Abstract
Particle crushing changes both particle size distribution and particle shape, which significantly affects the mechanical behavior of sand. This study uses a multi-scale discrete element method to investigate the direct-shear response of sand under prescribed post-crushing scenarios. Instead of modeling dynamic particle splitting during shearing, assemblies with predefined fractal particle size distributions and size-dependent angular shapes were assigned prior to testing. The performance of multi-shape assemblies was systematically compared against single-shape circular baselines. The numerical model was calibrated against plane-strain direct-shear laboratory experiments using granular analogs. Macro-scale findings reveal that shear strength and volumetric dilation exhibit non-monotonic trends, reaching a peak response at intermediate fractal dimensions. Angular fragments act as structural wedges that sustain interlocking. Micro-scale analysis demonstrates that peak shear strength is consistent with the evolution of contact force anisotropy. Conversely, particle rotations show an inverse relationship with shear strength and angular fragments impose anti-rotational constraints along the shear band.