Explained: Tunnel Boring Machines which will help build India’s widest tunnel

With less than two months for the arrival of the mammoth machine, the Brihanmumbai Municipal Corporation (BMC) has kicked off work at its Goregaon worksite in western suburbs — where the TBM will be launched.

How is the BMC prepping for the arrival of the TBM?

Gearing up for the incoming machines, the BMC has launched piling works inside Film city that will offer stability for the excavation of the launching shaft for the TBM machines. The launching shaft is the spot where the TBM machines will be lowered to start digging the tunnel. This launching spot is located near Whistling Woods institute at Film city.

The civic body has already completed works on 300 piles out of a total of nearly 700 piles. Once the piling work is completed, the BMC launches works on the excavation of the launching shift. A challenging task with nearly 3 lakh metric tonnes of excavated material slated to be dug out, the shaft works are likely to be completed over a period of 12 months. Following this, the TBM machine will be lowered and the tunnelling works will commence.

The civic body has also begun work on the casting yard at Manor where the casting for the RCC segments of the tunnel will be carried out. The special moulds for the RCC rings have also arrived from Korea.

When will the TBM machines arrive and how will they work?

With twin tunnels planned within the ambit of the GMLR project, two TBM machines are expected to arrive from China. Among these, the first TBM machine is set to be shipped from China in March. Packed in massive parcels, the dismantled parts of the first TBM will start arriving at the city’s dock in April. According to senior officials, all portions of the machinery will arrive in the city over the course of April.
Following this, the dismantled parcels will be transported from the dock to the Film city worksite in trailers where the civic body will commence assembling the machinery that is expected to take two months. The TBM will then be lowered to commence boring from the Goregaon launching shaft.

Raking beneath the SNGP, the TBM will dig a 5.3-kilometre tunnel (over 10.6-km on both arms) before finally achieving its breakthrough at Mulund’s Amar Nagar Junction, where the other end of the tunnel is proposed to open. Typically, the TBM has a cutter-head in front, which has “teeth”, spokes or sharp protrusions, that rotate and cut through the soil.

What are the features of the GMLR twin tunnels?

A key crucial segment of the GMLR project — which seeks to alleviate congestion along the existing east-west corridors — the twin tunnels will surpass beneath the SGNP, covering a complex topography of hillocks, forest and farmlands. Of its total length, nearly 1.35 km will be made up the approach roads and the box-tunnel, while nearly 5.30 km will comprise the portion dug by the tunnel boring machine.
Starting from the Film City in the western suburbs, the tunnel will open near Mulund’s Amar Junction, which houses a huge slum pocket. On completion, the GMLR project is projected to relieve 40 per cent of the existing traffic along JVLR.

The twin tunnels will be made with a gap of 15 metres between the two. Like the coastal road’s twin tunnels, the GMLR tunnels will also have cross passages at a distance of 300 metres to aid movement during emergencies.

Meanwhile, in a unique boost to the city’s water network, the BMC has also proposed to erect two 1,800-millimetre water pipelines inside the twin tunnels that will follow the route of the tunnel and supply water directly from the Bhandup Water Treatment Plant to Goregaon in the western suburbs.

What is the current status of the twin tunnels?

While the GMLR tunnel work has procured all permissions, it is presently awaiting a final stage 2 approval from the forest department. Once acquired, senior officials said that the BMC will be able to commence works in the forest area.

Being tucked in an ecologically sensitive zone, the GMLR project has also undergone a slew of studies, including Environmental Impact Assessment (EIA), environmental and biological studies by Bombay Natural History Society (BNHS), as well as engineering and geotechnical studies. Since the tunnel is aligned between the Tulsi and Vehar lakes, the project has also undergone hydrological studies.

It was in July 2024 that Prime Minister Narendra Modi carried out the Bhoomi Poojan ceremony on the GMLR twin tunnels. Pegged at a revised cost of over Rs 6,500 crore, the BMC has set a deadline of October 2028 for the completion of the work.