Characterization of Subgrade Resilient Modulus for Pavement Design

Resilient modulus (M_r) of subgrade soil is a key design parameter in all three hierarchical levels of the new mechanistic-empirical pavement design guide (MEPDG). A successful implementation of the MEPGD requires a comprehensive M_r database for local subgrade soils and its assessment to determine desired input parameters. To this end, a database containing subgrade M_r, index properties, standard Proctor, and unconfined compressive strengths for 713 soil samples from 39 different counties in Oklahoma was developed. The M_r data was randomly divided into two datasets: (i) a "development" dataset to develop statistical models, and (ii) a "evaluation" dataset to validate these models. A total of five stress-based regression models were evaluated using a statistical software ("SPSS"; Version 17), and pertinent material constants (k₁, k₂ and k₃) were determined for these soils categorized in accordance with the AASHTO classifications. 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 stress-based model was found to outperform the others. Furthermore, reasonably good correlations of material constants along with M_r with routine soil properties were established. The findings of this study are expected to help the implementation of the MEPDG in Oklahoma.