Coupling Calculation Of Mining-induced Stress-fracture-seepage In Coal Seam Overburden

The coal bases in western China are located in arid and semi-arid areas,where water resources are scarce and the ecological environment is very fragile.With the popularization of high-yield and high-efficiency mining technology in the western coal base,the overburden of coal seam shows a new pattern of failure evolution.The impact of coal mining on aquifer structure and ecological environment is becoming increasingly prominent.Therefore,the research on the development pattern of overburden stress field,fracture field and seepage field during coal mining is of great significance to the safe,green and efficient coal mining in the ecologically fragile mining areas in western China.In this paper,we focus on the first mining face of Jinjiitan mine field in Yushen mining area.First of all,through summarized relevant documents from the study area and collected large number of literature,the geological environmental background are analyzed,the calculation formula of local stability index(LSI)are derived,the mining stress-permeability coefficient relationship equation are optimized.Secondly,coupling calculation of mining-induced stress-fracture-seepage in coal seam overbu rden was conducted by computer numerical simulation.The main conclusions as follow:(1)The LSI can quantitatively delineate the mining-induced failure area in coal seam overburden,and coupling calculation of mining-induced stress-fracture in coal seam overburden was simulated by FLAC^3D software.Three main failure areas in the overlying strata of coal seam and their development rules are revealed.According to the law of mining-induced stress-fracture field(MSF)evolution,the concepts of "the ratio of the height of MSF to minining thickness"(RHM)and "the ratio of the width of MSF to mining thickness"(RWM)were proposed.The height of MSF is 108m when the mining thickness is 5.5m,and the RHM is 19.64,which is closer to the result determined by the observation of flushing fluid leakage(19.54).(2)Based on the hydrogeological parameters of the study area,the vertical permeability coefficient ratio(K_z/K_z0)of coal seam overburden under different working face is calculated by using the optimized rock mining stress permeability coefficient relationship.The results shows that:the vertical permeability increasing areas of coal seam overburden are distributed in three areas,which are directly above the mined-out area and obliquely above both sides of the mined-out area.The overall distribution was approximately "saddle-shaped",and the development law was controlled by the advancing distance of the working face.(3)In order to predict the drawdown depth of the groundwater and water inflow under different working face,the coupling calculation of mining-induced stress-fracture-seepage in coal seam overburden was simulated by Visual Modflow software on account of LSI and the optimized rock stress-permeability coefficient relationship equation.Under the calculation without considering the development of MSF,the maximum drawdown depth of the groundwater is 0.69m and the water inflow is 8932.5m³/d.Under the coupling calculation of mining-induced stress-fracture-seepage,the maximum drawdown depth of the groundwater is 1.32m,which is close to the field detection result(1.21m),and the water inflow is 34356.48m³/d,which is close to the calculation results of "big well method"(32810.4m³/d).