A seven-km undersea tunnel will be constructed for the bullet train project in a bid to save about 12 hectares of mangrove forests in Maharashtra’s Thane creek. This will escalate the construction cost of the Mumbai-Ahmedabad High Speed Rail Corridor project’s 21-km long stretch from Bandra Kurla Complex Station to Shilphata, from ₹100 crore to ₹10,000 crore.
“Building an underground tunnel has escalated the cost by 100 times. However, we are conserving nearly 12 hectares of mangroves in the creek,” a senior National High Speed Rail Corporation Ltd. (NHSRCL) official told The Hindu.
Constructing an undersea tunnel in the Thane creek will be a massive challenge as it will involve two tunnel boring machines (TBMs) which will meet half way under the sea to join two parts of the tunnel by a process called docking.
“We have to ensure that the docking is done smoothly. This is challenging because adequate care has to be taken to ensure that there is no seepage in the tunnel due to water pressure,” another NHSRCL official said.
For the first time, TBMs with a cutter head of 13.1 metres in diameter will be used. “Usually, urban tunnels used in urban metro systems are between 5 and 6 meters. The tunnel will be a single tube tunnel to accommodate both up and down tracks,” the official added.
508 km corridor
The total length of the corridor is 508 km, of which 156 km of construction will be in Maharashtra. It is slated to cut the shuttle time between Mumbai and Ahmedabad from over 6 hours to between 2 and 2.5 hours. The entire project cost is estimated to be ₹1.08 lakh crore of which ₹32,000 crore has been expended by the NHSRCL.
The project was stuck due to a failure in obtaining clearances from the erstwhile Shiv Sena government in the State, Railway Minister Ashwini Vaishnaw had earlier said.
One of the entry points of the 21-km tunnel falls on land owned by Godrej & Boyce. Godrej and the Indian government have been at loggerheads over land acquisition since 2019. On September 15, 2022, Godrej filed a petition challenging an order by the Maharashtra government awarding compensation to the company for the land. On Thursday, the Bombay High Court said the project was in public interest and that there was no illegality in the compensation.
Clarifying the status of tenders in Maharashtra, NHSRCL officials said financial bids for the BKC station were opened on December 28, 2022. Technical bids for awarding the tender on the 21-km corridor have been floated on February 9. Two bidders, Afcons Infrastructure Limited and Larsen & Toubro Limited have submitted their bids.
Further, for civil and building works for 135 km involving viaducts, bridges, tunnels, and maintenance depots at Thane, Virar, Boisar; and some connecting works for Thane depot between Shilphata and Zaroli village on the Gujarat-Maharashtra border, the tender was invited on November 15, 2022. The opening is scheduled for March 15 this year.
Another tender for design and construction of the Thane Depot is scheduled to be opened on April 26. These involve construction of viaducts comprising 36 bridges, including 11 bridges on rivers and six mountain tunnels.