Chennai Metro Rail (CMRL) achieved a rare feat on 29 November, 2025, when it launched tunnel boring machine (TBM) Kurinji just minutes after the successful breakthrough of TBM Mullai at Kolathur Station North Shaft.
TBM Mullai completed a 246 mtrs. drive through difficult terrain, facing challenges like a low overburden of 1.8m, a steep gradient of 3.8 percent, and heavy traffic in the area. Despite these obstacles, the breakthrough was completed without disrupting public movement.
TBM Kurinji, which will cover 1.06 km of rocky ground, including a 230 mtrs. curve, was launched immediately after Mullai’s success, marking the first time in tunnelling history that two TBMs have been used on the same spot within the same day. This work is part of the 47km-long Corridor 5 of the CMRL Phase II project.