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

Resilient modulus (M_r) of stabilized subgrade soil is a key input parameter in all three hierarchical levels of the mechanistic-empirical pavement design guide (MEPDG). This study evaluated M_r test data of 139 samples from four types (i.e., Carnasaw, Port, Kingfisher, and Vernon series) of soils in Oklahoma modified with different amounts of lime, class C fly ash (CFA), and cement kiln dust (CKD). Regression analyses of five selected stress-based models were conducted by using a statistical software ("SPSS", Version 17), and material constants (k₁, k₂ and k₃) for these soils were determined. The goodness of fit and the significance of these models were ranked with respect to their R² and F values, respectively. A significant increase in M^r values was observed for the selected additives. However, the extent of increase in the M^r value depends on the type of soil, and type and amount of additive. Among the selected models, the octahedral model was found to outperform the others. Furthermore, correlations of material constants with routine soil parameters were established. The findings of this study are expected to help the implementation of the MEPDG in Oklahoma and can be extended to soils from any other locations.