Union Housing and Urban Affairs Minister Manohar Lal on Thursday said Delhi Metro will make a big record as by December this year its network will become the longest for a single city.

The Union Minister said that at present, the largest Metro line in a single city is in New York, and it is 399 km long, while currently, Delhi Metro’s operation network is 394 km long.

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“With the opening of the 12-km stretch Aerocity to Tughlakabad, Golden line in December 2025, Delhi Metro’s network will become the largest single network in the world,” said Manohar Lal at a tunnel breakthrough event for Golden line, held at Vasant Kunj metro station.

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

Manohar Lal said Metro networks are operational or projects are in the pipeline across 29 states of the country, and the network length today is around 1,000 km, which is the third-largest in the world.

“Very soon we will become a country with the second-largest Metro network, behind China,” he said.

The breakthrough of the Tunnel Boring Machine (TBM) at the Vasant Kunj Station site of the Delhi Metro took place in the presence of Minister Manohar Lal and his deputy MoS Tokhan Sahu.

A Tunnel Boring Machine (TBM) broke through this morning at Vasant Kunj Station after boring a 1550-metre-long tunnel. This tunnel breakthrough was achieved using a mammoth 91-metre-long TBM. Two parallel circular tunnels for up and down movement are being constructed on this stretch as part of the Aerocity–Tughlakabad corridor. The breakthrough on the other parallel tunnel is planned to be achieved in June ’25.

This new tunnel has been constructed at an average depth of approximately 23.0 metres (min depth 15.7 mtr & max. 30.2). About 1107 rings have been installed in the tunnel, with an inner diameter of 5.8 meters.

The tunnel 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 mechanised casting yard set up at Mundka. The concrete segments were cured with a steam curing system to achieve early strength.

The tunnelling drive for this tunnel started on 30 October 2023, and challenges of steep gradient along with varied geology comprising mica and hard rock were encountered.

All necessary safety precautions were taken during the construction of the tunnel below the existing 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.

A TBM is a machine used to excavate tunnels with a circular cross-section through various soil and rock strata. They can be designed to bore through anything from hard rock to sand. TBMs have revolutionised tunnelling work worldwide, enabling tunnels to be bored without disturbing buildings and other surface structures.

TBMs are particularly useful for underground tunnelling 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.