Rat hole mining is the traditional method rescuers have fallen back upon to evacuate the 41 workers trapped there for the last 15 days following the failure of heavy machines including the American auger to drill through the rubble to prepare an escape passage for them.

Rat hole mining is a technique, famous in Meghalaya, where the workers drill small holes in the earth to do coal mining. At the Silkyara tunnel, at least 12 experts have been called by the companies - Trenchless Engineering Services Private Limited and Navayuga Engineers Private LTD - to do rat hole mining horizontally in the collapsed part of the main tunnel. They have come from Delhi, Jhansi and other parts of the country."

They will have to do at least 10 to 12 meters of drilling by their own hands. They will majorly use two tools - hand held drilling machine to remove the rubble and and gas cutter for cutting the iron hurdles," an official said.

According to Neeraj Khairwal, Additional Secretary, Uttarakhand government and the state nodal officer for the rescue operation, said a skilled team of workers called to do rat hole mining will remove the rubble by their hand.

"As they remove the muck, the tunnel pipe (800 mm) will be pushed gradually by the machine through the rubble," Khairwal said.

"We will do the drilling and collect the muck by our hand. We have been doing this for several years," a worker who named himself as Mohan Rai told PTI.

He said they will be in proper gear wearing oxygen masks and glasses to cover their eyes. "We can remove 5-6 meters of rubble using this method in 24 hours," Rai said.

Rakesh Rajput, another expert said three of them will go inside the tunnel, one will do the drilling, another will collect the muck and the third one will push the muck through the trolley. "We have been doing it for years," said Rajput.

Another rat hole mining expert said they can remove 10 metres of muck or rubble in 20 hours