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Delhi Metro Rail Corporation (DMRC) has successfully built a new underground tunnel at Pulbangash, right below the already running Red Line of the Delhi Metro. This tunnel is part of the upcoming Janakpuri West-RK Ashram Marg corridor, which will extend the Magenta Line. The construction took place between Pulbangash
and Sadar Bazar stations, and remarkably, trains on the busy Red Line above continued to run every day without any stoppage.
Operation Work
According to Anuj Dayal, the principal executive director of corporate communications at DMRC, this task was extremely challenging. The Tunnel Boring Machine (TBM) had to dig carefully beneath the elevated tracks on which Red Line trains operate. Open foundations support the Red Line viaduct and include a balanced cantilever span, making the structure sensitive. Digging a tunnel under such a setup requires very high engineering safety standards to avoid any risk to the existing metro line.
To make the tunnelling safe, DMRC used several specialised techniques. One major step was strengthening the soil around the Red Line pier. Engineers implemented a grouting method known as TAM (Tube-a-Manchette). In this process, 180 small boreholes were drilled around the pier. Through these boreholes, high-strength cement grout was injected to make the soil firm, fill up empty spaces, and increase its capacity to hold heavy loads. This ensured that the Red Line structure remained stable during tunnelling.
DMRC also installed several monitoring instruments to track ground movement, pier condition, and the safety of nearby buildings in real time. Skilled personnel worked around the clock to monitor these readings and respond quickly if required. The down-line tunnel on this stretch has now been completed, while work on the up-line tunnel is still underway.
