The story so far: Two scientific methods of mining — vertical drilling and auger or horizontal drilling — were employed to rescue 41 workers on November 28 after 17 days of being trapped in the partially-collapsed Silkyara tunnel in Uttarakhand. The last leg of the rescue involved rat-hole mining, once used extensively in Meghalaya.
What is rat-hole mining?
Among the rescued workers were Ramprasad Narzary and Sanjay Basumatary, both from the Ramfalbil area of western Assam’s Kokrajhar district. Locals could not help mark the irony of the rat-hole method being applied to rescue them from the Silkyara tunnel, because a few lives from that part of Assam were lost in the coal mines of Meghalaya dug using this crude method, before and after the National Green Tribunal (NGT) banned it in April 2014. Rat-hole mining, of two types, is so named as it involves digging tunnels 3-4 feet deep, barely allowing workers to crawl in and out. They have to squat while extracting coal with pickaxes. The side-cutting type of mining is usually done on hill slopes by following a coal seam — dark brown or black-banded coal deposited within layers of rock— visible from the outside. The second type called box-cutting entails digging a circular or squarish pit at least 5 sq. metre in width up to a depth of 400 feet. Miners who drop down in makeshift cranes or using rope-and-bamboo ladders dig horizontally after finding the coal seam. The tunnels are dug in every direction from the edge of the pit, resembling the tentacles of an octopus.
