Study On Overlying Rock Failure Above Large Mining Height Longwall Face With Shallow Cover And Development Height Of Water Flowing Fractured Zone

The Jurassic coalfield in northern Shaanxi is rich in shallow buried depths with a depth of less than 200 m,Bojiyan,and coal seams covered with loose sand layers.In the process of shallow burial,large mining height,long wall working face and rapid development of high-strength mining,the overlying rock formation usually can not form a stable masonry beam structure,often causing the roof to cut down thick along the coal wall,leading to underground power disasters,water resources damage and surface collapse.And other damage problems.However,the above-mentioned mining damage problems are closely related to overlying rock damage and rock strata mining fracture,and the mining area is located in arid and semi-arid water resources.Therefore,it is of great theoretical significance and engineering guidance value to study the failure of overlying strata,the development height of fractured water-conducting zone and its main influencing factors during the mining process of shallow-buried high mining work face.On the basis of overburden structure and key layer control theory,this paper takes Daliuta 5-2 coal tri-disk area 52306 working face as the research object,and fiber grating sensing technology as the core means.Theoretical analysis,physical similarity simulation test,numerical simulation,field measurement and other research methods are used comprehensively.Firstly,the paper analyzes the development law and characteristics of fractured water-conducting zone and the main factors affecting the development height of fractured water-conducting zone.Through the physical similarity simulation test,the failure process of the overlying rock layer along with the work surface is analyzed,and the optical fiber indicator system for the destruction of overlying rock in the model test is established.The corresponding relationship between the change of optical fiber frequency shift step and the deformation and failure of overlying rock is revealed.And from this,it is obtained that the initial pressure step distance of the working face is 76.50 m,the pressure step distance is 9.0?22.50 n periodically,and the average pressure step distance is 16.41 m during the average cycle.The fiber optic monitoring results in the height of fractured water-conducting zone of the working face was 142.5 m.Using UDEC numerical simulation,the height of fractured water-conducting zone was finally 140.0 m,and the overall development height of the water guide fissure zone on the working surface was 137.32 m by comparing the amount of fluid leakage and core characteristics of the drilling hole.The results of model test optical fiber monitoring,UDEC numerical simulation and field measurement are basically the same.Through the research of this paper,the optical fiber characterization model of overburden deformation structure is established,and the response relationship between overburden failure and optical fiber frequency shift change is revealed,which provides a theoretical basis for the optical fiber characterization of rock mass deformation structure.The method and its application can provide the basis for the deformation informatization of overlying rock in the future.