Kolkata:
India’s first underwater tunnel, built under the Hooghly River in West Bengal at a cost of around Rs 120 crore as part of the East West Metro Corridor, will be a dazzling experience for passengers as trains cross the 520m stretch in only 45 seconds.
The tunnel – the Indian version of the Eurostar London-Paris corridor – is 13 meters below the river bed and 33 meters below ground level.
The 520-meter tunnel is part of Kolkata’s East West Metro Corridor – from the IT hub of Salt Lake Sector V in the east to Howrah Maidan in the west across the river.
Construction of the tunnel is complete and is expected to begin operation in December 2023 following the completion of a 2.5 km stretch between Esplanade and Sealdah on the corridor.
“The tunnel is essential to the East West Corridor and was key. The alignment under the river was the only possible alignment with residential areas and other engineering issues,” said Kolkata Metro Rail Corporation General Manager (Civil) Sailesh Kumar.
“This subway route between Howrah and Sealdah cuts travel time to 40 minutes compared to 1.5 hours by road. It also reduces congestion at both ends,” he said.
It takes 45 seconds to cross the tunnel, he said.
Metro rail’s East West Corridor has been marred by delays and resulting cost escalations. It was approved in 2009 at a cost of Rs 4,875 crore and a completion date of August 2015. According to officials, the cost has now risen to Rs 8,475 crore, of which Rs 8,383 crore has already been spent.
The tunnel will have an inner diameter of 5.55 meters and an outer diameter of 6.1 metres. The distance between the ascending and descending tunnels will be 16.1 meters centre-to-centre.
The inner walls of the tunnel are made with high-quality M50 reinforced concrete segments, each 275 mm thick. Six of these segments form a circular liner the diameter of the tunnel. The segments are pre-cast in specialized molds imported from Korea.
Various protective measures have been taken to prevent water ingress and leaks in the tunnel. Concrete mixtures of fly ash and microsilica were used for the segments to minimize water permeability.
The segments are sealed using a complex grouting process that fills the space between the segments and the tunnel boring machine (TBM) shield.
To fill the gaps, a two-component grout mixture is used, consisting of a slurry of water, cement and bentonite and sodium silicate. The liner segments are fitted with German-made neoprene and hydrophilic auxiliary gaskets, which expand on contact with water to prevent inflow through segment joints.
Two German-made tunnel boring machines (TBMs), named Prerna and Rachna, were used for the process.
Emergency evacuation shafts of up to 760 meters in length are provided in the tunnel in accordance with National Fire Protection Association (NFPA) guidelines. Evacuation shafts will be provided at Howrah Station to the west and Strand Road to the east for passenger safety.
(Except for the headline, this story has not been edited by DailyExpertNews staff and is being published from a syndicated feed.)
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