Comparative analysis on shear mechanical properties of soil- rock mixture under direct shear and simple shear tests

Soil-rock mixture (SRM) is commonly used as backfill materials in high-fill roadbed slopes. The stability of these slopes depends on the mechanical properties of SRM, which are complex and difficult to accurately measure. To accurately assess the safety of the roadbed slopes constructed with SRM, it is crucial to develop a more precise experimental approach for investigating the shear mechanical properties of SRM. The discrete element method (DEM) is a powerful tool for analyzing the heterogeneous geomaterials. In this paper, a reverse reconstruction method to simulate rock blocks was initially proposed, along with a novel loading approach for simple shear tests. Subsequently, numerical models of SRM were established for direct shear and simple shear tests respectively. Finally, the shear mechanical properties of SRM under the two tests were systematically investigated, including block rotation, force chain distribution, crack distribution, particle damage state, normal displacementshear strain curve, and shear stress-strain curve. The numerical results demonstrate that, compared to the direct shear test, the shear zone of SRM in the simple shear test exhibits a more uniform distribution, with a greater thickness of the shear zone and a larger rotation angle of principal stresses. Therefore, the simple shear test is more representative of the actual slope load conditions and provides more accurate shear strength parameters.