Mumbai: In a major step forward for the Mumbai-Ahmedabad Bullet Train project, the first 350-tonne cutterhead of a Tunnel Boring Machine (TBM) has been lowered at Vikhroli, marking a key milestone in the construction of the high-speed rail corridor’s underground section. The giant cutterhead, measuring 13.6 metres in diameter, forms the front end of the TBM and completes the primary assembly of its main shield.The Mumbai tunnel, one of the most complex stretches of the project, will extend for 21km, of which 16 km will be built using two massive TBMs, each weighing more than 3,000 tonnes. The tunnel includes a 7km section beneath Thane Creek, set to become India’s first undersea rail tunnel. These are also the largest TBMs ever deployed for rail tunnel construction in the country.Designed to excavate a single large tunnel carrying both up and down lines of the bullet train corridor, the cutterhead is an engineering feat in itself. Weighing as much as nearly 250 midsize SUVs, it arrived at the site in five separate consignments and was assembled with 1,600 kg of precision welding.“The cutterhead is equipped with 84 cutter discs, 124 scrapers and 16 bucket lips. The cutter discs break through rock and soil at the tunnel face, while the scrapers help clear muck efficiently,” an official said. The bucket lips guide the excavated material into the muck chamber, from where it is transported out through the pipeline system.From Vikhroli, this TBM will bore nearly 6km towards Bandra-Kurla Complex (BKC), passing beneath a dense urban landscape and the Mithi river before being retrieved at the under-construction Mumbai Bullet Train station at BKC.Given the challenging geology and urban setting, extensive monitoring systems are being deployed to ensure safe tunnelling and protect nearby structures. These include surface settlement points, optical displacement sensors or tilt meters, 3D targets, strain gauges and seismographs to track vibration and ground movement in real time, an official said.The lowering of the cutterhead signals not just progress in construction, but the arrival of a new scale of tunnelling technology for India’s first bullet train project.
