Rescuers drill vertically as part of Uttarakhand tunnel rescue
The drilling operation is expected to take four days, provided there are no obstacles.
Rescuers managed to vertically drill through nearly 20 metres down the hill above the Silkyara-Barkot tunnel on Sunday, the first day of the new approached being adopted to reach the 41 workers trapped inside for 14 days, even as officials started work on two to three more options as anxiety mounted over the wellbeing of the trapped men.
In their new vertical approach, rescue workers have to drill down 86 metres to reach the tunnel, and by evening, the Satluj Jal Vidyut Nigam Limited (SJVNL) had bored down to about 19.5 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.
“SJVNL is drilling a 1.2 metre diameter hole vertically for evacuation of the trapped men. We identified spots where the drilling could be better... We think that this will complete in 100 hours (next four days) if there is no obstacle. One drilling rig of machine can only drill for 45 metres. We will have to change the rig,” Mahmood Ahmad, additional secretary, ministry of road transport and highways of India, and managing director of National Highways & Infrastructure Development Corporation Limited (NHIDCL), said.
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.
The latest approach, however, may bring up its own complications.
Drilling from the top of the hill may impact the stability of the tunnel which was still undergoing construction, officials said.
“Drilling from the hilltop may impact the stability of the tunnel. There is a risk of tunnel collapse or further structural damage, especially if the construction of the tunnel was not completed or if the tunnel is not adequately supported… maintaining communication between the drilling team and the trapped workers inside the tunnel is crucial,” an official from the Rail Vikas Nigam Limited (RVNL) said requesting anonymity.
The under-construction 4.5-km tunnel in Uttarakhand caved in early on November 12. But, authorities have not been able to identify a cause of the collapse.
Officials said that they have engaged geologists to ensure the operation proceeds safely. “But 100% assurance is not possible about anything. Each and every aspect is being looked into,” Uttarakhand government secretary Neeraj Khairwal said.
For the first two weeks of the operations, rescue officials tried digging 60m horizontally through the debris that had caved in. This technique, however, had proved unsuccessful as the auger machine repeatedly kept hitting hurdles such as hard rocks, or metal structures and steel girders within the debris.
A huge auger drill – a corkscrew like-device with a rotary blade at the front-end – that was drilling into this stretch of debris got stuck Friday evening, forcing officials to give up on the 25-tonne machine.
Individual workers have been entering this incomplete escape passage – in which a steel chute has been inserted – to cut through and bring out the stuck blades and the auger’s shaft in pieces.
On Saturday morning, a plasma cutter was airlifted from Hyderabad to supplement the gas cutter. A Defence Research and Development Organisation (DRDO) team and a unit of Army engineers, the Madras Sappers, also reached Silkyara.
By Sunday evening, only 8.15 metres of the auger shaft – of the 47 metres altogether – remained to be cut out, officials said.
“The exercise may be completed by Sunday midnight or tomorrow morning,” Khairwal had said earlier in the day.
Once the auger is completely extricated, rescuers will adopt another fresh approach – manual drilling to clear the remaining 10-12m stretch of the rubble.
One worker will enter the steel chute laid so far and operate the drill, and another man will send the debris up through a pulley in the time-consuming operation to be carried out in confined space, in what is known as the Rat hole mining process.
While the rescue work stalled at barely 10 metres from the trapped workers, international tunneling expert Arnold Dix said it was as if they were a “thousand kilometres away”.
“Because we still exactly don’t know what is in there. We don’t know if it is girders and if it is machines. We have used ground penetrating radar (GPR)… but this mountain has shown us that just when we think we know, we don’t. So, we have been very conservative making sure no one is hurt. We don’t want to jeopardise the men on the other side as well,” Dix told mediapersons.
Meanwhile, work on other options is also in progress, officials said.
From Tuesday, rescue workers will start drilling a 180m alternative escape tunnel into the side of the hill. This could take 12-14 days.
“The machinery has arrived. Concrete bed is about to be ready. We will start this drilling on November 28. It can take 12-14 days to complete at a rate of 12 metres per day,” the RVNL official cited above said.
Officials said drilling is also being carried out from the Barkot-end of the tunnel, and workers have progressed about 10 out of 483 metres.
“THDC is doing a drilling from Barkot side. They have already created a drift of 10 metres. They have to drill for 483 metres. It can take long time. I have also spoken to CMD, THDC if they have any other equipment which can drill at a fast rate,” Ahmed said.
Officials said they were consulting experts to ensure that there were no additional hazards if the work on different plans went on simultaneously.
“We have also consulted experts to know about the hazards if the work on different plans is undertaken simultaneously. Sensors have been installed to monitor vibrations. If working on one plan will hamper another, we will take a call,” Khariwal said.
Asked about the absence of an escape tunnel that some say should have been constructed at an earlier stage of the Silkyara-Barkot project, Ahmed said, “The same question is in our mind as well. A committee has been constituted…we will come to findings. However, our priority is to rescue 41 trapped men.”
The trapped workers are in a built-up two-kilometre stretch of the tunnel. They are being sent food, medicines and other essentials through a six-inch wide pipe.
A communication system has also been set up and families occasionally talk to them.
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