高位厚硬关键层破断致灾机制及弱化减灾效应研究

Disaster-inducing mechanism of fracture of high-position thick and hard key strata and their weakening and disaster-mitigation effects

  • 摘要: 目前针对高位厚硬关键层的致灾机制研究多侧重于关键层的破断行为及其对采场强矿压的影响作用,关于关键层与煤层间距(层间距)变化对高位关键层的破断形式转变现象及其对应变能“积聚−释放”过程影响的研究相对较少。针对上述问题,综合采用理论分析、数值模拟与相似模拟实验方法,揭示了高位关键层破断形式转变机制与能量聚散演化规律,比较了不同层位高位关键层弱化后工作面来压强度的衰减特征,阐明了高位厚硬关键层的弱化减灾效应。研究结果表明:关键层与煤层间距增大会导致关键层悬露区域面积发生变化,改变关键层走向及倾向边界上的弯矩大小及增长规律,促使其破断形式由竖向破断转变为横向破断;高位典型厚硬关键层因其承载能力强,悬露面积较低位关键层更大,弹性应变能积聚量更大,其破断弹性应变能快速释放诱发强矿压灾害的风险更高;水压致裂方法可显著改变关键层的破断步距及采场矿压显现强度,对煤层上方125 m处的高位关键层进行水压致裂弱化后,其破断步距较未弱化时减小40.94%,弹性应变能积聚量降低98.40%,工作面顶板压力下降了48.77%,因高位厚硬关键层断裂诱发的采场强矿压显现得到有效控制。

     

    Abstract: At present, studies on the disaster-inducing mechanism of high-position thick and hard key strata mainly focus on the fracture behavior of key strata and their influence on strong ground pressure in the mining face, while relatively little attention is paid to the effect of variations in the distance between the key strata and the coal seam (interlayer distance) on the transformation of fracture modes of high-position key strata and the associated strain energy "accumulation-release" process. To address this issue, theoretical analysis, numerical simulation, and similarity simulation experiments were comprehensively employed to reveal the transformation mechanism of fracture modes of high-position key strata and the evolution laws of energy accumulation and dissipation, to compare the attenuation characteristics of ground pressure intensity on the working face after weakening of high-position key strata at different horizons, and to clarify the weakening and disaster-mitigation effects of high-position thick and hard key strata. The results showed that an increase in the distance between the key strata and the coal seam led to changes in the area of the suspended region of the key stratum, altered the magnitude and growth pattern of bending moments at the strike and dip boundaries of the key stratum, and promoted the transformation of its fracture mode from vertical fracture to horizontal fracture. Due to its strong bearing capacity, a typical high-position thick and hard key stratum had a larger suspended area and a greater accumulation of elastic strain energy than low-position key strata, and the rapid release of elastic strain energy during fracture posed a higher risk of inducing strong ground pressure disasters. The hydraulic fracturing method significantly altered the fracture step distance of the key strata and the intensity of ground pressure manifestation in the working face. After hydraulic fracturing weakening of a high-position key stratum located 125 m above the coal seam, the fracture step distance was reduced by 40.94% compared with the unweakened condition, the accumulated elastic strain energy was reduced by 98.40%, and the roof pressure of the working face was reduced by 48.77%, effectively controlling the strong ground pressure manifestation induced by fracture of high-position thick and hard key strata.

     

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