Have you heard of undersea tunnels? There are a few around the world.

And now, there will be one in Mumbai too!

Mumbai’s undersea tunnel will be a part of the Coastal Road Project that will connect north and south Mumbai. It will be ready by 2023 and will cost about Rs 2,798.44 crore.

There will actually be two tunnels comprising a 10.58-km stretch, which would start from the Marine Drive promenade to the Worli-end of the Bandra-Worli Sea Link (which is an overhead tunnel).

The tunnel will be 20 meters below the seabed – this is relatively shallow when compared to other such undersea tunnels in the world. The Channel Tunnel that connects England and France, for instance, has gone as deep as 75 metres below the sea bed. In Japan, the Seikan Tunnel Japan is more than 100 metres below the seabed.

How are they being made?

A huge boring machine, weighing 2,800 tonnes is being used to dig the tunnels. A team of 30 people will be operating this machine. First, a shaft has been dug to lower the machine below the ground. Once this is done, the machine will start boring through the earth – solid rock in parts.

Tunnel boring machines are used in creating tunnels and the traditional methods of blasting and drilling are not used – these machines cause lesser disturbance to the surrounding ground.

Details about the tunnel

Both the tunnels will have two lanes each, apart from an emergency lane. There are also 11 cross-section tunnels that will connect the twin tunnels. These are for emergency use to allow people from one tunnel to be evacuated through the other tunnel in case of any problems.

The main challenge is to address the water seeping into the tunnels. One of the solutions to this is creating a great drainage system that regularly drains out the water and also oil that comes out of vehicles.

Another challenge is dealing with the carbon monoxide which is emitted by cars. Because it’s a tunnel, the carbon monoxide needs to be flushed out. To solve this problem a state-of-the-art ventilation system would be installed. Called Saccardo, this will monitor the emission levels inside the tunnel and then shoot air jets through big ventilation fans in order to remove the toxic fumes.