NUMERICAL SIMULATIONS OF MONOTONIC AND CYCLIC LOADING OF GRANULAR SOIL

The paper explores the use of discrete element simulations to model granular soil response to monotonic and cyclic loading. Two- and three-dimensional random arrays of quartz spheres of various diameters are used that crudely represent rounded uniform quartz sand. Computer program CONBAL, developed by the writers from existing code TRUBAL, is used. All simulated granular specimens are first isotropically consolidated, and are then subjected to monotonic drained loading or constant volume (undrained) cyclic ''simple shear'' simulations. The monotonic results exhibit similar pressure-dependent shea: strength and dilation behavior to that found in actual sands, but with the simulated specimens being stiffer and failing at a smaller strain. The simulated cyclic loading results closely resemble the ''pore water pressure'' buildup to initial liquefaction, hysteresis loop formation and degradation, ''banana loop'' shapes, and lines of phase transformation observed in sand experiments. The effect of intergranular friction coefficient mu(s), = tan phi(u) and particle rotation on the results of simulated material is also studied, and they are found to be very important.