急倾斜煤层冲击地压地面区域压裂防控机理及工程实践

Mechanism and engineering practice of rock burst prevention and control in steeply inclined coal seam with ground fracturing

  • 摘要: 坚硬顶板急倾斜煤层开采,受煤层倾角影响,坚硬顶板易大尺度悬顶,造成煤体夹持应力高,厚硬覆岩破断冲击动载强烈,易诱发急倾斜煤层冲击地压。为实现急倾斜煤层厚硬悬板 结构区域调控,提出一种急倾斜煤层冲击地压地面斜井区域压裂防控技术,削弱冲击力源,降低冲击风险。以甘肃靖远王家山煤矿为工程背景,分析矿井历年冲击地压案例及微震能量事件,明确急倾斜煤层冲击显现特征。研究了急倾斜煤层覆岩结构演化及破断动载扰动,给定冲击震源防控关键层;研究获得压裂影响采场煤岩体应力—能量场演化规律,揭示了急倾斜煤层厚硬覆岩地面压裂区域弱化减冲机理,研究表明:急倾斜坚硬覆岩应力及能量集中明显,其大范围悬顶结构在回转挤压作用下,造成低位—高位悬臂“支点”处应力极值达26.7、28.6 MPa。地面斜井压裂通过构建区域体积缝网,切断应力传递路径,同时使应力向深部煤岩体转移,改善采场应力水平,低位—高位悬顶结构应力极值分别降低14%、44%,能量极值降低10.5%、20.9%,卸压释能效果显著。给出了冲击震源防控层判定方法,建立了地面斜井布置全轨迹方程,现场开展了急倾斜煤层地面压裂工程实践,结果表明:地面压裂可形成沿岩层倾向分布、走向扩展、规模达400 m×200 m×50 m的体积缝网,实现厚硬覆岩区域压裂,杜绝了104 J级高能事件,震动波CT反演结果表明,压裂区波速异常系数An均在0.20以下,应力集中程度为中等及以下,波速梯度变化系数VG均在0.05以下,冲击危险程度为无。研究成果表明了地面斜井区域压裂防冲技术的可行性,形成了地面斜井压裂科学设计方法,为急倾斜煤层冲击地压防控提供了一种新型技术途径,完善了急倾斜煤层冲击地压防治体系。

     

    Abstract: In the mining of steeply inclined coal seams with hard roofs, the large dip angle of the coal seam leads to large-scale roof hanging of the hard roof, resulting in elevated clamping stress within the coal and dynamic impact loads from the fracture of thick and hard roofs, which readily triggers rock bursts in steeply inclined coal seams. To achieve regional control of the thick hard suspension plate structure in steeply inclined coal seams, a ground inclined well regional fracturing technology for rockburst prevention was proposed to weaken the impact source and reduce the impact risk. Taking the Wangjiashan Coal Mine in Gansu Province as the engineering background, the paper analyzed historical rock burst incidents and microseismic energy events, the characteristic manifestations of rock burst in steeply inclined coal seams were identified. The evolution of overburden structures and the dynamic load transfer mechanisms in steeply inclined coal seams were investigated, thereby identifying the key stratum for rockburst control. The evolution of stress and energy fields in the coal-rock mass before and after ground fracturing were obtained by simulation. The mechanism of regional weakening and rockburst prevention through ground fracturing in steeply inclined coal seams with thick, hard overburden. The results indicate that steeply inclined hard overburden exhibits significant stress and energy concentration. Under the rotational squeezing effect of its large-scale hanging roof structure, the stress extremes at the "fulcrum" of the low-high level cantilevers reach 26.7 MPa and 28.6 MPa. The regional volumetric fracture network formed through ground inclined well fracturing, disrupts the stress transfer pathway and redirects stress toward deeper coal-rock masses, leading to an improved stress environment in the stope. Following fracturing, the peak stresses in the low-high level hanging roof structures are reduced by 14% and 44%, respectively, while the peak energy values decrease by 10.5% and 20.9%, indicating significant pressure relief and energy release effects. A method for identifying key control layers for ground fracturing has been developed, and a full trajectory equation for ground inclined well was established, and engineering practices were conducted. The results demonstrate that ground fracturing can generate a volumetric fracture network distributed along the dip direction and extended along the strike of the rock layers, with dimensions reaching 400 m×200 m×50 m. The thick hard overburden was regionally fractured, completely eliminating 104 J level high-energy events. Seismic computed tomography results further indicate that the velocity anomaly coefficient (An) in the fractured zone remains below 0.20, corresponding to a stress concentration level rated as medium or lower, and the velocity gradient coefficient (VG) remained below 0.05, confirming an absence of rockburst risk. The research results demonstrate the feasibility of the ground inclined well regional fracturing technology for rockburst prevention. A scientific design methodology for ground inclined well regional fracturing was established, providing an innovative technical approach for rockburst control and improving the existing rock burst prevention and control system in steeply inclined coal seams.

     

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