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沿空留巷密集钻孔切顶机理及关键参数确定方法

Roof cutting mechanism of dense drilling in gob-side entry retaining and determination method of key parameters

  • 摘要: 为实现密集钻孔切顶条件下沿空留巷顶板结构安全稳定,研究正常情况与密集钻孔条件下顶板岩层结构受力状况,基于岩石断裂理论和弹性理论分析回采前后顶板密集钻孔孔间围岩受力分布及其破断过程,明确密集钻孔切顶机理及相邻钻孔的孔间集中应力相互作用机制,推导工作面端头弧形三角板结构巷道侧边界密集钻孔孔间围岩的拉剪应力计算公式。在此基础上,分析不同参数对孔间围岩所受拉剪应力的影响作用,提出沿空留巷密集钻孔切顶关键参数确定方法。研究表明:密集钻孔主要通过回采前后钻孔周围应力条件改变来增加钻孔围岩拉剪应力集中程度,引起孔间裂隙扩张联通,形成切缝线破断关键岩层。回采前钻孔主要受水平挤压应力影响,回采后钻孔受力逐渐转变为采空区顶板回转下沉产生的拉剪应力为主,钻孔孔间围岩状态随之由孔间围岩弱化阶段过渡到孔壁裂纹成形阶段,再转变为孔间围岩破断阶段。密集钻孔孔间围岩所受拉剪应力大小主要取决于关键岩层厚度及钻孔孔径与孔间距之比,与钻孔高度及间距成负相关,与角度及直径正相关。据此提出了密集钻孔关键参数确定方法,并根据龙滩矿3124 N工作面坚硬顶板条件设计了密集钻孔切顶留巷方案,确定钻孔长度为8.3 m,角度为15°,钻孔直径为48 mm,间距为500 mm。留巷后巷道顶帮变形可控且整体稳定性较好,由此可证明密集钻孔布置参数较为合理,密集钻孔关键参数确定方法有效可行。

     

    Abstract: To achieve the safe and stable structural condition of the roof along the goaf under the roof cutting by dense drilling method, the stress distribution and fracture process of the roof strata between normal and dense drilling conditions were studied. Based on rock fracture theory and elastic theory, the stress distribution of the surrounding rock between dense drilling and the fracture process were analyzed before and after mining, clarifying the cutting mechanism of dense drilling and the interaction mechanism of concentrated stress between adjacent drilling. The calculation formula for the tensile-shear stress of the surrounding rock between dense drilling in the arc-shaped triangular panel structure at the end of the working face was derived. Based on this, the influence of different parameters on the tensile-shear stress of the surrounding rock between drilling was analyzed, and a determination method for the key parameters of roof cutting by dense drilling holes along the goaf was proposed. Research has shown that the dense drilling mainly increases the concentration of the surrounding rock's tensile and shear stress by changing the stress conditions around the densely drilled holes before and after mining, causing the expansion and connection of fractures between drilling and forming key rock layers for cutting. Before mining, the drill holes are mainly affected by horizontal compression stress, and after mining, the stress gradually changes to the tensile and shear stress caused by the rotation and subsidence of the goaf roof, and the state of the surrounding rock between the holes transitions from the weakening stage to the formation of crack stage, and then to the fracture stage. The magnitude of the tensile and shear stress of the surrounding rock between the densely drilled holes mainly depends on the thickness of the key rock layer and the ratio of the hole diameter to the hole spacing, and is negatively correlated with the hole height and spacing, and positively correlated with the angle and diameter of the drill holes. Based on this, a method for determining the key parameters of intensive drilling and cutting is proposed, and a plan for intensive drilling and cutting in the goaf with hard roof conditions on the 3124 N working face of Longtan Mine is designed, with a hole length of 8.3 m, an angle of 15°, a hole diameter of 48 mm, and a spacing of 500 mm. The deformation of the goaf roof after cutting is controllable and the overall stability is good, which proves that the arrangement parameters of intensive drilling and cutting are reasonable, and the determination method for the key parameters of roof cutting by dense drilling holes is effective and feasible.

     

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