Arnold Dix, president of the International Tunnelling and Underground Space Association, has been advising Nepal's hydropower authorities on how to reach survivors trapped in the tunnel. Speaking to the BBC, Dix said the rescue faced multiple daunting challenges, beginning with locating the tunnel entrance in a landscape rendered almost unrecognisable by the flood.
"I've never known a rescue operation where you had to look for an entrance of a tunnel that was previously up the hill, that was now underground," Dix said. "You can imagine the enormity of the avalanche, it completely buried the entrance."
Using engineering techniques, old topographic maps, satellite imagery, helicopter footage, and surface clues such as power poles, the team triangulated the likely position of the entrance and began digging. Once found, the next challenge was locating the survivors. Rescuers had to navigate a tunnel blocked entirely by mud and rocks, some bigger than cars, and used explosives to clear the way—a tactic Dix said they would "normally never do because of the risk of blowing up people and blowing ourselves up."
He credited the Nepalese army for managing the explosions with precision to avoid destabilising the tunnel. The team also discovered the tunnel was still full of water. Using excavators and pumping machines, they dug a series of trenches from the tunnel to the river outside to drain the water.
Dix described the discovery of the two survivors as "layer upon layer of miracles." Rescuers continue to search for others who may be trapped.