Multi-slip gradient formulation for modeling microstructure effects on shear bands in granular materials

This paper presents a higher order gradient multi-slip formulation to model the effect of inhomogeneous deformation in granular materials. The effects of heterogeneity and porosity anisotropy within the multi-slip formulation are taken into consideration through the modification of the mobilized friction. The mobilized friction is assumed to be a direct function of either the gradient of the porosity distribution or the fabric tensor. The formulation with two active slip planes was implemented into a finite element code and used to simulate biaxial shear tests on dry sand. The analysis quantifies most of the shear band characteristics observed by past experimentation. It is shown that the localization and shear band characteristics in granular materials are very much dependent on the initial fabric and slip system arrangement.