Experimental evaluation of failure characteristics of coal using 2D digital image correlation approach
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ORIGINAL PAPER
Experimental evaluation of failure characteristics of coal using 2D digital image correlation approach Nutan Shukla 1
&
Manoj Kumar Mishra 1
Received: 4 December 2019 / Accepted: 18 September 2020 # Saudi Society for Geosciences 2020
Abstract Efficient execution of the underground coal extraction depends on the accuracy of deformation measurement of the pillars. The basic design information as stress-strain behavior is collected from the laboratory investigation. Contact-based deformation measurement approaches have limitations like data insufficiency, proneness to signal loss, physical damage, etc. In this investigation, a contactless technique like digital image correlation (DIC) has been evaluated for its applicability on coal specimen. Coal specimens from 100-m depth have been investigated for their stress-strain behavior through DIC as well as other conventional methods, i.e., strain gauge and linear variable differential transformer (LVDT). The deformation was found out from a set of images recorded and analyzed using the software StrainMaster. In the image analysis, the optimum subset size was found to be 99 × 99 pixels with a step size of 8 pixels. The average threshold stress levels of crack initiation and crack damage in uniaxial compression were observed to be 43.72% and 63.6%, respectively. DIC exhibits higher sensitivity to deformation of coal as compared to that by LVDT and strain gauges and proven to be a promising and dependable technique for coal pillar analysis. Keywords DIC; . LVDT; . Coal sample; . Strain; . Crack initiation; . Crack damage;
Background of the problem The ever-increasing demand for coal energy has forced mankind to opt for extending the mining activity to deeper levels. The safety of the underground mine operations depends largely on its pillars. Coal being a heterogeneous material contains inherent geogenic weaknesses such as cracks, fractures, and fissures. It is often observed that different inherent as well as developed cracks weakens the integrity of pillars due to overburden as well as mining operations. Those cracks propagate and eventually lead to failure. Hence, the knowledge of deformation magnitude suffered by coal pillar is very important for its safe design. In this study, the deformation behavior of the coal specimens has been investigated through digital image Responsible Editor: Murat Karakus * Nutan Shukla [email protected] Manoj Kumar Mishra [email protected] 1
Department of Mining Engineering, National Institute of Technology Rourkela, Rourkela, India
correlation, a non-contact-based way of measurement technique. The conventional mechanism to study the deformation behavior has been through contact-based approaches such as strain gauges, acoustic emission sensors, seismic, micro-seismic, etc. (Perez et al. 2015). Those have limitations like disturbances in contact, weakening of contact elements due to environmental factors, inaccurate data due to heterogeneity of the whole body and surrounding noise, and size of sample dataset
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