Mumbai Undersea Tunnel: All You need to know

The undersea tunnels will be built as a part of the Mumbai Coastal Road Project which comprises the land-filled roads on the areas that are reclaimed from the sea, tunnels, bridges.

Created On: Feb 25, 2021 14:13 ISTModified On: Feb 25, 2021 14:13 IST
Mumbai Undersea Tunnel

Mumbai will have the first undersea tunnel of India by the year 2023 which will part of the Coastal Road Project of the city. The undersea tunnels will be built as a part of the Mumbai Coastal Road Project which comprises the land-filled roads on the areas that are reclaimed from the sea, tunnels, bridges.

The Mumbai Coastal Road Project is an ambitious plan of linking South Mumbai with North with a toll-free freeway that has been expected to ease up the traffic in one of the most congested cities in the world. The project is also the most ambitious one that the city has seen in recent times.

According to BMC, each tunnel will take about 8 to 9 months to complete and the work will entirely be completed in about 2 years.

The drilling for the South Mumbai traffic tunnel has already been started. After completion, the Tunnel Boring Machines will be removed near Marine Drive and will go back to the Priyadarshini Park for the second time drilling for northbound traffic.

Read below to know more about India’s first undersea tunnel, how it is constructed and how it is in comparison to other undersea tunnels across the world.

Where the tunnels are being constructed?

With a length of 2.07 km of which a kilometer will be built under the sea, the twin tunnels are being built as part of the Mumbai Coastal Road Project which is a 10.58 km stretch starting from the Marine Drive Promenade to the Worli-end of the Bandra-Worli Sea Link.

It will be the first undersea road tunnel of India which will be passing through the Arabian Sea near Girgaon Chowpatty. The tunnel will start from Priyadarshini park. It will end at Netaji Subhash Road in Marine Drive.

Cost of constructing the tunnels:

The total cost of constructing the tunnel from Priyadarshini Park to Princess Street Flyover at Marine Drive of the Coastal Road will be of Rs. 2,798.44 crores. It will mainly include the construction of the twin tunnels and the allied works.

How deep will be these undersea tunnels?

The Twin Tunnels in Mumbai City are being constructed at a relatively shallow depth. It will be different from the other undersea big tunnels in the world, including the Channel Tunnel which connects England and France,

The undersea tunnel in Mumbai city will be 20 m below the seabed. The Channel Tunnel, in comparison, is 75 m at its deepest point below the sea bed and Japan’s Seikan Tunnel lies over 100 m below the seabed.

The twin tunnel in Mumbai is also being built very close to the coast, where the depth of the sea is not more than 4 to 5 m.

Procedure of digging undersea tunnels:

To dig the undersea tunnels in Mumbai, a 2,800-tonne tunnel boring machine which is also the biggest of its kind in India, has been deployed.

At Priyadarshini Park, an 18 m shaft has been dug for lowering the machine below the ground. From this place will start the boring through the strata.

The machine for digging will be operated by a team of 30 people. It has a diameter of 12.19 meters which will be boring through the solid rock.

 Tunnel Boring Machines- They are used as an alternative for drilling and blasting methods in rock and conventional ‘hand mining’. They also have the advantage to limit the disturbance to the surrounding ground and to produce a smooth tunnel well. The Tunnel Boring Machines consists of the rotating cutting wheel which chips away from the surface. It will dig one segment of the twin tunnels at a time.

Major challenges of building the undersea tunnel:

The tunnel being built undersea makes constructing it a significant challenge. The two major issues of concern while building the undersea tunnel are the fear of the tunnel caving in because of the pressure exerted by seawater and the seepage of seawater into the tunnel.

However, the fact that the tunnel is being constructed very close to the coast and is not in mid-sea has made things easier for the engineers who state that all the safety measures are being used while building the tunnels in order to maintain the stability of the structure.

Safety measures for commuters in twin undersea tunnels:

Each undersea tunnel will have two lanes each, which will be 3-3.2 meter wide, with one emergency lane.

Even though the two tunnels are separate, 11 cross-section tunnels will be built for connecting the twin tunnels with each other.

These cross-section tunnels will be used in case of an emergency where the people will be evacuated into the other one through the cross-section connections.

The drainage system is also being designed to cater to the seepages. There are slotted drains at every 50 meters intervals for collecting any seepages, oil spillages from vehicles, and discharge from the fire hydrants.

How the temperature will be regulated inside the tunnels?

It will be a confined space and will require ventilation for ensuring a tenable environment for the commuters. However, the fact that these tunnels are under the sea will make the dispensation of the Carbon Monoxide, emitted by cars, inside the tunnel a difficult proposition as the high level of Carbon Monoxide can be hazardous for commuters.

To solve the problem of hazardous gases inside the tunnel, a ventilation system called Saccardo, which is one of its kind, will be installed. The system will monitor the emission levels inside the tunnel and will shoot an air jet through the large ventilation fans for driving out the fumes.

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