Rescuers are facing a 17-hour mission to reach 41 workers who have now been trapped inside a tunnel in India for 11 days.
Crews have been working round the clock drilling through 60m (197ft) of debris after the under-construction highway tunnel in Silkyara, located in Uttarakhand state in the Himalayas, caved in on 12 November.
Rescue teams encountered an unexpected delay on Thursday after getting through 45m (150ft) of debris, when they discovered a lattice steel girder arch which required six hours to cut and remove.
A former advisor to the prime minister’s office, Bhaskar Khulbe, who is working on the mission, has said it could take 12-14 hours to reach the men.
It will then take a further two to three hours to assemble workers and get the men out, with the help of the National Disaster Response Force (NDRF).
The men are safe and have access to oxygen, food, water and medicine, authorities have said.
But some of the men have become unwell, suffering from fever, body aches and nervousness, leaving worried family and friends feeling frustrated and angry over the delays to free them.
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Mr Khulbe told reporters: “Our calculation as of now is…roughly 14 to 15 hours, unless something else happens, and we hope we will be able to do that.
“It is difficult to anticipate what more hurdles we might face,” he said, adding that no major problem is expected aside from another metal obstacle or rock.
Once drilling is completed, officials plan to send crews through an evacuation pipe with stretchers on wheels to bring the trapped men to safety.
The tunnel collapsed following a landslide in Uttarakhand – a region popular with tourists.
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The tunnel is located on the Char Dham pilgrimage route – one of the most ambitious projects of Prime Minister Narendra Modi‘s government.
The tunnel aims to link four key Hindu pilgrimage sites with 890km (550m) of two-lane road, in a project costing $1.5bn (£1.19bn).
A safety audit of 29 tunnels currently being built by the National Highways Authority of India will now take place, the government announced on Wednesday.
