Abstract: When the Three Geoges Reservoir impounding water and water level fluctuating, the hydrological condition of landslides will be greatly changed. Both the sudden drawdown of reservoir water level and rainstorm infiltration become major factors that effect on the stability of landslide. The stability evaluation of landslide is difficult in the sudden drawdown of reservoir water level. On the basis of the project that reservoir water level is controlled and the mechanical mode that the ground water acts on landslides in Three-Gorges Reservoir area, transient seepage due to the sudden drawdown of reservoir water level from 175 m to145 m is computed using the finite element. Disequilibrium push method is applied to stability evaluation of landslide under seepage forces. The results of the stability analysis show that permeability coefficient of landslides and the descending velocity of reservoir water level are main factors that effect on the stability of landslide When the permeability coefficient of landslides is less than 0.864 m/d and velocity is 2 m/d, the sudden drawdown of reservoir water level will take place. And water level on which safety factor of Landslide is minimum drops by 10m to 20m under 175m water level, which will provide scientific bases for the treatment of landslide in 175m water level in Three Gorges Reservoir.

Key words: sudden drawdown of reservoir water level, seepage, landslide, stability evaluation