Research Of Induced Mechanism And Prediction Of Pajiayan Landslide In Zhong County In Three Gorges Reservoir Area

Since the first impoundment started in2003, the stability of the bank slope has become the most important problem of engineering geology in Three Gorges reservoir area。Groundwater seepage of the Bank Slope also appears cyclical variation under the cyclical movements of the water level. Continuous flow of groundwater will result in continued softening of rock and soil, and the internal cracks of the slope expanding. Then it gradually reduced landslide stability, eventually leading to deformation and failure of the bank slope, thus making frequent occurrence of the landslide disasters in Three Gorges reservoir area. Research of the deformation, failure mechanism as well as forecasting research becomes a hot topic in the prevention of geological disasters. Commonly the prediction method were established on the basis of the analysis of displacement monitoring data, then use the mathematical model to predict, but the error of the model is generally larger, because we didn’t have a depth understanding of the formation mechanism of landslides. So the deformation, failure mechanism as well as forecasting research of Landslides is extremely important and far-reaching significant to the geological disaster prevention and mitigation of people’s lives and property safety.Taken Pajiayan landslide in Zhong County as a research object, based on the study of landslide geology and regional geology, Combined with the preliminary investigation and field geological survey data, build a landslide geology generalized model. Analyze the internal factors, which affect the deformation and failure of landslide, such as Topography, geological structure, material composition and structure of the landslide and so on; and induction factors, such as water level fluctuations, rainfall, river erosion, spring infiltration, earthquakes and human engineering activities and so on. Orthogonal design method was used to design calculation program, choosing L16(45) orthogonal table, analyzed the order of the factors leading to deformation and failure of Pajiayan landslide. Select several typical conditions and use SEEP/W module in Geo-studio simulate the distribution of groundwater seepage in different conditions. Using the finite element analysis software FLAC3D, author simulate the deformation mechanism of Pajiayan landslide during different conditions by analyzing the displacement equivalent cloud, shear strain increment equivalent cloud as well as the plastic zone maps. Based on the above analysis, we draw the following conclusions:1、The main deformation zone is located to the uplift in the leading edge and the tensile cracks and caving ground in the middle and rear end of the slip mass. It’s deformation model is Slip-crack type. The deformation in the leading edge of the landslide is evident, the rear relatively slow, shown as:the leading edge collapse�'eformation in the middle and back�'cut export form in the leading edge�'sliding surface through�'overall instability and failure, appears like the characteristics of "retrogressive failure"2、Based on the Sensitivity analysis method by orthogonal design, got the order of the influencing factors as follows:internal frictional angleφ>rainfall y>cohesion c> water level h>sliding unit weight y, in which the internal frictional angle is the most important factor that controls deformation and failure of landslide, the small changes can lead to large deformation. Pajiayan landslide located in the upstream section of the Three Gorges Reservoir Area, less affected by water level fluctuations, meanwhile rainfall in the region is larger and lasted for a long time, and the stability of the landslide is more affected by rainfall. Therefore, the result of the sensitivity analysis results is more in line with the laws which the influencing factors working on Pajiayan landslide.3、The analysis result of the seepage field based on Geo-studio and the deformation analysis based on Flac3D shows that stability of the landslide is changed with the changes in rainfall and reservoir water level, which were two main inducing factors of the deformation of landslide. In times of heavy rainfall, the infiltration of rainfall caused the landslide changes in groundwater seepage field, thus softening the rock and soil, reducing the shear strength of the rock mass, thereby reducing the stability of the landslide. It shows as following: larger displacement contours, larger shear strain increment, and larger plastic zone.4-. Based on the time series model, divide the displacement series into trend term displacement which is controlled by its own geological conditions and periodic term displacement affected by external factors. Use mathematical models to analyze the forecast displacement sequence. The results showed that the forecast accuracy of the displacement can be significantly improved, and is feasible and effective in landslide displacement prediction. And then predict the displacement series within the coming year of Pajiayan landslide. The prediction results show that the displacement curve of Pajiayan landslide changes moderating, currently in the stage of creeping. In accordance with the site survey results, obvious deformation and failure characteristics shown in the central of the landslide, so the landslide is still in the stage of slow deformation. The built models are adequate for landslide displacement prediction.