RailEnquiry

NEW DELHI: If you've been wondering about the kilometres of dug-up roads in the city, here's the reason: Delhi Metro is gearing up to construct 74 tunnels in phase III of its network. A record 33 tunnel-boring machines will work to construct the tunnels. While three tunnels in the Central Secretariat-Mandi House section are already ready, the rest are expected to be completed by mid-2015."The use of 33 tunnel-boring machines will be among the highest number of TBMs ever used in any urban centre at the same time in any part of the world. In phase II, when 34.89kms of underground corridors were built, we had used 14 TBMs," said a Metro spokesman.In phase III, Delhi Metro Rail Corporation will have underground corridors of 53km with 34 underground stations spread across three corridors—Mukundpur-Shiv Vihar, Janakpuri-Botanical Garden and Central Secretariat-Kashmere Gate.The tunnels will go through challenging terrains, say officials. "From corridors going under railway tracks and highrise buildings to flyovers, engineering challenges will be many. For instance, four stretches will go over existing corridors, which has never happened before.," added the DMRC official.The longest stretches will be at three points—South Extension to Lajpat Nagar (1.56km), Palam to the ramp located before Sadar Bazaar (1.5km) and Dabri More to Dashrathpuri (1.4km).

Also, for the first time, four different tunnel stretches will pass below existing underground Metro stretches, posing a major construction challenge, say officials. "During phase II, there was only one such instance at Connaught Place, where a 45m-deep tunnel was constructed for Airport Metro Express below Rajiv Chowk station," said the spokesman. In phase III, four such stretches will be at INA, the domestic airport, Hauz Khas, and Mandi House.

The tunnels will also cross existing corridors at 14 different points, including four points where it will cross elevated viaducts. "Two elevated Metro viaducts have not crossed each other so far anywhere in the network," added the DMRC spokesman. These are at the domestic airport, Hauz Khas, Kalkaji and Mandi House.