Generalized hydro-mechanically coupled hypoplastic constitutive model for unsaturated collapsible soils

In this study, a generalized hypoplastic constitutive model for unsaturated soils is presented. The constitutive model is formulated in terms of effective stresses, degree of saturation, and suction. A feature of the model is the introduction of a limiting surface (LS) in hypoplasticity, allowing for the description of the maximum achievable void ratio as a function of mean effective stress and degree of saturation. The LS allows to capture the wetting-induced collapse of initially unsaturated soils. Contrary to other models, a concept of curved normal compression lines without limiting the range of applicable stresses is proposed. The performance of the proposed model is demonstrated by back-calculation of a well-documented experimental study on over 30 samples of compacted Pearl clay under isotropic as well as triaxial loading conditions over a wide range of stresses and void ratios. For this purpose, the proposed model is coupled with a hypoplastic model for the soil-water retention curve, which interrelates the effective degree of saturation with the suction and the void ratio.