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Metro Takes A Plunge On Way To IGI
January 28, 2009

The Connaught Place station on Airport Express line will be 40 metres underground, below the two lines at Rajiv Chowk

After constructing the second deepest Metro station in the world at Chawri Bazaar, a good 25 metres below the surface, Delhi Metro is bracing up to perform yet another engineering marvel. The tunnel for the Airport Express Line is going under the existing Rajeev Chowk metro station at a depth of 40 metres. The lowest point of Delhi Metro so far, constructing the tunnel is going to be a huge challenge for Delhi Metro Rail Corporation (DMRC).

Like Chawri Bazaar, the new tunnel will also be constructed using a Tunnel Boring Machine (TBM) and will be equivalent to about 12 stories under the road level. The tracks for the highspeed link will come up under the existing station area as well as tracks for existing Line 3 (Dwarka to Indraprastha) and Line 2 (Central Secretariat to Vishwavidyalaya).

‘‘The tunnel had to be constructed at such a depth because we had to go under the foundation of the existing Metro station. At such low levels, the underground water pressure is very strong and can even blow up an entire station. A good foundation is created with deep tension piles to secure it. One needed to ensure that the tunnel doesn’t disturb this,’’ said a DMRC spokesperson.

The process will be monitored round the clock and several sophisticated guages and gadgetry are being installed on the tracks of the two existing Metro lines, the Rajeev Chowk station, and buildings in CP to ensure that there is no settlement. Even the TBM being used to drill at such a depth is differently designed to be able to withstand the high underground pressures. The TBMs have got retractable cutter heads which automatically change for rock and soil cutting. The tunnel will maintain a depth of 40 metres for a stretch of about 250 metres and the construction will take about a month.

The tunnel also passes directly under several heritage structures including Minto Bridge, Gol Dak Khana and old buildings of Connaught Place, which has posed another challenge before engineers. As the TBM cuts through soil and rock under the surface, the corporation needs to ensure that the vibrations don’t cause any cracks or disfigurement in the heritage structures. For this, each of these buildings will also be fitted with gauges and crack meters.

The tunnelling process has already been completed successfully under Minto bridge on January 12 this year without any impact on the structure, which is about 100 years old. DMRC had to obtain a clearance from the commissioner of railway safety before initiating the tunnelling process under it. The tunnel here is at a depth of about 25 metres. The tunnelling process for the stretch has already started and two TBMs have been lowered from shafts created near New Delhi station. The first tunnel is ready upto the Minto Road-Connaught Circus intersection. Over the next month, it will drill below the heritage structures of Connaught Place and reach the deepest point by March. ‘‘The entire tunnelling process will be complete by August this year,’’ the spokesperson added.

Modelled on the lines of London’s popular Heathrow Express, the Airport Express Line will start at New Delhi Railway Station and go to Dwarka via IGI airport. On the way, there will be stops at Shivaji Terminus, Dhaula Kuan and National Highway-8. The new service will be operational by July 2010 and promises a superfast ride from CP to IGI, in just 18 minutes. The trains will be different from the existing Delhi Metro ones, with five star facilities. The fare has been fixed at a maximum of Rs 150 till IGI and an additional Rs 30 to Dwarka, with a provision for monthly passes for airline staff and frequent fliers. This is the first Delhi Metro line to come up on a PPP model.

Useful information about IGI Express Line

• Length - 22.7 km — 7 km elevated, 15.7 km underground
• Stations - 6 — New Delhi Railway Station, Shivaji Terminus, Dhaula Kuan, NH-8, IGI Airport and Dwarka sector 21
• City Airport Terminal stations - New Delhi Railway station and Shivaji Terminus
• Train Speed - 135 kmph
• Estimated Journey time - 18 mins (from NDRS to IGI)
• Frequency - 10 mins in 2010; 6 mins by 2021
• Completion deadline - July 2010
• Expected ridership - 42,500 by 2010; 86,000 by 2021
• Construction cost - Rs 3,800 crore approx
• Number of tunnel boring machines to be used - 4
• Lowest point on tunnel - 40m
• Stretch where 40m depth maintained - 250m
• Maximum fare - Rs 150 (up to IGI), Rs 30 (IGI to Dwarka)
• Business Model - Public-private partnership (PPP) with DMRC developing the civil structures and later playing the watchdog for 30 years

Source: Times of India