Mumbai's 15.6-meter tunnel boring machines pass factory tests and will start digging by May 2027

The Brihanmumbai Municipal Corporation (BMC) ran the tests at Herrenknecht's plant in Chennai, according to ProjectsMonitor. After delivery, crews will put the machines together at Charkop, where the BMC is driving piles and building the launch shaft. Megha Engineering and Infrastructures (MEIL) holds the tunnel contract.

Herrenknecht's December 2024 announcement put each Mixshield at 15,620 mm in diameter and said they would be the biggest TBMs ever used in the country. Mixshields are slurry machines meant for unstable, water-bearing ground of the kind found near creeks and mangroves, and each will handle 2,900 cubic meters of slurry per hour, ProjectsMonitor said. Herrenknecht described the ground as including slightly weathered basalt of up to 150 MPa and said the shields are built for operating pressures up to 5 bar.

The tunnels will run between Mindspace in Malad and Charkop in Kandivali, about 40 meters below the surface, as part of the Coastal Road North corridor, which runs 22.93 km from Versova to Dahisar. The whole project, which also includes elevated roads and bridges, is estimated at Rs 16,621 crore (about $1.9 billion). The northbound tunnel package carries an estimate of Rs 2,911 crore; the southbound one, Rs 2,910 crore.

Some numbers have moved since the contract was announced. Herrenknecht's 2024 release listed two drives of 3.1 km each, with 13 to 23 meters of cover; the latest report gives 3.9 km and a depth of about 40 meters. The BMC has not explained the difference.