Cmrl redesigns tunnel ventilation system to trim underground metro stations by nearly 40%

Chennai: Six years after the city’s largest metro station was built in phase-1 project at Central, metrorail has shrunk the underground stations in phase-2 by nearly 40% to tighten its purse strings.

Trimming the stations required engineers to redesign the tunnel ventilation system, a key feature that protects passengers during fire emergencies in the tunnels and bring down the number of exhaust fans from eight in phase-1 to only two in phase-2 without compromising safety.

Sources said this has brought down the length of the station from 240m in phase-1 to 150m in phase-2 and saved more than Rs 2000crore in project cost on systems procurement alone but could save several thousand crores in construction cost. The 116.1km phase-2 will have 42 underground stations.

Officials said the new layout for the tunnel ventilation system involves placing two big exhaust fans on either ends of the stations on the concourse level. The fans will use the duct, built below the platforms, fitted steel nozzles to push or draw smoke as well as pump in fresh air in the tunnels through the ventilation shafts during fire emergencies. These ducts are otherwise used for storing large electrical cables that run through the stations. This redesign in TVS layout, which has also reduced the connected electrical load and cabling needs, brought down the use of space in a station from 2485sqm in phase-1 to 750sqm in phase-2 which helped in trimming the station. In phase-1, stations had eight fans to remove smoke in tunnels and pump in fresh air. The size of the platforms is 140m in both the phases.

“In phase 1 extension, tunnel ventilation fans were reoriented for space optimization. In phase 2, tunnel ventilation system will use only two fans, which will meet all functionalities, in normal mode and emergency mode. Due to this optimization of the station the box size has been reduced,” a metrorail official said. The tunnel ventilation system comprises big exhaust fans to draw out smoke in tunnels and stations, four small overtrack exhaust fans that will be turned on when there is fire in trains operated in tunnels.

The trimming of underground stations was one of the many efforts taken to cut down project cost from Rs 89000crore to Rs 63,432crore. The average construction cost of one kilometre underground line is Rs 500crore.

The new tunnel ventilation system was conceptulised by metrorail officials and designed by international experts, Aecom Hong Kong, Systra in France and Milan Metro, Italy, to meet the guidelines of National Fire Protection Association 130 and National Building Code to ensure safety. The design also underwent a series of validation from general consultant and external experts.

While the average length of metro stations in the country has been 220m to 230m, experts said metros projects across the country are now designed with smaller underground stations due to space constraints as they are planned in densely populated areas. “In 2016-17, we reduced the length of the underground stations in phase-1 extension to 150m and took a re-look at all the equipment and systems room we planned in phase-2 stations to trim the station size,” R Ramanthan, former CMRL director.

eom/Tejon


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