Study On The Deformation And Failure Mechanism Of Gentle Retrograde Mining Slope In Karst Mountainous Area

Guizhou province is rich in mineral resources,known as the "southwest Coal Sea",with frequent coal mining activities.Slope has unique characteristics in topography and geomorphology(high and steep frontiage),stratigraphic lithology,rock mass structure(steep dip joint surface,upper hard and lower soft),etc.Long-term underground mining intensifies slope deformation and failure,making slope deformation and failure mechanism extremely complex,and making it difficult to identify and control in the early stage.Therefore,in-depth study of deformation and failure process and evolution mechanism induced by underground mining has important guiding significance for disaster prevention and control of such mining slope.In this paper,field engineering geological survey,uav aerial photography,bottom friction test,numerical simulation and other methods are adopted to take The collapse of Pusa,Zhangjiawan,Nayong County,Guizhou Province as an example,find out the engineering geological conditions of the study area and sprinkle collapse disaster characteristics,analysis of the underground coal mining activities,factors such as rainfall,and the relationship between the deformation and failure of the cape is aspersed collapse,constructed the general engineering geological concept model of collapse deformation and destruction.The deformation and failure evolution process of collapse mass under underground mining conditions is studied by using the method of bottom friction and numerical simulation.The specific research contents and results are as follows:(1)The engineering geological model of slope multi-coal seam mining is established.According to the field engineering geological survey and data collection,combined with the mining situation of Putsa coal mine,the engineering geological environment conditions of Putsa collapse body are found out,and based on the analysis of slope mining history and the distribution of multi-coal seam goaf,the engineering geological model under the condition of multi-coal seam repeatedmining is constructed.(2)The process of overburden rock and slope deformation and failure under the condition of repeated mining of multiple coal seams was revealed by means of bottom friction test.The results show that coal mining has a very important influence on the formation and development of the collapse disaster.When the depth of the coal seam is large and the coal pillar is reserved,no obvious deformation signs are seen on the slope,and only small cracks appear on the roof of goaf.The cracks develop from bottom to top,showing an inverted "V" shape.When continuing to mine shallow coal seam,due to the small buried depth and large mining area,the roof of the coal seam begins to "arch" falling,showing an obvious "three-belt" feature.Tensile cracks corresponding to the boundary of the goaf begin to appear obviously at the top of the slope,and the vertical structure is continuously tracked to develop downward.When coal pillar is reserved for mining,the caving range of goaf roof is enlarged,the tensile crack of slope roof is further widened,and subsidence phenomenon occurs.Then,under the action of heavy precipitation and slope gravity,the upper rock of slope is cut out along the interface of soft and hard rock,and the slope is comprehensively damaged.(3)The deformation and failure process of the slope was revealed by means of numerical simulation.The results show that the deformation and failure of slope under natural conditions are mainly affected by rock mass joints and fissures.The mining of coal seam intensifies the deformation and failure process of slope.Mining in the lower coal seam causes the roof of goaf to collapse,and the top of slope produces tensile cracks corresponding to the boundary of goaf.Under factors such as repeated mining and rainfall,the collapse body will creep along the bottom of the tensile crack outward and then shear failure.(4)By the physical simulation and numerical simulation flat dip mining slope deformation and failure process includes the following several stages: goaf collapse-strata deformation slope cracking,repeated mining-creep instability and failure of cut,reveals the deformation failure mechanism of slope is: the goaf collapse-cracking,creep-cut.