穿层爆破各煤层动态应力分布与抽放效果探讨

DISCUSSION ON DISTRIBUTION OF DYNAMIC STRESS AND GAS DRAINING EFFICIENCY IN COAL SEAMS BY BLASTING THROUGH LAYERS OF COAL-ROCK

穿层深孔爆破在石门揭煤及局部地段防止瓦斯突出有重要作用,由于爆破区域跨越多层煤、岩介质以及扇形布孔造成孔口孔底最小抵抗线不相等因素影响,穿层深孔爆破研究较为困难。在大量矿井试验基础上,利用三维数值模拟方法,研究有代表意义的穿层深孔爆破相关理论问题。建立穿层爆破计算模型,获得不同位置抽放孔有效应力随时间变化规律;探讨各抽放孔有效应力随距炮孔水平距离增加而衰减,以及不同抽放孔轴线方向两层煤中应力分布的差异。计算结果表明:复合介质孔口、孔底煤层中爆破裂隙贯通范围分别为1.4,1.8 m;孔底由于锥形波的叠加和应力波反射双重作用影响,在相同距离时孔底有效应力平均值较孔口大73%;煤–岩复合介质中煤层爆破效果优于单煤层爆破效果,同等情况下,复合介质煤层中孔口处有效应力极值较单煤层增加17%～42%,孔底增加6%～24%。现场实践表明,当作用在抽放孔轴线的平均有效应力由7.12 MPa增到12 MPa后,瓦斯抽放总量增加3倍以上。

The deep-hole blasting through strata has important role for outburst prevention in rock cross-cut coal uncovering and some special area. The difficulty of the research is caused by the area blasted in layers of coal-rock media and different burden in fan-patterned holes. Based on lots of mine experiments, a representative blasting theory through layers of coal-rock is studied by three-dimensional numerical simulation method. The numerical calculation models for the blasting through strata are constructed. The effective stresses variations of different locations at different times are acquired; the law that the effective stresses of different draining holes decreases with increase of the distance is analyzed; and distribution of effective stress along axis in the holes is discussed in the coal seams. The calculation results show that： （1） The perforation range of blasting cracks at top and bottom of the draining hole in layers of coal-rock media is up to 1.4 and 1.8 m respectively. （2） The average value of effective stress in bottom of the hole is 73% higher than in top at the same location because of actions of the stress interference and reflection in bottom of the hole. （3） The blasting effect in coal seam in layers of coal-rock media is better than in single coal seam. Under the same condition, the maximum value of the effective stress at top and bottom of the draining hole in the multi-media is 17% -42% and 6% -24% higher than in single coal seam. When average values of effective stress increases from 7.12 MPa to 12 MPa along axis of the hole, the gas draining gross increases more than 3 times.