Stability analysis of a typical landslide mass in the Three Gorges Reservoir under varying reservoir water levels

Water level change upstream of a reservoir highlights the risk of a landslide-prone area on the banks of a reservoir. This paper conducted a study on the deformation mechanism of a selected landslide that occurred in the Three Gorges Reservoir (TGR) after the water level of the reservoir changed. The long-monitored surface deformation of the slide mass revealed that the deformation of the landslide was related to the water level changes in the reservoir, especially of the change between flood and floodless seasons. The measured internal lateral displacements in the landslide showed that such a landslide was characterized by a trail-mode. FLAC(3D) was adopted to model the landslide by examining the plastic zone, factor of safety, and the displacement in the x-direction in consideration of four conditions: the natural state of a landslide in the TGR, the initial impoundment, the subsequent rise of water level, and the drawdown of water level. The numerical results indicated that the landslide mass tended to be unstable during the initial impoundment; the subsequent rise of water level had a limited effect on the landslide happening, but the drawdown of water level directly triggered the landslide. The landslide changed from push-mode to trail-mode. It is strongly recommended that drawdown of the water level in the reservoir be carefully controlled to mitigate the effect on landslide mass.