A major milestone in DMRC’s Phase 4 work was achieved today as the first tunnel boring machine (TBM) of this phase started its drive to bore a 1.4 kilometre long tunnel from Vikaspuri to Krishna Park Extension on the Janakpuri West – R K Ashram Marg corridor in the presence of DMRC’s Managing Director, Dr. Mangu Singh and other senior officials. Two parallel circular tunnels for up and down movement will be constructed on this stretch which is a part of the 2.2 kilometre long underground section from Janakpuri West to Keshopur. The lowering and assembling process of this giant 73 metre long machine was started in October last year.The tunnelling has started from the Vikaspuri area in continuation of the Magenta line tunnel that has been already constructed for the presently operational 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 12 month’s time. The alignment of tunnel runs along the Outer ring road and below the multi-storied built up structures.The tunnel will be built up with proven technology of EPBM (Earth pressure balancing method) with concrete lining made up of precast tunnel rings. The tunnel rings are being cast at the fully mechanized casting yard setup at Mundka. These concrete segments are cured with steam curing system to achieve early strength. This TBM will be able to carry out tunnelling up to 10 metres per day.All necessary safety precautions are being taken while constructing the tunnel below the built up structures by monitoring the ground movements with highly sensitive instruments fixed on the nearby structures. After completion of tunnelling, this machine will be taken out from retrieval shaft being built with Krishna Park Extension underground station. 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 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 now tunnels can be bored without disturbing the buildings and other structures on the surface. TBMs are especially useful for underground tunnelling work in congested urban areas. 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.