Experimental evaluation of failure characteristics of coal using 2D digital image correlation approach

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 x 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.