In a first in the country, Kolkata Metro created history on Wednesday as it successfully conducted its maiden run through the underwater tunnel under Hooghly river.
Sharing the big feat, Kolkata Metro Rail Kolkata tweeted, “Kolkata Metro creates History! For the first time in India, a Metro rake ran under any river today! Regular trial runs from #HowrahMaidan to #Esplanade will start very soon. Shri P Uday Kumar Reddy,General Manager has described this run as a historic moment for the city of #Kolkata.”
Kolkata Metro’s first rake reached the Howrah Maidan under the river Hooghly, officials informed on Wednesday. “Kolkata Metro created another history on 12.04.2023. After a long wait Country’s first Metro has run under the mighty river Hooghly today. For the first time in India Metro has completed the river journey,” the official statement said.
“P Uday Kumar Reddy, General Manager, Metro Railway travelled from Mahakaran to Howrah Maidan station in Rake No. MR-612 to witness this historic event. This rake crossed river Hooghly at 11:55 hrs. Reddy offered puja at Howrah station once the rake reached there,” it added. On the occasion, General Manager P Uday Kumar Reddy informed that trial runs from Howrah Maidan to Esplanade will be conducted for the next seven months.
“Later, Rake No MR- 613 was also taken to Howrah Maidan station. Terming it a historic event, the General Manager has informed us that the trial runs from Howrah Maidan to Esplanade will be conducted for the next 7 months and after that regular services on this stretch will begin,” it said. He further stated that the operationalization of commercial services on the stretch can be expected in the year 2023.
“Soon the trial runs on the 4.8 kms underground section from Howrah Maidan to Esplanade will begin. It is expected that commercial services on this stretch will begin this year. Once this stretch is open then Howrah will be the deepest Metro station (33 meters below the surface) in the country. The Metro is expected to cover the 520-meter stretch under the river Hooghly in 45 seconds. This tunnel under the river is 32 meters below the water level,” it said. Earlier in the year 2022 Kolkata Metro Rail Corporation (KMRC) said that the East-West Metro Corridor project, India’s first underwater metro service, is expected to be completed by December 2023.
Terming it a ‘historic event’, the Metro general manager said, “Trial runs between Howrah Maidan and Esplanade station will be conducted for the next five to seven months, following which regular services on this stretch will begin.”Trial runs on the 4.8 km stretch of the underground section will commence soon, Reddy said. Stating that it is the deepest rail network in India, he said that it requires a lot of skill and hard work to construct and run it.
A look back
Work at Howrah Maidan started in March 2016. The section between Howrah Maidan metro station and Esplanade metro station has been built by Afcons – Transtonnelstroy JV team, two tunnel boring machines from Herrenknecht are being used to dig the tunnel. This section passes through the Hooghly River for a distance of 520 metres (1,706 ft 0 in). The section under the river is at a depth of 30 metres (98 ft 5 in) (roof to ground distance) whereas the average roof to ground distance is 17 metres (55 ft 9 in). The Howrah metro station on the west side of the river will be at a depth of 30 metres (98 ft 5 in).
Design and construction of India’s first underwater tunnel
The tunnel will have an internal diameter of 5.55m and an external diameter of 6.1m. The spacing between the tunnels will be 16.1m centre-to-centre.
The inner walls of the tunnel 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.
Several protective measures have been taken to prevent water inflow and leakages in the tunnel. Concrete mixes composed of fly ash and micro silica have been used for the segments to minimise water permeability.
The segments are being sealed using a complex grouting process that will fill the space between the segments and the shield of the tunnel boring machine (TBM).
A two-component grout mix, including slurry made of water, cement and bentonite and sodium silicate, is being used to fill the gaps. The liner segments are fitted with German-made neoprene and hydrophilic auxiliary gaskets, which expand when in contact with water to prevent inflow through segmental joints.
Boring the twin underwater tunnels
Boring the underwater tunnels, which are predominantly composed of soft and stiff clay, has been one of the complex challenges of the project.
Two German-made tunnel boring machines (TBMs), named Prerna and Rachna, were deployed for the process.
Equipped with earth pressure balancing (EPB) capabilities, the machines are suitable for projects on unstable terrain or under structures that are sensitive to ground disturbances. They can withstand three times more atmospheric pressure during the boring process.
Each TBM is 8.5m-long, as tall as a two-storey building and has backup gantries extending to 100m. Six generator sets of 1,010kVA will supply power to the boring machines, which are equipped with five motors exceeding 650HP and more than 35 other auxiliary motors. The TBMs will bore up to 15m a day, excavating up to 500m³ of the earth to complete 2.9m of the tunnel.
The two TBMs bored the east and west-bound tunnels in a record span of 66 days, from April 2017 to June 2017. While the first tunnel crossed the river in May 2017, the second one crossed it in June.
The underwater tunnel construction is technologically comparable to the Eurostar high-speed railway service that traverses the Channel Tunnel between the UK and France.
The TBM S-616 Urvi was deployed in March 2021 to construct the final stretch of the East-West Metro, 17m below Sealdah station.
Contractors involved
The construction contract for the underground tunnel project was awarded to a joint venture between Indian construction firm Afcons Infrastructure and Russian firm Transtonnelstroy. Afcons is also responsible for the construction of three underground stations and other works on the project.
The two tunnel boring machines were ordered from Herrenknecht. ITD Cementation constructed a diaphragm, also known as a D-wall in engineering parlance, which is needed to connect the station to the tunnel dug by the TBM.
The challenges faced
Completion of the total project has been delayed owing to accidents in Bowbazar area of central Kolkata.
“We took a decision, instead of waiting for the whole route to be cleared, we have focussed on the route that is clear now,” Reddy said.
The Metro Railway had earlier said that it plans to start services by the end of this year in the Howrah Maidan to Esplanade stretch if a problem persisting at Bowbazar, between Esplanade and Sealdah stations, is not sorted by then.
On August 31, 2019, a tunnel boring machine had hit an aquifer leading to severe ground subsidence and the collapse of a number of buildings at Bowbazar.
Several houses were damaged again in May 2022, owing to ground subsidence caused by water seepage during work for joining the tunnels coming from the Sealdah side in the east and the Esplanade side on the western side.
The underground water seepage caused cracks in 12 buildings at Madan Dutta Lane in Bowbazar on October 14, 2022, the last accident there to affect completion of the project.
Out of the 16.6 km length of East West Metro, the underground corridor constitutes 10.8 km between Howrah Maidan and Phoolbagan with the tunnel passing below the Hooghly river, while the rest is elevated corridor, according to an official of Kolkata Metrol Rail Corporation, the executing agency of the East West Metro corridor.
Stating that the construction of the tunnel from Howrah Maidan to Esplanade had to face several challenges, the Metro GM said that some emergency measures also had to be taken to overcome those.
The tunnel passes through very congested areas along the Brabourne Road in the Burrabazar area with several century-old houses there and the Metro had to shift residents to hotels during underground work there.
Once operational, Howrah will be the deepest metro station (33 meters below the surface) in India. It will cover a distance of 520-meter under Hooghly river in 45 seconds. Commercial services on the stretch expected to begin later this year.
Keep watching this space for more updates on Underground Kolkata Metro.
Reference, Railway technology.com, Kolkata Metro Rail Corporation Ltd., Zee news, timesofindia.indiatimes.com, Telegraphindia.com