India's largest tunnel boring machine (TBM) commenced excavation on Sunday, July 5, 2026, from the Vikhroli shaft in Mumbai, marking a major milestone for the Mumbai-Ahmedabad Bullet Train Project. The TBM will construct a 6-kilometer-long single-tube tunnel designed to accommodate both up and down tracks of the high-speed rail corridor.
Tunnel Specifications and Route
Of the total 21-kilometer underground tunnel section, a 16-kilometer stretch between Sawli (Ghansoli) and Bandra Kurla Complex (BKC) in Mumbai will be built using TBMs. The remaining 5-kilometer section has already been completed using the New Austrian Tunnelling Method (NATM). During its journey, the TBM will tunnel beneath multi-storeyed buildings, major roads, the Mithi River, and other critical infrastructure, requiring high precision and continuous monitoring.
Technical Details of the TBM
The TBM, the largest ever deployed for railway tunnel construction in India, features a 13.6-meter-diameter cutterhead, equivalent to the height of a four-storey building. It weighs about 3,100 tonnes—equivalent to 500 Asian elephants—and measures 96 meters in length. Key components include the cutter wheel, main bearing, jaw crusher, erector, main and tail shields, along with four specialised gantries supporting tunnelling operations. The cutterhead rotates at up to four revolutions per minute (RPM). The machine is a Mixshield TBM, an advanced slurry-type tunnelling system designed for large-diameter excavation in mixed geological conditions and areas with high groundwater pressure.
Launch Shaft and Monitoring Systems
To facilitate the TBM launch, a 56-meter deep shaft—equivalent to a 20-storey building below ground level—has been constructed at Vikhroli. A comprehensive real-time monitoring system has been installed to ensure safe tunnelling and protect nearby structures. The tunnel section excavated using TBMs is being designed as a fully waterproof structure, with continuous real-time monitoring systems for structural performance, groundwater behaviour, and overall construction safety.
Project Timeline
According to Railway Minister Ashwini Vaishnaw, the Mumbai-Ahmedabad High-Speed Rail Project is expected to begin operations on the Surat-Bilimora section in August 2027. This milestone brings the ambitious project closer to reality, promising to significantly reduce travel time between the two cities.
