Abstract: The Wujiagou landslide in the Three Gorges reservoir area was originally a loosely colluvium bank slope in a stable state. However, after the transformation of human engineering activities, the bank slope slipped during heavy rain and reservoir water drawdowns. The geological characteristics and sliding depth are identified by means of survey, field monitoring, and limit equilibrium analysis approaches. The impact of the three environmental variables of the terrain, the rainstorm, and the reservoir water on the factor of safety of the landslide is quantitatively analyzed by the theoretical analysis. The formation mechanism of the landslide was discussed. The main sliding surface of the Wujiagou landslide is the contact zone between the silty claystone spoil and the bedrock layer. It becomes the slip plane under the long-term softening effect of reservoir water drawdowns. Engineering activities such as surcharging at the top of the slope and unloading at the toe of the slope have resulted in a “steep up and gentle down” topography of the bank slope. The activity provided space for the formation and development of the landslide. The torrential rain happened now when the reservoir water level dropped to the most unfavorable water level, and finally induced a landslide. The research results provide a reference for the subsequent construction of the reservoir area.

Key words: Three Gorges Reservoir Area, Landslide, Loose Colluviums, Heavy Rain, Reservoir Drawdown, Terrain Modification