Two-dimensional discrete element simulation of the mechanical behavior and strain localization of anisotropic dense sands

This paper presents a microscopic investigation on the effects of initial anisotropy, drainage condition, and consolidation state on the mechanical behavior and strain localization of dense sands. Discrete element simulations with non-spherical clumps were carried out to simulate drained and undrained biaxial tests of isotropically and K-0 consolidated anisotropic sands. In drained tests, the stress-strain relationship shows an initial hardening and subsequent softening behavior, and the peak shear stress decreases as the bedding plane angle increases. K-0 consolidation has slight influence on the peak friction angle and does not affect the friction angle at zero dilatancy. In undrained tests, softening behavior occurs when the bedding plane angle is small, while for higher bedding plane angle, the strengthening response takes over. As the bedding plane angle increases, the peak friction angle decreases initially but increases afterwards. The relative displacement and rotation angle of clumps as well as the void ratio distribution within the specimen indicate the appearance of shear band. Shear bands leads to the inhomogeneous deformation field within specimens. Excessive dilation inside of shear band is produced, and it may induce re-contraction behavior under drained condition and may re-increase the pore water pressure under undrained condition. The appearance of shear band reduces the peak shear strength, and the specimen with a low bedding angle results in a larger reduction of shear strength than that from the specimen with a high bedding angle. Particle rotation mode and force chain network change along with the formation of a shear band. As the longest axis of clumped particle varies from vertical to parallel with respect to the loading direction, the majority of particle contacts inside of shear band changes from multi-point mode to single contact mode. The obtained shear band width and inclination angle were computed, and their variations with bedding angle were obtained.