Story behind the success of Indian first under river metro line
The Kolkata Metro is a rapid transit system serving the Kolkata metropolitan area in the Indian state of West Bengal. The network currently consists of one operational line of 27.22 km from Noapara to Kavi Subhash with five other lines in various phases of construction. The Kolkata Metro was the first metro railway in India, opening for commercial services from 1984.
Kolkata became the 17th zone of the Indian Railways, operated by the Ministry of Railways. There are 300 metro services daily carrying over 650,000 passengers making it the second busiest metro system in India.
Now, the tunneling work under the Hooghly river, the first such under-river project in the country, to provide metro connectivity between Howrah and Kolkata is slated to be completed in a few weeks.
Structure of tunnel
The under-river tunnel is a crucial link for the Railway's 16.6-km long East-West Metro project in Kolkata. The 520-meter twin tunnel, one eastbound and the other westbound, is built 30 meters below the riverbed. The tunneling covers 10.6 km. The internal diameter of each tunnel is 5.55 meter and the thickness of the wall is 275 millimeter. The distance between the two tunnels is 16.1 meter. It was a challenging task to dig a tunnel under the river.
The under-river tunnel is being built at an expense of Rs 60 cr while the total cost of the East-West Metro project is estimated at around Rs 9,000 crore.
Between Howrah and Mahakaran metro stations will be under the river for only about a minute when the metro train will pass through the tunnel at a speed of 80 km per hour.
Between Lal Dighi and Howrah Station, the metro will run under the Hooghly River – the first underwater metro in India. The line will be elevated between Salt Lake Sector 5 and Salt Lake Stadium, and the remaining stretch will be underground. Transfer stations will be located at Sealdah and Howrah.
Construction of tunnel
With the tunneling and construction of East-West Metro Project in full swing, there, however, have been a few glitches that require to be overcome. The digging by the German-made TBM machines led to cracks appearing in the Howrah District Library.
Employing about 250 people at the site of tunneling 24×7, a thick layer of concrete is used to seal the tunnel, with the intention of preventing disasters like the collapsing of earth along with water seepage: one major concern for the engineers working on any water tunnel.
Rachna, a giant tunnel-boring machine (TBM), was deployed to dig the underwater tunnel. The machine was brought from Herrenknecht AG plant in Schwanau, Germany.
KMRCL authorities had to be very cautious when the tunneling reached near Colvin Court, which is a 94-year-old railway building serving as residential quarters for railway staff, currently.
Another concern faced by the East-West Metro Project is the threat of damaging three heritage buildings that lay well within the vicinity of the Metro tunnels.
Union Minister of State for Heavy Industries Babul Supriyo, who inspected the project, expressed hope to The Hindu that the last hurdle would be cleared soon after the issue was raised by the Archaeological Survey of India, wherein an expert committee from the IIT Kharagpur, was constituted to look into the matter.
The tunneling work started in April 2016 and likely to be completed in the river section shortly, a senior Railway ministry official said. The East-West Metro is scheduled to be operational by August 2019.