BENGALURU: Sleepless nights for almost two years suffered by nearly 240 contract employees of Bangalore Metro Rail Corporation Limited (BMRCL), to blast hard rocks to bits and build underground stations, has ensured the South India’s first underground Metro corridor become a reality today.
The enormity of the task -- taken up by workers from West Bengal, Bihar and Andhra Pradesh -- can be gauged the quantum of debris excavated -- equivalent to 20,250 truckloads.
“Approximately 50,000 kg of explosives (gel nitrate) were used to carry out nearly 10,000 blasts at City railway station, Sir M Visvesvaraya, Vidhana Soudha and Cubbon Park Metro stations to break the hard rocks,” said Subrahmanya Gudge, Deputy Chief Engineer, Underground section, BMRCL.
The Kolar-based National Institute of Rock Mechanics, experts in the field of blasting, were consulted for the Metro underground corridor.
The blasts were carried out daily from 6 am to 7 am from March 2011 to early 2013. Since blasts were permitted only during day time, it was done early in the day when there is less population around.
“Each blast lasts a mere five seconds but preparation for it started from 3.30 am each day,” Gudge said.
Each station had around 60 workers who divided themselves into groups of four and carried out the blasting work. The area up to 100 metres of the blast site had to be cordoned off.
The Blasting Process
The portion of rock surface to be demolished is identified and holes are drilled into them using jackhammers. An explosive is inserted into each hole. Each gel nitrate explosive resembles a mammoth capsule and contains 125 gm powder. The fuse wires are jointly linked to a battery-operated control unit located at a distance. The holes are then closed with clay. A steel mesh is used to cover it so that rocks of small sizes are not missed. And finally, many Muffling Steel Rubber Mats are placed on it.
“As the name indicates, a muffling mat helps suppress sound and ensures flyash from the blasted rocks do not scatter around. Each mat weighs around 1,400 kg and can only be transported using a crane. It is made by flattening rubber from used tyres into a flat surface and steel wires to reinforce them together,” said Gudge.
They were brought in from Hyderabad and each mat could be used for around 50 blasts. The explosives are timed to blast one after another. “There is a time difference of 20 milliseconds from one blast to another,” he added. A red flag is placed near the blast site and a long, cautionary siren is sounded to warn people not to venture near it.
When asked if workers suffered any injuries during the blasts, the Deputy Chief Engineer ruled it out. “All the mentioned precautionary steps were taken only to ensure no individual is harmed.”
On the biggest challenge the teams encountered, Gudge said it was related to work at the Vidhana Soudha station. “We had to be extremely careful as the High Court was on one side and the historic Vidhana Soudha across it. Thankfully, we pulled through that,” he exclaims.
Work Pending at One Exit
One entrance of the City station (North West) is not yet ready for the public. Explaining the reasons for it, a top Metro official said that it was decided rather late to provide an underpass on the Magadi Road side that would be convenient to the public who alight at this station. “The work has begun recently and will take a few months to be completed.”
There are three other exits from the City station which commuters can use -- the South West, South East and North East exits -- he added.
Check, Re-check
The Metro station was abuzz with activity. Trains kept zooming in and out as trial runs were taking place non-stop to check and re-check smooth running along the underground corridor. A team, stated to be the CM’s security escort team, accompanied by two sniffer dogs, was checking every part of the station. The team later boarded a train for a security check.
‘too much’ WAter Posed Trouble
Elaborating on the issues faced by the drilling and excavation team, Executive Engineer in the Underground section, Shivayogi S Kabbinakautimath said, “When we started digging up to 4 or 5 metres, water started gushing out due to the good water table.”
“The water then had to be pumped out and released into the nearby storm water drain,” he added.
“The problem was acute when work on the Sir M Visvesvaraya Metro station began. Water began pouring out the minute we started digging at the ground level itself,” the engineer added.
No Water Crisis
Huge water filters were being installed at the station to provide water to the public and a water tanker has landed up at the station. The platforms are being swept and mopped repeatedly. The public display information systems were checked and smaller signboards inside were being put up.
Excitement In the Air
The excitement was palpable all around the Dr Ambedkar Metro station area on Thursday with the impending inauguration of the underground stretch (Cubbon Park station to City railway station) of the East-West Corridor on Friday evening. Curious onlookers kept coming and requesting the Home Guards posted at the entrance of the station that they be allowed to have a glimpse inside but the guards politely refused entry for security reasons. With the huge grand silky maroon ceremonial tent (shamiana) erected in front of the grand steps of Vidhana Soudha, everyone around appeared to be aware that something momentous was set to take place.