Resistivity imaging technique to investigate the subsurface strata conditions due to blasting in underground coal mines in India
Production from underground coal mining in India has been decreasing since the last three decades. Blasting-off-the-solid, in Indian underground mines, has been a widely practised method for winning coal while developing mine galleries in bord and pillar system. The blast holes are drilled in solid coal without free face in blasting-off-the-solid method of mining and are blasted with permitted types of explosives and delay detonators. Blasting-off-the-solid will play an important role in underground coal production. The mines that were planned earlier to be away from residential areas are now approaching to those areas. The coal reserves are being exploited very fast, and mine owners cannot ignore to take the coal beneath the structures/houses. In this paper, resistivity imaging technique has been used to document the change of subsurface structures/features between the surface and underground face, where blasting is carried out to extract the coal in underground coal mines. Resistivity imaging survey conducted at three mining sites revealed that there was no significant change in subsurface strata conducted during pre- and post-blasting conditions. The slight change in resistivity values up to 35 Ωm up to a few metres of peripheral area of the blasting face in the mine may be either due to the effect of blast vibration and/or same void created by blasting or increase in porosity of overlying subsurface strata.