Chennai Metro Rail Limited (CMRL) has achieved a construction milestone in Phase 2 after the downline Tunnel Boring Machine (TBM) “Noyyal” successfully broke through at the Mandaveli shaft on 7 February 2026, marking the eighth TBM breakthrough under the TU-02 contract.
The tunnelling stretch between Greenways Station and Mandaveli Station began in September 2023 using twin TBMs – “Noyyal” and “Vaigai”.
The upline TBM Vaigai had earlier achieved its breakthrough on 18 October 2025, while Noyyal has now completed the parallel downline drive.
Executed by Larsen & Toubro Ltd, the tunnel spans 763 metres and runs beneath densely built urban zones, passing below 75 buildings with an overburden ranging between 9 and 12 metres.
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Construction at the Mandaveli shaft presented additional engineering challenges due to the presence of critical underground utilities, including sewer lines, water pipelines and electrical cables, requiring careful planning and extended execution timelines.
Geotechnical conditions along the route consisted largely of silty sand and sandy soil, prompting the TBMs to operate predominantly in closed-face mode.
Engineers carried out 14 cutterhead interventions on TBM Noyyal during the drive.
The tunnelling work was completed in 449 days, excluding the waiting period near the shaft for completion of shaft construction.
The breakthrough was witnessed by CMRL Director (Projects) T. Archunan along with senior officials, project consultants and representatives from Larsen & Toubro.
