Bullet Train Project: L&T And Afcons In Race To Construct 7-Km India's First Long Undersea Tunnel In Mumbai

Larsen & Toubro and Afcons Infrastructure are the only firms that have submitted bids to construct a 21-km tunnel, including a 7-km undersea stretch for Mumbai-Ahmedabad High-Speed Rail (MAHSR) corridor.

The National High Speed Rail Corporation Ltd (NHSRCL) which is executing the MAHSR project opened the technical bids for 20.377 km Package C-2 on 9 February.

Undersea Tunnel

The tunnel will be built at Thane creek, between underground stations at Bandra-Kurla Complex and Shilphata in Maharashtra.

Since this area is a protected sanctuary for flamingo and nearby mangroves, rail tracks will be made undersea through a tunnel, thus ensuring no disturbance to existing ecosystem.

The undersea tunnel at Thane Creek (Intertidal Zone) will be longest rail transport and first under sea tunnel to come up in the country. 

This tunnel will be about 25-65 metres deep from the ground level and the deepest construction point will be 114 metres below the Parsik Hill near Shilphata.

Building an underground tunnel, however, has escalated the cost by 100 times. The initial cost of C2 package which was pegged at Rs 100 crore has now increased to Rs 10,000 crore.

Tunnelling Plan

The tunnel will be a single tube tunnel to accommodate twin track for both up and down track. The package also includes constructing 39 equipment rooms at 37 locations adjoining tunnel location.

For the first time, a tunnel boring machine (TBM) with a cutter head of 13.1-metre diameter will be used for constructing the tunnel. Usually, 5 to 6-metre diameter cutter heads are used for urban tunnels used in Mass Rapid Transit Systems (MRTS) or Metros.

Three TBM will be used to make about 16 km of the tunnel portion and the remaining 5 km will be through New Austrian Tunnelling Method (NATM). 

The tunnel is the biggest and most complex piece of civil engineering work for the 508-km Ahmedabad-Mumbai bullet train corridor.

Constructing an undersea tunnel in the Thane Creek will be a massive challenge as it will involve two TBMs which will meet half way under the sea to join two parts of the tunnel by a process called docking.

Docking is a challenging task as adequate care has to be taken to ensure that there is no seepage in the tunnel due to water pressure.

India’s First Bullet Train Project

Presently, the Mumbai-Ahmedabad High-Speed Rail is the only sanctioned high-speed rail project in the country.

The High-Speed Rail operating at 320 kmph will traverse along west India’s landscape, covering 508.17 km distance between Mumbai and Ahmedabad in just about two hours. This will save time compared to current travel time between the two terminal stations by about nine hours (by bus) or six hours (by conventional railways).

It will cover 155.76 km in Maharashtra, 4.3 km in the Union Territory of Dadra & Nagar Haveli and 348.04 km in Gujarat, with 12 stations en route.

The government is yet to determine a final deadline for the entire project, but the completion time for a 50-km stretch between Surat and Bilimora in Gujarat has been set for August 2026.