Numerical Investigation of Shear Mode Effects on the Mechanical Behavior of Soil–Rock Mixtures

Soil‐rock mixture (SRM) is a widely distributed geomaterial that occurs not only as engineered backfill but also as the primary constituent of many natural slopes, making its shear behavior critical for geotechnical design and geological hazard assessment. However, its pronounced heterogeneity and complex particle interactions hinder the reliable determination of shear strength and deformation characteristics. This study employs the discrete element method (DEM) to investigate the shear behavior of SRM under direct shear and simple shear conditions with varying volumetric block proportions (VBPs) and normal stresses. The results show that direct shear tests generally yield lower shear stress and exhibit post‐peak strain softening, whereas simple shear tests display continuous deformation with stronger stress fluctuations under high normal stress. Although both shear modes present similar overall normal displacement trends, their coordination number evolution and energy dissipation characteristics differ markedly. In particular, coordination number fluctuations are more frequent in direct shear, while rolling energy dissipation shows distinct growth patterns between the two modes. At high VBP, direct shear is associated with concentrated force chains near the shear plane, whereas simple shear exhibits more spatially distributed force chains and shear zones.