Clay hypoplasticity model including stiffness anisotropy

A hypoplastic model for clays is developed to predict anisotropy of very small strain stiffness. The existing hypoplastic model, with explicit formulation of the asymptotic state boundary surface, is combined with an anisotropic form of the stiffness tensor. The resulting model correctly predicts very small strain stiffness anisotropy. Trends in the anisotropy influence on undrained stress paths are also shown to be properly predicted. The model is evaluated using hollow cylinder apparatus experimental data on London Clay taken over from the literature.