TBM makes first breakthrough on Mumbai Coastal Road project

11 January 2022

India’s largest-diameter TBM has holed through on the first of two tunnels which will form part of the US$1.6bn Coastal Road Project – a roughly 29km freeway running alongside Mumbai’s western seafront.

Local authority Birhanmumbai Municipal Corp (BMC) announced the breakthrough on 10 January and said the project is now 20% complete.

The 12.19m-diameter slurry TBM ‘Mavala’, made by China’s CRCHI, was launched in January 2021 having arrived on site in truckloads in April 2020. Contractor Larsen & Toubro launched the machine from Priyadarshini Park and it holed through exactly a year later at Girgaum Chowpatty after mining through a complex geology comprising basalt (200MPa), breccia and shale.

Having passed 70m under Malabar Hill – home to rich celebrities – the machine bored a short stretch between Malabar and Girgaum at a depth of roughly 20m below the shore of the Arabian Sea. The machine will now be taken back to Priyadarshini Park to start boring the second tube. Lying at depths of between 20-70m below ground, the 3.4km-long twin tunnels will be connected by 11 cross-passages and have three traffic lanes each.

When complete, the project will allow travel between Mumbai’s south and north suburbs, bypassing the city centre and providing relief to thousands of commuters who currently can take up to three hours to travel the distance in peak-hour traffic.

AECOM is general consultant to the project. Lombardi was detailed design consultant.