CHENNAI: Chennai Metro Rail has hit a key milestone in its ambitious phase 2 expansion, completing a complex tunnelling breakthrough in Kolathur, while launching another tunnel boring machine from the same underground station — a first for India’s metro sector.
On Saturday, Tunnel Boring Machine (TBM) Mullai broke through at Kolathur station’s north shaft after driving 246 metres from the Kolathur ramp since May 23. Engineers navigated an unusually shallow overburden of just 1.8 metres, a steep -3.8% gradient and the need for continuous ground protection in one of north Chennai’s busiest traffic corridors.
Despite the risks, CMRL said the breakthrough was achieved without disrupting traffic or nearby residents.
Simultaneously, CMRL launched TBM Kurinji from the station’s south shaft. The machine will tunnel 1.06 km toward Srinivasa Nagar through Grade-4 and Grade-5 rock, negotiating a tight 230-metre curve — one of the trickier stretches in Corridor 5.
The twin operations mark a rare feat: one TBM breaking through while another is launched from the same underground station. Corridor 5 spans 47 km, including a 5.8 km underground section where four TBMs — Kurinji, Mullai, Marutham and Neithal — are deployed.
Senior officials from CMRL, Tata Projects and the project’s general consultants oversaw the breakthrough and launch.