The Delhi Metro Rail Corporation (DMRC) is developing more than 40 kilometers 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 kilometres. This is an extension of the Magenta Line, the officer said.
The Delhi Metro is constructing 40.109 kilometres 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, the Mehrauli Badarpur Road, Ajmal Khan Park, New Delhi etc., he said.
Generally, DMRC constructs the 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 technology (New Austrian Tunnelling Method). 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 kilometres of underground sections were built, about 30 TBMs were pressed into service in the national capital, he said.
Currently, seven different tunnelling drives have been completed across the Phase 4 corridors and nine drives are in progress at different locations.”While the Aerocity-Tughalakabad corridor will have about 19 kilometres of underground corridor, the Janakpuri West-RK Ashram Marg corridor will have about nine kilometres of underground sections. The Inderlok-Indraprastha corridor will have over 11 kilometres of underground lines. The Majlis Park-Maujpur and the Lajpat Nagar-Saket G Block sections will not have any underground stations,” the officer said.
DMRC is monitoring the tunnelling work closely and necessary instrumentation has been done to ensure that the condition of the buildings above are regularly monitored, he added.
