CIMFR Scientists make Bangalore Metro tunneling works Safer – Tunnels to be ready shortly

Nagpur (NGP)/Bangalore (SBC): CIMFR Scientists from Nagpur made a quiet contribution in making of Bangalore Metro Rail Project safer. Scientists at the Nagpur regional office of Central Institute for Mine and Fuel Research Institute (CIMFR) have used a controlled blasting technique that minimizes the ground vibrations and reduces the speed of fly rocks in open blasting making the entire operation safer not only for the personnel at the site but also for nearby buildings and structures.

Ramulu More, principal scientist from CIMFR who led the team, told that the controlled blasting technique was always there but it was never used on a mass scale for and in open blasting. ‘We have modified the technique to control ground vibrations and also reduce the speed at which the rock pieces fly into the air. The Delhi metro rail project used an imported method of controlled blasting which was very expensive. Our method reduces the cost by one third and makes the entire process safe,’ he said.

Controlled blasting, as followed in developed world, uses fool-proof covering of holes in which explosives are filled before blasting. It uses a three layered of muffling of mesh made of rubber connected to wire ropes. CIMFR technology called as ‘bottom hole decking technique’ has been used at City Market, Chikpet and Majestic stations of Bangalore metro. Work on the first station is completed and on the second one, it is nearing completion. At Majestic, work is still on.

Metro in Bangalore consists of both elevated and underground sections. Tunnels are being made using tunnel boring machines while the underground stations are excavated by drilling and blasting method, which is bound to generate environmental effects like ground vibrations, air blast and fly rock. Keeping in view of habitats and structures, it was decided to go for rock breakers and chemical expansion based rock excavation. But nothing could result in effective rock breakage and hence open blasting method, considered to be the most dangerous, had to be used. Rock excavation was carried out for the north-south corridor at City Market, Chikpet and Majestic stations. The distances from various sensitive and critical structures to periphery of these station areas are just 10 to 25m.

In view of such close proximity, it was a great challenge to conduct blasting without disturbing the surrounding structures and running traffic. The work is being carried out by M/s Coastal-TTS JV, for whom CIMFR is the technical consultant. CIMFR provided technical guidelines for blasting and monitoring of ground vibrations, air overpressure and fly rock during rock excavation at underground stations.

The sensitive and critical structures at City Market Station included children and maternity hospitals at 10m distance and historical museum at 100m distance. The sensitive and critical structures at Chikpet station included a temple at 15m and mosque at 10m. Also there are structures like tall buildings and residential structures at Chikpet station at 20m. Running traffic is the most sensitive part at Majestic Station and zero tolerance is the limitation for fly rock as the habitats are well in the vicinity. The single layer muffling used by CIMFR restricted the fly rock distance to within 10m.

The CIMFR team, besides more who is the project coordinator, comprised P B Choudhury, B K Jha and A K Soni. The team had an overall guidance from Amalendu Sinha, CIMFR director at Dhanbad.

One Namma Metro tunnel will be ready shortly – it is part of the 4.8-km underground network between BRV Parade Grounds and Magadi Road

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.

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.

Shifting of statue

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 work

Engineers 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 track

BMRCL 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.

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