Evaluation of stress and strain non-uniformity during cyclic simple shear test using DEM: effect of the horizontal platen asperities

Direct simple shear apparatus has been increasingly used to determine cyclic soil properties. Stress and strain non-uniformity inside the specimen, however, can be considered the main drawback in cyclic simple shear tests. In the current study, 3D discrete element method is employed to evaluate the effect of the shape of the horizontal surface asperities on the stress and strain distribution inside the constant volume specimen in stacked-ring simple shear device during cyclic loading. It was observed that limiting the potential slippage at the interface of the horizontal boundaries and particles, the stress ratio distributes more uniformly inside the specimen. Different types of asperities could cause different patterns as well as different degrees of strain non-uniformity inside the constant volume DSS specimens. The shear and volumetric strain non-uniformity grows with the number of cycles across all of the specimens. Overall, it was concluded that one could assure a uniform stress and strain distribution by preventing the slippage at the interface. However, limiting the degree of non-uniformity across the specimen demands close consideration of boundary condition.