DEM simulation for shear behavior in unsaturated granular materials at low-stress state

Abstract

Abstract In this study, the three-dimensional discrete element method (DEM) is used to model the unsaturated triaxial test at a low-stress state. The contact model, which considers the matric suction of soils as well as the contact area among particles, and the flexible boundary condition are proposed. Prior to the simulation for the unsaturated triaxial test, we identify the effect of them on the numerical results to get an optimal condition. The deformability of the lateral boundary highly affects the post-peck shear behavior. The specimens with the contact area become brittle like unsaturated soils because it makes interparticle bonding more fragile. According to the comparison of the numerical and experimental results, all the simulations can predict the pre-peck shear behavior as well as the shear strength of unsaturated soils, but some of them underestimate the post-peck shear behavior. In the simulation for the unsaturated soil at a relatively large stress state, the regenerated menisci have a key role in the residual state. In the simulation for the unsaturated soil with higher water content, not only the menisci at contact points but also the bulk water around particles should be taken into account. The particle-scale matric suction in the contact model can exhibit a linear relation with the matric suction of soils, while there is a nonlinear relation between the interparticle stiffness and the matric suction of soils. These relations can be criteria for choosing the input parameters related to the matric suction in further studies. DEM simulation can also provide the microscopic response such as the propagation of the particle-scale fractures and the distribution of particle’s angular velocities.