Work on a metro project in Kolkata has been halted after unknown piles were discovered, The Times of India has reported.
Plans for the tunnelling on the east-west section of the Kolkata Metro in India, have been delayed and the tunnel boring machines (TBMs) are now not expected to start in mid-May as planned.
Five steel H-piles that once supported a temporary iron road for the construction of an existing station in the 1980s have been found to be obstructing the path of the TBMs.
The construction firm working on the north-south Metro had left the H-piles, which extend to 30m depth, in the ground unaware that another metro alignment would be developed in the future.
In a statement to the paper, the Kolkata Metro Rail Corporation (KMRC) said: “It has become absolutely necessary to remove the H-piles to clear the TBMs’ path. TBMs can drill through rock and concrete but not steel.”
The H-piles were found during a survey in November but the impact on the current work has only just been revealed.
KMRC structural engineers have consulted with German, UK and South Korean experts and tunnellers ITD Cementation has proposed to adopt the hyperbaric method to split and cut the piles which would take around six weeks.
“We are trying to find out the best methodology for removing the piles,” a KMRC spokesperson said.
But a local source has told the paper that ITD Cementation asked for KMRC’s approval to remove the piles by the end of March so that they can start tunnelling by mid-May.
“It’s already 15 days into April. We are already 15 days behind schedule and can start tunnelling after June 1 if the proposal is cleared in the next 24 hours. More time taken would mean more delay,” a source told the paper.
It is planned for the metro to be open by June 2021.