INDIA’S FIRST UNDERWATER TRANSPORT TUNNEL

Trial runs are underway on India’s first underwater transport tunnel.
The 16.55-km East-West corridor is the second line of the Kolkata Metro network.
The East-West Corridor of the metro was approved in 2009.
The line, called the Green Line, will link Howrah station to Sealdah station, which is the hub of Kolkata’s suburban railway network.
When completed it will connect the IT hub of Salt Lake Sector V on Kolkata’s eastern flank to the western suburb of Howrah.
Of the total 16.55 km-long East-West stretch, 520 meters is under the Hooghly riverbed.
The western portion of the East-West Corridor is underground. There are 12 stations on the entire route, including the country’s deepest Howrah station at the depth of 33 metres.
The train will run 100 meters beneath the river waters and it will take 45 seconds to cross the tunnel.

Technology involved in the Project and challenges:

The tunnels under the Hooghly river have an internal diameter of 5.55 metres and an external diameter of 6.1 metres.
The centre-to-centre distance between the east- and west-bound tunnels is 16.1 metres.
The inner walls are of high-quality M50-grade reinforced concrete segments with a thickness of 275 mm each.
Six of these segments will complete a circular lining of the tunnel’s diameter. The segments are being pre-cast in specialised moulds imported from Korea.
There is a layer of sandy silt under the organic clay of the riverbed.
Apart from the underwater tunneling, tunneling in areas with historic buildings like Dalhousie posed a challenge for the project.

Conclusion:

It was Kolkata where India’s first Metro railway i.e., North-South line was opened in 1984. And the Kolkata Metro Rail Corporation (KMRC) is gearing up to make India’s first underwater metro train operational in the city by the year-end.
The East West Metro will pass through the highly congested parts of Kolkata that have narrow streets and historic buildings. The tunnel, and the corridor will significantly improve commuting on one of the city’s most congested stretches.

SOURCE: THE HINDU, THE ECONOMIC TIMES, PIB

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