Abstract: The revival of ancient bank landslide is a serious geological hazard in reservoir operation. In order to study the deformation characteristics and instability mechanism of ancient bank landslide, a large-scale physical test model was designed based on Outang landslide which is a typical multi-phase ancient bank landslide. By simulating the fluctuation of reservoir water, rainfall and their combination, the curves of pore water pressure and earth pressure with time and digital image data of landslide evolution were obtained. Results indicate that the three-phase sliding masses that compose the landslides have different deformation characteristics under the reservoir water level fluctuation and rainfall. The deformation due to the fluctuation of reservoir water is mainly concentrated in the first phase sliding mass. The rapid rise of the water level has no obvious effect on the first phase sliding mass. But the rapid decrease of water level induces a local retrogressive sliding at the toe of first phase sliding mass. Heavy rainfall causes a local retrogressive sliding at the toe of the first phase sliding mass, and the stability of the second and third phase landslides decrease obviously. The failure mode under the rapid decline of water level and heavy rainfall is local retrogressive sliding at the toe of the first phase sliding mass or/and sliding of the third phase sliding mass. The experimental phenomena coincide with the deformation characteristics and the developing tendency of actual reservoir landslide. This study provides the deformation characteristics and instability mechanism of the ancient landslide in reservoir bank under the condition of reservoir water level fluctuation and rainfall, which is helpful for the research and prevention of similar landslides.

Key words: ancient bank landslide, physical model test, water level fluctuation, rainfall, deformation evolution