Tata’s TBM Mullai Records Chennai Metro Line-5’s 2nd Breakthrough

Back in November-end, Tata Projects Ltd. (TPL) celebrated two major tunneling milestones at Kolathur Metro Station of 44.6 km Chennai Metro Line-5 which will connect Madhavaram and Sholinganallur via 45 stations.

The first was a tunnel breakthrough by Terratec tunnel boring machine (TBM) Mullai at Kolathur Station’s North Shaft after a short 246m journey from Kolathur Ramp for Line-5’s down-line. This machine was launched in May 2025 and took roughly 6 months to complete its first tunneling assignment.

The second was the launch of Terratec TBM Kurinji from Kolathur’s South Shaft for its second drive to build a 1060m tunnel towards Srinivasa Nagar Station for the up-line tunnel. This drive will see the TBM navigating grade 5 & 4 rocky strata and a sharp curve of 230m. Kurinji had arrived at Kolathur Station back in August 2025 to record Line-5’s very first breakthrough.

Both Ø6.61m Earth Pressure Balance (EPB) machines along with two others were supplied by Terratec for constructing underground twin tunnels for the 116.1 km Chennai Metro Phase 2 project’s 5.8 km Package UG-06/RT-01 connecting Kolathur – Nathamuni.

Per Chennai Metro Rail Ltd. (CMRL)’s press release, the main challenges faced during Mullai’s drive included an extremely low overburden of 1.8 m (tunneling almost at road level), a steep gradient of -3.8%, and the requirement for ground protection in a heavily trafficked region.

CMRL had awarded Tata Projects with a Package UG-06/RT-01’s Rs. 1445,98 crore contract in September 2023 with a 3.8 year construction deadline.

Tata’s scope of work includes constructing twin tunnels and 5 underground stations at Kolathur Junction, Srinivasa Nagar, Villivakkam Suburban Station (Villivakkam), Villivakkam Bus Terminus and Nathamuni (Villivakkam MTH Road).

Tata plans to eventually deploy 4 Terratec TBMs – Kurinji, Mullai, Marutham and Neithal – each named after distinct Tamil landscapes.

For more updates, check out the Chennai Metro section or my Home Page! Sign up for free instant email notifications on new posts over here. Like this post? Get early-access to updates and support the site over here.

– TMRG