In most of the coalfields in India, there are many mines where the seams are only developed by extracting 15-20% of coal but the pillars could not be extracted due to different constraints like presence of surface/subsurface features, forest area, danger of subsidence, lack of proper methodology, scarcity of suitable filling material, environmental issues, etc. As a result, a huge quantity of quality coal (around 3000 million tonnes) is locked-up in pillars for many years. This may lead to spontaneous heating and fire, accumulation of poisonous gases, severe stability problem leading to...