Constitutive Modelling of Fabric Anisotropy in Sand

Fabric and its evolution have significant effect on the mechanical behaviour of granular materials. A three-dimensional anisotropic model for granular material is proposed with proper consideration of fabric evolution. An explicit expression for the yield function is proposed in terms of the invariants and joint invariants of the stress ratio and fabric tensors. The material fabric is assumed to evolve with plastic shear deformation in a manner that its principal axes tend to become co-directional with those of the loading direction and its magnitude approaches a critical state value at large deformation. A non-coaxial and associated flow rule in the deviatoric stress space is employed based on the yield function. The model is capable of characterizing the complex anisotropic behaviour of granular materials under monotonic loading with fixed principal stress directions and meanwhile gives reasonable explanation for the micromechanical mechanism for static liquefaction and noncoaxiality between the stress and plastic strain increment axes