A Constitutive Model for Anisotropic Sand Considering Fabric Evolution Under Proportional and Non-Proportional Loadings

A critical state plasticity model is proposed to describe the anisotropic sand behaviour under both proportional and non-proportional loading conditions. An evolving fabric tensor is introduced into the model to reflect the influence of fabric anisotropy on the stress-strain relation of sand. By employing a fabric-dependent plastic flow direction, the non-coaxial response can be simulated in a simple way. A non-proportional loading mechanism is incorporated to consider the plastic deformation induced by the stress increment tangential to the yield surface. The influence of accumulative plastic strain on the dilatancy function and plastic modulus is properly considered, enabling the model to reasonably capture the evolutions of volumetric and deviatoric strains under both drained and undrained principal stress axes rotation. The model was validated based on the simulations of experimental results for monotonic loading and pure principal stress axes rotation tests covering a wide range of conditions.