Kolkata, Oct. 11 -- Tunnelling work for the Down line of Kolkata Metro's Purple Line (Joka-Esplanade Corridor) from Khidderpore to Victoria commenced on Saturday evening with the launch of Tunnel Boring Machine (TBM) Divya from the premises of St. Thomas School, Khidderpore.

The 37-metre-long, 22-metre-wide, and 17-metre-deep launching shaft was constructed within the school premises. Subhransu Sekhar Mishra, General Manager, Metro Railway, inaugurated the tunnelling operations in the presence of senior officials from Metro Railway, Rail Vikas Nigam Limited (RVNL) and St. Thomas School.

The tunnelling of the Up line began earlier on July 10 with the launch of the first TBM, Durga, from the same shaft. After nearly three months, Divya has joined the drive. Both machines will construct twin tunnels along the 2.65-km stretch between Khidderpore and Park Street. Breakthroughs are expected by December 2026 and March 2027, respectively.

Each TBM measures 95 metres in length, weighs around 600 tonnes. The machines were assembled in Chennai and brought to Kolkata in March 2025 for assembly and lowering operations.

They are equipped with inflatable seals, pressure transducers, Tail Skin Grease (TSG) lines and backup TSG pumps to ensure safe boring in local geological conditions.

The tunnels will have an inner diameter of 5.80 metres after being lined with 275 mm-thick precast M50-grade concrete segments. Officials said the TBMs can bore at a rate of 80 mm per minute.

GM Mishra said: "Durga has already crossed 150 metres and Divya has just started.

We must ensure that no nearby structure is affected, as the alignment passes through areas with several old and monumental buildings." An RVNL official added, "We are working through a densely built-up urban zone, which poses daily challenges. However, all safety systems are in place and tunnelling is progressing

as planned."

According to Metro officials, construction of the top slab at Victoria station has achieved 66 per cent completion, while diaphragm wall work at Park Street station stands at 50 per cent.

Published by HT Digital Content Services with permission from Millennium Post.