Research On Overburden And Slope Deformation Influenced By Repeated Mining Of Key Layers

Underground coal seam mining usually causes various geological disasters,resulting in greater casualties and property losses.Therefore,it is very important to study the process of mining overburden and slope deformation.to take the most effective measures to reduce or reduce the occurrence of disasters.The mining overburden and slope deformation are affected by many factors,which can be divided into two types: geological factors and mining factors.Among them,geological factors include overburden structure,coal seam occurrence conditions,topographic conditions,etc.;mining factors include coal mining method,roof management method,working face layout,cumulative mining,etc.Under different geological conditions and mining conditions,mining overburden and slopes show different deformation characteristics.Many scholars at home and abroad have shown that the structure of the key layer of the overlying rock controls the subsidence of the mining overlying rock,the evolution of the fissure,and the displacement of the mining surface slope.The characteristics of overburden and surface deformation are different,and the displacement changes are quite different.Therefore,it is of great significance to study the overburden and slope deformation under the condition of repeated mining combined with the theory of key layers.This paper takes the southwest mining area of Tai’an Coal Mine as the research object,through the collection of data and field investigation,the two-dimensional discrete element model and the three-dimensional finite element model of the study area are established,and the dynamic deformation laws of repeated mining overburden and slope under different key layer structures are established.,the spatial distribution characteristics of stress,the distribution law of surface displacement,etc.,and summarizes the law of overlying rock and surface migration in the study area.By designing multiple sets of comparative experimental programs,the two main effects of repeated mining under the overlying rock and slope deformation are studied.Factors: the controlling effect of overlying rock structure and slope structure.The repeated mining overburden migration process in the study area is summarized into five stages,namely,the upper coal seam mining,the vertical tension crack of the upper key layer floor;the upward expansion of the crack;the lower coal seam mining,the lower key layer breaking;the upper goaf The area subsides synchronously,and the width of the abscission fissures increases;the main key layer is broken,and the surface sinks synchronously.By analyzing the model of different key layer positions,the key layer plays a major role in controlling the migration of the overlying rock and the slope deformation.For the situation where there is a key layer between the upper and lower mining areas during repeated mining,the upper and lower mining areas are not broken when the key layer is not broken.The interaction between them is very small.After the key layer is broken,the two gobs are connected,and the displacement and stress change drastically.From the results of this study,it can be seen that when the main key layer is located at a certain position above the coal mining face and has sufficient strength,it can play a better role in reducing surface subsidence cracking.For mining areas with this type of overlying rock structure,when the key layer has not been broken at the end of the mining work,grouting can be used to fill the separation cracks in the lower part of the key layer,which can strengthen the bottom plate of the main key layer and increase its tensile strength.At the same time,it is the key layer.The bottom provides support to reduce the tensile stress of the key layer bottom plate and achieve the effect of reducing the surface displacement and the development of cracks.