Stress-fractional model with rotational hardening for anisotropic clay

Anisotropic clays are very common in practical engineering, where their constitutive relations were usually developed based on classical plasticity theory with associated flow rule. However, the softening responses of clays under compression following anisotropic consolidation can be non-associated and state-dependent. Fractional derivative is defined based on an integral form that can consider the material state and non-associativity from the initial mathematical definition. In this study, a new anisotropic constitutive method for clay is developed by enriching the fractional plasticity with combined isotropic and rotational hardening. The developed model can consider the effect of evolving material anisotropy on the state-dependent non-associated behaviour of clay. To validate the approach, undrained and drained test results of different clays, are simulated and discussed, where a good agreement between the model simulations and test results is observed. It is also found that the material anisotropy keeps evolving with shearing, until reaching the final value at critical state.