The Delhi Metro Rail Corporation (DMRC) has achieved a major engineering feat by constructing an underground tunnel beneath the operational Red Line at Pulbangash without suspending train services even for a single day. The tunnel forms part of the Janakpuri West–RK Ashram Marg extension of the Magenta Line under Phase IV. In an update shared on X, DMRC highlighted the complexity of the operation, noting that tunnelling between Pulbangash and Sadar Bazar stations was carried out while trains continued to run normally on the elevated Red Line viaduct above. The viaduct at this location stands on open foundations with a balanced cantilever span, requiring exceptional engineering precautions during tunnelling. To ensure structural stability, engineers implemented an extensive strengthening strategy around the Red Line pier. A grouting programme known as TAM (Tube-a-Manchette) was executed, involving the installation of 180 TAM boreholes around the pier. High-strength cement grouting was then undertaken to stabilise the soil, fill voids and enhance load-bearing capacity. DMRC added that every measure was taken to eliminate any risk of soil settlement during tunnelling. Real-time safety monitoring was conducted using advanced instrumentation, including surface settlement markers, deep inclinometers, building settlement points, pier tilt metres, load cells and an Automatic Total Station (ATS). A dedicated team monitored these parameters round the clock, and all readings remained within permissible safety limits throughout the operation. DMRC confirmed that the down-line tunnel on this stretch has now been completed, while work on the up-line tunnel is progressing with the same level of caution and monitoring. With the Red Line carrying around 7 lakh (0.7 million) passengers daily, the corporation emphasised that avoiding service disruption was critical to preventing widespread public inconvenience.