Response patterns of buoyancy weight loss landslides under reservoir water level fluctuation in the Three Gorges Reservoir area

Since the impoundment of the Three Gorges Dam in 2003, a large number of wading landslides have occured in the reservoir area. In the three Gorges Reservoir area of the Yangtze River, the buoyancy weight loss landslide increases with the rise and fall of the reservoir water level. The uncertainty of the relationship between the deformation of the landslide and the reservoir water level brings confusion to the monitoring, early warning and prediction of this kind of landslide. In this paper, the Muyubao landslide is taken as the research object, the landslide monitoring data obtained by automatic GPS deformation monitoring system are analyzed in combination with many field investigations and professional monitoring and reservoir water level rise and fall data of 15 years. The finite element software Geo-studio is used to simulate the influence of the reservoir water level on the stability of the landslide under the condition of rise and fall of the reservoir water level between 175 m and 145 m at different rates. The results show that (1) during the process of reservoir water level rising from 145 m to 175 m, the stability coefficient of landslide changes in the trend of decreasing first, then increasing and then decreasing, and the larger the rising rate of reservoir water, the shorter the time of stability coefficient decreasing in the early stage. (2) In the process of the reservoir water level falling from 175 m to 145 m, the whole stable coefficient changes from decreasing at first and then increasing, showing the ‘V’ shape, and there is the most dangerous water surface. The height of the most dangerous water level varies with the rate of decline of reservoir water. When the reservoir water level decreases at the rate of 0.4,0.6,0.8,1.0,1.6 m /d, the corresponding most dangerous water levels are about 169.8,167.8,162.6, 162.0， 162.2 m. (3) The Muyubao landslide is a typical floating body weight reducing landslide in the Three Gorges Reservoir area. Under the influence of large amplitude and periodic rise and fall of reservoir water level, the Muyubao landslide keepsa creep state all the time, and the average daily displacement is 0.4 mm/d. At present, it is in a basically stable state. The conclusion can be used for reference in the early warning and prediction of floating support and weight loss landslide in the three Gorges Reservoir area.