Inside Delhi Metro's engineering feat: Tunnel dug beneath Red Line without halting services

The tunnel is part of the Janakpuri West-RK Ashram Marg extension of the Magenta Line and connects the Pulbangash and Sadar Bazar stretch.

The Delhi Metro Rail Corporation (DMRC) has completed a technically challenging tunnelling task in its phase four expansion by constructing a tunnel beneath the operational Red Line at Pulbangash without disrupting train services, news agency PTI reported, citing officials.

The tunnel is part of the Janakpuri West-RK Ashram Marg extension of the Magenta Line and connects the Pulbangash and Sadar Bazar stretch.

According to the DMRC, trains on the busy Red Line continued to run throughout the operation, even as the tunnel boring machine (TBM) worked just below the elevated viaduct.

As per the report, the Red Line structure at the site sits on open foundations with a balanced cantilever span, making the task particularly sensitive, it stated, adding that engineers said tunnelling below such a structure required extraordinary safety measures.

DELHI METRO ACHIEVES NEW ENGINEERING FEAT; CONSTRUCTS TUNNEL BELOW OPERATIONAL ELEVATED METRO CORRIDOR WITHOUT DISRUPTING SERVICES

The Delhi Metro Rail Corporation (DMRC) has achieved a unique engineering feat in its Phase 4 expansion work by successfully constructing an… pic.twitter.com/weOCdiu7U2

— Delhi Metro Rail Corporation (@OfficialDMRC) December 1, 2025

A detailed ground-strengthening plan was put in place around the existing pier, including the use of the TAM (Tube-a-Manchette) grouting technique, it said.

As part of this, 180 boreholes were created around the pier and filled with high-strength cement grout to stabilise the soil, fill voids and prevent settlement during tunnelling, the corporation was quoted by the news agency as saying.

The DMRC also deployed an extensive set of instruments to monitor ground movement, pier behaviour and the condition of nearby buildings in real time.

The downline tunnel has now been completed, while the work on the up-line tunnel is continuing with similar precautions, it added.

The DMRC was quoted as saying that the operation was critical as the Red Line carries nearly seven lakh passengers daily, and any disruption could have caused significant inconvenience.