Rescue workers in mountainous northern India began new efforts on Monday to reach 41 men trapped in a collapsed tunnel, now trying to reach them by digging a vertical shaft.
This follows failed efforts to burrow in horizontally and extract the laborers, who were caught in a cave-in on November 12.
Officials on site said that a malfunction with the machinery and a "cracking sound" that caused "panic" prompted them to pause attempts to force a steel pipe through the debris just wide enough for the men to crawl through and reappraise their options.
Digging vertically to reach them presents new challenges, not least creating an access road in the hilly, forested area to the new starting point for the tunnel. Without this, workers and heavy equipment can't access the site.
Rescuers hope the digging could start as soon as Tuesday once new machinery arrives, according to Jasvant Kapoor, a general manager at state-run company SJVN, which is involved in the rescue efforts.
Foreign experts have been drafted in, including independent disaster investigator Arnold Dix, president of the International Tunneling and Underground Space Association.
"We are going to find a solution and get them out," Dix told reporters Monday at the site. "A lot of work is being done here. It is important that not only the men rescued but also the men who are [doing the] rescuing are safe."
Several potential solutions to reach the trapped men, including restarting the halted horizontal pipe insertion, are still under consideration.
What is their current condition? How are they being supplied?
"Every effort is being made," Uttarakhand chief minister Pushkar Singh Dhami said in a statement Monday, insisting that the "workers trapped in the tunnel are safe".
They are being supplied with light, oxygen, dry food like nuts, rice and chickpeas, water and medicines via a pipe. Communication is possible via radio.
Authorities are drilling a second pipeline into the debris to enable the delivery of cooked food.
Bhaskar Khulbe, officer on special duty for the tunnel project, said that roughly 42 meters of an estimated 60 meters had already been drilled.
Officials are also considering setting up an optical cable through this pipe, as they hope to provide the men with access to a phone so they can speak to their loved ones.
Roughly 50 to 60 workers had been on the overnight shift at the time of the collapse; those closest to the tunnel's exit were able to make it out in time while the others could not.
Frequent landslides in mountainous Himalayan region
The laborers were working on part of a new national highway, the Char Dham all-weather road, a flagship federal project by Prime Minister Narendra Modi's Hindu nationalist government that aims to reduce travel times between four ancient Hindu pilgrimage sites in Uttarakhand state that are in remote and inaccessible areas of the vast Himalayan mountain range.
The project would also improve access to strategic areas of the country near the border with regional rival China.
Authorities have not said what caused the roughly 4.5 kilometer (3 mile) tunnel to cave in, but the region is prone to landslides, earthquakes and floods.
