Study On The Mechanism Of The Deformation And Stability Of The Toppling Mass Of Zhengjiaping

Since the reservoir filling of Dagangshan hydropower station from October 2015,there has been settlement and cracking in the middle and frontal zone of Zhengjiaping slope located in the reservoir area,and small scale collapse has occurred in the local area.Under the condition of reservoir filling and other unfavorable working conditions,its deformation and failure may be further aggravated,and eventually collapse or landslide will be formed,which will endanger the safety of traffic,water operation,water conservancy engineering and so on.In this thesis,the geological investigation in the field and exploration of the toppling mass of Zhengjiaping slope are carried out,which generally master its engineering geological conditions.then the deformation failure characteristics and genetic mechanism of the toppling mass are comprehensively studied.Based on the above,the stability of the toppling mass is synthetically studied,and the engineering prevention measures are put forward to ensure the security and stability of the toppling mass.The main results are finally as follows:?1?According to the field geological survey,it is concluded that the types of the deformation and failure of Zhengjiaping slope mainly include the tension crack,settlement crack of road,the bulging deformation of the retaining wall,and the collapse in local area.?2?Accordingtotheengineeringgeologicalcharacteristicsandboundary conditions,the toppling mass can be divided into three regions:regions?,regions?and regions?.Combined with the degree of toppling deformation of rock mass,the toppling mass can be divided into broken and loose deformation zone,strong toppling deformation zone,weak toppling deformation zone and normal strata.?3?The internal cause of deformation failure of the toppling mass include the well developed bedding structure plane of the sandstone shale and the free surface condition of the slope which lead to the strong deformation of the rock mass;The external factors mainly include the excavation and cutting feet of the reconstruction road,the reservoir filling,the rainfall and so on,which result in the stable condition of the frontal zone of the slope and the decrease of the shear strength of the rock mass.as a result,the deformation and failure of the toppling mass are further aggravated.The rock mass of each deformed region shows a composite deformation failure mechanics model:toppling and breaking of rock mass occurring in the early stage,sliding and tensile cracking of rock mass occurring in the later stage,and landslide happening at last.?4?Based on the engineering geological investigation,the analysis of deformation monitoring data,stability calculation of limit equilibrium method and numerical simulation,it is synthetically concluded that the rock mass in region I is in the initial accelerated deformation stage after reservoir filling.Under the condition of reservoir filling,it is at a critical steady state.Under the condition of reservoir filling,rainstorm and reservoir filling,earthquake,the rock mass will lose stabilization.all the working conditions do not meet the standard of safety control.the zones?₁ and?₃ of region?are in stable state,but the zone?₂ is unstable and does not meet the standard of safety control under the various unfavorable condition.the rock mass of region?is in basic stable condition under reservoir filling,and is under the metastable state on the condition of rainstorm and reservoir filling.In addition,it is under the unstable state on the condition of the reservoir filling and earthquake.the results do not meet the standard of safety control under all the working condition.?5?According to the results of the stability evaluation of the toppling mass,it is suggested that the control measures by the combined method of"frame girder,prestressed anchor cable and anti-slide pile"should be adopted to reinforce the slope in order to achieve the purpose of treatment.In addition,the tunnel should also be excavated to avoid the toppling mass of Zhengjiaping completely in order to achieve the goal of permanent radical treatment.Due to the discontinuous distribution of cracks in region?,and the cracks in the rear edge of the toppling mass basically remaining unchanged after reservoir filling,it is in a basically stable state as a whole,but the local stability is poor.In order to achieve the purpose of permanent treatment,it can be considered that long tunnel is excavated in region?and?and the slope should be reinforced in region?.The choice of the final option is determined by comparison of the program of prevention and cure.