A 3D elastic-plastic-viscous constitutive model for soils considering the stress path dependency

In order to consider the stress path dependency of soils, this paper decomposes any arbitrary stress path into several infinitesimal stress paths. Then the infinitesimal stress path is further transformed into the superposition of two parts, i.e., a constant stress ratio part and a constant mean stress part, which are sufficiently close to the real stress path. The plastic strain increments under the transformed paths are determined separately, and then the plastic strain under any path is obtained. Based on the instantaneous loading line of normally consolidated soil, a reference state line is proposed to determine the overconsolidation ratio and creep time of soil. The overconsolidation ratio is introduced into the viscous flow rule to obtain the viscous strain increment. The stress-strain-time relationship for triaxial compression condition is extended to 3D stress condition by the transformed stress method. The proposed model adopts only seven material parameters and each of them has a clear physical meaning. Comparisons with test results demonstrate that the model can not only reasonably predict the plastic strain under typical stress paths of excavation, but adequately capture the time-dependent behaviours of soils, including creep, stress relaxation and strain rate effect.