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NCHRP Web-Only Document 264: Proposed Enhancements to Pavement ME Design: Improved Consideration of the Influence of Subgrade and Unbound Layers on Pavement Performance Robert L. Lytton Xue Luo Sajib Saha Yu Chen Yong Deng Fan Gu Meng Ling Texas A&M Transportation Institute The Texas A&M University System College Station, TX Contractorâs Final Report for NCHRP Project 01-53 Submitted February 2019 ACKNOWLEDGMENT This work was sponsored by the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the Federal Highway Administration, and was conducted in the National Cooperative Highway Research Program (NCHRP), which is administered by the Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, or TDC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research. They are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; or the program sponsors. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.
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CÂ OÂ OÂ PÂ EÂ RÂ AÂ TÂ IÂ VÂ EÂ RÂ EÂ SÂ EÂ AÂ RÂ CÂ HÂ PÂ RÂ OÂ GÂ RÂ AÂ MÂ SÂ CRP STAFF FOR NCHRP Web-Only Document 264 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Amir N. Hanna, Senior Program Officer Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications Kathleen Mion, Senior Editorial Assistant NCHRP PROJECT 01-53 PANEL Field of DesignâArea of Pavements Zhong Wu, Louisiana DOTD, Baton Rouge, LA (Chair) Mohammad A. Ahammed, Manitoba Infrastructure and Transportation, Winnipeg, MB Judith Corley-Lay, Michigan State University, East Lansing, MI (formerly with North Carolina DOT) Richard Y. Ji, Federal Aviation Administration, Atlantic City, NJ Jianhua Li, Washington State DOT, Issaquah, WA Mehdi Parvini, California DOT, El Dorado Hills, CA Iliya R. Yut, Connecticut Transportation Institute, Storres, CT Y. Jane Jiang, FHWA Liaison Nancy M. Whiting, TRB Liaison
v Contents CHAPTER 1. INTRODUCTION ................................................................................................... 1Â Introduction ................................................................................................................................. 1Â Objective ..................................................................................................................................... 1Â Research Scope and Approach ................................................................................................... 1Â Organization of the Report ......................................................................................................... 1Â CHAPTER 2. SYNTHESIS OF CURRENT KNOWLEDGE ....................................................... 3Â Characteristics of Unbound Layers and Subgrade Used in Pavement ME Design .................... 3Â Influence of Unbound Layers and Subgrade on Performance of Flexible and Rigid Pavements ................................................................................................................................... 5Â Unbound Layer and Subgrade Models for Performance Influence .......................................... 10Â CHAPTER 3. RESEARCH PLAN ............................................................................................... 18Â Evaluation and Screening of Unbound Layer and Subgrade Models ....................................... 18Â Soil Water Characteristics Curve of Base and Subgrade for Flexible and Rigid Pavements ................................................................................................................................. 18Â Equilibrium Suction of Base and Subgrade for Flexible and Rigid Pavements ....................... 19Â Resilient Modulus of Base and Subgrade for Flexible and Rigid Pavements .......................... 19Â Modulus of Subgrade Reaction for Rigid Pavements ............................................................... 19Â Shear Strength of Base and Subgrade Layers for Flexible and Rigid Pavements .................... 20Â Permanent Deformation of Base and Subgrade Layers for Flexible and Rigid Pavements ................................................................................................................................. 20Â Faulting of Base for Rigid Pavements ...................................................................................... 20Â Prediction of Pavement Performance and Sensitivity Analysis ................................................ 21Â CHAPTER 4. FINDINGS ............................................................................................................. 23Â Introduction ............................................................................................................................... 23Â SWCC of Base and Subgrade for Flexible and Rigid Pavements ............................................ 23Â Development of ANN Models .............................................................................................. 24Â Prediction of SWCC Fitting Parameters Using ANN Model ............................................... 26Â Comparison of ANN Model with Other Regression Models ................................................ 29Â Validation of the Developed ANN Models........................................................................... 33Â Equilibrium Suction of Base and Subgrade for Flexible and Rigid Pavements ....................... 37Â GIS-Based Map of TMI ........................................................................................................ 38Â Relationship between TMI and Equilibrium Suction ............................................................ 42Â Resilient Modulus of Base and Subgrade for Flexible and Rigid Pavements .......................... 44Â Prediction of Suction at Test Specimen Water Content ........................................................ 46Â Development of ANN Models for MR Model Coefficients .................................................. 48Â Prediction of MR Model Coefficients Using ANN Model .................................................... 49Â Comparison of ANN Model with Other Regression Models ................................................ 53Â Validation of the Developed ANN Models........................................................................... 56Â Modulus of Subgrade Reaction for Rigid Pavements ............................................................... 57Â Development of Modified k-value Model ............................................................................ 59Â Estimation of Modified k-value for LTP Pavement Sections ............................................... 64Â
vi Development of ANN Model ................................................................................................ 69Â Shear Strength of Base and Subgrade for Flexible and Rigid Pavements ................................ 74Â Prediction Model for Unbound Base .................................................................................... 75Â Prediction Model for Subgrade ............................................................................................. 76Â Permanent Deformation of Base and Subgrade for Flexible and Rigid Pavements ................. 78Â Mechanistic-Empirical Permanent Deformation Model for Unbound Materials ................. 78Â Regression Models for Permanent Deformation Model Coefficients for Unbound Base Layers ........................................................................................................................... 80Â Faulting of Base Layer for Rigid Pavements ............................................................................ 82Â Illustration of Development of Faulting ............................................................................... 82Â Development of Faulting Model in Jointed Concrete Pavement .......................................... 83Â Model Development for Entire Faulting Progression ........................................................... 84Â Critical Faulting Depth Model .............................................................................................. 84Â Use of LTPP Data for Entire Faulting Progression............................................................... 85Â Comparison between Measured and Predicted Faulting ....................................................... 85Â Calibration of Model for Entire Faulting Progression .......................................................... 86Â Faulting Modeling Based on Permanent Deformation Characterization .............................. 91Â Determination of Stress State in the Faulting Model ............................................................ 93Â Categorization of Traffic Loads ............................................................................................ 93Â Comparison between Measured and Predicted Faulting Based on Permanent Deformation Characterization ............................................................................................... 94Â Calibration of Model for Faulting on Deformation Characterization ................................... 94Â CHAPTER 5. INTERPRETATIONS, APPRAISAL, AND APPLICATIONS ........................... 97Â Introduction ............................................................................................................................... 97Â Moisture-Sensitive, Stress-Dependent, and Cross-Anisotropic Resilient Modulus ................. 97Â FE Model of Pavement Structures ............................................................................................ 97Â Pavement Performance Predicted by the Proposed Model and Pavement ME Design Model ...................................................................................................................................... 101Â Fatigue Cracking in Asphalt Mixtures ................................................................................ 101Â Permanent Deformation in the Base Layer ......................................................................... 102Â Comparisons of Proposed Models and Pavement ME Design Models .................................. 104Â Check the Nonlinearity of the Unbound Granular Base ..................................................... 104Â Check the Anisotropy of the Unbound Granular Base ....................................................... 105Â Check the Nonlinearity of the Subgrade ............................................................................. 106Â Comparison of Resilient Modulus Models for Unbound Granular Base ............................ 107Â Comparison of Rutting Models in Unbound Granular Base ............................................... 107Â Sensitivity Analysis of Proposed Models and Pavement ME Design Models ....................... 108Â Different Loading Levels .................................................................................................... 108Â Different Thicknesses of the Asphalt Layer ....................................................................... 109Â Different Thicknesses of the Base Layer ............................................................................ 109Â Different Moisture Conditions of the Base Layer ............................................................... 110Â Sensitivity Analysis of Proposed Faulting Models ................................................................. 111Â Use of Dowel ...................................................................................................................... 112Â Type of Base Layer ............................................................................................................. 113Â Thickness of Base Layer ..................................................................................................... 114Â
vii Freeze-Thaw Cycles ............................................................................................................ 114 Annual Average Number of Days with Temperature Greater than 32°C ........................... 115 Effect of Climatic Zone ...................................................................................................... 116 Sensitivity Analysis of Proposed Modulus of Subgrade Reaction Model .............................. 116 Sensitivity Analysis of Rigid Pavement Performance to Proposed Models ........................... 121 CHAPTER 6. SUMMARY ......................................................................................................... 126 Conclusions ............................................................................................................................. 126 Soil Water Characteristics Curve of Base and Subgrade for Flexible and Rigid Pavements ........................................................................................................................... 126 Resilient Modulus of Base and Subgrade for Flexible and Rigid Pavements .................... 127 Modulus of Subgrade Reaction for Rigid Pavements ......................................................... 127 Faulting of Base Layer for Rigid Pavements ...................................................................... 128 Prediction of Pavement Performance and Sensitivity Analysis .......................................... 129 Future Work and Recommendations ...................................................................................... 130 REFERENCES ........................................................................................................................... 131 Appendix A. Annotated Bibliography of Influence of Unbound Layers and Subgrade ............. A-1 Appendix B. Definitions of Model Parameters of Unbound Layer and Subgrade Models ........ B-1 Appendix C. Evaluation and Screening of Unbound Layer and Subgrade Models .................... C-1 Appendix D. Moisture-Sensitive, Stress-Dependent, and Cross-Anisotropic Resilient Modulus ............................................................................................................................. D-1 Appendix E. Slab-Base Interface Shear Bonding Model ............................................................. E-1 Appendix F. Sensitivity Analysis of Modulus of Subgrade Reaction Model .............................. F-1 Appendix G. Determination of Stress State in the Faulting Model ............................................ G-1 Appendix H. Categorization of Traffic Loads State in the Faulting Model ............................... H-1 Appendix I. Subgrade Subroutine for Flexible and Rigid Pavements .......................................... I-1 Appendix J. Unbound Base Course Subroutine for Flexible Pavements ..................................... J-1 Appendix K. Unbound Base Course Subroutine for Rigid Pavements ...................................... K-1 Appendix L. Rigid Pavement Structure Model Subroutine ......................................................... L-1 Appendix M. Conversion 2-Layer Model for Rigid Pavements Subroutine ............................. M-1
ix List of Figures and Tables Table 1. Inputs from Unbound Layers and Subgrade in Pavement ME Design. ............................ 4Â Table 2. Influential Factors of Unbound Layers on Performance of Flexible Pavements. ............. 6Â Table 3. Influential Factors of Unbound Layers on Performance of Rigid Pavements. ................. 7Â Table 4. Influential Factors of Subgrade on Performance of Flexible Pavements. ........................ 8Â Table 5. Influential Factors of Subgrade on Performance of Rigid Pavements. ............................. 9Â Table 6. Modulus Models of Unbound Layers and Subgrade. ..................................................... 11Â Table 7. Permanent Deformation Models of Unbound Layers and Subgrade. ............................. 13Â Table 8. Shear Strength Models of Unbound Layers and Subgrade. ............................................ 15Â Table 9. Erosion Models of Unbound Layers. .............................................................................. 16Â Table 10. Foundation Models of Subgrade. .................................................................................. 16Â Table 11. Thickness Sensitive Models of Unbound Layers. ........................................................ 17Â Figure 1. Illustration of Three-Layered Neural Network Architecture. ........................................ 26Â Figure 2. Comparison of Measured versus Predicted SWCC Fitting Parameters Using ANN Model for Plastic Soils. ........................................................................................... 28Â Figure 3. Comparison of Measured versus Predicted SWCC Fitting Parameters Using ANN Model for Non-plastic Soils. ................................................................................... 29Â Table 12. List of Existing SWCC Fitting Parameter Prediction Models. ..................................... 30Â Table 13. Prediction Accuracy of SWCC Fitting Parameter Models. .......................................... 31Â Figure 4. Comparison of Measured versus Predicted Suction at Various Saturation Levels for Plastic Soils. ................................................................................................................ 32Â Figure 5. Comparison of Measured versus Predicted Suction at Various Saturation Levels for Non-plastic Soils. ........................................................................................................ 33Â Figure 6. Validation of Measured versus Predicted SWCC Fitting Parameters Using ANN Model for Plastic Soils. ..................................................................................................... 34Â Figure 7. Validation of Measured versus Predicted SWCC Fitting Parameters Using ANN Model for Non-plastic Soils. ............................................................................................. 35Â Figure 8. Validation of Measured versus ANN Predicted Suction at Various Saturation Levels for Unbound Materials. ......................................................................................... 36Â Table 14. Input Parameters Collected from Literature for Model Validation. ............................. 36Â Figure 9. Comparison of Measured versus Predicted SWCC Curves for Unbound Materials. .......................................................................................................................... 37Â Figure 10. TMI Distribution in United States (121). .................................................................... 38Â Figure 11. Average Annual (a) Precipitation; (b) Mean Temperature GIS Map (1981 to 2010). ................................................................................................................................ 39Â Figure 12. Average Annual Potential Evapotranspiration GIS Map (1981 to 2010). ................... 40Â Figure 13. GIS Based Contour Map of TMI (1981 to 2010). ....................................................... 41Â Figure 14. GIS Based Equilibrium Suction Map. ......................................................................... 42Â Figure 15. TMI versus Equilibrium Suction (pF) (cm) for (a) A-1; (b) A-2; (c) A-3; (d) A-4; (e) A-6; and (f) A-7-6 Soil. ....................................................................................... 43Â Figure 16. Calculated versus Predicted Equilibrium Suction (pF). .............................................. 44Â Figure 17. Comparison of Measured versus Predicted Saturation (%) at 0.1, 0.33, and 15 Bars Suction Level for Unbound Granular Base Materials Using ANN Model. .............. 47Â Figure 18. Illustration of Three-Layered Neural Network Architecture (a) Plastic; (b) Non-plastic Soil. ............................................................................................................... 49Â
x Figure 19. Predicted MR Model Coefficients of Plastic Base Materials from Physical Properties Using the ANN Approach. .............................................................................. 50Â Figure 20. Predicted MR Model Coefficients of Plastic Subgrade Materials from Physical Properties Using the ANN Approach. .............................................................................. 51Â Figure 21. Predicted MR Model Coefficients for Non-plastic Base Materials from Physical Properties Using the ANN Approach. ................................................................ 52Â Figure 22. Predicted MR Model Coefficients for Non-plastic Subgrade Materials from Physical Properties Using ANN Approach. ...................................................................... 53Â Table 15. Prediction Accuracy of SWCC Fitting Parameter Models. .......................................... 54Â Figure 23. Comparison of ANN Model Predicted Resilient Moduli against Measured Values for Base Materials. ................................................................................................ 55Â Figure 24. Comparison of ANN Model Predicted Resilient Moduli against Measured Values for Subgrade Materials. ......................................................................................... 55Â Figure 25. Comparison of Measured versus Predicted Resilient Moduli Using Regression Models............................................................................................................................... 56Â Table 16. Input Parameters Collected from Literature for Model Validation. ............................. 57Â Figure 26. Validation of Measured versus ANN Predicted MR at Various Stress Levels for Collected Unbound Materials. .......................................................................................... 57Â Figure 27. Foundation Models for Rigid Pavement (a) Winkler Model; (b) Pasternak Model. ............................................................................................................................... 58Â Figure 28. Flowchart of Corrected Base Modulus due to Cross Anisotropy. ............................... 61Â Figure 29. Illustration of Transformed-Section Method for a Cooperated Concrete Slab and Base Course System. .................................................................................................. 62Â Table 17. Steps of Moment of Inertia Calculation for a Cooperated Slab and Base System. .............................................................................................................................. 62Â Figure 30. Illustration of In-situ Shear Stress in the Base Course on the PCC-Base Interface Using a Mohr-Coulomb Failure Envelope. ....................................................... 63Â Table 18. Collected MR Coefficients and the Simulated Stress Values at the Mid Depth of Base Layer for LTPP Section 27-4054. ............................................................................ 65Â Figure 31. Base Resilient Modulus Convergence with Iteration Number. ................................... 65Â Figure 32. Formulation of Friction Angle from Mohr Coulomb Failure Envelope for (a) Treated Base; (b) Unbound Base. ..................................................................................... 66Â Figure 33. Comparison of Calculated Slab-Base Interface Degree of Bonding Ratio with the BBF Approach for (a) Treated Base; and (b) Unbound Base Layer. .......................... 68Â Figure 34. Sensitivity of Slab-Base Degree of Bonding on Wheelpath Fault (mm). ................... 68Â Figure 35. Comparison of Modified versus LTPP k-values. ........................................................ 69Â Figure 36. (a) Schematic Plot of a Typical Pavement Structure; (b) Axisymmetric Model of Pavement in ABAQUS. ................................................................................................ 71Â Table 19. Selected Range of Input Parameters in ANN Training Data Set. ................................. 72Â Figure 37. Illustration of Three-Layered Neural Network Architecture for k-values. ................. 72Â Figure 38. Target and Output k-values for Training, Validation, and Overall Data Sets for 1296 Simulation Cases. ..................................................................................................... 73Â Figure 39. Comparison of Calculated versus Predicted Modified k-values. ................................ 73Â Figure 40. Modified k-values at 0, 0.3, 0.6, and 1 Degree of Bonding for Selected LTPP Pavement Sections. ........................................................................................................... 74Â
xi Figure 41. Schematic Plot of Mohrâs Circle Showing Dependence of Shear Strength on Matric Suction. .................................................................................................................. 75 Figure 42. Comparison of Predicted and Measured Shear Strength Model Parameters (a) câ and (b) Ïâ. ..................................................................................................................... 76 Figure 43. Illustration of Three-Layer Neural Network Architecture to Predict câ Parameter. ......................................................................................................................... 77 Figure 44. Target and Output câ Values for Training, Validation, and Overall Data Sets for 432 Subgrade Soils. ..................................................................................................... 78 Figure 45. Comparison of Predicted and Measured Permanent Deformation Model Parameters (a) 0ï¥ , (b) ï² , (c) ï¢ , (d) m, and (e) n. ........................................................... 81 Figure 46. Schematically Illustration of the Development of Faulting. ....................................... 83 Figure 47. Illustration of Field Faulting Data, including the Critical Faulting Depth. ................. 84 Figure 48. Comparison between Measured and Predicted Faulting Depth. ................................. 86 Table 20. Results of Multiple Regression Analysis for Coefficients in the First Faulting Model. ............................................................................................................................... 88 Figure 49. Comparison between Measured and Predicted Coefficients in Faulting Model. ........ 89 Figure 50. Comparison between Measured and Predicted Faulting at Inflection Point. .............. 90 Table 21. Results of Multiple Regression Analysis for Faulting at Inflection Point. ................... 90 Figure 51. Mean Critical Faulting Depth with or without Dowels. .............................................. 91 Figure 52. Plastic Deformation Curve before the Inflection Point. .............................................. 92 Figure 53. Comparison between Measured versus Predicted Faulting before Critical Depth. ................................................................................................................................ 94 Table 22. Results of Multiple Regression Analysis for Coefficients in the Load-Related Faulting Model. ................................................................................................................. 95 Figure 54. Comparison between Measured and Predicted Coefficients in the Permanent Deformation Faulting Model. ........................................................................................... 96 Figure 55. The 2D Axisymmetric Model Used in FE Analysis. ................................................... 98 Table 23. Material Properties of Pavement Layers. ...................................................................... 98 Table 24. Example of Base Material Information. ....................................................................... 99 Table 25. Material Parameters of Pavement Layers. .................................................................. 101 Figure 56. (a) Tensile Strain at the Bottom of the Surface and (b) Average Compressive Strain in the Centerline of the Base under Different Loading Levels. ............................ 104 Figure 57. Vertical Modulus Contours in the Base Layer under the Loading Level (a) 201 kPa, (b) 566 kPa, (c) 756 kPa, and (d) 1006 kPa (Unit: MPa)................................. 105 Figure 58. Vertical Modulus Contours in the Base Layer at (a) Dry Condition, (b) Medium Condition, and (c) Wet Condition (unit: MPa). ................................................ 105 Figure 59. (a) Tensile Strain at the Bottom of the Surface; (b) Compressive Strain at the top of the Subgrade the Pavement with Different Anisotropy (1/n) of Base Layers. ..... 106 Figure 60. Vertical Modulus Contours in the Subgrade at Different Loading Levels. ............... 106 Table 26. Base Material Information for Rut Depth Calculation. .............................................. 107 Figure 61. Rut Depth in the Base Layer Using Different Models. ............................................. 107 Figure 62. Pavement Performance Including (a) Load Repetitions to the Fatigue Cracking Failure; (b) Rut Depth in the Base at Different Loading Levels. .................................... 108 Figure 63. Pavement Performance Including (a) Load Repetitions to the Fatigue Cracking Failure; (b) Rut Depth in the Base at Different Thickness of the Asphalt Layer. .......... 109Â
xii Figure 64. Pavement Performance Including (a) Load Repetitions to the Fatigue Cracking Failure and (b) Rut Depth in the Base at Different Thickness of the Base Layer. ......... 110 Figure 65. Pavement Performance Including (a) Load Repetitions to the Fatigue Cracking Failure and (b) Rut Depth in the Base at Different Moisture Conditions of the Base Layer. ..................................................................................................................... 111 Figure 66. Pavement Structure for LTPP Section 1-3028. ......................................................... 112 Table 27. Basic Information of LTPP Section 1-3028 for Sensitivity Analysis. ........................ 112 Figure 67. Effect of Use of Dowels on Faulting Based on (a) Full Faulting Model and (b) Load-Related Faulting Model. ........................................................................................ 113 Figure 68. Effect of Types of Base Layer on Faulting Based on (a) Full Faulting Model and (b) Load-Related Faulting Model. ............................................................................ 113 Figure 69. Effect of Thickness of Base Layer on Faulting Based on (a) Full Faulting Model and (b) Load-Related Faulting Model. ................................................................ 114 Figure 70. Effect of Freeze-Thaw Cycles on Faulting Based on (a) Full Faulting Model and (b) Load-Related Faulting Model. ............................................................................ 115 Figure 71. Effect of Number of Days with Temperature Greater than 32°C on Faulting Based on (a) Full Faulting Model and (b) Load-Related Faulting Model. ..................... 115 Figure 72. Effect of Climatic Zone on Faulting Based on (a) First Faulting Model and (b) Second Faulting Model. .................................................................................................. 116 Table 28. Selected LTPP Pavement Sections and FWD Backcalculated Modulus Values for Each Layer. ................................................................................................................ 117 Table 29. Calculated MR Values at the Mid-depth of Base Layer at Different Moisture Conditions. ...................................................................................................................... 118 Figure 73. Sensitivity of Degree of Bonding on Subgrade k-value Using (a) ANN Model and (b) Pavement ME Design Model. ............................................................................. 119 Figure 74. Sensitivity of Moisture on Subgrade k-value Using (a) ANN Model and (b) Pavement ME Design Model. ......................................................................................... 120 Figure 75. PCC Slab-Base Interface Bond Sensitivity on (a) Tensile Stress at Top of Slab; (b) Tensile Stress at Bottom of Slab; and (c) Deferential Deflection on Transverse Joints. .............................................................................................................................. 123 Figure 76. Base Layer Moisture Sensitivity on (a) Tensile Stress at Top of Slab; (b) Tensile Stress at Bottom of Slab; and (c) Deferential Deflection on Transverse Joints. .............................................................................................................................. 125Â