Uttarkashi tunnel collapse: What is rat-hole mining & how does it work?

Rat-hole mining is a controversial and hazardous procedure in which miners in small groups go down narrow burrows to excavate small quantities of coal.

Rescuers at Silkyara tunnel have crossed the 50-metre mark and they need to dig through around 10 metres of rubble using rat-hole mining technique to bring out the 41 workers trapped there for the last 16 days.

While 12 rat-hole mining experts are involved in the horizontal excavation through the last 10 or 12-metre stretch of debris of the collapsed portion of the under-construction tunnel, let us find out what rat-hole mining is and how the process will be carried out.

Rat-hole mining, deemed to be a controversial and hazardous procedure involves miners in small groups going down narrow burrows to excavate small amounts of coal.

The practice was prevalent in Meghalaya where pits were dug and miners went down the narrow pits that were usually wide enough for just one person. Once they descended using bamboo ladders and ropes, coal was extracted manually using tools such as pickaxes, shovels, and baskets.

However, rat hole mining posed significant safety hazards as the mines were unregulated and miners would go down the pit without any proper safety measures.

Therefore, the National Green Tribunal in 2014 banned the practice in Meghalaya owing to the rise in deaths and other tragedies.

"It is also informed that there are umpteen number of cases where by virtue of rat-hole mining, during the rainy season, water flooded into the mining areas resulting in death of many number of individuals including employees/workers", the NGT observed.

On the 17th day of the rescue, a skilled team of workers involved themselves in removing muck by hand, using the rat-hole mining technique. An 800-mm diameter pipe was earlier inserted by the augur machine through the rubble.

Neeraj Khairwal, Uttarakhand government's nodal officer, clarified that the men brought to the site were not rat-hole miners but were experts in the technique.

They are likely to be divided into teams of two or three, with each team going into the steel chute laid into the escape passage for brief periods. Rajput Rai, a rat-hole drilling expert, said one man does the drilling, another collects the rubble with his hands and the third places it on a trolley to be pulled out.

This drilling was earlier carried out by a huge auger machine that got stuck in the rubble on Friday at around 47 metres, hence the team resorted to rat-hole mining.