Elastic wave velocities during triaxial shearing influenced by particle morphology

Abstract

This contribution investigates the characteristics of elastic wave velocities (Vp and Vs) during triaxial shearing tests under dry and drained conditions. Samples of tested materials with different particle morphologies (i.e., particle shape and surface roughness) were prepared under three strategies, namely, similar initial void ratios (e0), relative densities (Dr0), and side tapping numbers (Nt). Regarding the elastic wave velocities as functions of e0 and confinement σ′ at very small strain ranges, i.e., V=a(B-e0)(σ′1kPa)b, a was seen to increase for more angular materials or smoother surfaces, while b and B were seen to decrease as the particles became more angular or the surfaces became smoother. During triaxial shearing, Vp increased initially and then tended to decrease more gently, whereas Vs increased initially and then showed a marked decrease before convergence upon shearing regardless of the e0 for the given material. The influence of particle morphology on the absolute values for Vp and Vs was found to be complex during shearing, whereas the wave ratio (Vp/Vs) was consistently greater under rougher conditions for the same shape. Importantly, the wave ratio (Vp/Vs) was found to correlate well with the particle morphology: more angular materials and rougher surfaces exhibited a greater Vp/Vs ratio normalized by the stress and density conditions for each material, which further indicates a higher degree of fabric anisotropy with reference to the microscopic evidence in the literature.