Study On Hydrodynamic Load-unload Effect And Stability Evolution Rule Of Reservoir Landslide

The Three Gorges Reservoir area is a high frequency zone of geological hazard outbreak of reservoir landslide due to its undulating surface,wide topographic disparity and complex and diverse landforms.Most of them are caused by the dynamic change of the lower water level in the interior of the slope affected by the rise and fall of the water level in the reservoir outside the slope,which breaks the original balance of seepage field and stress field in slope and threatens the safety and stability of slope.Therefore,the study of the failure mechanism and stability evolution trend of reservoir landslide under the fluctuation of reservoir water level is a topic of wide concern to scholars in engineering geology and other related fields at home and abroad,and also an urgent problem to be solved in the prevention and treatment of landslide disasters in the Three Gorges Reservoir Area.In this paper,Bazimen landslide,a typical accumulation landslide in the Three Gorges Reservoir area,is taken as the main research object.Based on the basic principle of seepage,the influence of permeability coefficient k of landslide rock and soil mass and the rate v of reservoir water level rise and fall on slope stability is studied.At the same time,the evolution laws of seepage field,stress field,displacement field and stability of slope under different k/v conditions are analyzed by using Geostudio finite element simulation software.On this basis,using the theory of load-unload displacement response ratio,a model of load-unload displacement response ratio is established,and the relationship between parameters of load-unload displacement response ratio and stability coefficient is studied by combining the actual monitoring data of water level and displacement deformation at monitoring point of Bazimen landslide reservoir.Through the above analysis and research,the following understandings are obtained:(1)The distribution of infiltration line is related to k and v factors,so the relationship between k,v and sliding force can be determined by analyzing the force of each soil strip.Therefore,the coupling parameters k/v of permeability coefficient and rise and drop rate of water level can be used as the main influencing parameters of landslide seepage stability.(2)In the process of reservoir water level rising and falling,when k/v <1,the infiltration line in the slope presents a concavo convex shape,and the seepage field type is inner drainage or outer drainage;When k/v >1,the trend of infiltration line in the slope is gentle,and the seepage field type is synchronous.Among the four types of landslides with chair-like,straight-line,fold-line and arc-shaped landslides,the seepage velocity of the landslide with chair-shaped landslide is the largest and the straight-line landslide is the smallest.(3)Using Geostudio finite element simulation software,the variation trend of minimum effective stress,X direction,Y direction and XY direction displacement deformation and stability coefficient with the rise and fall of reservoir water level is analyzed under different k/v conditions.The evolution law of stress field,displacement field and stability of landslide is determined,and the load-unload intervals of various landslides under the rise and fall of reservoir water level are divided.(4)Taking Bazimen landslide in Zigui County of Hubei Province as an example,the load-unload displacement response ratio evaluation model of Bazimen landslide is established by using the theory of load-unload displacement response ratio.And the displacement response ratio of ZG110 and ZG111 in the key part of the landslide is calculated by the load-unload displacement response ratio evaluation model.Through the comparison and analysis with the slope stability coefficient simulated by Geostudio finite element software,it is found that there is a negative correlation between the load-unload displacement response ratio parameters and the slope stability coefficient in the key parts of the landslide.When the load-unload displacement response ratio of slope is equal to 1,its corresponding stability coefficient is large,indicating that the slope is in the stable stage,and when the load-unload displacement response ratio of slope is greater than 1,its corresponding stability coefficient is small,moreover,the more the load-unload displacement response ratio deviates from 1,the smaller the corresponding stability coefficient is.