The factors affecting permeability change under repeated mining of coal seams are important study aspects that need to be explored. This study combined various stress variation characteristics of protective seam mining and simplified the stress path of repeated mining in protective seam mines. Based on the results from the bespoke gas flow and displacement testing apparatus, seepage tests for simulated repetitive mining were carried out. The results simulated the actual behavior very well. With any drastic increase in the mining influence, the axial deviation stress in the stress path increased, and the greater the difference in coal permeability during the unloading and stress recovery stage, the more substantial the increase in permeability. The change in coal permeability was significantly influenced by the severity of simulated repeated mining cycles. When the mining stress exceeded a critical value, the permeability of the coal sample increased with the increase in the number of loading and unloading cycles, but the reverse was true when the mining stress was lower than the critical value. The effective sensitivity of seepage to the applied stress decreased with an increase in the number of stress cycles. With a decrease in the deviation stress, that is, with lower severity of mining influence, the effective sensitivity of coal seepage to stress gradually decreased.

中文翻译：

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重复开采活动引起应力变化条件下烟煤渗透率变化特征

在重复开采煤层中影响渗透率变化的因素是需要研究的重要研究方面。这项研究结合了保护性煤层开采的各种应力变化特征，并简化了保护性煤层重复开采的应力路径。根据定制气流和位移测试设备的结果，进行了模拟重复开采的渗流测试。结果很好地模拟了实际行为。随着开采影响的急剧增加，应力路径中的轴向偏移应力会增加，并且在卸荷和应力恢复阶段，煤渗透率的差异越大，渗透率的增加就越大。模拟的重复开采周期的严重性显着影响了煤渗透率的变化。当开采应力超过临界值时，煤样的渗透性随装卸次数的增加而增加，但当开采应力低于临界值时，反之。渗流对所施加应力的有效敏感性随应力循环次数的增加而降低。随着偏移应力的减小，即开采影响的严重性降低，煤渗流对应力的有效敏感性逐渐降低。但是当采矿应力低于临界值时，情况正好相反。渗流对所施加应力的有效敏感性随应力循环次数的增加而降低。随着偏移应力的减小，即开采影响的严重性降低，煤渗流对应力的有效敏感性逐渐降低。但是当采矿应力低于临界值时，情况正好相反。渗流对所施加应力的有效敏感性随应力循环次数的增加而降低。随着偏移应力的减小，即开采影响的严重性降低，煤渗流对应力的有效敏感性逐渐降低。