Mumbai-Ahmedabad bullet train project latest update: The Mumbai-Ahmedabad bullet train project reached another major milestone on Sunday as India’s largest rail tunnel boring machine (TBM) began excavating the underground tunnel beneath Mumbai, a key section of India’s first high-speed rail (HSR) corridor. The TBM launched from Vikhroli will excavate a 6-km-long single-tube tunnel designed to accommodate both the up and down tracks of the bullet train.
According to the National High-Speed Rail Corporation Limited (NHSRCL), the tunnel boring machine will pass beneath dense urban areas during its journey, including multi-storeyed buildings, roads, the Mithi River and other critical infrastructure.
India’s largest rail Tunnel Boring Machine starts excavation from Vikhroli for the Mumbai-Ahmedabad bullet train project (Image: NHSRCL)
Mumbai-Ahmedabad bullet train project underground tunnel
The Mumbai-Ahmedabad bullet train project includes a 21-km underground tunnel section. Of this, a 16-km stretch between Sawli (Ghansoli) and Bandra Kurla Complex (BKC) in Mumbai will be excavated using tunnel boring machines (TBMs), while the remaining 5-km section has already been completed using the New Austrian Tunnelling Method (NATM).
(Image: NHSRCL)
India’s largest rail TBM launched in Mumbai’s Vikhroli
According to the NHSRCL, the tunnel boring machine (TBM) is among the largest ever deployed for rail tunnel construction in the country. It features a 13.6-metre-diameter cutterhead-equivalent to the height of a four-storey building- weighs about 3,100 tonnes, roughly the weight of 500 Asian elephants, and measures 96 metres in length, nearly the length of a football field.
The machine comprises several key components, including the cutter wheel, main bearing, jaw crusher, erector, main shield, tail shield, and four specialised gantries that support tunnelling operations. The cutter wheel rotates with a speed of 4RPM (revolutions per minute), i.e 4 revolutions per minute, it said.
(Image: NHSRCL)
How India’s largest rail TBM will dig the Mumbai-Ahmedabad bullet train tunnel at Vikhroli
In a statement, the NHSRCL said the advanced tunnelling method was selected for the Mumbai suburban section because of its superior ability to control ground settlement and minimise surface disruption in densely populated areas.
It also added that the machine being deployed is a Mixshield tunnel boring machine (TBM), an advanced slurry-type tunnelling system specifically designed for large-diameter tunnel excavation in mixed ground and high groundwater pressure conditions.
“One of the key advantages of this TBM is its ability to carry out tunnel excavation and segment ring installation simultaneously. This parallel operation enhances safety and significantly improves tunnelling speed, helping accelerate project execution,” the corporation said.
According to the NHSRCL, the tunnel being excavated by the TBMs is being built as a fully waterproof structure. To prevent water leakage, the tunnel lining will be fitted with double-layer EPDM (Ethylene Propylene Diene Monomer) gaskets and hydrophilic seals, ensuring long-term durability and safety.
India’s largest rail TBM starts work at Vikhroli in Mumbai (Image: NHSRCL)
How the bullet train tunnel will be built without affecting Mumbai’s buildings
To facilitate TBM launch, the NHSRCL constructed a 56-metre deep shaft – equivalent to a 20-storey building below ground level at Vikhroli in Mumbai. The shaft area is equipped with multiple support systems essential for TBM operations, including: a water treatment plant, a slurry treatment plant, bentonite storage tanks, a dedicated power substation, backup generator sets, a ready-mix concrete plant for grouting, a slurry transport system, a sewage treatment plant, backup gantries, and other logistics infrastructure.
Apart from this, a comprehensive real-time monitoring system has been installed to ensure safe tunnelling operations and protect nearby buildings and other infrastructure. “The instruments being used include: Surface Settlement Points (SSP), Optical Displacement Sensors (ODS) / Tilt Meters, Bi-Reflective Target (BRT/3D Targets), Strain Gauges, Seismographs for monitoring vibration and seismic waves,” it added.
Why is this tunnel so important?
The underground section is among the most technically challenging parts of the 508-km Mumbai-Ahmedabad bullet train project because it passes beneath densely built areas of Mumbai before connecting to the Bandra Kurla Complex (BKC) station.
An 11.17-hectare casting yard in Mahape, Thane district, is already operational for manufacturing tunnel lining segments for the 16-km TBM section.
Around 77,000 concrete segments are being manufactured to build 7,700 tunnel rings. Each ring is made up of nine curved segments and one key segment. Each segment is 2 metres wide and 500 mm thick, while a complete tunnel ring weighs about 100 tonnes.
What happens next?
Once excavation is completed, the NHSRCL will install tracks, signalling and other railway systems before train operations begin on the underground section.
Mumbai-Ahmedabad Bullet Train project has marked a significant construction milestone with India's largest rail tunnel boring machine beginning excavation work. (Image: NHSRCL) 
India’s largest rail Tunnel Boring Machine starts excavation from Vikhroli for the Mumbai-Ahmedabad bullet train project (Image: NHSRCL)
(Image: NHSRCL)
(Image: NHSRCL)
India’s largest rail TBM starts work at Vikhroli in Mumbai (Image: NHSRCL)
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