New Delhi: Delhi Metro Rail Corporation (DMRC) constructed an underground tunnel at Pulbangash below the already operational Red Line of the Delhi Metro network. This tunnel was constructed as part of the upcoming Janakpuri West–RK Ashram Marg corridor, an extension of the Magenta Line. The tunnel was built between the Pulbangash and Sadar Bazar stations, even as trains on the busy Red Line above were not halted for a single day.“This tunnelling work was challenging as the Tunnel Boring Machine (TBM) carefully constructed the tunnel below the elevated viaduct on which trains were operational. Even the Red Line viaduct stands on open foundations with a balanced cantilever span. Tunnelling beneath such a structure required extraordinary engineering precautions to ensure its safety,” said Anuj Dayal, principal executive director, corporate communications, DMRC.DMRC said several measures were taken to achieve this tunnelling feat. “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 done to stabilise the soil, fill the voids and in the process, increase the load-bearing capacity,” Dayal said. He added that several instruments were installed during the tunnelling work to monitor ground movement, pier behaviour, and building safety in real time.Specialised personnel were deployed round the clock to monitor the readings of this equipment.The construction of the downline tunnel on this section has now been completed with work on the up-line tunnel is in progress.
