超大断面巷道支护关键技术及采动应力演化规律

Key technologies for supporting ultra large section tunnels and the evolution law of mining induced stress

  • 摘要: 针对超大断面巷道围岩变形控制难题,以曹家滩煤矿超大采高工作面回采巷道为研究背景,研究了曹家滩煤矿顶板岩层分布规律,分析了“高+低层位厚硬顶板”结构特征,明确了动压巷道围岩变形呈现非对称性、分区性、持续性的特征及其形成机理。采用数值计算分析了巷道断面尺寸对围岩稳定性的影响及支护预应力场分布特征,确定了合理的锚杆支护参数,提出了高预应力锚杆支护提高近场围岩稳定性、顶板水力压裂降低远场矿压动载的协同控制技术,分析了不同煤柱宽度下围岩应力及塑性破坏分布规律,确定了超大采高工作面合理护巷煤柱宽度为25 m,制定了超大断面巷道锚杆支护及水力压裂卸压技术方案。采用自主研发的超大断面巷道矿压监测预警系统平台,揭示了超大采高工作面动压巷道采动应力演化规律,获取了压裂区顶板微震能量演化规律及空间分布特征。结果表明:超大断面巷道掘进期间巷道未发生明显变形,锚杆受力很快趋于稳定。工作面回采阶段超前影响范围135.7 m,辅助运输巷滞后工作面229.6 m矿压基本趋于稳定,工作面超前支承压力峰值位于25.3~31.7 m内,锚杆受力及煤柱应力剧烈变化周期短,且很快趋于稳定,锚杆最大受力142 kN,锚索最大受力178 kN,煤柱最大应力增量8.6 MPa。相对于普通综放工作面,留巷巷道矿压影响周期明显减小,顶板水力压裂显著弱化了坚硬厚顶板,有效减小了煤柱侧向支承压力的持续作用。煤柱侧向顶板微震能量在超前工作面170 m至滞后工作面220 m显著增大,在滞后工作面20~60 m顶板活动最为强烈,随后迅速减小,表明顶板高低层位岩层及时有序垮落,微震能量与采动应力演化规律具有较好的一致性,揭示了顶板高低位岩层运移状态与矿压形成机理。超大断面巷道围岩全周期内均未出现明显变形,表明超大断面巷道采用高预应力锚杆支护与顶板压裂卸压协同控制技术,达到了较好的围岩变形控制效果。

     

    Abstract: In response to the problem of controlling the deformation of surrounding rock in ultra large cross-section tunnels, taking the mining roadway of the ultra high mining face in Caojiatan Coal Mine as the research background, the distribution law of the roof rock strata in Caojiatan Coal Mine was studied, and the structural characteristics of “high+low layer thick hard roof” were analyzed. The characteristics and formation mechanism of the deformation of surrounding rock in dynamic pressure tunnels were clarified, including asymmetry, zoning, and persistence. The influence of tunnel section size on surrounding rock stability and the distribution characteristics of support prestress field were analyzed using numerical calculations. Reasonable anchor bolt support parameters were determined, and a collaborative control technology was proposed to improve near-field surrounding rock stability with high prestress anchor bolt support and reduce far-field mining pressure dynamic load with hydraulic fracturing of the roof. The distribution law of surrounding rock stress and plastic failure under different coal pillar widths was analyzed, and the reasonable width of the roadway coal pillar for ultra high mining face was determined to be 25 m. A scheme for ultra high section roadway anchor bolt support and hydraulic fracturing pressure relief technology was formulated. The self-developed ultra large section roadway mining pressure monitoring and early warning system platform was used to reveal the evolution law of mining stress in the dynamic pressure roadway of the ultra high mining face, and to obtain the evolution law and spatial distribution characteristics of microseismic energy in the fracturing zone roof. The results showed that there was no significant deformation during the excavation of the ultra large section roadway, and the force on the anchor rod quickly tended to stabilize. The advanced impact range of the working face during the backfilling stage is 135.7 m, and the auxiliary transportation roadway lags behind the working face by 229.6 m. The mining pressure basically tends to stabilize, and the peak value of the advanced support pressure of the working face is within the range of 25.3−31.7 m. The stress on the anchor rod and the coal pillar changes dramatically and quickly stabilizes. The maximum stress on the anchor rod is 142 kN, the maximum stress on the anchor rod is 178 kN, and the maximum stress increment on the coal pillar is 8.6 MPa.Compared to ordinary fully mechanized top coal caving working faces, the period of influence of mining pressure in the reserved roadway is significantly reduced, and hydraulic fracturing of the roof significantly weakens the hard and thick roof, effectively reducing the sustained lateral support pressure of the coal pillar. The microseismic energy of the lateral roof of the coal pillar significantly increases from the leading working face 170 m to the lagging working face 220 m, and the roof activity is most intense at the lagging working face 20−60 m, followed by a rapid decrease, indicating that the high and low strata of the roof collapse in a timely and orderly manner. The microseismic energy is consistent with the evolution law of mining stress, revealing the migration state of the high and low strata of the roof and the formation mechanism of mining pressure. There was no significant deformation observed in the surrounding rock of the ultra large section roadway throughout the entire period, indicating that the use of high prestressed anchor support and roof fracturing pressure relief collaborative control technology in the super large section roadway has achieved good control effect on surrounding rock deformation.

     

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