First TBM under Delhi metro's Phase-4 project being lowered

The lowering of the first-ever tunnel boring machine (TBM) under Delhi Metro's Phase-4 has started at Vikaspuri on the Janakpuri West–RK Ashram Marg corridor, officials said on Thursday.

The work on Phase-4 had begun in December 2019 with a groundbreaking ceremony but it was hit after the outbreak of COVID-19 in March.

As part of the tunnelling drive, two tunnels (for up and down movement) of a length of 1.4 km will be bored between Vikaspuri and Krishna Park Extension.

The tunnelling work with the TBM is expected to start next month, after the lowering and assembling of the giant 73 metre long machine is completed. These tunnels will be located between the Janakpuri West and Krishna Park Extension stations of the corridor.

The tunnelling will start from Vikaspuri area in continuation of the Magenta line tunnel that has already been constructed for the current operational stretch of Botanical Garden-Janakpuri West corridor.

The tunnel will be constructed approximately at a depth of 14 to 16 metres. About 2,040 concrete rings will be installed in these tunnels. Each tunnel will have an inner diameter of 5.8 metres. The entire tunnelling work on this stretch is expected to be completed in about 15 months. The alignment of the tunnel will be along the Outer Ring Road.

"As part of the Phase-4 work approved so far, about 27 kilometres of underground lines will be constructed. The Janakpuri West-RK Ashram Marg corridor will have underground sections of 7.74 kilometres in total," a senior DMRC official said.

A TBM is a machine used to excavate tunnels with a circular cross-section through a variety of soil and rock strata. They can be designed to bore through anything from hard rock to sand.

TBMs have revolutionised the way tunnelling work is done all over the world as tunnels can be bored without disturbing the buildings and other structures on the surface, they said. TBMs are especially useful for underground tunnelling work in congested urban areas.

The DMRC has been using TBMs for its tunnelling work since Phase-1. In Phase-3, when about 50 km of underground sections were built, about 30 TBMs were pressed into service in the national capital, they said.

Under the approved segment of Phase-4, 61.679-km of new metro lines shall be constructed across three different corridors comprising 45 metro stations. These new sections shall provide inter-connectivity among the already operational lines of the Delhi Metro.

According to the government, the Mukundpur-Maujpur, RK Ashram Marg-Janakpuri West and Aerocity-Tughlakabad corridors were approved by the Cabinet.