Undrained Biaxial Simulation of Breakable Particles Using DEM-XFEM Coupling

Particle breakage and its effect on granular materials have a significant influence on the shear strength and compressibility of soil specimens. While the majority of studies have focused on the drained condition, the current research explores the particle breakage under undrained conditions. A combined discrete element method (DEM) and extended finite element approach has been used to simulate the biaxial loading. The model enables simulation of the crack propagation path and progressive strength reduction of particles in a computationally efficient approach. Moreover, a novel scheme by using variable time-steps has been employed in the DEM simulations to reduce the computational cost. The results, in qualitative agreement with those from experimental studies, show that the particle breakage causes a decrease in shear strength and dilative behavior and an increase in the induced pore water pressure. The findings indicate that the particle breakage under drained conditions is significantly higher than under the undrained conditions. The results suggest that the pore water pressure creates a “hydrostatic-cushioning effect” between particles and reduces the magnitude of the contact forces. This ultimately increases the relative density of the assembly, which increases the rate of particle breakage.