Weak shale roof falls have long been the main cause for fatalities in underground coal mines. Moisture-induced swelling is one of the root causes for the degradation of roof shales. In this study, slake durability tests are conducted on shale samples collected from Illinois basin coal mines, and different levels of durability are analyzed according to Gamble slake durability classification. There are two main mechanisms influencing the shape of retained fragments after two cycles of wetting and drying: mechanical abrasion and swelling pressure. A prototype optically based shale swelling apparatus is designed and manufactured for the shale free-swelling measurement. The experimental results suggest that swelling pressure tends to deteriorate shale laminations. Moisture-induced swelling of the No. 6 roof shale from Bear Run Mine was measured under 100% relative humidity condition. The measured swelling strain normal to beddings is ~5 to 7 times greater than the swelling strain parallel to beddings. This suggests that interlayer expansion plays a key role in moisture-induced swelling. Cracks induced by swelling pressure tend to occur along the bedding plane and lead to shale deterioration.
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机译：长期以来，页岩薄弱的屋顶塌陷一直是造成地下煤矿死亡的主要原因。水分引起的膨胀是屋顶页岩退化的根本原因之一。在这项研究中，对从伊利诺伊州盆地煤矿采集的页岩样品进行了耐盐性测试，并根据Gamble耐盐性分类分析了不同等级的耐性。在两个润湿和干燥周期后，有两种主要机制会影响保留碎片的形状：机械磨损和溶胀压力。设计并制造了基于光学的原型页岩溶胀设备原型，用于页岩自由膨胀测量。实验结果表明，膨胀压力趋于使页岩层合恶化。在100％相对湿度条件下测量了Bear Run Mine的6号屋顶页岩的水分诱导溶胀。垂直于被褥测得的溶胀应变比平行于被褥的溶胀应变大约5至7倍。这表明层间膨胀在水分引起的膨胀中起关键作用。由膨胀压力引起的裂纹倾向于沿着顺层平面发生，并导致页岩变质。
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