Abstract: Granular materials are mostly composed of irregularly shaped particles, such as sand, grain and so on. Resistance to the rotation is an inherent characteristic of irregularly shaped particles. Previous studies have shown that the anti-rotation characteristics of particles have a significant effect on their macro-mechanical responses. Therefore, the non-spherical particles or the spherical particles with a contact model considering rolling resistance are widely employed in the mesoscopic numerical simulations of granular materials. In this paper, the combined finite and discrete element method (FDEM) and discrete element method (DEM) are used to simulate the triaxial tests of ellipsoidal particles and spherical particles with rolling resistance, respectively. The limitations of the rolling resistance model capturing particle shape effects are pointed out, and the meso sources of shape influence are revealed from the perspective of particle configuration structure. Peak deviatoric stress and dilatancy both change monotonically with rolling friction coefficient and the degree of deviation from a spherical shape, but the influence of particle shape on them shows obvious convergence. The mesoscopic fabric analysis also shows that although both particle shape and rolling resistance can significantly enhance the fabric anisotropy, but there are significant differences in the fabric anisotropy evolution mode between the two particle systems. The difference of the above results lies in the different influence mechanism of rotation resistance. Rolling friction enhances the stable bearing capacity of particles by limiting the rotation of particles, while non-spherical particles form a stable local arrangement structure through interlocking. Since the middle of ellipsoid particles can transfer greater contact force than the end, the particles rotate during shearing, and the long axis of the particles tends to be orthogonal to the direction of the largest principal stress, presenting a staggered arrangement, which means that particles lock together.

Key words: rolling resistance, particle shape, mesoscopic fabric, anisotropy, configuration structure