The Delhi Metro Rail Corporation (DMRC) is advancing the construction of over 40 kilometers of underground corridors as part of its Phase 4 expansion, accounting for nearly 50% of the total 86 kilometers of new lines. The ambitious project spans five corridors and includes 27 underground stations, according to a senior DMRC official. Phase 4's underground corridors will traverse densely populated areas such as Sadar Bazar, Nabi Karim, Mehrauli Badarpur Road, and New Delhi, presenting significant engineering challenges. A 2-kilometer underground section between Janakpuri West and Krishna Park, part of the Magenta Line extension, has already been completed. Key corridors with extensive underground stretches include: • Aerocity–Tughlakabad: Approximately 19 kilometers • Janakpuri West–RK Ashram Marg: Around 9 kilometers • Inderlok–Indraprastha: Over 11 kilometers In contrast, the Majlis Park–Maujpur and Lajpat Nagar–Saket G Block corridors will remain elevated. DMRC employs advanced methods like tunnel boring machines (TBMs) and the New Austrian Tunnelling Method (NATM) to navigate urban congestion while minimising surface disruptions. Seven tunnelling drives have been completed so far, with nine more underway. Monitoring systems ensure the structural safety of buildings above tunnelling zones. The construction involves navigating complex urban landscapes and varied soil strata, making it one of DMRC's most challenging engineering tasks. Drawing from its experience in Phase 3, where 50 kilometers of underground sections were completed, DMRC is well-equipped to handle these challenges. Once completed, Phase 4 will enhance connectivity and reduce congestion across Delhi, solidifying the metro's role as a cornerstone of urban transport. (Financial Express)