By 2028, India will witness a groundbreaking feat in rail infrastructure with the introduction of the Ahmedabad-Mumbai bullet train, which will traverse beneath the ecologically sensitive Thane Creek. This ambitious project includes the construction of India’s first undersea tunnel, a pivotal segment of the 21-kilometre underground stretch on the Mumbai-Ahmedabad corridor.
The tunnel, which will stretch 7 kilometres beneath the Thane Creek, is set to commence with the launch of the tunnel boring machine (TBM) by the end of this year. This segment represents a significant engineering challenge due to the complex geological conditions under the creek. Distinct from existing underwater tunnels, such as Kolkata Metro’s Hooghly River crossing and Mumbai Metro’s Line 3 under the Mithi River, this new tunnel will feature a single-tube structure designed to accommodate dual tracks.
The TBMs deployed for this project will be equipped with cutter heads of 13.6 metres in diameter, a size considerably larger than the 6-8 metre cutter heads typically used for urban metro tunnels. Excavation work is currently underway at three key sites—Ghansoli, Shilphata, and Vikhroli. At Ghansoli, excavation for lowering the TBMs is progressing, with 120 metres completed towards BKC and 110 metres towards Shilphata. The process has involved 218 controlled blasts using gelatin to facilitate the excavation.
Despite an accelerated pace in Gujarat, where 352 kilometres of the 502-kilometre route is under construction, the Maharashtra section has faced delays. The Surat-Bilimora stretch, a 50-kilometre segment, is expected to open in August 2026, with the full project projected to be completed by late 2028, extending six years beyond the original timeline. The undersea tunnel will be bored at depths ranging from 25 to 57 metres below ground. Three mega TBMs will be used to excavate 16 kilometres of the 21-kilometre underground stretch, with the remaining 5 kilometres being constructed using the New Austrian Tunnelling Method (NATM).
This method involves meticulous monitoring and adjustment of wall reinforcement techniques based on the geological conditions encountered. To ensure safety, highly sensitive geotechnical monitoring instruments are being deployed across all construction sites in Maharashtra. These instruments are crucial for safeguarding both the ongoing excavation work and the surrounding structures.
