Study on shear surface morphology and failure mechanism of soil-rock mixture under wet-dry cycle action

The present study investigates the failure modes and formation mechanisms of shear surfaces in soil-rock mixtures from various perspectives. Firstly, through in-situ direct shear tests, two main shear failure modes, namely planar and non-planar, are identified. Subsequently, using PFC 2D numerical simulation, an in-depth exploration of the characteristics and causes of these two typical failure modes is conducted. The findings reveal that in the natural state, the material is relatively dry, and the matrix suction within the soil-rock mixture is significant. During shearing, the inter-particle force chains are prone to rupture, exhibiting characteristics akin to brittle failure. This leads to nearly planar shear surfaces, with force chain ruptures primarily localized near the planar regions adjacent to the shear surface. However, after multiple dry-wet cycles, the plastic enhancement of the soilrock mixture reduces the matrix suction to almost zero. The continuous rupture and reorganization of force chains deepen the shear band under their influence, resulting in non-planar shear surfaces. It is noteworthy that the characteristic point fitting curve of non-planar shear surfaces exhibits a nonlinear trend. In summary, our study elucidates the evolution process and causes of shear surface morphology in soil-rock mixtures, which holds significant implications for understanding their mechanical properties and engineering behavior.