Mumbai-Ahmedabad bullet train project: Work on 21-km underground tunnel between BKC, Shilphata in full swing

A total of 1,111 metres of tunnelling work has been achieved so far, with 622 metres completed towards BKC and 489 metres towards Ahmedabad.

A 21-km-long underground/undersea tunnel is being constructed between the Mumbai-Ahmedabad bullet train station at Bandra-Kurla Complex (BKC) and Shilphata in Maharashtra. Of this 21 km, 16 km will be built using tunnel-boring machines (TBM), while the remaining 5 km will be constructed using the New Austrian Tunneling Method (NATM). This includes a 7-km undersea tunnel at Thane Creek.

The construction work for the Mumbai-Ahmedabad bullet train has made significant progress across various locations. At ADIT (Additionally Driven Intermediate Tunnel) portal, a 394-metre-long tunnel was completed last May in a record time of six months. This has facilitated two additional NATM faces for excavation, in addition to the Shilphata site. As a result, 1,111 metres of tunnelling work has been achieved so far, with 622 metres completed towards BKC and 489 metres towards Ahmedabad. ADIT, which measures 11x6.4 metres, will provide direct vehicular access to the main tunnel during both construction and operations and could also be used for emergency evacuations if necessary.

Shafts

Excavation is underway at Shaft 1, located at the Mumbai High-Speed Rail (HSR) station construction site, with a shaft depth of 36 metres. At Shaft 2 in Vikhroli, the shaft has been completed to a depth of 56 metres. This shaft will allow the lowering of two tunnel boring machines, one towards BKC and another towards Ahmedabad. Additionally, excavation work at Shaft 3 in Savli, near Ghansoli, has been completed, with a shaft depth of 39 metres. The tunnel portal at Shilphata, located at the NATM end of the tunnel, has already seen completion of portal work, and 602 metres of tunnel work has been achieved out of the planned 1,628 metres.

Precautions undertaken

During excavation, several safety precautions are being implemented. Ventilation is ensured within the tunnel to provide a safe and breathable environment for the workforce. Excavated materials are being disposed of according to state government guidelines. Continuous monitoring of structures and buildings around the tunnel sites is in place to detect any potential damage. Geotechnical instruments, such as inclinometers, vibration monitors, ground settlement markers, and tilt meters, have been installed around the construction sites to measure tilt, settlement, vibrations, cracks, and deformation. These instruments play a crucial role in ensuring the safety of both the ongoing underground work and the surrounding structures.

A dedicated casting yard for the tunnel lining has been set up in Mahape, Thane district, for the 16-km TBM section. The yard will produce 77,000 segments, which will form 7,700 rings. Each ring consists of nine curved segments and one key segment, with each segment measuring 2 metres in width and 0.5 metres in thickness. High-strength M70-grade concrete is being used for these segments to ensure superior structural integrity and long-term durability. The casting yard spans an area of 11.17 hectares and includes nine sets of moulds, each containing ten pieces. Three batching plants, with a combined capacity of 69 cubic metres per hour, are operational at the yard. After casting, the segments undergo steam curing, followed by final curing with a curing compound. Additionally, steel reinforcement of 4.368 tonnes is used in each ring, and 39.6 cubic metres of concrete are poured into each ring. To control cracking, Glass Fibre Reinforcement Polymer (GFRP) bars are used at the edges of the segments.

The yard is equipped with various cranes, gantries, and machines to automate and mechanise the casting operations, ensuring high-quality assurance during the production of the tunnel lining segments. The facility also includes casting sheds, a stacking area, a batching plant, and a steam curing area.