For the first time in India, the construction work of two parallel tunnels were completed together at Dabri Mor, with two Tunnel Boring Machines (TBMs) breaking through today after boring twin tunnels from Janakpuri West to Dabri Mor on the Janakpuri West – Botanical Garden corridor of Phase 3.
The two TBMs named ‘Riddhi’ and ‘Siddhi’ emerged out at the Dabri Mor station after boring 1.2 km long twin tunnels. While one of the TBMs was inserted in December last year, the other TBM had started work in January earlier this year. These are the first tunnels to be completed on this corridor.
The tunnels have been constructed at a depth of 16.5 m and the internal diameter of the tunnels is 5.8 m. The casting of the segments has been done at the Dwarka Casting Yard.
This is the first occasion when twin tunnels have been completed together in any Metro project in India. The decision to go for a twin TBM breakthrough was taken since both the TBMs were progressing almost simultaneously. The first such instance of a twin breakthough had happened during work on the 8.6 km long Toronto-York Spadina subway extension in the year 2002.
The construction of these tunnels was a major engineering challenge as they passed below thickly populated residential as well as commercial areas consisting of schools, temples, hospitals etc. Extensive geotechnical instrumentation and monitoring was done to ensure the safety of the structures above. Various monitoring instruments like Inclinometers, Magnetic extensometers, Piezometers, Rod extensometers, Precise level markers, Bi-Reflex targets, Crack Meters etc were used for the purpose.
This tunnel is a part of the 36 km long Janakpuri West – Botanocal Garden corridor of Phase 3 under which about 21 km of underground lines are being built. This corridor is expected to be operational in the year 2016.
As part of its third phase of expansion, DMRC is slated to construct about 53 km of underground lines for which 35 TBMs are expected to be used. Presently, about 28 TBMs are engaged in tunneling works in different parts of the national capital. In Phase 2, 14 TBMs were used for the construction of tunnels.
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