The Phase II project envisions a sprawling 118.9-kilometre transit network. Of this, Corridor 4 — stretching 26.1 kilometres from Light House to Poonamallee — includes nearly 10 kilometres of underground rail running through densely populated urban areas such as T Nagar, Kodambakkam, and Thirumayilai.

The Lighthouse–Thirumayilai tunnel, in particular, is being constructed using two tunnel boring machines (TBMs) named Flamingo and Eagle. Flamingo began its 1.96-kilometre journey in September 2023 from Lighthouse, tunnelling beneath Kutchery Road towards Thirumayilai, while Eagle is boring a parallel tunnel.

Flamingo has encountered multiple challenges along the route, including technical halts and delays due to the area’s abrasive soil conditions. A significant glitch in its cutter head led to a 40-day pause for repairs. Nonetheless, the machine has successfully covered 1.3 kilometres, while Eagle has completed 1.2 kilometres and is expected to enter Kutchery Road station shortly.

Despite the difficult terrain and complex subsoil profiles, officials remain optimistic. The tunnel’s progress has been steady, and once complete, it will enable driverless metro operations in about three years — offering a direct and efficient connection from Thirumayilai and Kutchery Road to Marina Beach.

The tunnel is not only a feat of engineering but also a crucial part of Chennai’s vision to establish a robust, city-spanning metro network.