Failure mechanism of a large-scale composite deposits caused by the water level increases

The failure of slope caused by variations in water levels on both banks of reservoirs is common. Reservoir landslides greatly threaten the safety of reservoir area. Taking large-scale composite deposits located on the Lancang River in Southwest China as a study case, the origin of the deposits was analyzed based on the field investigation and a multi-material model was established in the physical model test. Combined with numerical simulation, the failure mechanism of the composite deposits during reservoir water level variations was studied. The results indicate that the deformation of the large-scale composite deposits is a staged sliding mode during the impoundment process. The first slip deformation is greatly affected by the buoyancy weight-reducing effect, and the permeability of soil and variation in the water level are the factors controlling slope deformation initiation. The high water sensitivity and low permeability of fine grained soil play an important role in the re-deformation of deposits slope. During the impoundment process, the deformation trend of the deposit slope is decreasing, and vertical consolidation of soil and increasing hydrostatic pressure on the slope surface are the main reasons for deformation attenuation. It is considered that the probability of large-scale sliding of the deposits during the impoundment period is low. But the damage caused by local bank collapse of the deposit slope still needs attention. The results of this paper will further improve our understanding of the failure mechanism of composite deposits caused by water level increases and provide guidance for the construction of hydropower stations.