Study on the unloading mechanism of layered rock slopes with weak interlayers during excavation based on the FDM-DEM method

The excavation of slopes frequently leads to landslides, posing significant risks to infrastructure and human safety. To investigate the damage mechanisms of rocky slopes with weak interlayers resulting from the unloading effects of excavation, we propose a three-dimensional finite difference method-discrete element method (FDM-DEM) slope excavation model that accounts for these unloading effects. This study establishes and analyzes a numerical model situated within the context of a typical rocky slope featuring a weak interlayer located behind the Pankou Pumping and Storage Hydropower Station. The simulation results indicate that the overall deformation of the slope increases due to the unloading effects of excavation. Notably, the majority of the interfaces between the weak interlayer and the overlying rock mass experience shear damage, which facilitates the downward sliding of the overlying rock along the shear surface. This phenomenon leads to bulging at the foot of the slope, ultimately resulting in routed deformation. The weak interlayer is identified as a critical factor influencing the damage associated with slope excavation. We further investigate the relationship between the bond strength of slightly weathered siliceous slate and the bond strength/friction coefficient of the weak interlayer to better understand their impact on slope stability. The results demonstrate a negative correlation between the bond strength and friction coefficient of the weak interlayers and slope displacement; as the bond strength/friction coefficient decreases, slope deformation increases. However, the favorable mechanical properties of the rock mass at the foot of the slope inhibit sliding along the interlayer. A reduction in the bond strength of siliceous slate to levels below its original strength results in an increased bending of the rock mass at the slope's base. When bond strength decreases to 0. 5 times its original value, noticeable bending occurs. Additionally, excessive moisture contributes to the fracturing of the upper rock mass, prompting downward sliding. Throughout this process, the upper rock body undergoes tension, cracking, and disintegration, leading to the bending, sliding, and cracking of the slope. This study provides valuable insights into the damage mechanisms associated with slope instability during excavation and unloading.