Research On Protection Scope And Pressure Relief Gas Drainage Of Protective Layer Under Thin Coal Seam

With the increasing of the depth of coal mining, coal and gas outburst risk is gradually increasing.As the most effective and economical regional outburst prevention measure, the protective layer mining is widely used in our country.However, there are a lot of outburst mines only thin coal seamwith the conditions as a protective layer mining. Therefore, it is veryimportant to study and analyze the thin coal seam mining. DaHe coal mine of Tongzi County of Guizhou Province using thin coal seam as the lower protective seam mining.This paper takedit as the researchbackground. The protection scope and the pressure relief gas extraction were studied by the theoretical analysis, computer numerical simulation and field investigation.It achieved the following conclusions:(1)The movement characteristics and fracture distribution characteristics of the overlying coal and rock after mining were analyzed.The results showed that after the lower protective layer mining, the overlying coal and rock would form the caving zone, the fracture zone and the bending subsidence zone.The height of caving zone was 4.8m, and the height of fracture zone was30.6mafter mining the No. 10 coal seam of DaHe mine. The protected 7 main coal seam was above caving zone and in the fractured zone.So it was not only extremely beneficial to release stress and gas pressure but also to drainage pressure relief gas.(2) Used the FLAC3D numerical simulation software to study the vertical stress distribution, the size of vertical displacement and extent of damage of overlying coal and rock.The results showed that after the protective layer mining, the corresponding protective layer on toward the direction of the vertical stress was roughly "W" shape distribution; The distribution of vertical displacement was pan shape, the maximum vertical displacement occurred in the middle of mined-out area.(3)Using computer numerical simulation combined with the different protection scope criterion to delimit the protection range of protected coal seam.The protection scope of the field was investigated.And through the field investigation, the gas contentdistribution trend line of study points were drawn. The results showed that the scope of protection which was delimited by the method of computer numerical simulation combined with coal deformation criterion was closest to the actual inspection results,and tend to be safe.So it can provide a scientific basis for delimiting protection scope of DaHe coal mine in the next step of mining work.(4)The paper put forward two kinds of methane extraction methods,namely,gas drainage in the bottom of the roadway,upper and lower trough wear layer gas drainage.The field statistics showed that working face gas extraction rate reached 76.5% ~82.3% and the gas volume fraction of the return air in the mining face is stable at0.41% ~ 0.62%.Therefore,the pressure relief gas control effect was remarkable, that met the production needs of working face.