Mumbai-Ahmedabad Bullet Train tunnel work advances in Maharashtra

The Mumbai-Ahmedabad Bullet Train project is moving ahead in Maharashtra. Tunnel boring machine assembly has started for a stretch of the route. It combines deep underground works with an undersea section beneath Thane Creek.

Mumbai-Ahmedabad Bullet Train project tunnel section

The current tunnelling programme covers the 21 km section between Bandra Kurla Complex (BKC) and Shilphata. Of that length, 16 km will be excavated with tunnel boring machines. This means most of the section will be TBM-driven. The remaining 5 km has already been completed using the New Austrian Tunnelling Method (NATM).

Key engineering parameters for this tunnel package are:

• total length of the tunnel: 21 km
• section to be driven by TBMs: 16 km
• section already completed with NATM: 5 km
• undersea portion: 7 km under Thane Creek
• configuration: single-tube, twin-track tunnel
• diameter: 13.1 metres
• depth below ground level: 25 to 57 metres
• deepest point: 114 metres below Parsik Hill

TBM assembly at Vikhroli and Sawli

At Vikhroli, TBM assembly started with the lowering of a shield segment weighing about 170 metric tonnes. The component is around 8.66 metres long and 7 metres wide. It was placed at a depth of 56 metres, roughly equivalent to a 20-storey building.

Meanwhile, a second TBM is also being assembled at Sawli, near Ghansoli. Work there is taking place 39 metres below ground level. Space is limited at the shaft location. The assembly sequence has been carefully organised to maintain both precision and safety.

Three shafts have been built to support the tunnelling works:

• Shaft 1: retrieval shaft at BKC
• Shaft 2: launch shaft at Vikhroli
• Shaft 3: launch shaft at Sawli

The machines are scheduled to work on different sections of the route. TBM-1 will advance from Vikhroli toward BKC, while TBM-2 will travel from Sawli to Vikhroli. This arrangement is intended to support efficient excavation and help keep tunnel delivery on schedule.

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Also, the project uses two of the most advanced TBMs deployed in India. They are designed for challenging geological conditions.

Their technical specifications are as follows:

▪ TBM-1 weight: 3080 tonnes

▪ TBM-2 weight: 3184 tonnes

▪ length of each machine: 95.32 metres

▪ cutter head diameter: 13.6 metres

▪ system type: Mix Shield / slurry-based technology

▪ maximum operating speed: 4 RPM

▪ excavation rate: 49 mm per minute

Each unit includes the cutter wheel, main bearing, jaw crusher, erector, main shield, tail shield, and four specialised gantries. These gantries support excavation, ring segment installation, waterproofing, and logistics during tunnelling.

Tunnel lining, monitoring and construction timeline

A dedicated casting yard has been set up at Mahape in Thane district. It covers 11.17 hectares and supports tunnel lining. The facility is designed to manufacture 77,000 segments that will form 7,700 rings. Each ring consists of nine curved segments and one key segment. Each segment measures 2 metres in width and 0.5 metres in thickness.

In addition, the casting yard has been equipped with mechanised infrastructure. It includes cranes, gantries, batching plants, and steam-curing areas. These support production quality and operational efficiency.

Separately, the project is also using an extensive monitoring system for safety and structural control. Monitoring measures include:

▪ Surface Settlement Points (SSP)

▪ Optical Displacement Sensors (ODS) or tilt meters

▪ 3D targets (BRT)

▪ strain gauges for tunnel surface observation

▪ seismographs to track vibration and seismic activity

These systems are intended to provide real-time monitoring. They also reduce the effect on nearby infrastructure and support safe excavation. The TBM programme will move ahead in stages. The initial drive is scheduled for July 2026. The main drive is planned for October 2026.

The Mumbai-Ahmedabad Bullet Train project is one of India’s most ambitious infrastructure projects. It includes the country’s first 7 km undersea rail tunnel beneath Thane Creek. At the same time, the use of high-capacity TBMs and a mechanised segment production facility highlights the engineering scale of the work now under way.

Still, with TBM assembly now in progress, work on the tunnel section has moved forward. Deep excavation and undersea tunnelling form part of that corridor. Specialised machinery and dedicated segment production do as well.

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