FAILURE MECHANISM ANALYSIS OF GUANTAN LANDSLIDE INDUCED BY WENCHUAN EARTHQUAKE

Guantan landslide,located on the right side of the Jushui River,at Jushui town,An xian county,Sichuan Province,is generated in the laminated structure slope dipping inward with soft rock at the bottom.It is located in the bedding slope dipping inwards with soft rock at the bottom.Its volume is up to 4.68 million m3.The landslide is induced by the Wenchuan Earthquake and the storm,and occurred 8 hours after the Wenchuan Earthquake.Guantan landslide is located on the upper plate of the Jiangyou-Guanxian Fault.The orientation of the slope is parallel to the fault with a distance of 400 meters.A branch of the Jiangyou-Guanxian Fault goes through the slope at the lower part,which forms the boundary of dolomite rocks in the upper part and the mudstone in the lower part.According to the engineering geological survey and analysis,the landslide is controlled by three factors: 1) the structure of the slope with soft rock in the bottom and hard rock in the upper part is the basis of landslide,2) strong tectonic movements form crushed rock mass in the slope,and 3) heavy earthquake motion and storm induced the movement of the landslide.The mechanism and process of the landslide can be divided into three stages as follows: 1) the stage of compression and toppling of the slope before the Wenchuan Earthquake,2) the stage of sliding surface developing,and 3) the stage of integral movement of the landslide.The sliding mass composed a deposit dam,400 meters long along river,880 meters along the slope,and with a plain area of 18.2 thousand m2.And the Guantan barrier lake is formed because of the dam blocking the Jushui River.