The Delhi Metro Rail Corporation (DMRC) on Wednesday completed the longest underground tunnel between the Tughlakabad Airforce Launching Shaft and Maa Anandmayee Marg on the Tughlakabad-Aerocity corridor of Phase-IV, an official statement said.

A 105-metre-long tunnel boring machine (TBM) broke through at Maa Anandmayee Marg station this morning, after boring a 2.65-km-long tunnel, the statement added.

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 expected to be achieved in January 2025, it said.

The new tunnel has been constructed at an average depth of around 16 metres and about 1,894 rings have been installed in the tunnel, with an inner diameter of 5.8 metres, it added.

The tunnelling work posed significant technical challenges, including the relocation of a sewer line and navigation through hard rock strata.

The tunnel has been built using the proven Earth Pressure Balancing Method (EPBM) technology, with a concrete lining made of precast tunnel rings, the statement said.

These tunnel rings were cast at a fully mechanised casting yard set up in Mundka. The concrete segments were cured with a steam curing system to achieve early strength, it added.

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

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