Tunnelling begins for Kolkata Metro’s Purple Line; breakthrough at Victoria expected by May 2026
Kolkata: Tunnelling work for Kolkata Metro’s Purple Line (Joka–Esplanade Corridor) from Khidderpore to Victoria began on Thursday with the launch of Tunnel Boring Machine (TBM) ‘Durga’.
The machine was launched from a 37-metre-long, 22-metre-wide, and 17-metre-deep shaft built within the premises of St. Thomas School in Khidderpore.
In the first phase, ‘Durga’ will bore the 1.7-km tunnel from Khidderpore to Victoria, with breakthrough expected by May 2026. A second TBM, ‘Divya’, is slated to start work on the down-line tunnel in September from the same shaft.
Metro Railway General Manager P Uday Kumar Reddy flagged off the tunnelling by pressing a button in the presence of the Consul General of Nepal and senior officials from Metro Railway, Rail Vikas Nigam Ltd (RVNL), the Defence Authority, CMRI Hospital, West Bengal Transport Corporation, and St. Thomas School.
“TBM Durga has started off. It is a very important and joyous occasion for the people of Kolkata. We are grateful to the state authorities for permitting us to proceed,” Reddy said.
The underground stretch from Khidderpore to Park Street will involve twin-tube tunnelling using two Earth Pressure Balancing (EPB) type TBMs, Durga and Divya, designed to handle Kolkata’s soft soil conditions and high groundwater table. Each machine is 95 metres long, weighs nearly 600 tonnes, and comes equipped with inflatable seals, pressure transducers Tail Skin Grease (TSG) lines, and backup TSG pump. The tunnel’s outer diameter will be 6.63 metres, and after lining it with 275 mm thick precast M50-grade concrete segments, the inner diameter will be 5.80 metres. The TBM’s initial stabilisation drive will take about a month, followed by a tunnelling rate of 200 metres per month. The second phase, from Victoria to Park Street (950 metres), is expected to be completed by December 2026.
The final 500-metre stretch to Esplanade from Park Street will be constructed using the conventional cut-and-cover method. Esplanade station will serve as a multi-line interchange for the Blue, Green and Purple lines. In light of the 2019 Bowbazar subsidence, enhanced safety measures have been adopted.
“The number of seals has been increased,” Reddy said. “All necessary precautions have been taken to avoid any untoward incident,” added an RVNL official. The 14-km Joka–Esplanade corridor will extend by another 1.6 km to Eden Gardens.
