Landslide Monitoring And Stability Analysis Of Xuankou Landslide In Zipingpu Reservoir Area

ZiPingPu Reservoir completed in2005is an important national hydro-junction project. Instability deformation of reservoir bank began to appear. In2008, the WenChuan earthquake trigged a series of landslides and collapse. XuanKou landslide is located in the western reservoir and river confluence reaches of Minjiang river and Shouxi river. Rock formation is bedded silty sandstone which interbedded with shale and coal line. XuanKou landslide is about150x104m3, and begin to appear compatible deformation after WenChuan earthquake. There is a tendency of slide. For the risk of blocking river and reservoir surge, the monitoring of the surface and deep displacement, underground water level, reservoir water level and rainfall were held on. A further study of seepage characteristics and the stability of XuanKou landslide were also held on with the help of the software GeoStudio. The results are as follows:(1) The surface deformation is reached360mm from July2012to February2014. Slip Surface with a slide angle of18°, is located18-32m below the ground surface. The sliding direction has reversed. Significant tension cracks were formed in the upper and middle part of the slope. Partial collapse was appeared in the front of the slope which has a poor overall stability.(2) Daily rainfall infiltration is about8X1O-4m/d with the consideration of plant interception, foliar evaporation and rainfall runoff.(3) Safety factor reached extreme values during the water level rising or falling at different speeds. A maximum value is reached in the process of reservoir water level rising, and a minimum value is reached in the process of reservoir water level falling. The extreme values of safety factor are related to the reservoir water level height and the rising or falling velocity. The faster the reservoir water level decline the smaller the safety factor is. Seepage velocity got outwards direction perpendicular to the surface in the toe of the slope, and is not conductive to the slope stability.(4) Structural joints and fractures providing good channels for rainfall infiltration are the main reason of XuanKou landslide’s instability.(5) The falling of water level in combination with rainfall is the worst condition. Making reasonable arrangements for reservoir storage especially in rainy season are necessary.