Uttarakhand tunnel collapse: How workers were rescued after 17 days

All 41 workers trapped inside the Silkyara tunnel in Uttarakhand since November 12, were successfully rescued late Tuesday. 

The initial plan under the multiple-agency led rescue operation was to evacuate workers through horizontal drilling with the expertise of international tunnelling experts. However, in the final stretch of the operation, the banned manual "rat-hole"-mining technique was employed after high-tech machines, or augers, failed to drill through the nearly 60 metres of rock that has threatened to bury the workers. 

The workers were pulled out through a passageway made of welded pipes which rescuers previously pushed through rocks. 

They survived on food and oxygen supplied through narrow steel pipes. According to offiicials, all the workers are in good health.

Silkyara tunnel and the collapse

The 4.5 km-long Silkyara tunnel is part of the Centre's Char Dham project aimed to provide all-weather connectivity between four Hindu shrines of Badrinath, Kedarnath, Gangotri and Yamunotri. The tunnel connects Silkyara and Dandalgaon in the Uttarkashi district. Once complete, the tunnel is expected to cut down travel time between the two cities by an hour.

Hyderabad-based Navayuga Engineering Company Limited is constructing the tunnel.

On November 12, a section of the tunnel between 205 and 260 metres from Silkyara collapsed. Workers were beyond 260 metres and got trapped as the exit was blocked.

What is the reason for the Uttarakhand tunnel collapse?

The government has said that there will be a probe into the reason for the collapse. However, several theories are floating on the internet. One such theory states that a landslide in the region led to the collapse. Another said that it was triggered by a blast carried out by the team.

Media reports have also stated that the hasty development of the fragile Himalayan region may also be a reason for the collapse. The exact reason, however, will only be ascertained after the government probe.

The rescue operation

The drilling was, till last week, being carried out by an auger machine. It is also known as a horizontal boring machine or directional drill. It creates horizontal bores without disturbing the surface. The machine got stuck on November 24. By Monday evening, the last bit of the stuck auger was cut out, and a steel pipe was inserted further into the partially complete escape passage.

The failure of the auger machine forced the officials to focus on an alternative option -- drilling down from above the tunnel, also known as vertical drilling.

For the horizontal option, the rescue officials decided that experts in rat-hole mining techniques would handle the final stretch.

What is rat-hole mining?

Rat-hole mining is a technique where mines are dug manually by workers using hand-held tools. These mines, which are of small size, were primarily used for extracting coal. The miners dug small pits, not more than 4 feet wide, to reach the coal. Once they reach the seam, tunnels are made sideways. It derives its name from the kind of tunnels rats dig, small and long.

This practice was banned by the National Green Tribunal in 2014 for being unscientific. However, it continues to be in practice in several states, especially in the Northeast region of India. These states argue that there is no feasible mining option in the region.

The rescue operation in Uttarakhand

After the augur machine failed to cut through the debris, 12 men who specialised in rat mining were flown in from New Delhi to carry out the rescue operation. Since Monday, the miners have been at work inside an 800 mm pipe to remove the debris. They are using a shovel and some special tools. For oxygen, they have been provided with a blower.

The rat-hole mining experts dug the last two metres of the rubble. An eight-bed makeshift health centre had been set up inside the tunnel to provide immediate medical care to the workers after their evacuation.

Ambulances were lined up at the mouth of the tunnel to rush the rescued workers to the community health centre about 30 kilometres away, after the initial checkup at the site.

A stretch of mud road was re-laid to make the passage of ambulances easier. Stretchers were taken inside the mouth of the tunnel.

A special ward with 41 oxygen-supported beds was readied days earlier at the community health centre in Chinyalisaur, about 30 km from Silkyara. Doctors are standing by and arrangements have been made to fly the workers to more advanced hospitals if needed.

Rescue act

(Timeline of the tunnel collapse and a 16-day operation that followed)

Nov 12: 41 labourers trapped inside the Silkyara-Barkot tunnel after it collapses

Nov 13: Authorities contact workers through a pipe used to supply oxygen. More rubble falls, stretching the debris into a 30-metre area

Nov 14: 900-mm steel pipes brought to the site, but their width reduced to 80mm after safety concerns. Two labourers sustain minor injuries as more rubble falls on them

Nov 15: IAF ferries an American auger machine after another belonging to the Uttarakhand Jal Vidyut Nigam fails

Nov 16: The new auger machine is installed for horizontal boring

Nov 17: Rescuers drill through 24 metres of debris; insert 4-mm pipes in the tunnel. The operation is suspended after a loud sound in the tunnel and earth movements raise fears of further collapse

Nov 18: Horizontal boring deemed too risky; authorities explore alternatives

Nov 19: Horizontal boring deemed best bet; authorities initiate four alternatives — drift, micro-tunnelling, blasts from Barkot end, and vertical drilling

Nov 20: Rescuers lay a six-inch wide pipeline in the debris to push through food and other essential items to the workers. International tunnelling experts are called to the scene

Nov 21: Horizontal boring resumes, work on drift tunnel begins

Nov 22: Cooked food supplied to trapped workers; auger machine reaches 48 metres; NHAI orders safety audit of all under-construction tunnels

Nov 23: Drilling is halted after iron girders obstruct auger machine and dent steel pipe

Nov 24: The shaft and blade of auger machine are damaged in the rescue tunnel being built

Nov 25: The auger machine, which is stuck, is partially removed; contact established between trapped workers and their families

Nov 26: Authorities focus on alternative routes as delays in removal of auger machine slow down rescue plan

Nov 27: Manual drilling begins after auger is pulled out. Rat-hole miners and Indian Army engineers begin scraping through the muck

Nov 28: Rescue workers break through the last stretch of the rubble at about 7 pm; all 41 workers rescued after an operation that lasted over 400 hours

(With agency inputs)