Work is currently underway on a 21-km-long tunnel in the state of Maharashtra, India, which includes the country’s first undersea rail tunnel featuring approximately 7 km long, as part of the Mumbai-Ahmedabad High Speed Rail (MAHSR) corridor.

The tunnel runs between the underground station at Bandra Kurla Complex (BKC) and Shilphata, with the 7-km undersea tunnel at Thane Creek. According to the National High Speed Rail Corporation Limited (NHSRCL), three tunnel boring machines (TBMs) will be deployed to build about 16 km of the tunnel portion and the remaining 5 km will be adopting the New Austrian Tunnelling Method (NATM). 

The construction work is taking place at several locations:

• Shaft 1 at BKC station construction site in Mumbai (shaft depth of 36 m): The secant piling work has been completed, while the excavation work is ongoing.

• Shaft 2 in Vikhroli (shaft depth of 56 m): The piling work has been completed, while the excavation work is ongoing. This shaft will be used to lower two TBMs in different directions, one towards BKC and the other towards Ghansoli.

• Shaft 3 in Sawli, near Ghansoli (shaft depth of 39 m): The excavation work is ongoing. 

• Shilphata: This is the NATM end of the tunnel. The portal work has already begun at the site.

• ADIT (Additionally Driven Intermediate Tunnel) Portal: This portal will facilitate additional access to the underground/undersea tunnel for faster construction progress.

The shafts are being built in areas with a high population density and adjacent utilities, such as various pipelines, electrical installation and other infrastructure projects like metro systems, highways, etc. Thus the construction work has to be carried out with minimal disruption to the public.

To build the 21-km tunnel, which has a diameter of 13.1 m, TBMs with a 13.6-m-diameter cutterhead will be used, said NHSRCL. This single-tube tunnel will accommodate twin tracks for both up and down track. A total of 39 equipment rooms will also be constructed, as part of the package.

The tunnel will be about 25- to 57-m-deep from the ground level and the deepest construction point will be 114 m below the Parsik hill.

The three shafts at BKC (under package C1), Vikhroli and Sawli at approximate depths of 36, 56 and 39 m respectively will facilitate the construction of the tunnel with TBMs. An inclined shaft of 42 m at Ghansoli and the tunnel portal at Shilphata will facilitate the construction of the approximately 5-km tunnel through the NATM method. 

All images: National High Speed Rail Corporation Limited

Note: This story has also been published in the Mar/Apr 2024 issue of SEAC (with more images). Click here to read online or here to download the PDF file (pages 52-55).