Failure Law Of Coal Seam Floor And Water Inrush Risk Evaluation Zoning In Dengcao Coal Mine

Dengcao coal mine belongs to the karst fissure water disaster area of Permo Carboniferous coalfield in North China.With the continuous transfer of coal seam mining to the deep,the geological structure environment becomes more complex and the stability of floor rock stratum becomes worse.The mine will face a serious threat of floor water inrush in the process of production.On the basis of summarizing and analyzing the hydrogeological data and theoretical research of the mine,this paper uses FLAC3D numerical simulation software to simulate the22031 working face in mining area 22 of the coal mine The failure law of the bottom slab is analyzed from three aspects:the failure characteristics of the plastic zone of the top and bottom slab and the variation characteristics of the vertical displacement of the top and bottom slab.Through the field investigation and research of Dengcao coal mine,it is determined to select the water pressure,permeability coefficient,water yield of L_7-8limestone aquifer and the equivalent impermeable layer thickness of the floor of No.Ⅱ1 coal seam as the four main control factors of water inrush risk evaluation,and evaluate the water inrush risk of No.Ⅱ1 coal seam floor with AHP vulnerability index method based on GIS.The research results are as follows:（1）In the process of advancing the working face,the vertical stress in the stress concentration area of the surrounding rock of the stope increases continuously.After advancing to 220m,the stress value gradually stabilizes between 33～34MPa;The stress reduction area mainly produces tensile failure,and the stress concentration area mainly produces shear failure.A plastic failure area with an approximate"spoon"shape distribution is formed under the coal body on both sides of the working face along the inclined direction of the coal seam.In the process of advancing the working face,the rock mass of the top and bottom plates continuously produce secondary cracks until they are developed and connected.The maximum failure height of the top plate in the plastic area is 29.51m,and the maximum failure depth of the bottom plate is 13.67m,This is close to the theoretical formula calculation result of 14.83m;The vertical displacement of the roof and floor of the goaf formed behind the working face decreases in a gradient from the midpoint of the goaf to both sides.After the working face advances to 220m,the bulging displacement of the floor remains basically stable,and the sinking displacement of the roof also begins to stabilize gradually.Coal mining will cause certain damage to the integrity of the roof and floor strata,and the resulting cracks will be connected with the aquifer.It is necessary to prevent the threat of floor water inrush caused by the destruction of coal seam floor in the mining process.（2）The risk degree of water inrush from the floor of No.Ⅱ1 coal seam in the mining area gradually intensifies from the southwest to the northeast.The risk area is distributed in the east of the mining area,accounting for 15.09%of the total area of the mining area;The more dangerous areas are mainly distributed in the middle and north of the mining area,accounting for 26.42%of the total area of the mining area;The transition area is mainly distributed in the southwest and Southeast,accounting for 29.51%of the total area of the mining area;The relative safety zone and safety zone are mainly distributed in the southwest and northeast of the mining area,accounting for 15.77%and 13.21%of the total area of the mining area respectively.According to the zoning results,the corresponding water control countermeasures and preventive measures can be formulated purposefully.There are 31figures,16 tables and 111 references.