Simulation of Critical State Behavior of Granular Soils with Polygonal Particles Using Discrete Element Method (DEM)

In this study, the numerical Discrete Element Method (DEM) is used for simulating drained and undrained behavior of 2D polygonal granular materials in order to find critical state line. For undrained behavior simulation, two methods including constant volume and cylinder methods have been used. In the constant volume method, it is assumed that the volume of the soil remains constant during the loading due to the incommensurability of water. In the cylinder method, however, a pipe is considered among adjacent pores that provides the water transformation between them. Undrained simulation was performed for sandy samples at the confining pressure of 200 kPa by both methods. Simulations show that the results obtained by cylinder method have good conformity with those of the constant volume method. As the water becomes less compressible, i.e., stiffer, the results of both methods become closer. Also, the effect of confining pressure on the drained and undrained behavior by constant volume and cylinder methods was investigated. The results of the simulations showed that by increasing the confining pressure, the deviatoric stress and the contraction tendency increase in drained and undrained simulations. To achieve critical state, the simulations were performed until large strains where the deviatoric stress and void ratio become constant. Then the critical state line locus and also its parameters are determined. The results show that the critical state line locus does not depend on the stress path and the simulation method for undrained condition has very little impact on the critical state line locus.