Prediction And Risk Analysis Of Reservoir Landslide Under Precipitation And Reservoir-level Fluctuation

The Three Gorges Reservoir area has complex geological conditions,and its banks have developed fissures,making it the worst-hit areas of geological disasters in our country.Monitoring and early-warning of the geological disasters in the Three Gorges Reservoir area play an important role in ensuring the safety of local residents' lives and property and maintaining the safety of shipping on the Yangtze River channel.Due to the periodic fluctuation of reservoir level and seasonal heavy precipitation in the Three Gorges reservoir,the response mechanism of landslide deformation is very complex.The prediction accuracy of numerical model is very low,which seriously restricts the early warning analysis of landslide disaster.Based on the above problems,this paper establishes a reservoir bank landslide deformation prediction model considering the factors of precipitation and reservoir level delay,and studies the risk threshold of reservoir bank landslide deformation.The main ideas are as follows:(1)Firstly,the characteristics of the displacement response of Xinpu landslide in the Three Gorges Reservoir area are analyzed,and the delay time of the displacement rate of Xinpu landslide in response to precipitation and reservoir level change is quantitatively analyzed;(2)Secondly,the short-term prediction of the landslide displacement rate is carried out by using the grey system modeling principle of time-delay and multi parameter,with the consideration of precipitation and the time delay of the reservoir level.(3)Finally,Copula function is used to establish the combined probability distribution functions of landslide displacement rate,reservoir level and precipitation,and the threshold values of precipitation and reservoir level that affect the deformation state of landslide are extracted by value at risk method,which can provide reference for landslide early warning.The main achievements and innovations of this paper are as follows:(1)The characteristics of the displacement response and mechanism of the landslide along the reservoir bank in the Three Gorges Reservoir area are analyzed.The response delay time of the displacement rate of Xinpu landslide to precipitation and reservoir level changes is quantitatively analyzed by the time-lag cross-correlation analysis method.The results show that:the displacement rate of Xinpu landslide is significantly related to precipitation,the response delay time to precipitation is about 5 days,and the mid-rear parts of the landslide are more susceptible to precipitation;the displacement rate is strongly correlated with the elevation of reservoir level,the response delay time to the change of reservoir level in the Three Gorges Reservoir area is about 31 days,and the influence of reservoir level fluctuation on the front edge of landslide is more obvious,and the closer to the Yangtze River,the shorter the delay time.(2)In this paper,a multi parameter grey prediction model of landslide deformation considering the time delay of precipitation and reservoir level is established,and its prediction accuracy is compared and analyzed.The example shows that the accuracy and reliability of landslide deformation prediction can be significantly improved by introducing time delay parameters into the prediction model,and the goodness of fit reaches 0.70.Compared with GM(1,1)model and GM(1,3)model without considering time delay factors,the prediction accuracy(RMSE)of the new model is improved by 53.8% and 58.3%,and the mean absolute error percentage(MAPE)is reduced by 7.19% and 7.47% respectively.(3)The precipitation and reservoir level risk thresholds that induce the acceleration of the displacement of the Xinpu landslide in the Three Gorges reservoir area are extracted.The copula function is used to establish the combined probability distribution function of landslide displacement rate,reservoir level and precipitation,and the value at risk method is used to analyze the risk threshold value of reservoir bank landslide under the influence of precipitation and reservoir level.The results show that: when the precipitation reaches 55mm/D and the reservoir level elevation is lower than 147 m,if the heavy precipitation continues and the reservoir level elevation remains low,the displacement rate of landslide may further accelerate or even go to failure.