Fluid coupled-DEM modelling of undrained behavior of granular media

A 2D coupled continuum-discrete model is utilized to simulate the undrained behavior of saturated granular media subjected to monotonic biaxial shearing. The fluid phase is considered as continuum, and its flow is modeled using equation of continuity and according to Darcy Law. Discrete element method is employed to model the solid phase discrete particles. Fluid–particle interactions are taken into account based on semi-empirical relations. Loose and dense samples are prepared and biaxially sheared in drained and undrained conditions. The undrained condition is simulated using the constant volume method as well as the present coupled method. The macroscopic behavior, including stress–strain response, stress path and volumetric change, of the assemblies is studies. The results of the undrained responses comply fully with each other in the constant volume and coupling methods; they also show good compatibility with their drained behavior. Bulk modulus of the pore fluid has a substantial effect on pore pressure generation, with negligible effect on the effective stress–strain response of the assemblies.