| Under the condition of mining,the evolution law of overburden rock failure and stress distribution is more complicated,especially in the process of mining the overburden coal seam,the overburden rock stress redistribution of the overburden coal seam produces a large number of cracks,which causes the gas of the underlying coal seam to flood into the mining area of the overburden coal seam.In order to solve this problem,taking a mine Yang Mei 12#coal seam in fully mechanized coal face 81403 as the research object,through a combination of numerical simulation and theoretical analysis,the stress distribution in the process of the overlying coal seam mining and change law under different ventilation extraction method,the gas and the distribution regularity of flow field analysis,on this basis,according to the coal seam of fully mechanized face the actual situation of the stress distribution rule and gas migration,put forward suitable for coal seam group mining goaf gas control method,and applied to the concrete practice of mining face.The main results are as follows:By way of theory modeling and FLAC3Dnumerical simulation,the different recovery period of surrounding rock stress distribution and stress the rule of evolution and its influence scope is analyzed,simulation results show that in the process of the overlying coal seam mining,the floor stress overall appeared to compression,expansion and recovery period,and with the working face advancing circulation.The overall shape of the supporting stress presents an"M"shape.When the working face is mined to 200m,the pressure relief affected area can reach 120m,the maximum vertical stress can reach 33MPa,and the maximum compression deformation of the underlying coal seam is 2.2‰.The maximum value of relative expansion was 7.7‰.According to the actual conditions of 81403 fully mechanized mining face,the Fluent numerical simulation model of U-type ventilation,U-type+L-type ventilation and U-type+high suction roadway ventilation were established under three different conditions.By analyzing the gas concentration in goaf,the gas concentration at z=1 m and the change of gas concentration in the working face,the reasonable ventilation and extraction method was determined.Studies have shown that U+high drainage type ventilation conditions,high alley pumping set 20 m above the coal seam,return air lane fault within 25 m,high alley pumping gas concentration between 10%?20%,smoke Cai Liang stability between 10?30 m after/min,the gas concentration in working face a maximum 0.48%,on the corner low concentrations remain below 0.3%,final U+high alley pumping ventilation mode in accordance with all relevant safety mining.On the basis of the numerical simulation results,combined with the actual situation of81403 fully mechanized mining face and the practical experience of mine production,the comprehensive gas control measures such as pre-drainage of this coal seam,high drainage roadway,high borehole and buried pipe in goaf are put forward.During the mining period,a total of 2.575 million m 3 of gas was extracted from the pre-drainage hole along the bed,and the gas extraction rate was 61.8%.The average extraction purity of the high drainage roadway was 12.9 m3/min with an average concentration of 36.1%,the average extraction purity of the high drilling hole was 5.1 m3/min with an average concentration of 51.2%,and the average extraction purity of the buried pipe in the goaf was 2.5 m3/min with an average concentration of 6.7%and an average gas extraction rate of 89.9%.The above data show that through the application of comprehensive gas control measures,the gas concentration in the return air roadway and upper corner is less than 1%,which meets the requirements of relevant regulations and can ensure the safety of mining at the working face. |
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