| Apparent dip landslide is a very typical instability mode in southwest karst mountain areas in China.Its deformation development is usually affected by both dissolution degradation and underground mining disturbance.It shows complex spatial deformation characteristics and instability mechanism of rock slope structure,and is one of the key contents of disaster prevention and mitigation in karst mountainous areas.Therefore,the paper relies on the National Key R&D Program of China(2018YFC1504802).Taking Jiweishan landslide in Wulong,Chongqing as a geological prototype,combined with field geological survey,laboratory test and numerical simulation methods,the evolution law of apparent tendency loosening of karst mountain and its slide-control mechanism under mining action were studied.The degradation law of engineering mechanics properties of dissolved discontinuity and the apparent deformation and failure characteristics of mining karst mountain are revealed.From the perspective of geomechanics,the apparent instability mechanism of karst mountain under mining action is clarified,and the influence law of mining height,dip Angle,single seam and multiple periods of repeated mining on rock slope stability and mine spatial structure is discussed.A coordinated control mining method is proposed to reduce overburden movement and deformation.The main research contents and achievements are as follows:(1)By means of field survey,aerial survey by UAV,historical data collection and other methods,the typical disaster formation mode of complex apparent direction landslide in the disaster inducing geological environment is proposed.It consists of four stages: formation of structural joints and initial infiltration of surface water and weak dissolution,formation of local catchment topography and erosion of hard karst and accelerated reformation of soft rock with mud,gradual connection of dominant structural planes and formation of local independent sliding body units,stress concentration of dissolution structural planes and external trigger of apparent breakthrough slip out.The nature of slope deformation and instability in self-organization from high energy state to low energy state is revealed.(2)Based on the laboratory seepage corrosion test of limestone discontinuities,the seepage corrosion evolution model and shear mechanical corrosion degradation law of limestone discontinuities under acidic environment are clarified.Under continuous dissolution,the structure surface microtopography by native disordered structure gradually transition to a low level orderly structure,and finally form a relatively stable high ordered structures,concretely shows four stages: at the beginning of soluble point,selective grooves line stable seepage corrosion,advantage pipe flow strong dissolution,seepage and dissolution equilibrium.Accordingly,the shear strength of dissolved limestone discontinuities shows a general trend of decreasing first and then increasing.Based on this,a prediction model for the shear strength of dissolved limestone discontinuities considering dissolution rate is proposed.(3)Through block discrete element numerical simulation,the evolution process of apparent loosening of mining karst mountain and the basic law of overlying rock movement and deformation are proved.The neutral-point earthing buckling deformation of slow evolution can be divided into long-term corrosion degradation,short-term goaf unloading strong reform in two stages,among them the former make karst mountain gradually into a metastable state,after the stage of mining activities by changing the environment of surrounding rock stress reducing should stability,accelerating the regard to the effect of deformation process.At the same time,with the increase of mined-out area,the overburden caving deformation presents the S-shape change characteristics of slight disturbance in the early stage,accelerated expansion in the middle stage and flattening down in the later stage.The surface mining subsidence also responds strongly and gradually transforms from incomplete mining dynamic to full mining dynamic.(4)From the perspective of the complexity of factors affecting mine safety,the control law of mining height,dip Angle and multi-stage repeated mining on the evolution process of adaptive adjustment of spatial structure of mine rock mass was discussed.Based on the principle of orthogonal test range analysis,a coordinated control mining method was proposed to reduce the movement and deformation of overburden rock.The vertical plane of overburden loose fracture surface extends upward and connects more thoroughly and the development scale of water-conducting fracture zone is larger with the increase of mining height or the decrease of inclination angle or the number of repeated mining decreases.Correspondingly,the subsidence deformation of slope surface strata is more intense and is closer to the full state of adoption.Among the three factors,dip angle has the greatest influence on the structural integrity of overburden,followed by mining height,and the effect of repeated mining is weak. |
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