Failure mechanism on Qianjiangping landslide in the Three Gorges Reservoir region

The Qianjiangping landslide,24 million m~3 in volume,occurred while the storage of the Three Gorges Reservoir from nature to 139m elevation and was one of the largest landslide recently in this regions.The landslide is translational along the declining interbeded shale layer,consisted of the old sliding and falling accumulation in the upper and the bedrock on the bottom.The moving processes could be divided into three zone: the translational sliding,the shear sliding, and the river-damming and thrusting.The stability index is calculated under various situation.In the natural condition without rainfall and water storage,the stability index K=1.18,which could be the baseline for other situations.Under the rainfall with 162.7mm from June 21 to July 11,K=0.97,declining by 20.9%,compared with the natural condition.Under the water level rising of storage with no rainfall,K=0.99,declining by 18.3%,compared with the natural condition.The stability index K=0.93 under the combination of the storage and rainfall,declined by 24.8%,compared with the natural condition,which shows the obvious triggers on the sliding.