Independent Review of the Mechanistic Empirical Pavement Design Guide and Software (2006) / Chapter Skim
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Research Results Digest 307 September 2006 C O N T E N T S PART I, 1 1 Background, 1 2 The Design Process, 3 3 Flexible Pavement Design, 5 3.1 Resilient Modulus for Subgrade, 5 3.2 HMA Complex Modulus, 5 3.3 Fatigue Cracking, 6 3.4 Rutting, 6 3.5 Thermal Cracking, 7 3.6 Other Materials, 7 4 Rigid Pavement Design, 7 4.1 JPCP Design, 7 4.2 CRCP Design, 8 5 Pavement Rehabilitation, 9 5.1 Pavement Evaluation, 10 5.2 Rehabilitation with HMA, 10 5.3 Rehabilitation with Concrete, 11 6 Design Reliability, 11 7 Design Software, 12 8 Recommendations, 13 8.1 Flexible Pavement Design, 13 8.2 Rigid Pavement Design, 13 8.3 Pavement Rehabilitation Design, 14 8.4 Software, 14 8.5 Other Matters, 14 9 Concluding Discussion, 15 PART II, 15 REFERENCES, 30 Appendix A: Brief for Review Teams, 31 Appendix B: Membership of Review Teams, 32 NCHRP Project 1-40A was an independent, comprehensive review of the Mechanistic-Empirical Pavement Design Guide (MEPDG) and companion software Version 0.7 delivered under NCHRP Project 1-37A in June 2004.
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between 1998 and 2004. This was colloquially known as the "AASHTO 2002 Design Guide," but it was not completed by 2002 and has not, to date, been adopted by AASHTO; it is now termed the MechanisticEmpirical Pavement Design Guide (MEPDG)
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marily on existing technology." This is an important point in presenting this evaluation. Since the 1-37A work began in 1998, there had been substantial progress in pavement engineering research, the findings of which were not considered for incorporation in the Guide.
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those required for the design computations. Level 2 requirements fall between these two extremes.
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cepts for various aspects of the design process and modifying them through field calibration based, almost entirely, on data from the LTPP GP sections. This approach to deriving material "models" generally involves the use of multiple regression analyses to derive material constitutive models from laboratory or field data -- an application of a philosophy that has been used extensively in the United States for many years.
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situation is derived from an estimation of load pulse duration in the HMA sublayer under consideration. Given that this assumption is inherent in the Witczak model, the conversion of loading time (t)
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field evidence shows that rutting is principally a shearing phenomenon, at least for well-constructed HMA layers, and a major output from the SHRP research supported this (18)
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are accounted for in the neural network computation environment. More documentation on top-down versus bottom-up cracking and further validation of both phenomena are needed.
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behavior and performance of pavement. The analysis procedures provide valuable guidance on the importance of key parameters affecting the performance of CRCP.
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(e.g., traffic, material properties, and structural integrity) through field and laboratory testing.
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linear scale, can be incorporated in the analysis for calculating load-induced stresses and strains. The concept is believed to be based on assumptions in the JULEA program.
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Variability and, hence, reliability has been estimated by comparing predictions with measured values from LTPP sites. Depending on the level of the input data, variability will include factors such as measurement errors and errors associated with material characterization parameters, traffic and environmental conditions, and errors associated with the model prediction algorithms.
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acteristics of HMA binders in their "as-new" state after short-term aging, are impossible to determine for an in-service pavement. The various changes proposed for the design process, which have been outlined in this report, should be incorporated into the software.
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with regard to raveling. Review the permanent warp assumptions when a granular base is used.
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