Tunnelling through this central business district has been found to be the most challenging as the geological conditions forced BMRCL to suspend boring work 713 times for repair/maintenance of the seven Tunnel Boring Machines (TBMs).
Bangalore Metro Rail Corporation Limited (BMRCL) has suspended boring work for Namma Metro 713 times due to unfavourable geological conditions. The difficult underground with rocks and rocky soil between Shivajinagar and MG road has also made it even more difficult for BMRCL to complete the Namma Metro’s phase 2 underground section.
The MG Road-Shivajinagar stretch is part of the city’s longest underground Metro corridor. Tunnelling through this central business district has been found to be the most challenging as the geological conditions forced BMRCL to suspend boring work 713 times for repair/maintenance of the seven Tunnel Boring Machines (TBMs) which have completed 5.7km of tunnelling including Shivajinagar-mg road, South ramp- dairy circle, Vellara junction- Langford town and cantonment- Shivajinagar.
It is reported that the cutter discs are either worn out or there is a delay in installing suitable ones to cut through rocky soil or rocks based on the geological conditions. Often when a rock is encountered in the route the cutter discs, which usually are mounted on the cutter head of the TBMs, need to be changed. Depending upon how hard the rock is, the no of cutter discs varies.
Interestingly, 325 such cutter discs were replaced in TBM Avni in just 388 days, which was drilled between a 1,086m stretch between Shivajinagar and MG Road (southbound). Also, TBM Lavi which was building a tunnel on the same section (1076m, northbound), is known to have required 295 discs.
As per an official from BMRCL, each cutter disc costs the contractors around ₹1. 5-3 lakh. But most of the time these discs become unrepairable and often not fit for reuse as they get damaged when they encounter hard rock or boulders in the soil.
As per Mr Gudge, the BMRCL plans to finish the remaining tunnelling work in another 1.5 years with Metro operations on the Pink Line to commence by 2025. BMRCL has also announced that it has till date completed 40% of the tunnelling work.
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