Study On The Pressure Relief Law Of Repeated Upper Protective Layer Minging In Short Distance Coal Seams

Among the regional anti-outburst measures,mining the protective layer is the first choice for preventing coal and gas outburst.After the upper protective layer is mined,the coal and rock bodies near the roof(floor)of the goaf have moved and deformed.There will be a certain range of pressure relief zone near the protected layer.The coal bed adsorbs gas desorption in the pressure relief area,which provides an excellent opportunity for pressure relief gas drainage.In this paper,the COMSOL Multiphysics software is used to conduct a numerical simulation study on the mining of the upper protective layer in Donglian Coal Mine.The pressure relief effect of the protected layer(No.13 coal)after repeated mining in No.10 and No.12 coal seams was investigated on site.The numerical simulation results of COMSOL Multiphysics show that after repeated mining of the upper protective layer,the pressure relief angle increases and the protection range increases significantly.In the strike direction,after repeated mining,the pressure relief angle of the protective layer increases from 48.1°to 50.1°.In the trend direction,the pressure relief angle on the upper side of the trend direction increases from 50.7°to 80.5°,and the pressure releases on the lower side.The pressure angle increased from 72.3°to 80.5°.After the No.10 coal seam is mined,the vertical deformation of the protected layer takes the form of"W".After repeated mining,the vertical deformation of the protected layer takes the form of"wave".A numerical simulation study on the influencing factors of the pressure relief effect of repeated mining in Donglian Coal Mine was carried out.The results show that the maximum peak value of the expansion and deformation rate of the protected layer as the mining depth increases from 263.6 m to 363.6 m and finally to 463.6 m From 5.06‰to 6.82‰,and finally to 8.57‰,the scope of protection gradually increased.As the mining height increases from 0.58 m to 2.58 m,and finally to 3.58m,the maximum peak value of the expansion and deformation rate of the protected layer increases from 4.15‰to 4.28‰,and finally to 4.35‰,the protection scope gradually increases.As the coal seam spacings increases from 3 m to 9 m,and finally to 12 m,the maximum peak value of the expansion deformation rate of the protected layer decreases from 6.23‰to 3.51‰,and finally to 2.85‰,the protection scope gradually decreases.When the mining sequence is different,the maximum peak protection range of the expansion deformation rate of the protected layer is quite different.Therefore,coal seam mining height,coal seam spacings and mining sequence are the main factors that affect the repeated mining effect of the protective layer.According to the numerical calculation results,the roadway layout of the 11302working face of Donglian Coal Mine was carried out,and the anti-outburst effect of the protected face of the working face was investigated.The investigation results show that:after repeated mining,the residual gas content of No.13 coal seam in Donglian Coal Mine is less than 8 m~3/t,the maximum value is 4.6903 m~3/t;the residual gas pressure is less than 0.74 MPa,the maximum value is 0.365 MPa;According to the requirements of the effect evaluation index system,the working face of No.13 coal seam No.13 of Donglian Coal Mine is within the scope of protection.According to the coal quality report of the Guizhou mining area,the mining area is mostly coal seam mining.It is of great theoretical and practical significance to study the pressure relief rule of the protected layer under the condition of repeated mining of the protective layer.This paper has 50 pictures,13 tables,and 87 references.