Tunnelling starts on Mumbai coastal project

15 January 2021


India’s largest TBM has been launched to excavate two 3.4km-long tunnels forming part of the Coastal Road Project – a 22km freeway running along Mumbai’s western seafront.

Contractor Larsen & Toubro launched the 12.9m-diameter TBM ‘Mavala’ to mine from Priyadarshini Park to the Princess Street flyover. Having arrived on site in April 2020 in 17 truckloads, the Chinese-made CRCHI machine was partially assembled on the surface, then lowered underground for final assembly. However, the start of tunnelling has been delayed by the pandemic.

With launch and reception shafts at both ends of the parallel tunnels completed at the end of 2020, excavation of each tube is expected to take around nine months. Local authority Birhanmumbai Municipal Corporation (BMC) is expecting the tunnels to be ready by June 2022.

The 12m-diameter tunnels will have three traffic lanes and will lie at depths of between 25-70m below ground. The tunnel alignment runs through a difficult geology comprising mainly basalt of 200MPa maximum compressive strength. A small stretch of the alignment between Girgaum and Malabar Hill runs under the sea.

Having been launched from Priyadarshini Park, the TBM will bore the length of one tube, then be pulled out at Girgaum Chowpatty to be taken back to Priyadashini Park to start the second tube. When complete, the project will allow travel between Mumbai’s south and north suburbs by bypassing the city centre.