DMRC developing over 40-km new underground corridors

The Delhi Metro Rail Corporation (DMRC) is developing more than 40 kms of new underground corridors as part of its Phase 4 expansion, which constitutes around 50 per cent of the total lines being developed across five different corridors, according to a senior DMRC official.

It is constructing a total of 27 underground stations in Phase 4. The DMRC has already completed a small underground section from Janakpuri West to Krishna Park of about two kms. This is an extension of the Magenta Line, the official said.

The Delhi Metro is constructing 40.109 kms of new underground corridors as part of its Phase 4 expansion, under which about 86 kilometres of new lines are being laid across five different corridors.

This is a major engineering challenge since the underground corridors are passing through a variety of strata such as crowded residential as well as commercial areas in Sadar Bazar, Nabi Karim, Mehrauli Badarpur Road, Ajmal Khan Park, New Delhi, etc., he said.

Generally, DMRC constructs underground metro stations using conventional cut-and-cover technology while the tunnels are built with the help of tunnel boring machines (TBM), the officer 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, he stated.

A small section on the Aerocity-Tughlakabad corridor near Tughlakabad will also be built using the NATM (New Austrian Tunnelling Method) technology. This method of tunnelling has also been used earlier by the DMRC with great success, the officer 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 kms of underground sections were built, about 30 TBMs were pressed into service in the national capital, he said.

At present, seven different tunnelling drives have been completed across the Phase 4 corridors and nine drives are in progress at different locations.