New Delhi [India], December 1 : The Delhi Metro Rail Corporation (DMRC) has achieved a significant engineering milestone by successfully constructing an underground tunnel beneath the operational Red Line at Pulbangash, without halting train services even for a single day.
The tunnel is part of the Janakpuri West-RK Ashram Marg extension of the Magenta Line under the Phase IV expansion.
In an update shared on X, DMRC wrote, "This tunnelling work between the Pulbangash and Sadar Bazar stations was especially challenging, as trains on the busy Red Line above were not halted for even a single day, even as the Tunnel Boring Machine (TBM) carefully constructed the tunnel below the elevated viaduct on which trains were operational. Moreover, the Red Line viaduct here stands on open foundations with a balanced cantilever span. Tunnelling beneath such a structure required extraordinary engineering precautions to ensure its safety."
To ensure structural stability, engineers implemented several specialised measures. "A detailed strategy was adopted to strengthen the area around the pier of the Red Line. A grouting programme called TAM (Tube-a-Manchette) was implemented. According to this technology, 180 TAM boreholes were installed around the pier. After that, high-strength cement grouting was carried out to stabilise the soil, fill the voids, and, in the process, increase the load-bearing capacity. In addition, it was also ensured that all possibilities of settlement of soil during tunnelling were eliminated," the post read.
"Elaborate instrumentation was deployed during the tunnelling work to monitor ground movement, pier behaviour, and building safety on a real-time basis. Some of this equipment was Surface Settlement Markers, Deep Inclinometers, Building Settlement Points, Pier Tilt Meters, Load Cells, and Automatic Total Station (ATC)," the post further stated.
Specialised personnel monitored these parameters round the clock, and all readings remained well within safety limits throughout the operation.
"The construction of the downline tunnel on this section has now been completed. Work on the up-line tunnel is in progress with the same level of precautions and monitoring. This was extremely critical construction work, since the Red Line carries about 7 lakh passengers on average every day. Any disruption to train movements on this line would have caused tremendous inconvenience to the public", the X post said.