FAILURE OF SUPER-HUGE LANDSLIDE IN COLLAPSED DEBRIS DEPOSITS WITH NEARLY HORIZONTAL SLIDING SURFACE INDUCED BY EXCESS PORE WATER PRESSURE

Super-huge landslides in collapsed debris deposits with nearly horizontal sliding surface widely develop in Wanzhou District and Yunyang District, Chongqing Municipality in the Three Gorges Reservoir Region. Based on the two typical landslides, Taibaiyan Ancient Landslide in Wanzhou District and Laoyaopu Landslide in Yunyang District, this paper analyzes their structures and failure characteristics, and establishes a mechanical model of failure for super-huge deposit landslides with nearly horizontal sliding surface under the condition of heavy rainfall. This paper explains the failure process for this kind of landslide. Therefore, the excess pore water pressure produced in sliding band(or sliding surface) is the cause of this kind of landslide failure. Taking into account of the internal relation of pore water pressure and soil stress state, this paper deduces expressions of pore water pressure and hydraulic pressure of each soil slip in sliding surface, and obtains landslide stability coefficient expression considering the pore water pressure. The case of Laoyaopu Landslide in Yunyang District indicates the follows. Laoyaopu Landslide can be divided into two landslides by the location of zk5. The higher pore water pressure is located in the center of two landslides. The value of the pore water pressure calculated by this paper is bigger than the measure value in borehole. Its calculation error is 5.8%~10%. The cause can be the dissipated pore water pressure. The stability coefficient of Laoyaopu Landslide was 0.862 under the condition of heavy rainfall(i.e. the condition of excess pore water pressure). This landslide was unstable and has failed, which verified the induced action of the pore water pressure to landslide failure. This paper suggests that drain hole should be hit in the center of two landslides divided by zk5 in landslide project of management, which can eliminate or decrease the pore water pressure in the sliding surface. Besides Laoyaopu Landslide is governed with interception and drain engineering around landslide and in landslide surface, filling cracks.