

combinations such as Strength I, Service I, etc. 

The load factors for various load types relevant to this example problem are discussed in Step 

5. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 6 November 2009
 
 

 

 

cf bf

b5 b1 b2 b3 b4 

K' K F

G 

H/3 

D 

E heq 

D' M

E' Vs1 Joint 

F2 

DL 

LL M'

 h2

 h 

h3 V3

 V0

X C

h1 V1

 V2

 A 

F4 

Fs1 

h/2 

J I 

F1 

h/3 

2ef 

3, γ3 

Y 

1, γ1

 L1

 H 

V4

 L

 B 

45° + 1/2 

F3 

H/2 

FS2 

q= γ2 heq 

d 

2, γ2

 hb

 FA 

Figure E5-2. Legend for computation of forces and moments (not-to-scale). 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 7 November 2009
 
 

 

Table E5-4.1. Equations of computing unfactored vertical forces and moments 

Vertical Force 

(Force/length units) 

LRFD 

Load Type 

Moment arm (Length units) 

@ Point A @ Point B 

V0=(γ2)(h2+h3)(b5) EV  5  f 

5 bb 

2 

b 

  5  ff 

5 bcb 

2 

b 



V1=(γc)(bf)(h1) DC 

2 

bf 

2 

b 

c f 

f 

V2=(γc)(b2+b3+b4)(h2) DC 

2 

bbb b 432

1 

 



2 

bbb bc 432 

1f 





V3=(γc)(b4)(h3) DC 321 

4 bbb 

2 

b 

 321 

4 

f bbb 

2 

b 

c 

V4=(γ1)(H)(L) EV - L/2 

V5=(γ2)(h)(L) EV - L/2 

VS=(γ2)(heqF)(L) = qL LS - L/2 

VS1=(γ2)(heqF)(b4+b5) LS 321

54 bbb

2 

bb 





321

54

f bbb

2 

bb 

c 





DL DC b1 + b2 cf + b1 + b2 

LL LL b1 + b2 cf + b1 + b2 

Notes: 

1. Forces V5 and VS are needed later (see Figures E5-3 and E5-4). 

2. The load DL can include both “DC” and “DW” type of loads. As a simplification, herein 

DL is assumed to include both and a “DC” load factor is used. 

Table E5-4.2. Equations of computing unfactored horizontal forces and moments 

Horizontal Force 

(Force/length) 

LRFD 

Load Type 

Moment arm (Length units) 

@ Point A @ Point B 

F1 = 1/2 (Ka2)(γ2)h2 EH h/3 (h/3) + H 

F2 FR h1 + h2 + hb h1 + h2 + hb + H 

F3 = (Ka3)[(γ2)(h)](H) EH - H/2 

F4 = 1⁄2(Ka3)(γ3)H2

 EH - H/3 

FS1=(Ka2)[(γ2)(heqF)](h) LS h/2 (h/2) + H 

FS2=(Ka3)[(γ2)(heqM)](H) LS - H/2 

FA = F1 + F2 + FS1 

Based on 

each 

component 

-

H 

(for external stability) 

H – (L1/3) 

(for internal stability) 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 8 November 2009
 
 

 

Table E5-4.3. Unfactored vertical forces and moments 

Force Value 

k/ft 

Moment 

Arm @ 

Point A, ft 

Moment 

Arm @ 

Point B, ft 

Moment 

Moment at 

Point A, 

k-ft/ft 

Moment at 

Point B, 

k-ft/ft 

V0 = 5.81 8.13 8.63 MV0 = 47.19 50.09 

V1 = 2.42 5.38 5.88 MV1 = 13.00 14.21 

V2 = 2.31 3.50 4.00 MV2 = 8.09 9.24 

V3 = 0.75 5.00 5.50 MV3 = 3.75 4.13 

V4 = 82.88 13.00 MV4 = 1077.38 

V5 = 33.64 13.00 MV5 = 437.29 

Vs = 9.62 13.00 MVs = 125.06 

Vs1 = 2.31 7.63 8.13 MVs1 = 17.63 18.79 

DL = 10.60 3.00 3.50 MDL = 31.80 37.10 

LL = 5.70 3.00 3.50 MLL = 17.10 19.95 

Notes: 

1. Vs and Vs1 is computed based on heqF = 2.96 ft since h = 10.35 ft 

Table E5-4.4. Unfactored horizontal forces and moments 

Force Value 

k/ft 

Moment 

Arm @ 

Point A, ft 

Moment 

Arm @ 

Point B, ft 

Moment 

Moment at 

Point A, 

k-ft/ft 

Moment at 

Point B, 

k-ft/ft 

F1 = 1.89 3.45 28.95 MF1 = 6.53 54.80 

F2 = 0.82 5.43 30.93 MF2 = 4.43 25.21 

F3 = 11.00 12.75 MF3 = 140.21 

F4 = 13.55 8.50 MF4 = 115.15 

FS1 = 1.08 5.18 30.68 MFS1 = 5.60 33.21 

FS2 = 2.13 12.75 MFS2 = 27.09 

FA = * 25.50 MFA = FA (25.50) 

Notes: 

1. FA = F1 + F2 + FS1 and each of the components of FA is a different load type and hence 

has a different load factor. 

2. FS1 is computed based on heqF = 2.96 ft since h = 10.35 ft 

3. FS2 is computed based on heqM = 2 ft since H > 20 ft 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 9 November 2009
 
STEP 5. SUMMARIZE APPLICABLE LOAD AND RESISTANCE FACTORS 

Table E5-5.1 summarizes the load factors for the various LRFD load type shown in the 

second column of Tables E5-4.1 and E5-4.2. Throughout the computations in this 

example problem, the forces and moments in Tables E5-4.1 and E5-4.2 should be 

multiplied by appropriate load factors. For example, if computations are being done for 

Strength I (maximum) load combination, the forces and moments corresponding to load V2 

should be multiplied by 1.25 which is associated with load type DC assigned to load V2. 

Table E5-5.1. Summary of applicable load factors 

Load 

Combination 

Load Factors 

(after AASHTO, 2007 Tables 3.4.1-1 and 3.4.1-2) 

EV DC LL/LS ES EH FR 

Strength I 

(maximum) 1.35 1.25 1.75 1.50 1.50 1.00 

Strength I 

(minimum) 1.00 0.90 1.75 0.75 0.90 1.00 

Service I 1.00 1.00 1.00 1.00 1.00 1.00 

For computation of factored resistances during evaluation of strength limits states, 

appropriate resistance factors have to be used. Table E5-5.2 summarizes the applicable 

resistance factors. For service limit state, all resistance factors are equal to 1.0. 

Table E5-5.2. Summary of applicable resistance factors for evaluation of resistances 

Item Resistance 

Factors 

AASHTO (2007) 

Reference 

Sliding of cast-in-place spread footing on MSE wall s = 0.80 Table 10.5.5.2.2-1 

Sliding of MSE wall on foundation soil s = 1.00 Table 11.5.6-1 

Bearing resistance of MSE wall b = 0.65 Table 11.5.6-1 

Tensile resistance (for steel strips) t = 0.75 Table 11.5.6-1 

Pullout resistance p = 0.90 Table 11.5.6-1 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 10 November 2009
 
 

STEP 6. EVALUATE EXTERNAL STABILITY OF SPREAD FOOTING 

6.1 Limiting Eccentricity at base of Spread Footing 

Since the computations are related to limiting eccentricity, the beneficial contribution of live 

load to resisting forces and moments is neglected. Limiting eccentricity is a strength limit 

state check and therefore only the strength limits state calculations are necessary. However, 

service limit state calculations are also included since some of the results will be needed later 

in internal stability analysis. The critical values from strength limit state calculations based 

on max/min result in the extreme force effect and govern the limiting eccentricity mode of 

failure. 

Table E5-6.1. Computations for evaluation of limiting eccentricity for spread footing 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Sum of overturning moments about Point A 

MOA = MF1+MFs1 +MF2 

k-ft/ft 24.03 20.11 16.56 

Sum of resisting moments about Point A 

MRA = MV0+MV1+MV2+MV3+MDL k-ft/ft 134.50 98.16 103.82 

Net moment at Point A, MA = MRA - MOA k-ft/ft 110.47 78.05 87.27 

Sum of vertical forces from the footing 

VA =V0+V1+V2+V3+DL k/ft 27.94 20.28 21.89 

Location of resultant from Point A, anl = MA/VA ft 3.95 3.85 3.99 

Eccentricity from center of footing, ef = 0.5*bf - anl ft 1.42 1.53 1.39 

Limiting eccentricity, e = bf/4 for Strength limit state 

and e = bf/6 for service limit state ft 2.69 2.69 1.79 

Is the limiting eccentricity criteria satisfied? - Yes Yes Yes 

CRITICAL VALUES BASED ON MAX/MIN 

Overturning moments about Point A, MOA-C k-ft/ft 24.03 

Resisting moments about Point A, MRA-C k-ft/ft 98.16 

Net moment about Point A, MA-C = MRA-C - MOA-C k-ft/ft 74.13 

Vertical force, VA-C k/ft 20.28 

Location of resultant from Point A, anl = MA-C/VA-C ft 3.66 

Eccentricity from center of footing, ef = 0.5*bf - anl ft 1.72 

Limiting eccentricity, e = bf/4 ft 2.69 

Is the limiting eccentricity criteria satisfied? - Yes 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 11 November 2009
 
 

6.2 Sliding Resistance at base of Spread Footing 

The purpose of these computations is to evaluate the sliding resistance at the base of the 

spread footing. Since the computations are related to sliding resistance, the beneficial 

contribution of live load to resisting horizontal forces is neglected. Note that sliding 

resistance is a strength limit state check and therefore only the strength limits state 

calculations are necessary. However, service limit state calculations are also included since 

some of the results will be needed later in internal stability analysis. Since the friction angle 

of reinforced soil, '1, is same as the friction angle for random fill above base of footing, '2, 

the sliding check will be performed using '1='2=34o . The critical values based on max/min 

result in the extreme force effect and govern the sliding mode of failure. 

Table E5-6.2. Computations for evaluation of sliding resistance for spread footing 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Sum of horizontal forces on footing that contribute to 

sliding = FA = F1+FS1+F2 

k/ft 5.55 4.41 3.79 

Sum of vertical forces from the footing 

VA =V0+V1+V2+V3+DL = k/ft 27.94 20.28 21.89 

Nominal sliding resistance, VN = VA*tan('1) k/ft 18.85 13.68 14.76 

Factored sliding resistance, VF =s*VN k/ft 15.08 10.94 11.81 

Is VF > FA? - Yes Yes Yes 

Capacity:Demand Ratio (CDR) = VF:FA dim 2.72 2.48 3.12 

CRITICAL VALUES BASED ON MAX/MIN 

Minimum VF (VFmin) k/ft 10.94 

Maximum FA (FAmax) k/ft 5.55 

Is VFmin > FAmax? - Yes 

Capacity:Demand Ratio (CDR) = VFmin:FAmax dim 1.97 

6.3 Bearing Resistance at base of Spread Footing 

The purpose of these computations is to evaluate the bearing resistance at the base of the 

spread footing. Since the computations are related to bearing resistance, the contribution of 

live load is included to create the extreme force effect and maximize the bearing stress. The 

bearing stress is compared with bearing resistance to ensure that the footing is adequately 

sized. Later on, the bearing stress is also used in internal stability computations. Similarly, 

later the value of dimension L1 that defines the incremental lateral pressures due to lateral 

load FA (see Figure E5-2) will be needed and hence has been computed in Table E5-6.3. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 12 November 2009
 
Table E5-6.3. Computations for evaluation of bearing resistance for spread footing 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Sum of overturning moments about Point A = MOA 

=MF1+MFs1 +MF2 

k-ft/ft 24.03 20.11 16.56 

Sum of resisting moments about Point A = MRA = 

MV0+MV1+MV2+MV3+MDL+MLL+MVS1 

k-ft/ft 195.28 158.94 138.56 

Factored net moment at Point A, MA = MRA - MOA = k-ft/ft 171.26 138.84 122.00 

Sum of vertical forces from the footing for bearing 

stress analysis=VAb=V0+V1+V2+V3+DL+LL+VS1 

k/ft 41.96 34.30 29.90 

Location of resultant from Point A for bearing stress 

analysis, awl = MA/VAb 

ft 4.08 4.05 4.08 

Eccentricity from center of footing, ef = 0.5*bf - awl ft 1.29 1.33 1.29 

Limiting eccentricity, e = bf/4 for strength limit states 

and e= bf/6 for service limit state ft 2.69 2.69 1.79 

Is the resultant within limiting value of ef? - Yes Yes Yes 

Effective width of spread footing, bf'=bf -2ef = ft 8.16 8.10 8.16 

Bearing stress, σv = VAb / (bf-2ef) ksf 5.14 4.24 3.66 

Factored bearing resistance, qR (given) ksf 7.00 7.00 4.00 

Is bearing stress < factored bearing resistance? dim Yes Yes Yes 

Capacity:Demand Ratio (CDR) = qR:σv dim 1.36 1.65 1.09 

Depth of influence for the lateral force at base of 

footing, L1 = {cf + (bf - 2ef)} tan(45°+34°/2) ft 16.29 16.17 16.29 

CRITICAL VALUES BASED ON MAX/MIN 

Overturning moments about Point A, MOA-C k-ft/ft 24.03 

Resisting moments about Point A, MRA-C k-ft/ft 158.94 

Net moment about Point A, MA-C = MRA-C - MOA-C k-ft/ft 134.91 

Vertical force, VAb-C k/ft 34.30 

Location of resultant from Point A, awl = MA-C/VA-C ft 3.93 

Eccentricity from center of footing, ef = 0.5*bf - anl ft 1.44 

Limiting eccentricity, e = bf/4 ft 2.69 

Is the limiting eccentricity criteria satisfied? - Yes 

Effective width of spread footing, bf'=bf - 2ef ft 7.87 

Bearing stress, σv-c = VAb-C / (bf-2ef) ksf 4.36 

Factored bearing resistance, qR (given) ksf 7.00 

Is bearing stress < factored bearing resistance? dim Yes 

Capacity:Demand Ratio (CDR) = qR:σv-c dim 1.61 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 13 November 2009
 
STEP 7. EVALUATE EXTERNAL STABILITY OF MSE WALL 

The external stability of MSE wall is a function of the various forces and moments above 

plane XY in Figure E5-2. In the LRFD context the forces and moments need to be 

categorized into various load types. The primary load types are soil loads (EV, EH), live 

load (LL), and permanent loads (DC, DW). The principle of superposition shown in Figure 

11.10.10.1-1 of AASHTO (2007) is used in achieving the separation of load types as well as 

performing external stability computations of the MSE wall. This separation of various load 

types will also permit a proper evaluation of the internal stability of the MSE wall. 

The separation of the loads by principle of superposition is primarily achieved by use of 

uniform loads and concentrated loads. The uniform loads are used to represent soil and live 

loads while the concentrated loads are used to represent permanent bridge loads due to the 

bridge superstructure and the concrete spread footing. Since LL is treated differently in the 

computations of limiting eccentricity, sliding resistance and bearing resistance, Figures E5-3 

and E5-4 show separation of various load types without and with live load components, 

respectively. The equations shown in these figures are for computing unfactored forces and 

moments. The relevant LRFD load type (e.g., “EV”, “LL”, etc.) are shown in the figures to 

permit computations of factored forces and moments using the appropriate load factors as 

identified in Table E5-5.1 in Step 5. 

It should be noted that use of principle of superposition results in an approximate 

representation of a very complex system. A case can conceivably be made for further 

separation of forces. However, a more refined system of forces is not justified given that the 

behavior of most elements of the system is designed to be within elastic range. One case 

where the approximations shown in Figure E5-3 and E5-4 may not be applicable is that of 

integral bridge abutments. In such specialized cases, additional forces may need to be 

considered depending on the actual abutment configuration. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 14 November 2009
 
 

V5

FA

V4

cf bf

anL

B B

 

Uniform Loads + Permanent Bridge Loads 

h SOIL “EV” 

SOIL “EV” 

PnL = VA– hγ2(bf+cf) 

“EV” 

A 

Fs2 F3 H 

F4 

Not-To-Scale 

Summary of relevant equations 

FA = F1 + F2 + FS1 

VA = V0 + V1 + V2 + V3 + DL 

MRA = MV0 + MV1 + MV2 + MV3 + MDL 

MOA = MF1 + MF2 + MFS1 

MA = MRA – MOA 

Location of PnL from Point A, anL = MA/VA 

Eccentricity of PnL from center of footing, ef = 0.5*bf – anl 

Note: See Figure E5-2 and Table E5-4.1 and E5-4.2 for additional information related to 

notations for various forces and moments and associated LRFD load types. 

Figure E5-3. Superposition of load effects without Live Loads on MSE Wall. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 15 November 2009
 
 

awL

cf bf - 2ef

1H:2V 

B B 

V4

V5

LIVE “LS” VS

 

Uniform Loads + Permanent Bridge Loads 

heqF 

h 

H 

Location of 

Pwl for bf – 2ef 

A 

PwL = VAb–(h+heqF) γ2(bf+cf) 

PwL = VAb–hγ2(bf+cf)-γ2heqF(bf+cf) 

“EV” “LS” 

F3 Fs2 

F4 

SOIL “EV” 

FA 

SOIL “EV” 

Not-To-Scale 

Summary of relevant equations 

FA = F1 + F2 + FS1 

VAb = V0 + V1 + V2 + V3 + DL + LL + VS1 

MRAb = MV0 + MV1 + MV2 + MV3 + MDL+ MLL+ MVS1 

MOAb = MF1 + MF2 + MFS1 

MAb = MRAb – MOAb 

Location of PwL from Point A, awL = MAb/VAb 

Eccentricity of PwL from center of footing, ef = 0.5*bf - awl 

Note: See Figure E5-2 and Table E5-4.1 and E5-4.2 for additional information related to 

notations for various forces and moments and associated LRFD load types. 

Figure E5-4. Superposition of load effects with Live Loads on MSE Wall. 

7.1 Limiting Eccentricity at Base of MSE Wall 

The purpose of these computations is to evaluate the limiting eccentricity at the base of the 

MSE wall. Since the computations are related to limiting eccentricity, the beneficial 

contribution of live load to resisting forces and moments is neglected. The computations for 

limiting eccentricity at the base of the MSE wall are illustrated in Table E5-7.1. Limiting 

eccentricity is a strength limit state check. However, in Table E5-7.1, the calculations are 

also performed for service limit state to obtain the effective footing width which will be used 

to determine the equivalent uniform (Meyerhof) bearing stress in Step 7.3 that will be 

compared to limiting bearing resistance from serviceability considerations (see Step 2). 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 16 November 2009
 
 

 

Table E5-7.1. Computations for evaluation of limiting eccentricity for MSE wall 

Item (Refer to Figure E5-2 for block CDMJ). The 

top 13 rows in this table are related to computation 

of Pwl, PnL, awL and anL values that will also be used 

in internal stability calculations. 

Unit Str I 

(max) 

Str I 

(min) Ser I 

Unfactored soil weight in block CDMJ in the 

abutment footing area = (h)[(bf+cf)*2] k/ft 14.55 14.55 14.55 

Load factor for soil weight in block CDMJ 

[Load Type "EV"] dim 1.35 1.00 1.00 

Factored soil weight in block CDMJ in the abutment 

footing area k/ft 19.65 14.55 14.55 

Unfactored LL weight on block CDMJ in the 

abutment footing area = (bf+cf)*q =(bf+cf)*(γ2)(heqF) k/ft 4.16 4.16 4.16 

Load factor for LL on block CDMJ 

[Load Type "LS"] dim 1.75 1.75 1.00 

Factored LL weight on block CDMJ in the abutment 

footing area k/ft 7.28 7.28 4.16 

Vertical weight due to soil weight and LL in block 

CDMJ k/ft 26.93 21.84 18.72 

Vertical weight from abutment footing including 

soil on heel and LL = VAb 

k/ft 41.96 34.30 29.90 

Vertical weight from abutment footing including 

soil on heel and no LL = VA 

k/ft 27.94 20.28 21.89 

Net load, P, on base of spread footing from the 

bridge (with consideration of LL), PwL 

k/ft 15.03 12.46 11.18 

Net load, P, on base of spread footing from the 

bridge (no consideration of LL), PnL 

k/ft 8.29 5.72 7.33 

Moment arm of net load PnL from Point B, 

Lp = anl + cf 

ft 4.45 4.35 4.49 

Resisting moment at Point B due to net load P, MPnL 

= PnL(Lp) k-ft/ft 36.93 24.89 32.90 

Vertical load at base of MSE wall without LL, VB = 

V4+V5 + PnL 

k/ft 165.58 122.24 123.84 

Resisting moments about Point B without LL 

surcharge= MRB =MV4+MV5+MPnL 

k-ft/ft 2081.72 1539.56 1547.56 

Overturning moments about Point B = MOB = 

MFS3+MF3+MF4 +MFA (For MFA See Note 1) k-ft/ft 666.03 454.90 448.67 

Location of the resultant force on base of MSE wall 

from Point B, b =(MRB - MOB)/VB 

ft 8.55 8.87 8.87 

Eccentricity at base of MSE wall, eL = L/2 – b ft 4.45 4.13 4.13 

Limiting eccentricity, e = L/4 for strength limit 

states and e= L/6 for service limit state ft 6.50 6.50 4.33 

Is the resultant within limiting value of eL? - Yes Yes Yes 

CRITICAL VALUES BASED ON MAX/MIN 

Overturning moments about Point B, MOB-C k-ft/ft 666.03 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 17 November 2009
 
 

Resisting moments about Point B, MRB-C k-ft/ft 1539.56 

Net moment about Point A, MB-C = MRB-C - MOB-C k-ft/ft 873.53 

Vertical force, VB-C k/ft 122.24 

Location of resultant from Point B, b = MB-C/VB-C ft 7.15 

Eccentricity from center of footing, eL = L/2 - b ft 5.85 

Limiting eccentricity, e = L/4 ft 6.50 

Is the limiting eccentricity criteria satisfied? - Yes 

Note 1: MFA = (FA)(H) = (F1 + F2 + FS1)(H) and each of the components of FA is a different 

load type and hence has a different load factor. 

7.2 Sliding Resistance at Base of MSE Wall 

The purpose of these computations is to evaluate the sliding resistance at the base of the MSE 

wall. Since the computations are related to sliding resistance, the beneficial contribution of 

live load to resisting forces and moments is neglected. The computations for sliding 

resistance at the base of the MSE wall are illustrated in Table E5-7.2. Note that sliding 

resistance is a strength limit state check and therefore service limit state calculations are not 

performed. Since the friction angle of foundation soil, ′fd, is less than the friction angle for 

reinforced soil, 1, the sliding check will be performed using ′fd. 

Table E5-7.2. Computations for evaluation of sliding resistance of MSE wall 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Lateral load on the MSE wall, Hm = 

F1+F2+F3+F4+FS1+FS2 

k/ft 46.08 30.22 NA 

Vertical load at base of MSE wall without LL 

surcharge = V4+V5+PnL 

k/ft 165.58 122.24 NA 

Nominal sliding resistance at base of MSE wall, VNm 

= tan(′fd)(V4+V5+PnL) k/ft 95.60 70.57 NA 

Factored sliding resistance at base of MSE wall, VFm= 

s*VNm 

k/ft 95.60 70.57 NA 

Is VFm > Hm? - Yes Yes NA 

Capacity:Demand Ratio (CDR) = VFm:Hm dim 2.07 2.34 NA 

CRITICAL VALUES BASED ON MAX/MIN 

Minimum VFm (VFmmin) k/ft 70.57 

Maximum Hm (Hmmax) k/ft 46.08 

Is VFmmin > Hmmax? - Yes 

Capacity:Demand Ratio (CDR) = VFmmin:Hmmax dim 1.53 

7.3 Bearing Resistance at base of MSE Wall 

For bearing resistance computations, the effect of live load is included since it creates larger 

bearing stresses. Figure E5-4 is used for bearing resistance computations. The bearing stress 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 18 November 2009
 
at the base of the MSE wall is due to the effect of (1) net bridge load, and (2) the MSE wall. 

Each of these two components is briefly discussed below and their computation is illustrated 

in Table E5-7.3 in conjunction with Figure E5-4. 

Component 1: The net bridge load on the footing is assumed to include live load and is 

denoted as PwL which is assumed to be centered on bf – 2ef. The stress due to net bridge load 

Pwl is diffused at 1H:2V distribution through the height of the MSE wall. Thus, the vertical 

stress at the base of the MSE wall due to the net bridge load, Pwl is as follows: 

P

Component 2: The MSE wall by itself will create a certain bearing stress at its base due to 

the effect of other loads, i.e. the effect of V4, V5, VS, FS2, F3, F4, and FA. The bearing stress 

due to these loads is as follows: 

 

where ΣV = V4 + V5 + VS and the load eccentricity eL is calculated by principles of statics 

using appropriate loads and moments with the applicable load factors. 

Total equivalent uniform (Meyerhof) bearing stress: The total equivalent uniform 

(Meyerhof) bearing stress at the base of the MSE wall is obtained as follows: 

 wL

v footing 

  H  b c f  2ef  f    2 

 V

v  L  2eL 

v v  max v footing   

In LRFD, σvmax is then compared with the factored bearing resistance when computed for 

strength limit state and used for settlement analysis when computed for service limit state. 

The various computations for evaluation of bearing resistance are presented in Table E5-7.3. 

6.4 Settlement Analysis 

It is critical that the settlement under σvmax be evaluated because the performance of the 

bridge will be directly affected by the settlement at the back of the MSE wall. Settlement is 

evaluated at Service I Limit State. Note that due to the reinforced MSE wall the settlement of 

the spread footing on top of the MSE wall is assumed to be very small, i.e. negligible if the 

footing is sized such that the bearing stress is less than 4 ksf under Service I load 

combination. Conservatively, all the settlement at the base of the MSE wall is assumed to 

occur at the spread footing level, i.e. the MSE wall is assumed to be a rigid block. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 19 November 2009
 
 

 

Table E5-7.3. Computations for evaluation of bearing resistance for MSE wall 

Item Unit Str I 

(max) 

Str I 

(min) Ser I 

Component 1: Bearing Stress due to PwL acting 

over bf-2ef and distributed 1H:2V through the 

MSE wall height 

Base width of stress distribution based on 1H:2V 

distribution and Pwl acting on bf'= bf-2ef 

ft 21.41 21.35 21.41 

Bearing stress due to PwL ksf 0.70 0.58 0.52 

Component 2: Bearing stress due to MSE wall 

Vertical load at base of MSE wall including LL on 

top, V = V4+V5+VS 

k/ft 174.13 133.35 126.13 

Resisting moments @ Point B on the MSE wall, 

MRB = MV5+MVS+MV4 

k-ft/ft 2263.65 1733.52 1639.72 

Overturning moments @ Point B on the MSE wall, 

MOB = MFS2+MF3+MF4 

k-ft/ft 571.95 389.77 379.11 

Net moment at Point B, MB = MRB - MOB k-ft/ft 1691.70 1343.74 1260.61 

Location of Resultant from Point B, b = MB/V ft 9.72 10.08 9.99 

Eccentricity from center of wall, eL = 0.5*L – b ft 3.28 2.92 3.01 

Limiting eccentricity, e = L/4 for strength limit states 

and e = L/6 for service limit state ft 6.50 6.50 4.33 

Is the resultant within limiting value of eL? - Yes Yes Yes 

Effective width of base of MSE wall, B' = L-2eL ft 19.43 20.15 19.99 

Factored bearing stress due to MSE wall = V/(L-2eL) ksf 8.96 6.62 6.31 

Total bearing stress due to Component 1 + 2 = σvmax ksf 9.66 7.20 6.83 

Factored bearing resistance, qR (given) ksf 15.00 15.00 7.00 

Is σvmax < qR? - Yes Yes Yes 

Capacity:Demand Ratio (CDR) = qR:σvmax dim 1.55 2.08 1.02 

CRITICAL VALUES BASED ON MAX/MIN FOR COMPONENT 2 

Overturning moments about Point B, MOB-C k-ft/ft 571.95 

Resisting moments about Point B, MRB-C k-ft/ft 1733.52 

Net moment about Point B, MB-C = MRB-C - MOB-C k-ft/ft 1161.57 

Vertical force, VBb-C k/ft 133.35 

Location of resultant from Point B, b = MB-C/VBb-C ft 8.71 

Eccentricity from center of wall, eL = 0.5*L – b ft 4.29 

Limiting eccentricity, e = L/4 ft 6.50 

Is the limiting eccentricity criteria satisfied? - Yes 

Effective width of base of MSE wall, B' = L-2eL ft 17.42 

Bearing stress, σv-c = VBb-C / (L-2eL) ksf 7.65 

Compute critical total bearing stress 

Total bearing stress due to Component 1+2=σvmax-C ksf 8.35 

Factored bearing resistance, qR (given) ksf 15.00 

Is bearing stress < factored bearing resistance? dim Yes 

Capacity:Demand Ratio (CDR) = qR:σvmax-C dim 1.80 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 20 November 2009
 
STEP 8: EVALUATE INTERNAL STABILITY ANALYSIS OF MSE WALL
 

8.1 Estimate critical failure surface, variation of Kr and F* for internal stability 

The quantity cf + bf (=11.25 ft), is greater than H/3 (25.5/3=8.5 ft). Therefore, the modified 

shape of the maximum tensile force line (i.e., critical failure surface) shown in Figure 5-1 of 

Chapter 5 has to be used. For the case of inextensible steel ribbed strips, the profile of the 

critical failure surface, the variation of internal lateral horizontal stress coefficient, Kr, and 

the variation of the pullout resistance factor, F*, are as shown in Figure E5-5 wherein other 

definitions such as measurement of depths Z and z are also shown. It should be noted that 

the variation of Kr and F* are with respect to depth z that is measured from top of the spread 

footing while the critical failure surface is with respect to depth z that is measured from top 

of coping. The value of Ka is based on the angle of internal friction of the reinforced 

backfill, 1, which is equal to Ka1 = 0.283 calculated in Step 4. Thus, the value of Kr varies 

from 1.7(0.283) = 0.481 at z = 0 to 1.2(0.283) = 0.340 at z =20 ft. For steel strips, 

F*=1.2+log10Cu. Using Cu = 7.0 as given in Step 2, F*= 1.2+log10(7.0) = 2.045 > 2.000. 

Therefore, use F*=2.000. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 21 November 2009
 

 

H' H 

h 

H'/2 

H'/2 

Resistant 

Zone 

Active 

Zone 

0.3H' 

1 

0.6 

z=20 ft 

Kr F* 

z=0 z=0 1.7 Ka 

1.2 Ka 

2.0 

tan (1) 

= 0.675 

z=20 ft 

Z 

z=H' z=H' 

z' 

L 

bf cf Finished grade 

z z 

Notes: 

 Z is measured below bottom of footing; z is measured from top of finished grade 

 H is measured from top of leveling pad to bottom of spread footing 

 z = Z + h; z' = H – (cf + bf)/0.6 

 Within height z' the length of the reinforcement in the active zone is La = cf + bf
 

Figure E5-5. Geometry definition, location of critical failure surface and variation of Kr and 

F* parameters for steel ribbed strips. 
 

8.2 Establish vertical layout of soil reinforcements and tributary areas 

Using the definition of depth Z as shown in Figure E5-5 the following vertical layout of the 

soil reinforcements is chosen. 

 

Z = 1.12 ft, 2.35 ft, 4.81 ft, 7.27 ft, 9.73 ft, 12.19 ft, 14.65 ft, 17.11 ft, 19.57 ft, 22.03 ft, 

24.49 ft. 

The above layout leads to 11 levels of reinforcements. The vertical spacing was chosen 

based on a typical vertical spacing, Sv, of 2.46 ft that is commonly used in the industry for 

steel ribbed strip reinforcement. The vertical spacing near the top and bottom of the walls 

are locally adjusted as necessary to fit the height of the wall. 

For internal stability computations, each layer of reinforcement is assigned a tributary area, 

Atrib as follows 

Atrib = (wp)(Svt) 

where and wp is the panel width of the precast facing element and Svt is the vertical tributary 

spacing of the reinforcements based on the location of the reinforcements above and below 

the level of the reinforcement under consideration. The computation of Svt is summarized in 

Table E5-8.1 wherein S    vt Z Z . Note that wp = 10.00 ft per Step 2. 

Table E5-8.1. Summary of computations for Svt 

Level Z (ft) Z (ft) Z (ft) Svt (ft) 

1 1.12 0 1.12+0.5(2.35–1.12)=1.735 1.735 

2 2.35 2.35-0.5(2.35–1.12)=1.735 2.35+0.5(4.81-2.35)=3.58 1.845 

3 4.81 4.81-0.5(4.81-2.35)=3.58 4.81+0.5(7.27-4.81)=6.04 2.460 

4 7.27 7.27-0.5(7.27-4.81)=6.04 7.27+0.5(9.73-7.27)=8.50 2.460 

5 9.73 9.73-0.5(9.73-7.27)=8.50 9.73+0.5(12.19-9.73)=10.96 2.460 

6 12.19 12.19-0.5(12.19-9.73)=10.96 12.19+0.5(14.65-12.19)=13.42 2.460 

7 14.65 14.65-0.5(14.65-12.19)=13.42 14.65+0.5(17.11-14.65)=15.88 2.460 

8 17.11 17.11-0.5(17.11-14.65)=15.88 17.11+0.5(19.57-17.11)=18.34 2.460 

9 19.57 19.57-0.5(19.57-17.11)=18.34 19.57+0.5(22.03-19.57)=20.80 2.460 

10 22.03 22.03-0.5(22.03-19.57)=20.80 22.03+0.5(24.49-22.03)=23.26 2.460 

11 24.49 24.49-0.5(24.49-22.03)=23.26 25.50 2.240 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 22 November 2009
 
 

8.3 Calculate horizontal stress and maximum tension at each reinforcement level 

The horizontal spacing of the reinforcements is based on the maximum tension (Tmax) at each 

level of reinforcements which requires computation of the horizontal stress, σH, at each 

reinforcement level. The reinforcement tensile and pullout resistances are then compared 

with Tmax and an appropriate reinforcement pattern is adopted. This section demonstrates the 

calculation of horizontal stress, σH, and maximum tension, Tmax. 

The horizontal stress, σH, at any depth within the MSE wall is based on the following 

components each of which is summarized in Table E5-8.2. 

σH = σH-soil + σH-surcharge + σH-footing + ΔσH 

Table E5-8.2. Summary of load components leading to horizontal stress 

Load Component Load 

Type Horizontal Stress 

Soil load, σv-soil EV σH-soil = [Kr σv-soil]γP-EV 

Surcharge traffic live load, q EV σH-surcharge = [Krq]γP-EV = [Kr(r heqM)]γP-EV 

Vertical footing load, Δσv-footing ES* σH-footing = [Kr Δσv-footing]γP-ES 

Horizontal surcharge, FA ES* ΔσH = (2FA/L1)γP-ES at zo=0 ; ΔσH =0 at zo=L1 

*As per Article 3.116 of AASHTO (2007 with 2009 Interims), the value of ES may be 1.50 

or 1.00 based on how the horizontal stresses are computed. First, compute horizontal 

stresses by using factored loads and use ES=1.0 since the horizontal stresses are based on 

factored loads. Second, compute horizontal stresses by using nominal loads and then apply 

ES=1.50. Choose horizontal stresses that are larger from the two approaches as per Article 

3.116. of AASHTO (2007 with 2009 Interims). 

Using the unit weight of the reinforced soil mass and heights Z, h, and heqM, the equation for 

horizontal stress at any depth Z within the MSE wall can be written as follows (also see 

Chapter 4): 

 

 

σH = Kr (r Z) γP-EV + Kr (r h) γP-EV + Kr (r heqM) γP-EV + Kr (Δσv-footing) γP-ES + (σH) γP-ES 

σH = Kr [r (Z + h + heqM) γP-EV + (Δσv-footing) γP-ES] + (σH) γP-ES 

Once the horizontal stress is computed at any given level of reinforcement, the maximum 

tension, Tmax, is computed as follows: 

Tmax = (σH)(Atrib) 

where Atrib is the tributary area for the soil reinforcement at a given level as discussed earlier. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 23 November 2009
 
The computations for Tmax are illustrated at Z = 7.27 ft which is Level 4 in the assumed 

vertical layout of reinforcement. Assume Strength I (max) load combination for illustration 

purposes and use appropriate load factors from Table E5-5.1. 

	 At Z=7.27 ft, the following depths are computed 

z = Z + h = 7.27 ft + 10.35 ft = 17.62 ft 

Z = 6.04 ft (from Table E5-8.1) 

Z = 8.50 ft (from Table E5-8.1) 

z  	  Z  h = 6.04 ft + 10.35 ft = 16.39 ft 

z



	  Z   h = 8.50 ft + 10.35 ft = 18.85 ft 

 Obtain Kr by linear interpolation between 1.7Ka = 0.481 at z = 0.00 ft and 1.2Ka = 

0.339 at z = 20.00 ft as follows: 

At z = 16.39 ft, Kr(z-)= 0.339 + (20.00 ft – 16.39 ft)(0.481-0.340)/20.00 ft = 0.365 

At z

 = 18.85 ft, Kr(z+)= 0.339 + (20.00 ft – 18.85 ft)(0.481-0.340)/20.00 ft = 0.348 

	 Compute σH-soil = [kr σv-soil]γP-EV due to soil surcharge as follows: 

γP-EV = 1.35 from Table E5-5.1 

At z = 16.39 ft, 

v-soil(z-) = (0.125 kcf)(16.39 ft) = 2.05 ksf 

σH-soil(z-) = [Kr(z-)σv-soil(z-)]γP-EV = (0.365)(2.05 ksf)(1.35) = 1.01 ksf 

At z

 = 18.85 ft, 

v-soil(z+) = (0.125 kcf)(18.85 ft) = 2.36 ksf 

σH-soil(z+) = [Kr(z+)σv-soil(z+)]γP-EV = (0.348)(2.36 ksf)(1.35) = 1.11 ksf 

σH-soil = 0.5(1.01 ksf + 1.11 ksf) = 1.06 ksf 

	 Compute σH-surcharge = [Kr q] γP-EV due to traffic (live load) surcharge as follows: 

γP-EV = 1.35 from Table E5-5.1 

q = (γf)(heqM) = (0.125 kcf)(2.00 ft) = 0.25 ksf 

At z = 16.39 ft, σH-surcharge(z-) = [Kr(z-) q] γP-EV = (0.365)(0.25 ksf)(1.35) = 0.12 ksf 

At z

 = 18.85 ft, σH-surcharge(z+) = [Kr(z+) q] γP-EV = (0.348)(0.25 ksf)(1.35) = 0.12 ksf 

σH-surcharge = 0.5(0.12 ksf + 0.12 ksf) = 0.12 ksf 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 24 November 2009
 
 Compute σH-footing = [Kr Δσv-footing] γP-ES as follows: 

Method A: Use factored loads and γP-ES = 1.00
 

From Table E5-6.3, bf -2ef = 8.16 ft 

From Step 2, cf = 0.5 ft 

From Table E5-7.1, PwL = 15.03 k/ft 

From Table E5-8.1, Z = 6.04 ft and Z = 8.50 ft 

Using above values 

Δσ - footing(Z ) = 1.29 ksf and Δσ + v- v-footing(Z ) = 1.16 ksf 

γP-ES = 1.00 since the factored loads were used. 

σ - -)Δσ - H-footing(Z ) = [Kr(Z v-footing(Z )] γP-ES = (0.365)(1.29 ksf)(1.00) = 0.47 ksf 

σ

+ + + H-footing(Z ) = [Kr(Z )Δσv-footing(Z )] γP-ES = (0.348)(1.16 ksf)(1.00) = 0.40 ksf 

σH-footing = 0.5(0.47 ksf + 0.40 ksf) = 0.44 ksf 

Method B: Use nominal loads and γP-ES = 1.50
 

From Table E5-6.3, bf -2ef = 8.16 ft 

From Step 2, cf = 0.5 ft 

From Table E5-7.1, PwL = 11.18 k/ft 

From Table E5-8.1, Z = 6.04 ft and Z = 8.50 ft 

Using above values 

Δσ - + 

v-footing(Z ) = 0.96 ksf and Δσv-footing(Z ) = 0.87 ksf 

γP-ES = 1.50 since the nominal loads were used. 

σ - = [K - ) Δσ - H-footing(Z r(Z ) v-footing(Z )] γP-ES = (0.365)(0.96 ksf)(1.50) = 0.53 ksf 

σ + H-footing(Z ) = [K + + r(Z )Δσv-footing(Z )] γP-ES = (0.348)(0.87 ksf)(1.50) = 0.45 ksf 

σH-footing = 0.5(0.53 ksf + 0.45 ksf) = 0.49 ksf 

Use σH-footing = 0.49 ksf 

 Compute ΔσH = (2FA/L1)γP-ES at Z = 0 ; ΔσH = 0 at Z = L1 as follows: 

Method A: Use factored loads and γP-ES = 1.00
 

From Table E5-6.3, L1 = 16.29 ft 

From Table E5-6.2, FA = 5.55 k/ft 

From Table E5-8.1, Z = 6.04 ft and Z = 8.50 ft 

γP-ES = 1.00 since the factored loads were used. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 25 November 2009
 

P  wL

v footing  

b  2e   Z 

f f cf  
  2 
 
At Z = 6.04 ft 

 ΔσH(Z-) = [(2)(5.55 k/ft)/16.29 ft)][16.29 ft – 6.04 ft)/16.29 ft)] [1.00] = 0.43 ksf 

At Z = 8.50 ft 

 ΔσH(Z+) = [(2)(5.55 k/ft)/16.29 ft)][16.29 ft – 8.50 ft)/16.29 ft)] [1.00] = 0.33 ksf 

ΔσH = 0.5(0.43 ksf + 0.33 ksf) = 0.38 ksf 

Method B: Use nominal loads and γP-ES = 1.50
 

From Table E5-6.3, L1 = 16.29 ft 

From Table E5-6.2, FA = 3.79 k/ft 

From Table E5-8.1, Z = 6.04 ft and Z = 8.50 ft 

γP-ES = 1.50 since the nominal loads were used. 

At Z = 6.04 ft 

 Δσ - H(Z ) = [(2)(3.79 k/ft)/16.29 ft)][16.29 ft – 6.04 ft)/16.29 ft)] [1.50] = 0.44 ksf 

At Z = 8.50 ft 

 Δσ + 

H(Z ) = [(2)(3.79 k/ft)/16.29 ft)][16.29 ft – 8.50 ft)/16.29 ft)] [1.50] = 0.33 ksf 

ΔσH = 0.5(0.44 ksf + 0.33 ksf) = 0.39 ksf 

Use ΔσH = 0.39 ksf 

	 Using values calculated above, compute σH = σH-soil + σH-surcharge + σH-footing + ΔσH as 

follows: 

σH = 1.06 ksf + 0.12 ksf + 0.49 ksf + 0.39 ksf = 2.06 ksf 

	 Based on Table E5-8.1, the vertical tributary spacing at Level 4 is Svt = 2.46 ft 

	 The panel width, wp, is 10.00 ft (given in Step 1) 

	 The tributary area, Atrib, is computed as follows: 

Atrib = (2.46 ft)(10.00 ft) = 24.60 ft2
 

 

	 The maximum tension at Level 4 is computed as follows: 

Tmax = (σH)(Atrib) = (2.06 ksf)(24.60 ft2

) = 50.7 k/panel of 10 ft width 

Using similar computations, the various quantities can be developed at other levels of 

reinforcements and load combinations. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 26 November 2009
 
 

8.4 Establish nominal and factored long-term tensile resistance of soil reinforcement 

The nominal tensile resistance of galvanized steel ribbed strip soil reinforcement is based on 

the design life and estimated loss of steel over the design life during corrosion. 

As per Step 1, the soil reinforcement for this example is assumed to be Grade 65 (Fy = 65 

ksi), 1.969 in. x 0.157 in. (50 mm wide x 4 mm) thick galvanized steel ribbed strips with zinc 

coating of 3.386 mils (86 m). As per Step 2, the reinforced backfill meets the AASHTO 

(2007) requirements for electrochemical properties. For this reinforced backfill, the basis for 

calculating the thickness losses due to corrosion is as follows per Article 11.10.6.4.2a of 

AASHTO (2007): 

Zinc loss = 0.58 mil for first 2 years and 0.16 mil per year thereafter 

Steel loss = 0.47 mil/year/side 

Based on the above corrosion rates, the following can be calculated: 

Life of zinc coating (galvanization) = 2 years + (3.386 – 2*0.58)/0.16 ≈ 16 years 

As per Step 1, the design life is 100 years. The base carbon steel will lose thickness for 100 

years – 16 years = 84 years at a rate of 0.47 mil/year/side. Therefore, the anticipated 

thickness loss is calculated as follows: 

ER = (0.47 mil/year/side) (84 years) (2 sides) = 78.96 mils = 0.079 in., and 

EC = 0.157 in. – 0.079 in. = 0.078 in. 

Based on a 1.969 wide strip, the cross-sectional area at the end of 100 years will be equal to 

(1.969 in.) (0.078 in.) = 0.154 in2 

. 

For Grade 65 steel with Fy = 65 ksi, the nominal tensile resistance at end of 100 year design 

life will be Tn = 65 ksi (0.154 in2

) = 10.00 k/strip. Using the resistance factor, t = 0.75 as 

listed in Table E5-5.2, the factored tensile resistance, Tr = 10.00 k/strip (0.75) = 7.50 k/strip. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 27 November 2009
 
8.5 Establish nominal and factored pullout resistance of soil reinforcement 

The nominal pullout resistance, Pr, of galvanized steel ribbed strip soil reinforcement is based 

on various parameters in the following equation: 

Pr = (F*)(2b)(Le)[(σv-soil)(γP-EV)] 

For this example problem, the following parameters are constant at levels of reinforcements: 

b = 50 mm = 1.97 in. = 0.164 ft 

 = 1.0 for inextensible reinforcement per Table 11.10.6.3.2-1 of AASHTO (2007) 

The computations for Pr are illustrated at Z = 7.27 ft which is Level 4 as measured from top 

of the wall. Assume Strength I (max) load combination for illustration purposes and use 

appropriate load factors from Table E5-5.1. 

	 At Z = 7.27 ft, z = Z + h = 7.27 ft + 10.35 ft = 17.62 ft 

	 Obtain F* at z =17.62 ft by linear interpolation between 2.000 at z = 0 and 0.675 at 

z=20 ft as follows: 

F* = 0.675 + (20.00 ft – 17.62 ft)(2.000 – 0.675)/20 ft = 0.832 

	 Compute effective length Le as follows: 

z' = H – (cf + bf)/0.6 = 25.5 ft – (0.5 ft + 10.75 ft)0.6 = 6.75 ft 

Since Z > z', Le = L – [0.6(H – Z)] 

Le = 26 ft – 0.6(25.5 ft – 7.27 ft) = 15.06 ft 

	 Per Article 11.10.6.3.2 use unfactored vertical stress for pullout resistance. Thus, 

γP-EV = 1.00. Thus, compute (σv-soil)(γP-EV) = (0.125 kcf)(17.62 ft) (1.00) = 2.20 ksf 

	 Compute nominal pullout resistance as follows: 

Pr = (F*)(2b)(Le)[(σv-soil)(γP-EV)] 

Pr = (1.0)(0.832)(2)(0.164 ft)(15.06 ft)(2.20 ksf) = 9.04 k/strip 

	 Compute factored pullout resistance as follows: 

Prr = Pr = (0.90)(9.04 k/strip) = 8.14 k/strip 

Using similar computations, the various quantities can be developed at other levels of 

reinforcements and load combinations. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 28 November 2009
 
8.6 Establish number of soil reinforcing strips at each level of reinforcement 

Based on Tmax, Tr and Prr, the number of strip reinforcements at any given level of 

reinforcements can be computed as follows: 

	 Based on tensile resistance considerations, the number of strip reinforcements, Nt, is 

computed as follows: 

Nt = Tmax/Tr 

	 Based on pullout resistance considerations, the number of strip reinforcements, Np, is 

computed as follows: 

Np = Tmax/Prr 

Using the Level 4 reinforcement at Z = 7.27 ft, the number of strip reinforcements can be 

computed as follows: 

	 Tmax = 50.7 k/panel of 10 ft width, Tr = 7.50 k/strip, Prr = 8.14 k/strip 

	 Nt = Tmax/Tr = (50.7 k/panel of 10 ft width)/(7.50 k/strip) = 6.8 strips/panel of 10 ft 

width 

	 Np = Tmax/Prr = (50.7 k/panel of 10 ft width)/(8.14 k/strip) = 6.2 strips/panel of 10 ft 

width 

	 Since Nt > Np, tension breakage is the governing criteria and therefore the governing 

value, Ng, is 6.8. Round up to select 7 strips at Level 4 for each panel of 10 ft width. 

The computations in Sections 8.4 to 8.6 are repeated at each level of reinforcement. Table 

E5-8.3 presents a summary of the computations at all levels of reinforcement for Strength I 

(max) load combination. The last column of Table E5-8.3 provides horizontal spacing of the 

reinforcing strips which is obtained by dividing the panel width, wp, by the governing 

number of strips, Ng. Similar computations can be performed for Strength I (min) and 

Service I load combination but they will not govern the design because the load factors for 

these two load combinations are less than those for Strength I (max) load combination. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 29 November 2009
 
 

Note to users: All the long-form step-by-step calculations illustrated in Step 8 were based on 

hand-calculations in which numbers were rounded to the third or fourth significant digit as 

appropriate in each step. Table E5-8.3 was generated using a spreadsheet in which numbers 

at all calculation steps were not rounded. Thus, the end result in Table E5-8.3 may be 

somewhat different when compared to long-form hand calculations. However, the difference 

should be less than 0.2 in most cases. 

Table E5-8.3. Summary of internal stability computations for Strength I (max) load 

combination 

Level 

Z 

ft 

Kr 

dim 

H

ksf 

Tmax

k/10 ft 

wide 

panel 

F* 

dim 

Le 

ft 

p(Pr) 

k/strip 

s(Tn) 

k/strip 

Np Nt Ng Sh 

ft 

1 1.12 0.399 2.30 39.86 1.240 14.75 7.74 7.50 5.1 5.3 6 1.7 

2 2.35 0.391 2.22 41.00 1.158 14.75 8.01 7.50 5.1 5.5 6 1.7 

3 4.81 0.373 2.14 52.65 0.995 14.75 8.21 7.50 6.4 7.0 8 1.3 

4 7.27 0.356 2.05 50.46 0.832 15.06 8.15 7.50 6.2 6.7 7 1.4 

5 9.73 0.339 1.99 48.87 0.675 16.54 8.27 7.50 5.9 6.5 7 1.4 

6 12.19 0.339 1.97 48.39 0.675 18.01 10.12 7.50 4.8 6.4 7 1.4 

7 14.65 0.339 1.97 48.52 0.675 19.49 12.14 7.50 4.0 6.5 7 1.4 

8 17.11 0.339 2.02 49.63 0.675 20.97 14.34 7.50 3.5 6.6 7 1.4 

9 19.57 0.339 2.14 52.55 0.675 22.44 16.73 7.50 3.1 7.0 8 1.3 

10 22.03 0.339 2.26 55.54 0.675 23.92 19.29 7.50 2.9 7.4 8 1.3 

11 24.49 0.339 2.38 53.22 0.675 25.39 22.04 7.50 2.4 7.1 8 1.3 

STEP 9: DESIGN OF FACING ELEMENTS 

Facing panels for true bridge abutment applications require special attention and project 

specific design. As per Article 11.10.11 of AASHTO (2007), due to the relatively high 

bearing pressures near the panel connections, the adequacy and nominal capacity of panel 

connections should be determined by conducting pullout and flexural tests on full-sized 

panels. 

STEP 10: CHECK OVERALL AND COMPOUND STABILITY AT SERVICE LIMIT 

STATE 

From Step 2, it is given that the foundation soil is dense clayey sand that has fd = 30°, fd = 

120 pcf. Furthermore, the ground in front of the wall is horizontal and the foundation soil 

has no water table. Therefore, based on observation, overall stability is adequate. For actual 

projects, overall stability should be investigated at the Service I load combination and a 

resistance factor of 0.65. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 30 November 2009
 
STEP 11: DESIGN WALL DRAINAGE SYSTEMS 

See Chapters 5 and 6 for wall drainage considerations. For a true bridge abutment, the 

drainage system for the MSE wall must be carefully integrated with the other bridge drain 

systems, such as the deck drainage. Often storm drain pipes are placed through the MSE 

wall backfill in true bridge abutments. Every attempt must be made to relocate these drain 

features behind the reinforced backfill. 

E5-2 PRACTICAL CONSIDERATIONS 

The design of a true bridge abutment is a complex process. The actual detailing of the 

abutment is particularly important given that a number of disciplines ranging from 

geotechnical, structural, hydraulics, roadway, utilities and aesthetics have specific 

requirements at abutment locations. All relevant input must be sought and incorporated into 

the project plans and specifications. Following is a general list of practical considerations 

from a geotechnical and structural viewpoint: 

1. As noted in Article 11.10.11 of AASHTO (2007), the governing density, length, and 

cross-section of the soil reinforcements in Table E-4-8.3 shall be carried on the 

wingwalls of a minimum horizontal distance equal to 50 percent of the height of the 

abutment. Since the height of the abutment is 25.5 ft, the minimum horizontal 

distance along the wing wall is therefore 25.5 ft/2 = 12.5 ft. This dimension is greater 

than cf + bf = 0.5 ft + 10.75 ft = 11.25 ft. Thus, the 2-way reinforcement is equal in 

both directions under the full width of the spread footing which provides a consistent 

bearing resistance across the footing. 

2. Use of an approach slab is redundant for a true bridge abutment since the MSE wall 

and the spread footing above it settle as a unit. However, some agencies require the 

use of approach slab in which case special details may be necessary. Depending on 

the design of the approach slab system, live load may be omitted on the bridge 

approaches. 

3. Commonly bridge abutments on spread footings on top of MSE walls are stand alone 

abutments with wing walls. Assuming that the wing walls are part of the MSE wall 

system, there will be 2-way reinforcement within the length of reinforcement 

perpendicular to the abutment face. It is preferable that reinforcement is not placed 

on top of each other in the zone of 2-way reinforcement. The overlapping 

reinforcement should be separated by 3 in. to 6 in. of soil or some multiple of 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 31 November 2009
 
compacted fill height. This may be achieved by appropriately stepping of the leveling 

pad between the abutment face wall and the wing walls. 

4. To prevent adverse stress concentrations at the reinforcement connections, the 

minimum vertical clearance between the bottom of the footing and the top level of 

reinforcement should be 1 ft. 

5. In the height h1 and h2 shown in Figure E5-1, a false panel can be placed to cover the 

step in the footing. Often the coping is extended up in this area. Styrofoam or similar 

lightweight material which is fairly impermeable is placed in this area to minimize 

lateral loads on the coping or MSE panel and prevent migration of moisture into the 

backfill at the corrosion critical panel-reinforcement connection location. 

FHWA NHI-10-025 Example E5 – Spread Footing Bridge Abutment
 

MSE Walls and RSS – Vol II E5 – 32 November 2009
 
 

EXAMPLE E6 

TRAFFIC BARRIER IMPACT LOADING ON 

SEGMENTAL PRECAST PANEL MSE WALL WITH 

STEEL GRID REINFORCEMENT 

E6-1 INTRODUCTION 

This example problem is an extension of Example Problem E4, and demonstrates the analysis 

of a MSE wall with a traffic barrier impact load. The MSE wall is assumed to include a 

segmental precast panel face with steel grid (bar mat) reinforcements. The MSE wall 

configuration to be analyzed is shown in Figure E4-1. 

The analysis is based on various principles that were discussed in Section 7.3. Table E6-1 

presents a summary of steps involved in this traffic barrier analysis. The analysis uses the 

reinforcement spacing and sizing developed in Example E4. Practical considerations are 

presented in Section E6-2 after the illustration of the step-by-step procedures. 

Table E6-1. Summary of additional steps for traffic barrier impact load on 

a MSE wall with level backfill and live load surcharge 

Step Item 

4 Estimate unfactored loads 

5 Summarize applicable load and resistance factors 

7 Evaluate internal stability of MSE wall 

7.3 Calculate horizontal stress and maximum tension at each reinforcement level 

7.4 Establish nominal and factored long-term tensile resistance of soil reinforcement 

7.5 Check/eEstablish nominal and factored pullout resistance of soil reinforcement 

7.6 Check/establish number of soil reinforcing elements at each level of reinforcement 

8 Design of facing elements 

STEP 4. ESTIMATE UNFACTORED LOADS 

Traffic barrier impact affects the internal stability of the reinforced soil wall. Therefore, only 

internal loads are discussed below. See Example E4 for external loads. 

The coefficients of active lateral earth pressure for internal stability is: 

FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 1 November 2009
 

Kar = (1 - sin34°)/(1 + sin34°) = 0.283 
 

 

 

STEP 5. SUMMARIZE APPLICABLE LOAD AND RESISTANCE FACTORS 

Table E4-5.1 summarizes the load factors for the various LRFD load type. 

Table E6-5.1. Applicable load factors 

Load 

Combination 

Load Factors 

(after Tables 3.4.1-1 and 3.4.1-2 (AASHTO, 2007)) 

EV LL CT 

Strength I 

(maximum) P = 1.35 1.75 – 

Extreme II P = 1.35 0.50 1.00 

For computation of factored resistances during evaluation of extreme limits states, 

appropriate resistance factors have to be used. Article 11.5.7 Extreme Event Limit 

(AASHTO, 2007) states: The applicable load combinations and load factors specified in 

Table 3.4.1-1 shall be investigated. Unless otherwise specified, all resistance factors shall 

be taken as 1.0 when investigating the extreme limit state. Table E6-5.2 summarizes the 

applicable resistance factors. 

Table E6-5.2. Summary of applicable resistance factors for evaluation 

of extreme limit states 

Item Resistance 

Factors 

AASHTO (2007) 

Reference 

Tensile resistance 

(for steel bar mats) 

Strength Limit State t = 0.65 Table 11.5.6-1 

Extreme Limit State t = 1.0 Article 11.5.7 

Pullout resistance Strength Limit State p = 0.90 Table 11.5.6-1 

Extreme Limit State t = 1.0 Article 11.5.7 

STEP 7: EVALUATE INTERNAL STABILITY ANALYSIS OF MSE WALL 

Only the upper two layers of soil reinforcement are examined for the traffic barrier impact. 

Tensile and pullout resistance are checked. 

7.2 Establish vertical layout of soil reinforcements 

The following vertical layout of the top three soil reinforcements was chosen in Problem E4. 

Z = 1.87 ft, 4.37 ft, and 6.87 ft, 

FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 2 November 2009
 
 

 

For internal stability computations, each layer of reinforcement is assigned a tributary area, 

Atrib as follows: 

Atrib = (wp)(Svt) 

where wp is the panel width of the precast facing element and Svt is the vertical tributary 

spacing of the reinforcements based on the location of the reinforcements above and below 

the level of the reinforcement under consideration. The computation of Svt is summarized in 

 Table E6-7.1 wherein Svt  z  z . Note that wp = 5.00 ft per Step 2. 

Table E6-7.1. Summary of computations for Svt 

Level Z (ft) Z (ft) Z (ft) Svt (ft) 

1 1.87 0 1.87+0.5(4.37–1.87)=3.12 3.12 

2 4.37 4.37-0.5(4.37–1.87)=3.12 4.37+0.5(6.87-4.37)=5.62 2.50 

3 6.87 6.87-0.5(6.87-4.37)=5.62 

7.3 Calculate horizontal stress and maximum tension at each reinforcement level 

The computations for Tmax are computed for Level 1 and 2 Reinforcements, at zo = 1.87 ft 

and 4.37 ft, respectively. Extreme Event II load combination is used, with appropriate load 

factors from Table E6-5.1. The maximum load at a given level is: 

T max  σ H A trib  γ CT (T CT )

where Atrib = tributary area for the soil reinforcement at a given level 

TCT= tensile load for the impact loading 

The impact loads vary between reinforcement tensile rupture design and pullout design. 

Therefore, two maximum loads must be computed for traffic barrier impact loading – Tmax-R 

and Tmax-PO. For tensile rupture check, the upper layer of soil reinforcement is designed for a 

rupture impact load of 2,300 lb/lft of wall; and the second layer is designed with a rupture 

impact load of 600 lb/lft. Pullout is resisted over a greater length of wall than the 

reinforcement rupture loads. Therefore, for pullout, the upper layer of soil reinforcement is 

designed for a pullout impact load of 1,300 lb/lft of wall; and the second layer is designed 

with a pullout impact load of 600 lb/lft. 

FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 3 November 2009
 
 

 

 

 

 

Top Layer (Level 1): 

 At Z = 1.87 ft, the following depths are computed 

Z = 0 ft (from Table E6-7.1) 

Z = 3.12 ft (from Table E6-7.1) 

	 Obtain Kr by linear interpolation between 2.5Ka = 0.707 at Z = 0 and 1.2Ka = 0.340 at 

Z = 20.00 ft as follows: 

At Z = 0 ft, Kr(z-)= 0.707 

At Z = 3.12 ft, Kr(z+)= 0.340 + (20.00 ft – 3.12 ft)(0.707-0.340)/20.00 ft = 0.650 

	 Compute σH = kr [ r (Z + heq)]γP-EV per EQ 4-34, as follows: 

γP-EV = 1.35 from Table E6-5.1 

At Z = 0 

σH(Z-) = Kr(z-) [r (Z(z-) + heq ] γP-EV = (0.707)[ 125 pcf (0 + 2)](1.35) = 239 psf 

At Z = 3.12 ft, 

σH-soil(Z+) = Kr(z+) [r (Z(z+) + heq ] γP-EV = (0.650)[ 125 pcf (3.12 + 2)](1.35) = 562 psf 

σH = 0.5(239 psf + 562 psf) = 400 psf 

	 Based on Table E6-7.1, the vertical tributary spacing at Level 1 is Svt = 3.12 ft 

	 The panel width, wp, is 5.00 ft (given in Step 1, Example E4) 

	 The tributary area, Atrib, is computed as follows: 

Atrib = (3.12 ft)(5.00 ft) = 15.60 ft2
 

	 The maximum tension at Level 1 with the 2,300 lb/lft impact load is computed as 

follows: 

Tmax-R = (σH)(Atrib) + CT (2,300 wp) = (400 psf)(15.60 ft2

) + 1.0 [2,300 lb/ft (5 ft)] 

= 6,240 + 11,500 = 17.74 k/panel of 5-ft width 

Second Layer (Level 2): 

 At Z = 4.37 ft, the following depths are computed 

Z = 3.12 ft (from Table E6-7.1) 

Z = 3.12 ft (from Table E6-7.1) 

FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 4 November 2009
 
 

	 Obtain Kr by linear interpolation between 2.5Ka = 0.707 at Z = 0 and 1.2Ka = 0.340 at 

Z = 20.00 ft as follows: 

At Z = 3.12 ft, Kr(z-)= 0.340 + (20.00 ft – 3.12 ft)(0.707-0.340)/20.00 ft = 0.650 

At Z = 5.62 ft, Kr(z+)= 0.340 + (20.00 ft – 5.62 ft)(0.707-0.340)/20.00 ft = 0.604 

	 Compute σH = kr [ r (Z + heq)]γP-EV per EQ 4-34, as follows: 

γP-EV = 1.35 from Table E6-5.1 

At Z = 3.12 ft, 

σH(Z-) = Kr(z-) [r (Z(z-) + heq ] γP-EV = (0.650)[ 125 pcf (3.12 + 2)](1.35) = 562 psf 

At Z = 5.62 ft, 

σH-soil(Z+) = Kr(z+) [r (Z(z+) + heq ] γP-EV = (0.604)[ 125 pcf (5.62 + 2)](1.35) = 777 psf 

σH = 0.5(562 psf + 777 psf) = 670 psf 

	 Based on Table E6-7.1, the vertical tributary spacing at Level 2 is Svt = 2.50 ft 

	 The panel width, wp, is 5.00 ft (given in Step 1, Example E4) 

	 The tributary area, Atrib, is computed as follows: 

Atrib = (2.50 ft)(5.00 ft) = 12.50 ft2
  

	 The maximum tension at Level 2 with the 600 lb/lft impact load is computed as 

follows: 

T ft2

max-R = (σH)(Atrib) + CT (600 wp) = (670 psf)(12.50 ) + 1.0 [600 lb/ft (5 ft)] 

= 8,375 + 3,000 = 11.38 k/panel of 5-ft width 

7.4 Establish factored long-term tensile resistance of soil reinforcement for extreme 

event 

The nominal tensile resistance of galvanized steel bar mat soil reinforcement is based on the 

design life and estimated loss of steel over the design life during corrosion – see Example E4 

for corrosion loss calculations. 

FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 5 November 2009
 
 

For W11 wires 

Tn = 65 ksi (0.0795 in2) = 5.17 k/wire. 

Using the extreme event resistance factor, t = 1.0 as listed in Table E6-5.2, the factored 

tensile resistance, Tr = 5.17 k/wire (1.0) = 5.17 k/wire. 

7.5 Establish nominal and factored pullout resistance of soil reinforcement 

The nominal pullout resistance, Pr, of galvanized steel bar mat (grid) reinforcement is based 

on various parameters in the following equation: 

Pr = (F*)(2b)(Le)[(σv)(γP-EV)] 

Where σv =  (Z + heq) 

Since the steel bar mat has welded connections, it can be considered inextensible with  = 1. 

Assume a W11 transverse wire which has a nominal diameter of 0.374 in. The transverse 

spacing of transverse wires, St, is equal to 6 in. for the top two layers of reinforcement, as 

determined in Example Problem E4. 

For, St = 6 in., t/St = 0.3748 in./6 in. = 0.0623 

Based on the value of t/St, the F* parameter varies from 20(t/St) at z = 0 ft to 10(t/St) at z ≥

20 ft and greater. 

For t/St = 0.0623, F* = 1.247 at Z = 0 ft and F* = 0.623 at Z ≥ 20 ft 

Assume bar mat width, b = 1 ft for computing pullout resistance on a per foot width basis. 

The actual bar mat width will be computed based on comparison of the pullout resistance 

with Tmax. The number of longitudinal wires and thus the width of the bar mats will be 

determined in Example E4.. 

The computations for Pr are for the top two layers at z = 1.87 and 4.37, respectively. For 

pullout, the upper layer of soil reinforcement be designed for a pullout impact load of 1,300 

lb/lft (19.0 kN/m) of wall; and the second layer be designed with a pullout impact load of 600 

lb/lft (8.8 kN/m). 

FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 6 November 2009
 
 

 

 

Top Layer (Level 1) 

	 Obtain F* at z = 1.87 ft by linear interpolation between 1.247 at Z = 0 and 0.623 at Z 

= 20 ft as follows: 

F* = 0.623 + (20.00 ft – 1.87 ft)(1.247 – 0.623)/20 ft = 1.189 

	 Compute effective length Le as follows: 

The pullout resistance of the soil reinforcement to the impact load is resisted over the 

full-length of the reinforcements (i.e., L). 

Therfore, Le = L = 18 ft 

	 Compute (σv)(γP-EV) 

Per Article 11.10.6.3.2 of AASHTO (2007), use unfactored vertical stress for pullout 

resistance. Thus, 

γP-EV = 1.00 

(σv-soil + heq)(γP-EV) = (125 pcf)(1.87 ft + 2 ft)(1.00) = 484 psf 

	 Compute nominal pullout resistance as follows: 

Pr = (F*)(2b)(Le)[(σv-soil)(γP-EV)] 

Pr = (1.0)(1.189)(2)(1.00 ft)(18 ft)(484 psf) = 20,717 lb/ft 

	 Compute factored pullout resistance as follows: 

Prr = Pr = (1.0)(20.72 k/ft) = 20.72 k/ft 

	 The maximum pullout tension at Level 1 with the 600 lb/lft impact load and H from 

Step 7.3 is computed as follows: 

Tmax-PO = (σH)(Atrib) + CT (1,300 wp) = (400 psf)(15.60 ft2

) + 1.0 [1,300 lb/ft (5 ft)] 

= 6,240 + 6,500 = 12.74 k/panel of 5-ft width 

Second Layer (Level 2) 

	 Obtain F* at z = 4.37 ft by linear interpolation between 1.247 at Z = 0 and 0.623 at Z 

= 20 ft as follows: 

F* = 0.623 + (20.00 ft – 4.37 ft)(1.247 – 0.623)/20 ft = 1.111 

	 Compute effective length Le as follows: 

The pullout resistance of the soil reinforcement to the impact load is resisted over the 

full-length of the reinforcements (i.e., L). 

Therfore, Le = L = 18 ft 

FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 7 November 2009
 
 

	 Compute (σv)(γP-EV) 

Per Article 11.10.6.3.2 of AASHTO (2007), use unfactored vertical stress for pullout 

resistance. Thus, 

γP-EV = 1.00 

(σv-soil + heq)(γP-EV) = (125 pcf)(4.37 ft + 2 ft)(1.00) = 796 psf 

	 Compute nominal pullout resistance as follows: 

Pr = (F*)(2b)(Le)[(σv-soil)(γP-EV)] 

Pr = (1.0)(1.111)(2)(1.00 ft)(18 ft)(796 psf) = 31,836 lb/ft 

	 Compute factored pullout resistance as follows: 

Prr = Pr = (1.0)(31.84 k/ft) = 31.84 k/ft 

 

	 The maximum pullout tension at Level 2 with the 600 lb/lft impact load and H from 

Step 7.3 is computed as follows: 

T 2

max-PO = (σH)(Atrib) + CT (600 wp) = (670 psf)(12.50 ft ) + 1.0 [600 lb/ft (5 ft)] 

= 8,375 + 3,000 = 11.38 k/panel of 5-ft width 

7.6 Establish number of longitudinal wires at each level of reinforcement 

Based on Tmax-R, Tr, Tmax-PO, and Prr, the number of longitudinal wires at any given level of 

reinforcements can be computed as follows: 

	 Based on tensile resistance considerations, the number of longitudinal, Nt, is 

computed as follows: 

Nt = Tmax-R/Tr 

	 Based on pullout resistance considerations, the number of longitudinal wires, Np, is 

computed as follows: 

Np = 1 + (Tmax-PO/Prr)/(Sl) 

Top Layer (Level 1) Reinforcement at Z = 1.87 ft, the number of W11 longitudinal wires 

for 5 ft wide panel can be computed as follows: 

	 Tmax-R = 17.74 k/panel of 5-ft width, Tr = 5.17 k/wire 

FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 8 November 2009
 
 

	 Nt = Tmax-R/Tr = (17.74 k/panel of 5-ft width)/(5.17 k/wire) = 3.4 longitudinal 

wires/panel of 5-ft width 

 Np = Tmax-PO/Prr = 1 + [(12.74 k/panel of 5-ft width)/(20.72 k/ft)]/(0.5 ft) 

= 1 + 1.4 = 2.4 longitudinal wires/panel 

	 Since Nt > Np, tension breakage is the governing criteria and therefore the governing 

value, Ng, is 4.0. Select 4 longitudinal wires at Level 1 for each panel of 5-ft width. 

Thus, the Strength I steel bar mat configuration at Level 1 of 4W11 + W11x0.5' is 

sufficient for the Extreme Event II traffic barrier loading. 

Second Layer (Level 2) Reinforcement at Z = 4.37 ft, the number of W11 longitudinal wires 

for 5 ft wide panel can be computed as follows: 

	 Tmax-R = 11.38 k/panel of 5-ft width, Tr = 5.17 k/wire, 

	 Nt = Tmax-R/Tr = (11.38 k/panel of 5-ft width)/(5.17 k/wire) = 2.2 longitudinal 

wires/panel of 5-ft width 

 Np = Tmax-PO/Prr = 1 + [(11.38 k/panel of 5-ft width)/(31.84 k/ft)]/(0.5 ft) 

= 1 + 0.87 = 1.7 longitudinal wires/panel 

	 Since Nt > Np, tension breakage is the governing criteria and therefore the governing 

value, Ng, is 4.0. Select 3 longitudinal wires at Level 2 for each panel of 5-ft width. 

Thus, the Strength I steel bar mat configuration at Level 2 of 3W11 + W11x0.5' is 

sufficient for the Extreme Event II traffic barrier loading. 

STEP 8: DESIGN OF FACING ELEMENTS 

The precast facing elements must be designed as structural elements with appropriate 

connection strength as discussed in Chapter 4. The upper facing panel should be separated 

from the barrier slab with 1 to 2 in. of expanded polystyrene (see Figure 5-2(b)). The 

distance should be adequate to allow the barrier and slab to resist the impact load in sliding 

and overturning without loading the facing panel. 

FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 9 November 2009
 
FHWA NHI-10-025 Example E6 – Traffic Barrier Impact Loading 

MSE Walls and RSS – Vol II E6 – 10 November 2009
 
 

EXAMPLE E7 

SEGMENTAL PRECAST PANEL MSE WALL WITH SEISMIC LOADING 

E7-1 INTRODUCTION 

This example problem demonstrates the analysis of the Example #4 MSE wall for earthquake 

loading. The MSE wall has a level backfill and live load surcharge, and is assumed to 

include a segmental precast panel face with steel grid (bar mat) reinforcements. The MSE 

wall configuration to be analyzed is shown in Figure E4-1. The analysis is based on various 

principles that were discussed in Chapter 7. Table E7-1 presents a summary of steps 

involved in the analysis. Each of the steps and sub-steps is sequential and if the design is 

revised at any step or sub-step then all the previous computations need to be re-visited. Each 

of the steps and the sub-steps in Table E7-1 is explained in detail herein. 

Table E7-1. Summary of steps in analysis of MSE wall with seismic loading 

Step Item 

GENERAL 

1 Complete static analysis/design 

2 Summarize applicable load and resistance factors 

EXTERNAL STABILITY 

1 Establish initial wall design based on static loading 

2 Establish seismic hazard, and estimate peak ground acceleration (PGA) and spectral 

acceleration at 1-second, S1. 

3 Establish site effects 

4 Determine maximum accelerations, kmax, and peak ground velocity (PVG) 

5 Obtain an average peak ground acceleration, kav, within the reinforced soil zone 

6 Determine the total (static + dynamic) thrust PAE, using one of the following two 

methods 

1 Mononobe-Okabe (M-O) formulation 

2 Generalized Limit Equilibrium (GLE) slope stability 

7 Determine the horizontal inertial force, PIR, of the total reinforced wall mass 

8 Check sliding stability 

 if sliding stability is met, go to Step 11 

 if sliding stability is not met, go to Step 9 

9 Determine the wall yield seismic coefficient, ky, where wall sliding is initiated. 

10 Determine the wall sliding displacement based on the following relationships between 

d, ky/kmax, kmax, PGV, and site location 

11 Evaluate the limiting eccentricity and bearing resistance 

12 If Step 11 criteria are not met, adjust the wall geometry and repeat Steps 6 to 11, as 

needed 

13 If Step 11 criteria are met, assess acceptability of amount of sliding displacement 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 1 November 2009
 
 

INTERNAL STABILITY 

1 Compute the internal dynamic force, Pi, of the active wedge 

2 Compute maximum combined factored loads in the soil reinforcements 

3 Check tensile resistance of soil reinforcements 

4 Check pullout resistance of the soil reinforcements 

5 Check connection resistance 

GENERAL 

STEP 1. COMPLETE STATIC ANALYSIS/DESIGN 

Initial wall design based upon static loading was established in Example E4. 

STEP 2. SUMMARIZE APPLICABLE LOAD AND RESISTANCE FACTORS 

Table E7-2 summarizes the load factors for the various LRFD load type, including seismic 

(extreme event I), shown in second column of Tables E4-4.1 and E4-4.2. Throughout the 

computations in this example problem, the forces and moments in Tables E4-4.1 and 

E4-4.2 should be multiplied by appropriate load factors. 

Table E7-2. Summary of applicable load factors 

Load Combination 

Load Factors 

(after AASHTO, 2007 Tables 3.4.1-1 and 3.4.1-2) 

EV EH LS EQ 

Extreme Event I p p EQ = 1.00 1.00 

Strength I (maximum) p = 1.35 p = 1.50 1.75 – 

Strength I (minimum) p = 1.00 p = 0.90 1.75 – 

Service I 1.00 1.00 1.00 – 

For computation of factored resistances during evaluation of extreme event I limits states, 

appropriate resistance factors have to be used. Table E7-3 summarizes the applicable 

resistance factors. 

Table E7-3. Summary of applicable combined static/earthquake resistance factors 

Item Resistance 

Factors 

AASHTO (2007) 

Reference 

Sliding of MSE wall on foundation soil s = 1.00 Table 11.5.6-1 

Bearing resistance b = 1.00 Article 10.5.5.3.3 

Tensile resistance (for steel bar mats) t = 0.85 Table 11.5.6-1 

Pullout resistance p = 1.20 Table 11.5.6-1 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 2 November 2009
 
 

EVALUATE XTERNAL STABILITY ANALYSIS OF MSE WALL 

STEP 1. ESTABLISH INITIAL WALL DESIGN 

Initial wall design based upon static loading was established in Example E4. 

STEP 2. ESTABLISH SEISMIC HAZARD, AND ESTIMATE PEAK GROUND 

ACCELERATION (PGA) AND SPECTRAL ACCELERATION AT 1-

SECOND, S1. 

The USGS Seismic Design Parameters CD (Version 2.10) {provided with AASHTO LRFD 

Bridge Specifications) was used to determine these design parameters. An assumed location 

of Latitude 40.66 and Longitude –111.51 was used for this design example. The following 

parameters were established: 

 PGA = 0.206 g 

 S1 at 1.0 sec Period = 0.177 g 

STEP 3. ESTABLISH SITE EFFECTS 

From the assumed location (Latitude and Longitude) and the USGS Seismic Design 

Parameters CD (Version 2.10). The following Site Class was found. 

 Site Class B 

From AASHTO Table 3.10.3.2-1, and using Site Class B and PGA = 0.206g, the Fpga value at 

zero-period on acceleration spectrum is established. 

 Fpga = 1.00 

From AASHTO Table 3.10.3.2-3, and using Site Class B and S1 = 0.177g, Fv value is 

established. 

 Fv = 1.0 

STEP 4. DETERMINE MAXIMUM ACCELERATIONS, kmax, AND PEAK 

GROUND VELOCITY (PVG) 

With Equation 7-1: 

kmax = Fpga (PGA) = 1.00 (0.206 g) = 0.206 g 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 3 November 2009
 
 

With Equation 7-2: 

PGV (in/sec) = 38 Fv S1 = 38 (1.0) (0.177 g) = 6.726 

STEP 5. OBTAIN AN AVERAGE PEAK GROUND ACCELERATION, kav, 

WITHIN THE REINFORCED SOIL ZONE 

The average peak ground acceleration, using a wall height dependent reduction factor, , 

within the reinforced soil zone, using Equation7-3, is equal to: 

kav =  kmax 

For Site Class B and using Equation 7-4 the wall height factor, , is equal to: 

 = 1.0245 

Therefore, 

kav =  kmax = 1.024 (0.206g) = 0.211g 

STEP 6. DETERMINE THE TOTAL (STATIC + DYNAMIC) THRUST PAE 

The total (static + dynamic) thrust PAE, may be determined using one of the following two 

methods 

1 Mononobe-Okabe (M-O) formulation 

2 Generalized Limit Equilibrium (GLE) slope stability 

The M-O formulation is used for this design example. 

Assumptions: 

 kv = 0 

 kh = kmax = 0.206g 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 4 November 2009
 



 
  F 
 v S    
  1.0  0.177g   




 
 120%
 1 
0.01H
  0.5
  1    
    	 
 
   
 k 1  120% 1 0.01 25.64 ft0.5   1   
 
 max    
   
 0.206g 
 



 

With the Mononobe-Okabe (M-O) formulation (see Equation 7-5): 

PAE 0.5KAE f h2 

where h is the wall height along the vertical plane within the reinforced soil mass as shown 

below (and in Figure 7-1), b is the unit weight of the retained backfill and KAE is obtained as 

per Equation 7-6, as follows. 

h 

H 

h/2 

tan I (0.5H) h  H  ;where I is the backfillslopeangle 10.5tan I

tan 0 0.5 25.64 h  25.64  

  25.64 ft 1  0.5 tan0 

Per Equation 7-6, KAE is equal to: 

2 ' cos (b 90) K AE  2  sin( ' '   )sin( I) coscos 2 (90 )cos(  b 90)1 b   cos( 90)cosI 90  

with 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 5 November 2009
 
 

g  ξ  1  k   0.206 

tan   h   tan 1 

      11.64 

 

1 k v   1 - 0 

 = angle of wall friction = lesser of the angle of friction for the reinforced soil mass (' r) 

and the retained backfill (' b) = 30

I = the backfill slope angle = β = 0

' b = angle of internal friction for retained backfill = 30

 = the slope angle of the face = 90

Therefore 

cos2 (3011.64 90 90) KAE   2 

 2 sin(30 30)sin(3011.64 0) 

cos11.64cos (90 90)cos(30 90 9011.64)1  cos(30 90 9011.64)cos0 90  90 

 

cos2 (18.36) 0.9008 KAE    0.4782

 2 2  sin(60)sin(18.36)  0.7320 1  0.6042 cos11.64 cos(41.64)1   cos(41.64)  

PAE  0.5K 2 

AE γ bh  0.5 0.4782 125 lb/ft 3 25.64 ft 

2  19.65 k/lft 

STEP 7 DETERMINE THE HORIZONTAL INERTIA FORCE, PIR 

Determine the horizontal inertial force, PIR, of the total reinforced wall mass with Equation 7-7, 

as follows: 

PIR = 0.5(kav)(W) 

where W is the weight of the full reinforced soil mass and any overlying permanent slopes 

and/or permanent surcharges within the limits of the reinforced soil mass. The inertial force is 

assumed to act at the centroid of the mass used to determine the weight W. 

W = 25.64 ft (18 ft) (125 pcf) = 57.68 k/lft 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 6 November 2009
 
 

PIR = 0.5(kav)(W) = 0.5 (0.211 g) (57.68 k/lft) = 6.09 k/lft 

STEP 8 CHECK SLIDING STABILITY 

From page 7-6, check the sliding stability using a resistance factor, , equal to 1.0 and the full, 

nominal weight of the reinforced zone and any overlying permament sucharges. If the sliding 

stability is met, the design is satisfactory and go to Step 11. If not, go to Step 9. 

Compute the total horizontal force, THF, for M-O Method as follows: 

THF =	 Horizontal component of PAE + PIR + EQ(qLS)(H)(KAE) + other horizontal nominal 

forces due to surcharges (with load factor =1.0) 

where, EQ is the load factor for live load in Extreme Event I limit state and qLS is the 

intensity of the live load surcharge. 

THF	 

 = PAE cos+ PIR + EQ(qLS) 

= 19.65 k/lft (cos 30) + 6.09 k/lft + 0.5(0.25 ksf)(25.64 ft)(0.4785) = 

 = 17.02 k/lft + 6.09 k/lft + 1.53 k/lft 

 = 24.64 k/lft 

Compute the sliding resistance, R, as follows: 

R = V (

where  is the minimum of tan' r, tan' f or (for continuous reinforcement) tan (as discussed in 

Section 4.5.6.a) and V is the summation of the vertical forces as follows: 

V = W + PAEsin + permanent nominal surcharge loads within the limits of the reinforced 

soil mass 

V = W + PAEsink/lft + 19.65 k/lft (sin 30) = 57.68 + 9.84 = 67.52 k/lft 

R = V (k/lft (tan 30) = 38.98 k/lft 

The sliding stability capacity to demand (CDR) ratio is calculated as: 

CDRsliding = R / THF = 38.98 k/lft / 24.64 k/lft = 1.58 > 1.0  O.K., and go to Step 11 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 7 November 2009
 
 

STEP 11. EVALUATE ECCENTRICITY AND BEARING RESISTANCE 

Evaluate the limiting eccentricity and bearing resistance. Include all applicable loads for 

Extreme Event I. For the M-O method, add other applicable forces to PAE. Check the limit 

states using the following criteria: 

1. For limiting eccentricity, for foundations on soil and rock, the location of the resultant of the 

applicable forces should be within the middle two-thirds of the wall base for EQ = 0.0 and 

within the middle eight-tenths of the wall base for EQ = 1.0. Interpolate linearly between 

these values as appropriate. 

2.	 For bearing resistance compare the bearing pressure to the nominal bearing resistance (i.e., 

use a resistance factor of 1.0) based on full width of the reinforced zone. 

11.1 Limiting Eccentricity at Base of MSE Wall 

The purpose of these computations is to evaluate the limiting eccentricity at the base of the 

MSE wall. Since the computations are related to limiting eccentricity, the beneficial 

contribution of live load to resisting forces and moments is neglected. The computations for 

limiting eccentricity at the base of the MSE wall are illustrated in Table E4-6.2. Limiting 

eccentricity is a strength limit state check and therefore service limit state calculations are not 

performed. The critical values based on max/min result in the extreme force effect and 

govern the limiting eccentricity mode of failure. 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 8 November 2009
 
 

 

 

 

 

Table E7-4. Computations for evaluation of limiting eccentricity for MSE wall 

Item Unit 

Extreme Event I 

(p = max) (p = min) 

Total vertical load at base of MSE wall without LL, 

VA = V1 

k/ft 77.88 57.69 

PAE sin k/ft 9.84 9.84 

Resisting moments about Point A without LL 

surcharge = MRA = M1V1 + L (PAE sin k-ft/ft 878.05 696.33 

Total thrust seismic overturning moment about Pt A 

= PAE coshk/ft (cos 30) (25.64/2 ft) k-ft/ft 218.16 218.16 

LL component overturning moment about Point A = 

1.53 k/ft (25.64/2 ft) k-ft/ft 19.65 19.65 

Inertial force, PIR overturning moment about Pt A = 

max: 6.09 k/lft (1.35)(25.64/2 ft) 

min: 6.09 k/lft (1.00)(25.64/2 ft) 

k-ft/ft 105.36 78.04 

Overturning moment, MOA (static + seismic) k-ft/ft 343.17 315.85 

Net moment about Point A = MA = MRA – MOA k-ft/ft 534.88 380.48 

Location of the resultant force on base of MSE wall 

from Point A, a = MA/(VA + PAE sin ft 6.10 5.63 

Eccentricity at base of MSE wall, eL = L/2 – a ft 2.9 3.37 

Limiting eccentricity, e = 0.40L for extreme event I 

limit state ft 6.60 6.60 

Is the resultant within limiting value of e? - Yes Yes 

Calculated eL/L - 0.16 0.19 

CRITICAL VALUES BASED ON MAX/MIN 

Overturning moments about Point A, MOA-C k-ft/ft 343.17 

Resisting moments about Point A, MRA-C k-ft/ft 696.33 

Net moment about Point A, MA-C = MRA-C - MOA-C k-ft/ft 353.16 

Vertical force, VA-C = V1 + PAE sin k/ft 67.52 

Location of resultant from Point A, anl = MA-C/VA-C ft 5.23 

Eccentricity from center of wall base, eL=0.5*L - anl ft 3.76 

Limiting seismic eccentricity, e = 0.4L ft 7.20 

Is the limiting eccentricity criteria satisfied? - Yes 

11.2 Bearing Resistance at Base of MSE Wall 

For bearing resistance computations, the effect of live load is included since it creates larger 

bearing stresses. For seismic bearing resistance compare the bearing pressure to the nominal 

bearing resistance (i.e., use a resistance factor of 1.0) based on full width of the reinforced zone. 

Therefore, seismic bearing stress at the base of the MSE wall can be computed as follows: 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 9 November 2009
 
V

 v  

L  2e

 

 

 

where ΣV = R = V1 + VS + PAE sinis the resultant of vertical. 

Table E7-5. Computations for evaluation of seismic bearing resistance 

(see Table E4-6.3. for static values0 

Item Unit 

Extreme 

Event I 

(p = max) 

Static Vertical load at base of MSE wall including 

LL on top, ΣV = R = V1 + VS 

k/ft 80.13 

Seismic Vertical load at base of MSE wall, PAE sin k/ft 9.84 

Total vertical load at base of MSE wall without LL, 

VA = R = V1 + VS + PAE sin k/ft 89.97 

Resisting moments about Point A = MRA 

= MV1 + MV5 + MPV 

k-ft/ft 898.03 

Overturning moments about Point A = MOA 

= MF1 + MF2 + MFIR 

k-ft/ft 343.17 

Net moment at Point A, MA = MRA - MOA k-ft/ft 554.86 

Location of the resultant force on MSE block from 

Point A, a = (MRA – MOA)/VA 

ft 6.17 

Eccentricity at base of MSE block, eL = L/2 - a ft 2.83 

Limiting eL ft 4.50 

Is the resultant within limiting value of eL? ft YES 

Effective width of base of MSE wall, B' = L – 2e ft 12.34 

Bearing stress due to MSE wall =ΣV/(B') = v ksf 7.29 

Bearing resistance (10.50 ksf given in E4 for static 

resistance, seismic / static = 1.0/0.65, therefore, 

seismic resistance = 16.15 ksf) 

ksf 16.15 

Is bearing stress less than the bearing resistance? – YES 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 10 November 2009
 
EVALUATE INTERNAL STABILITY ANALYSIS OF MSE WALL 

STEP 1.	 COMPUTE INTERNAL DYNAMIC FORCE, Pi 

 

For internal stability, the active wedge is assumed to develop an internal dynamic force, Pi, that 

is equal to the product of the mass in the active zone and the wall height dependent average 

seismic coefficient, kav. Pi is computed as: 

Pi = kav Wa 

Wa is the soil weight of the active zone as shown by shaded area in Figure E7-1. 

Wa = [0.3H(H/2) + 0.5(0.3H)(H/2)] r 

W 2 2 a = [0.3 (25.64 ft) (1/2) + 0.5(0.3)(25.64 ft) (1/2)] 125 pcf 

Wa = [98.61 ft2

 + 49.31 ft2 ] 125 pcf = 18.49 k/lft 

Pi = 0.211g (18.49 k) = 3.90 k/lft 

The inertial force is distributed to the n number of reinforcement layers equally as follows. 

From Example E4, n = 10. 

P 3.90 k / lft T  i 

md   0.39 k / lft  1.95 k / 5 ft panel width

n 10 

STEP 2. COMPUTE MAXIMUM FACTORED LOADS IN THE 

 REINFORCEMENTS 

 

The load factor for seismic forces is equal to 1.0. The total factored load applied to the 

reinforcement on a load per unit of wall width basis is determined as follows, with Tmax the 

factored static load applied to the reinforcements determined using the appropriate equations in 

Chapters 4 and 6. 

T total  T max  Tmd 

Ttotal for each layer of reinforcement is listed in Table E7-6, with Tmax from Table E4-7.4 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 11 November 2009
 
Figure E7-1. 	 Seismic internal stability for inextensible reinforcements. 

(from Figure 4-9 and Figure 7-5) 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 12 November 2009 
STEP 3. CHECK TENSILE RESISTANCE OF THE SOIL REINFORCEMENTS 

As listed in Table E7-3, the resistance factor for metallic bar mats while evaluating tensile 

failure under combined static and earthquake loading is equal to 0.85. 

Ttotal for each layer of reinforcement is listed in Table E7-6, with Tmax and Ng from Table E4-

7.4. 

Table E7-6. Summary of tensile resistance computations for 

Extreme Event I load combination 

Level Z 

ft 

H

ksf 

Tmax Tmd Ttotal

kips/ 5 ft panel 

Tn 

k/wire 

 Bar 

Mat Ng  Tn) Ng 

k/5’ panel 

CDR 

1 1.87 0.40 6.25 1.95 8.20 5.17 0.85 4W11 4 17.58 2.14 

2 4.37 0.67 8.36 1.95 10.31 5.17 0.85 3W11 3 13.18 1.28 

3 6.87 0.87 10.80 1.95 12.75 5.17 0.85 4W11 4 17.58 1.38 

4 9.37 1.03 12.77 1.95 14.72 5.17 0.85 4W11 4 17.58 1.19 

5 11.87 1.15 14.26 1.95 16.21 7.42 0.85 4W15 4 25.23 1.56 

6 14.37 1.23 15.23 1.95 17.18 7.42 0.85 4W15 4 25.23 1.47 

7 16.87 1.26 15.71 1.95 17.66 7.42 0.85 4W15 4 25.23 1.43 

8 19.37 1.27 16.03 1.95 17.98 7.42 0.85 4W15 4 25.23 1.40 

9 21.87 1.37 17.10 1.95 19.05 7.42 0.85 4W15 4 25.23 1.32 

10 24.37 1.51 19.05 1.95 21.00 7.42 0.85 4W15 4 25.23 1.20 

Capacity to demand ratios (CDR) are greater than 1.00, therefore, tensile resistance under 

seismic loading is adequate for all layers of soil reinforcement. 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 13 November 2009
 
 

STEP 4. CHECK PULLOUT RESISTANCE OF THE SOIL REINFORCEMENTS 

The seismic tensile and total tensile loads are summarized below in Table E7-7. The static 

factor pullout resistance values listed below, in terms of k/lft, are from Table E4-7.4. 

For seismic loading conditions, the value of F*, the pullout resistance factor, is reduced to 80 

percent of the value used for static design, unless dynamic pullout tests are performed to directly 

determine the F* value. Therefore, the static values listed must be reduced by 80% to determine 

seismic pullout resistance. 

The pullout resistance factor is equal to 0.9 and to 1.20 for static and for seismic conditions, 

respectively. Therefore, the factored static values listed must be multiplied by a ratio of 1.20/0.9 

to determine factored seismic pullout resistance. 

Ttotal is presented in terms of kips per 5-foot panel width. Therefore, the static pullout values 

listed must be multiplied by 5 to go from a per foot to a per panel basis. 

Table E7-7. Summary of pullout computations for 

Extreme Event I load combination
 

Level Z 

ft 

H

ksf 

Tmax Tmd Ttotal 

kips/ 5 ft panel 

Static 

 Pr 

k/ft 

x 

80% 

x 

1.20 

/0.9 

x 

5 ft 

Seismic 

 Pr 

k/5’ panel 

CDR 

1 1.87 0.44 6.25 1.95 8.20 5.16 0.8 1.33 5 27.52 3.36 

2 4.37 0.67 8.36 1.95 10.31 11.25 0.0 1.33 5 60.00 5.82 

3 6.87 0.87 10.80 1.95 12.75 16.47 0.8 1.33 5 87.84 6.89 

4 9.37 1.03 12.77 1.95 14.72 20.75 0.8 1.33 5 110.7 7.52 

5 11.87 1.15 14.26 1.95 16.21 12.06 0.8 1.33 5 64.32 3.97 

6 14.37 1.23 15.23 1.95 17.18 14.50 0.8 1.33 5 77.33 4.50 

7 16.87 1.26 15.71 1.95 17.66 17.41 0.8 1.33 5 92.85 5.26 

8 19.37 1.27 16.03 1.95 17.98 13.27 0.8 1.33 5 70.77 3.94 

9 21.87 1.37 17.10 1.95 19.05 16.12 0.8 1.33 5 85.97 4.51 

10 24.37 1.51 19.05 1.95 21.00 19.66 0.8 1.33 5 104.8 4.99 

Capacity to demand ratios (CDR) are greater than 1.00, therefore, pullout resistance under 

seismic loading is adequate for all layers of soil reinforcement. 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 14 November 2009
 
 

 

STEP 5: CHECK CONNECTION RESISTANCE 

The precast facing elements must be designed as structural elements with appropriate 

connection strength as discussed in Chapter 4. For the Extreme Event I limit state the 

connection, at each level, must be designed to resist the total (static + seismic) factored load, 

Ttotal. The factored long-term connection strength, Tac, must be greater than Ttotal. The 

resistance factor for combined static and seismic loads for steel grid reinforcement is 0.85 (the 

static resistance factor is 0.65). 

FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 15 November 2009
 
FHWA NHI-10-025 Example E7 – Seismic Loading 

MSE Walls and RSS – Vol II E7 – 16 November 2009
 
EXAMPLE E8 

REINFORCED SOIL SLOPE DESIGN – ROAD WIDENING
 

E8-1 INTRODUCTION 

A 0.6 mile (1 km) long, 16.5 ft (5 m) high, 2.5H:1V side slope road embankment in a suburban 

area is to be widened by one lane. At least a 20 ft (6.1 m) width extension is required to allow 

for the additional lane plus shoulder improvements. A 1H:1V reinforced soil slope up from the 

toe of the existing slope will provide 25 ft (7.6 m) width to the alignment. The following 

provides the steps necessary to perform a preliminary design for determining the quantity of 

reinforcement to evaluate the feasibility and cost of this option. The reader is referred to the 

design steps in section 9.2 to more clearly follow the meaning of the design sequence. 

STEP 1. SLOPE DESCRIPTION 

a. Geometric and load requirements 

 • H = 16.5 ft (5 m)

 

 •	 β = 45o 

 

 • 	 q = 200 psf (10 kPa) (for dead weight of pavement section) + 2% road grade 

b. Performance requirements 

• External Stability: 

 Sliding Stability: FSmin = 1.3 

 Overall slope stability and deep seated: FSmin = 1.3 

 Dynamic loading: no requirement 

 Settlement: analysis required 

• Compound Failure: FSmin = 1.3 

• Internal Stability: FSmin = 1.3 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E8 – 1 November 2009
 
STEP 2. ENGINEERING PROPERTIES OF FOUNDATION SOILS
 

•	 Review of soil borings from the original embankment construction indicates 

foundation soils consisting of stiff to very stiff, low-plasticity, silty clay with 

interbedded seams of sand and gravel. The soils tend to increase in density and 

strength with depth. 

• γ 3

d = 121 lb/ft (19 kN/m3

), ω  o opt = 15%, cu = 2000 psf (96 kPa),  ́= 28 , and c= 0 

• At the time of the borings, dw = 6.6 ft (2 m) below the original ground surface. 

STEP 3. PROPERTIES OF REINFORCED AND EMBANKMENT FILL 

The existing embankment fill is a clayey sand and gravel. For preliminary evaluation, 

the properties of the embankment fill are assumed for the reinforced section as follows: 

• U.S. Sieve Size Percent passing 

 4 in. (100 mm) 100 

 3⁄4 in. (20 mm) 99 

 No. 4 (4.75 mm) 63 

 No. 20 (0.425 mm) 45 

 No. 200 (0.075 mm) 25 

 PI (of fines) = 10 

 Gravel is durable 

 pH = 7.5 

• γ 3 3 r = 133 lb/ft (21 kN/m ), ωopt = 15 % 

• ' = 33o

, c' = 0 

• Soil is relatively inert, based on neutral pH tests for backfill and geology of area. 

STEP 4.	 DESIGN PARAMETERS FOR REINFORCEMENT 

 For preliminary analysis use default values. 

• Long-Term Allowable Strength for Geosynthetic Reinforcement: 

 Tal = TULT/RF 

• Pullout Factor of Safety: FSPO = 1.5 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E8 – 2 November 2009
 
STEP 5. CHECK UNREINFORCED STABILITY
 

Using STABL4M, a search was made to find the minimum unreinforced safety factor and 

to define the critical zone. Both rotational and wedge stability evaluations were performed 

with Figure E8-1 showing the rotational search. The minimum unreinforced safety factor 

was 0.68 with the critical zone defined by the target factor of safety FSR as shown in Figure 

E8-1b. Remember that the critical zone from the unreinforced analysis roughly defines the 

zone needing reinforcement. 

STEP 6. CALCULATE TS FOR THE FSR 

From the computer runs, obtain FSU, MD, and R for each failure surface within the critical 

zone and calculate TS from equation 9-1 as follows. (Note: with minor code modification, 

this could easily be done as part of the computer analysis.) 

a. Calculate the total reinforcement tension TS, required: 

Evaluating all of the surfaces in the critical zone indicates maximum total tension 

TS-MAX = 3400 lb/ft (49.6 kN/m) for FSU = 0.89 as shown in Figure 9-11c. 

a. Checking TS-MAX by using the design charts in Figure 9-5: 

 

 From Figure 9-5, K ≈ 0.14 

and, 

H = H + q/γr + 0.3 ft (for 2% road grade) 

 = 16.5 ft + (200 psf ÷ 133 lb/ft3

) + 0.3 ft = 18.3 ft (5.6 m) 

 then, 

 T  0.5K γ H' 2  0.50.14133lb/ft 3

18.3ft

2

SMAX r  3120 lb/ft (46.5kN/m) 

The evaluation using Figure 9-5 appears to be in reasonably good agreement with the 

computer analysis for this simple problem. 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E8 – 3 November 2009
 

 FSU  M T D

s  1.3 R



  tan 1  tanr  

f tan 1  tan33           26.5

 

 FS R   1.3 
9.5 ft 

17.4 ft 

(1 m = 3.28 ft) 

(1 m = 3.28 ft) 

Figure E8-1. Unreinforced stability analysis results. 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E8 – 4 November 2009
 
Ts-max = 0.89 

3400 lb/ft (49.6 kN/m) 

R = 41 ft (12.5 m) 

4.9 ft (1.5 m) 

For R = 41 ft, Md = 340 kip-ft/ft 

(1 m = 3.28 ft) 

Figure E8-1. Unreinforced stability analysis results (continued). 

c. Determine the distribution of reinforcement. 

Since H < 20 ft (6 m), use a uniform spacing. Due to the cohesive nature of the 

reinforced fill, maximum compaction lifts of 8 in. (200 mm) are recommended. 

d. As discussed in the design section, to avoid wrapping the face and surficial stability 

issues, use Sv = 16 in. (400 mm) reinforcement spacing; therefore, N = 16.5 ft / 1.33 ft 

= 12.4, use 12 layers with the bottom layer placed after the first lift of embankment fill. 

T 3400 / ft  S MAX lb Tmax 

   283lb / ft N 12 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E8 – 5 November 2009
 
(Note: Other reinforcement options such as using short secondary reinforcements at 

every lift with spacing and strength increased for primary reinforcements may be 

considered and evaluated in order to select the most cost-effective final design.) 

e. Since this is a simple structure, rechecking Ts above each layer or reinforcement is 

not performed. 

f. For preliminary analysis of the required reinforcement lengths, the critical zone 

found in the computer analysis (Figure 9-11b) could be used to define the limits of 

the reinforcement. This is especially true for this problem since the sliding failure 

surface with FS ≥ 1.3 encompasses the rotational failure surface with FS ≥ 1.3. 

 

From direct measurement at the bottom and top of the sliding surface in Figure E8­

1b, the required lengths of reinforcement are: 

Lbottom = 17.4 ft (5.3 m)

 Ltop = 9.5 ft (2.9 m) 

Check length of embedment beyond the critical surface Le and factor of safety 

against pullout. 

Since the most critical location for pullout is the reinforcement near the top of the 

slope (depth Z = 8 in. {200 mm}), subtract the distance from the critical surface to 

the face of the slope in Figure E8-1c (i.e., 4.9 ft) from Ltop. This gives Le at top = 

4.6 ft (1.4 m). 

Assuming the most conservative assumption for pullout factors F* and α from 

Chapter 3, Section 3.4 gives F* = 0.67 tan  and α = 0.6 

Therefore, 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E8 – 6 November 2009
 

L e F*ασv C 4.6ft 0.67 tan 33 	 0.60.67ft133lb/ft 3  200psf   2 FS   Tmax	 283lb/ft 

FSPO  2.4  1.5 required 
Check the length requirement using Figure 9-5. 

 

 For LB, use min from foundation soil 

 tan 28

1  ' f  tan 	     22.2

 

 1.3  

 From Figure 9-5: LB/H = 0.96 

thus, LB = 18.3 ft (0.96) = 17.6 ft (5.4 m)

 For LT, use min from reinforced fill 

1  tan 33  ' f  tan      26.5

 

 1.3 
 

 From Figure 9-5: LT/ H = 0.52 

thus, LT = 18.3 ft (0.52) = 9.5 ft (2.9 m)
 

The evaluation again, using Figure 9-5, is in good agreement with the computer 

analysis. 

g. This is a simple structure and additional evaluation of design lengths is not required. 

For a preliminary analysis, and a fairly simple problem, Figure 9-5 or any number of 

proprietary computer programs could be used for a rapid evaluation of TS-MAX and Tmax. 

In summary, 12 layers of reinforcement are required with a long-term allowable 

material strength Tal of 284 lb/ft (4.14 kN/m) and an average length of 13.4 ft (4 m) 

over the full height of embankment. 

E8-2. COMPUTER-AIDED SOLUTION 

Users of this manual will likely use a computer program(s) to work though reinforced slope 

design. Before using any program, users should be very familiar with the method of analysis 

used in the computer program. One method of checking the results produced by the software is 

to work through examples of problems with known solutions. Users are encouraged to use the 

previous two examples in evaluating and gaining familiarity with computer software. For 

example, Design Example E8 is contained as an input file in the program ReSSA and a stepby-step tutorial of this example is located on the software developer’s web page: 

http://www.geoprograms.com/. 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E8 – 7 November 2009
 
FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E8 – 8 November 2009
 
EXAMPLE E9 

REINFORCED SOIL SLOPE DESIGN – HIGH SLOPE FOR NEW ROAD 

CONSTRUCTION
 

E9-1 INTRODUCTION 

An embankment will be constructed to elevate an existing roadway that currently exists at th

toe of a slope with a stable 1.6H: 1V configuration. The maximum height of the propose

embankment will be 62 ft (19 m) and the desired slope of the elevated embankment i

0.84H:1.0V. A geogrid with an ultimate tensile strength of 6,850 lb/ft (100 kN/m) based o

ASTM D6637 wide width method is desired for reinforcing the new slope. A unifor

surcharge of 250 lb/ft2

 (12 kPa) is to be used for the traffic loading condition. Availabl

information indicated that the natural foundation soils have a drained friction angle of 34o

 an

effective cohesion of 250 lb/ft2

 (12 kPa). The fill to be used in the reinforced section will hav

a minimum friction angle of 34o 

. 

The reinforced slope design must have a minimum factor of safety of 1.5 for slope stability

The minimum design life of the new embankment is 75 years. 

Determine the number of layers, vertical spacing, and total length required for the reinforce

section. 

STEP 1. GEOMETRIC AND LOADING REQUIREMENTS FOR DESIGN 

a. Slope description: 

• Slope height, H = 62 ft (19 m) 

• Reinforced slope angle, θ = tan-1(1.0/0.84) = 50o 

• Existing slope angle, β = tan-1(0.61/1.0) = 31.4o 

• Surcharge load, q = 250 psf (12.5 kN/m2

) 

 

b. Performance requirements: 

• External stability 

 - Sliding: FS ≥ 1.5 

 - Deep seated (overall stability): FS ≥ 1.5 

 - Dynamic loading: no requirement 

 - Settlement: analysis required 

e 

d 

s 

n 

m 

e 

d 

e 

. 

d 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 1 November 2009
 
 • Internal stability 

 Slope stability: FS ≥ 1.5 

STEP 2. ENGINEERING PROPERTIES OF THE NATURAL SOILS IN THE SLOPE 

For this project, the foundation and existing embankment soils have the following strength 

parameters: 

  = 34o

, c = 250 psf (12 kPa) 

 Depth of water table, dw = 1.5 m below base of embankment 

STEP 3. PROPERTIES OF AVAILABLE FILL 

The fill material to be used in the reinforced section was reported to have the following 

properties: 

γ = 120 pcf (18.8 kN/m3

),  = 34o, c = 0 

STEP 4. REINFORCEMENT PERFORMANCE REQUIREMENT 

Allowable tensile force per unit width of reinforcement, Tal, with respect to service life and 

durability requirements: 

 Tal = TULT/RF and RF = RFID x RFCR x RFD 

For the proposed geogrid to be used in the design of the project, the following factors are 

used:
 

RFD = durability factor of safety = 1.25. 

RFID = construction damage factor of safety = 1.2. 

RFCR = creep reduction factor = 3.0. 

Note: A FS = 1.5 will be applied to the geogrid reinforcement in stability analysis. 

Reduction factors were determined by the owner based on evaluation of project conditions 

and geogrid tests and field performance data submitted by the manufacturer. Therefore: 

6850lb/ft Tal  1520lb/ft (22 kN/m) 1.25 1.2  3 

Pullout Resistance: FS = 1.5 for granular soils with a 3 ft (1 m) minimum length in the 

resisting zone. 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 2 November 2009
STEP 5. CHECK UNREINFORCED STABILITY
 

The unreinforced slope stability was checked using the rotational slip surface method, as 

well as the wedge shaped failure surface method, to determine the limits of the reinforced 

zone and the required total reinforcement tension to obtain a factor of safety of 1.5. 

The proposed new slope was first analyzed without reinforcement using a hand solution 

(e.g., the FHWA Soils and Foundations Reference Manual, {Samtani and Nowatzki, 

2006}) or computer programs such as STABL4M, ReSSA, XSTABL, or RSS. The 

computer program calculates factors of safety (FS) using the Modified Bishop Method for 

circular failure surface. Failure is considered through the toe of the slope and the crest of 

the new slope as shown in the design example Figure E9-1a. Note that the minimum factor 

of safety for the unreinforced slope is less than 1.0. The failure surfaces are forced to exit 

beyond the crest until a factor of safety of 1.5 or more is obtained. Several failure surfaces 

should be evaluated using the computer program. 

Next, the Janbu Method for wedge shaped failure surfaces is used to check sliding of the 

reinforced section for a factor of safety of 1.5, as shown on the design example Figure E9­

1a. Based on the wedge shaped failure surface analysis, the limits of the critical zone to be 

reinforced are reduced to 46 ft (14 m) at the top and 56 ft (17 m) at the bottom for the 

required factor of safety. 

STEP 6. CALCULATE TS FOR FSR = 1.5 

a. The total reinforcement tension TS required to obtain a FSR = 1.5 is then evaluated for 

each failure surface. The most critical surface is the surface requiring the maximum 

reinforced tension TS-MAX. An evaluation of all the surfaces in the critical zone 

indicated TS-MAX = 66.7 kips/ft (1000 kN/m) and is determined as: 

 MD M T D

S  FSR FSU   1.5FSU  D	 R 

The most critical circle is where the largest TS = TS-MAX. As shown on the design 

example Figure 9-12a, TS-MAX is obtained for FSU = 0.935. 

For this surface, MD = 14,827 kips-ft/ft (67,800 kN-m/m) as determined stability analysis. 

D = R for geosynthetics = radius of critical circle 

R = 125.6 ft (38.3 m)
 

14827 k  ft/ft TSMAX  1.50.935	  66.7 kips/ft (1000kN/m) 125.6 ft 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 3 November 2009
 
Reinforcement alternatives: 

From computer program: Simplified distribution:

 TBottom = 67 – 31.3 = 35.7kips/ft TBottom = 1⁄2 Ts-max = 33.5 kips/ft 

TMiddle = 31.3 - 10 = 21.3 kips/ft TMiddle = 1/3 Ts-max = 22.3 kips/ft 

TTop = 10 kips/ft TTop = 1/6 Ts-max = 11.2 kips/ft 

Figure E9-1. Unreinforced stability analysis results. 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 4 November 2009
 
 

 

 

 

 

 

 

 

 

 

b. Check using chart design procedure: 

For θ = 50o

, and
 

f = tan-1 (tan r /FSR) = tan-1(tan 34o

/1.5) = 24.2o
 

Force coefficient, K = 0.21 (from Figure 9-5a) and, 

H = H + q/γr = 62 ft + (250 psf)/(120 pcf) = 64 ft 

then, 

TS-MAX = 0.5 Kγr(H)

2

 = 0.5(0.21)(120 pcf) (64 ft)2
 

= 52 kips/ft (766 kN/m)
 

Values obtained from both procedures are comparable within 25 percent. Since the 

chart procedure does not include the influence of water, use TS-MAX = 1000 kN/m. 

c. Determine the distribution of reinforcement 

Based on the overall embankment height divide the slope into three reinforcement 

zones of equal height as in equations 9-4 through 9-6. 

Tbottom = 1⁄2 TS-MAX =(1⁄2)(67 k/ft) = 33.5 kips/ft (500 kN/m) 

Tmiddle = 1/3 TS-MAX =(1/3)(67 k/ft) = 22.3 kips/ft (330 kN/m)

 Ttop = 1/6 TS-MAX =(1/6)(67 k/ft) = 11.2 kips/ft (170 kN/m)
 

d. Determine reinforcement vertical spacing Sv 

T 67 k / ft Minimum number of layers, SMAX N    44.7

T 1.5k / ft allowable 

33.5k/ft Distribute at bottom 1/3 of slope: NB   22.3 use 23 layers 1.5k/ft 

22.3k/ft At middle 1/3 of slope: NM   15layers 1.5k/ft 

11.2k/ft At upper 1/3 of slope: NT   7.5 use 8 layers 1.5k/ft 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 5 November 2009
 
Total number of layers: 46 > 44.7 OK 

Vertical spacing: 

Total height of slope = 62 ft (19 m) 

Height for each zone = 62 ft / 3 = 21 ft (6.3 m)

 Required spacing: 

 At bottom 1/3 of slope: 

62ft Srequired   0.91ft, use8in. spacing 23layers 

 

 At middle 1/3 of slope: 

62ft Srequired   1.4in., use18in spacing 15layers 

 At top 1/3 of slope: 

62ft Srequired   2.6ft, use 24in. spacing 8layers 

Provide 6 ft length of secondary reinforcement layers in the upper 1/3 of the slope, 

between primary layers (based on primary reinforcement spacing at a 16 in. vertical 

spacing. 

e. The reinforcement tension required within the middle and upper 1/3 of the unreinforced 

slope is then calculated using the slope stability program to check that reinforcement 

provided is adequate as shown in the design example Figure E9-1b. 

Top 2/3 of slope: TS-MAX = 31.3 k/ft < N · Tal = 23 layers x 1.5 k/ft = 34.5 kips/ft OK 

Top 1/3 of slope: TS-MAX = 10 k/ft < N · Ta = 8 layers x 1.5 k/ft = 12 kips /ft OK 

f.	 Determine the reinforcement length required beyond the critical surface for the entire 

slope from Figure E9-1a, used to determine Tmax as, 

Tmax FS 1520 k / ft1.5 26.4 ft Le	     F *  v C 0.8tan 34 0.66 120 pcf Z  2  Z 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 6 November 2009
 
At depth Z, from the top of the crest, Le is found and compared to the available length 

of reinforcement that extends behind the TDESIGN failure surface, as determined by the 

sliding wedge analysis: 

Z = 2 ft, Le = 13.2 ft, available length, Le = 17 ft OK 

Z = 4 ft, Le = 6.6 ft, available length, Le = 16 ft OK 

Z = 6 ft, Le = 4.4 ft, available length, Le = 16 ft OK 

Z = 8 ft, Le = 3.3 ft, available length, Le = 16 ft OK 

Z > 8 ft, Le = 3.0 ft, available length, Le = > 16 ft OK 

 Further checks of Z are unnecessary. 

Checking the length using Figure 9-5b for f = 24° 

LT/H = 0.65 → LT = 42 ft 

LB/H = 0.80 → LB = 51 ft 

Results from both procedures check well against the wedge failure analysis in step 5a. 

Realizing the chart solution does not account for the water table use top length LT = 46 

ft (14 m) and bottom length LB = 56 ft (17 m) as determined by the computer analyses 

in step 5a. 

g. The available reinforcement strength and length were checked using the slope stability 

program for failure surfaces extending beyond the TS-MAX failure surface and found to 

be greater than required. 

STEP 7. CHECK EXTERNAL STABILITY

 a. Sliding Stability. 

The external stability was checked using the computer program for wedge shaped 

failure surfaces. The FS obtained for the failure surface outside the reinforced section, 

defined with a 46 ft (14 m) length at the top and a 56 ft (17 m) length at the bottom, 

was 1.5. 

́

́

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 7 November 2009
 
b. Deep Seated Global Stability. 

The overall deep-seated failure analysis indicated that a factor of safety of 1.3 exists for 

failure surfaces extending outside the reinforced section (as shown in the design 

example Figure E9-1b). This is due to the grade at the toe of the slope that slopes down 

into the lake. The factor of safety for deep-seated failure does not meet requirements. 

Therefore, the reinforcement would have to be extended to a greater length, the toe of 

the new slope should be regraded, or the slope would have to be constructed at a flatter 

angle. 

For the option of extending the reinforcement length, local bearing must be checked. 

Local bearing (lateral squeeze) failure does not appear to be a problem as the 

foundation soils are granular and will increase in shear strength due to confinement. 

Also, the foundation soil profile is consistent across the embankment such that global 

bearing and local bearing will essentially result in the same factor of safety. For these 

conditions, the lower level reinforcements could simply be extended back to an external 

stability surface that would provide FS = 1.5 as shown in Figure E9-2. 

If the foundation soils were cohesive and limited to a depth of less than 2 times the base 

width of the slope, then local stability should be evaluated. As an example, assume that 

the foundation soils had an undrained shear strength of 2080 psf (100 kPa) and 

extended to a depth of 33 ft (10 m), at which point the granular soils were encountered. 

Then, in accordance with equation 9-15, 

2c 4.14c

 

s 

21040 psf  4.141040psf  FSsqueezing     1.02

120pcf 33 fttan50  62 ft 120 pcf  

u u FS squeezing   

γD tanθ H γ

Since FSsqueezing is lower than the required 1.3, extending the length of the 

reinforcement would not be an option without improving the stability conditions. This 

could be accomplished by either reducing the slope angle or by placing a surcharge at 

the toe, which effectively reduces the slope angle. 

c. Foundation Settlement. 

Due to the granular nature of the foundation soils, long-term settlement is not of 

concern. 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 8 November 2009
 
Figure E9-2. Design Example 2: global stability. 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 9 November 2009
 
FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E9 – 10 November 2009
 
EXAMPLE E10 

REINFORCED SOIL SLOPE DESIGN – FACING STABILITY CALCULATION
 

E10-1 INTRODUCTION 

Economies can sometimes be achieved by using higher strength primary reinforcement at 

wider spacing combined with short intermediate reinforcement layers to meet maximum 

spacing requirements, provide compaction aids and face stability. The calculations for face 

stability evaluation of slopes using intermediate reinforcement will be demonstrated for the 

slope in Example E8, with modified primary reinforcement. The guidelines for intermediate 

reinforcement presented under Step 6 of section 9.2 Reinforced Slope Design Guidelines will 

be followed. 

To evaluate cost alternatives in Example E8, modify primary reinforcement by doubling 

strength to 570 lb/ft (8.3 kN/m) and doubling vertical spacing. Intermediate reinforcement will 

be placed at 24 in. (800 mm) vertical spacing, centered between the primary reinforcement (at 

24 in. {800 mm} spacing). The length of intermediate reinforcement will be set at 4 ft (1.2 m) 

and minimum long term tensile strength, Tal, of 380 lb/ft (5.5 kN/m) will be used to meet 

constructability requirements. 

Surficial failure planes may extend to a depth of about 3 to 6% of the slope height. Therefore, 

the stability safety factor will be checked for depths up to 6% of slope height, for dry 

conditions. Also, checks will be performed at various depths assuming saturation to that depth, 

to see if project conditions (e.g., local rainfall) need to be further evaluated. 

E10-2. CHECK STABILITY SAFETY FACTOR FOR VARIOUS DEPTHS TO 

POTENTIAL FAILURE PLANE. 

 Compute depth equal to 6% of slope height. 

(0.06) 16.5 ft = 1 ft 

Check stability at 6 in., 12 in. and 24 in. depths to potential failure plane. Use Equation 

9-8 with the following parameters. 

   

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E10 – 1 November 2009
 

c'H  γ  γ H z cos 2β

	 tan'  F cosβsinβ  sin 2

β tan' F.S. g w g 

γg H z cosβsinβ
 

where 

c = effective cohesion — assume equal to zero, which conservatively neglects 

vegetative reinforcement. See Gray and Sotir (1995), for guidance of estimating 

strength of vegetation, if desired to include in analysis. 

 = effective friction angle — 33° 

γ = unit weight of fill soil — 134 lb/ft3 

z = vertical depth to failure plane — 1⁄2 ft, 1 ft, 2 ft

 H = vertical slope height — 16.5 ft 

β = slope angle — 45° 

Fg = summation of geosynthetic resisting force — varies by z, as strength at shallow 

embedment will likely be controlled by pullout resistance, therefore, compute 

by failure plane depth 

Geosynthetic available reinforcement strength is based on pullout toward the front face 

of the slope (i.e., the geosynthetic resistance to the outward movement of the wedge of 

soil above and below the geosynthetic). 

Primary reinforcement – 

Ta (= Tal) = 570 lb/ft 

Strength limited by pullout resistance near the face, with FSPO = 1.0, 

equals 

T = F* α σv C Le 

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MSE Walls and RSS – Vol II E10 – 2 November 2009
 

 Where, F* and α are as assumed for the geogrid in Example 1, and 

 σv = the weight of the triangular wedge of soil over the 

geosynthetic = 1⁄2γz 

Le = z / tan 45° = z 

C = 2 

T = (0.8 tan 33°) (0.66) [1⁄2 (134 lb/ft3

) (z)] (2) (z) 

T = 46 z2

 lb/ft 

Therefore,
 

@ 0.5 ft, T = 11 lb/ft 

@ 1.0 ft, T = 46 lb/ft 

@ 2.0 ft, T = 184 lb/ft 
 

 

 

Intermediate reinforcement – 

Ta (= Tal) = 380 lb/ft 

Strength limited by pullout resistance, with FSPO = 1.0, equals 

T = F* α σv C Le 

assuming F* and α parameters equal to those of the primary 

reinforcement again leads to, 

@ 0.5 ft, T = 11 lb/ft 

@ 1.0 ft, T = 46 lb/ft 

@ 2.0 ft, T = 184 lb/ft 

The slope contains 6 layers of primary reinforcement and 6 layers of 

intermediate reinforcement. Therefore, 

 @ 0.5 ft – Fg = 6 (11 lb/ft) + 6 (11 lb/ft) = 132 lb/ft 

 @ 1.0 ft – Fg = 6 (46 lb/ft) + 6 (46 lb/ft) = 552 lb/ft 

 @ 2.0 ft – Fg = 6 (184 lb/ft) + 6 (184 lb/ft) = 2208 lb/ft 

 

 With c = 0 and dry conditions, equation (9-8) reduces to 

 

Therefore, 

@ 0.5 ft, FS = 0.84 

@ 1.0 ft, FS = 1.1 

@ 2.0 ft, FS = 1.5 

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MSE Walls and RSS – Vol II E10 – 3 November 2009
 

γH z cos 2 β tan'  F g cosβ sin β  sin 2β tan' F.S.  γH z cosβsinβ

134lb/ft 3 16.5ftcos 2 45 tan 33 z  F g cos 45 sin 45 sin 2 45 tan 33  F.S.  134lb/ft 3 16,5ftcos 45 

 sin 45 z 

717 lb/ft 2 z  F 0.82 F.S.  g 

1105 lb/ft2 z 
Thus, assuming cohesion equal to zero, it is computed that the slope face is 

unstable at shallow depths (0.5 ft to 1 ft). A small amount of cohesion may be 

provided by the soil fill and/or vegetation. Assume a nominal amount of 

cohesion (e.g., 42 psf {2 kPa}), and recompute factors of safety. 

 

 cH = 42 psf (16.4ft) = 688 lb/ft 

 

 Then, the factor of safety is equal to 

and 

 @ 0.5 ft, FS = 2.1 

 @ 1.0 ft, FS = 1.7 

 @ 2.0 ft, FS = 1.8 

Thus, with only a small amount of cohesion the slope face would be stable. 

E10-3. CHECK THE SAFETY FACTOR FOR VARIOUS DEPTHS TO 

POTENTIAL FAILURE PLANE ASSUMING SATURATION TO THAT 

DEPTH, TO SEE IF REASONABLE FOR PROJECT CONDITIONS. 

 With parameters of γ - = 72 lb/ft3

g γw and cohesion of 42 psf (implies cohesion is 

derived from vegetation, and is retained under saturated conditions) 

 Then, the factor of safety is equal to 

and 

 @ 0.5 ft, FS = 1.8 

 @ 1.0 ft, FS = 1.4 

 @ 2.0 ft, FS = 1.5 

Again, the slope is stable provided vegetation is established on the slope face. 

A geosynthetic erosion mat would also help maintain the face stability. 

 

688 lb/ft 2  717 lb/ft 2 z  F g 0.82 F.S.  1105 lb/ft2 

z 

FHWA NHI-10-025 RSS Design Examples 

MSE Walls and RSS – Vol II E10 – 4 November 2009
 

 

688 lb/ft 2  385 lb/ft 2

z  F 0.82 F.S. 	 g 

1105 lb/ft 2

z 
 

 

APPENDIX F 

OTHER DESIGN PROCEDURES AND ANALYSIS MODELS 

F.1 Simplified Method and ASD Platform 

F.2 Coherent Gravity Method 

F.3 National Concrete Masonry Association Procedure 

F.4 GRS 

F.5 FHWA Structure Stiffness Method 

F.6 K-Stiffness Method 

F.7 Deep Patch 

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MSE Walls and RSS – Vol II F –1 November 2009
 
 

 

There are several means, other than the Simplified Method analysis model with the LRFD 

platform, which can be used for the design of MSE walls. Several of these are summarized 

below. Note that some design methods can be used in either a LRFD or an ASD platform. 

The use of the Simplified Method analysis model with the LRFD platform is recommended 

for the design of transportation MSE wall structures. 

F.1 Simplified Method and ASD Platform 

As previously (Section 4.1.1) noted, Engineers have been designing MSE highway walls 

using an ASD (allowable stress design) procedure since MSE walls were introduced in the 

early 1970’s. All uncertainty in applied loads and material resistance are combined in a 

single factor of safety or allowable material stress. The advantages of progressing to a LRFD 

procedure were summarized in Section 4.4.1. 

Future MSE walls will be designed with the LRFD procedure. Therefore, current guidance, 

i.e., AASHTO Standard Specifications for Highway Bridges, 17th Edition (2002) and FHWA 

NHI-00-043 (Elias et al., 2001), on MSE wall design using ASD procedures will not be 

updated. Note that the AASHTO (2002) and FHWA (2001) ASD references will not be 

updated by AASHTO or FHWA, respectively. Any designers engineering MSE walls with 

the ASD procedures in the future may want to refer to current LRFD procedures for any 

updates which may also be applicable to ASD procedure designs (e.g., seismic loading for 

external stability analysis). 

The Simplified Method of analysis has been used with ASD procedures since 1996. This 

method was developed using FHWA research (Christopher et al., 1990) and existing design 

methods (i.e., coherent gravity method, tie-back wedge method) as a starting point to create a 

single method for agencies and vendors to use (Elias and Christopher, 1997; AASHTO, 

1997; Allen et al., 2001). The simplified method uses a variable state of stress for internal 

stability analysis. This variable state of stress is defined in terms of a multiple of the active 

lateral earth pressure coefficient, Ka, and is a function of the type of reinforcement used and 

depth from the top of wall. This single method of design is applicable to all types of soil 

reinforcement. Thus, the simplified method offers the following advantages over other 

methods: 

C Straight forward by avoiding iterative processes to determine the reinforcement 

requirements (i.e., it is simple and easy to use). 

C Justified empirically in comparison to other methods available at the time of its 

development based on instrumented full scale structures, and the simplifications do not 

appear to compromise the Simplified Method’s accuracy (Allen et al., 2001). 

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MSE Walls and RSS – Vol II F –2 November 2009
 
 

 

C Found to be more accurate for upper reinforcements in sloped surcharges (Allen et al., 

2001). 

C Eliminates variations in method to determine internal lateral stress. 

C Eliminates variations in assumptions of the critical failure surface. 

C Accounts for the differences in reinforcement type and is easily adapted to new MSE wall 

reinforcement types as they become available. 

The simplified method has been adapted to LRFD procedures in AASHTO (2007) and in 

this manual. As noted in the introduction to this section, today, the use of the Simplified 

Gravity analysis model with the LRFD platform is recommended for the design of 

transportation MSE wall structures. 

F.2 Coherent Gravity Method 

The coherent gravity method, or analysis model, has been used for several decades in the 

ASD procedure. It can also be used with the LRFD procedure. The 2009 AASHTO Interims 

note that the maximum reinforcement loads shall be calculated using the Simplified Method 

or the Coherent Gravity Method. For state and agencies using the Coherent Gravity Method, 

the load in the reinforcements shall be obtained in the same way as the Simplified Method, 

except: (i) for steel reinforced wall systems, the lateral earth pressure coefficient used shall 

be equal to ko at the point of intersection of the theoretical failure surface with the ground 

surface at or above the wall top, transitioning to a ka at a depth of 20.0 ft below the 

intersection point, and constant at ka at depths greater than 20.0 ft. and (ii) If used for 

geosynthetic reinforced systems, ka shall be used throughout the wall height. 

AASHTO also states that other widely accepted and published design methods for 

calculation of reinforcement loads may be used at the discretion of the wall owner or 

approving agency, provided the designer develops method-specific resistance factors for the 

method employed. AASHTO recommends that the resistance factors recommended for the 

Simplified Method should also be used for the Coherent Gravity Method. 

The primary differences between the coherent gravity method and the simplified method are: 

(i) the coherent gravity method includes the pressure at each reinforcement elevation in the 

vertical pressure sum; (ii) the effect of the overturning moment caused by the retained 

backfill lateral earth pressure is included in the vertical pressure at each reinforcement 

elevation; and (iii) the lateral pressure varies from Ko at the top of the soil to Ka at a depth of 

20 ft (6 m) below, and constant at Ka below the 20 ft (6 m) depth for metallic reinforcements. 

This is illustrated in Figure F-1. As discussed in Chapter 4 (and illustrated in Figure 4-9), the 

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MSE Walls and RSS – Vol II F –3 November 2009
 
 

 

metallic reinforcement lateral pressure varies from 1.7 Ka (strips) or 2.5 Ka (mats and grids) 

at top of soil to Ka at a depth of 20 ft (6 m), and constant at Ka thereafter. For comparison 

purposes, for a  = 34◦ soil, K = 1 – sin 34◦ = 0.50; for a  = 34◦ o soil, Ka = 0.283; thus, Ko 

= 1.77 Ka. 

For geosynthetic reinforcements, the lateral pressure is constant at Ka for both the coherent 

gravity method and the simplified method. Therefore, the coherent gravity method is 

typically used only for metallic reinforcements. 

Previous research (FHWA RD-89-043) focused on defining the state of stress for internal 

stability, as a function of Ka, type of reinforcement used (geotextile, geogrid, metal strip or 

metal grid), and depth from the surface. The results from these efforts were synthesized in a 

simplified method, which can be used for all types of soil reinforcements. The simplified 

coherent gravity method is a single, logical method that can be used with LRFD or ASD 

procedure. As previously indicated in the Simplified Method section, there are a number of 

advantages to agencies. The method has been used for the past 12 years to safely design 

retaining walls. In comparison studies with field measured data, Allen et al. (2001) found the 

following: 

 Overall, the Simplified Method and the FHWA Structure Stiffness Method produce a 

prediction that is slightly conservative, whereas the Coherent Gravity Method 

produces a prediction that is slightly nonconservative. 

 The Coherent Gravity Method has been found to consistently provide lower predicted 

loads in structures with stiff reinforcement systems and in the upper reinforcements of 

sloped surcharges than measured field loads, while the Simplified Method more 

accurately predicts these reinforcement loads (Allen et al., 1993). 

 The assumption that the reinforcement stress is reduced with increased reinforcement 

length is questionable and not supported by field measurements. 

 

FHWA supports the use of a single method in order to maintain consistency in design. There 

are always concerns that designers will be confused and combine aspects of alternate 

methods that could produce nonconservative results. Agencies should be cognizant of the 

pending change to the AASHTO LRFD code and evaluate whether or not to allow the use of 

the Coherent Gravity Method (and/or other methods) in addition to the Simplified Method. 

Agencies specifications should be updated to reflect use of just the Simplified Method or the 

acceptance of either method. 

Again, the use of the Simplified Gravity analysis model with the LRFD platform is 

recommended for the design of transportation MSE wall structures. 

FHWA NHI-10-025 Appendix F – Other Design Procedures
 

MSE Walls and RSS – Vol II F –4 November 2009
 
 

 

Figure F-1. Coherent gravity method lateral pressure coefficient for internal stability 

(2009 Interims to AASHTO, 2007). 

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MSE Walls and RSS – Vol II F –5 November 2009
 
 

 

F.3 National Concrete Masonry Association Procedure 

The National Concrete Masonry Association (NCMA) method and analysis model was 

developed in 1993 (Simac et al.) specifically for, and is widely used with, modular block 

faced (a.k.a. segmental blocks), geosynthetic reinforced soil walls. It is an ASD procedure. 

It was updated in 1997 (NCMA), and a third update is reportedly in-progress. 

The principal differences between the NCMA method and the ASD Simplified Method are: 

(i) internal stability lateral pressure is set equal to the Coulomb active earth pressure 

coefficient, instead of the Rankine coefficient; (ii) assumed failure plane is the Coulomb 

active pressure wedge, instead of the Rankine active pressure wedge; (iii) the minimum 

reinforcement length to height ratio is 0.6, versus 0.7; and (iv) the connection strength 

requirements are based upon short-term testing, instead of being based upon long-term 

testing, as required by AASHTO. 

F.4 GRS 

The Geosynthetic Reinforced Soil (GRS) analysis model is used with ASD procedure. This 

method was developed in Colorado specifically for geosynthetic soil reinforcements and 

wrap-around or block facings. The GRS design method is documented in NCHRP Report 

556 (Wu et al., 2006). The GRS design method is a modification of the FHWA ASD 

Simplified Method (Elias et al., 2001). The soil reinforcement model is based upon closelyspaced vertically adjacent layers of reinforcement and soil arching, versus the FHWA 

method that this based upon a tied-back wedge model. 

Addtional principal differences between the GRS method and the ASD Simplified Method 

are: (i) the default vertical reinforcement spacing is 8 in. (0.2 m), and maximum spacing (for 

abutments) is 16 in. (0.4 m); (ii) the reinforcement length may be truncated in the bottom 

portion of the wall where the foundation is competent; (iii) the soil reinforcement is specified 

on a basis of minimum ultimate tensile strength and a minimum tensile stiffness; and (iv) 

connection strength is not a design requirement where the maximum reinforcement vertical 

spacing is 8 in. (0.2 m) and reinforced fill is a compacted select fill. 

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F.5 FHWA Structure Stiffness Method (from Allen et al., 2001; Christopher et al., 

1990) 

The Structure Stiffness Method was developed as the result of a major FHWA research 

project in which a number of full-scale MSE walls were constructed and monitored. 

Combined with an extensive review of previous fully instrumented wall case histories 

(Christopher et al., 1990; Christopher, 1993), small-scale and full-scale model walls were 

constructed and analytical modeling was conducted (Adib, 1988). This method is similar to 

the Tieback Wedge Method, but the lateral earth pressure coefficient is determined as a 

function of depth below the wall top, reinforcement type, and global wall stiffness, rather 

than using Ka directly. Furthermore, the location of the failure surface is the same as is used 

for the Coherent Gravity Method (Figure 3) for MSE walls with inextensible soil 

reinforcement. It is a Rankine failure surface for MSE walls with extensible soil 

reinforcement. The design methodology is summarized in equations 8, 9, and 10. Note that 

because the reinforcement stress, and the strength required to handle that stress, varies with 

the global wall stiffness, some iteration may be necessary to match the reinforcement to the 

calculated stresses. 

Tmax Sv Rc Kr (Z S q) 

Kr = KaSrif Z≤ 6 m 
 


 

Kr = Ka if Z > 6 m
 

Sr = EA / (H/n) 

Where, Kr is the lateral earth pressure coefficient, 

Sr is the global reinforcement stiffness for the wall (i.e., the average reinforcement 

stiffness over the wall face area), 

1 is a dimensionless coefficient equal to 1.0 for strip and sheet reinforcements or 

equal to 1.5 for grids and welded wire mats, 

2 is a dimensionless coefficient equal to 1.0 if Sr is less than or equal to 47880 kPa 

or equal to 1 if Sr is greater than 47880 kPa, EA is the reinforcement modulus 

times the reinforcement area in units of force per unit width of wall, 

H/n is the average vertical spacing of the reinforcement, and n is the total number of 

reinforcement layers. 

This stiffness approach was based on numerous full-scale observations that indicated that a 

strong relationship between reinforcement stiffness and reinforcement stress levels existed, 

and it was theoretically verified through model tests and numerical modeling. 

FHWA NHI-10-025 Appendix F – Other Design Procedures
 

MSE Walls and RSS – Vol II F –7 November 2009
 
 

 

F.6 K-Stiffness Method 

The K-Stiffness Method, or analysis model, is relatively new method that may be used with 

the ASD or LRFD procedure. This method was researched and developed by Allen and 

Bathurst (2003), Allen et al. (2003), Allen et al. (2004) and was calibrated against 

measurements of loads and strains from a large database of full-scale geosynthetic and fullscale steel reinforced soil walls. The method is targeted to accurately predict working loads 

in the soil reinforcement, though wall behavior near failure of some of the walls by excessive 

deformation or rupture was considered in the development of the design model (see Allen et 

al., 2003) to insure that such behavior would be precluded if the K-Stiffness Method is 

properly used and design parameters properly selected. From that research, the K-Stiffness 

method defined a design limit state that has not been considered in the other design models – 

a soil failure limit state. This is especially important for geosynthetic walls, since the 

geosynthetic reinforcement continues to strain and gain tensile load long after the soil has 

reached its peak strength and begun dropping to a residual value. Therefore, if the strain in 

the soil is limited to prevent it from going past peak to a residual value, failure by excessive 

deformation or rupture is prevented and equilibrium is maintained. This is a key design 

philosophy in the K-Stiffness design model. 

An analysis of the K-Stiffness predictions relative to the full scale measurements indicate 

that the K-Stiffness method is a more accurate method for estimating loads in the soil 

reinforcements than other currently available design models and thereby has the potential to 

reduce reinforcement requirements and improve the economy of MSE walls (Allen et al., 

2003 and 2004). The improvement (i.e., economy) is significant for both geosynthetic and 

steel reinforcement, though more pronounced for geosynthetic reinforcements. A couple of 

geosynthetic reinforced walls have been designed using the K-Stiffness Method, built, and 

fully instrumented by the Washington State Department of Transportation (WSDOT). 

Because they were designed with the K-Stiffness Method, the amount of soil reinforcement 

in the wall was reduced by a third to one-half of the reinforcement required by the AASHTO 

Simplified Method. Results reported by Allen and Bathurst (2006) for the largest wall (36 ft 

high, 600 ft long) indicate that the K-Stiffness method accurately predicted the strains in the 

reinforcement, and the wall has performed well since its construction. The other wall has 

also performed well, and full results for both walls will be available in a forthcoming 

WSDOT research report. The K-Stiffness Method’s ability to accurately predict 

reinforcement strains provides promise for having the ability to accurately predict wall 

deformations for the serviceability limit state. See Allen and Bathurst (2003) for additional 

details on this issue. 

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MSE Walls and RSS – Vol II F –8 November 2009
 
 

 

The K-Stiffness method has been adapted to LRFD design procedure by the Washington 

DOT, and load and resistance factors to use with this method are detailed in the WSDOT 

Geotechnical Design Manual (2006), as well as step-by-step procedures for use of the KStiffness Method for design of MSE walls. The method begins with a prediction of the total 

lateral load to be resisted by the soil reinforcement which is consistent with the approach 

used by the Simplified Method. The K-Stiffness Method then takes that total lateral load and 

adjusts it empirically based on the effects of global reinforcement stiffness, local 

reinforcement stiffness, facing stiffness/toe restraint, facing batter, soil shear strength, and 

distribution of the total lateral force to the individual layers based on observations from many 

full scale wall case histories. The formulation of global reinforcement stiffness is consistent 

with that used in the FHWA Structure Stiffness Method (Christopher et al., 1990; 

Christopher, 1993). The soil shear strength (the plane strain shear strength is used for this 

method) is used as an index to correlate to the stiffness of the soil backfill, which is the real 

property of interest with regard to prediction of soil reinforcement loads at working stress 

conditions. Note that the methods used in historical practice (e.g., the Simplified Method) 

calculate the vertical stress resulting from gravity forces within the reinforced backfill at each 

level, resulting in a linearly increasing gravity force with depth and a lateral stress 

distribution that continuously increases with depth below the wall top. The K-Stiffness 

Method instead calculates the maximum gravity force resulting from the gravity forces 

within the reinforced soil backfill to determine the maximum reinforcement load within the 

entire wall reinforced backfill, Tmxmx, and then adjusts that maximum reinforcement load 

with depth for each of the layers using a load distribution factor, Dtmax to determine Tmax. 

The method is summarized as follows: 

 V   p rH  p f S  LL q  p V , and 

Tmax  0.5SvK  V Dt max glocal fb fs   p H Sv

where, 

V = the factored pressure due to resultant of gravity forces from soil self weight 

within and immediately above the reinforced wall backfill, and any surcharge loads 

present (KSF) 

P = the load factor for vertical earth pressure EV 

LL = the load factor for live load surcharge per the AASHTO LRFD Specifications 

q = live load surcharge (KSF) 

H = the total vertical wall height at the wall face (FT) 

S = average soil surcharge depth above wall top (FT) 

FHWA NHI-10-025 Appendix F – Other Design Procedures
 

MSE Walls and RSS – Vol II F –9 November 2009
 
 

 

V = vertical stress increase due to concentrated surcharge load above the wall 

(KSF) 

Sv = tributary area (assumed equivalent to the average vertical spacing of the 

reinforcement at each layer location when analyses are carried out per unit length of 

wall), in FT 

K = is an index lateral earth pressure coefficient for the reinforced backfill, and shall 

be set equal to K0 as calculated per Article 3.11.5.2 of the AASHTO LRFD 

Specifications. K shall be no less than 0.3 for steel reinforced systems. 

Dtmax = distribution factor to estimate Tmax for each layer as a function of its depth 

below the wall top relative to Tmxmx (the maximum value of Tmax within the wall) 

Sglobal = global reinforcement stiffness (KSF) 

g = global stiffness factor 

local = local stiffness factor 

fb = facing batter factor 

fs = facing stiffness factor 

H = horizontal stress increase at reinforcement level resulting from a concentrated 

horizontal surcharge load per Article 11.10.10.1 of the AASHTO LRFD 

Specifications (KSF) 

The WSDOT GDM (2006, or most current update) should be consulted for the details on the 

calculation of Tmax for each layer and how to apply this methodology to MSE wall design. 

It should be noted that the K-Stiffness Method has been updated to consider a number of 

additional wall case histories, and additionally to consider the effect of backfill soil cohesion. 

See Bathurst et al. (2008) for details. While consideration of soil cohesion does help to 

improve the K-Stiffness Method prediction accuracy for wall backfill soil that contain a 

significant cohesive component to its soil shear strength, in general, it is not recommended to 

consider soil cohesion in the soil backfill for design purposes due to unknown long-term 

effect of moisture infiltration in the backfill and possibly soil creep. 

FHWA NHI-10-025 Appendix F – Other Design Procedures
 

MSE Walls and RSS – Vol II F –10 November 2009
 
 

 

F.7 Deep Patch 

The deep patch is a mitigation technique for sliding roadway sections. It is typically used on 

roads that suffer from chronic slide movements that are primarily the result of side cast fill 

construction. One of the main advantages of the deep patch technique is that it is constructed 

with equipment that works from the roadway and does not require accessing the toe of the 

failed area. This technique is generally not expected to completely arrest movement seen in 

the road but rather slow it down to manageable levels. 

Deep patch repairs consist of reinforcing the top of a failing embankment with several layers 

of soil reinforcement. This work is typically done with a small construction crew consisting 

of a laborer, hydraulic excavator, and a dump truck. The design is based on determining the 

extent of the roadway failure based on visual observations of cracking and then and then 

using analytical or empirical methods for determining the reinforcement requirements. An 

empirical design procedure is presented in Highway Deep Patch Road Embankment Repair 

Application Guide which was produced by the U.S. Department of Agriculture (USDA) 

Forest Service in partnership with FHWA Federal Lands Highway Division. An analytical 

approach is summarized as follows: 

1. Characterize the existing soil properties, new fill properties if applicable, and establish 

the desired slope stability factor of safety after the deep patch mitigation technique is 

implemented. 

2. Generate a cross section of the failed embankment at a location that represents the most 

severe movement. 

3. Locate the cracks furthest from the edge of the embankment slope break (hinge point) on 

the cross section. Similar to the concept of MSE wall internal active and restive 

mechanisms the active portion of the embankment movement will be considered to be 

taking place on the outside of the embankment crack limits and the resisting portion on 

the inside of the crack limits. 

4. Determine the distance from the crack limits to the embankment slope hinge. 

5. Determining the total reinforcement tension required per unit width as described in 

Chapter 9 or using reinforced soil slope software. 

6. Based on the site limitations and geometry determine the reinforcement spacing and 

corresponding number of reinforcement layers (Typically 2-5 layers). Divide Ts by the 

FHWA NHI-10-025 Appendix F – Other Design Procedures
 

MSE Walls and RSS – Vol II F –11 November 2009
 
 

 

number of layers to obtain the required reinforcement tensile strength per layer and per 

unit width (Treq’d). 

7. Determine the minimum required pullout length (Le) by using a factor of safety of 1.5 

and setting Treq’d = Tmax. Determine the minimum reinforcement length by adding Le 

to the distance from the crack to the slope face for each layer. 

8. Select a reinforcement in which the long-term allowable strength per unit width (Chapter 

3) is greater then Treq’d. 

FHWA NHI-10-025 Appendix F – Other Design Procedures
 

MSE Walls and RSS – Vol II F –12 November 2009