New Delhi, Aug 31 (UNI) Delhi Metro has achieved the third tunnel breakthrough of phase-II with successful completion of a 951 m-long tunnel from INA to Jorbagh late last evening, sources in the Delhi Metro Railway Corporation said today.
Being built on the down line between Central Secretariat and Qutub Minar, the tunnel, work on which started from March 28, 2008, was completed on schedule late yesterday evening with a Tunnel Boring Machine (TBM) emerging at Jorbagh after making the 951 metre-long tunnel from INA, DMRC spokesperson Anuj Dyal said.
This TBM was lowered in INA shaft on February 19, 2008 and after assembly of the TBM below the ground, tunneling was started from March 28, 2008. The tunneling was done 12 metres below the earth surface.
The tunnel passes under the Indian railways track and the Safdarjung flyover. Rail movement was not affected at all during the tunneling process.
A German laser system was used to guide the TBM along its precise alignment. During the tunneling process, about 38,000 cubic metres of earth was excavated. This earth was deposited in the low-lying areas of Sarai Kale Khan.
A total of 791 rings, each 1.2 m. in length, were installed simultaneously along with the tunneling process. Each ring has six segments and these segments and rings are connected by using bolts.
402 bolts have been used on the stretch.
To make the tunnel water-tight, hydrophilic gaskets were used between ring joints. Extensive grouting was done all around the rings to avoid settlement of the ground between the top surface of rings and soil surface.
While this breakthrough was achieved on the down line between Central Secretariat and Qutub Minar, another parallel tunnel is being built on the up line by another TBM which will also achieve its breakthrough in about a month's time by the end of September.
TBMs are manufactured by Herrenknecht of Germany.
CEC-Soma JV is the executing agency for the Race Course - AIIMS stretch.
For Phase-II of the Delhi Metro, DMRC will use 14 TBMs. This is for the first time in any Indian city and perhaps for the first time in any Asian city that so many TBMs will be used simultaneously for building Metro tunnels. The second phase of Delhi Metro will comprise about 30 kms of underground section of which about 16 kms are to be built using TBMs.
UNI AR NY AS1909