Tunnelling on 176-metre Metro line using NATM.

The Delhi Metro Rail Corporation (DMRC) was faced with a challenge while constructing a tunnel on the Janakpuri West-Botanical Garden corridor to pass below the presently operational Nehru Place-Kalkaji elevated section of the violet line.

The tunnel was to pass below piers 135 and 136 of the violet line which are 28 metres apart.

As it would have been impossible to construct twin tunnels within such a short space, the DMRC decided to construct a single tube twin tunnel through which both the tracks would pass.

The New Austrian Tunnelling Method (NATM) is being used to carry out tunnelling work on a stretch of 176 metres instead of using a Tunnel Boring Machine (TBM) that would have been more time-consuming and inconvenient.

The DMRC has earlier used this technology that involves tunnelling through mechanical excavation or controlled blasting at Chawri Bazar (phase 1), Buddha Jayanti Park and Saket (Phase 2), and at other sites where tunnelling through TBM is not possible.

The NATM tunnel starts right from the Kalkaji Mandir metro station, which will have interchange facility with the presently operational Kalkaji Mandir metro station of the violet line.

The Kalkaji Mandir metro station will be an important interchange hub after the completion of phase 3 with direct connectivity to Faridabad and Noida. The construction of the tunnel began in September 2013 and is expected to be completed by June 2015. At present, out of the 176 metres, part construction of 158 metres has been completed.

THE HINDU