KOLKATA (Metro Rail News): The East-West Metro’s first “construction-related” challenge after the subterranean accident on Saturday threatens to push back the project, but by six months in the worst-case scenario.
The deadline for commissioning the line from Salt Lake to Howrah was internally revised to end 2021 or early 2022 after officials assessed the problem and consulted engineers on how long it would take to resolve the situation, both over and under the ground, on Monday.
Tunnel-boring machine Chundee, working 14 meters under Bowbazar, hit an aquifer, damaging 18 buildings, of which four were seriously damaged. As many as 375 residents had to be evacuated. Under the surface, water started gushing into the machine, and then into the tunnel itself, on Saturday.
Kolkata Metro Rail Corporation (KMRC) — the implementing agency of the Rs 8,575 crore project that promises to transform commuting in Kolkata — now faces a problem how to plug the breach, especially as initial grouting attempts were washed away by the aquifer water.
All through Monday, engineers struggled to arrest the water flow by plugging the boring machine. Finally, they built a barricade between it and the tunnel. Engineers expect to complete sealing the mouth of the giant borer by Wednesday, stopping the flow of water from the aquifer into the tunnel.
But this will also render the 75m-long machine useless. Chundee will have to be replaced by another machine to complete the remaining 600m to Sealdah station. An engineer said, sealing the boring machine’s mouth will seal Chundee’s fate. “It will have to be extracted from the tunnel and a fresh borer has to be lowered into it to resume tunneling after the breach is sealed.” He added that it would be a while before west-bound tunneling is resumed. Some ‘uncertainty’ around project now, KMRC works on the new deadline.
The accident site, just over 0.5km from the point of completion, has left project officials devastated. Of the 10km underground tunneling in the 16.5km Salt Lake-Howrah link, 9.4km of tunneling has been completed.
The overhead section that was earlier completed is ready for operations. Though the project has, so far, encountered several hurdles that caused delays, those were primarily over land availability. This is the first time a construction-related challenge has affected progress.