18 July,2026 11:06 PM IST | Mumbai | mid-day online correspondent
Work underway on the Mumbai-Ahmedabad bullet train project`s tunnel beneath Thane creek. The tunnel includes a 7-km undersea section, which will be India`s first undersea rail tunnel. FILE PIC
A second tunnel boring machine (TBM) on Saturday began excavation for the rail tunnel beneath Thane creek as part of the Mumbai-Ahmedabad bullet train project, officials told news agency PTI.
In a statement, the National High Speed Rail Corporation Limited (NHSRCL) said the TBM has started its drive from Sawli (Ghansoli) towards Vikhroli. Of the 10-km underground stretch, a crucial 7-km section will pass beneath the seabed at Thane creek, making it India's first undersea rail tunnel.
The undersea stretch is part of the 21-km underground section of the Mumbai-Ahmedabad high-speed rail corridor. Of this, 16 km between Sawli and the Bandra-Kurla Complex (BKC) in Mumbai is being constructed using tunnel boring machines, while the remaining 5 km has already been completed using the New Austrian Tunnelling Method.
The first TBM had commenced its 6-km drive from Vikhroli towards BKC on July 5.
According to the NHSRCL, the TBM is among the largest ever deployed for rail tunnel construction in the country.
The machine has a cutterhead measuring 13.6 metres in diameter - equivalent to the height of a four-storey building - and weighs around 3,200 tonnes, comparable to the weight of nearly 500 Asian elephants. It has an overall length of 96 metres.
The TBM uses a pressurised liquid bentonite slurry circuit to stabilise the tunnel face during excavation. The technology has been adopted to minimise surface disruption while tunnelling through densely populated parts of the Mumbai Metropolitan Region.
The NHSRCL said the underground excavation is supported by multiple safety measures.
Apart from an active water sprinkler network along designated escape routes, the TBM is equipped with a real-time multi-gas monitoring system to monitor methane, oxygen, carbon monoxide and carbon dioxide levels.
The surface shaft has also been equipped with water and slurry treatment plants, bentonite storage tanks, a dedicated power substation with backup generators, and a ready-mix concrete plant for grouting operations.
To safeguard nearby structures and ensure long-term structural stability, the project includes a real-time monitoring system comprising surface settlement points, optical displacement sensors, strain gauges and seismographs.
The 508-km Mumbai-Ahmedabad bullet train corridor is being developed at an estimated cost of Rs 1.08 lakh crore.
Under the funding arrangement, the Government of India will contribute Rs 10,000 crore, while Maharashtra and Gujarat will contribute Rs 5,000 crore each. The remaining cost will be financed by Japan through a long-term loan carrying an interest rate of 0.1 per cent.
(With PTI inputs)
