Numerical and experimental estimation of anisotropy in granular soils using multi-orientation shear wave velocity measurements

Soils can have direction-dependent characteristics reflected in the anisotropy of their responses. Studies have demonstrated the impact of the stress state and history (i.e., stress-induced anisotropy) and the depositional processes and particle arrangements (i.e., fabric-induced anisotropy) on the anisotropy of macroscopic behaviors. However, quantifying the stress- and fabric-induced anisotropies remains a challenge. This study presents two investigations on the effects of stress- and fabric-induced anisotropy on the anisotropy of shear wave velocity (V-S). A framework based on the V-S measurements along various orientations and polarization planes obtained from discrete element method (DEM) simulations and experimental bender element (BE) tests is presented; this framework is tested using the results from specimens of spherical and non-spherical particles under isotropic and 1D compression. The observed trends indicate that the angular distributions of V-S are related to the angular distributions of particle alignment and interparticle contact forces. This framework, when presented in terms of the ratio of V-S measurements along different orientations and polarization planes and of the newly introduced Anisotropy parameter (A(e)), can assist in evaluating the stress- and fabric-induced anisotropy of soil specimens. The results also highlight the challenges in discerning the effects of stress and fabric anisotropy when both influence the soil response.