Deformation Mechanism And Stability Analysis Of Glide–outburst Landslide Under Complicated Conditions

The sliding outburst type occurs in the middle-steep dip outer slope,especially in the thin layered rock mass and the carbonate layered rock mass with strong ductility.The characteristics of this type of landslide are that the slip surface is transformed into a chair-shaped slip surface with upper bedding and lower cut bedding after repeated resurrection of slip bending outburst.Slip is a kind of slip-curved landslide dam landslide(engineering geological analysis principle of geological mechanics model of slope deformation and destruction)after damage state,this kind of landslide has a wide distribution in the southwest mountainous area,especially on the distribution of the three gorges reservoir area is more,huge volume,strong concealment,formation mechanism of the complex,difficult,high risk of disaster prevention and reduction;Since the impoundment of the Three Gorges Reservoir,the geological environment around the reservoir bank has changed.Due to the further influence of complex conditions,including slope structure,heavy rainfall and reservoir water level change,the reservoir bank is prone to the resurrection or instability of such landslides,which seriously threatens the safety of the Yangtze River golden waterway.Taking this kind of landslide as the research object,it is of great theoretical significance and practical value to clarify the deformation and failure mode of landslide and to study its deformation mechanism and stability.Tanjiahe landslide is a typical representative of the sliding outburst landslide.Some scholars in the 7th Five-year Plan period considered that the landslide was still in a stable state when the landslide was 175m.However,the landslide has been revived since the impounding of the Three Gorges Dam,and the boundary crack has been trapped.At present,the displacement of the front platform is up to 2.5m.According to the monitoring data,the displacement of the front platform is 2/3 of that of the middle and rear sliding body.These inconsistent conclusions have brought confusion to the early warning and prediction of geological disasters.It can be seen that the slope structure characteristics of this kind of landslide are special,the deformation mechanism is complex,and the landslide type needs to be clarified.Therefore,this paper takes Tanjiahe landslide as an example for in-depth study.According to detailed field engineering geological survey,aerial photography of UAV and years of on-site monitoring data,the evolution process and sliding outburst mode of landslide are systematically studied in depth.The typical sliding outburst landslide was compared and the formation conditions of the sliding outburst landslide were explored.The deformation mechanism and deformation characteristics of the landslide under the complicated conditions of reservoir water level fluctuation and rainfall are analyzed.The seepage field,displacement field and stability of the landslide are analyzed under the conditions of actual rainfall and reservoir water level,as well as under the combined rainfall conditions of different reservoir water level rise and fall.The research contents and results are as follows:1)Fields according to the detailed engineering geological survey,data collection,comparative research and analysis Tan Jiahe landslide,the lotus pond topples landslide such as landslide,the old county typical slip type landslide geological characteristics and characteristics of deformation and in-depth study of slide the conditions of the dam,concluded that adverse geological structure and the existence of weak rock should slip type dam landslide formation of the main control condition;The main external dynamic environmental factors of landslide slip outburst are the floating weight reduction effect,the hydrodynamic pressure effect and the lubrication effect caused by rainfall.2)Taking Tanjiahe landslide as the research object,the formation conditions,characteristics and genesis model of Tanjiahe landslide are found out.The landslide developed in the Jurassic Xiangxi Formation(J₁X)thick layer of quartz sandstone with coal seam at the intersection of Badong syncline and Zigui syncline.The profile shape is step shape,steep at the back and slow at the front.The macro-deformation characteristics of Tanjiahe landslide and the investigation data show that the Tanjiahe landslide is ancient landslide,which has slipped several times.The deformation and failure modes include the unweathered slope stage,the slight bending and uplifting stage,the strong bending and uplifting stage at the slope toe,the sliding outburst and instability failure stage,the natural reconstruction and restoration stage,and the resurrection stage induced by rainfall and the rise and fall of reservoir water level.3)The deformation of Tanjiahe landslide is controlled by geological factors such as slope structure,lithology and geological structure,and the reservoir water level is the main driving factor.By analyzing the monitoring data of Tanjiahe landslide,the surface displacement monitoring data showed that the minimum cumulative displacement of the front monitoring point ZG290 was 1552.78mm,and the cumulative displacement of the middle and rear monitoring points ZG287,ZG288 and ZG289 were 2358.33mm,2379.83mm and 2437.27mm,respectively.The displacement difference is significant with the accumulated displacement of the front monitoring point.The annual cumulative displacement curve of each monitoring point of the landslide presents a zigzag fluctuation trend,and the landslide is in a regular creeping deformation state.At present,the annual displacement of the landslide shows a decreasing trend,and the landslide tends to be stable.4)Explore Tan Jiahe deformation mechanism of the landslide can be concluded that it is whole structure Tan Jiahe landslide landslide chairs,on steep slow under(the upper 20°?35°,lower 2°?5 DHS),easy accumulation slope form a powerful potential energy,in the steep slow junction stress concentration,sliding surface containing hydrophilic and swell-shrink sex strong weak intercalations have promoting effect on landslide deformation.In the early stage of reservoir impoundment,the reservoir water level rose in 2007 and 2008,and the floating support and weight reduction caused by the rise of the reservoir water level had a great impact on the deformation and stability of the landslide.The water level regulation of the Three Gorges Reservoir lasted for 15 years,and the landslide body underwent initial stress adjustment.During the operation stage of high water level of170m-175m,the weight reduction effect of floating support was enhanced,and the cumulative displacement curve of the landslide rose.In the stage of reservoir water level decline,the groundwater level of the slope lags behind the reservoir water level decline,which shows that the reservoir water level decline produces dynamic water pressure,which leads to the increase of the displacement rate of the landslide,and further shows that the activity of the landslide increases in the stage of high water level operation and reservoir water level decline.5)Based on the variation law of water level and rainfall in the Three Gorges Reservoir Area,the numerical simulation was carried out with GEO-STUDIO software:The changes of seepage field,stability coefficient and displacement field of landslide are simulated under the conditions of actual rainfall and reservoir water.The results show that the change rule of seepage field is that the faster the reservoir water drops,the denser the seepage vector is.There is a negative correlation between landslide stability coefficient and reservoir water level.The overall trend of the simulated displacement has a high degree of fit with the actual displacement,which verifies that the model has a certain practical analysis significance.Through the simulation of reservoir water level rising at different speeds,it can be seen that the infiltration line gradually presents concave shape with the rise of reservoir water level,and the landslide stability coefficient increases first and then decreases with the rise of reservoir water level.By analyzing the simulation results,the seepage and stability of the landslide under the condition that the reservoir water level drops at different speeds can be obtained.It can be seen that with the decrease of the reservoir water level,the infiltration line has an obvious convex trend,and the stability coefficient of the landslide decreases first and then increases with the decrease of the reservoir water level.The greater the decrease of the reservoir water level,the larger the deformation range of the landslide.In the case of reservoir water level decline combined with rainfall,the water pressure contour curve is distributed in a curved state after being affected by rainfall,which has a negative impact on landslides.