Abstract
The knowledge and behavior of support pillar stability at different depths of cover is an important aspect of mine design and its safety assessment. Geo-material as coal exhibits multiple stages of weakening under load, often from the over lying strata for mining activities. The failure process of coal in underground mining undergoes stages as crack closure, crack initiation, crack damage until peak. The detail information about those stages as well as corresponding deformation are very important for design and safety of the system. In this investigation, digital image correlation (DIC) was used to measure deformation and was observed to be more sensitive to provide weakening stages as compared to that by conventional measurement approaches as LVDT and strain gauge. Coal samples from 30 m, 75 m and 100 m were evaluated under uniaxial loading. The crack initiation and crack damage stresses at varying depths were evaluated. The coal samples exhibited weakening at an early stage for shallow depths through its physical disintegration occurred at a later stage. The behavior is contrast for coal from 100 m deep with higher degree of damage. Porosity, shape and size of the particles, inter-granular distance between voids as well as constituent minerals influenced the observed behavior. Total energy, elastic energy as well as dissipated energy involved in the process at each stage were also determined. A DIC based pre-failure indicator (α) was developed to predict the threshold values of onset of cracks at varying depths. The threshold value varied between 0.38 % and 0.4 % of axial strain. An algorithm was developed to predict precursor failure in coal pillars at varying depths.
Article highlights
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A comparative study between contact based measurement methods such as LVDT and Strain gauge and a non-contact based measurement method digital image correlation is conducted.
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The crack damage evolution of coal specimens at varying depths have been investigated.
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A DIC based prefailure indicator have been developed to predict the precursor failure of coal specimens.
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Shukla, N., Mishra, M.K. Assessment of crack stress thresholds and development of a pre-failure indicator using Digital Image Correlation approach for coal specimen. Geomech. Geophys. Geo-energ. Geo-resour. 7, 103 (2021). https://doi.org/10.1007/s40948-021-00300-2
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DOI: https://doi.org/10.1007/s40948-021-00300-2