Slope Stability Analysis And Bank Collapse Prediction Of Jingyugou Loess Reservoir

The newly built Checun Reservoir project located in Jingyugou in the eastern suburbs of Xi’an is listed as an important regulation and storage project of the Han-Han-to-Weihe River Diversion Project.It undertakes the task of regulation and storage of the Bahe branch line and also serves as a backup water source for Xi’an.The geological environment on the bank of the proposed reservoir will change significantly during the process of water storage and operation,which will easily induce the instability of old landslides and bank slopes,forming landslides and bank collapses,directly affecting the engineering benefits of the reservoir construction.For this reason,based on the detailed investigation and exploration of the engineering area,this paper conducts a systematic study on the bank slopes of the study area through indoor and outdoor tests,data statistical analysis,numerical simulation and other methods.The main research contents and results are as follows:(1)The basic physical indicators,permeability and strength characteristics of the rock and soil mass in the reservoir area were studied,and the strength indicators of the Quaternary overburden and the tertiary Bahe Formation mudstone strata in the reservoir area were determined based on the test results and engineering experience in the study area..(2)The basic characteristics of slope shape,structure type,geological structure,deformation and failure mode of the bank slope in the reservoir area are studied.The average slope height and slope angle of the left bank slope in the downstream and middle and lower reaches of the reservoir area are higher than that of the right bank,and the slopes of the slopes from the mouth to the end of the reservoir slow down;the structure types include loess bank slope,loess-sloped soil bank slope,loess-sand Mudstone bank slope and loess-landslide accumulation soil bank slope accounted for 39.22%,40.20%,8.82%and 11.76%respectively;from the dam site area to the end of the reservoir,the sand and mudstone strata of the Bahe Formation on the left bank slope from the middle reaches to the downstream,and the right bank is relatively gentle;Bank slope failure modes mainly include erosion and denudation type,slip type and collapse type.(3)Based on the numerical simulation of typical bank slopes based on seepage theory,a stability evaluation method suitable for bank slopes with poor permeability in loess areas is proposed.This method is used to evaluate the stability of the bank slopes during the rise and fall of the reservoir water level.The law of the influence of reservoir water on the stability,damage range and mode of the reservoir bank slope is discussed.(1)In the process of water level surge,the most unfavorable situation of bank slope is the stable condition of water level change from beginning to end.In the case of a sudden drop in water level,the most unfavorable situation is the stability of the original high-water level submerged slope before groundwater seepage;(2)The overall minimum stability coefficients of the four bank slopes are all higher than the safety coefficients,and the overall sliding probability is relatively high.small.During the process of reservoir water changes,the local potential sliding surface range controls the change of the stability coefficient.The gentle slope area is dominated by slippage failure,and the steep area is dominated by collapse failure.The bedrock interface and the overburden layer have local damage.The loess is affected by the reservoir water.Reservoir bank reconstruction activities are intense;(3)At various storage heights of different bank slopes,the drop in the reservoir water level obviously increases the possibility of local bank slope instability.For the slope where the slope changes from gentle to steep,the stability is affected by the fluctuation of the reservoir water.The impact is significant,and it is easy to cause local bank slope instability.(4)Comprehensive bank slope structure method and Kachukin method,proposed methods and principles for bank collapse prediction suitable for Jingyugou reservoir area(canyon-type reservoir in the loess plateau),and used this method to carry out long-term bank collapse in the reservoir area.Scope prediction shows that the loess bank slope has a strong bank collapse activity.The bank collapse volume of the loess reservoir is predicted.The total bank collapse volume is about 3.964 million m~3,accounting for 69.8%of the predicted total bank collapse volume,which is the main bank collapse part of the reservoir area.