Delhi Metro completes high-risk tunnel beneath Pulbangash Red Line with services running

The Delhi Metro Rail Corporation (DMRC) has completed a technically complex tunnelling operation under the operational Red Line at Pulbangash without disrupting train services, officials said on Sunday.

The tunnel forms 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 operate even as the tunnel boring machine (TBM) worked directly below the elevated viaduct.

The corporation said the Red Line structure at the site rests on open foundations with a balanced cantilever span, making the operation particularly sensitive. Engineers noted that tunnelling beneath such a structure required extraordinary safety measures.

A detailed ground-strengthening plan was implemented around the existing pier using the TAM (Tube-a-Manchette) grouting technique. As part of this, 180 boreholes were drilled around the pier and filled with high-strength cement grout to stabilise the soil, fill voids and prevent settlement during tunnelling, the DMRC said.

An extensive instrumentation system was also deployed to monitor ground movement, pier behaviour and the condition of nearby buildings in real time.

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

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