CFD-DEM modeling of suffusion effect on undrained behavior of internally unstable soils

Abstract

Abstract This paper investigates the effect of suffusion on the undrained behavior of an internally unstable soil using the coupled computational fluid dynamics and discrete element method (CFD-DEM). A series of eroded specimens are prepared by exerting an upward flow through the granular assembly under a range of hydraulic gradients and suffusion durations. Both the eroded and non-eroded specimens are then subjected to undrained triaxial compression (or equivalently constant volume tests). The results indicate that the erosion rate and volumetric response of the soil skeleton are closely related to the hydraulic conditions. The eroded specimens exhibit a non-uniform distribution of fine particles, higher coordination numbers, higher global void ratio, and lower equivalent intergranular void ratio. The undrained behavior of the specimen changes from a strain hardening behavior before suffusion to a softening behavior with limited flow deformation after suffusion. The undrained shear strength of eroded specimen is enhanced at small axial strain due to the enhanced connectivity of particles, but can increase or decrease at larger strain levels depending on the degree of erosion. It is also observed that both suffusion and shearing can induce some degree of fabric anisotropy by inspecting the directional distribution of contact unit normals and contact normal forces.