Calibration of MEPDG Performance Models for Flexible Pavement Distresses to Local Conditions of Ontario

Abstract

The implementation of the American Association of State Highway and Transportation Officials (AASHTO) Mechanistical-Empirical Pavement Design requires the development of a design procedure that can be used by the agencies and engineering consultants to design new and reconstructed rigid and flexible pavements. To calibrate the design procedure for a region, a large dataset representing the particular local conditions is needed. It includes traffic, climate, site material characteristics, performance requirements and historical data. The performance models were calibrated in North America using the Long Term Pavement Database Program (LTPP), therefore, the models must be calibrated to local conditions in order to obtain more suitable parameters, formulas and predictions. It is expected that calibrated performance models using site-specific data will predict pavement performance approximated to the performance measured in the field. Gathering data related with observed distresses is essential for subsequent comparison with predicted distresses. The primary objective of this project is to calibrate the performance models of flexible pavement distresses, including total rutting (permanent deformation) and asphalt concrete (AC) bottom-up fatigue cracking, to the local conditions of new flexible pavement in Ontario, Canada. Sixteen (16) representative pavement sections from widening and reconfiguration highway projects were selected. Performance data, traffic data, structure information, materials properties and performance data were obtained from site-specific investigation and pavement design reports provided by the Ministry of Transportation Ontario (MTO). The AASHTOWare Pavement ME DesignTM was used to run the initial predictions using the global calibration coefficients. Then, the obtained predicted distresses were compared with the measured distresses to assess for local bias and goodness of fit. The analysis showed that, using the global calibration coefficients, the AASHTOWare model under predicted alligator cracking and over predicted total rutting. Statistical analysis, such as, Regression Analysis and the Microsoft Solver numerical optimization routine were used to find the regression coefficients, using the approach of minimizing the sum of squared error (SSE). Concerning alligator cracking, the local calibration factors have improved the bias and standard error of the estimate (SEE). Plots also showed that points are randomly scattered along equality line and predicted values closer to the measured values. Regarding permanent deformation (rutting), the local calibration factors have improved the bias and standard error of the estimate. The accuracy of the transfer function has increased in comparison to the use of the global calibration values, suggesting that the local calibration procedure has improved the rutting model. Analyzing the plots measured versus predicted, points are better scattered and a shift is clearly noted in the chart from global to local calibration, indicating that local calibration coefficients improved distress estimations.