Local Calibration of Mechanistic-Empirical Pavement Design Guide for Flexible Pavement Design

This paper presents the calibration of the Mechanistic-Empirical Pavement Design Guide (MEPDG) for flexible pavements located in North Carolina. Two distress models, permanent deformation and bottom-up fatigue cracking, were used for this effort. A total of 53 pavement sections were selected from the Long-Term Pavement Performance (LTPP) program and the North Carolina Department of Transportation databases for the calibration and validation process. The verification runs for the LTPP sections performed with the parameters developed during the national calibration effort under NCHRP Project 1-37A showed promising results. The Microsoft Excel Solver program was used to fit the predicted rut depth values to the measured values by changing the coefficients in the permanent deformation models for hot-mix asphalt (HMA) and unbound materials. In this process, the sum of the squared errors was minimized for each of the permanent deformation models separately. For the alligator cracking model, the only possibility of reducing the standard error and bias was through the transfer function. Again, the Microsoft Excel Solver program was used to minimize the sum of the squared errors of the measured and the predicted cracking by varying the C₁ and C₂ parameters of the transfer function. The standard error for the HMA permanent deformation model, as well as that for the alligator cracking model, was found to be significantly less than the global standard error after the calibration. It was decided that both models would be kept for a more robust calibration in the future that would increase the number of sections and include more detailed inputs (mostly Level 1 inputs).