India’s largest rail tunnel boring machine cutterhead lowered for Mumbai bullet train project

Mumbai (Maharashtra) [India], May 17 (ANI): India's largest cutterhead for a rail tunnel boring machine (TBM) has been lowered at Vikhroli in Mumbai for the Mumbai-Ahmedabad Bullet Train project, marking a major milestone in the construction of the country's first undersea rail tunnel, according to the National High Speed Rail Corporation Limited (NHSRCL).
The cutterhead, which has a diameter of 13.6 metres and weighs around 350 tonnes, marks the final stage in the primary assembly of the TBM's main shield. NHSRCL said the machine will be used for excavation of a section of the underground tunnel for the high-speed rail corridor.
"Two TBMs, each weighing over 3,000 tonnes, are currently being assembled to construct a 16 km portion of the 21 km Mumbai tunnel," the release said.
The tunnel section includes a 7 km stretch beneath Thane Creek, which NHSRCL described as "India's first undersea rail tunnel." The corporation also said these are the "largest ever" TBMs deployed for rail tunnel construction in the country.
Union Railway Minister Ashwini Vaishnaw also shared the development on X, stating, "Railway's biggest TBM cutter head lowered at Vikhroli, Mumbai."
According to the release, the 13.6-metre diameter cutterhead has been designed to excavate a single large tunnel that can accommodate both the up and down lines of the bullet train corridor.
"Its 350-tonne weight is equivalent to approximately 250 passenger cars (midsize SUVs)," the release stated.
NHSRCL said the cutterhead arrived in five separate shipments and was assembled on-site using 1,600 kg of high-precision welding. The unit has been equipped with 84 cutter discs, 124 scrapers and 16 bucket lips to cut through rock and remove excavated material during tunnelling operations.
Explaining the functioning of the system, the release said cutter discs are the primary tools that cut through the rock face, while scrapers help in muck clearance at the excavation face. The bucket lips act as openings through which the excavated material enters the muck chamber and is directed to the pipeline system for removal from the tunnel.
The TBM will excavate an approximately 6 km tunnel stretch from Vikhroli towards the Bandra Kurla Complex (BKC), passing beneath dense urban areas and the Mithi River before being retrieved at the under-construction Mumbai Bullet Train station at BKC.
NHSRCL said several monitoring systems are being deployed to ensure safe tunnelling activity and protect nearby structures. These include Surface Settlement Points (SSP), Optical Displacement Sensors (ODS), strain gauges and seismographs to monitor vibration, displacement and tunnel surface strain during excavation. (ANI)