Abstract: An elastoplastic constitutive model of unsaturated soils with capillary hysteresis and skeletal deformation coupling, is developed based on the modified Cam clay model. The new model considers the effects of matric suction and saturation on the yield stress, and can be used to describe simultaneously the elastoplastic deformation and capillary hysteresis of unsaturated soils. Based on the fact that the entry air value increases with plastic volume deformation, a formulation is developed to describe the effect of deformation on the soil-water characteristic curve. The new model can account for the effect of saturation on the prophase yield stress, properly represent the difference of soil strength under different soil-water states, and effectively describe the effect of drying/wetting history on the skeletal deformation. The simulations are compared to the experimental data available in the literature. It is shown that the new model can simulate the main mechanical features of unsaturated soil behavior.

Key words: unsaturated soil, capillary hysteresis and deformation coupling, elastoplastic constitutive model