Mumbai: A major milestone has been achieved in the Mumbai-Ahmedabad Bullet Train project with the lowering of the first Tunnel Boring Machine (TBM) cutterhead at Vikhroli in Mumbai. The massive cutterhead, measuring 13.6 metres in diameter and weighing 350 tonnes, marks the final stage in the primary assembly of the TBM’s main shield for the high-speed rail corridor project.
The cutterhead is part of two giant TBMs, each weighing more than 3,000 tonnes, that are currently being assembled for the construction of a 16-km stretch of the 21-km-long Mumbai tunnel. The tunnel includes a 7-km undersea section beneath Thane Creek, which will become India’s first undersea rail tunnel.
These are the largest TBMs ever deployed for rail tunnel construction in the country. The cutterhead has been specifically designed to excavate a single large tunnel capable of accommodating both the up and down lines of the bullet train corridor.
The 350-tonne structure weighs nearly the equivalent of around 250 midsize passenger SUVs. It arrived at the site in five separate shipments and was assembled using around 1,600 kg of high-precision welding work.
The cutterhead has been equipped with 84 cutter discs, 124 scrapers and 16 bucket lips to carry out excavation work efficiently. The cutting discs will cut through the rock face, while the scrapers positioned on the cutterhead will help clear muck from the excavation face. The bucket lips act as openings through which excavated muck enters the machine’s muck chamber before being transported through the pipeline system for removal from the tunnel.
The TBM will begin its approximately 6-km tunnelling journey from Vikhroli towards Bandra Kurla Complex (BKC), passing beneath densely populated urban areas and the Mithi River before being retrieved at the under-construction Mumbai Bullet Train station at BKC.
Multiple monitoring instruments are being used throughout the excavation process to ensure safety and minimise impact on nearby structures. These include Surface Settlement Points (SSP), Optical Displacement Sensors (ODS) or tilt meters, BRT or 3D targets, strain gauges for monitoring micro strains on tunnel surfaces, and seismographs to measure vibration and seismic wave movement through Peak Particle Velocity (PPV) monitoring.
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