Numerical Investigation on Wave Propagation in Anisotropic Granular Soils by Discrete Element Method

Measurements of shear/compression wave velocity by bender/extender elements are closely associated with the elastic properties of granular soils. Generated by point sources, the wave differs with the propagation directions. To examine the wave propagation anisotropy, mono-sized spheres structured in face-centered cubic packing were generated and bender/extender element tests were simulated using discrete element method. Isotropic and anisotropic consolidations were conducted during the modeling. Meanwhile, by changing the geometry and relative location of the transmitters and the receivers, the required directions of wave propagating and particles vibrating were achieved. Based on previous techniques to avoid near-field effects and determine wave arrival time, the responses of receivers were recorded and analyzed. Static loading simulations were carried out to obtain the small strain stiffness at a small strain level. A general consistency of static loading results and wave velocities measurements shows that continuum assumption for elastic wave in granular materials is reasonable. Since fabric anisotropy is eliminated in regular packing structure, the contribution made by contact normal force is same as prediction. The revelation of micromechanics of wave propagation stands as a solid proof that wave propagation depends on the soil state.