03-08-2025
Bengaluru's twin tunnel project to use slurry boring machines for excavation: Report
Plans for Bengaluru's new twin tunnel road, which will link Hebbal's Esteem Mall Junction and Silk Board Junction, will rely on slurry tunnel boring machines (TBMs) to do the heavy digging. A Tunnel Boring Machine (TBM). (Representative image)(PTI)
The organization overseeing the project, B-SMILE, opted not to use hard rock TBMs — machines generally preferred when excavating through areas riddled with boulders. Their decision comes after evaluating the city's subsurface, which blends both stones and softer soil, making slurry TBMs a better fit for the job.
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BS Prahlad, the project's technical director, shared that lessons from an earlier tunnel build in Mumbai pushed the team toward slurry-based machines this time around, according to The Hindu.
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For the twin tunnel project, a total of eight tunnel boring machines will be brought in, starting work from five or six launch sites along the nearly 17-kilometre route. The massive venture is structured under a Build, Own, Operate, and Transfer (BOOT) model, which means successful bidders will be responsible for acquiring and managing the machinery, whether they import or locally assemble the TBMs themselves, the report stated.
Past tunnel work in Bengaluru — like the Namma Metro — has achieved boring rates between 1.6 and 2 kilometres per year using similar technologies. The exact pace on this project will ultimately depend on the ground composition encountered during the drilling process.
As part of the tendering process, the government is providing borewell survey information, but insists that detailed site investigation and analysis will be the winning bidder's responsibility.
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The twin tunnel itself, spanning roughly 16.7 kilometres, aims to ease congestion by providing a new north-south route beneath the city's surface. Geological experts say the use of slurry TBMs may also help fill and secure natural fractures in Bengaluru's ancient, complex underground rock, some parts of which date back several billion years.
