Mechanical and micro-structural damage mechanisms of coal samples treated with dry–wet cycles
Mechanical and micro-structural damage mechanisms of coal samples treated with dry–wet cycles
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DOI：
10.1016/j.enggeo.2022.106637
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发表时间：
2022-03
影响因子：
7.4
通讯作者：
Liqiang Yu;Qiang-ling Yao;Zhaohui Chong;Y. Li;Q. Xu;H. Xie;Pingyu Ye
中科院分区：
文献类型：
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作者：
Liqiang Yu;Qiang-ling Yao;Zhaohui Chong;Y. Li;Q. Xu;H. Xie;Pingyu Ye
建设采空区地下水库储存和利用矿井水，可以有效缓解中国西部干旱矿区的煤水矛盾。了解水对煤的力学性质和微观结构的影响，对于多次水蚀作用下的煤柱坝稳定性设计具有重要意义。本研究对0~5次干湿循环煤样进行了超声、X射线衍射、扫描电子显微镜、核磁共振和单轴压缩试验，研究了随着干湿循环次数n的增加，煤样的吸水特性、孔结构、微观形态和力学性能的变化。此外，还建立了孔结构和微观形态与力学损伤之间的联系。结果表明，峰值应力和弹性模量均为n的负指数函数。随着煤样含水率的增加，煤样的含水率、饱和度和均匀度增加，孔隙数量增加，煤样内部的小孔隙转变为中大孔隙。此外，峰值应力与T2曲线积分面积定义的孔隙率和内部损伤有很好的负线性拟合。根据扫描电子显微镜测试结果，煤在干湿循环过程中经历了原始结构均匀致密、颗粒聚集、孔隙发育、裂隙萌发和整体结构破碎五个阶段，结构完整性逐渐降低。损伤变量D由扫描电子显微镜图像的分维F定义，能够定量描述煤在干湿循环过程中的微观损伤，并且D/Ff是n的指数函数。最后，从宏观(即核磁共振)和微观(即扫描电子显微镜)两个角度对煤样的损伤机理进行了解释，两者具有较好的一致性。研究结果可为煤柱坝的长期稳定性评价和设计提供参考。
The construction of mine goafs as an underground reservoir to store and utilise mine water can effectively alleviate the contradiction between coal and water in the arid mining areas in western China. Understanding the effects of water on the mechanical properties and micro-structure of coal is essential for the stability design of coal pillar dams subjected to repeated water erosion. In this study, ultrasonic, X-ray diffraction, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and uniaxial compression tests were conducted on coal samples with zero to five dry–wet cycles to investigate the changes in water absorption characteristics, pore structure, microscopic morphology, and mechanical properties as the number of dry–wet cycles,n, increased. Moreover, the connection of the pore structure and microscopic morphology with the mechanical damage was established. The results showed that the peak stress and elastic modulus were negative exponential functions ofn. Asnincreased, the moisture content saturation and homogeneity of the coal sample increased, the number of pores increased, and tiny pores within the coal converted to medium-to-large pores. Further, the peak stress had a good negative linear fit to the porosity and internal damage defined by the integrated area of theT2curve. According to the SEM test results, the coal underwent five stages during a dry–wet cycle: uniform and dense original structure, particle aggregation, pore development, fracture sprouting, and overall structural fragmentation, with a gradual decrease in structural integrity. The damage variable,D, was defined by the fractal dimension,F, of the SEM images, enabling the quantitative characterisation of the coal microscopic damage during the dry–wet cycle; moreover,D/Fwas an exponential function ofn. Finally, the damage mechanism of coal samples was interpreted from both macroscopic (i.e. NMR) and microscopic (i.e. SEM) perspectives, and they showed good agreement. Our results could provide a reference for the long-term stability assessment and design of coal pillar dams.