On The Formation Mechanism And Stability Assessment Of Landslide Group On The Right Bank Of Trevally River In The Reservoir Area Of Wudongde Hydropower Station

Recent decades have seen the rise of large hydropower plants in the southwest of China,and the accompanying result is the increase of geological hazards in the reservoir area.Among them,the landslide cluster on the right bank of the Trevally River,as the nearest landslide gathering zone to the hydropower station in the Wudongde reservoir area,seriously threatens the safe and stable operation of the Wudongde hydropower station.In view of this,it is of indispensable importance to study the genesis mechanism,evolution trend and stability of the landslide cluster on the right bank of the Trevally River.In this paper,field geological survey is used as a prerequisite and theories of tectonic geology,geotechnics,engineering geology and other related disciplines are adopted to study the landslide group on the right bank of Trevally River;By applying the evaluation method of“landslide group”,the mechanism of landslide group’s genesis and evolution trend are clarified;The geotechnical distribution characteristics of individual landslides are sorted out on the basis of the combination of drilling data and field investigations;Based on the monitoring data of typical landslides,deformation characteristics are explored and used to analyze the trend of later evolution,In addition,this paper also combines monitoring data with numerical simulation to comprehensively evaluate the stability of typical landslides.The following results are achieved with the help of the above research methods.(1)According to the theory of tectonic geology,the formation of “stepped” landscapes is divided into four stages: “initial,natural unloading,local deformation and destruction,and overall deformation and destruction”.(2)Taking the evaluation method of “landslide group” as the premise,the relationship between the group landslides and local tectonics is established,and the evolution trend and spatial distribution pattern of the slope body can be derived.Specifically,it can be reflected as follows: The landslide on the south flank of the tilted slope slides along the bedrock toward NE;The landslide on the north flank of the tilted slope(south flank of the back slope)slides along the bedrock toward SE;The landslide on the north flank of the back slope slides along the bedrock toward NE;The spatial distribution pattern of the landslide body mainly shows the decreasing to both sides centered on the Dapingdi landslide and the Dacun landslide.(3)Through the combination of drilling data and field investigation,the geotechnical structure of the area is revealed and used to analyze the development characteristics of each landslide and determine the type of landslide.Specifically,it can be reflected as follows: The stratigraphic body of the area is mainly composed of Jurassic and Cretaceous,and most of the boreholes encountered are silty mudstone,argillaceous siltstone,mudstone and sandstone of Jurassic Niugundang formation;Similarly,individual landslides and group landslides show the same distribution characteristics of “stepped” landforms,with their deformation evolution also controlled by local tectonics;Huotoudi,Daopo,and Dapingdi landslides are cascading bedrock landslides,Xiaxintian,Shangxintian,and Dacun landslides are mounding landslides,and the cliff foot-turning ditch is a collapse mound.(4)According to the monitoring data of typical landslides,the analysis focuses on the deformation rate,accumulated displacement,change amplitude and later evolution of the slope body.The concrete conclusions are as follows: The deformation of the slope body is mainly affected by the change of reservoir water level,with deformation mainly occurs in the period of reservoir water level decline,specifically manifested as dynamic water pressure type;The strength of the deformation amplitude of the slope body mainly depends on the change of dynamic water,and the law of the longitudinal deformation amplitude of the landslide is controlled according to the distance from the Trevally River;The deformation time of the landslide lags behind the reservoir water level change,with a lag time of about 3 weeks;the Daopo landslide is bounded by the middle ridge,with the rock and soil body on the south side of the ridge sliding toward the Trevally River,while the soil body on the north side of the ridge slides toward the Chenjia Dagou;The deformation direction of the Dapingdi landslide from the trailing edge to the leading edge is in the order of south east→south east of east→due east.(5)Combined with the monitoring data,Geo Studio numerical simulation is to simulate the change of seepage field and safety coefficient of a typical landslide,and the conclusion obtained is consistent with the monitoring data.The concrete conclusions are as follows:Landslide deformation is formed by the action of dynamic water pressure,with deformation mainly concentrated in the reservoir water level decline stage,and atmospheric rainfall plays a positive role in promoting landslide deformation;With the change of reservoir water level,the groundwater level line,circulation path,unit flow and pore water pressure produce certain changes,among which the groundwater level line and reservoir water level produce head difference and appear relative hysteresis;As the typical landslides are all in the deformation stage,there is no sign of sliding damage.