New Delhi, February 23 As the Chennai-Jammu-Andaman Express, Paschim Express, and other trains passed through the Sadar Bazar railway station on Sunday, passengers were unaware that, 15 meters below, a tunnel boring machine was digging a 6.35-meter tunnel for the upcoming Delhi Metro corridor.
This was an unprecedented challenge that the Delhi Metro Rail Corporation (DMRC) overcame when it completed tunneling work beneath an operational railway line, a flyover, and the elevated Red Line Metro corridor – all within a distance of 203 meters.
"This is a rare achievement. We accomplished it without disrupting train, metro, or road traffic," said Satya Narayan Kunwar, Project Manager, Afcons Infrastructure.
We faced this situation for the first time while digging a tunnel using a tunnel boring machine for the Delhi Metro. The distance between the tunnel ceiling and the railway track is only 15 meters, he said.
"While several trains, each weighing between 800 and 1,200 tonnes, crossed the railway line, the tunnel boring work continued without any hindrance as we used advanced technologies to safely assess the overburden and ensure the safety of train operations," Kunwar added.
Officials said that services on the DMRC's Red Line, vehicular movement on the busy Rani Jhanshi flyover, and railway operations continued safely even as tunneling progressed below for the upcoming Janakpuri West-RK Ashram Metro corridor.
This was achieved through rigorous instrumentation, monitoring, and strict adherence to safety protocols, they added.
According to officials, though it took 117 days to complete only 203 meters of tunneling, the major delay was caused by obtaining approvals from various authorities, as it was an extremely complex scenario.
"The meticulous planning and close coordination among Afcons, DMRC, Indian Railways, and other stakeholders have ensured that tunneling activities proceed smoothly without disturbing the live traffic on the elevated metro corridor, flyover, or railway line above," a railway official said.
As the entire corridor has been divided into several packages, this complex situation arose in the DC-05 package. This package also includes 11.4 km of TBM tunneling, six underground stations such as Derawal Nagar, Ghanta Ghar, Pulbangash, Sadar Bazar, Nabi Karim, and RK Ashram Station, among other crucial construction works.
Talking about the complex geological conditions, Afcons said that the project alignment presents extreme geological challenges, with 50 per cent passing through rock strata and 50 per cent through soil.
"The twin tunnels include approximately 3 km through rocky strata of Grade 4 and above, and another 3 km through soil strata where the water table is almost at ground level. The varying geology required the adoption of multiple construction methodologies," Kunwar said.
DMRC officials said that the alignment passes through one of Delhi's most densely populated areas, with nearly 3,500 buildings located within the influence zone – many of them in dilapidated or distressed condition.
"The alignment passes through extremely congested areas with difficult access for pre-emptive mitigation during tunneling. We adopted well-planned instrumentation and monitoring systems for tunnel and station works.
"Extensive grouting, structural support, and strengthening of buildings have been undertaken to ensure safe tunnelling and station construction throughout the project," Kunwar said.
Once completed, this section of the corridor is expected to significantly enhance connectivity and improve transit efficiency in one of the city's most congested areas, strengthening Delhi Metro's expanding Phase IV network and easing daily commutes for thousands of residents.