Generation Mechanism Of Secondary Disaster And Landslide Surge At Zhexi Hydropower Station

A large scale of slope instability will cause a huge disaster to the society.Meanwhile,due to the specificity of the location where the bank slope of reservoir is,a serious secondary disaster will be further caused,stirring up huge surge,which not only bring threats to the dam safety,but also will cause serious damage to the life and property safety of coastwise and downstream people.A case of the reservoir bank landslide in Zhexi Hydroelectric Power Station,basing on the numerical stimulation method,the paper has made a deep analysis on the stability of side slope of landslides and the change rules of surge generation,propagation and climb processes,which is intended to provide a reliable basis for the decision-making of disaster prevention and reduction.The study content thereof is summarized as follows:(1)Comprehensively elaborate the project profile and hydrogeological condition of Zhexi Hydroelectric Power Station;thoroughly introduce the general situation of its bank slope of reservoir,Tangjiaxi landslide,and the geological structure and hydrological environment in slope area;systematically analyze the formation mechanism of Tangjiaxi landslide.Thus it is known that the generation of landslide is mainly effected by the lithological character of the slope where has poor geological conditions of bed rock,the geomorphological factors of steep slope,the inducing factor of heavy rainfall and the project activities of improper excavation and road works which have emptied the slope.Some corresponding measures for landslide control also are proposed to provide the basis of slope stability improvement.Meanwhile,the classification also is made for the secondary disasters induced by landslide,and its perniciousness also is analyzed for each kind of secondary disasters.(2)Based on the fem strength reduction theory,a stability analysis is made for the landslide of reservoir bank in Zhexi Hydroelectric Power Station.Using ANSYS to establish the finite element model of slope A-A typical section,and calculate the deformation characteristics under different working conditions.The result shows that:in the case of slope under a natural working condition,the computation is convergent,but the area of plastic zone is relatively large,and the value of maximum plastic strain is about 3.22 cm,although no collapse occurs,the safety coefficient is 1.0,lower than the safety standard 1.15,thus the side slope of landslide is in a unstable status;in the case of rainstorm,collapse occurs,the safety coefficient is 0.8,and the slippage area is basically similar to the real condition.Aiming at such unstable slope,a engineering measure for anchor rod strengthening is proposed.The safety coefficient after strengthening is 1.4,which is obtained by strength reduction method and much higher than safety standard 1.15.Moreover,the area of plastic zone is obviously smaller than before,and does not form a continuous penetration.The slope is in a stable status.Thus an effective engineering measure is provided to solve the stability problem of rock-soil slope.(3)Using hydrodynamic numerical simulation software "Flow-3d" to simulate the secondary disaster(surge)caused by reservoir bank landslide.Through the comprehensive analog computation of surge generation,propagation and climb processes,a deep analysis is made on the relations between surge height and landslide speed of entering water,gradient of unstable slope and depth of water and on the change rules of surge climbing on the opposite bank.Thus a corresponding measure for engineering prevention and control is proposed to minimize the damage caused by small landslide surge,and provide favorable conditions for scientific decisions.In this paper,the two-dimensional model can not be used to reflect the actual form of landslide process and surge propagation,and can be further calculated by three-dimensional numerical simulation.