NEW DELHI: In a major milestone for the Delhi Metro, the urban transporter on Friday achieved the completion of its first-ever tunnelling stretch under Phase-IV project of its network, officials said.
This was achieved at Krishna Park Extension on the Janakpuri WestR K Ashram Marg corridor with a tunnel boring machine (TBM) breaking through after boring a 1.4 km-long tunnel, they said.
The work on Phase-IV had begun in December 2019 with a groundbreaking ceremony but it was hit after the outbreak of COVID-19 in March 2020.
The lowering of the first-ever TBM under the Phase-IV project had started at Vikaspuri on the Janakpuri WestR K Ashram Marg corridor in October 2020, and following the initial drive, the main tunnelling had started early 2021, officials said.
As part of this 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, officials had then said.
"The main tunnelling work on this stretch was started in April this year after completing the initial drive. Despite the many constraints posed by the COVID-19 pandemic, work was continued and this major milestone could be achieved," the Delhi Metro Rail Corporation (DMRC) said in a statement.
This tunnel breakthrough using a mammoth 73 m-long TBM was achieved today in the presence of DMRC's Managing Director, Mangu Singh and other senior officials, it 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.
This new tunnel is a continuation of the earlier Magenta Line tunnel that was already constructed for the 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 metre, the officials said.
The alignment of tunnel runs along the Outer Ring Road and below multi-storied built-up structures, they said. Two parallel circular tunnels for up and down movement are being constructed on this stretch which is a part of the 2.2 km-long underground section from Janakpuri West to Keshopur.
Tunneling work on the other parallel tunnel shall commence soon, the statement said.
The tunnel has been built with the proven 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 mechanised casting yard setup at Mundka. These concrete segments were cured with steam curing system to achieve early strength, it added.
All necessary safety precautions were taken while constructing the tunnel below built-up structures by monitoring the ground movements with highly sensitive instruments fixed on the nearby structures, the officials said.
As part of the Phase-IV work approved so far, about 27 km of underground lines will be constructed.
The Janakpuri WestR K Ashram Marg corridor will have underground sections of 7.74 km in total, they said.
TBMs are especially useful for underground tunnelling work in congested urban areas.
DMRC has been using TBMs for its tunnelling work since Ph-I. In Ph-III, when about 50 km of underground sections were built, about 30 TBMs were pressed into service in the national capital, the DMRC said.
Under approved segment of Phase-IV, 61.679-km of new metro lines shall be constructed across three different corridors comprising 45 metro stations. These new sections shall provide interconnectivity among the already operational lines of the Delhi Metro.
According to the government, the Mukundpur-Maujpur, R K Ashram-Janakpuri West and Aerocity-Tughlakabad corridors were approved by the Cabinet.