A Basic Hypoplastic Model with Fabric Evolution

The fabric anisotropy has great impacts on the behaviour of granular soils but constitutive modelling considering fabric evolution still pose difficulties. In this paper, a hypoplastic constitutive model is developed within the realm of anisotropic critical state theory. A deviatoric fabric tensor is introduced into a critical state hypoplastic enhanced by Matsuoka-Nakai failure criterion. The critical state function and failure criterion are embedded with a fabric anisotropic variable indicating fabric evolution during loading. In such way, the impacts of fabric anisotropy on the dilatant and strength behaviours can be characterized, and the conditions of fabric anisotropy are concurrently satisfied along with the traditional conditions at the critical state. Moreover, the material parameters can be readily obtained from conventional undrained triaxial compression tests without resorting to any complicated calibration procedures. The comparison between numerical simulations and experimental findings indicate that the new model is robust and can reasonably captures the salient annisotropic behaviours of geomaterials at various scenarios of different bedding angles and intermediate principal stress ratios.