Theoretical Thickness of Protective Layer Mining and its Application on Pressure Relief Gas Drainage
Wang Haifeng, Sun Jianzhong, Cheng Yuan-ping, Wei Guangjian
National Engineering Research Center of Coal Gas Control, China University of Mining & Technology, Xuzhou, Jiangsu 221116, China
Protective layer technology is one of the most effective methods to control mine gas. But if there arenít minable coal seams, thin mine seam and soft stone could be chosen as protective layer. At this point, it is particularly important to make research on mining thickness of protective layer theory. Firstly, we analyzed the ground stress changes of the roof and floor, fracture development, expansion deformation and permeability changes of the coal seam after mining the 11th coal seam as protective layer. Secondly, take the Hongling coal mine of Shenyang mining area as the geological background, we used the finite difference software, FLAC3D, to make a numerical simulation of coal seam ground stress changes and expansion deformation of the protected layer at various mining thickness of 11th coal seam, and obtained the internal relationship between mining thickness of protective layer and expansion deformation, shown by the fitted formulas. If 3% is taken as critical value of expansion deformation, according to the fitted formulas, the theoretical mining thickness of 11th protective layer is 0.67m. Finally, we determined the mining thickness of protective layer is 1.4m on the basis of objective conditions in field trials. In field test, after mining the 11th coal seam as the protective layer, the expansion deformation value of 12th coal seam (protected layer) reached 26.3Č, the permeability coefficient increased 1010 times. In addition, with the action of penetration boreholes, the amount of gas was reduced to 5.06m3/t and the gas pressure declined to 0.35MPa, which caused the danger of the outbursts in the coal seams to be eliminated.
Keywords: protective layer mining technology; theoretical mining thickness; expansion deformation; pressure relief gas drainage
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