Tunnel below a tunnel at four sections of Metro Phase-III

On four stretches in the upcoming phase,the Delhi Metro will have to pass below existing underground Metro tunnels,digging around 40 metres below ground level.

The underground stretch from Sarojini Nagar to INA on the Mukundpur-Yamuna Vihar corridor will pass below the existing underground section of the Jahangirpuri-HUDA City Centre line at INA. The tunnel from domestic airport (T2) to Vasant Vihar on the Janakpuri (West) to Botanical Garden corridor will go below the underground section of the Airport Express Link.

A tunnel between Hauz Khas and Panchsheel Park on the Janakpuri (West)-Botanical Garden corridor will pass below the underground portion of the Jahangirpuri-HUDA City Centre stretch at Hauz Khas. The underground stretch from Mandi House to ITO on the Central Secretariat-Kashmere Gate corridor will pass below the underground section of the Noida-Dwarka corridor at Mandi House.

The DMRC officials said this engineering challenge will be a first for the agency and several tests and technology solutions are being worked out for it. In Phase II,the DMRC had constructed a similar tunnel at Connaught Place for the Airport Metro Express Line,but this time it is being looked at as a bigger challenge as there are four stretches at different locations in the city where the tunneling will go deeper than usual,officials said.

“During Phase-II,there was only one such instance when a new corridor had to cross below an already operational corridor. At Connaught Place,a 45-metre-deep tunnel was constructed for the Airport Express Link below the Rajiv Chowk Metro station,which is currently the deepest point of the Delhi Metro system,” said an official spokesperson of the DMRC.

Usually,Metro tunnels are constructed at a depth of 20 metres; the diameter of a tunnel is usually 5.8 metres. For construction of another tunnel the authorities need to leave a buffer space of 20 metres between the two.

“When an underground tunnel is dug below an existing tunnel,a certain distance has to be maintained. If this distance is not proper,pressure could be created between the two tunnels. During construction,the existing tunnel is constantly monitored to see if cracks are developing,” the spokesperson said.

At present,preliminary tests and surveys related to the quality of soil and presence of utilities ducts are being conducted on these sections.