Away from the hustle and bustle of Poonamallee High Road and deep in the silence of the earth, one of the largest underground metro stations in the country, Central metro station, is taking shape.
With a majority of the work complete, Chennai Metro Rail Ltd is gearing up to open by the first quarter of 2018 a part of the station that will connect Central metro station and the airport via Nehru Park.
The rest of the station is expected to be ready by 2018-end, almost seven years after construction began.
Central metro station, which will be an underground transit hub with facilities for easy commuter access and travel, will connect both corridors Central to St Thomas Mount and Washermenpet to Chennai airport of the 45 km phase-1 project. Afcons, the infrastructure company which is building the tunnels for phase-1, is also building the station. With three decks, the 390 m-long, 33 m-wide and 28 m-deep Central metro station will be one of the largest underground transport structures in the country. Hauz Khas in New Delhi is one of the deepest stations, at 29 m, and has six decks; Majestic metro station in Bengaluru is one of the largest, built across 48,000 sqm.
Being a transit hub, the station will have several facilities that are not present at other underground stations in the city. Commuters can walk down the station's entry exit points on either side of the road to the top deck of the station which will be the ticketing or concourse level. The entrance will link two levels instead of one built in other underground stations. Commuters heading to the station by car or bike can get into the station through one of the entry points and head to an underground parking lot before walking to the ticketing level.
The second and the third decks of the station will be the platform levels for the two corridors of phase-1. While the second or upper deck will connect Central and St Thomas Mount (corridor 2), the third or lower deck will connect Washermenpet and the airport (corridor 1). Pedestrians on the arterial road will also find it easy to cross the busy road as the station will be opened along with two new subways that will facilitate easy access to either side of the road.
The station will also have several other features for train operations like a siding line, where trains can begin operations for the day and chug to the main line in both directions and in both the corridors simultaneously. Like the Shenoy Nagar underground station, Central metro station too will have crossover lines where trains can cross tracks in an emergency on either deck.
The construction posed a challenge from the time work to build the station began. Extreme variation in the soil strata, excavation under several heritage structures, multi-storeyed buildings with shallow foundation, railway tracks and Buckingham Canal slowed down construction. There was a thick layer of rock, under a layer of loose soil below the road level, which had to be cut and covered with curved concrete slabs that formed the rings of the tunnels. The concourse level was built around a different type of loose soil, while the upper and lower decks were built on rocks. The mixed soil strata drastically reduced the average speed of tunnel boring on the stretch.
At one point, engineers took more than six months to excavate a 300 m stretch between Rajiv Gandhi Government General Hospital and Chennai Central due to rocky soil condition. Engineers did not apply more pressure while drilling through the rocks as it would have affected the weak structures as well as heritage buildings on the road.