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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2017. Quantifying the Influence of Geosynthetics on Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24841.
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iii TABLE OF CONTENTS LIST OF FIGURES ....................................................................................................................... vi  LIST OF TABLES ......................................................................................................................... xi  CHAPTER 1. INTRODUCTION ................................................................................................... 1  Introduction ................................................................................................................................. 1  Objective ..................................................................................................................................... 1  Research Scope and Approach ................................................................................................... 1  Organization of the Report ......................................................................................................... 4  CHAPTER 2. SYNTHESIS OF CURRENT KNOWLEDGE ....................................................... 5  Laboratory Characterization of Granular Materials with Geosynthetics .................................... 5  Modeling of Pavements with Geosynthetics .............................................................................. 6  Design Methods for Pavements with Geosynthetics .................................................................. 7  CHAPTER 3. RESEARCH PLAN ................................................................................................. 9  Full-Scale Laboratory Testing .................................................................................................... 9  Triaxial Laboratory Testing ...................................................................................................... 10  Finite Element Modeling .......................................................................................................... 11  Development of ANN Models of Critical Strains and Stresses ................................................ 11  Performance Data Collection of In-Service Pavement Sections with Geosynthetics ............... 12  CHAPTER 4. EXPERIMENTS, MODELING, AND FINDINGS .............................................. 13  Introduction ............................................................................................................................... 13  Geosynthetic Application and Reinforcement Mechanisms ..................................................... 13  Available Test Methods for Evaluating Geosynthetic Properties Related to Pavement Performance .............................................................................................................................. 14  Selection of Test Methods for Determining Geosynthetic Properties ...................................... 15  Direct Tension Test to Determine Geosynthetic Sheet Stiffness .......................................... 15  Pullout Test to Determine Geosynthetic-Aggregate/Soil Interfacial Properties ................... 16  Laboratory Methodology for Quantifying Influence of Geosynthetics .................................... 17  Influence of Geosynthetics on Cross-Anisotropic Properties of UGMs ............................... 17  Influence of Geosynthetics on Permanent Deformation Properties of UGMs...................... 24  Analytical Model for Quantifying the Influence of Geosynthetics .......................................... 30  LST Test on Pavement Layers with Geosynthetics .................................................................. 34  Experimental Plan and Setup ................................................................................................ 35  Data Analysis Methodologies ............................................................................................... 43  Flexible Pavement ................................................................................................................. 43  Rigid Pavement ..................................................................................................................... 65  Finite Element Modeling of Pavements with Geosynthetics .................................................... 77  Characterization of Materials Used in LST Test .................................................................. 80  Development of Nonlinear Cross-Anisotropic User-Defined Material Subroutine .............. 85  Development of Goodman Model Friction Subroutine ........................................................ 87  Numerical Modeling Techniques for Geosynthetic-Reinforced Pavement Structures ......... 88  Effect of Geosynthetic Reinforcement on Pavement Responses .......................................... 89  Parametric Study of Material Properties on Pavement Performance .................................... 93  Comparison of Finite Element Simulations with LST Measurements ................................. 98  ANN Approach for Predicting Pavement Performance .......................................................... 105  Experimental Computational Plan for ANN Models .......................................................... 106  Development of ANN Models ............................................................................................ 107 

iv Determination of Modified Material Properties.................................................................. 113  Prediction of Pavement Performance .................................................................................. 117  Validation of the Proposed ANN Approach ....................................................................... 120  CHAPTER 5. INTERPRETATIONS, APPRAISAL, AND APPLICATIONS ......................... 124  Introduction ............................................................................................................................. 124  LST Testing Program .............................................................................................................. 124  Measurement of Geosynthetic-Aggregate/Soil Interfacial Slippage ...................................... 127  Determination of Geosynthetic-Aggregate/Soil Interfacial Properties ................................... 129  Impact of Geosynthetics on Cross-Anisotropy and Permanent Deformation of UGMs ........ 129  Mechanistic-Empirical Permanent Deformation Model for Unreinforced and Geosynthetic-Reinforced UGMs ............................................................................................ 132  Analytical Model for Quantifying Influence of Geosynthetics .............................................. 134  Development of Finite Element Model for Geosynthetic-Reinforced Pavement ................... 135  Predictions of Geosynthetic-Reinforced Pavement Performance ........................................... 136  CHAPTER 6. SUMMARY AND SUGGESTED RESEARCH ................................................. 145  Summary ................................................................................................................................. 145  Suggested Research ................................................................................................................ 146  REFERENCES ........................................................................................................................... 148  ATTACHMENT A. STANDARD METHOD OF TEST FOR DETERMINING THE PERMANENT DEFORMATION PROPERTIES OF GEOSYNTHETIC- REINFORCED AND UNREINFORCED GRANULAR MATERIAL ............................... 153  ATTACHMENT B. STANDARD METHOD OF TEST FOR DETERMINING THE CROSS-ANISOTROPIC RESILIENT MODULUS OF GEOSYNTHETIC- REINFORCED AND UNREINFORCED GRANULAR MATERIAL ............................... 157 FINAL REPORT APPENDICES ............................................................................................... 165  APPENDIX A. REVIEW OF AVAILABLE TEST METHODS FOR DETERMINING PERFORMANCE-RELATED GEOSYNTHETIC PROPERTIES ..................................... A-1  APPENDIX B. DETERMINATION OF GEOSYNTHETIC-AGGREGATE INTERFACIAL PROPERTIES USING PULLOUT TEST ................................................. B-1  APPENDIX C. LABORATORY EVALUATION OF INFLUENCE OF GEOSYNTHETICS ON CROSS-ANISOTROPY AND PERMANENT DEFORMATION OF UNBOUND GRANULAR MATERIAL ......................................... C-1  APPENDIX D. ANALYTICAL MODEL FOR QUANTIFYING INFLUENCE OF GEOSYNTHETICS .............................................................................................................. D-1  APPENDIX E. INSTRUMENTATION PLANS FOR FLEXIBLE PAVEMENT EXPERIMENTS .................................................................................................................... E-1  APPENDIX F. SUMMARY CHARTS FOR FLEXIBLE PAVEMENT EXPERIMENTS ....... F-1  APPENDIX G. FLEXIBLE PAVEMENT EXPERIMENTS: COMPARISON OF TEST MEASUREMENTS .............................................................................................................. G-1  APPENDIX H. INSTRUMENTATION PLANS FOR RIGID PAVEMENT EXPERIMENTS ................................................................................................................... H-1  APPENDIX I. ANALYSIS METHODOLOGIES OF LST TEST DATA................................... I-1  APPENDIX J. SUMMARY CHARTS OF RIGID PAVEMENT EXPERIMENTS .................. J-1  APPENDIX K. RIGID PAVEMENT EXPERIMENTS: COMPARISON OF TEST MEASUREMENTS .............................................................................................................. K-1 

v APPENDIX L. CHARACTERIZATION OF MATERIALS USED IN LST TEST ................... L-1  APPENDIX M. COMPARISON OF FINITE ELEMENT SIMULATIONS WITH LST MEASUREMENTS ............................................................................................................. M-1  APPENDIX N. DEVELOPMENT OF ARTIFICIAL NEURAL NETWORK MODELS FOR PREDICTING GEOSYNTHETIC-REINFORCED PAVEMENT PERFORMANCE ................................................................................................................. N-1  APPENDIX O. VALIDATION OF ARTIFICIAL NEURAL NETWORK APPROACH FOR PREDICTING GEOSYNTHETIC-REINFORCED PAVEMENT PERFORMANCE ................................................................................................................. O-1  APPENDIX P. LIST OF GEOSYNTHETIC-REINFORCED IN-SERVICE PAVEMENT SECTIONS IDENTIFIED FROM LONG-TERM PAVEMENT PERFORMANCE (LTPP) DATABASE AND TEXAS PAVEMENT MANAGEMENT INFORMATION SYSTEM (PMIS) ................................................................................................................... P-1 APPENDIX Q. EXAMPLES OF PROGRAM RUNS OF THE COMPOSITE GEOSYNTHETIC–BASE COURSE MODEL .................................................................... Q-1

vi LIST OF FIGURES Figure 1.1. Compatibility of Proposed Program with AASHTOWare Pavement ME Design ................................................................................................................................. 3  Figure 4.1. Mechanisms of Geosynthetics in Pavement ............................................................... 14  Figure 4.2. Schematic Plot of the Pullout Test ............................................................................. 16  Figure 4.3. Pullout Force versus Geosynthetic Displacement in a Pullout Test ........................... 17  Figure 4.4. Schematic Plot of Aggregate Specimens with/without Geosynthetic ........................ 18  Figure 4.5. Configuration of Rapid Triaxial Test ......................................................................... 19  Figure 4.6. Effect of Stress Level on Reduction of Permanent Strain .......................................... 24  Figure 4.7. Illustration of the Stress-Related Terms in the Proposed Model ................................ 26  Figure 4.8. Comparison of Lab-Measured and Proposed Model-Predicted Permanent Deformation Curves .......................................................................................................... 27  Figure 4.9. Validation of Prediction Accuracy of Proposed Permanent Deformation Model ................................................................................................................................ 28  Figure 4.10. Effect of Type of Geosynthetic on Permanent Deformation of UGM ..................... 29  Figure 4.11. Effect of Location of Geosynthetic on Permanent Deformation of UGM ............... 29  Figure 4.12. Schematic Plot of Geosynthetic Reinforcement on UGM Specimen ....................... 31  Figure 4.13. Comparison of Resilient Moduli Predicted by Analytical Models with Measured Values ............................................................................................................... 34  Figure 4.14. FWD Loading Plate Used in the LST Experiments: (a) Top View; (b) Bottom View ............................................................................................................... 36  Figure 4.15. Plastic Sheet Covering the Wave-Absorbing Material in the LST ........................... 36  Figure 4.16. Completed Large-Scale Test Setup for Flexible Pavement Experiment .................. 37  Figure 4.17. Instrumentation Plan for Flexible Pavement Experiment 4: (a) Profile View at X = 0 inch; (b) Plan View at Z = 0 inch ........................................................................ 39  Figure 4.18. Instrumentation Plan for Rigid Pavement Experiment 9: (a) Profile View at Y = 0 inch; (b) Plan View at Z = 0 inch ........................................................................... 40  Figure 4.19. Placement of the 4-inch Earth Pressure Cell in the Subgrade .................................. 41  Figure 4.20. (a) In-Place Asphalt Strain Gauge; (b) Final In-Place Asphalt Strain Gauge with Temperature Sensor .................................................................................................. 42  Figure 4.21. LST Configuration for Flexible Pavements with Thin CAB (Experiments 1, 3, and 5) Showing Only Earth Pressure Cells across Geosynthetic .................................. 47  Figure 4.22. Vertical Stresses at the Centerline of the Loading Plate for Thin CAB Layer (Experiments 1, 3, and 5) .................................................................................................. 48  Figure 4.23. Vertical Stresses at the Edge of the Loading Plate for Thin CAB Layer (Experiments 1, 3, and 5) .................................................................................................. 49  Figure 4.24. Horizontal Stresses at the Edge of the Loading Plate for Thin CAB Layer (Experiments 1, 3, and 5) .................................................................................................. 50  Figure 4.25. LST Configuration for Flexible Pavements with Thick CAB (Experiments 2, 4, and 6) Showing Only Earth Pressure Cells across Geosynthetic .................................. 50  Figure 4.26. Vertical Stresses at the Centerline of the Loading Plate for Thick CAB Layer (Experiments 2, 4, and 6) .................................................................................................. 51  Figure 4.27. Vertical Stresses at the Edge of the Loading Plate for Thick CAB Layer (Experiments 2, 4, and 6) .................................................................................................. 52  Figure 4.28. Horizontal Stresses at the Edge of the Loading Plate for Thick CAB Layer (Experiments 2, 4, and 6) .................................................................................................. 53 

vii Figure 4.29. LST Configuration for Flexible Pavements with Thin CAB (Experiments 1, 3, and 5) Showing Only the Instrumentations on and around Geosynthetic .................... 54  Figure 4.30. LST Configuration for Flexible Pavements with Thick CAB (Experiments 2, 4, and 6) Showing Only the Instrumentations on and around Geosynthetic .................... 55  Figure 4.31. Horizontal Strains in the Geosynthetic Reinforcements—Flexible Pavements: (a) Experiment 3 (geogrid); (b) Experiment 5 (geotextile) ........................... 56  Figure 4.32. Horizontal Strains in the Geosynthetic Reinforcements—Flexible Pavements: (a) Experiment 4 (geogrid); (b) Experiment 6 (geotextile) ........................... 57  Figure 4.33. Tensile Strains at the Centerline of the Load and at the Bottom of the AC Layer (Experiments 1, 3, and 5) ........................................................................................ 57  Figure 4.34. Tensile Strains at the Centerline of the Load and at the Bottom of the AC Layer (Experiments 2, 4, and 6) ........................................................................................ 58  Figure 4.35. Vertical Displacements of the Geosynthetic and Adjacent Unbound Material in Experiments 3 and 5 for Various Load Levels: (a) 9 kip; (b) 12 kip; (c) 16 kip .......... 60  Figure 4.36. Horizontal Displacements of the Geosynthetic and Adjacent Unbound Material in Experiments 1, 3, and 5 for Various Load Levels: (a) 9 kip; (b) 12 kip; (c) 16 kip ........................................................................................................................... 61  Figure 4.37. Horizontal Slippage of the Geosynthetic and Adjacent Unbound Material in Experiments 3 and 5 for Various Load Levels—Flexible Pavements .............................. 62  Figure 4.38. Vertical Displacements of the Geosynthetic and Adjacent Unbound Material in Experiments 4 and 6 for Various Load Levels: (a) 9 kip; (b) 12 kip; (c) 16 kip .......... 63  Figure 4.39. Horizontal Displacements of the Geosynthetic and Adjacent Unbound Material in Experiments 2, 4, and 6 for Various Load Levels: (a) 9 kip; (b) 12 kip; (c) 16 kip ........................................................................................................................... 64  Figure 4.40. Horizontal Slippage of the Geosynthetic and Adjacent Unbound Material in Experiments 4 and 6 for Various Load Levels—Flexible Pavements .............................. 65  Figure 4.41. LST Configuration for Rigid Pavements (Experiments 7, 9, and 10) Showing Only Earth Pressure Cells across Geosynthetic—Profile View ....................................... 68  Figure 4.42. LST Configuration for Rigid Pavements (Experiments 7, 9, and 10) Showing Only Earth Pressure Cells across Geosynthetic—Plan View at 8 inches below Pavement Surface .............................................................................................................. 68  Figure 4.43. Vertical Stresses at the Centerline of the Loading Plate for Rigid Pavements (Experiments 7, 9, and 10—Dry and Wet) ....................................................................... 69  Figure 4.44. Vertical Stresses at Two Similar Locations in the CAB across the Joint and at 8 inches from the Centerline of the Loading Plate for Rigid Pavements (Experiments 7, 9, and 10—Dry and Wet) ....................................................................... 70  Figure 4.45. Vertical and Horizontal Stresses at the Edge of the Loading Plate in the X-direction (Parallel to the Edge of the PCC Slab) for Rigid Pavements (Experiments 7, 9, and 10—Dry and Wet) ....................................................................... 71  Figure 4.46. LST Configuration for Rigid Pavements (Experiments 7, 9, and 10) Showing Only Strain Gauges on Geosynthetic—Profile View ....................................................... 72  Figure 4.47. LST Configuration for Rigid Pavements (Experiments 7, 9, and 10) Showing Only Strain Gauges on Geosynthetic—Plan View at 10 inches below Pavement Surface .............................................................................................................................. 72  Figure 4.48. Horizontal Strains in the Geogrid Reinforcement (Experiment 9)—Rigid Pavement (Dry and Wet) .................................................................................................. 73 

viii Figure 4.49. Tensile Strains in the X-direction (Parallel to the Edge of the PCC Slab) at the Centerline of the Load and at the Bottom of the PCC Layer (Experiments 7, 9, and 10) .............................................................................................................................. 74  Figure 4.50. LST Configuration for Rigid Pavements (Experiments 7, 9, and 10) Showing Only the LVDT Used for Assessing Slippage at the PCC Edge—Profile View .............. 76  Figure 4.51. LST Configuration for Rigid Pavements (Experiments 7, 9, and 10) Showing Only the LVDT Used to Assess Slippage at the PCC Edge—Plan View at 6 inches below Pavement Surface ........................................................................................ 76  Figure 4.52. PCC-CAB Interface Slippage at the Edge of the PCC Slab (Experiments 7, 9, and 10): (a) Dry Condition; (b) Wet Condition ............................................................ 77  Figure 4.53. Typical Geosynthetic-Reinforced Flexible Pavement Structure in LST Test .......... 78  Figure 4.54. Meshed Geosynthetic-Reinforced Pavement Structure in ABAQUS ...................... 78  Figure 4.55. Typical Geosynthetic-Reinforced Rigid Pavement Structure in LST Test .............. 79  Figure 4.56. Meshed Geosynthetic-Reinforced Rigid Pavement Structure in ABAQUS ............ 80  Figure 4.57. Comparison between the Measured Dynamic Moduli and the Fitted Dynamic Moduli ............................................................................................................... 83  Figure 4.58. Direct Tension Test for Determining Sheet Stiffness of Geosynthetics ................... 84  Figure 4.59. Relationships between Tensile Force and Tensile Strain for Geosynthetics ............ 85  Figure 4.60. Flowchart of the Developed UMAT Subroutine ...................................................... 87  Figure 4.61. Simulation of Lateral Confinement in Geosynthetic-Reinforced Pavement Structure ............................................................................................................................ 89  Figure 4.62. Surface Deflections of Flexible Pavement Structures with and without Geosynthetic ..................................................................................................................... 90  Figure 4.63. Vertical Stress Distribution within Geosynthetic-Reinforced and Unreinforced Flexible Base Layer .................................................................................... 91  Figure 4.64. Tensile Bending Stresses at the Bottom of the PCC Slab for the Geosynthetic-Reinforced and Unreinforced Rigid Pavements ......................................... 92  Figure 4.65. Tensile Stresses at the Top of the PCC Slab for the Geosynthetic-Reinforced and Unreinforced Rigid Pavements .................................................................................. 93  Figure 4.66. Sensitivity of Model-Predicted Pavement Responses to Subgrade Modulus ........... 95  Figure 4.67. Sensitivity of Model-Predicted Pavement Responses to Geosynthetic Sheet Stiffness............................................................................................................................. 97  Figure 4.68. Sensitivity of Model-Predicted Pavement Responses to Thickness of Base Course ............................................................................................................................... 98  Figure 4.69. Location of Instruments in Flexible Pavement Structures ....................................... 99  Figure 4.70. Location of Instruments in Rigid Pavement Structures .......................................... 100  Figure 4.71. Comparison of Measured and Predicted Surface Deflections for Pavement Structures with and without Geosynthetic ...................................................................... 101  Figure 4.72. Comparison of Measured and Predicted Tensile Strains at the Bottom of Asphalt Layer for Pavement Structures with and without Geosynthetic ........................ 102  Figure 4.73. Comparison of Measured and Predicted Vertical Stresses within the Base and Subgrade for Pavement Structures with and without Geosynthetic ......................... 103  Figure 4.74. Comparison of Measured and Predicted Surface Deflections for Rigid Pavement Structures with and without Geosynthetic ..................................................... 104  Figure 4.75. Comparison of Measured and Predicted Vertical Stresses within the Base and Subgrade for Rigid Pavement Structures with and without Geosynthetic ............... 104 

ix Figure 4.76. Illustration of Three-Layered Neural Network Architecture .................................. 108  Figure 4.77. Comparison of Tensile Strain at the Bottom of the Asphalt Layer ........................ 109  Figure 4.78. Comparison of Average Vertical Strain in the Asphalt Layer ............................... 110  Figure 4.79. Comparison of Average Vertical Strain in the Base Layer .................................... 111  Figure 4.80. Comparison of Vertical Strain at the Top of the Subgrade .................................... 112  Figure 4.81. Comparison of Vertical Strain at 6 inches below the Top of the Subgrade ........... 113  Figure 4.82. Flowchart of the Process of Predicting Pavement Performance ............................ 115  Figure 4.83. Geosynthetic-Reinforced Pavement Structures for Case Studies ........................... 116  Figure 4.84. Effect of Geosynthetic Location and Geosynthetic Type on Fatigue Cracking ..... 118  Figure 4.85. Effect of Geosynthetic Location and Geosynthetic Type on Rutting Depth .......... 119  Figure 4.86. Effect of Geosynthetic Location and Geosynthetic Type on IRI ........................... 119  Figure 4.87. Flowchart of the Process of Validating the Proposed ANN Approach .................. 121  Figure 4.88. Comparison of Rutting Depth between ANN Approach Prediction and Field Measurement for Pavement Section 16-9032 ................................................................. 122  Figure 4.89. Comparison of Fatigue Cracking between ANN Approach Prediction and Field Measurement for Pavement Section 16-9032 ........................................................ 123  Figure 4.90. Comparison of IRI between ANN Approach Prediction and Field Measurement for Pavement Section 16-9032 ................................................................. 123  Figure 5.1. Measured Horizontal Displacements of Geogrid and UGM When Geogrid Was Placed in the Middle of the Base Course ................................................................ 127  Figure 5.2. Measured Horizontal Displacements of Geogrid and UGM When Geogrid Was Placed at the Bottom of the Base Course ................................................................ 128  Figure 5.3. Measured Horizontal Displacements of Geotextile and UGM When Geotextile Was Placed in the Middle of the Base Course .............................................. 128  Figure 5.4. Measured Horizontal Displacements of Geotextile and UGM When Geotextile Was Placed at the Bottom of the Base Course .............................................. 129  Figure 5.5. Horizontal and Vertical Moduli of Unreinforced UGM at Each Stress State .......... 130  Figure 5.6. Effect of Geosynthetics on Horizontal Modulus of UGM ....................................... 130  Figure 5.7. Effect of Geosynthetics on Vertical Modulus of UGM ............................................ 131  Figure 5.8. Effect of Geosynthetics on Anisotropic Ratio of UGM ........................................... 131  Figure 5.9. Effect of Geosynthetic Reinforcement on Reducing Permanent Strain of UGMs .............................................................................................................................. 132  Figure 5.10. Comparison of Lab-Measured and Proposed-Model-Predicted Permanent Strain Curves for Unreinforced UGMs ........................................................................... 133  Figure 5.11. Comparison of Lab-Measured and Proposed Model-Predicted Permanent Strain Curves for Geogrid-Reinforced UGMs ................................................................ 133  Figure 5.12. Comparison of Lab-Measured and Proposed-Model-Predicted Permanent Strain Curves for Geotextile-Reinforced UGMs ............................................................ 134  Figure 5.13. Effect of Geosynthetic Sheet Stiffness on Predicted Horizontal Modulus of UGM ............................................................................................................................... 135  Figure 5.14. Effect of Geosynthetic Sheet Stiffness on Predicted Vertical Modulus of UGM ............................................................................................................................... 135  Figure 5.15. Effect of Base Modulus on Average Compressive Strain in Base Layer ............... 137  Figure 5.16. Effect of Base Modulus on Compressive Strain at the Top of Subgrade ............... 137  Figure 5.17. Effect of Subgrade Modulus on Average Compressive Strain in Base Layer ....... 138  Figure 5.18. Effect of Subgrade Modulus on Compressive Strain at the Top of Subgrade ........ 138 

x Figure 5.19. Effect of Tensile Sheet Stiffness of Geogrid on Average Compressive Strain in Base Layer .................................................................................................................. 139  Figure 5.20. Effect of Tensile Sheet Stiffness of Geogrid on Compressive Strain at the Top of Subgrade .............................................................................................................. 139  Figure 5.21. Effect of Base Modulus on Rutting Depth of Geosynthetic-Reinforced and Unreinforced Pavements ................................................................................................. 140  Figure 5.22. Effect of Base Modulus on Fatigue Cracking of Geosynthetic-Reinforced and Unreinforced Pavements .......................................................................................... 140  Figure 5.23. Effect of Base Modulus on IRI of Geosynthetic-Reinforced and Unreinforced Pavements ................................................................................................. 141  Figure 5.24. Effect of Subgrade Modulus on Rutting Depth of Geosynthetic-Reinforced and Unreinforced Pavements .......................................................................................... 141  Figure 5.25. Effect of Subgrade Modulus on Fatigue Cracking of Geosynthetic- Reinforced and Unreinforced Pavements ....................................................................... 142  Figure 5.26. Effect of Subgrade Modulus on IRI of Geosynthetic-Reinforced and Unreinforced Pavements ................................................................................................. 142  Figure 5.27. Effect of Sheet Stiffness of Geogrid on Rutting Depth of Reinforced Pavements ....................................................................................................................... 143  Figure 5.28. Effect of Sheet Stiffness of Geogrid on Fatigue Cracking of Reinforced Pavements ....................................................................................................................... 143  Figure 5.29. Effect of Sheet Stiffness of Geogrid on IRI of Reinforced Pavements .................. 144 

xi LIST OF TABLES Table 2.1. Summary of Finite Element Model Studies on Geosynthetic-Reinforced Pavements ........................................................................................................................... 7  Table 2.2. Summary of Design Methods for Pavements with Geosynthetics ................................ 8  Table 3.1. LST Experiment Design for Flexible Pavement .......................................................... 10  Table 3.2. LST Experiment Design for Rigid Pavement .............................................................. 10  Table 3.3. Loading Protocol for Flexible and Rigid Pavement in LST Experiments ................... 10  Table 4.1. Triaxial Test Protocol for Determining Cross-Anisotropic Properties ........................ 20  Table 4.2. Influence of Geosynthetic on Material Properties—Geosynthetic Location: Mid-Height ........................................................................................................................ 21  Table 4.3. Influence of Geosynthetic on Material Properties—Geosynthetic Location: One-Quarter below the Middle ......................................................................................... 22  Table 4.4. Influence of Geosynthetic on Material Properties—Geosynthetic Location: Bottom............................................................................................................................... 23  Table 4.5. Proposed Permanent Deformation Test Protocol—Proposed Stress Levels for Calibration of Model Coefficients .................................................................................... 26  Table 4.6. Proposed Permanent Deformation Test Protocol—Proposed Stress Levels for Validation of Model Coefficients ..................................................................................... 27  Table 4.7. Determination of Model Coefficients for the UGM with and without Geosynthetics .................................................................................................................... 28  Table 4.8. General Description of the Instrumentation Plan in LST ............................................ 38  Table 4.9. Selected Laboratory Tests for Material Characterization ............................................ 81  Table 4.10. Determined Prony-Series Model Coefficients for the Plant-Mixed, Laboratory-Compacted (PMLC) Asphalt Concrete .......................................................... 82  Table 4.11. Cross-Anisotropic Properties of the UGM Used in LST Test ................................... 83  Table 4.12. Comparison of Geosynthetic Sheet Stiffness Values between Laboratory Test and Manufacturer’s Specifications ................................................................................... 85  Table 4.13. Computed Critical Strains for Geosynthetic-Reinforced and Unreinforced Flexible Pavement Structures ........................................................................................... 92  Table 4.14. Selected Input Parameters for Geosynthetic-Reinforced Pavement Structures ....... 106  Table 4.15. Selected Input Parameters for Unreinforced Pavement Structures .......................... 107  Table 4.16. Material Properties of Geosynthetic-Reinforced Pavements for Case Studies—Material Properties of Control Pavement ........................................................ 117  Table 4.17. Material Properties of Geosynthetic-Reinforced Pavements for Case Studies—Material Properties for Geosynthetic Products ............................................... 117  Table 4.18. Determination of Modified Material Properties for Case Studies ........................... 117  Table 5.1. Summary of Specifics of LST Experiments on Flexible Pavements ......................... 125  Table 5.2. Summary of Specifics of LST Experiments on Rigid Pavements ............................. 126 

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TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 235: Quantifying the Influence of Geosynthetics on Pavement Performance develops a methodology for quantifying the influence of geosynthetics on pavement performance for use in pavement design and analysis. This project focused on the use of geosynthetics in unbound base/subbase layers or as a base/subgrade interface layer for flexible and rigid pavements. The AASHTOWare Pavement ME Design software provides a methodology for the analysis and performance prediction of pavements. However, use of geosynthetics in pavement layers and their influence on distress models have not been included in Pavement ME Design.

The Composite Geosynthetic-Base Course Model is a computer subroutine written for incorporation into the Pavement ME Design software to predict the performance of pavements with geosynthetics.

In November 2017, an errata for this publication has been issued, and corrections have been made to the version available for download.

This software is offered as is, without warranty or promise of support of any kind either expressed or implied. Under no circumstance will the National Academy of Sciences, Engineering, and Medicine or the Transportation Research Board (collectively "TRB") be liable for any loss or damage caused by the installation or operation of this product. TRB makes no representation or warranty of any kind, expressed or implied, in fact or in law, including without limitation, the warranty of merchantability or the warranty of fitness for a particular purpose, and shall not in any case be liable for any consequential or special damages.

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