Investigation And Research On Pressure Reduction And Permeability Enhancement And Protective Effect Of Upper Protective Layer Mining On Lower Extra Thick Coal Seam

The 6124 working face of the second coal layer of Hai shiwan Coal Mine has the danger of coal and gas outburst,which seriously affects the normal safe and efficient production of the mine.This article takes the 6124 working face of the ultra-thick coal seam in Hai shiwan Coal Mine as the research object,comprehensively uses basic theories such as rock mechanics,seepage mechanics,and similarity theory,and uses theoretical analysis,numerical simulation,physical simulation and other research methods to systematically study the upper protective layer The influence of mining on the movement and deformation and permeability of the lower extra-thick coal seam,and the protection effect of the protective layer after mining was investigated.Through the above research,the following research conclusions are obtained:(1)Obtained the variation law of coal bed permeability with stress after mining the upper protective layer,and constructed the calculation formula of coal body permeability of Haishiwan Coal Mine.(2)A physical similarity simulation experiment model was established,based on which the pressure relief degree and stress variation law of the undermining coal and rock layers were analyzed with the mining process;the permeability variation law and the seepage velocity with the mining process were analyzed.The variation law of the coal was analyzed,and it was found that the upper and lower coal bodies of the 6124 extra-thick coal seam of Haishiwan Coal Mine showed a decrease first-then rapidly increase-then slowly decrease-and finally remained stable,but the upper coal body The degree of permeability change is significantly larger than that of the lower coal body.(3)The FLAC3D numerical simulation model was established,and the plastic deformation,stress,vertical displacement of the protected layer extra thick coal seam during the mining process of the upper protective layer working face was analyzed with the excavation distance.The development trend of the cracks in the bottom plate of the protected layer is gradually expanding from top to bottom.The rupture depth increases with the increase of the mining distance.After the mining of the working face,the destruction depth tends to be stable.The stress change of the protected layer is in a "V" shape and symmetrical distribution along the depth direction,that is,the stress change of the coal seam in the middle of the floor of the goaf is the largest;the displacement change of the protected layer shows an inverted"V" shape,and the deformation of the roof of the protected layer is greater than that of the floor Deformation.(4)The theoretical calculation obtained the trend,tendency and vertical protection range of the upper protective layer mining in Hai shiwan Coal Mine;the COMSOL software was used to simulate the effect of gas relief after the upper protective layer was mined,and the protected layer coal was analyzed The distribution pressure cloud map of gas pressure and permeability after pressure relief extraction,and measured the gas extraction volume,residual gas content and residual gas pressure after extraction,the maximum residual gas pressure measured was 0.58MPa,the maximum residual gas content It is 7.74m3/t,the gas drainage rate reaches 61.69%,the effect test value is less than its critical value,and the protective layer mining effect is effective.