| Protective layer mining can effectively prevent coal and gas outburst, when the coal mining and gas outburst the coal seam groups of mine, domestic and overseas coal mines are extensively using the exploitation of protective layer as the regional anti-conflict measure to prevent outburst.The main coal seam of Xuecun coal mine, a subordination of Fengfeng Group, is the Coalseam2;of which thickness is about5.5m and has better occurrence conditions, but also has high gas content, so for the safe and efficient recovery, we usually take Coalseam4as a protective layer to mine. But with the expansion of mining area, parts of the Coalseam4are no longer qualified as a protective layer of mining. The Coalseam3is located between coalseam2and coalseam4, of which coal seam is relatively thin, and has never mined due to the factors of technology and economic cost. This paper is on the basis of the detailed research of Xuecun coal mine’s geological data, through the theoretical analysis of931302working face of Coalseam3as the protective layer mining of its overlying Coalseam2and the analysis of mining height optimization and selection, as well as the pressure law and overlying strata movement law of931302working face of Coalseam3and its overlying Coalseam2during mining and the influence of Coalseam3mining to the mining conditions of Coalseam2, we can get the following conclusions:(1) The931302working face of the Coalseam3in Xue Village coal mine has no outburst risk, and its normal distance to Coalseam2is30m as an average, which is in the scope of effective protection and can be used as a protective layer for Coalseam2in theory.(2) We comprehensively analyze the overlying strata of931302working face of Coalseam3and its stress field changes and fissures development degree during mining, it considers that if take the mining height of1.2m, it will not only achieve the effects of liberated mining, but also more economical reasonable, in the context of this mining conditions, the mining of Coalseam3can fully liberate the gas of coa.lseam2and formed a fractured channel for gas migration, meanwhile won’t generate more serious fracture of Coalseam2and its roof which will lead to mining and support difficulties later.(3) When931302working face of Coalseam3was mine to20～40m, the critical layer was shear broke, the first cycle of pressure to the old roof; when the working face was mine to80m, the Coalseam2was shear failure, while the overlying strata fissures field of Coalseam3has been extended to coalseam2, in the whole mining process, most regions of the overlying strata failure zone of coalseam3were closed under the coalseam2, the roof of Coalseam2was only partially destroyed, this indicates that under the mining conditions of1.2m, the coalseam3not only let coalseam2reached the liberated effect, but also make little damage to the coal seams above coalseam2, it can maintain the stability of overlying strata of coalseam2.(4) The fissures field formed in931302gob of Coalseam3affects the coalseam2, which let Coalseam2appears a certain degree of fissures and lead to shear failure, most regions of the overlying strata failure zone of coalseam3were closed under the Coalseam2, and the roof of great coal seam was only partially destroyed, according to the distribution range of the failure zone of Coalseam2, it can be determined the length and width of the liberated coalseam2is separately400m and120m, z is in this range, the liberated mining of Coalseam3has good unloading effects on coalseam2and its overlying strata.(5) Through the observation of the gas pressure and roof displacement of Coalseam2which above the931302working face, we consider that do the protective layer mining on931302working face of Coalseam3can obviously effect on the protection of the overlying great coal seam, so it’s suit for protective layer mining. |
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