Mesoscale Investigation of Anisotropic Shear Failure Mechanisms in Cemented Soil–Rock Mixtures Using 3D DEM Approach

Cemented soil–rock mixtures (CSRMs) consist of a bonded soil matrix embedded with rigid rock blocks. The shear behavior exhibits pronounced anisotropy depending on block geometry and orientation. In this study, a three-dimensional (3D) heterogeneous discrete-element method framework is developed to perform numerical direct-shear simulations of CSRM with rock blocks oriented at 0°, 30°, 60°, and 90° to the shear plane. At the macroscale, after precise microstructural reconstruction and parameter calibration, block-induced anisotropy in CSRM shear behavior is captured by the 3D model. At the microscale, 3D heterogeneous statistics of contact forces and crack networks elucidate the anisotropic shear failure mechanisms in CSRM. Additionally, fracture-surface topology is reconstructed from particle slip data to illustrate how block orientation governs stress transmission. Results reveal a two-stage response: an initial peak-strength hardening followed by residual softening. Block inclination significantly influences residual strength, which increases with inclination, whereas peak strength remains relatively insensitive to block angle. At the mesoscopic level, residual strength arises from a combination of high-stiffness block–block contacts and geometrical interlocking induced by block inclination. These findings illuminate multiscale mechanisms, crack propagation, volumetric dilation, and force-chain distribution, providing the insight basis for improved anisotropic strength models and assessing engineering stability.