Not cut-&-cover, Kolkata metro decides to use TBMs to bore Maidan tunnel
Times of India | 1 April 2025
Kolkata Metro Railway revised its plan for the Purple Line's Esplanade-Eden Gardens extension by deciding to use tunnel boring machines (TBMs) instead of the cut-and-cover method KOLKATA: Metro Railway decided to deploy tunnel borers to build Purple Line's 1.6-km extended Esplanade-Eden Gardens section.
From L20 bus stand to Eden
The initial plan was to build the added stretch with the cut-and-cover method. In the revised plan, the tunnel boring machine (TBM) launching shaft will be dug at the site of the L20 bus stand, and the retrieval shaft at the Maidan, opposite Eden Gardens.
A second crossover, other than the one below Manohar Das Tarag near the proposed Esplanade station, will be built for rakes to switch tracks on the Strand Road end, beyond the Mohun Bagan grounds, opposite Eden Gardens.
The second crossover will be constructed using the cut-and-cover method, as will the five underground stations: Kidderpore, Victoria, Park Street, Esplanade, and Eden Gardens.
Cut-and-cover is a conventional tunnel construction technique where a trench is excavated and covered with an overhead support. The method can be executed in bottom-up and top-down ways. Either approach would result in substantial traffic disruptions. Sources saidRaj Bhavan objected to the cut-and-cover method as it would lead to prolonged construction activity inside the protected area and could lead to security issues.
Roughly, the TBMs' path seems like this: launched from the L20 bus stand, they would dig through Rani Rashmoni Road, skirt past the underground East-West Metro station, dig below Raj Bhavan, and cross over to the proposed Eden Gardens Metro station on the other side.
Rail Vikas Nigam Ltd (RVNL) is implementing the Purple line. The former procured two TBMs, which were mostly made in India (Tamil Nadu's Alinjivakkam factory). "It's not decided if the same TBMs will dig the Esplanade-Eden Gardens section," a railways official said. Despite the ongoing impasse over land for the construction of the Purple line's Kidderpore Metro station, the authorities will proceed with the underground tunnelling from Kidderpore to Park Street.
The TBMs, weighing 650 tonnes each, will first dig 1.7 km from St Thomas' to Victoria. The second drive will span 950 m from Victoria to Park Street. The 500 m Park Street-Esplanade section will be built in the cut-and-cover method because it is too short for TBM operations. "Also, TBMs dig linearly, so can't be used to build crossovers," the official said.
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