With 1.4 Km-Long Tunnel, First Tunneling Stretch For Delhi Metro 4th Phase Completed

The tunnel breakthrough using a 73 metre long TBM was done on December 31

The first-ever tunnelling stretch of Delhi Metro’s fourth phase was completed at Krishna Park Extension on the Janakpuri West – RK Ashram Marg corridor with a tunnel boring machine (TBM) breaking through after boring a 1.4 kilometre long tunnel. The main tunnelling work on this stretch began in April last year after completing the initial drive. The tunnel breakthrough using a 73 metre long TBM was done on Friday, according to details shared by metro operator Delhi Metro Rail Corporation (DMRC).

Two parallel circular tunnels for up and down movement are being constructed on this stretch which is a part of the 2.2 kilometre long underground section from Janakpuri West to Keshopur. The new tunnel is a continuation of the earlier Magenta line tunnel that was already constructed for the presently operational Botanical Garden – Janakpuri West corridor.

The tunnel has been constructed approximately at a depth of 14 to 16 metres. Over a thousand rings have been installed in the tunnel. It has an inner diameter of 5.8 metres. The alignment of the tunnel runs along the Outer ring road and below the multi-storied built-up structures.

The tunnel has been built with the technology of EPBM (Earth pressure balancing method) with concrete lining made up of precast tunnel rings. The tunnel rings have been cast at the fully mechanized casting yard setup at Mundka. These concrete segments were cured with steam curing system to achieve early strength, according to DMRC.

As part of the Delhi Metro network’s Phase IV work approved so far, about 27 kilometres of underground lines will be constructed. The Janakpuri West – RK Ashram Marg corridor will have underground sections spread across 7.74 kilometres in total.

A tunnel boring machine is 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. These machines have revolutionised the way tunnelling work is done all over the world as now tunnels can be bored without disturbing the buildings and other structures on the surface.

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