Explained: How the Silkyara tunnel rescue operation is being carried out
A stretch of mud road was re-laid to make passage of ambulances easier. Stretchers were being taken inside the mouth of the tunnel
Authorities on Tuesday managed to push a pipe through the debris to rescue the 41 labourers trapped after a part of the 4.5km-long Silkyara-Barkot tunnel collapsed in Uttarakhand’s Uttarkashi 17 days ago, officials said.
The rescue operation was possible through the assistance of rat-miners from the Bundelkhand region of Uttar Pradesh and Madhya Pradesh.
The rescue operations started with excavators followed by the use of augur drilling machines and culminated with manual drilling for the final 12 meters.
Here is an explainer on how it was done.
How rat-miners completed the rescue?
A group of three rat-miners entered the pipe and crawled to the debris on Monday night. One person did the digging, the second put the debris in the trolley and the third person kept the trolley on a shaft through which it was pulled out. On average, they were able to dig 0.9 meters per hour. Officials said a group of rat-miners were replaced with a fresh group of 3 almost every hour. By 3pm on Tuesday, they had drilled 12-13 meters to reach the workers. In all 12, rat-miners from Uttar Pradesh and Madhya Pradesh were brought in.
How the people will be brought out of the tunnel?
According to officials, once the drilling was done, the wide pipes are pushed through the debris to create a tunnel. Once that was done, a team of National Disaster Response Force (NDRF), wearing oxygen kits crawled through the pipe carrying wheel-fitted stretchers, a rope, and oxygen kits for workers. The doctors and paramedics were then sent inside on wheel-fitted stretchers after which they checked the vitals of the trapped workers. All workers would be counselled on how to come out of the pipe tunnel. The stretchers were tied with ropes from both sides. One by one, the workers will be taken out. NDRF personnel will be the last ones to come out of the tunnel. The entire operation will last three hours.
How was food and essentials sent for the trapped workers?
The food was earlier being sent to the trapped men through a 4-inch pipe with compressed air. On November 20, the rescuers installed the bigger six-inch pipe to send solid food items. Using the earlier pipe, food items like nuts and roasted chickpeas were being sent to those trapped. With the new pipe, the rescuers have been sending solid food items like chapati, vegetables and fruits for their nutrition. Cylindrical bottles and a special tray attached to a rope were used to send food to the other side.
What help did the augur machines provide for the final rescue?
The augur machine, which consists of a helical screw-like blade, known as an auger bit, which rotates to create a hole as it moves into the material, was vital in completing the operation as it drilled for 55 meters before it broke on Friday.
In the Silkyara tunnel operation, the American Auger 600-1200, high powered horizontal drilling was used. It is manufactured by American Augers, the US company specialised in trenchless technology.
The machine can drill holes ranging from 5-10 feet in diameter.
The debris or material brought up by auger machines during drilling is typically removed using the design of the auger itself. The auger features a helical screw-like blade that not only drills into the material but also serves to lift the excavated material out of the hole as it rotates.
The spiral design of the auger flights helps to move the material upward and away from the drilling point.
The machine drilled took an hour to drill a meter and 4-5 hours were taken to fit in the pipes.
In the Silkyara case, 900 mm and 800 mm pipes, which were six feet long, were inserted using the auger machine and two pipes were welded to make a tunnel.