| In recent years,as most of China’s mines enter the stage of high-strength mining,the increasing coal output leads to the increase of gas emission,resulting in frequent gas anomalies and other accidents in the working face,which directly affects the safe production and green development of the coal industry.Based on the geological conditions of the main mining face of a high gas mine in Heshun,Shanxi Province,this paper carried out an experimental study or the influencing factors of the evolution law of the high permeability area of mining pressure relief gas by physical similarity simulation experiment and 3DEC numerical simulation experiment,combined with fractal theory and seepage mechanics,and obtained the following preliminary results:(1)Physical similarity simulation experiment of geometric boundary identification of mining-induced pressure relief gas hyperpermeability zone was carried out by using physical similarity simulation experiment platform of mining-induced overburden fracture evolution,and the variation characteristics of characteristic parameters of mining-induced overburden fracture morphology distribution,overburden layer separation amount,surface fracture rate fracture density and fractal dimension were obtained.Based on the characteristic parameters of the fracture network,the geometric boundary criterion of the hyperpermeability zone of the pressure relief gas was established,and the geometric range and dynamic evolution process of the hyperpermeability zone of the pressure relief gas were finally obtained.(2)Through 3DEC numerical simulation software,the working face numerical model was established under the conditions of different working face mining height,coal seam dip Angle,working face recovery rate and propulsion speed,and the numerical simulation experiment was carried out.The process of formation,expansion,development,connection and then compaction and closure of rock fissures in the upper part of working face during mining is systematically analyzed,and the dynamic distribution characteristics of goaf form under different mining conditions are obtained.(3)The TECPOLT data post-processing software was used to monitor the strata subsidence and stress variation of working face after mining under different conditions.Based on permeability coefficient theoretical calculation method,permeability coefficient variation rule of working face with different influencing factors was obtained.Combined with the stress distribution characteristics in the process of mining in high permeability area,the evolution relationship between stress change and permeability coefficient in the process of deformation and failure of overlying strata was further analyzed.It was concluded that the change of working face mining height had the greatest influence on the permeability of overlying strata,and the maximum permeability coefficient was 0.56m/s,2.02m/s,10.06m/s and 24.7m/s with the increase of mining height.(4)Carry out gas extraction test based on the main mining face of the test mine.The results show that the average gas concentration increases with the increase of vertical distance.When the vertical distance increases from 7.94m to 17.92m,the average gas extraction concentration of boreholes in the high permeability area is 44.82%,and that of boreholes in the caving zone is 10.34%,and the gas extraction concentration of boreholes increases by 4.3 times.The experimental results are extended to the inclined working face of a high gas mine in Xinjiang and good drainage effect is achieved.Through the above research,the characteristic parameters of strata fracture network is used to determine the scope of gas mining in high permeability zone geometry,with the use of numerical simulation to obtain the different factors affecting the working face gas mining in high permeability zone coefficient of permeability of strata subsidence,stress variation and evolution,and disaster prevention and control of mine gas extraction technology such as field practical problems provides an important theoretical support. |
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