Study On Loosening Mechanism And Stability Of Slope With Deep Large Structural Plane Under Underground Mining In Karst Area

In Southwest China,karst mountainous areas are widely distributed,with strong karstification,vertical and horizontal gullies,steep terrain,deep valleys and concentrated rainfall,forming large high and steep rocky slopes.These rock slopes are usually hard at the top and flowing at the bottom,steep at the top and gentle at the bottom.In the stratum,most of them are thick limestone strata,and the structural plane of deep and large karst fissures is developed.Under the induction of underground mining activities,the original structural plane and new fissures expand and connect,leading to large-scale landslides.In view of this,relying on the national key research and development project "formation mechanism of large landslide under underground mining in karst mountain area"(2018YFC1504802),taking the collapse of Pusa coal mine in Nayong County of Guizhou Province as the research object,combined with field investigation,indoor physical model test and numerical simulation method,the loose failure mechanism of karst slope with deep large structural plane under mining action is studied.The main research results and conclusions are as following:(1)By means of field survey,data collection and UAV aerial photography,the study area of "8.28 pusha landslide disasters" was investigated deeply.Typical geological environment characteristics of the disaster area were found out,and the slope failure mode was put forward,that is,three stages of "mountain subsidence tensile deformation stage slope crack extension through sliding stage overall collapse stage".(2)Through the indoor similar model test,the paper reveals the expansion law of the original deep large structural plane,the fracture development law of the overlying strata in the golf and the slope instability failure mechanism of the karst slope with deep large structural plane under the action of mining.The results show that the deep large fracture of the karst slope has a controlling effect on the deformation and failure of the slope,and in the process of deformation and failure of the slope,the original deep large karst fracture first occurs from the bottom of the fracture The rock mass in the middle of the slope extrudes to the free face,and the original deep karst fracture runs through the free face,resulting in the slope instability.(3)The results show that the influence of mining action on the stability of karst slope is mainly manifested in the development of new fractures in the overlying rock and the expansion of the original deep and large karst fractures of the slope;the development of fractures in the slope has the spatial and temporal effect.The height of the fracture zone in the karst slope is with the goaf The area scope increases;with the expansion of goaf,cantilever beam structure is formed on the upper part of karst slope,and the cantilever beam breaks along the original deep karst fracture of the slope body.The fractured rock body slides along the deep karst fissure,which will generate thrust on the soft rock in the middle of the slope,and the soft rock in the middle of the slope is extruded,and the original deep karst fracture and the slope body face will penetrate through,and the final slope will occur Collapse and sliding failure.(4)Through numerical simulation,the effects of discontinuity depth,distance from discontinuity to loose face and angle of discontinuity on fracture loosening mechanism and slope stability of karst slope are discussed.The results show that the depth of discontinuity,distance from discontinuity to free face and angle of discontinuity have little effect on the deformation of overlying strata in golf;the distance from discontinuity to free face and angle of discontinuity have little effect on the deformation of overlying strata The depth,the distance between the structural plane and the free face of the slope and the angle of the structural plane mainly affect the deformation of the rock at the top of the slope;under the action of mining,when the graph is the same,the greater the depth of the structural plane of the slope and the closer the position is to the free face of the slope,the easier the slope is to expand from the bottom of the structural plane,and the larger the range of the expansion cracks at the bottom of the structural plane,the earlier it cracks with the overlying strata of the golf Under the action of mining,the angle of structural plane plays an important role in controlling the deformation of the top of the slope.The position of the crack expansion at the top of the slope is at the bottom of the structural plane,and under the same golf,the smaller the angle of the structural plane is,the easier the slope is to expand from the bottom of the structural plane.