Anisotropy of elastic wave velocity influenced by particle shape and fabric anisotropy under K0 condition

Abstract

Non-cohesive granular materials exhibit fabric-induced anisotropy of small-strain stiffness. The stiffness anisotropy is often measured using dynamic wave measurements in the laboratory. It is widely accepted that elastic wave velocities are influenced by stress state, while the role of particle shape in the wave velocity anisotropy, and thus the stiffness anisotropy, has not been fully understood. The difficulty arises partially from the incomplete understanding of particle-scale responses of granular materials. Considering 1D vertical compressoin with zero lateral strains (K0 condition) analogue to in-situ ground, this contribution performs wave propagation simulations using discrete element method and explores how particle shape and packing characteristics influence the anisotropy of elastic wave velocity. Sphere clumps with various aspect ratios are used. The orientation of the particle major axis is varied systematically by inhibiting particle rotation during dry-pluviation process. The simulation results reveal that the wave velocity anisotropy is largely affected by the combined effect of the particle aspect ratio and the orientation of particle major axis. Micromechanical analyses on assemblies of sphere clumps and ellipsoids shed light on the importance of the inter-particle contact stiffness, in addition to the particle aspect ratio and fabric, to determine the wave velocity anisotropy when non-spherical particles are used.