临空巷道坚硬顶板水力割缝−压裂联合控顶卸压技术

Theoretical and applied research on hydraulic slit-fracture joint roof control and pressure relief of hard roof in goaf roadway

  • 摘要: 煤矿坚硬顶板工作面回采后易形成侧向悬臂梁结构,导致回采动压和侧向悬顶岩层引起的高静压叠加并通过关键层传递至采动大巷,造成邻近工作面回采巷道围岩结构失稳大变形。为改造顶板岩体结构、调整坚硬岩层破断运移规律,进而控制临空巷道强矿压显现,笔者在分析采动巷道矿压分布规律的基础上,采用数值模拟手段研究了坚硬顶板下临空巷道支承压力分布情况,探究了不同切顶参数条件下围岩结构传递载荷机理,提出了磨料射流水力割缝−压裂联合切顶卸压方法。研究结果表明,临空巷道矿压显现是动静载共同作用的结果,主要表现为回采引起的高采动压力及临空巷道侧向悬顶静载压力叠加作用下,经巷道两侧极限平衡区内围岩传递至底板,进而在底板产生大范围塑性变形。通过磨料射流水力割缝技术在坚硬顶板内预置缝槽,可为水力压裂裂纹扩展起导向作用,并导通岩体内原有裂隙增加水力压裂裂纹影响范围,在坚硬顶板中形成连续弱面达到削弱顶板应力传递目的,割缝深度与割缝压力和混砂比呈正相关。顶板岩层在垮落过程中会相互作用,破断角度及高度改变会导致破断岩体的下滑速度改变并对高位岩层的支撑力产生显著差别,破断角度在66°~86°,破断处岩层所受到的拉应力随破断角度减小呈升高趋势,且随着破断高度的增加拉应力升高速率越快;破断高度范围为26~56 m时,破断处岩层拉应力高于极限抗拉强度所允许的破断角度随着破断高度的增加而升高;依据上述研究在华阳一矿81403工作面开展了工业性试验,以支护结构载荷和围岩变形量为指标的现场监测结果表明,通过水力割缝−压裂联合控顶卸压后巷道顶板锚索受力降低35%,巷帮应力降低44%,巷道顶底板移近量减小57%,巷道两帮移近量减小42%,卸压效果良好,研究成果可为坚硬顶板条件下临空巷道矿压治理提供一种新技术手段。

     

    Abstract: Lateral cantilever beam structure is easy to be formed after extracting coal from working face under hard top plate, resulting in the superposition of the dynamic pressure of mining and the high hydrostatic pressure caused by the lateral overhanging rock layer and transferring to the mine roadway through the key layer, which causes the destabilization and large deformation of the peripheral rock structure of the roadway in the neighboring working face. In order to improve the rock structure of roof plate, adjust the breaking and transporting law of hard rock layer, and then control the strong mine pressure in the adjacent roadway, this paper analyzes the distribution law of mine pressure in the mine roadway, adopts numerical simulation means to study the distribution of the support pressure in the adjacent roadway under the hard roof plate, investigates the mechanism of the peripheral rock structure transferring loads under the conditions of different roof-cutting parameters, and puts forward a joint method of cutting top plate to remove the pressure by the abrasive jet ultra-high pressure hydraulic cutting - hydraulic fracturing. The method of roof cutting and pressure relief is proposed. The results of the study show that the mine pressure in the goaf roadway is the result of the coupling of dynamic and static loads, which is mainly manifested in the coupling of the high dynamic pressure caused by mining and the static load pressure of the lateral overhanging roof of the goaf roadway. The coupling effect is transmitted to the bottom plate by the surrounding rock in the limit equilibrium area on both sides of the roadway, and then produces a large range of plastic deformation in the bottom plate. Through the abrasive jet ultra-high-pressure hydraulic slitting technology, the slots are preset in the hard top plate, which can play a guiding role for the hydraulic fracturing cracks to drag and expand, and increase the influence range of hydraulic fracturing cracks by opening up the original cracks in the rock body, forming a continuous weak surface in a hard roof to weaken the stress transmission of the roof, and the depth of the slits is positively correlated with the slit pressure and the sand mixing ratio. The roof strata will interact with each other during the collapse process, and the changes in fracture angle and height will lead to changes in the sliding speed of the fractured rock mass and significant differences in the support force of the high-level rock strata. In the range of 66°~86°, the tensile stress on the rock layer at the top of the cut-off is increasing with the decrease of the top-cutting angle, and the rate of tensile stress increase is faster with the increase of the top-cutting height. When the range of the top-cutting height is 26~56 m, the fracture angle at which the tensile stress of the rock formation at the fracture point is higher than the ultimate tensile strength increases with the increase of the top-cutting height. Based on the above research, an industrial test was carried out at the 81403 working face of the Huayang mine. The on-site monitoring results with the loads of supporting structure and deformation of surrounding rock as the indexes show that the anchor cable stress of the roof plate of the roadway was reduced by 35%, the stress of the roadway wall was reduced by 44%, the amount of roadway top and bottom plate migration was reduced by 57%, and the migration amount of the roadway two walls was reduced by 42%, which has a good effect of pressure relief. The research results can provide a new technical means for controlling the ground pressure in the gob roadway under the condition of hard roof.

     

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