Wang Beifang, Zhou Duo, Zhang Jing, Liang Bing
School of Mines, Liaoning Technical University, Fuxin, 123000, Liaoning, China.
State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, Beijing, 102299, China.
Sci Rep. 2024 Mar 15;14(1):6338. doi: 10.1038/s41598-024-56741-8.
The continuous operation of coal mine underground reservoirs exposes the coal pillar dams to mining disturbances and prolonged water immersion, resulting in the deterioration of coal pillars' mechanical properties and posing a serious threat to the dam stability. To this end, coal samples from the proposed pillar dam in the 5-2 coal seam of Daliuta Mine in Shendong Mining Area were selected for conducting water absorption tests and triaxial compression tests under conditions of repeated water immersion, in order to study the deterioration of the mechanical properties and acoustic emission damage characteristic of coal samples as well as the mechanism behind the deterioration of coal samples under the water-rock interaction. The results indicated that: (1) the saturated water content of coal samples exhibited a progressive increase as the water immersion times increased, but with a diminishing rate of growth. (2) As the water immersion times increased, the compressive strength, cohesive force, and internal friction angle of coal samples gradually decreased. Notably, the deterioration effect was more pronounced in compressive strength and cohesive force, while the decline in internal friction angle was relatively minor, and the total deterioration degree and the stage deterioration degree of the above three had evident cumulativity and non-uniformity. The progressive rise in water immersion times led to a gradual attenuation of the deterioration effect. Meanwhile, the confining pressure exhibited a certain inhibitory impact on the strength deterioration of coal samples. (3) Compared to the dry coal samples, the average AE count rate of coal samples subjected to a single water immersion exhibited a significant decrease, and subsequent water immersion for two, three, and four times resulted in a very minor decrease in the average AE count rate. (4) The AE cumulative ringing counts in coal samples exhibited varying degrees of reduction as water immersion times increased. Specifically, the most significant decrease in AE cumulative ringing counts occurred after the initial water immersion, followed by a gradual decrease thereafter. The energy-releasing capacity of coal samples decreased, while their plasticity exhibited a gradual increase. (5) A damage model was developed for coal samples based on the water immersion times. The model indicated that the damage to coal samples increased as the water immersion times increased, and the damage rate gradually decreased and eventually stabilized. (6) The deterioration mechanism of coals under the water-rock interaction was explained. Through repeated water immersion, the physical, chemical, and mechanical interactions between water and coal induced alterations in the internal microstructure of coal samples, resulting in the deterioration of mechanical properties such as compressive strength, cohesive force, and internal friction angle, which was a cumulative damage process from the microscopic to the macroscopic level.
煤矿地下水库的持续运行使煤柱坝受到采动扰动和长期水浸，导致煤柱力学性能劣化，对坝体稳定性构成严重威胁。为此，选取神东矿区大柳塔煤矿5-2煤层拟建煤柱坝的煤样，进行反复水浸条件下的吸水性试验和三轴压缩试验，以研究煤样力学性能劣化及声发射损伤特征，以及水岩相互作用下煤样劣化的机理。结果表明：(1)煤样饱和含水量随水浸次数增加呈渐进式增长，但增长速率逐渐减小。(2)随着水浸次数增加，煤样抗压强度、内聚力和内摩擦角逐渐降低。值得注意的是，抗压强度和内聚力的劣化效应更明显，而内摩擦角下降相对较小，上述三者的总劣化程度和阶段劣化程度具有明显的累积性和不均匀性。水浸次数的逐渐增加导致劣化效应逐渐减弱。同时，围压对煤样强度劣化具有一定的抑制作用。(3)与干燥煤样相比，单次水浸煤样的平均声发射计数率显著降低，随后水浸两次、三次和四次导致平均声发射计数率的降低幅度很小。(4)随着水浸次数增加，煤样声发射累计振铃计数呈不同程度降低。具体而言，首次水浸后声发射累计振铃计数降低最为显著，此后逐渐降低。煤样的能量释放能力降低，而塑性逐渐增加。(5)基于水浸次数建立了煤样损伤模型。该模型表明，煤样损伤随水浸次数增加而增大，损伤速率逐渐减小并最终趋于稳定。(6)解释了水岩相互作用下煤的劣化机理。通过反复水浸，水与煤之间的物理、化学和力学相互作用导致煤样内部微观结构发生改变，从而使抗压强度、内聚力和内摩擦角等力学性能劣化，这是一个从微观到宏观的累积损伤过程。
