The National High-Speed Rail Corporation Limited (NHSRCL) has announced that Larsen & Toubro and Afcons Infrastructure have entered bids to build India’s first undersea tunnel for the high-speed rail line between Mumbai and Ahmedabad.

The project involves the construction of a single-pipe 21-km tunnel with a width sufficient for two tracks. It will run between the Bandra Kurla complex on the Mumbai waterfront and Shilfat Kalyan to the east of the city. The 7-km section will run under Thane Creek, the Arabian Sea gulf that separates Mumbai and the planned city of Navi Mumbai. Three tunnel boring machine (TBM) will be used for the 16 km tunnel and the new Austrian tunneling method (NATM) will be used for the remaining 5 km. The deepest point of the tunnel construction is 114 m below Parsik Hill, near Shilfata, and the total depth will vary from 25 to 65 m from ground level.

The tender will be awarded to the organization that meets the agency's requirements to complete the section of the underground tunnel, which is considered the most difficult part of the project.