Anisotropic sand model and fabric evolution until the critical state

This paper presents a simple anisotropic sand model within a recently proposed anisotropic critical state theory (ACST). The model adopts the SANISAND constitutive model platform and uses a fundamental ingredient of ACST, namely the fabric anisotropy variable A that equals the first joint invariant of properly defined and evolving deviatoric fabric and loading direction tensors. The A evolves towards its critical state value that constitutes a concurrent additional requirement to that of critical stress-ratio and void-ratio, for attaining critical state. The A is used for the definition of evolving dilatancy state lines that delineate contractive and dilative states in the void ratio - mean effective stress space, the plastic modulus and the evolution equation of the fabric tensor. Since the development is within ACST, the thermodynamically consistent uniqueness of the critical state line is guaranteed. The model is shown to be capable of simulating the anisotropic behavior of sands, based on comparisons to Toyoura sand experiments.