Mumbai-Ahmedabad Bullet Train: Second TBM Begins Excavation For India's First Undersea Rail Tunnel

Mumbai: Construction of India's first undersea railway tunnel moved a step forward on Saturday after the second Tunnel Boring Machine (TBM) began excavation from Sawli (Ghansoli) towards Vikhroli for the Mumbai-Ahmedabad Bullet Train project. The machine will excavate a 10-km stretch, including a 7-km tunnel beneath Thane Creek, marking a major milestone in the country's first high-speed rail corridor. The first TBM had already started tunnelling from Vikhroli towards Bandra Kurla Complex (BKC) on July 5.

21-Km Underground Section Among Most Complex Parts

The 21-km underground section between BKC and Sawli is one of the most complex parts of the project. Of this, 16 km will be built using two giant TBMs, while the remaining 5 km has already been completed using the New Austrian Tunnelling Method (NATM). The newly launched Mixshield TBM has a 13.6-metre cutterhead, weighs about 3,200 tonnes and is designed to safely excavate through Mumbai's challenging geology while minimising ground settlement and disruption on the surface. It also uses a semi-continuous advance system that allows tunnel excavation and lining work to take place simultaneously, speeding up construction.

Launching the massive machine required a 39-metre-deep shaft at Sawli, where its components were lowered and assembled underground due to space constraints. The TBM is equipped with advanced safety features, including real-time gas monitoring, automatic fire protection systems and emergency refuge chambers. Officials said the tunnel will be fully waterproof, with double-layer EPDM gaskets and hydrophilic seals to prevent water ingress. The project is also being monitored through a network of sensors tracking ground movement, vibration and structural behaviour to ensure safe tunnelling beneath one of Mumbai's busiest urban regions.

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