KOLKATA (Metro Rail News): India’s first underwater river tunnel is almost ready. As part of the east-west corridor, Kolkata Metro Rail Corporation (KMRCL) has dug tunnels below the Hooghly River to lay train tracks.

Of the 16.6-km-long east-west stretch, 520 m will be under the river bed. Constructing the tunnels has been an engineering feat. The tunnels are built more than 33 meters below the riverbed and will connect Kolkata to Howrah. The fact that not one drop of water can enter the tunnel was the biggest challenge.

The time taken to cross the 520-m tunnel will be around 60 seconds. Using the ferry to cross the river takes 20-odd minutes. And crossing the Howrah Bridge may take hours if you are stuck in a traffic jam.

The metro tunnel has several other marvels. The structure is actually made of rings that are 1.4 m wide. A special gasket has been made which will swell five times if it comes in contact with water. In case of water ever enters the tunnel there are enough precautionary steps that have been taken.

This is the first big tunnel under any river in India. Within a few months, the metro will start running here. Here the width of the Ganga is 500 m and the tunnel is 13 m under the Ganga. The diameter of the tunnel is 5.8 m, B Dewanjee, chief engineer (civil ), KMRCL said.

Talking about the safety issue Dewanjee said: The tunnel is made of concrete and we have brought the entire composed concrete and put it over here. There are hydrophilic gaskets are kept in between these concretes so that if in any case water comes inside the tunnel, the gaskets will open up. Here four-stage safeties are used so that the water cannot enter the tunnel.

Around 150 trucks of mud have been taken out every day to ensure that this entire stretch was built very smoothly. More than 1,000 workers worked tirelessly 24×7 to complete the tunnels by the due date. So what if an emergency happens? Walkways have been built and enough fire alarms have been set up. There will be a smooth process for fire tenders to enter so that the passenger evacuation route does not collide with the route that is being taken by the fire workers who will be on duty round the clock.

There have been several other challenges. The cost of the project has been rising and is likely to touch Rs 8,500 crore by the time people are able to use the entire metro system in 2021. The twin tunnels will also ease movement of trains as at no pint will two trains cross each other.

One of the challenges faced by KMRCL was to keep the old building intact in the construction site. The area is dotted with centuries-old building dating back to the British period. The foundations of these buildings had to safeguarded so that they did not crumble.

As a precautionary measure, several buildings were evacuated before construction began more than 500 people were temporarily shifted and put up in hotels.

For the 1,000-odd workers too it was a huge challenge. In the tunnels the temperatures would rarely go below 50 degree Celsius, making the surroundings very hot and unbearable. The oxygen supply was also an issue.

The wait for the people of Kolkata and Howrah will soon be over. Seamless connectivity between Howrah railway station, one of the busiest in the country, and the eastern metropolis will help in saving travel time.