Evaluation of Mechanistic-Empirical Design Guide Input Parameters for Resilient Modulus of Subgrade Soils in Oklahoma

Resilient modulus ( M r ) of subgrade soil is a key input parameter in all three hierarchical levels of the new mechanistic-empirical pavement design guide (MEPDG). A successful implementation of the MEPDG requires a comprehensive evaluation of M r database(s) for local subgrade soils and its assessment to determine desired input parameters. To this end, a database containing subgrade M r values, index properties, standard Proctor, and unconfined compressive strengths for 712 soil samples from 39 different counties in Oklahoma was developed. A total of five stress-based regression models were evaluated using a statistical software package (“SPSS,” Version 17), and material constants (k1, k2, and k3) for these soils, categorized in accordance with the American Association of State Highway and Transportation Officials Classification system, were determined. The goodness of fit and the significance of these models were ranked with respect to their R2 and F values, respectively; the MEPDG recommended octahedral model was found to outperform the others. Furthermore, reasonably good correlations of material constants with routine soil properties were established for Level 2 analysis and design. Typical M r values of common Oklahoma soils for Level 3 analysis and design were also estimated. The findings of this study are expected to help the implementation of the MEPDG in Oklahoma.