Abstract: The Baiyang bay landslide in the Three Gorges Reservoir area is a typical landslide with multistage weak slip zones. Through aerial photography and site surveys, we identified the deformation characteristics of the landslide and the location of the multistage slip zone by drilling, geophysical prospecting, displacement monitoring, and numerical simulation. The formation and development of the landslide are controlled by external inducing factors and internal geological conditions. Drilling and geophysical interpretation manifest that the landslide is a deep-seated rock-soil mixed landslide with multi-level slip zones with weak interlayers, divided into two sliding zones. Surface deformation and displacement monitoring reveal large deformation in the middle and front part of the landslide, with the daily deformation reaching 1.3-4.0 mm uniformly. The deep displacement curve shows two abrupt change points of bulge displacement with notable characteristics of primary and secondary sliding surfaces, which is verified by survey data. Moreover, numerical simulation results reflect that the landslide is in an under-stable state under current working conditions; in particular, the safety factor of the landslide under heavy rain condition declines remarkably, indicating an unstable state. The topography, geomorphology, geological structure, and stratum lithology of the landslide provide the source and site conditions for the formation of the landslide. Human engineering activities and rainfall have also exacerbated the deformation of the landslide.

Key words: Baiyang bay landslide, multistage slip zone, deformation characteristics, formation mechanism, Three Gorges Reservoir area