National High Speed Rail Corporation (NHSRCL) achieved a major milestone in its Mumbai-Ahmedabad Bullet Train project with the lowering of the first cutterhead of Tunnel Boring Machine (TBM) at Vikhroli in Mumbai (Maharashtra). With a diameter of 13.6 meters, weighing a massive 350 tonnes, this component marks the final step in the primary assembly of the TBM’s main shield.
Two TBMs, each weighing over 3,000 tonnes, are currently being assembled to construct a 16 km portion of the 21 km Mumbai tunnel. This includes a 7 km stretch under Thane Creek, which will serve as India’s first undersea rail tunnel. These machines are the largest ever deployed for rail tunnel construction in the country.
Engineering Marvel at a Glance:
Dimensions: With a diameter of 13.6 meters, the cutterhead is designed to excavate a single tunnel large enough to accommodate both the up and down lines of the high-speed corridor.
Its 350-tonne weight is equivalent to approximately 250 passenger cars (midsize SUVs).
Arriving in five separate shipments, the unit was joined on-site using 1,600 kg of high-precision welding.
The unit is equipped with 84 cutter discs, 124 scrapers, and 16 bucket lips to efficiently cut and remove muck during excavation.
Cutting discs are the main tool which cut through the rock face followed by Scrapers that are positioned on the cutterhead. Their primary function include muck clearance at the face.
The bucket lip is the opening in the cutterhead through which muck enters to the muck chamber of the machine. It helps in collection, directing flow of the muck on to the pipeline system for removal from the tunnel.
This TBM will start its journey of approx. 6 km from Vikhroli and head towards Bandra Kurla complex under dense city landscape and Mithi river before being retrieved at under construction Mumbai Bullet train station at BKC.
Various monitoring instruments are being used to ensure safe excavation of the tunnel and all the structures in the nearby area. These include Surface Settlement Points (SSP), Optical Displacement Sensors (ODS) or tilt meters, BRT (By reflect target/3D targets), Strain Gauge for micro strains in tunnel surface, Seismograph for Peak Particle Velocity (PPV) or vibration & seismic wave monitor.
NHSRCL launches five portal beams at Maninagar
NHSRCL, on May 4, 2026 had successfully launched five precast-prestressed heavy portal beams (girders) over the Amdavad–Vadodara railway line in Maninagar within 22 days.
The portal beam is a precast concrete structure measuring 34 metres in length, with a cross-section of 5.5 metres by 4.5 metres. These beams are being precast at site and erected as heavy integrated units.
