A major milestone was achieved in the Phase 2 metro project with the launch of a tunnel boring machine for a fresh tunnelling drive between Panagal Park and Boat Club on Corridor 4. The machine had earlier completed a successful 2-km drive from Panagal Park to the Kodambakkam Ramp Retrieval Shaft, achieving the first breakthrough of Corridor 4 on July 23, 2025.

This earlier drive was particularly significant as tunnelling was carried out safely beneath active railway tracks, one of the most critical engineering challenges along the corridor. The twin tunnel in this stretch was completed using another tunnel boring machine. Following the breakthrough, the machine was dismantled at Kodambakkam, transported back to Panagal Park, and reassembled at the station’s launching shaft for the new 1,898-metre drive toward Boat Club.

The new tunnelling stretch involves several engineering complexities, including passage beneath existing operational metro tunnels near Nandanam Metro Station. The alignment reaches depths of up to 30.2 metres (about 100 feet) below ground level, requiring precise navigation and stringent safety protocols. Completion of this tunnelling drive is expected by November 2026.

Corridor 4, running from Light House to Poonamallee Bypass over a length of 26.1 km, includes a major underground section between Marina Beach and Kodambakkam Flyover. This underground stretch is divided into two tunnelling packages, each comprising nearly 4 km of twin tunnels. In total, four tunnel boring machines, each with an excavated diameter of 6.67 metres, are being deployed to complete approximately 16 km of tunnelling. 

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