On Wednesday, Kolkata Metro scripted history when a rake, for the first time in the country, completed a journey through an underground tunnel in river Hoogly.
In a "historic move," the rake, with officials and engineers on board, ran under the river Hooghly from Kolkata to Howrah on the other side of the river. The 520-metre-long tunnel connects the soon-to-open metro station of Howrah Maidan and the existing Esplanade station and is expected to become operational in the next five to seven months.
Engineering marvel
At 33 metres below water level, the tunnel is the deepest rail network in India. The Indian version of Eurostar's London-Paris corridor, the tunnel is a part of the East-West Metro Project and aims to connect Howrah Maidan with Rajarhat along the 16.6-km route.
The tunnel became a necessity for the East-West Corridor due to the technical difficulties associated with the stretch being a residential area.
The work on the East-West Corridor began in 2009, and the contract for building the underground section was given the next year. Two Tunnel Boring Machines - Prerna And Rachna - were brought to Kolkata from Germany and the tunnelling work was completed in 2017.
The tunnel has an internal diameter of 5.55m and an external diameter of 6.1m. Its inner walls are being made with M50 grade, reinforced concrete segments with a thickness of 275mm 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.
The construction is such that there wouldn't be water spillage or leaks. To minimise water permeability, concrete mixes composed to fly ash and micro silica have been used.
As for safety, the tunnel is equipped with emergency evacuation shafts. According to Mithun Ghosh, site supervisor, there will be walkways in the tunnels for evacuation of passengers in case of emergency. "Important Passage work has also been done keeping in mind that if a technical problem arises inside the water tunnel area, passengers can be taken out through the special passage," Mithun told ANI in an earlier interview.
That said, the tunnel travel is just 45 seconds, making it a blink-and-you-miss-it experience for passengers.