Tunnelling between Greenways Station and Mandaveli Station began in September 2023 using two tunnel boring machines. Noyyal was deployed for the Downline and Vaigai for the Upline. The Upline TBM Vaigai completed its tunnel on October 18, 2025, while Noyyal finished its drive on February 7, 2026. This is the eighth tunnel breakthrough under the TU-02 contract, reflecting steady progress in the Phase 2 works.

The 763-metre-long tunnel, built by Larsen and Toubro Limited, runs below densely populated areas and passes beneath 75 buildings. The soil cover above the tunnel ranged from 9 to 12 metres. Construction near the Mandaveli shaft was challenging due to several underground utilities, including sewer lines, water pipelines and electrical cables, which required careful coordination and additional time.

The machines mainly passed through silty sand and sandy soil and were operated in closed-face mode for safety in the shallow urban stretch. TBM Noyyal required 14 cutterhead interventions during the drive. The tunnel was completed in 449 days, excluding the waiting period near the shaft for completion of shaft works.

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