Estimation of Equivalent Modulus of Fine-Grained Subgrade Soil from Numerical Model

Resilient modulus of subgrade represents soil stiffness with regard to in-situ stress in a controlled laboratory environment that can be measured from repeated load triaxial test. However, the expensive and time-consuming procedure involved in its measurements induces various researchers to develop a methodology to estimate parameters analogous to the resilient modulus. Recently, the California bearing ratio (CBR) test was used to estimate equivalent modulus as the soil stiffness using a repeated load approach. The present paper proposed a rational methodology to estimate the equivalent modulus of soil (M-e) using a numerical approach. The mechanical characterization of a soil sample was investigated by conducting a CBR test, repeated load CBR (RLCBR) test, and direct shear test. Modeling of the RLCBR test was done using the MC soil model to estimate the equivalent modulus of a CBR sample that was then converted to M e under half-space boundary conditions using a finite element model (FEM). The comparison of M e with resilient modulus M r obtained from a soaked CBR sample indicated strong agreement with a coefficient of determination of 0.96, indicating that the proposed methodology provides an equivalent modulus of soil as a resilient modulus with acceptable accuracy.