Chennai Metro Rail Limited has achieved a major tunnelling milestone on Corridor-4 of its Phase-2 network, with the tunnel boring machine Flamingo S-1352A completing its breakthrough at the Thirumayilai station shaft on 27 February 2026.
The breakthrough marks the completion of the first downline tunnel between Light House and Thirumayilai under the UG-01 contract.
The Flamingo TBM completed a 1,985-metre underground tunnel drive executed by Cemindia Projects Limited.
The alignment passed beneath several sensitive and congested areas, including the Lighthouse area, the All India Radio campus, the Russian Embassy zone, Rosary Church, and several heritage and high-importance structures such as the MRTS bridge and Buckingham Canal.
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This milestone follows the earlier breakthrough of the upline tunnel by TBM Eagle S-1073B on 9 February.
With the completion of Flamingo’s downline tunnel, both tunnels on the Light House–Thirumayilai section under the UG-01 package have now been fully completed.
The tunnelling work encountered multiple engineering challenges, including rocky strata, shallow and deep overburden conditions due to stacked tunnel configuration, and gas pockets along the alignment.
CMRL had deployed two TBMs, Flamingo S-1352A and Eagle S-1073B, for this section.
CMRL stated that the breakthrough of Flamingo S-1352A marks an important step in advancing Corridor-4, which will significantly enhance connectivity across Mylapore, Luz and Central Chennai upon commissioning.
Following the breakthrough at Thirumayilai, both machines will be relaunched for the next tunnelling drive towards Boat Club as part of Corridor-4 construction.
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