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大采高临空面“L”型顶板结构形成机制及断裂失效与能量演化特征

Formation mechanism, fracture failure and energy evolution characteristics of L-shaped roof structure of large mining height working face adjacent to goaf

  • 摘要: 大采高工作面坚硬顶板破断运动与结构失稳是诱发采场冲击地压显现的根源,揭示顶板岩层断裂运动与矿震事件的关联效应,对科学防治冲击地压具有重要意义。以兖矿能源权属公司鄂尔多斯营盘壕煤矿高能矿震及冲击地压显现为案例,针对2215临空工作面大能量事件集中发生于工作面前方与临空侧的现象,综合理论分析、数值模拟与现场实测,基于弹塑性力学板结构极限载荷分析方法,获得了大采高临空工作面开采条件下顶板岩层破裂特征及塑性铰接块体几何尺寸大小;开发了采动岩层断裂耗散能演化Fish程序,获得了工作面推进过程中顶板岩层耗散能分布特征及其动态演化规律,查明了大采高工作面顶板岩层主断裂迹线分布特征及断块结构形态,并据此揭示了工作面顶板岩层断裂结构形态及工作面超前煤岩体与临空侧大能量事件集聚机制。结果表明: 工作面顶板岩层随着推进距离的增大,其极限承载能力呈指数型快速衰减,直至达到工作面顶板岩层初次及周期破断步距,且大采高临空工作面顶板呈现偏心断裂特征,主断裂位置向临空侧与采空区后方偏移。大采高工作面顶板岩层于超前煤岩体及临空侧形成悬露结构,前后两次断裂迹线合围形成近似“L”型顶板结构,该“L”型顶板岩层的破裂运动是造成大采高工作面临空侧及超前大能量微震事件的根源。针对厚硬岩层群,于两巷道开采周期内布置高密度超前致裂卸压钻孔,破坏多层“L”型顶板结构组合效应与整体运动特征,有效减少了营盘壕煤矿大采高坚硬顶板工作面大能量微震事件的发生。可为类似条件下优质煤炭资源安全开采提供有益借鉴。

     

    Abstract: The fracture movement and structural instability of hard roof strata in large-mining-height faces are fundamental triggers for rock burst occurrences in mining panels. Elucidating the correlation between the fracturing of roof strata and mining-induced seismic events is therefore of significant importance for the scientific prevention and control of rock burst. The high-energy seismic events and rock burst manifestations at the Yingpanhao Coal Mine, operated by a subsidiary of Yankuang Energy Group in Ordos City, are investigated with the 2215 gob-side face employed as a case study. Focusing on the concentration of large-energy events ahead of the working face and along the gob-side edge, the research integrates theoretical analysis, numerical simulation, and field measurement. By applying an elastoplastic plate structure ultimate load analysis method, the fracture characteristics of roof strata and the geometric dimensions of plastic hinged blocks under conditions of a large-mining-height gob-side face were determined. A Fish program was developed to simulate the evolution of dissipated energy during strata fracturing, enabling the characterization of the distribution and dynamic evolution of dissipated energy in roof strata as the face advances. The main fracture trace distribution and the structural morphology of broken blocks in the roof strata of large-mining-height faces are identified, thereby revealing the structural configuration of roof fracturing. Through this, the mechanism behind the concentration of high-energy events in the front abutment pressure zone and the gob-side area is elucidated. The findings indicate that: The ultimate load-bearing capacity of the roof strata decreases exponentially with increasing face advance distance until the initial and periodic fracturing intervals are reached. Moreover, the roof in the large-mining-height gob-side face exhibits eccentric fracture characteristics, with the main fracture location shifting toward the gob-side edge and the rear of the goaled area. An overhanging structure is formed in the roof strata above the front abutment and the gob-side area. The interaction of successive fracture traces results in the formation of an approximately “L”-shaped roof block, whose rupture and movement are identified as the primary cause of high-energy microseismic events in these zones. In thick and hard multi-layer strata, the implementation of high-density advanced destressing boreholes during the mining cycle of the two gate roads effectively disrupts the combined structural effect and holistic movement behavior of multi-layered “L”-shaped roof blocks. This measure has proven effective in reducing the occurrence of high-energy microseismic events in large-mining-height faces with hard roof strata at the Yingpanhao Mine, which provide valuable references for safe extraction of high-quality coal resources under similar geological and mining conditions.

     

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