Assessment Of Landslide Risk Along Wanzhou Area In Three Gorges Reservoir

The water level in the dam area of the library cyclical fluctuations greatly increases the probability of reactivation even the instability of existing and potential landslide on both sides of the reservoir area, which threatens the life and property safety of coastal residents in the reservoir area. In view of this, this paper carries on the risk assessment of landslide in reservoir area. In the first part, some basic problems of landslide risk assessment of reservoir are studied, that is, the spatial scale, time scale and landslide classification, and puts forward the main content of the strip risk assessment study on the strip distribution characteristics of the landslide strip distribution. Then, token the Wanzhou bank landslide of Three Gorges reservoir as the research object, based on the collection of various types of monitoring data and basic data, selected representative Tangjiao landslide, Huayuanyangjichang landslide and Sifangbei landslide, established the groundwater level calculation method for Wanzhou District bank section. Finally, considering the different drawdown rate and different rainfall conditions, carried out the susceptibility, hazard, vulnerability and risk assessment study of bank landslide based on deterministic model, the thesis gets some achievements and conclusions as follows:(1) Summarizes and discusses some basic problems of bank landslide risk assessment, and puts forward the main content of strip risk assessment research based on the strip distribution characteristics of bank landslide. In view of the particularity of the risk assessment of reservoir bank landslide on spatial scale and time scale and around the time range of landslide hazard and risk assessment research, scale space and landslides type key issues. It proposed the main content of strip risk assessment research based on the strip distribution characteristics of bank landslide, including susceptibility evaluation, hazard assessment and the determination, value assessment and vulnerability assessment for the elements at risk during the risk evaluation.(2) On the basis of the relevant literature and documents of bank landslides in Wanzhou segment of Three Gorges Reservoir, the statistical analysis of Wanzhou bank landslide distribution and development characteristics is carried out, and the basic characteristics of bank landslide are introduced. Based on existing data, distribution and development features of landslide of Wanzhou reservoir section are analyzed. the distribution characteristics included town scale and thickness of landslide; development characteristics included elevation distribution, profile features, hydrological and geological conditions, the stability status of landslide.Through the analysis of the basic characteristics of Wanzhou bank landslides, it summarizes the basic characteristics of typical landslide within the landslide shape, groundwater and movement.(3) Based on the actual landslide geological model and the monitoring data, the establishment and validation of the permeability coefficient inversion method for different monitoring data of reservoir bank landslide are carried out. According to the characteristics of groundwater table change with reservoir water in existed bank landslide, the calculation method of groundwater table of reservoir bank slope is obtained by using the one dimensional unsteady seepage analytical model in bank groundwater. Combined with the commonly used monitoring methods, the groundwater monitoring data and displacement monitoring data of Tangjiaoyihao and Huayuanyangjichang landslide are used to calculate the permeability coefficient of landslide by us ing the fitting analysis method. The calculation results show that the method of permeability coefficient inversion based on monitoring data can be used to obtain the average permeability coefficient of landslide. The Boussinesq method is used to solve the unsteady motion equation of the water in the slope of the water partition plate, and according to the boundary conditions of the boundary condition of the groundwater seepage line in the slope with different seepage orders in Wanzhou reservoir, then using the generalized model for calculating the Wanzhou reservoir, the elevation of the water infiltration line in the hinterland of Wanzhou area can be calculated.(4) Based on the three-dimensional the spherical sliding surface slope stability calculation model(Scoops 3D), the acquisition mode of the basic input parameters of the calculation model is introduced in detail, and according to the water level drawdown rate and rainfall in different combinations, it applied the three-dimensional slope stability calculation model to study the accumulative landslide hazard in Wanzhou reservoir section. The hazard analysis is on the basis of the slope stability calcalation, the stability is based on the transient stability during a certain elevation of reservoir water level fluctuation process and a combanation of rainfall. The main conclusions are as follows:1. In the process of the reservoir water level slowly decreased, the bank slope are mainly damaged in the form of deep and ultra deep slip surface. Most of them are nearly horizontal strata deep-seated landslide, Most of the area is low hazard 2. In the process of the reservoir water level rapid decreased, it can be seen the two conditions of shallow and middle landslide ratio increased significantly, and the condition 2 increaed more than condition. The deep and ultra deep landslides decrease, the risk of the whole reservoir is increased, and the two increase is more significant, the risk level of the landslide disaster is higher and the region is basically distributed along the two sides of the river; 3. Bank slope of the reservoir water level decline rate and rainfall intensity response is more sensitive to the combined effect is caused by the main factors of bank slope body shallow layer landslide number increase. With the construction of the Three Gorges Dam, It also consistent with the shallow surface slip and secondary landslide occurred frequently, such as secondray slide in the front of Tangjiao 1 Landslide, soil slide in the front of pile in Dazhou landslide, deformation of front of Sifangbei landslide.(5) According to the data collection of Wanzhou urban land use planning and the population distribution, The elements at risk in the whole Wanzhou area is divided into population and economy, and then under different conditions of different reservoir status, the vulnerability assessment and risk analysis of casualties and economic losses of landslide disaster in the Wanzhou reservoir were carried out.The conclusions are as follows:1. The risk of casualties in all the conditions nearby the Wanzhou District are the biggest. Through all the conditions it can be found, the risk of the casualties number in the other areas of the Wanzhou reservoir area is increasing; 2. Under the no groundwater condition, high economic risk areas are mainly concentrated around the District areas, mostly are transportation economic risk. With the groundwater condition, high risk areas began to the other bank area, the risk of entire economic losses in the city is at a moderate level.3. After reservoir water level dropped to 159 m, the risk of the city and the area along the bank of the reservoir area has increased, but the increase in the value of the total economic risk is not high. After reservoir water level at a rate of 0.6m/d decreased from 159 m to 145 m, it can obviously see the increase of the risk value within the District areas, and the increase position are mainly in the area of the reservoir fluctuation zone. When the dropdown rate rised to 1.2m/d, the increased risk was more obvious.5. With the reservoir water level drop and the drop rate increases, the casualties risk and the total economic loss risk in the Wanzhou District and other bank area of the reservoir bank region showed a significant increasing trend, which are positively correlated with the reservoir bank landslide hazard.