DEM analysis on the stress wave response of spherical particle assemblies under triaxial compression

It is challenging to understand the stress wave response of cohesionless particle assemblies including compression and shear wave velocities (V_p and V_s) due to complicated particle-scale interactions particularly during a loading process. This contribution adopts the discrete element method to simulate triaxial compression experiments using spherical particles. Four samples are isotropically confined at various initial packing densities and then sheared monotonically up to the critical state. Small-amplitude wave propagation simulation is performed during shearing along the axis of loading. The results reveal that V_p is affected by the major principal stress and the coordination number contributing to the vertical direction rather than horizontal direction, while V_s is more influenced by the geometric mean stress and the mean coordination number. The wave velocity ratio (V_p/V_s) is well correlated with the fabric anisotropy, having a linear relationship. This enables prediction of microscopic change in fabric from macroscopic wave velocity values. Besides, a material-specific relationship between stress levels and wave velocities is found at the critical state with a unique fabric anisotropy, independent of initial packing. V_s in the isotropic state is found to be always larger that at the critical state under an equivalent stress level.