Hydro-mechanical constitutive model for overconsolidated unsaturated soils

Based on the concept of subloading plasticity, a constitutive framework, using mean skeleton stress and effective degree of saturation as fundamental variables, is proposed for capturing coupled hydro-mechanical behaviours for overconsolidated unsaturated soils. This framework can be reduced to the Modified Cam-Clay model when suction becomes zero and the initial overconsolidation ratio (OCR) is equal to 1.0. Compared with the models in literature, the main advantage of the proposed model that it is capable of modelling the hydro-mechanical interaction behaviours of overconsolidated unsaturated soils, such as strain-hardening coupled with shear contraction for normally consolidated and lightly overconsolidated unsaturated soils, strain-softening coupled with shear dilatancy for heavily overconsolidated unsaturated soils, and the effect of OCR on the shear-induced variation in the degree of saturation. Meanwhile, the dependence of mechanical behaviours of unsaturated soils on degree of saturation can be adequately described. The performance of the presented model is illustrated through numerical examples with different initial degrees of saturation and overconsolidation ratios. Finally, the proposed model is validated against a variety of experimental data from suction-controlled triaxial compression tests.