Numerical simulation on undrained triaxial behavior of saturated soil by a fluid coupled-DEM model

A fluid coupled-DEM model is developed in this paper based on particle flow methods. In the model, soil grain is represented by using a sphere particle, and the motion of soil grain is depicted by Newton's laws of motion and the force-displacement law at contact point. The flow of fluid obeys Darcy's law and fluid-particle interactions are depicted by multi-physics coupled formulation. A numerical scheme for this model is developed to consider the mechanism for pore pressure generation and volume change induced by deformation. Undrained triaxial compression tests of saturated soil are simulated by using the coupled method. The calculated results are compared with that from constant volume methods and experiments of Beijing clayey silt. The results show that the deviatoric stress and pore pressure obtained by coupled method are comparable with that of constant volume methods and experiments. A series of drained and undrained triaxial compression tests for saturated soil under different confining pressures are also simulated. Deviatoric stress increases with the increase of confining pressure in both drained and undrained tests. The results of undrained test show that stress ratio decreases with increasing confining pressure. The decrease of pore pressure drives effective mean stress path to move right-upward. A loss of soil strength can be found in undrained test by comparing with the strength in drained test, and this may be caused by reduction of effective stress.