Distinct Element Simulations of Shear Rupture in Dilatant Granular Media

The development of shear rupture in granular media due to boundary deformation was captured using the distinct element method (DEM). Assemblages of nonspherical, three-dimensional particles undergoing direct shear test simulations exhibited a range of soil responses, from highly contractive to highly dilative depending on their initial void ratio as well as the applied normal stress. Arched structures of strong contact forces that are consistent with the stress-arching phenomenon developed during anchor pull-out and trapdoor simulations. Earthquake fault rupture propagation through soil varied systematically for reverse and normal faults dipping at various angles. The final shapes of the shear rupture surfaces were consistent with those expected based on a model developed through sandbox experiments. Key details of the shear rupture mechanisms during surface fault rupture were elucidated through examination of particle rotations, frictional dissipation, shear strains, volumetric strains, and contact forces. The mechanism of graben formation was shown through the reduction of the magnitude of the contact forces at the top of the soil arch that formed above the bedrock fault. DEM simulations provided useful insights into boundary deformation problems.