Mumbai-Ahmedabad Bullet Train Project: India's First Undersea Tunnel Takes Shape In Maharashtra — All About It

The National High-Speed Rail Corporation Limited (NHSRCL) has announced significant progress in the construction of India’s first underground/undersea tunnel for the Mumbai-Ahmedabad bullet train project.

NHSRCL is the implementing agency for the Rs 1.08 lakh crore high-speed rail project connecting India's financial capital in Maharashtra to Ahmedabad in Gujarat.

Spanning 21 km, this underground tunnel will connect the Bandra-Kurla Complex (BKC) in Mumbai to Shilphata in Maharashtra, including a 7-km undersea section at Thane Creek.

Tunnel Construction Details

The 21-km stretch is being constructed using two methods:

• 16 kilometers will be excavated using Tunnel Boring Machines (TBMs).

• 5 kilometers will be constructed using the New Austrian Tunneling Method (NATM).

Key Milestones Achieved:

1. ADIT (Additionally Driven Intermediate Tunnel) Portal

   • A 394-meter-long ADIT tunnel was completed in May 2024 in a record six months.

   • The ADIT has facilitated two additional NATM excavation faces, enabling the completion of 1,111 meters of tunneling.

   • This tunnel, measuring 11 x 6.4 meters, provides vehicular access for construction and emergency evacuation.

2. Shaft Progress

   • Shaft 1 (Mumbai HSR Station): Excavation work for a 36-meter-deep shaft is ongoing.

   • Shaft 2 (Vikhroli): A 56-meter-deep shaft is completed and will deploy TBMs in two directions—towards BKC and Ahmedabad.

   • Shaft 3 (Savli near Ghansoli): A 39-meter-deep shaft has been successfully completed.

3. Tunnel Portal at Shilphata

   • The NATM tunnel portal is completed, and 602 meters of the 1,628-meter stretch has been excavated.

Safety Measures and Monitoring

The NHSRCL is taking extensive precautions to ensure the safety of workers and nearby structures:

• Adequate ventilation is maintained inside the tunnels.

• Excavated material is disposed of as per state guidelines.

• Continuous monitoring of surrounding structures is conducted using geotechnical instruments, including inclinometers, vibration monitors, and tilt meters, to prevent risks related to tilt, settlement, or deformation.

Casting Yard for Tunnel Linings

A dedicated casting yard has been established in Mahape, Thane district, for the tunnel’s TBM-excavated section:

• Specifications:

  • The yard will produce 77,000 segments, forming 7,700 rings for the tunnel lining.

  • Each ring consists of nine curved segments and one key segment, made of M70 grade high-strength concrete for long-term durability.

  • Steel reinforcement per ring: 4.368 MT; Concrete per ring: 39.6 cubic meters.

• Facilities:

  • Nine sets of moulds, batching plants (69 cubic meters per hour capacity), and a state-of-the-art QA-QC laboratory are in operation.

  • Advanced equipment, including cranes, gantries, and steam curing systems, ensure precision and quality control during casting operations.

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