The Delhi Metro Rail Corporation (DMRC) has completed tunneling on its deepest underground section in Phase 4, marking a tunnel boring machine (TBM) breakthrough at IGNOU station.

Part of the Aerocity-Tughlakabad Corridor (Golden Line), the tunnel runs from Chhatarpur Mandir to IGNOU at an average depth of 27 meters, reaching up to 39 meters. The parallel tunnel was finished on February 25, 2025, completing both tracks. Using the Earth Pressure Balancing Method (EPBM), DMRC installed 1,048 precast concrete rings with a 5.8-meter internal diameter, overcoming challenges like steep slopes, mica, and hard rock, which required replacing a damaged screw auger.

Chief Minister Rekha Gupta and Environment Minister Manjinder Singh Sirsa attended the milestone event. The 40.1-km Phase 4 expansion includes 19.3 km of underground sections, with DMRC achieving three TBM breakthroughs in the past month, ensuring rapid progress with minimal surface disruption.