The giant 13.6-metre TBM cutterhead being lowered at Ghansoli for the Mumbai-Ahmedabad Bullet Train project. (Image courtesy: ViaX/@AFCONSOfficial)
MUMBAI: The Mumbai-Ahmedabad High Speed Rail Corridor has achieved another significant construction milestone after the successful lowering of the cutterhead of the second Tunnel Boring Machine (TBM) at Sawli near Ghansoli in Navi Mumbai, marking the final stage of primary TBM assembly before commissioning and tunnelling operations.
The cutterhead, measuring 13.6 metres in diameter and weighing around 350 tonnes, was lowered into a launch shaft approximately 38 metres below ground level. The operation completes the primary assembly of the TBM’s main shield, paving the way for tunnelling work on one of the most complex sections of India’s first bullet train corridor. According to the National High Speed Rail Corporation Limited (NHSRCL), the machine will begin its underground journey from Sawli towards Vikhroli after final assembly and commissioning trials are completed.
The Mumbai-Ahmedabad High Speed Rail Corridor is a 508-kilometre project being developed by NHSRCL and is India’s first dedicated high-speed rail network. The corridor will connect Mumbai and Ahmedabad using trains capable of operating at speeds of up to 320 kmph.
Why This Milestone Matters
The lowering of the cutterhead is far more than a routine engineering operation. The cutterhead forms the front section of a Tunnel Boring Machine and acts as the cutting face that breaks through soil, rock and mixed geological formations during excavation.
NHSRCL said the lowering of the cutterhead “marks the final step in the primary assembly of the TBM’s main shield.”
The first cutterhead for the project was lowered earlier at Vikhroli, while the second has now been installed at Sawli near Ghansoli. Media reports indicate tunnelling may begin around July 2026 following commissioning and testing.
How the Giant TBM Works
Tunnel Boring Machines are among the largest and most advanced construction machines used in infrastructure projects worldwide.
The TBMs deployed for the Mumbai-Ahmedabad Bullet Train project are among the largest railway tunnel boring machines ever used in India. Each machine weighs more than 3,000 tonnes and stretches over 95 metres in length. The machines use Mix Shield and Slurry-based technology, allowing them to safely excavate through varying geological conditions, including soft ground, rock formations and water-bearing strata.
The cutterhead rotates continuously while pushing against the ground. Equipped with 84 cutter discs, 124 scrapers and 16 bucket lips, it cuts and loosens soil and rock. The excavated material, known as muck, is then transported out of the tunnel through a slurry circulation system. Concrete tunnel lining segments are simultaneously installed behind the machine, creating a permanent tunnel structure as excavation progresses.
One of the most notable features of these machines is their massive diameter. The 13.6-metre-wide cutterhead is designed to excavate a single large tunnel capable of accommodating both the up and down high-speed rail tracks within the same tunnel structure.
While the cutterhead measures 13.6 metres in diameter, the finished tunnel will have an internal diameter of around 13.1 metres.
The Challenging Mumbai Underground Section
The TBMs will be used for the construction of a 21-kilometre underground corridor, including around 16 kilometres to be excavated using TBMs.
Out of this, around 16 kilometres will be excavated using the two giant TBMs, while other sections are being built using the New Austrian Tunnelling Method (NATM). The alignment includes India’s first undersea high-speed rail tunnel, a 7-kilometre stretch passing beneath Thane Creek.
The underground route extends between Bandra Kurla Complex (BKC), the future Mumbai bullet train station, and Shilphata. Parts of the tunnel pass beneath densely populated urban areas, critical infrastructure and water bodies, making it one of the most technically demanding railway projects undertaken in India.
The second TBM will tunnel from Sawli towards Vikhroli, while the first machine will excavate from Vikhroli towards BKC. Together, the machines will construct major portions of the underground corridor.
Engineering Scale of the Machines
According to NHSRCL, the two TBMs are engineering giants.
Key specifications include:
– Cutterhead diameter: 13.6 metres
– Total machine length: 95.32 metres
– Weight of TBM-1: 3,080 tonnes
– Weight of TBM-2: 3,184 tonnes
– Technology: Mix Shield and Slurry-based TBM
– Cutter discs: 84
– Scrapers: 124
– Bucket lips: 16
The machines comprise multiple critical components including the cutter wheel, main bearing, jaw crusher, erector, main shield, tail shield and four specialised gantries that support tunnelling operations.
Afcons Leading Underground Construction
The underground package of the Mumbai bullet train project is being executed by Afcons Infrastructure, one of India’s largest engineering and construction firms.
In a social media update, the company announced that it had “successfully lowered another of India’s biggest TBM cutter heads” at the Sawli shaft near Ghansoli, highlighting the complexity of the operation conducted deep below ground level.
The cutterhead was lowered through a specially constructed launch shaft where engineers are assembling the machine piece by piece before it begins excavation. The components were transported separately and assembled on-site due to their enormous size and weight.
Growing Momentum for India’s First Bullet Train
The latest milestone comes as construction activity accelerates across the Mumbai-Ahmedabad High Speed Rail Corridor.
In recent months, NHSRCL has reported multiple breakthroughs in tunnel construction, viaduct launches and station development. A 4.88-kilometre underground tunnel breakthrough between Shilphata and Ghansoli was achieved earlier, while work on major station structures and elevated sections continues across Maharashtra and Gujarat.
NHSRCL Managing Director Rajendra Prasad has previously described the Mumbai underground section as one of the most challenging components of the project because of the complex geology, dense urban environment and undersea tunnel segment beneath Thane Creek.
NHSRCL has already completed more than 300 kilometres of viaduct construction across Gujarat and Maharashtra, while station and track works continue across multiple sections of the corridor.
With both giant TBMs now entering their final assembly and commissioning stages, the project is preparing to begin one of the most complex phases of construction. The underground Mumbai section is considered a critical engineering component of India’s first high-speed rail corridor and will play a key role in connecting the future Bandra Kurla Complex bullet train station with the rest of the 508-kilometre network.
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