DEHRADUN: As Nepal battles the aftermath of a catastrophic glacial collapse and flash flood near its border with China, a tunnelling expert who helped plan the Silkyara rescue operation has said there is “reason for cautious optimism” over workers feared trapped inside the affected tunnels.
The disaster has reportedly claimed 1,252 lives, while 4,875 people remain missing.
Rescue teams are continuing operations despite unstable terrain, heavy debris and difficult weather conditions.
Speaking exclusively to the TNIE, Colonel Deepak Patil (Retd), a former Corps of Engineers officer from the Madras Sappers, said debris entering a tunnel during a glacial flood could choke its portal without necessarily penetrating deep inside the structure.
Patil, a former general manager of the Silkyara-Barkot tunnel project, played a key role in planning and leading the 2023 operation that rescued 41 workers trapped inside the under-construction tunnel in Uttarakhand.
“Based on my experience in glaciated areas, my understanding of glacial bursts and my involvement in several tunnelling projects, I believe there is reason for cautious optimism,” he said.
A glacial burst, Patil explained, initially carries enormous quantities of ice, boulders, moraine material, uprooted trees and other debris. As the flow travels downstream, sometimes for several kilometres, the ice melts and the surge turns into a powerful mixture of water and debris.
“Heavier material, particularly large boulders and tree trunks, may have entered the tunnel portals at high velocity. However, it is likely to have blocked the portals relatively close to the entrance,” he said.
Such debris may not have travelled beyond 100 to 200 metres, though this would depend on the tunnel’s alignment, gradient, geometry and the nature of the flow, he added.
Patil stressed that his assessment was provisional as he did not have access to the precise layout of the affected tunnels.
“If the portal has been effectively sealed by debris, the volume of water penetrating deeper into the tunnel may have been significantly reduced. That could provide rescuers with a critical window,” he said.
Workers trapped farther inside should, therefore, not be presumed dead, Patil said. Their survival prospects could be considerably better if the deeper sections have escaped inundation and retain breathable air pockets.
Seepage water may also be available. Major tunnelling projects generally store food, medicines and emergency materials at different underground locations, potentially enabling workers to survive for days or even weeks.
The immediate priority, he said, must be to determine how far debris has entered, identify accessible sections and establish communication with survivors.
Alternative access could be created from the surface or other points along the alignment. Depending on geological conditions, oil-rig equipment could also be used to drill a vertical rescue shaft.
“There is a window of opportunity, and operations must continue with urgency,” Patil said. “The possibility that the workers are alive and can be rescued must not be discounted.”
Of course, their chances of survival will depend on several factors, including the tunnel’s condition, the extent of flooding and debris intrusion, access to air and water, the workers’ location, the presence of open caverns or vertical shafts, and the stability of the surrounding rock.