Nagpur: A new technology developed by Visvesvaraya National Institute of Technology (VNIT), Nagpur, could significantly improve the recovery of coal from underground mines, potentially raising extraction from the conventional 60–65% to as much as 95% of mineable coal.The technology is particularly significant for coal deposits where extraction is restricted by the presence of railways, highways, buildings, forests and other sensitive structures on the surface.The technology has been developed by AK Agarwal, associate professor, and Anupam Anant Kher, assistant professor, department of mining engineering, VNIT Nagpur. A patent for the technology has already been published.The technology focuses on extraction of coal pillars under the bord-and-pillar system (an underground mining method in which coal is extracted in a pattern of openings, or bords, while blocks of coal called pillars are left behind to support the roof). These pillars can contain a substantial amount of coal that is normally difficult or unsafe to recover.The proposed method combines mechanised pillar extraction with simultaneous backfilling of the voids created during mining.A continuous miner is a highly mechanised underground machine that cuts and loads coal continuously, allowing much faster extraction than conventional methods. However, the speed of such machines can make conventional sand stowing (filling underground voids with sand after coal extraction) inadequate.Under the VNIT technology, coal pillars are divided into smaller sections and extracted in a predetermined sequence using a continuous miner. As coal is removed, the resulting voids are progressively filled with a suitable pumpable material. Roof bolting and other strata-control measures (methods used to support and stabilise the surrounding rock and mine roof) are carried out in coordination with extraction and backfilling.The researchers said the integrated approach could provide near-continuous support to the overlying strata, reducing large unsupported underground voids and stress concentration while improving safety and resource recovery. Suitable industrial and mining wastes, including fly ash and mine waste, can also potentially be used as backfill, supporting resource utilisation and the principles of a circular economy.Vaidehi Dakwale, assistant professor, department of civil engineering, VNIT, contributed to designing and developing the backfilling material. Gaurav Tiwari, assistant professor, department of mechanical engineering, VNIT, carried out thermal analysis of the heat generated during setting of the cementitious backfill.The research was carried out with the encouragement of Rajesh Gupta, HOD, Mining, and motivation from YB Katpatal, Dean (R&C), and Prem Lal Patel, Director, VNIT Nagpur, Agrawal and Kher said.
