New Delhi [India], July 5 (ANI): The first Tunnel Boring Machine (TBM) will begin tunneling from the Vikhroli shaft toward the under-construction Mumbai Bullet Train station on Monday as part of the Mumbai-Ahmedabad Bullet Train Project.
According to a press release, 16 kilometers of the project’s 21-kilometer underground tunnel section, between Sawli (Ghansoli) and the Bandra Kurla Complex (BKC) in Mumbai, will be constructed using Tunnel Boring Machines. The remaining 5-kilometer section has already been completed using the New Austrian Tunneling Method (NATM).
The TBM launched from Vikhroli will excavate a 6-kilometer single-tube tunnel designed to accommodate both the up and down bullet train tracks. During its journey, the machine will pass beneath densely populated urban areas, including multistory buildings, roads, the Mithi River, and other critical infrastructure.
The TBM is among the largest ever deployed for rail tunnel construction in India. It features a cutterhead with a diameter of 13.6 meters—roughly the height of a four-story building—weighs 3,100 metric tons, equivalent to about 500 Asian elephants, and has a total length of 96 meters.
The machine comprises several major components, including the cutterhead, main bearing, jaw crusher, erector, main shield, tail shield, and four specialized gantries that support tunneling operations.
The cutterhead rotates at four revolutions per minute. The project is using a Mixshield TBM, an advanced slurry-type tunneling system specifically designed for large-diameter tunnel excavation in mixed ground conditions and areas with high groundwater pressure.
The Mixshield technology uses pressurized bentonite slurry to stabilize the tunnel face during excavation. The technology is particularly well-suited for complex geological conditions and challenging urban environments.
According to the release, this tunneling method was selected for the Mumbai suburban section because of its ability to control ground settlement and minimize surface disruption in densely populated areas.
One of the key advantages of the TBM is its ability to excavate the tunnel and install concrete segment rings simultaneously. This parallel process improves safety and significantly increases construction speed.
To facilitate the TBM launch, a 56-meter-deep shaft—equivalent to a 20-story building below ground level—has been constructed at Vikhroli.
The shaft is equipped with essential support infrastructure, including a water treatment plant, slurry treatment plant, bentonite storage tanks, a dedicated power substation, backup generators, a ready-mix concrete plant for grouting, a slurry transport system, a sewage treatment plant, backup gantries, and other logistical facilities.
A comprehensive real-time monitoring system has also been installed to ensure safe tunneling operations and protect nearby structures. The monitoring network includes Surface Settlement Points (SSP), Optical Displacement Sensors (ODS), tilt meters, Bi-Reflective Targets (BRT/3D Targets), strain gauges, and seismographs to monitor vibrations and seismic activity.
An 11.17-hectare casting yard at Mahape in Thane district is already operational to manufacture tunnel lining segments for the 16-kilometer TBM section.
A total of 77,000 concrete segments are being produced to create 7,700 tunnel rings. Each ring consists of nine curved segments and one key segment. Each segment measures 2 meters in width and 500 millimeters in thickness, while a completed tunnel ring weighs approximately 100 metric tons.
The tunnel section excavated using TBMs is being designed as a fully waterproof structure. Continuous real-time monitoring systems have been installed to track structural performance, groundwater behavior, and overall construction safety.
To prevent water infiltration, the tunnel lining is protected with double-layer Ethylene Propylene Diene Monomer (EPDM) gaskets combined with hydrophilic seals, ensuring long-term structural durability and operational safety. (ANI)
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