Analysis of Coal Pillar Strength and Stability in Underground Coal Mines

Coal pillar stability is one of the most significant geotechnical concerns in underground coal mining operations because coal pillars act as the primary support system for overlying strata in bord and pillar workings. Improper pillar design can result in catastrophic failures such as roof collapse, rib spalling, and progressive pillar crushing, thereby threatening mine safety and productivity. The present study investigates the behaviour of coal pillars under varying geological and mining conditions with special emphasis on Indian underground coal mines. Important parameters, including pillar geometry, width-to-height ratio, depth of cover, gallery width, and in situ stress conditions, were evaluated using empirical and analytical approaches. The study comparatively analyses the CMRI, Bieniawski, and Salamon–Munro pillar strength models for assessing pillar stability. Laboratory investigations such as point load testing, Brazilian tensile strength testing, and moisture content analysis were conducted to determine the geomechanical properties of coal samples. The findings reveal that increasing pillar width significantly enhances pillar strength and factor of safety, whereas increasing gallery width leads to greater tributary loading and stress concentration. The study further confirms that the CMRI formula is more reliable for Indian geo-mining conditions due to its calibration with local coalfield characteristics. The outcomes of this research provide a scientific basis for optimising coal pillar design, improving underground mine stability, and minimising ground control hazards in deep underground coal mines.