The Delhi Metro Rail Corporation (DMRC) on Saturday achieved a major construction milestone in Phase 4 with the completion of an underground tunnel between Chhatarpur and Chhatarpur Mandir Station on the Tughlakabad-Aerocity corridor.

The breakthrough of the Tunnel Boring Machine (TBM) at the Chhatarpur Mandir site of the Delhi Metro took place in the presence of Dr. Vikas Kumar, MD, DMRC and other senior officials.

A TBM broke through this morning at Chhatarpur Mandir Station after boring an 860-meter-long tunnel. This tunnel breakthrough was achieved using a mammoth 97-metre-long TBM. Two parallel circular tunnels for up and down movement have been constructed on this stretch as part of the Aerocity–Tughlakabad corridor. The breakthrough on the other parallel tunnel was achieved on August 21.

This new tunnel has been constructed at an average depth of about 12 meters. About 613 rings have been installed in the tunnel, with an inner diameter of 5.8 meters.

The tunnelling work involved numerous challenges, such as shifting a 66 KV electrical HT line. Additionally, the TBM had to cross below the existing Yellow Line viaduct without disrupting Metro train operations on the Yellow Line.

It has been built using the proven technology of EPBM (Earth Pressure Balancing Method) with a concrete lining made of precast tunnel rings. These tunnel rings were cast at a fully mechanized casting yard set up at Mundka. The concrete segments were cured with a steam curing system to achieve early strength.

All necessary safety precautions were taken during the construction of the tunnel below the existing viaduct and built-up structures. Ground movements were monitored with highly sensitive instruments fixed on nearby structures, ensuring that there was no settlement anywhere.

As part of the Phase 4 work approved so far, 40.109 kilometres of underground lines are being constructed. The Aerocity-Tughlakabad corridor has underground sections totaling 19.343 kilometres.

TBMs are particularly useful for underground tunneling work in congested urban areas.

The DMRC has been using TBMs for its tunneling work since Phase 1. In Phase 3, when approximately 50 kilometres of underground sections were built, about 30 TBMs were deployed in the national capital.