DEM Simulation of Undrained Cyclic Behavior of Saturated Dense Sand Without Stress Reversals

Abstract

Two-dimensional discrete element method (DEM) is used to study the undrained behavior of dense granular materials under cyclic loading without stress reversals, and to clarify the effect of initial static shear on cyclic resistance and the underlying mechanism. A series of undrained stress-controlled cyclic triaxial tests were simulated with varying values of cyclic stress ratio (CSR) and initial static shear stress ratio (α), and the type of “residual deformation accumulation” cyclic response was identified. The evolution of internal microstructure of the granular materials was quantified using a contact-normal-based fabric tensor and the coordination number. The higher α (i.e., smaller consolidation stress ratios in tests) leads to higher stress-induced initial fabric anisotropy. The cyclic resistance of dense granular materials increases with initial fabric anisotropy. During the loading process, the dense granular materials with higher initial fabric anisotropy exhibited slower reduction in coordination number. The study shed lights on the underlying mechanism that why the presence of initial static shear is beneficial to the cyclic resistance for dense sand.