Study On Deformation And Instability Mechanism Of Steeply Dipping-layered Rock Slope Induced By Mining

The metallogenic geological background of karst mountainous areas in Southwest China is superior,but the karst ecological environment is fragile.Collapse and slide disasters induced by mining occur frequently,resulting in many problems of life and property safety.The steeply dipping layered rock slope is prone to bending and toppling under the action of its own weight.However,the fixed end of the cantilever rock beam will be greatly weakened by underground mining,which will undoubtedly aggravate the deformation,instability,and failure process of the slope.Therefore,the Jiguanling catastrophic rockslide disaster is taken as the research object,the deformation and failure characteristics,the rock movement,the fracture evolution process,the mining disturbance stress transmission,and the instability evolution mechanism of slope are studied by using the methods of model test,numerical simulation,and theoretical analysis.The research results have certain significance for revealing the instability evolution mechanism of steeply dipping layered rock slopes induced by underground mining,which is beneficial to improve the prevention ability of rockslide disasters.The main research contents and results are as follows:(1)Through similar model tests,the response mechanisms of joints loosening,the deformation failure and the stress transmission of steeply dipping layered slopes induced by underground mining are revealed under two different working conditions of downhill mining in the whole area and downhill mining in the upper section,downhill mining in the lower section.The results show that: underground mining plays a controlling role in the crack propagation and collapse failure of steeply dipping layered slopes;The slope has experienced the deformation and failure process of ‘roof caving and filling-bending and toppling of the upper part of the slope-tensile cracking of the rear edge of the slope-compression cracking of the front edge of the slope-sliding(shearing)of the front edge and instability of the rear edge’;during the mining process,the rock mass within a certain range at the lower end of the coal seam goaf is always pressurized,while the rock mass near the slope surface forms an unloading zone.(2)The evolution mechanism of deformation and instability of steeply dipping layered slopes induced by mining is revealed by using discrete element numerical simulation.The results show that: the failure mode of steeply dipping layered karst slopes is toppling-slip(shear).And the disaster-pregnancy mechanism can be generalized as four typical development stages: ‘the initial movement stage of the roof-the direct roof caving and fissure expansion stage-key block locking,sliding resistance and deterioration stagekey block slip(shear)and slope instability stage’.(3)Based on the superimposed cantilever beam model,a calculation theory for the stability of steeply dipping rock slopes induced by mining is proposed.The key blocks underlying the goaf are divided into shear failure zones Ⅰ and Ⅱ,and the overlying rock layer is regarded as the tensile fracture zone.The theoretical analysis model of topplingshear failure of steep dipping layered rock slope induced by mining is established.The instability process of the slope can be described as ‘the fracture in shear failure zone Ⅰ-the fracture in the tensile fracture zone-the fracture in shear failure zone Ⅱ’.Compared with the model test results,it is found that the two results are in good agreement.Dip angle and overburden thickness are positively correlated with the stability coefficient of shear failure zone.(4)Using discrete element numerical simulation method,the effects of coal seam occurrence conditions(coal seam thickness and dip angle),mining methods(mining sequence and mining step vertical height)and mining scope are discussed.The results show that: The thickness of the coal seam increases the deformation space;the dip angle of the coal seam develops length of the fracture and increases the influence range of the displacement;the mining sequence changes the force failure mode of the underlying key blocks;the mining step vertical height changes the potential sliding surface and failure mode of underlying key blocks;the distance from the goaf to the surface and the height of mining affect the stability of the steeply dipping layered slope at the same time.