India’s first bullet train project between Ahmedabad and Mumbai includes a significant engineering challenge—a 7-kilometer undersea tunnel beneath the ecologically sensitive Thane Creek. The construction of this tunnel represents a crucial phase in the development of the Mumbai-Ahmedabad bullet train corridor, with the tunnel boring machine (TBM) expected to be operational by the end of this year.
Advanced Engineering for Unique Challenges
The undersea tunnel will form part of a larger 21-kilometer underground stretch of the corridor, presenting unique engineering challenges due to the complex undersea geological layers. This project is distinct from previous underwater tunnels in India, such as the Kolkata Metro’s tunnel under the Hooghly River and Mumbai Metro Rail Corporation’s Line 3 under the Mithi River. Unlike these river-based tunnels, the upcoming undersea tunnel will feature a single-tube structure designed to accommodate two tracks—one for each direction.
The tunnel’s construction requires TBMs equipped with large cutter heads, measuring 13.6 meters in diameter. This is notably larger than the 6-8 meter diameter cutter heads typically used for urban metro tunnels, which are designed for single-track systems. The large cutter heads are necessary to create a tunnel wide enough for the high-speed bullet train’s dual tracks.
Excavation and Construction Progress
Excavation efforts are underway at three key locations: Ghansoli, Shilphata, and Vikhroli. At Ghansoli, the first TBM is set to be installed by the end of the year. It will dig towards Thane Creek from a shaft located 39 meters below ground. To facilitate this, engineers have already completed 120 meters of excavation towards BKC and 110 meters at Shilphata, using 218 controlled blasts with gelatin.
The bullet train project’s pace has been notably faster in Gujarat compared to Maharashtra. Of the total 502-kilometer route, the 352 kilometers in Gujarat are anticipated to become operational by 2027, with the Surat-Bilimora section opening in August 2026. The entire corridor is expected to be completed by the end of 2028, which is a six-year extension beyond the initial deadline.
Technological and Safety Measures
The construction of the tunnel beneath the creek will involve boring at depths ranging from 25 to 57 meters below ground level. Three large TBMs will handle 16 kilometers of the 21-kilometer underground stretch, including the 7-kilometer section under the creek. The remaining 5 kilometers will be constructed using the New Austrian Tunneling Method (NATM), a sophisticated technique that relies on real-time monitoring to adjust reinforcement methods based on the encountered rock types. (With TOI inputs)
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