Simulation Research And Engineering Practice Of Extended Protective Area In The Mining Of Lower Protective Coal Seam

Gas has always been the"first killer"affecting coal mine safety production.Protective coal seam mining is the most economical and effective regional method to control gas so far.However,according to the relevant suggestions of the coal mine safety regulations and the detailed rules for the prevention and control of coal and gas outburst,whether the upper protective coal seam or the lower protective coal seam is mined,the protective area of the protected coal seam is reduced layer by layer,which is inconsistent with the actual effect,resulting in serious loss of minable coal.Therefore,it is of great theoretical and practical significance to carry out the research on the expansion of the protective area of the protected coal seam.Taking the?10310 working face of Zhuxianzhuang Coal Mine in Anhui Province as the research object,this paper uses FLAC3D finite element analysis software to simulate the pressure relief influence process of the mining of the?10310 working face of 10 coal seam on the outburst coal seam 8 with an upper distance of 78m.By analyzing the variation law of its stress and strain,combined with the coal seam stress protection criterion,strain pressure relief protection criterion and field investigation results,the effective protection range of the upper protected coal seam is obtained.The main conclusions are as follows:(1)The mining of the lower protective coal seam?10310 working face will lead to the redistribution of the stress of the upper protected coal seam of 8 coal.When the mining distance of working face?10310 is 20m,the maximum vertical stress of coal 8 decreases from the original value of 16.5MPa to 15.5MPa.With the increase of mining distance from40m to 160m,the maximum vertical stress of coal 8 in the protected coal seam decreases from 13.7MPa to 7.55MPa,that is,with the increase of mining distance of working face,the vertical stress of the protected coal seam decreases gradually,with a decrease range of54.2%.Therefore,the mining of coal seam 10 will lead to the stress release of coal seam 8in the upper protected coal seam.(2)The mining of working face?10310 in the lower protected coal seam will cause the strain of coal 8 in the upper protective coal seam to change.As the mining distance of working face?10310 increases from 20m to 160m,the maximum vertical displacement of coal 8 increases from 7.62mm to 55.3mm.The displacement values at different positions of the protected coal seam are different,resulting in uneven settlement distribution.Therefore,the mining of coal seam 10 will lead to a large number of cracks in coal seam 8 of the upper protected coal seam,and the pressure relief protection effect is very obvious.(3)Based on the FLAC3D simulation results,according to the stress protection criteria,the strike protection range of 8 coal is 90.8°?97.23°,the upper dip protection range is 90.40°?91.95°,and the lower dip protection range is 90.10°?93.15°;According to the strain relief protection criterion,the strike protection range of coal 8 is 90.74°?97.29°,the upper dip protection range is 90.20°?95.26°,and the lower dip protection range is93.15°?103.49°.According to the comprehensive stress and strain results,for the sake of safety,the strike and dip protection angle of coal 8 in the upper protected coal seam are designated as 90°due to the mining of coal 10.(4)The actual protection range of?836 working face of 8 coal seam in the upper protected coal seam was investigated on site.The measured results show that the maximum residual gas content of the protected coal seam is 3.41m~3/t,the maximum residual gas pressure is 0.13MPa,and the maximum drilling cuttings gas desorption index?h₂ of dry coal sample is 60Pa within the range of pressure relief angle of 60°?104°;In the upper part of the strike open cut side,the maximum residual gas content of the protected coal seam is4.09m~3/t within the pressure relief angle of 60°?90°,and the maximum drilling cuttings gas desorption index?h₂ of dry coal sample is 50Pa;In the lower part of the strike open cut side,the maximum residual gas content of the protected coal seam is 3.01m~3/t within the pressure relief angle of 60°?90°,and the maximum gas desorption index?h₂ of dry coal sample is 60Pa;In the lower part of the inclined direction,the pressure relief angle is75.5°?90°,the maximum residual gas content within the effective protection boundary of the protected coal seam is 2.90m~3/t,the maximum residual gas pressure is 0.06MPa,and the maximum gas desorption index?h₂ is 60Pa.all measurement results are less than the critical values(0.74MPa,8m~3/t)specified in the 2019 detailed rules for the prevention and control of coal and gas outburst,and meet the critical values of 5m~3/t,0.5MPa and 180Pa specified in the implementation opinions of Huaibei Mining Group on"one ventilation and three prevention"in 2021.Therefore,affected by the mining of coal 10,the strike and tendency of coal 8 in the upper protected coal seam are delineated according to 90°,and the field investigation results are consistent with the simulation results of FLAC3D software.The results of FLAC3D simulation and field investigation show that the actual protection range of coal seam 8 in the protected coal seam on Zhuxianzhuang Coal Mine is expanded to 90°in strike and tendency.Compared with the protection angle recommended in the detailed rules for the prevention and control of coal and gas outburst,the mining length on strike is increased by 100m,the mining length on tendency is increased by29.84m,the minable area is expanded by 28000m~2,an increase of 53.43%,the output is increased by about 390000t,an increase of 44.32%,It has produced huge safety,economic and social benefits.This result can not only provide a basis for increasing production and income in Huaibei mining area and even mines with similar conditions in China,but also further enrich the theory and practice of protective coal seam mining.Figure[54]table[19]reference[75]...