BENGALURU: THE frequent breakdown of cutters on the Cutter Head (the crucial part of the machine) due to wear and tear was a mammoth challenge experienced during the boring work carried out by Kaveri Tunnel Boring Machine, 60 feet below the ground, spells out the contractor carrying out the work for Namma Metro.
Speaking to Express, G Hari Hara Rao, Managing Director of Coastal Projects Limited, said, “I do not have an exact count of the cutters; but over 1,000 cutters were easily damaged as the machine tunnelled the 757-metre distance from Chickpet to Kempegowda Interchange Station.”
“The `43 crore Herrenknecht TBM ‘Kaveri’ was imported from Germany. The cutters also had to be imported from Germany and the US. Thankfully, work did not stop because of non-availability of the spare parts as we had stocked excess cutters in advance,” Rao added.
A cutter head is the most crucial part of the TBM. The cutter head generally has 45 cutters embedded onto it when carrying out boring work. “We had to stop whenever any damage occurred to any of the cutters, replace it, and carry on the work. There were times when 10 or even 12 cutters were damaged in a day,” he explained.
The soil conditions and water seepage were other major issues, he added.
“However, frequent interventions, (stopping of the machine to carry out replacement and then restarting), that we had to undertake was the biggest issue,” he said.
When asked about the cost involved, the MD said that the cost of a single Cutter worked out to around `1 lakh.
Elaborating on the impact the machine had to take before it completed its journey, Jim Clark, Project Manager (India), The Robbins Company, whose staff operated ‘Kaveri’, said, “The stretch the machine completed was a mix of very hard rock as well as residual soil. It had to burrow through hard soil and then soft soil. Since it operated in a circular fashion, the machine had to keep on switching between both kinds of soil and that caused a lot of damage to it.”
This also caused much vibration to the machine overall. “The advance rate of the machine too had to be slowed down so that it could manage the impact,” he added.
Shift-in-charge Reddy shares his spine-chilling experience
Nagarjun Reddy, Shift-in-charge, Kaveri TBM, who was on board for a major part of the drilling operations, shared his experience of working 60 feet below ground level. “At any given time, 14 of us used to be on board. We worked a 12-hour shift with 2 mechanics, 2 electricians, 1 TBM operator, 1 Erector operator, 1 Grout Operator, 6 unskilled labourers and 1 person who was shift-in-charge.” “We have a back-up cabin which has motors and all spares required,” he said. “It was not a frightening experience as there is sufficient ventilation and good communication systems to contact anyone at ground level in case of any emergency. We had oxygen sensors around,” he added.
Commuters are expected to travel by Metro when both the North-South as well as the East-West Corridors become operational, said Metro Director, Rolling Stock, BMRCL, S M Dhoke. “We have learnt from our experience in Phase-I. Hence for Phase-II, instead of conducting soil surveys every 20 mts like we did for Phase-I, it is being done for every 10 metres,” he said.
Kaveri-- the pride
Journey began 3.5 yrs ago from KIMS Hospital near K R Market
Emerged at Chickpet underground station on BVK Iyengar Road on October 17, 2014
Started its second operation from Chickpet Station on March 14, 2015
Ended on June 8, 2016 at 4.40 pm.
Cost of machine A43crDistance covered1,582 mts
Used 60 ft below the groundCutter head has 45 cutters; over 1,000 cutters used in total
Cost of single cutter A1L