Chennai Metro Rail has achieved a major milestone in its Phase 2 expansion, completing a challenging tunnelling breakthrough in Kolathur while simultaneously launching another tunnel boring machine (TBM) from the same underground station — a first for any metro system in India.

On Saturday, TBM Mullai broke through at the north shaft of Kolathur station after tunnelling 246 metres from the Kolathur ramp since 23 May. Engineers had to navigate an unusually shallow overburden of just 1.8 metres, a steep –3.8 per cent gradient and the need for continuous ground protection, all while working beneath one of north Chennai’s busiest traffic corridors. CMRL confirmed that the breakthrough was completed without disrupting traffic or affecting nearby residents.

At the same time, TBM Kurinji was launched from the station’s south shaft. It will tunnel 1.06 kilometres towards Srinivasa Nagar through Grade-4 and Grade-5 rock, negotiating a tight 230-metre curve — one of the more challenging sections of Corridor 5.

The simultaneous breakthrough and launch represent a rare engineering achievement: two TBMs operating from the same underground station at the same time. Corridor 5 spans 47 kilometres, including a 5.8-kilometre underground stretch where four TBMs — Kurinji, Mullai, Marutham and Neithal — have been deployed.

Senior officials from CMRL, Tata Projects and the project’s general consultants were present to oversee the operations.