Mumbai-Ahmedabad bullet train project: India's largest rail tunnel boring machine starts excavation

📌 Summary:

• India's largest rail tunnel boring machine (TBM) began excavation from Vikhroli, Mumbai, for a 6-km single-tube tunnel that will carry both up and down tracks of the Mumbai-Ahmedabad high-speed rail (HSR) corridor — India's first bullet train project

• TBM specs: 13.6-metre-diameter cutterhead (height of a four-storey building), ~3,100 tonnes, 96 metres long; a Mixshield slurry-type TBM designed for mixed ground and high groundwater pressure; can excavate and install segment rings simultaneously

• The project has a 21-km underground section: 16 km between Sawli (Ghansoli) and Bandra Kurla Complex will be excavated by TBMs; the remaining 5 km is already complete via the New Austrian Tunnelling Method (NATM)

• The tunnel passes beneath dense urban areas — multi-storeyed buildings, roads, the Mithi river; the method was chosen to control ground settlement and minimise surface disruption

• Waterproofing: double-layer EPDM gaskets and hydrophilic seals; a 56-metre-deep launch shaft (like a 20-storey building underground) built at Vikhroli with slurry/water treatment plants and real-time monitoring

• Executing agency: National High-Speed Rail Corporation Limited (NHSRCL)

🎯 UPSC Relevance: GS3 Infrastructure — high-speed rail, urban tunnelling technology, mega-project execution

📝 Prelims Facts:

• Mumbai-Ahmedabad HSR — India's first bullet train corridor; executing agency NHSRCL; 21-km underground section, 16 km by TBM + 5 km by NATM
• TBM cutterhead diameter 13.6 m; tunnelling methods: Mixshield (slurry) TBM vs NATM

🔑 Key Term: Tunnel Boring Machine (TBM) — a machine that excavates tunnels with a rotating cutterhead while simultaneously erecting precast lining segments, minimising surface settlement compared with drill-and-blast methods.