The cracking behavior of lignite during drying–wetting cycles impacts the efficiency of coal mining, underground coal gasification, and coalbed methane development. Lignite is known to have high water content, and it exhibits strong hydrophilic properties, resulting in a weak and rigid gel structure caused by water interactions with coal matrix molecules. Even at ambient temperatures, dehydration causes violent shrinkage of the lignite matrix and numerous fractures. Due to the shallow burial depth of lignite, it is often mined in open pits, and it often undergoes cycles of dehydration and rewetting in the open-air environment, resulting in significant changes to its physical structure and mechanical properties. Thus, a detailed characterization of this evolution process is necessary. In this study, lignite samples with different compositional properties were collected from the Shengli Coalfield in the Erlian Basin, and their physical structure and mechanical properties were characterized using nondestructive testing methods such as nuclear magnetic resonance, environmental scanning electron microscopy, X-ray computed tomography, and atomic force microscopy. The results provide insights into the impact of material composition on the syneresis behavior and destruction process of lignite. Upon removal of water from the coal matrix, rapid shrinkage occurs, resulting in the simultaneous formation of numerous fractures. Significant differences were observed in the contraction characteristics and fracture propagation patterns among the various lignite lithotypes. Xylite lignite exhibited the highest degree of contraction following dehydration, with the macropore reduction rate being the most significant. Matrix lignite showed a lower degree of syneresis compared to xylite lignite, while fusain-rich lignite demonstrated the weakest syneresis ability. The homogeneous xylite lignite shrinks as a whole after dehydration, and its fractures are long and straight, with good orientation. Fractures formed in the detrital humic groundmass of matrix lignite are short, convoluted, and poorly oriented. Fusain-rich lignite fractures are thin, and straight, with the best orientation. The expansion of fractures can cause geological disasters such as land subsidence, collapse, and landslides. Fusain hinders fractures’ expansion and acts as a “skeleton” to support the lignite structure. The presence of fusain is advantageous to maintaining the steadiness of the lignite. The differential evolution of the physical structure of lignite during the drying–wetting cycles, which aids to avert and mitigate disasters linked to dehydration cracking in different lignite-related engineering geological fields, is discussed in this paper.

褐煤在干湿循环过程中的裂解行为影响煤炭开采、煤炭地下气化和煤层气开发的效率。众所周知，褐煤含水量高，并且具有很强的亲水性，由于水与煤基质分子的相互作用，导致形成弱且刚性的凝胶结构。即使在环境温度下，脱水也会导致褐煤基质剧烈收缩和大量裂缝。由于褐煤埋深较浅，常在露天开采，在露天环境中经常经历脱水和再润湿的循环，导致其物理结构和力学性能发生显着变化。因此，有必要对这一演化过程进行详细的描述。本研究从二连盆地胜利煤田采集了不同成分性质的褐煤样品，利用核磁共振、环境扫描电镜、X射线计算机断层扫描等无损检测手段对其物理结构和力学性能进行了表征。和原子力显微镜。结果提供了关于材料成分对褐煤脱水收缩行为和破坏过程的影响的见解。从煤基质中除去水后，会发生快速收缩，导致同时形成许多裂缝。不同褐煤岩型之间的收缩特征和裂缝扩展模式存在显着差异。木糖岩褐煤脱水后收缩程度最高，大孔隙减少率最显着。与木糖岩褐煤相比，基质褐煤表现出较低程度的脱水收缩能力，而富含纺丝褐煤则表现出最弱的脱水收缩能力。均质木岩褐煤脱水后整体收缩，其裂缝长而直，定向性好。在基质褐煤的碎屑腐殖质基质中形成的裂缝短、曲折且定向不良。富纺纱褐煤裂缝细、直、方向性最好。裂缝扩展可引起地面沉降、塌陷、滑坡等地质灾害。Fusain阻碍裂缝扩展并充当支撑褐煤结构的“骨架”。纺丝素的存在有利于维持褐煤的稳定性。本文讨论了干湿循环过程中褐煤物理结构的差异演化，这有助于避免和减轻不同褐煤相关工程地质领域中与脱水开裂相关的灾害。