Formation mechanism and failure analysis under fluctuating reservoir water level conditions of a large-scale accumulation slope

Problems related to the slope stability of accumulation bodies are frequently encountered in hydropower construction projects in southwestern China. A field study was conducted, and the genetic mechanism of the accumulation slope is proposed based on a combination of geological phenomena observed on the ground surface, in exploration tunnels, and from drill core data. Fracture cutting and weathering drive the upper part of the bedrock to weaken, collapse, and be destroyed. The debris then slides and accumulates at the lower part of the slope because of gravity, which leads to further accumulation and rainwater infiltration of the slope surface. The accumulation body is pushed from the rear edge to the front edge, which causes consolidation and compaction deformation from the surface to the interior. In situ direct shear tests were performed to measure the mechanical parameters of the rock and soil, and the FLAC3D software was used for numerical analysis. The slope deformation and failure characteristics of the reservoir were monitored under fluctuating reservoir water level conditions. The results reveal that deformation mainly occurred inside the accumulation body and could be divided into three zones: the front traction deformation area with the maximum deformation, the middle transition area with the minimum deformation, and the posterior passive traction deformation area. The increased shear strain implies that the slope of the accumulation body can form two potential sliding failure surfaces in response to reservoir water fluctuations.