Construction of India’s first undersea high-speed rail tunnel has entered a new phase after a second tunnel boring machine (TBM) began excavation for the Mumbai–Ahmedabad Bullet Train corridor. The milestone advances one of the country’s most technically complex transport projects and signals steady progress on infrastructure designed to reshape intercity mobility while strengthening engineering capabilities for future high speed rail networks.
The newly deployed TBM has started tunnelling from the Sawli launch shaft towards Vikhroli in Maharashtra, contributing to the underground section that forms part of the 508-kilometre Mumbai–Ahmedabad high-speed rail corridor. Of the 21 kilometre underground alignment, 16 kilometres will be excavated using tunnel boring machines, while a 7 kilometre stretch will pass beneath Thane Creek, creating India’s first undersea railway tunnel. The Mumbai Ahmedabad Bullet Train project is widely regarded as a test case for advanced rail engineering in India. A first TBM had already commenced excavation earlier this month from the Vikhroli end, while the remaining underground section has been completed using the New Austrian Tunnelling Method (NATM). The deployment of multiple TBMs is expected to accelerate excavation while maintaining precision beneath densely populated urban areas and environmentally sensitive zones.
Infrastructure experts note that underground construction beneath coastal terrain presents significant engineering challenges, requiring waterproof tunnel linings, continuous geological monitoring and advanced safety systems. Successfully executing this phase could strengthen India’s capacity to deliver future underground transport projects, including metro systems and high-speed rail corridors in other metropolitan regions. Beyond engineering, the corridor is expected to improve regional connectivity between Gujarat and Maharashtra by reducing travel times and supporting economic integration. Urban economists suggest that high-speed rail infrastructure can stimulate investment around station precincts, encourage transit-oriented development and improve business mobility. However, they emphasise that these benefits will depend on effective multimodal integration, sustainable land use and well-planned urban growth.
The project also illustrates the growing role of domestic engineering expertise in delivering complex infrastructure. Large-scale tunnel construction, specialised machinery and advanced construction management are contributing to the development of local technical capabilities that may support future national infrastructure programmes. Environmental planning remains another critical consideration. The undersea alignment beneath Thane Creek was selected to minimise surface disruption and reduce ecological impacts compared with alternative construction methods. Experts nevertheless stress that long-term monitoring of sensitive coastal ecosystems and careful environmental management will remain essential throughout construction and subsequent operations. As excavation progresses, attention will increasingly shift towards integrating tunnel works with track installation, signalling systems and station infrastructure. The Mumbai Ahmedabad Bullet Train corridor continues to represent one of India’s most ambitious transport investments, with its success likely to influence the future direction of sustainable high-speed rail development across the country.
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