Numerical study on the particle shape-induced fabric anisotropy and wave velocity anisotropy in granular soils

Inherent anisotropy of granular materials arising from particle morphology can be characterized through fabric anisotropy, a key index linking grain-scale characteristics to macroscopic mechanical responses. We develop a theoretical framework that utilizes directional elastic wave velocity to quantify the fabric anisotropy induced by particle shape in transversely isotropic granular media. Discrete element method simulations are performed to investigate the effect of void ratio and to validate the proposed macro–micro relationships. The results reveal that the mechanical coordination number decreases with increasing void ratio, leading to a reduction in wave velocity. Branch vector anisotropy exhibits a stronger correlation with the evolution of wave velocity anisotropy than contact normal anisotropy. The analysis further confirms that, in random packings, wave velocity is primarily governed by contact stiffness and the projection of branch vector length along the wave propagation direction. A simplified particle shape-induced fabric descriptor is proposed, and the relationship with elastic wave velocity anisotropy is established based on effective medium theory with contact-stiffness linearization about the current state and Hertz–Mindlin contact law. This study enables practical characterization of inherent anisotropy and improves predictive capability of constitutive models incorporating fabric evolution in granular soils with diverse shapes.