Rescuers initiated the process of manual drilling to rescue 41 workers trapped behind a 60m thick wall of debris under the Silkyara-Barkot tunnel late on Monday evening, after removing a part of an augur machine stuck inside the evacuation pipes, even as vertical drilling from the top of the mountain continued, with about 50 metres left.

Officials are focusing on the two methods to evacuate the men, trapped in increasingly desperate conditions since a part of the 4.5km-long tunnel collapsed two weeks ago, as the augur machine — a corkscrew-like device with a rotary blade at the front — went bust on Friday, upon getting entangled in an iron girder after drilling 46.8 metres into the debris.

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Prime Minister Narendra Modi, who is in Hyderabad, on Monday said that all government agencies are working round-the-clock to rescue the workers. “In this campaign, nature is constantly giving us challenges, but we are standing firm and trying round the clock,” he said.

An official release on the operation on Monday said, “After visual inspection by welders it was found that the cutter of the augur has been entangled with lattice girder bars, which damaged 1.5m length of the 800mm-wide passage pipe.”

Now that it has been removed, “rat miners” have started manually drilling through the narrow pipe to reach the workers, officials said.

Explaining the process, officials said that three miners will go inside the pipe at a time — one will drill, another will collect muck and the third will push the muck through a trolley to the other side of the pipe.

Rat-hole mining is a primitive method of extracting coal deposits through narrow, horizontal passages, prevalent in Meghalaya. The term “rat hole” refers to the narrow pits dug into the ground, typically just large enough for one person to descend into and extract coal. The name comes from its resemblance to rats burrowing through narrow holes. A team of six rat-hole miners has been called in from Madhya Pradesh for the operation.

“According to our estimates, it is only about 12 metres to reach the trapped men. We will do manual excavation,” Mahmood Ahmad, additional secretary, ministry of road transport and highways, and MD, National Highways & Infrastructure Development Corporation Limited (NHIDCL), said.

The augur machine broke down just about 10-12 metres from the breakthrough point on November 24, stalling the progress of the operation even as officials had hoped to bring the workers out that day itself.

Once it became clear that the augur machine was irreparable, officials shifted to the next best option — of drilling down 86 metres to reach the tunnel.

Till Monday evening, Satluj Jal Vidyut Nigam (SJVNL) had managed to drill through 36 metres. At this rate, if there are no other obstacles, the rescuers should be able to reach the workers by Thursday in an operation that has already dragged on much longer than was previously expected.

On Monday, however, the machine hit a water aquifer, which slowed down the rescue effort.

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“We got water in the bore. Dewatering was done. We are also facing difficulty due to hard rock coming in the way, but it is going well. We have to do about 85-90 metres. We are expecting it to be completed by November 30,” said Ahmad.

As the drilling progresses, 700mm wide pipes are being inserted to create an escape passage. A little distance away, a thinner, 200mm probe is being pushed in. It has reached the 70-metre mark. Once the rescuers reach the requisite height, choppers will be used to airlift the trapped men, lieutenant general (retd) Syed Ata Hasnain, member, National Disaster Management Authority, said.

The authorities are working on at least three other methods of rescue.

Giving details of the progress, Ahmad said, “From the Barkot side, we have done six blasts and penetrated 12 metres. The distance to go is 483 metres. But this is not our main plan.”

The Tehri Hydroelectric Development Corporation (THDC) has been tasked with constructing a rescue tunnel from the Barkot end using the conventional drill-and-blast method. However, as the method can take long, it is only a contingency plan.

The Rail Vikas Nigam Limited, meanwhile, is expected to start perpendicular drilling for 170-180 metres by Tuesday or Wednesday. “RVNL is also doing vertical drilling as trial to get geological findings,” he said.

Separately, for vertical drilling by ONGC all the associated materials are on standby in Rishikesh, while officials from the Border Roads Organisation prepared the access path and location for placement of the rig, officials said. “Track preparation for 24-inch vertical drilling is complete, but the rig work is pending,” Hasnain said.

Officials are still unable to reach a consensus on a timeline for the operation, even as they said that all efforts are being made to ensure mental and physical well-being of the workers.

“No harm to physical or mental health is being caused; provisions include power, oxygen, and communication lines to family members and psychosocial therapists,” Hasnain said.

Meanwhile, principal secretary to the Prime Minister, PK Mishra, Union home secretary, Ajay Bhalla, visited the site of the tunnel collapse on Monday to take stock of the operations.