Modeling the resilient modulus of subgrade soils with a four-parameter constitutive equation

Abstract

A new constitutive model for the resilient modulus (MR) of subgrade soils was developed in this study based on existing models. The general form of three-parameter model which is common in many constitutive equations for MR was extended here to have four parameters. The proposed model relates MR with the bulk stress, confining pressure and deviatoric stress of the soil using four coefficients. The performance of the model was tested by fitting it to an MR test data obtained from the long-term pavement performance database. A multi-variable nonlinear curve fitting was done using the SciPy library. The results showed that the model has a very good fit to the data with coefficient of determination, root mean square error and mean absolute error values of 0.94, 2.20 and 1.76, respectively. The results of the proposed model were also compared with the bulk stress model and the universal model, which is currently used by the mechanistic-empirical pavement design guide (MEPDG), and obtained to be generally better than both models. The proposed model could potentially be a good alternative to the existing constitutive models if methods for the determination of the k-coefficients could be developed.