A hydromechanical model for unsaturated soils based on state boundary hypersurface

This paper presents an elastoplastic model to estimate the hydromechanical behavior of unsaturated soils based on state boundary hypersurface. Through mechanical hypersurface, the influence of saturation on yield stress can be expressed in a full form rather than an incremental form. Two hydraulic hypersurfaces and one mechanical hypersurface are proposed to establish the model. Two hydraulic hypersurfaces, composed of degree of saturation, void ratio and matrix suction, define the plastic hydraulic boundary. The elastic hydraulic behavior of unsaturated soils can be represented by scanning lines between these two hydraulic hypersurfaces. The mechanical hypersurface, composed of degree of saturation, void ratio and effective stress, defines the plastic mechanical boundary. The elastic mechanical behavior of unsaturated soils can be represented by scanning lines below the mechanical hypersurfaces. A large number of laboratory tests are used to validated the proposed model, showing that it can reasonably capture important features of the hydromechanical behavior of unsaturated soils.