Coupled DEM-SPH model for geotechnical undrained simulations

DEM (Discrete Element Method) simulates geotechnical materials such as sand using a particle-based approach. SPH (Smoothed Particle Hydrodynamics) is also a mesh-free method for simulating fluids. In this study a coupled DEM-SPH model was developed to simulate the undrained behavior of saturated geotechnical materials such as saturated sand. The solid phase was simulated using DEM and the fluid phase was simulated using SPH. The both methods were coupled by applying interaction forces to the fluid and solid phases. The presented DEM-SPH model resolved the need for a spatial mesh. The model was validated by comparing its results to existing experimental data. The undrained triaxial shear test was simulated to show the capabilities of the numerical model. Using the developed DEM-SPH model the fluid pressure and velocity distributions were studied at several axial strains. The fluid velocity in upper parts of the sample has similar magnitude to the loading velocity with approximately vertical direction. In the lower parts the fluid velocity was close to zero with different directions. Three stages of pressure distribution were recognized; (i) transient stage related to wave propagation, (ii) stable stage related to elastic deformations of the sample, and (iii) instable stage related to particle sliding. The results showed that the numerical model can satisfactory predict the response of the granular material to undrained loading and accurately simulate the distribution of the inter-particle fluid local parameters.