The construction of Delhi Metro's two underground parallel tunnels was completed here Tuesday, a statement said.
The drilling of one of the tunnels began in December 2013 and the other in January this year using two tunnel boring machines (TBM) named "Riddhi" and "Siddhi", the Delhi Metro Rail Corporation (DMRC) said.
"The two TBM's emerged at the Dabri Mor station after boring 1.2 km-long twin tunnels which have been constructed at a depth of 16.5 metres and have an internal diameter of 5.8 metres. These are the first tunnels to be completed on this corridor," the DMRC said.
"This is the first occasion when twin tunnels have been completed together in any metro project in the country," it added.
According to DMRC, the construction was a "major engineering challenge" as the tunnels passed underneath thickly populated residential and commercial areas and needed "extensive geotechnical instrumentation and monitoring".
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The tunnels are part of the 36-km-long Janakpuri West - Botanical Garden corridor under phase three which is expected to be operational by 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 to be used.
At present, about 28 TBMs are engaged in tunnelling works in different parts of Delhi as compared to 14 TBMs used in phase two.
