特厚煤层高强度综放开采水力压裂顶板控制技术研究

STUDY OF ROOF CONTROL BY HYDRAULIC FRACTURING IN FULL-MECHANIZED CAVING MINING WITH HIGH STRENGTH IN EXTRA-THICK COAL LAYER

针对塔山煤矿临空顺槽矿压显现剧烈的问题,进行水力压裂弱化煤层上覆坚硬K3老顶的现场试验,通过水力压裂期间监测钻孔以及巷道两侧锚杆出水情况与水压的变化分析水力压裂的影响范围,通过水力压裂前后周期来压步距、动载系数、顶板下沉量、两帮移近量、煤壁片帮统计、工作阻力与瓦斯涌出情况,深入分析水力压裂弱化坚硬老顶的特点。试验结果表明:(1)切槽裂隙在水力压裂的作用下其扩展范围不超过55 m;(2)裂缝所处的煤岩体环境使得裂缝扩展的压力时间曲线呈现3种轨迹形态;(3)水力压裂前后,周期来压步距分别为18.69,16.76 m,平均周期来压动载系数分别为1.69,1.53;顶板下沉量与两帮移近量都明显缩小,巷道顶板整体完整;煤壁片帮深度平均值由原来的31.18 m变为7.06 m;瓦斯涌出相对稳定,上隅角瓦斯浓度由原来的0.20%降低为0.15%。工作面顶板完整性和强度得到了弱化,随工作面推进顶板能够及时垮落,5106临空顺槽顶板的压力明显减弱,说明水力压裂的效果良好,研究结果对类似条件下的工作面具有积极的指导意义。

The hydraulic fracturing field tests to weaken the hard K3 upper roof above coal layer were conducted when severe problems occurred in the open-air and crossheading strata at Tashan Coal Mine. The water pressures in the boreholes and water oozing from bolt locations at two sides of roadways were monitored during the process of hydraulic fracturing to analyze the range of influence of hydraulic fracturing. The characteristics of weakening the hard roof by hydraulic fracturing were analyzed according to the step size of periodic pressure, the dynamic loading factor, the deflections of roof, the displacements of roadways, the statistical analysis of rib wall and gas discharge before and after hydraulic fracturing. It was found that the range of grooving fractures produced by hydraulic fracturing was no more than 55 m. Three types of the pressure-time curve of crack propagation in the coal and rock mass were obtained. The step sizes of periodic pressure are 18.69 and 16.76 m respectively and theaverage periodic dynamic pressure factors are 1.69 and 1.53 respectively before and after hydraulic fracturing. Both the deflection of roof and the displacement of roadways were greatly reduced and the roof of the roadways remained unbroken. The average depths of coal wall rib spalling were reduced from the original 31.18 m to 7.06 m Besides, the gas release is relatively stable. The gas density at the upper comer was reduced from the original 0.20% to 0.15%. Meanwhile, the completeness and strength of the roof at the working front were weakened and roof was dropped as working front proceeds.