Chennai: It is ten at night on the now quite Poonamallee high road. Across the closed gates of Pachaiyappa’s college, a set of workers in gum boots, fluorescent jackets and yellow helmets make a journey into a barricaded zone lit up by halogen lights. They further travel underground , where 15 meters below the ground a machine churns out soil, eating through the belly of the city.
The men and their machines together are in the process of creating one of the most magnificent structures that the city has seen in modern times -the Chennai metro rail. From the road, all that is visible of the barricaded zone are the orange colored gantry cranes, accompanied by loud noises of machines at work. But six meters below the surface at the site of metro’s underground station, it is a different world. While Chennai settles down for the night, men and machines at the metro construction sites work with renewed vigour to build the city’s integrated, rapid transport system.
It is 10 at night and movement on Poonamallee high road has receded to a few vehicles and fewer people. The college opposite has shut down with a lone watchman arranging his seat for a night’s undisturbed sleep, and so have employees at the nearby petrol pump.But a few metres across the road, a shift has just started for a set of workers, who, in gum boots, fluorescent jackets and yellow helmets, make a journey into the barricaded zone lit by halogen lights.
Eighteen metres below the ground, a machine churns out soil, eating through the belly of the city, and creating one of the most magnificent structures that the city is ever going to see - the Chennai metro rail. All that is visible and audible of the barricaded zone from the road are the orange coloured gantry cranes and the loud noise of machines inside. But six metres below the surface at the metro worksite near Pachaiyappa’s college, it is a different world.
The site houses the underground metro station presently under construction. Inside the barricades filled with trucks and construction material, a series of steps lead to the station below. The escalator is yet to come, remarks an official. Steps lead six metres below the ground to the concourse where the ticket vending area will be located. The overbearing smell of concrete fills the air. Pipes and rugged white walls surround the concourse.
The walls around the structure were first made and sunk into the soil even before excavation began. One metre thick and 25 metres deep, the diaphragm walls make a secure structure inside. “Three metres below the ground, water starts coming out when we dig. The diaphragm walls seals the structure and then we begin excavation,” explains Venkata Raman, manager of the site.
The concourse also holds a temporary multipurpose shed with tables, benches and charts on safety precautions. The shed is a place for workers to relax and also for debriefing meetings on the work.After the concourse, another series of stairs lead to the platform below, nine metres further down. The platforms are in various stages of construction. The station will have two platforms, one for the up and the other for the down line train, each emerging from the four tunnels on either side of the two platforms. Work on the up line is almost complete, while on the other, the TBM is working its way in.
Officials posted at the site say that the pace of work is the same, be it night or day. Excavation and station works go on throughout the day. It is only the transportation of the soil from the site that takes place in the night as there are restrictions on the movement of heavy vehicles in the day. Till then, the excavated soil is collected in a large pit. A mini train runs into the platform from one of the unfinished tunnels where the TBM is digging. Called the loco muck skip, it carries three loads, each containing 6 cubic metres of soil, every hour. The loco stands below a gaping hole through which the gantry cranes located on the surface lift up the soil.
Fifteen metres below, the temperature rises drastically, compared to the outside. To make it viable for workers, a cooler runs, maintaining the temperature at 31 degrees Celsius. The large machine is one source of the noise heard outside, working on the same principles as that of an air-conditioner.Through the station, two tunnels move out towards Shenoy Nagar and Kilpauk stations on either side. White coloured and illuminated with tubes, the tunnels look endless. Made of rings of concrete slabs interlocked with each other, the 983-metre-long tunnel towards Shenoy Nagar is almost complete. The Kilpauk tunnel is 900 metres long.
Mobile phone signals work till 50 metres into the tunnel. The signals then shut and walkie-talkies are used. A few months from now, the tunnels will have rail tracks laid and train cars will run through them. Under feet, under roads, houses, city scrapers and parks the Chennai metro train will ferry passengers, creating an engineering marvel.
