Characteristics and mechanism of deformation of chair-shaped soil landslides in Three Gorges Reservoir area

Since its impoundment, the displacement-time curve of many landslides especially the chair-shaped soil ones in the Three Gorges Reservoir area has gradually changed, which makes the identification of stable state difficult and seriously affects the early warning and forecast of landslides. Based on the example of Baijiabao landslide, through many field geological surveys and long-term on-site inspections, and by use of more than 10 years of GPS displacement monitoring data, more than one year of fully automatic monitoring data and landslide theories, the deformation and evolution laws of the landslide under water fluctuations and rainfalls are studied in depth. The results show that the main factor inducing the deformation during the flood season and rise and fall of reservoir water level is the fall of reservoir waterlevel. The annual displacement is 35~250 mm, the historical displacement has a fluctuation of "W" type, and the first step of 30~180 mm of displacement is completed in about 20~30 d. When the water level of the reservoir drops by 25 m and the elevation of the water level is about 150 m, the displacement step starts. When the reservoir water level drops to 145 m, after one week the maximum displacement of the step is 5~8 mm/d. During the rise of the reservoir water level, the rainfall has no effect on the deformation of the landslide. Restricted by the structural characteristics of the chair-shaped slopes, the slope will be repeatedly deformed under the action of the rise and fall of water level, but it is difficult to cause overall damage.