CMRL achieves second Tunnel Breakthrough at Thirumayilai for Chennai Metro Phase 2 Corridor 4

Chennai, India (Metro Rail Today): Chennai Metro Rail Limited (CMRL) has reached another major milestone under Phase-2 with the second Tunnel Boring Machine (TBM) under the UG-01 contract completing its breakthrough at the Thirumayilai shaft on Corridor-4.

The downline TBM, Flamingo S-1352A, achieved breakthrough at the Thirumayilai station site on 27 February, successfully completing the 1,985-metre tunnel drive between Light House and Thirumayilai. This follows the earlier breakthrough of the upline tunnel by TBM Eagle S-1073B on 9 February, marking the completion of both parallel tunnels on this stretch.

The tunnelling works were executed by Cemindia Projects Limited and involved navigating beneath some of Chennai’s most sensitive and densely built areas. The alignment passed under the Lighthouse precinct, All India Radio campus, Russian Embassy zone, Rosary Church, MRTS bridge and Buckingham Canal, along with other heritage and high-importance structures.

The drive presented significant engineering challenges, including rocky strata, shallow overburden sections, deeper overburden due to stacked tunnel configuration, and the presence of unforeseen gas pockets. A particularly complex segment involved a stacked tunnel “drive-through” beneath Kutcheri Road before reaching Thirumayilai. The tunnel depth at Thirumayilai is approximately 28 metres, making it the deepest underground station in Phase-2.

Thirumayilai is also a critical interchange point where Corridor-4 intersects with Corridor-3, enhancing its strategic importance within the network.

With the successful breakthrough of TBM Flamingo, both TBMs deployed for this section—Eagle and Flamingo—have completed their respective drives under the UG-01 package. The completion of twin tunnelling works significantly de-risks the underground construction phase for this stretch of Corridor-4.

Commenting on the achievement, Mrs. Mamta Shah, MD & CEO, Urban Infra Group, said, “Executing deep, stacked tunnelling beneath heritage and high-security zones is a complex engineering feat. The successful completion of both tunnel drives between Light House and Thirumayilai reflects the technical capability and meticulous planning that underpin Chennai Metro’s Phase-2 expansion.”

The milestone reinforces steady progress on Corridor-4, bringing Chennai closer to expanding its underground metro network and strengthening multimodal urban connectivity.