Source : The Hindu Date : 18.06.2009
Delhi Metro achieves another first
Staff Reporter
| Uses new technology in tunnelling work on ‘soft’ soil |
Photo: V. V. Krishnan 
Inside the tunnel: Delhi Metro Rail Corporation workers and engineers after the final breakthrough of tunnelling on its Qutub Minar-Saket stretch in New Delhi on Wednesday.
NEW DELHI: The Delhi Metro Rail Corporation on Wednesday achieved the final breakthrough in tunnelling work on the Qutub Minar-Saket stretch using the New Austrian Tunnelling Method (NATM) on Phase II of its upcoming new Central Secretariat-Gurgaon line.
This is the first time that the new technology has been used on “soft” soil.
According to a senior DMRC official, so far NATM was used in hard rock conditions at the Chawri Bazar station and the Ridge area near Talkatora Garden.
NATM is a technology that is used for tunnelling in rocky areas. The surface is first broken with the help of controlled blasting, the pieces are then removed using machinery, and then concrete lining is done.
“Tunnel construction in soft soil is very tricky as the soil has to be immediately cemented and strengthened to prevent collapse. The Tunnel Boring Machine (TBM) was not used here as the distance was small and lowering the TBM near the Archaeological Survey of India-protected monument could have been difficult and very expensive,” said the DMRC official.
The 185-metre NATM tunnel breakthrough achieved at the South end of the Saket metro railway station is a part of the 1.85-km Qutub Minar-Saket stretch which also covers a cut-and-cover underground tunnel of 1,020 metres and 645 metres elevated section.
Work in this area was difficult as DMRC had to divert an old 247-metre-long, six-metre-wide and five-metre-deep natural storm-water drain which was flowing over the alignment of the NATM tunnel. “All precautions prescribed by the Archaeological Survey of India had to be observed as construction activity was done close to Petheora Rai Ka Kila, a historic monument situated in the vicinity of the Saket metro station,” the official said.
