The ecology of arid mining areas in western China is facing serious problems because underground coal mining destroys overlying aquifers, causing groundwater to shift along fracture zones and groundwater levels to drop. Therefore, it is important to construct strategically coal mine goafs as underground water reservoirs to store and utilize mining-affected water resources. During the long-term operation of underground water reservoirs, the stability of coal pillar dams is affected by the repeated rise and fall of mine water levels. To understand the repeated effects of water, nondestructive water immersion, ultrasonic velocity, uniaxial compression, and acoustic emission (AE) tests were performed to study the mechanical properties and damage mechanisms of coal samples under repeated drying–saturation conditions. The ultrasonic velocity test mainly achieved two functions: selecting consistent coal samples and providing evidence of changes after each drying and saturation process. Coal samples were grouped according to the number of drying–saturation processes (DSPs) to investigate and compare the mechanical and AE parameters. The post-peak phases of full stress–strain curves present perpendicular, L-shaped, and stepped forms, among which the latter two show obvious residual strength. The AE count, cumulative AE count, and stress can jointly determine the various stages and stress thresholds of the sample failure process (or crack development process), except the boundary between elastic stage and stable crack growth stage. Multiple immersions in water reduces the fractal dimension of broken blocks; that is, the degree of fragmentation decreases and the quantity and mass of large-size blocks increase.

由于地下采煤破坏上覆含水层，导致地下水沿断裂带移动，地下水位下降，西部干旱矿区生态面临严重问题。因此，战略性地将煤矿采空区建设为地下水库以储存和利用受采矿影响的水资源非常重要。在地下水库长期运行过程中，煤柱坝的稳定性受到矿井水位反复升降的影响。为了了解水的重复效应，进行了无损水浸、超声波速度、单轴压缩和声发射 (AE) 测试，以研究煤样在重复干燥-饱和条件下的力学性能和损伤机制。超声波速度测试主要实现两个功能：选择一致的煤样和提供每次干燥和饱和过程后变化的证据。煤样根据干燥-饱和过程 (DSP) 的数量进行分组，以研究和比较机械和 AE 参数。全应力-应变曲线峰后相呈垂直、L形和阶梯形，其中后两者显示出明显的残余强度。AE 计数、累积 AE 计数和应力可以共同确定样品失效过程（或裂纹发展过程）的各个阶段和应力阈值，但弹性阶段和稳定裂纹扩展阶段之间的边界除外。多次浸泡在水中，降低了碎块的分形维数；那是，