The National High-Speed Rail Corporation Ltd (NHSRCL) is spearheading the Mumbai-Ahmedabad bullet train project, marking a significant milestone with the commencement of construction on a 21-kilometer tunnel between Bandra Kurla Complex (BKC), Mumbai, and Shilphata, Thane in Maharashtra.
Distinguished as India’s inaugural undersea rail tunnel, the 7-kilometer segment between Shilphata and BKC will employ cutting-edge techniques, including Tunnel Boring Machine (TBM) and New Austrian Tunneling Method (NATM).
Designed to accommodate twin tracks for both up and down lines, the single tube tunnel involves the construction of 39 equipment rooms at 37 locations along its route. The use of TBMs with a substantial 13.6-meter cutter head diameter, surpassing the typical 5-6 meter diameter, will cover around 16 kilometers of the tunnel, while the remaining 5 kilometers will be constructed using the NATM.
With depths ranging from 25 to 57 meters below ground level, the tunnel’s deepest point will be 114 meters beneath the Parsik hill near Shilphata. Key construction facilitators include three shafts at BKC, Vikhroli, and Sawli, Thane district, with depths of approximately 36, 56, and 39 meters respectively. An inclined shaft of 42 meters at Ghansoli and a tunnel portal at Shilphata will contribute to the construction of approximately 5 kilometers of the tunnel using the NATM method.
Construction activities are underway at pivotal locations:
- Mumbai High-Speed Rail (HSR) Station Construction Site – Shaft 1: This 36-meter deep shaft has completed 100% of its secant piling work and is currently undergoing excavation.
- Vikhroli – Shaft 2: With a depth of 36 meters, Shaft 2 has concluded its piling work and is undergoing excavation. It serves as the entry point for two tunnel boring machines, each heading towards BKC and Ghansoli.
- Sawli (near Ghansoli) – Shaft 3: Excavation is in progress at this 39-meter deep location.
- Shilphata, Thane: Marking the NATM end of the tunnel, portal work has already commenced.
- ADIT (Additionally Driven Intermediate Tunnel) Portal: This portal enhances construction efficiency by providing additional access to the underground/undersea tunnel.
Construction of these shafts presents challenges, including controlled blasting techniques to mitigate noise and air pollution, construction in densely populated areas with existing utilities, and proper disposal of excavated material under regulatory supervision.
Various supporting facilities, such as gantry cranes, labor colonies, and site offices, are concurrently under construction to facilitate project progress.