多孔线性控制套筒致裂效果影响因素分析

针对坚硬难垮落顶板弱化问题,在分析多孔线性控制套筒致裂机理的基础上,建立700mm×300mm×400mm试块。通过套筒致裂压力及钻孔孔壁周围应变变化情况,分析孔壁周围应力大小、分布及应力集中现象,研究钻孔直径、孔间距、套筒致裂压力对应力集中现象的影响,同时分析这三者对裂纹扩展方向的影响,得出套筒致裂最优法。试验结果表明:(1)套筒致裂效果受钻孔直径、孔间距和套筒压力等综合因素影响,采用大直径、大间距的布孔方式可获得较好的致裂效果;(2)多孔线性控制致裂试验的张性裂缝扩展方向主要沿着各钻孔中心连线方向;(3)钻孔直径30mm、间距300mm的试块致裂压力为18.6MPa,远大于顶板岩体抗拉强度,将套筒致裂法应用于顶板弱化是可行的。本研究对解决采空区坚硬顶板大面积悬顶具有理论意义和应用价值。

Analysis of Influencing Factors of Fracture Effect on Porous Linear Control Sleeve

Aiming at the weakening problem of hard and difficult to break down roof, 700×300×400mm block samples were prepared, based on the analysis of fracturing mechanism of porous linear control sleeve. Through the variation of sleeve fracture pressure and strain around borehole wall, the phenomena of stress value, distribution and stress concentration around borehole wall were analyzed; the effect of borehole diameter, borehole spacing and sleeve fracturing pressure on stress concentration was studied. Meanwhile, the influence of above-mentioned three factors on crack propagation direction was also analyzed, based on which, the optimal method of sleeve fracturing was obtained. Experimental results show that: (1) sleeve fracturing effect is affected comprehensively by the borehole diameter, borehole spacing and sleeve pressure, with large borehole diameter and spacing, better cracking effect can be obtained; (2) the tensile crack propagation direction in porous linear control sleeve fracturing experiment is mainly along the direction of drilling center; (3) sleeve fracturing pressure of block sample with 30mm borehole diameter and 300mm borehole spacing is 18.6MPa, which is much greater than the roof rock tensile strength. Thus, sleeve fracturing method is feasible to weaken the hard roof. Above results may provide theoretical reference and application value to solve large area hanging hard roof problem.