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.