Work on entry points to 21-km bullet train tunnel underway

MUMBAI: The railways have begun digging deep into the earth at four locations to construct a 21-km-long tunnel for the Mumbai-Ahmedabad bullet train project. Apart from BKC, where the main station is, work is currently underway at Vikhroli, Thane and Sawli near Ghansoli, all entry points to the underground rail tunnel.

At 56 metres underground, the tunnel’s deepest stretch will be in Vikhroli, the land for which was handed over by Godrej & Boyce to the National High Speed Rail Corporation Limited (NHSRCL) in February 2023 after a court battle.

Actual work on the tunnel will begin after a year when the entry points are ready and tunnel-boring machines (TBMs) are brought in. “In all, three shafts are being built at BKC, Vikhroli and Sawli which will facilitate the construction of the tunnel,” said an NHSRCL official. “The shafts or entry points will be used to lower two tunnel-boring machines in two different directions—towards BKC and Ghansoli. The tunnel will be about 25 to 57 metres deep from the ground level, and the deepest construction point will be 114 metres below Parsik Hill near Shilphata.”

The three TBMs will be used to construct about 16 km of the tunnel portion, including the seven-km stretch under Thane Creek. The remaining work on five km will be through a simpler method called the New Austrian Tunnelling Method.

The tunnel will be a single tube with twin tracks for the up and down rail lines.

Controlled blasting is being used to construct shafts in areas that have a high population density, utilities like pipelines and electrical installations and where other infrastructure projects are going on. In November last year, there were air pollution issues at the BKC site on account of which NHSRCL was asked by the BMC to take adequate measures during construction.

BKC bullet train station

NHSRCL has acquired the approximately 4.8 hectares of land required for constructing BKC Station. The station will be built using the bottom-up method, which means that excavation work will commence from the ground level and concrete work will start from the foundation.

The excavation required for the station will reach a depth of 32 metres, with an approximate volume of around 18 lakh cubic metres (cum) of excavated materials. About 1.5 lakh cum of earth has already been disposed of. “To safely carry out such deep excavation, we have constructed 3,382 secant pile walls, each ranging from 17 to 21 metres in depth,” said a NHSRCL engineer.

Currently, there are 681 labourers and supervisors on site, working day and night. According to estimates, the maximum workforce required per day during peak times goes up to 6,000 individuals.