Influence of moisture on crack propagation in coal and its failure modes

Research output: Contribution to journalArticle

  • External authors:
  • Qiangling Yao
  • Chuanjin Tang
  • Songwei Wang
  • Qingxiang Huang

Abstract

Understanding of effects of water on crack propagation and crack failure modes of coal is important to determinethe required width of the coal pillars in underground reservoirs and calculate the area of fractured zones con-tainingflowing water. In this paper, we apply acoustic emission (AE) techniques, X-ray diffraction (XRD),scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP), alongside uniaxial compressivetests to develop new insights into the mechanics of crack developments and failure modes of partially saturatedcoal samples with a range of moisture contents (0%, 6.00%, 9.75%, and 10.96%). We present new relationshipsbetween tensile/shear cracks and failure modes incorporating the effects of water intrusion on the micro-tensile/shear cracks and macro tensile/shear failure modes.The results show that the presence of hydrophilic illite (clay mineral) has strong influence on water ab-sorption capacity of coal. The uniaxial compressive tests carried out in this study, show that the AE activity ismainly appeared after the crack damage threshold (point D) and it is independent to water content. The AEactivity decreases with increasing moisture content as the water reduces the internal connections between thecoal particles and increases the possibility of sliding failure. Studying the RA (rise time divided by peak am-plitude) and AF values (counts divided by duration) demonstrated that the cracks generated in the coal samplesconsist of a large number of micro tensile and shear cracks, whilst tensile- or shear-only cracks were not found tobe evident. For the samples studied, the higher moisture content is associated with the lower AF and higher RAvalues. Under the scope of the experimental investigations, we conclude that the higher moisture content cor-responds to a lower number of total cracks and tensile cracks in coal. However, a greater proportion of shearcracks can be created by the increasing water content. Increasing the water level can reduce the number oftensile failure planes and the percentage of tensile failure planes against total failure planes. Therefore, thehigher water content can increase shear failure planes and promote the possibility of shear failure in coal.

Bibliographical metadata

Original languageEnglish
JournalEngineering Geology
Early online date23 May 2019
DOIs
Publication statusPublished - 14 Aug 2019

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