Dem simulation of wave propagation in anisotropic granular soil

Abstract

The anisotropy of elasticity in soil can be evaluated using the velocities of compression waves and shear waves propagated in different manner. In this paper, discrete element simulations were performed to determine the wave velocities in Toyoura sand where isotropic confining stress and anisotropic consolidations in vertical direction were conducted. Based on the discussion of the launch conditions of elastic wave and travelling time interpretation, satisfying output wave signals were presented. The elastic constants determined by wave velocities were compared with those obtained by drained triaxial tests and simple shear tests at very small strain levels. It was found that the elastic constants determined by these two methods are consistent with each other, which stands as a solid proof to apply the continuum assumption to wave propagation in granular soils. Since affected by the anisotropy of fabric and stress state, the wave velocities experience nonlinear change. At anisotropic stress states, there is a threshold stress ratio reflecting dramatic velocity decreasing and fabric rearrangement. Moreover, the ratio of stress-normalized wave velocities can capture the evolution of fabric and reflect the granular nature of stress-dependency, which can also be served as a macroscopic index of the soil fabric.