Seepage law of bedrock aquifer and water-preserved mining technology in deep coal seam mining

Huanglong Coalfield,located in the northwest of China,has low rainfall and strong evaporation,and belongs to arid and semi-arid areas. The protection of aquifers during coal mining is extremely important. In order to study the water-preserved mining technology applied to the Cretaceous Luohe Formation sandstone aquifer in the deep coal seam mining,the Binchang mining area was selected as the research area. Sandstone porosity test combined with nonlinear regression analysis was used to study the permeability variation of sandstone in different depths of the Luohe Formation. Moreover,this study analyzed the vertical water chemical field heterogeneous characteristics of the Luohe Forma-tion aquifer by using hydrochemical tests. In addition,the Luohe Formation heterogeneous medium parameters were quantitatively studied through the surface and underground hydrogeo-logical exploration. Based on the heterogeneity of the Luohe Formation aquifer,a numerical model of groundwater seepage under the condition of the water-flowing frac-tured zone only affects the lower aquifer was developed,and the seepage law in this condition was studied. According to the seepage laws,the water-preserved mining technology in deep coal seam mining is studied. Combined with the water level changes in the mining conditions of coal mining face in Binchang mining area,the water-preserved mining technology was verified. The results showed that the permeability of the Luohe Formation aquifer decreases negatively, and the chemical type of the aquifer is converted from the type of HCO3 -Ca to the SO4 -Na,and the specific yield of the upper aquifer is about seven times that of the lower with the increase of the depth of the formation. The groundwa-ter seepage conditions in the upper and lower sections of the Luohe Formation aquifer are different,and the law of ver-tical heterogeneity is confirmed. When the water-flowing fractured zone only affects the lower section of the aquifer,on-ly the drawdown of the lower section and adjacent layers is significantly,and the water lever change of upper section is not evident. The drawdown is not uniform in the whole aquifer,and the seepage laws of different sections are different. Based on the law of seepage,the water-controlled mining technology is proposed by using the heterogeneity characteris-tics of the aquifer to control the drawdown of the upper section of aquifer. It is permissible to be affected by the water-flowing fractured zone in the lower section of aquifer. The technology helps to alleviate the contradiction between coal mining and water protection. Through the application of Hujiahe Coal Mine in Binchang Mining Area,the seepage field of the Luohe Formation aquifer is consistent with the results of this study. The water-controlled technology can realize the purpose of water conservation of the Luohe Formation sandstone aquifer.