Abstract: Rolling resistance between particles significantly influences the mechanical properties of granular media, yet the underlying mechanisms remain incompletely understood. We conducted several drained triaxial shear tests on granular media using the three-dimensional discrete element method. The simulation results were quantitatively analyzed at macroscopic, microscopic, and mesoscopic scales, followed by a detailed correlation analysis. The study revealed the load transfer and deformation processes in dense granular media, and explored the internal mechanism of the influence of rolling resistance on the mechanical behavior of granular medium. The results show that in the strain hardening stage, the mechanical coordination number decreases, the fabric anisotropy increases, the number of chained particles increases, the force chains become longer, the number of force chains decreases, the average normal contact force increases, the number and volume proportion of small clusters decrease while the number and volume proportion of large clusters increase, and so dilatancy occurs immediately in the specimen after its initial elastic compaction. As the triaxial shear load increases, the contact force between particles in force chains becomes substantial, and the proportion of large clusters surrounding them rises significantly. Consequently, some force chains buckle or collapse, leading to decreased fabric anisotropy, a reduction in the number of chained particles, shortened force chains, and macroscopic strain softening. During the strain hardening stage, large rolling resistance effectively inhibits relative rolling between particles in force chains and reduces the deformability of surrounding large clusters, thereby enhancing force chain stability and increasing the shear strength of the granular medium. During the strain softening stage, rolling resistance prevents timely rearrangement of particles, causing deformation to concentrate in local areas where force chains have bent or collapsed. In these areas, particle rotation increases, leading to the formation of larger clusters. Consequently, the softening and dilatancy of the sample become more pronounced, resulting in the formation of a clear shear band. This study provides deep insights into the complex mechanical behavior of granular media and offers inspiration for the development of multi-scale constitutive theories.

Key words: granular medium, discrete element method, rolling resistance, force chain, cluster