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Publication Number: FHWA-HRT-13-066
Date: August 2013

 

Geosynthetic Reinforced Soil Performance Testing - Axial Load Deformation Relationships

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FOREWORD

The use of geosynthetic reinforced soil (GRS) for load bearing applications such as bridge abutments and integrated bridge systems (IBS) has expanded among transportation agencies looking to save time and money while delivering a better and safe product to the traveling public. GRS has been identified by the Federal Highway Administration (FHWA) as a proven, market-ready technology, and is being actively promoted through its Every Day Counts (EDC) initiative. FHWA interim design guidance for GRS abutments and IBSs is presented in Publication No. FHWA-HRT-11-026. The guidance includes the procedure and use of the GRS performance tests, also termed a mini-pier experiment. This report presents a database of nineteen performance tests performed by the FHWA, largely at the Turner-Fairbank Highway Research Center. It also presents findings, conclusions, and suggestions regarding various design parameters related to the performance of GRS, such as backfill material, reinforcement strength, reinforcement spacing, facing confinement, secondary reinforcement, and compaction.

A reliability analysis for load and resistance factor design (LRFD) was performed based on the results of this performance testing to determine a calibrated resistance factor for the soil-geosynthetic capacity equation. The results of this analysis can also be used by bridge designers to estimate capacity and deformation of GRS. In addition, an insight into the behavior of GRS as a new composite material due to the close reinforcement spacing is described.

Jorge E. Pagán-Ortiz
Director, Office of Infrastructure
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

 

Technical Report Documentation Page

1. Report No.

FHWA-HRT-13-066

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

Geosynthetic Reinforced Soil Performance Testing-Axial Load
Deformation Relationships

5. Report Date

August 2013

6. Performing Organization Code
7. Author(s)

Nicks, J.E., Adams, M.T., Ooi, P.S.K., Stabile, T.

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101

10. Work Unit No.

11. Contract or Grant No.

N/A

12. Sponsoring Agency Name and Address

Office of Infrastructure R&D
FHWA Research, Development and Technology
6300 Georgetown Pike
McLean, VA 22101

13. Type of Report and Period Covered

Technical

14. Sponsoring Agency Code

 

15. Supplementary Notes

The FHWA Contracting Officer's Technical Representative (COTR) was Mike Adams, HRDI-40.

16. Abstract

The geosynthetic reinforced soil (GRS) performance test (PT), also called a mini-pier experiment, consists of constructing alternating layers of compacted granular fill and geosynthetic reinforcement with a facing element that is frictionally connected, then axially loading the GRS mass while measuring deformation to monitor performance. This large element load test provides material strength properties of a particular GRS composite built with unique combinations of reinforcement, compacted fill, and facing elements. This report describes the procedure and provides axial load-deformation results for a series of PTs conducted in both Defiance County, OH, as part of the Federal Highway Administration's (FHWA) Every Day Counts (EDC) GRS Validation Sessions and in McLean, VA, at the FHWA's Turner-Fairbank Highway Research Center as part of a parametric study.

The primary objectives of this research report are to: (1) build a database of GRS material properties that can be used by designers for GRS abutments and integrated bridge systems; (2) evaluate the relationship between reinforcement strength and spacing; (3) quantify the contribution of the frictionally connected facing elements at the service limit and strength limit states; (4) assess the new internal stability design method proposed by Adams et al. 2011 for GRS; and (5) perform a reliability analysis of the proposed soil-geosynthetic capacity equation for LRFD calibration. (1,11)

17. Key Words

Geosynthetic reinforced soil, performance test, mini-pier experiment, abutment, integrated bridge system, geotextile, capacity, deformation

18. Distribution Statement

 

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

169

22. Price
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

Table of Contents

  1. Introduction

  2. Testing Conditions

  3. Test Setup

  4. Results Database

  5. Comparison To Plane Strain Conditions

  6. Parametric Analysis

  7. Applications Of Performance Testing To Design

  8. Conclusions

Appendix A. Soil Testing Data

Appendix B. Nuclear Density Testing for TFHRS PTS

Appendix C. Deformation Instrumentation Layouts for PTS

Appendix D. Raw Data for PTS

Acknowledgements

References

LIST OF FIGURES

Figure 1 Photo. Vegas mini-pier experiment
Figure 2. Illustration. Plan view of Vegas mini-pier experiment
Figure 3. Illustration. Face view of Vegas mini-pier experiment
Figure 4. Illustration. Side view of Vegas mini-pier experiment
Figure 5. Illustration. Reinforcement schedule for Vegas mini-pier experiment
Figure 6. Illustration. Plan view of Defiance County experiment
Figure 7. Illustration. Elevation view of Defiance County (DC) test
Figure 8. Equation. Ultimate vertical capacity for a GRS composite
Figure 9. Equation. W factor
Figure 10. Equation. Required reinforcement strength
Figure 11. Equation. Confining stress (Wu et al. 2010)
Figure 12. Graph. Predictive capability of the soil-geosynthetic  composite capacity equation
Figure 13. Graph. Predictive capability of the required reinforcement strength equation
Figure 14. Graph. Reinforced backfill gradations
Figure 15. Graph. LSDS testing results
Figure 16. Photo. DC-1 GRS PT (before testing)
Figure 17. Illustration. Concrete footing on GRS composite, inset from facing
Figure 18. Photo. Hollow core hydraulic jacks for PT assembly
Figure 19. Photo. TF-1 PT setup with reaction frame
Figure 20. Photo. TF-6 PT setup with reaction frame
Figure 21. Photo. TF-10 PT setup with reaction frame
Figure 22. Photo. TF-9 at failure with reaction frame
Figure 23 Photo. Spherical bearing to apply load to the footing on the GRS composite
Figure 24. Illustration. Instrumentation layout for DC tests and TF-1
Figure 25. Illustration. General additional instrumentation layout TF PT series
Figure 26. Graph. Load-deformation behavior for the Defiance County PTs
Figure 27. Graph. Load-deformation behavior for the Turner Fairbank PTs
Figure 28. Photo. Tilting of the footing during TF-4 testing
Figure 29. Graph. TF-4 results
Figure 30. Graph. TF-1 results
Figure 31. Graph. TF-5 results
Figure 32. Graph. TF-6 results
Figure 33. Graph. Repeatability of PT at TFHRC
Figure 34. Photo. TF-11 at failure with Sv = 3-13/16 inches, Tf = 1,400 lb/ft, and 21A material
Figure 35. Photo. TF-3 at failure with Sv = 7⅝ inches, Tf = 2,400 lb/ft, and 21A material
Figure 36. Photo. TF-13 at failure with Sv = 11¼ inches, Tf = 3,600 lb/ft, and 21A material
Figure 37. Photo. TF-10 at failure with Sv = 15¼ inches, Tf = 4,800 lb/ft, and 21A material
Figure 38. Photo. Rupture pattern for geotextiles in TF-6 (qult,emp = 43,828 psf); the lowest layer of reinforcement is the closet fabric in the picture
Figure 39. Photo. Post-test picture of TF-6 (Sv = 7⅝ inches, Tf = 4,800 lb/ft)
Figure 40. Equation. Mohr-Coulomb shear strength
Figure 41. Equation. Ultimate capacity of an unconfined GRS PT
Figure 42. Equation. Ultimate capacity of a strip footing on slope
Figure 43. Equation. Ultimate capacity of a strip footing on a vertical GRS abutment
Figure 44. Equation. Ratio of plane strain capacity to PT capacity
Figure 45. Equation. Stability Factor
Figure 46. Graph. Ratio of plane strain capacity to PT capacity  for different stability factors
Figure 47. Graph. Mohr-Coulomb failure envelope for Pham (2009)  plane strain GSGC tests
Figure 48. Graph. Plane strain capacity to PT capacity for a stability factor of 0.29
Figure 49. Illustration. Infinitely Long Unconfined GRS abutment
Figure 50. Equation. Stiffness of an Infinitely Long Unconfined GRS abutment
Figure 51. Illustration. Solution for strip footing on top of a wall
Figure 52. Equation. Vertical displacement of a GRS abutment with a strip footing
Figure 53. Equation. Vertical strain
Figure 54. Equation. Stiffness of a GRS abutment supporting a strip footing
Figure 55. Equation. Vertical displacement of a GRS abutment with a strip footing.
Figure 56. Graph. Ratio of plane strain stiffness of a strip footing on top of a wall (SGRS) to that of a PT (SPT) for the case of constant stiffness with depth
Figure 57. Graph. Comparison between compacted and uncompacted GRS composites
Figure 58. Design service limit for uncompacted sample DC-5
Figure 59. Graph. Comparison of compacted and uncompacted strains  between the DC-1
and DC-5 tests
Figure 60. Graph. Effect of bearing bed reinforcement for TF-7 and TF-8
Figure 61. Graph. Measured lateral deformation at 3,600 psf applied stress for TF-7 (no bearing bed reinforcement)  and TF-8 (2 courses of bearing bed reinforcement)
Figure 62. Graph. Measured lateral deformation at 26,600 psf applied stress for TF-7 (no bearing bed reinforcement)  and TF-8 (2 courses of bearing bed reinforcement)
Figure 63. Graph. Comparison of open-graded and well-graded backfills  for TF-1 and TF-2
Figure 64. Graph. Stress-strain curves for PTs with CMUs at Tf/Sv = 3,800 psf
Figure 65. Graph. Stress-strain curves for PTs with no CMU facing at Tf/Sv = 3,800 psf
Figure 66. Graph. Capacity of GRS with no CMU facing at various reinforcement spacing for different Tf/Sv
Figure 67. Graph. Capacity of GRS with CMU facing at various reinforcement spacing for different Tf/Sv Ratios
Figure 68. Graph. Capacity of GRS with no CMU facing at various reinforcement strength for different Tf/Sv ratios
Figure 69. Graph. Capacity of GRS with CMU facing at various reinforcement strength for different Tf/Sv ratios
Figure 70. Graph. Stress-strain response for TF-2 (CMU facing) and TF-3 (No CMU facing) with Sv = 7⅝ inches and Tf = 2,400 lb/ft
Figure 71. Stress-strain response for TF-6 (CMU facing) and TF-7 (No CMU facing) with
Sv = 7⅝ inches and Tf = 4,800 lb/ft
Figure 72. Graph. Stress-strain response for TF-9 (CMU facing) and TF-10 (No CMU facing) with Sv = 15¼ inches and Tf = 4,800 lb/ft
Figure 73. Graph. Stress-strain Response for TF-12 (CMU facing) and TF-11 (No CMU facing) with Sv = 3-13/16 inches and Tf = 1,400 lb/ft
Figure 74. Graph. Stress-strain response for TF-14 (CMU facing) and TF-13 (No CMU facing) with Sv = 11¼ inches and Tf = 3,600 lb/ft
Figure 75. Graph. Effect of CMU facing on ultimate capacity  as a function of reinforcement spacing 
Figure 76. Graph. Effect of CMU facing on ultimate capacity  as a function of reinforcement strength
Figure 77. Graph. Calculated confining pressure due to CMU facing  at the ultimate capacity
Figure 78. Graph. Comparison of predicted capacity and measured capacity
Figure 79. Graph. Cumulative distribution function plot for DC and TF PTs
Figure 80. Graph. Cumulative distribution function plot for all GRS composite tests
Figure 81. Graph. Normalized applied stress versus strain for all PT
Figure 82. Graph. Normalized load-deformation behavior for the DC and TF PTs up to 5 percent vertical strain
Figure 83. Graph. Cumulative distribution function for proposed service limit pressure
Figure 84. Graph. Load-deformation behavior for the Turner Fairbank PTs at low strain levels
Figure 85. Graph. Normalized load-deformation behavior for the DC and TF PTs up to 0.5 percent vertical strain     
Figure 86. Graph. PTs strictly meeting FHWA GRS abutment design specifications
Figure 87. Equation. Limit state function for FOSM approach
Figure 88. Graph. Reliability index for lognormal R and Q
Figure 89. Equation. LRFD format
Figure 90. Equation. Resistance factor using FOSM
Figure 91. Equation. Coefficient of variation for factored load
Figure 92. Equation. Coefficient of variation for resistance
Figure 93. Graph. Resistance factor for footings on GRS composites for different dead to dead plus live load ratios and target reliability indices based on PT series
Figure 94. Graph. Resistance factor for footings on GRS composites for different dead to dead plus live load ratios and target reliability indices based on all testing to date
Figure 95. Graph. AASHTO No. 8 LSDS test results (DC tests)
Figure 96. AASHTO No. 8 LSDS deformation test results (DC tests)
Figure 97. Graph. AASHTO No. 8 pea gravel LSDS test results (DC tests)
Figure 98. Graph. AASHTO No. 8 pea gravel LSDS deformation test results (DC tests)
Figure 99. Graph. AASHTO No. 57 LSDS test results (DC tests)
Figure 100. Graph. AASHTO No. 57 LSDS deformation test results (DC tests)
Figure 101. Graph. AASHTO No. 9 LSDS test results (DC tests)
Figure 102. Graph. AASHTO No. 9 LSDS deformation test results (DC tests)
Figure 103. Graph. AASHTO No. 8 LSDS test results (TFHRC tests)
Figure 104. Graph. AASHTO No. 8 LSDS deformation test results (DC tests)
Figure 105. Graph. AASHTO A-1-a (VDOT 21A) LSDS test results (TFHRC tests)
Figure 106. Graph. AASHTO A-1-a (VDOT 21A) LSDS deformation test results (DC tests)
Figure 107. Illustration. Instrumentation layout for DC tests and TF-1
Figure 108. Illustration. Instrumentation layout for TF-2, TF-9
Figure 109. Illustration. Instrumentation layout for TF-3, TF-4
Figure 110. Illustration. Instrumentation layout for TF-5, TF-7
Figure 111. Instrumentation layout for TF-6, TF-12
Figure 112. Illustration. Instrumentation layout for TF-8
Figure 113. Illustration. Instrumentation layout for TF-10
Figure 114. Illustration. Instrumentation layout for TF-11
Figure 115. Illustration. Instrumentation layout for TF-13
Figure 116. Illustration. Instrumentation layout for TF-14

LIST OF TABLES

Table 1. Summary of PT conditions
Table 2. PT reinforced backfill gradations
Table 3. PT backfill gradation properties
Table 4. Maximum dry density for PT aggregates
Table 5. LSDS testing results
Table 6. Geosynthetic reinforcement properties
Table 7. PT dimensions
Table 8. PT measured results summary
Table 9. Parametric study on aggregate size
Table 10. Effect of aggregate type results
Table 11. Parametric study on compaction
Table 12. Parametric study on bearing bed reinforcement
Table 13. Parametric study on gradation (Tf = 2,400 lb/ft, Sv = 7⅝ inches)
Table 14. Parametric study on gradation (Tf = 4,800 lb/ft, Sv = 7⅝ inches)
Table 15. Parametric study on reinforcement strength with open-graded aggregates
Table 16. Parametric study on reinforcement strength with well-graded aggregates
Table 17. Parametric study for 3,800 lb/ft2 Tf/Sv ratio (with facing)
Table 18. Parametric study for 3,800 lb/ft2 Tf/Sv ratio (with no facing)
Table 19. Tf /Sv ratios for each PT
Table 20. Effect of CMU facing on stiffness and capacity
Table 21. Effect of CMU facing on strain
Table 22. PTs meeting GRS strength and service limit design criteria
Table 23. Predicted and measured vertical capacity for DC and TF PTs
Table 24. Predicted and measured vertical capacity for all GRS composite tests
Table 25. Estimation of allowable dead load to limit vertical strain to 0.5 percent using the GRS capacity equation
Table 26. Statistics for dead and live loads
Table 27. AASHTO No. 8 sieve analysis (DC tests)
Table 28. AASHTO No. 8 pea gravel sieve analysis (DC tests)
Table 29. AASHTO No. 57 Sieve analysis (DC tests)
Table 30. AASHTO No. 9 Sieve analysis (DC tests)
Table 31. AASHTO No. 8 Sieve analysis (TFHRC tests)
Table 32. AASHTO A-1-a (VDOT 21A) sieve analysis (TFHRC tests)
Table 33. Summary of AASHTO No. 8 LSDS results (DC tests)
Table 34. Summary of AASHTO No. 8 pea gravel LSDS results (DC tests)
Table 35. Summary of AASHTO No. 57 LSDS results (DC tests)
Table 36. Summary of AASHTO No. 9 LSDS results (DC tests)
Table 37. Summary of AASHTO No. 8 LSDS results (TFHRC tests)
Table 38. Summary of AASHTO A-1-a (VDOT 21A) LSDS results (TFHRC tests)
Table 39. TF-2 Nuclear density test results
Table 40. TF-2 Nuclear density test results
Table 41. TF-3 Nuclear density test results
Table 42. TF-4 Nuclear density test results
Table 43. TF-5 Nuclear density test results
Table 44. TF-6 Nuclear density test results
Table 45. TF-7 Nuclear density test results
Table 46. TF-8 Nuclear density test results
Table 47. TF-9 Nuclear density test results
Table 48. TF-10 Nuclear density test results
Table 49. TF-11 Nuclear density test results
Table 50. TF-12 Nuclear density test results
Table 51. TF-13 Nuclear density test results
Table 52. TF-14 Nuclear density test results
Table 53. DC-1 PT Data
Table 54. DC-2 PT Data
Table 55. DC-3 PT Data
Table 56. DC-4 PT Data
Table 57. DC-5 PT Data
Table 58. TF-1 PT Data
Table 59. TF-2 PT Data
Table 60. TF-3 PT Data
Table 61. TF-4 PT Data
Table 62. TF-5 PT Data
Table 63. TF-6 PT Data
Table 64. TF-7 PT Data
Table 65. TF-8 PT Data
Table 66.  TF-9 PT Data
Table 67. TF-10 PT Data
Table 68. TF-11 PT Data
Table 69. TF-12 PT Data
Table 70. TF-13 PT Data
Table 71. TF-14 PT Data

LIST OF ABBREVIATIONS AND SYMBOLS

Abbreviations

AASHTO American Association of State Highway and Transportation Officials
CMU Concrete masonry unit
DC Defiance County, OH
EDC Every Day Counts initiative
FHWA Federal Highway Administration
GP-GM Poorly graded-silty gravel
GRS Geosynthetic reinforced soil
IBS

Integrated bridge systems

LFD

Load factor design

LRFD Load and resistance factor design
LSDS Large scale direct shear
LVDT

Linear voltage displacement transducers

MARV Minimum average roll value
POT Potentiometer
PT Performance test
SRW Segmental retaining wall
TFHRC

Turner-Fairbank Highway Research Center

USCS Unified Soil Classification System

Symbols

β Reliability index
βs

Slope angle

βT Target reliability index
γ Unit weight of the backfill
γb

Bulk unit weight of the facing block

γd Maximum dry density
γD Load factor for dead load
γL Load factor for live load
γGRS Unit weight of the GRS composite
γi Load factor for load component i
δ

Interface friction angle between the geosynthetic and the facing element for a frictionally connected GRS composite

ε@q=4000psf Measured vertical strain at an applied load of 4000 psf
ε@qult Measured vertical strain at failure
εmax Maximum recorded vertical strain
εv Vertical strain
εv,compact Vertical strain for a compacted GRS composite
εv,uncompact Vertical strain for an uncompacted GRS composite
λ

Bias, ratio of measured to predicted

λD Bias factor for dead load
λL Bias factor for live load
λR Bias factor for resistance
νGRS Poisson’s ratio of the GRS
ρ Vertical displacement
σ Applied normal stress
σc External confining stress due to the facing
σh Total lateral stress within the GRS composite at a given depth and location
τ

Shear strength of soil

Φ Peak friction angle
ΦGRS Friction angle of the GRS composite
Ф

Resistance factor

Фcap Resistance factor for capacity
ω Optimum moisture content
a

Footing offset from the edge of the wall face (i.e., setback distance)

b Footing width on top of the GRS composite
B Base width of the GRS composite
Btotal Total width of the PT with the CMU facing
c Cohesion of the backfill
cGRS Cohesion of the GRS composite
Cc Coefficient of Curvature
Cu

Coefficient of Uniformity

d Depth of the facing block unit perpendicular to the wall face
dmax Maximum aggregate size
D10 Aggregate size in which 10 percent of the sample is finer
D30 Aggregate size in which 30 percent of the sample is finer
D60 Aggregate size in which 60 percent of the sample is finer
D85

Aggregate size in which 85 percent of the sample is finer

Eo Initial stress-strain ratio
Eo,CMU Initial stress-strain ratio for tests with CMU facing
Eo,noCMU Initial stress-strain ratio for tests without any facing
EGRS Young's modulus of the GRS composite
ER

Ratio of stress to strain for the reload cycle

symbol for mean safety margin

Mean safety margin

H Height of the GRS composite
Kar

Coefficient of active earth pressure for the backfill

Kpr Coefficient of passive earth pressure for the backfill
L

Length of footing/bearing area

Nγq

Bearing capacity factor

Ncq

Bearing capacity factor

Ns Stability factor
SGRS Plane strain stiffness of a strip footing on top of GRS
SPT

Stiffness of the unconfined GRS column

Sv Reinforcement spacing
Tf Wide width tensile strength of the geosynthetic, expressed as the minimum average roll value (MARV)
Treq,c Required reinforcement strength in the direction perpendicular to the wall face
q Applied stress
q@ε=0.5% Applied stress at 0.5 percent vertical strain
q@ε=0.5%,predicted Predicted applied stress at 0.5 percent vertical strain
q@ε=0.5% Applied stress at 5 percent vertical strain
qmax Maximum applied pressure during testing
qult,an,c Ultimate capacity using semi-empirical theory
qult,emp

Measured failure pressure

qult,emp CMU Measured failure pressure for tests with CMU facing
qult,emp no CMU

Measured failure pressure for tests without any facing

qult,PS Ultimate capacity of strip footing under plane strain conditions
qult,PT Ultimate capacity of the GRS column
Q Load
QD Dead load
QL Live load
Qi Load component i
R Resistance
Vdmax Coefficient of variation of the maximum aggregate size
VD Coefficient of variation of the dead load
VKp Coefficient of variation of the coefficient for passive earth pressure
VL

Coefficient of variation of the live load

VM

Coefficient of variation of the model

VQ

Coefficient of variation of the loads

VR Coefficient of variation of the resistance
VTf Coefficient of variation of the reinforcement strength
W Factor accounting for the effect of reinforcement spacing and aggregate size
z Standard normal variable
 

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