geology report

Namma Metro

Bangalore

BMRCL

geological investigation

According to the geologist hired by us, the rocks of Phase II underground section are easier to tunnel than those in Phase I. We have also used the failure data of Phase I to prevent a repeat of those failures – BMRCL official

Bengaluru

underground corridor

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Bengalureans

Bengaluru top stories, February 6, 2020:Russell Market to get a makeover 02:00

shows 34% of hard rock in the city’s soil. Willbe able to cut through the rocks in time and rescue B’lureans stuck in traffic above?While tunnelling the underground section of the Phase-1 of Namma Metro, theMetro Rail Corporation Ltd () came up against hard rock which caused long delays in the getting the project up and running.Now in the tunnelling work for Phase II, ahas revealed that BMRCL is up against the same challenges and it is now caught against a rock and a hard place. The geological investigation conducted by the Bangalore Metro Rail Corporation Ltd (BMRCL) has revealed that 34% of the 14-km underground stretch is hard and weathered rock, while 46% is soft soil. The remaining 20% of the stretch comprises mixed geology conditions.Other challenges that BMRCL will have to deal with are the dense population and old buildings along the stretch of underground line between Shivajinagar and Nagawara. In Phase I, several buildings had suffered cracks due to neling. Residents fear that similar problems could occur in Phase II as well.Going by past experience, the Metro is likely to take about five years to complete the project that runs between Nagawara and Dairy Circle. The underground stretch (Reach 6), which passes through the heart of, is part of the 72-km Phase II network and is the costliest stretch. In the future, the stretch will connect Kempegowda International Airport to the central part of Bengaluru.“We are using slurry-based machines similar to the ones used in Phase-1 on the East-West. These Tunnel Boring Machines (TBMs) are customized to work in all kinds of strata available in Bengaluru. We expect the machines to tunnel three metres a day on an average,” a senior BMRCL official said.Four of the nine TBMs required for the 14-km underground stretch have already been dispatched from China. While two machines are expected to reach in a week’s time, the other two TBMs will reach the City by the end of the month. The BMRCL had deployed six TBMs to tunnel the 10-km underground portion of Phase I, which went on from 2011 to 2016.BMRCL MD Ajay Seth said, “We are aware of the geological conditions. The selection of TBMs was made purely after conducting an investigation.”As the Earth Pressure Balance-type (EPB) TBMs have performed poorly compared to Slurry-based TBMs in Phase I, the BMRCL has specifically instructed the contractors to procure the latter. “The TBMs will be able to tunnel 2.4 metres a day in the hard rock and mixed conditions while theperformance will be around 5 metres in soft soil condition,” the official explained.The BMRCL, which earned a bad name in Phase I for delaying the underground Metro project by hiring inexperienced contractors, appears to have done its homework well for Phase II. Besides conducting an extensive geological investigation to ascertain the soil condition, the government agency has hired experienced contractors for tunnelling in Phase II.While construction major L&T is tunneling the 7-km stretch between Vellara Junction and Pottery Town, Mumbai-based Afcons Infrastructure has won the contract to tunnel 3.65-km stretch from Swagath Road to Vellara junction. ITD Cementation India will tunnel the remaining 4.5-km stretch from Pottery Town to Nagawara. The construction cost of the entire tunnelling project is estimated to cost around Rs 5,700 crore.“The 3-metre tunnelling per day is the thumb rule but it cannot be made applicable everywhere. According to the geologist hired by us, the rocks of Phase II underground section are easier to tunnel than those in Phase I. We have also used the failure data of Phase I to avoid repeat of those failures,” another official of BMRCL said.are keeping their fingers crossed. And their toes too.