Constructing pumped-storage power stations using underground reservoirs in mines offers a promising method for large-scale energy storage. Watertight coal pillars have the potential to destabilize under the mine-shock cyclic dynamic loading and the drying–wetting cycles (DWCs). Understanding the fatigue damage mechanism and failure precursors in watertight coal pillars under cyclic dynamic loading disturbances in overburdened rock strata has become challenging. This study investigated the fatigue fracture behavior and precursor information of coal samples under acoustic emission (AE) monitoring over 1–7 DWC times. We analyzed the effects of DWC and fatigue cycles on the dynamic parameters and AE response, investigated crack spatial extension behaviors and the tensile-shear cracking evolution law, and analyzed the fatigue damage evolution law and failure precursor with energy and b-value. The results demonstrated that fatigue loading produced a strengthening effect on the DWC coal samples, and DWC promoted plastic softening damage to the specimens and increased the percentage of the elastic phase. The average dynamic fatigue strength and life of the specimens decreased exponentially under 7 DWC times. The average dynamic axial stiffness decreased by 15.67 %, the axial deformation increased by 6.1 × 10−4 in a single cycle, and the dynamic elasticity modulus of the fatigue damage instant decreased by 8.86 %. The greater the number of DWC, the smaller the b-value and the larger the fluctuation amplitude at fatigue failure of the specimen. A large short-term increase or decrease in the b-value can be regarded as a precursor to fatigue failure. This study provides a reference for the stability monitoring and forewarning of underground pumped-storage facilities.

中文翻译：

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通过声发射和核磁共振研究干湿循环处理煤样品的疲劳断裂行为和损伤演变


利用矿山中的地下储层建造抽水蓄能电站为大规模储能提供了一种很有前途的方法。水密煤柱在矿井冲击循环动态载荷和干湿循环 （DWC） 下有可能不稳定。了解覆重岩层中循环动载荷扰动下水密煤柱的疲劳损伤机制和失效前兆已成为一个挑战。本研究调查了在 1-7 DWC 次的声发射 （AE） 监测下煤样品的疲劳断裂行为和前驱体信息。我们分析了 DWC 和疲劳循环对动力学参数和 AE 响应的影响，研究了裂纹空间扩展行为和张剪开裂演变规律，并分析了疲劳损伤演变规律和失效前兆与能量和 b 值。结果表明，疲劳加载对DWC煤样产生强化作用，DWC促进了试件的塑性软化损伤，提高了弹性相的百分比。试样的平均动态疲劳强度和寿命在 7 次 DWC 以下呈指数下降。平均动态轴刚度降低了 15.67 %，轴向变形在单循环中增加了 6.1 × 10−4，疲劳损伤瞬间的动弹性模量降低了 8.86 %。DWC 的数量越多，b 值越小，试样疲劳失效时的波动幅度越大。b 值的短期大幅增加或减少可被视为疲劳失效的前兆。本研究为地下抽水蓄能设施的稳定性监测预警提供了参考。