Pressure relief and permeability enhancement effect of double working face mining in upper protective seams
To solve the problems of coal and gas outburst,large face length in protective seams and limit extraction capacity in No.2 coal seam of Zhongxing Coal Industry,the method of double working face mining in upper protective layers is proposed.Based on the combination of theoretical calculation,numerical simulation and field measurement,the distribution law of vertical stress and vertical displacement of the protective layer working face is studied to analyze the pressure relief effect of No.2 coal seam.The results show that with the increase of the length of the protective layer working face,the pressure relief ratio generally decreases.With the increase of working face length in protective layers,pressure relief proportion tends to decrease.When the working face length in protective layers is 110 m,the pressure relief ratios of the vertical stress and vertical displacement of the protective layer working face reaches 91%and 87.4%,respectively.After pressure relief,the maximum residual gas content and maximum residual gas pressure of No.2 coal seam are reduced to 5.37 m3/t and 0.44 MPa,respectively,the porosity is increased to 4.05%,the permeability coefficient of coal seam is increased to 1.08 m2/(MPa2·d),and the maximum expansion deformation is greater than 3‰.All indexes show that the effect of pressure relief and permeability is remarkable.
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