Tunnel Boring Machine ‘Noyyal’ Makes Breakthrough at Mandaveli

Chennai:The Chennai Metro Rail Limited (CMRL) achieved a significant milestone in Phase 2 Corridor-3, with the successful breakthrough of downline Tunnel Boring Machine (TBM) ‘Noyyal’ at the Mandaveli shaft on Saturday.

Tunnelling between Greenways and Mandaveli stations commenced in September 2023, with two TBMs — Noyyal and Vaigai — deployed for the twin tunnels. While the upline TBM ‘Vaigai’ achieved breakthrough on October 18 last year, the downline TBM ‘Noyyal’ completed its drive on Saturday.

This marks the eighth TBM breakthrough reflecting steady progress in the implementation of Chennai Metro Phase 2.

The tunnel, executed by Larsen & Toubro Limited, has a total length of 763 metres and runs beneath densely built-up areas, passing below 75 buildings with an overburden ranging from 9 to 12 metres. The Mandaveli shaft area posed additional challenges due to the presence of major underground utilities, including sewer lines, water pipelines and electrical cables.

Officials said these constraints required careful planning, continuous monitoring and extended construction time to ensure safety.

During the drive, the TBM encountered predominantly silty sand and sandy soil conditions and was operated largely in closed-face mode. A total of 14 cutterhead interventions were carried out on TBM Noyyal. The tunnel drive was completed in 449 days, excluding the waiting period near the shaft due to ongoing shaft construction.

T. Archunan, Director (projects), CMRL, along with senior officials, consultants and representatives of the contractor witnessed the breakthrough.