Abstract: The results of professional monitoring implemented in 2006 shows the Muyubao landslide in Three Gorges reservoir area has been continuously deformed, which brings a huge threat to the Three Gorges Dam Project and the Yangtze River Channel. Qualitative analysis indicates that the reservoir water level plays a key role in the surface deformation of the landslide. Through many field geological survey data, long-term on-site inspection, artificial GPS displacement monitoring data, and automatic monitoring data for nearly one year, the deformation characteristics, evolution law and deformation mechanism of the landslide under reservoir water fluctuation and rainfall conditions are analysed in depth. The results show that the geological factors such as landslide slope structure, lithology and geological structure control the deformation of Muyubao landslide, and the reservoir water level is the main driving factor. During the rise of the reservoir water level, when the reservoir water level rises from 145 m to 155 m, the monthly displacement is the minimum; when the hydrodynamic pressure is towards inside slope, the landslide deformation is the smallest; when the reservoir water level rises from 155 m to 175 m, the reservoir water infiltrates the front slope, which leads to form a floating weight-reducing effect on the anti-sliding section in front of the landslide and increases the deformation. When the reservoir water level reduces from 175 m to 170 m, the monthly displacement reaches the maximum value and the cumulative displacement forms a step, which is affected by the dynamic water pressure and the floating weight loss effect of the slope. When the reservoir water level decreases from 170 m to 145 m, the floating weight loss effect is reduced and the monthly displacement is reduced. At present, the deformation trend of the Muyubao landslide is less, and the possibility of large-scale sliding is smaller, but the monitoring and mechanism research must be further strengthened.

Key words: Muyubao landslide, displacement step, weight loss effect on floating conveyor, deformation law