The Bangalore Metro Rail Corporation Ltd. (BMRCL) will be achieving a major feat in a day or two when tunnel boring machine (TBM) Helen breaks through the diaphragm wall at the City Railway Station Underground Metro Station.
After this breakthrough, work on laying the track can commence on one of the twin tunnels in the 4.8-km underground network between BRV Parade Grounds and Magadi Road on the East-West corridor of Namma Metro Phase 1.
Tunnelling work was inaugurated at Majestic on May 20, 2011 by the then Chief Minister B.S. Yeddyurappa. Actual burrowing commenced towards BRV Parade Grounds on May 31, 2011 by Helen and on July 21, 2011 by another TBM Margarita. They were to burrow the ‘Up’ track (towards Byappanahalli) and ‘Down’ track (towards Mysore Road Terminal) tunnels.
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The machines took approximately nine and seven months respectively to reach Central College UG station; six and nine months to reach Vidhana Soudha UG station from Central College and 15 and 16 months respectively to reach Cubbon Park UG station from Vidhana Soudha. A third TBM burrowed twin tunnels each 153 metres long between Cubbon Park UG station and BRV Parade Grounds in nine months.
The latest tunnelling work, covering a distance of 256 metres between Majestic and City Railway Station UG station, was commenced by Helen on November 1, 2013. On reaching City Railway Station UG station, the machine would be made to take a ‘U’ turn and burrow in the direction of Majestic.
BMRCL will be taking almost 31 months to complete the ‘Down’ track tunnel while it expects to complete the ‘Up’ track tunnel in the next two months.
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The row over shifting of the statue of Dr. B.R. Ambedkar, which was close to the underground alignment of Vidhana Soudha station, delayed tunnelling work between Vidhana Soudha and Cubbon Park, a distance of 480 metres, which otherwise should have been completed within six months. Also, the machines encountered hard rock during tunnelling in this stretch further delaying the process.
Challenging workEngineers said that tunnelling on the stretch between Majestic and City Railway Station UG station was challenging. On the one hand, it had loose soil and on the other, hundreds of trains were moving atop the tunnelling path. The tunnel has passed beneath at least 17 railway tracks.
Pocket trackBMRCL is also constructing a pocket track between Majestic UG station and City Railway Station UG station. This third track, to be connected through a ‘Y’ junction to the main track, would be used to stable metro trains in the event of a breakdown. BMRCL has already said that trains would run between Byappanahalli and Nayandahalli by September-October while commencing commercial operations depends on safety certifications.