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Passengers travelling through the Nandanam Metro station on Chennai Metro's Phase I line may not notice it, but a giant tunnel boring machine (TBM) will soon begin working deep underground to construct a new tunnel for the upcoming Phase II network.
Chennai Metro Corridor 4
The new tunnel is part of Corridor 4, which will connect Poonamallee and Light House. The route will pass below the existing Phase I metro tunnel at Nandanam. Since the section between Kodambakkam and Light House is underground, Chennai Metro Rail Limited (CMRL) is constructing the tunnel in smaller stretches.
So far, tunnel construction between Light House and Thirumayilai, and Panagal Park and Kodambakkam, has been completed. In December 2025, tunnelling work resumed from Panagal Park towards Boat Club, passing through the Nandanam area.
Chennai Metro's Tunnelling Work
According to CMRL officials, the TBM has now reached a location near the existing Nandanam Metro station after digging 868 metres. During the excavation process, the machine moved through different underground layers, including sand, clay and shale rock. Engineers also carried out eight cutter head interventions, a maintenance procedure where the machine's cutting tools are repaired or replaced to ensure smooth tunnelling operations.
CMRL Director (Projects) T. Archunan said that the Commissioner of Railway Safety (CRS) has approved the construction work beneath the existing metro tunnel. The TBM will soon move 29.8 metres below the surface, directly underneath the Phase I metro line.
To maintain safety, CMRL has installed sensors to track vibrations and ground movement in real time. Monitoring has been carried out for the past two weeks, and all readings have remained within safe limits. As a result, metro services at Nandanam are continuing normally without any speed restrictions.
However, if any increase in vibrations or ground movement is detected, train speeds near the station may be reduced as a safety measure. The TBM is expected to take around two weeks to cross below the existing tunnel and is likely to reach Boat Club by December 2026.