A bounding surface plasticity model for unsaturated structured soils

A bounding surface plasticity model based on the effective stress concept is presented to describe the behaviour of unsaturated structured soils subjected to hydro-mechanical loadings. The structural degradation effects on the compressive and tensile strength are considered through controlling the size of the bounding surface, allowing for a smooth transition of the response from structured to unstructured states. The structural degradation is modelled using a work hardening approach, considering both the effects of stress magnitude and accumulated plastic strain on the degradation process. A void ratio-dependent water retention model is adopted, taking the effect of hydraulic hysteresis into account. Attention is also given to the stiffening effect of a decrease in the degree of saturation on the mechanical response of unsaturated structured soils and the wetting-induced collapse. A radial mapping rule with a mobile centre of homology is adopted to capture the response of the soil under unloading–reloading conditions. The predictive capability of the model is demonstrated through the comparison of the model simulations with experimental data for different conventional laboratory tests including constant-suction oedometer and triaxial shearing and wetting tests