Calibration and Validation of the Enhanced Integrated Climatic Model for Pavement Design (2008)

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TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2008 www.TRB.org N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 602 Subject Areas Pavement Design, Management, and Performance Calibration and Validation of the Enhanced Integrated Climatic Model for Pavement Design C. E. Zapata A N D W. N. Houston ARIZONA STATE UNIVERSITY Tempe, AZ Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. 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The members of the technical committee selected to monitor this project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. The opinions and conclusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical committee, they are not necessarily those of the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation Officials, or the Federal Highway Administration, U.S. Department of Transportation. Each report is reviewed and accepted for publication by the technical committee according to procedures established and monitored by the Transportation Research Board Executive Committee and the Governing Board of the National Research Council. 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CRP STAFF FOR NCHRP REPORT 602 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Edward T. Harrigan, Senior Program Officer Eileen P. Delaney, Director of Publications Hilary Freer, Senior Editor NCHRP PROJECT 9-23 PANEL Field of Materials and Construction—Area of Bituminous Materials Larry A. Scofield, American Concrete Pavement Association, Mesa, AZ (Chair) Hussain Bahia, University of Wisconsin–Madison, Madison, WI Luis Julian Bendana, New York State DOT, Albany, NY E. Ray Brown, US Army Corps of Engineers, Vicksburg, MS Dale S. Decker, Eagle, CO Jon A. Epps, Granite Construction Inc., Sparks, NV Eric E. Harm, Illinois DOT, Springfield, IL Dallas N. Little, Texas A&M University, College Station, TX Carl L. Monismith, University of California–Berkeley, Berkeley, CA James A. Musselman, Florida DOT, Gainesville, FL Linda M. Pierce, Washington State DOT, Olympia, WA John Bukowski, FHWA Liaison Thomas Harman, FHWA Liaison Larry L. Michael, Other Liaison Frederick Hejl, TRB Liaison C O O P E R A T I V E R E S E A R C H P R O G R A M S

This report summarizes the results of research to evaluate, calibrate, and validate the Enhanced Integrated Climatic Model (EICM) incorporated in the original Version 0.7 (July 2004 release) of the Mechanistic-Empirical Pavement Design Guide (MEPDG) software with measured materials data from the Long-Term Pavement Performance Seasonal Monitor- ing Program (LTPP SMP) pavement sections. The report further describes subsequent changes made to the EICM to improve its prediction of moisture equilibrium for granular bases. The report will be of particular interest to pavement design engineers in state high- way agencies and industry. The EICM is a one-dimensional coupled heat and moisture flow model initially devel- oped for the FHWA and adapted for use in the MEPDG developed under NCHRP Projects 1-37A and 1-40. In the MEPDG, the EICM is used to predict or simulate the changes in behavior and characteristics of pavement and unbound materials in conjunction with nat- ural cycles of environmental conditions that occur over many years of service. The objective of research conducted in NCHRP Project 9-23, “Environmental Effects in Pavement Mix and Structural Design Systems,” and reported here was to evaluate, calibrate, and validate the moisture predictive capabilities of the EICM. In particular, the equilibrium moisture condition in the EICM used in the Version 0.7 MEPDG was based on a soil suc- tion model that depends on the water table depth and on a soil-water characteristic curve (SWCC) model that is functionally dependent on simple soil properties. Prior research indi- cated that sources of error in the prediction of moisture content were primarily derived from the implementation of the Suction Model in the EICM and that a more accurate approach to soil suction computations would be through the use of the Thornthwaite Mois- ture Index (TMI). With the TMI approach, lateral infiltration is balanced with evaporation for a project-specific climatic region, potentially leading to significant improvement in the prediction of the equilibrium moisture for granular bases. NCHRP Project 9-23 was specifically aimed at improving the predictive capabilities of the EICM through the analysis of data from the LTPP SMP and other relevant field exper- iments. The variables required to run and validate the EICM were identified, as well as the variables needed to select the pavement sections for the analysis. A statistically based exper- iment for the calibration and validation of the EICM was designed, and site investigation and laboratory testing of materials from 30 LTPP sections were completed. Results of the statistical analysis of the results of the EICM validation confirmed that all its component models and, in particular, the Suction Model needed improvement and cal- ibration. The individual models were calibrated with the best dataset available, gathered from the field sites visited during the project and from the LTPP database. Individual vali- F O R E W O R D By Edward T. Harrigan Staff Officer Transportation Research Board

dation of the models showed improvement in all predictions. Finally, the individual EICM models were revised to incorporate the TMI formalism and then recalibrated and validated. This substantially improved version of the EICM was incorporated in Version 1.0 (June 2007 release) of the MEPDG software developed in NCHRP Project 1-40D. This report is an abridgement of the contractor’s final report for Part II of NCHRP 9-23. The full text of the Part II final report and its six appendixes listed below are available online through a link at http://www.trb.org/TRBNet/ProjectDisplay.asp?ProjectID=959: 1. Appendix A. Detailed Field Information 2. Appendix B. Measured Soil Water Characteristic Curves 3. Appendix C. Measured Moisture And Field Density For Field Sites 4. Appendix D. TDR Moisture Content Data From Database 5. Appendix E. Measured Versus Predicted Water Content—Stage IV Runs 6. Appendix F. Sections With Measured TDR Moisture Content That Do Not Correspond To Equilibrium Conditions.

C O N T E N T S 1 Chapter 1 Introduction 1 1.1 Statement of the Problem 1 1.2 Current Knowledge 1 1.2.1 Enhanced Integrated Climatic Model 2 1.2.2 Moisture Content Changes 2 1.2.3 Effects of Temperature 3 1.3 Organization of the Report 4 Chapter 2 Experiment Design for Calibration and Validation of the ICM Version 2.6 (EICM) 4 2.1 Introduction 4 2.2 Parameters Needed for the Calibration and Validation of the EICM 4 2.2.1 Input Parameters Needed to Run and Evaluate the EICM 7 2.2.2 Variables Needed for the Validation of the EICM 7 2.2.3 Variables Needed for Site Selection 8 2.2.4 Available Databases 8 2.2.5 Selection of the Sections for Analysis 13 Chapter 3 Field and Laboratory Sampling and Testing 13 3.1 Field Sampling and Testing 13 3.1.1 Gathering Initial Site Information 13 3.1.2 Pavement Coring 14 3.1.3 Sand Cone Tests on Granular Base 14 3.1.4 Tube Sampling 14 3.1.5 Side Samples and Disturbed Samples 14 3.1.6 Moisture Content near Cracks 16 3.2 Data Collection from Existing Databases 16 3.2.1 Parameters Required to Run the EICM 17 3.2.2 Parameters Required to Validate the EICM 19 3.3 Laboratory Testing Program 20 3.3.1 Moisture Content and Dry Density 20 3.3.2 Grain Size Distribution 21 3.3.3 Atterberg Limits 21 3.3.4 Specific Gravity 21 3.3.5 Saturated Hydraulic Conductivity 22 3.3.6 Hydraulic Conductivity on Asphalt Cores 22 3.3.7 Soil-Water Characteristic Curves 24 Chapter 4 Evaluation of the Enhanced Integrated Climatic Model 24 4.1 Introduction 24 4.2 Gathering Data 24 4.3 EICM Runs

24 4.3.1 Stage I Runs 24 4.3.2 Stage II Runs 25 4.3.3 Stage III Runs 25 4.3.4 Stage IV Runs 25 4.4 EICM Runs Within the MEPDG Hierarchical Levels of Analysis 26 4.5 Statistical Analysis 27 4.5.1 Stage I Analysis 29 4.5.2 Stage II Analysis 33 4.5.3 Stage III Analysis 37 4.5.4 Stage IV Analysis 42 Chapter 5 Calibration of the Enhanced Integrated Climatic Model 42 5.1 SWCC Model Calibration 42 5.1.1 Background 43 5.1.2 Existing SWCC Models 44 5.1.3 Method Adopted in Developing a New Set of SWCCs 45 5.1.4 Correlation Parameters and Curve Fitting Procedure 46 5.1.5 Application of Volume-Change Correction 46 5.1.6 Databases Used in SWCC Model Calibration 47 5.1.7 Correlation Equations for Nonplastic Soils 48 5.1.8 Correlation Equations for Plastic Soils 48 5.1.9 Error Analysis 48 5.2 Gs Model Calibration 48 5.2.1 Gs Model Currently Implemented into the EICM 49 5.2.2 New Gs Model for Nonplastic Soils 50 5.2.3 New Gs Model for Plastic Soils 50 5.2.4 Sensitivity Analysis of Gs Model for Nonplastic Soils 51 5.2.5 Sensitivity Analysis of Gs Model for Plastic Soils 51 5.2.6 Summary 54 5.3 K-Sat Model Calibration 54 5.3.1 K-Sat Model Currently Implemented in EICM Version 2.6 55 5.3.2 Validation of the K-Sat Model Implemented in EICM Version 2.6 55 5.3.3 Development of a New K-Sat Model 57 5.4 Compaction Model Calibration 58 5.4.1 Compaction Model Currently Implemented in the EICM Version 2.6 58 5.4.2 Improvement to the Compaction Model 59 Chapter 6 Summary and Conclusions 61 References