Research On Stability Analysis Method And Treatment Technology For Water-rich Open-pit Mine Slope In Sandy Gravel Strata

It is a worldwide problem to excavate open-pit mine in water-rich strata,and how to prevent the infiltration of groundwater has become the key problem affecting the stability of open-pit mine slope and safety production.Many similar mines at home and abroad have carried out a lot of exploration work in this field,but there are few successful precedents.Water-rich open-pit mines are faced with the dilemma of "water disaster is difficult to stop,slope is difficult to reinforce,and mining is difficult".In order to solve the problem of water cutoff and slope reinforcement in water-rich open-pit mines,this paper studied the evaluation method of mine slope stability,the limited earth pressure and the analytical solution of diaphragm wall stability,taking Tenglong open-pit mine as the engineering background.On this basis,the technical scheme of water stop and slope reinforcement by the diaphragm wall is put forward,and the construction parameters are optimized.The stress state,damage characteristics and freeze-thaw fatigue life of diaphragm wall under Frost Heaving in winter are also studied.The project has successfully solved the major technical problems of slope excavation in water-rich open-pit mine.The diaphragm wall can avoid the groundwater environment damage and water resource waste caused by drainage,which meets the requirements of "green,safe and sustainable development",and can provide a useful reference for anti-seepage engineering in similar open-pit mines.At the same time,it has positive significance to improve the ore output of China and even the world.The main findings of this study are summarized as follows:(1)Study on the evaluation method of double safety factors for slope stability of open-pit mine.Based on the softening characteristics of rock mass(or soil)materials and the variation of parameters from peak strength to residual strength,the mathematical relationship between non proportional reduction factors is established.Combined with the strength theory and the stress state of rock(or soil)element on the slip surface,the point safety factor and the comprehensive safety factor of the slope are calculated,defined by the ratio of shear strength before and after reduction.Then,a new search method of slip surface was proposed by taking the maximum shear strain rate of the element as the characteristic parameter.In this method,the points on each line with the maximum characteristic parameter were searched through both the vertical and horizontal paths,and the data was processed using the Gauss filter technology to obtain a smooth slip surface.Finally,the influence of reduction mode,strength parameters and slope shape parameters on the slip surface is analyzed.(2)Study on the earth pressure for finite soil considering the width of platform of open-pit mine slope.According to the limit equilibrium theory and plane sliding assumption,the calculation models of earth pressure for finite soil with different shapes are constructed,considering the size parameters,strength parameters and friction angle between wall and soil.And the calculation formulas of active and passive earth pressure for finite soil are established respectively,as well as their application ranges.Finally,the influence of various factors on the earth pressure for finite soil is studied.(3)Study on the stability of diaphragm wall with complex conditions considering the effect of finite soil.The formula of seismic passive earth pressure for finite soil is derived,firstly.On this basis,the stability calculation model of diaphragm wall considering earthquake(blasting vibration),groundwater and frost-heave is established.The analytical solutions of anti-sliding safety factor,anti-overturning safety factor and anti-kicking safety factor of diaphragm wall are derived,and the influence of different factors on the safety factors are analyzed The research provides a theoretical basis for the design of diaphragm wall.(4)Research of the technology of water cutoff and slope reinforcement in water-rich open-pit mine.In order to solve the problem of water cutoff and slope reinforcement in open-pit mine with sandy gravel aquifer,the technology of large-scale diaphragm wall is introduced,in view of the complex conditions of slope with high water pressure and low strength.According to the different passive earth pressure of the wall,two kinds of diaphragm wall structures are developed:the single diaphragm wall structure and the pre-stressed and pulled diaphragm wall structure.Taking the single diaphragm wall structure as an example,the construction parameters of diaphragm wall is optimized through the orthogonal experiment.In view of the problem that the gravel layer is thick and easy to collapse,the paper put forward the technology of "three drilling and two grasping" combined with grabs and percussion drills,and the technology of "high pressure jet grouting before grooving " to overcome the problem of grooving of diaphragm wall.The project has successfully solved the major technical problems of slope excavation in water-rich open-pit mine.The diaphragm wall can avoid the groundwater environment damage and water resource waste caused by drainage,which meets the requirements of "green,safe and sustainable development",and can provide a useful reference for anti-seepage engineering in similar open-pit mines.(5)Study on the force-deformation characteristics and damage mechanism of diaphragm wall under the action of frost-heave.Considering the variation characteristics of rock and soil thermodynamic parameters with temperature,a thermo-hydro-mechanical coupling model of diaphragm wall is established,and the deformation and stress characteristics of slope and diaphragm wall are analyzed,under the conditions of no frost-heave,one-way frost-heave and two-way frost-heave in different excavation stages of mine.The effects of temperature and freezing time on the stress,deformation and damage mechanism of diaphragm wall are also studied in detail.Finally,the compressive,tensile and tension and compression fatigue life of concrete at different parts of diaphragm wall are studied,based on the ’S-N’ curve.