India’s Largest Rail Tunnel Boring Machine Launched for Mumbai Ahmedabad Bullet Train Project
The Mumbai–Ahmedabad Bullet Train Project achieved a major construction milestone on Sunday with the launch of India’s largest rail Tunnel Boring Machine (TBM) from the Vikhroli shaft in Mumbai. The advanced machine has begun excavating the underground tunnel towards the under-construction Mumbai Bullet Train station at Bandra Kurla Complex (BKC), marking a significant step in the country’s first high-speed rail corridor.
The underground section of the project stretches for 21 kilometres, of which 16 kilometres between Sawli (Ghansoli) and Bandra Kurla Complex will be constructed using Tunnel Boring Machines. The remaining five-kilometre section has already been completed using the New Austrian Tunnelling Method (NATM).
The TBM launched from Vikhroli will excavate a six-kilometre-long single-tube tunnel that will accommodate both the up and down tracks of the Bullet Train. During its journey, the machine will pass beneath densely populated urban areas, including high-rise residential and commercial buildings, major roads, the Mithi River, and several critical public utilities, making it one of the most challenging tunnelling operations undertaken in India.
The machine is among the largest ever deployed for rail tunnel construction in the country. It features a cutterhead measuring 13.6 metres in diameter, roughly equal to the height of a four-storey building. Weighing around 3,100 tonnes—comparable to the combined weight of nearly 500 Asian elephants—the TBM is 96 metres long, almost the length of a football field.
The machine consists of several sophisticated components, including the cutter wheel, main bearing, jaw crusher, erector, main shield, tail shield, and four specialised gantries that support continuous tunnelling operations. Its cutterhead rotates at a speed of four revolutions per minute to excavate soil efficiently while maintaining tunnel stability.
The project uses a Mixshield TBM, an advanced slurry-based tunnelling system specifically designed for excavating large-diameter tunnels through mixed geological formations and areas with high groundwater pressure. The technology employs pressurised bentonite slurry to stabilise the tunnel face during excavation, making it particularly suitable for Mumbai’s complex subsurface conditions and densely built urban environment.
Officials said the Mixshield technology was selected because of its ability to minimise ground settlement and reduce surface disruption, ensuring the safety of nearby buildings and infrastructure. One of the major advantages of this system is that it allows simultaneous excavation and installation of concrete tunnel lining segments, improving safety while significantly increasing construction speed.
To facilitate the launch of the TBM, engineers constructed a 56-metre-deep shaft at Vikhroli, equivalent to the height of a 20-storey building below ground level. The launch shaft is equipped with extensive support infrastructure, including water and slurry treatment plants, bentonite storage tanks, a dedicated power substation, backup generators, a ready-mix concrete plant for grouting operations, slurry transport systems, a sewage treatment plant, and logistics facilities required for continuous tunnelling.
A comprehensive real-time monitoring system has also been installed to ensure safe excavation and protect surrounding structures throughout the tunnelling process. The system includes surface settlement points, optical displacement sensors, tilt meters, three-dimensional reflective targets, strain gauges, and seismographs to continuously monitor ground movement, structural behaviour, and vibration levels.
Meanwhile, an 11.17-hectare casting yard at Mahape in Thane district is already producing the precast concrete lining segments required for the tunnel. Around 77,000 concrete segments will be manufactured to assemble 7,700 tunnel rings. Each ring consists of nine curved segments and one key segment, with every ring weighing nearly 100 tonnes.
The tunnel being constructed with TBMs is designed as a fully waterproof structure. Engineers are using double-layer Ethylene Propylene Diene Monomer (EPDM) gaskets along with hydrophilic seals to prevent water ingress and ensure long-term durability, structural integrity, and operational safety. The launch of India’s largest rail TBM marks another major milestone in the progress of the Mumbai–Ahmedabad Bullet Train Project, one of the country’s most ambitious infrastructure initiatives.
