Breeze Candy: From Marine Drive to Breach Candy, in 3.20 minutes

Come February and Mumbaikars too will save time and fuel as they breeze through the toll-free tunnel. Set to be inaugurated in the second week of February, the tunnels start near Girgaon (ahead of Marine Drive), extend north under the Arabian Sea, Girgaon Chowpatty and Malabar Hill, and end at Breach Candy’s Priyadarshini Park. They are a part of the 10.58-km high-speed Mumbai Coastal Road Project (MCRP) being built by the Brihanmumbai Municipal Corporation (BMC) at a cost of Rs 12,721-crore. The Indian Express drove through the tunnel on January 13.

The 2.07-km tunnel runs from Marine Drive to Breach Candy in Mumbai. (Express photo by Amit Chakravarty)

The MCRP, which will connect Marine Drive to the Bandra-Worli Sea Link, aims to cut down overall travel time from nearly one hour during peak hours to little less than 10 minutes. The larger MCRP project envisages linking Marine Drive with suburban Dahisar via a toll-free freeway, bringing seamless connectivity to the Maximum City’s western coast.

On January 8, Chief Minister Eknath Shinde had said the ongoing construction for the MCRP will be completed by January 31. He had said the entire corridor will be completely operational from May.

Though the project is nearly 84 per cent complete at present, some bit of work on the tunnel catering to Marine Drive till Breach Candy is still left to be done. This includes just ancillary works like painting, setting up traffic lights and signages.

A 900-metre stretch of the tunnels runs 17-20 metres below sea level, hitting peak depth of around 67 metres at Malabar Hill. (Express photo by Amit Chakravarty)

Civic officials have said the MCRP will initially be operational only between 8 am and 8 pm from Monday to Friday to facilitate peak-hour traffic. An official had said, “…we plan to carry out (the balance work, like heavy lifting of metals and civil work like rolling the roads) at night and on weekends”.

Inside the twin tunnels, the look and feel
The southern ramp of the tunnels starts between the Hindu and Islam Gymkhanas at Charni Road. Going ahead, the cut and cover ramps merge with the cylindrical tunnel and extend northwards under the Arabian Sea, ending at Priyadarshini Park.

With a diameter of 11 metres each, the twin tunnels are the widest cylindrical tunnels in the country that were dug over two years using a Tunnel Boring Machine (TBM).

The tunnel is set to be inaugurated in the second week of February. (Express photo by Amit Chakravarty)

A 900-metre stretch of the tunnels runs 17-20 metres below sea level, hitting peak depth of around 67 metres at Malabar Hill, where it passes beneath a centuries-old reservoir. Resembling the shape of the Queen’s Necklace, the famous C-shaped Marine Drive promenade, the tunnel’s entry and exit points are covered by an oval fibreglass canopy

White counter-beam lights have been installed inside the tunnel, making it heavily illuminated. The contrast of these lights adjusts automatically to ensure a motorist’s visibility is not affected when one switches from daylight to artificial lights.

Each tunnel has three lanes of 3.2 metres each for smooth vehicular movement. Namkak Cho, a senior tunnel engineer with South Korea-based Yooshin Engineering Company, one of the project management consultants (PMCs), said only two lanes in each tunnel will be operational at present. “The third lane will be used in an emergency. It will be made fully operational if vehicular density in Mumbai increases in the long run,” he added.

With a diameter of 11 metres each, the twin tunnels are the widest cylindrical tunnels in the country. (Express photo by Amit Chakravarty)

Talking about the signage, a civic official said, “The tunnel will have digital signage projected through LED screens. One screen will be placed at every 300 metres above each lane. The signboards will display everything, including speed limit and emergency messages.”

To keep the tunnels safe from natural and man-made hazards, the BMC has put in place several preventive measures.

One such measure is multiple cross-passages, which allow pedestrians or motorists to cross one tunnel and enter the other in case of emergencies like vehicular breakdown, a fire, medical issues or a natural calamity. Cross passages are accessible through an emergency door, marked prominently with an illuminated sign.

The entire 10.58-km route has 10 cross passages, while six of them are located inside the tunnels at an interval of 300 metres each. Of the six cross passages, two are for vehicular crossing and four for pedestrians. To dig cross passages within the tunnel, the BMC used the New Austrian tunnelling method (NATM). It involves sequential excavation, where surrounding rock or soil formations are integrated into an overall ring-like support structure.

Of the six cross passages, two are for vehicular crossing and four for pedestrians. (Express photo by Amit Chakravarty)

Fire safety measures
For fire safety, the tunnels are equipped with an automatic fire detection system, fire extinguishers, pressurised fire hydrants and a ventilation system for smoke control.

Besides these, the BMC also made pioneering use of a Belgian fire protective mechanism involving ‘Fire Board’ technology.

Made of calcium silicate, these fire resistant boards act as the secondary layer of insulating material applied directly to the tunnel’s concrete lining. The lining will protect the tunnel’s concrete walls from exploding in case of a fire. An official said the first test on the fire boards was first carried out by IIT-Roorkee.

“The tunnel ceiling has been layered with these fire boards. In case of a major fire — say an accident involving a petrol tanker… — only the fire board will develop cracks upon cooling. The concrete walls in the tunnel will remain intact,” said Cho.

Namkak Cho is a senior tunnel engineer with South Korea-based Yooshin Engineering Company, which is one of the project management consultants (PMCs). (Express photo by Amit Chakravarty)

Another first for the tunnel is the use of the Saccardo ventilation system, which pushes fresh air from the opening throughout the tunnel. Officials said most tunnels use jet fans in the ceiling area for ventilation, which causes the structure to heat up inside due to vehicular combustion. In contrast, the Saccardo ventilation system will keep the tunnel cool. Each tunnel has three Saccardo ventilation fans, of which two will operate on most days. The third fan will become operational only in case of emergencies.

“The problem with normal jet fans is that when one of them stops working, both the cost and time for maintenance is massive. In addition to this, the temperature inside the tunnel also increases,” an official said.

According to Cho, the Saccardo system only requires two stations at each end — “one system for air intake, the other one for air injection”.

The ventilation system is also helpful in case of a fire. “In case of a fire, air with greater pressure will be generated from the (ventilation) system that will push the smoke (out). Fire hydrants will come into force after that,” said an official.

A map of the tunnel, which starts near Girgaon (ahead of Marine Drive), extends north under the Arabian Sea, Girgaon Chowpatty and Malabar Hill, and ends at Breach Candy’s Priyadarshini Park. (Map: Abhishek Mitra)

The roads in the tunnel have been made with a mix of cement and concrete (CC) to ensure vehicles are able to cruise at an average speed of 80 km per hour without skidding. However, to keep traffic violations like lane cutting and overspeeding in check, civic officials said, high resolution Pan-Tilt-Zoom (PTZ) cameras have been installed in the tunnel to catch offenders.

The tunnel will also be equipped with a Traffic Management Control System (TMCS), an integrated facility through which officials will be able to monitor movement inside the tunnel 24/7. Each tunnel will have a dedicated technical branch to monitor activities and deploy countermeasures immediately in case of a mishap. A dedicated command and control centre building of the MCRP will also be constructed near Amarsons Garden to keep an eye on the entire 10.58-km stretch through CCTV cameras.