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Explained: Why a tunnel boring machine has been stuck in Mumbai slush for a year

With major cities in India opting for urban transportation systems underground, Tunnel Boring Machines, that help dig tunnels underground, are being deployed extensively in the country.

Written by Zeeshan Shaikh , Laxman Singh , Edited by Explained Desk | Mumbai | Updated: December 3, 2020 11:25:54 am
In India, TBMs have been deployed in Delhi, Mumbai, Pune, Chennai, Bangalore and Kolkata, among others, to help build underground Metro lines. (Express Photo: Ashish Kale, File)

A tunnel boring machine, used to dig underground tunnels, has been stuck in Mumbai for the past one year. The Brihanmumbai Municipal Corporation (BMC), which had deployed the machine to dig a tunnel for its water supply project, has not been able to retrieve it due to lack of expertise and an overreliance on foreign entities to operate these machines.

We explain the TBM market in India, and how it is dominated by foreign firms:

What are Tunnel Boring Machines?

With major cities in India opting for urban transportation systems underground, Tunnel Boring Machines, that help dig tunnels underground, are being deployed extensively in the country. They are used to excavate tunnels through a variety of soil and rock strata –– from hard rock to sand. These machines are capable of digging tunnels with diameters 3.3 feet to 58 feet.

In which Indian cities are these Tunnel Boring Machines deployed

In India, TBMs have been deployed in Delhi, Mumbai, Pune, Chennai, Bangalore and Kolkata, among others, to help build underground Metro lines. These TBMs are also being used to help build water tunnels as well as the coastal road in Mumbai.

Where are these machines procured from?

In most Indian cities, the TBMs procured are from China or Europe. Of the 19 tunnel boring machines being used to dig underground tunnels in Mumbai for major infrastructure projects, eight have been manufactured by Chinese-owned companies, while 11 are by Western companies, but manufactured in China.

The biggest of these machines, manufactured by the China Railway Construction Heavy Industry Co, arrived in Mumbai on April 29. The TBM, said to be the largest such machine deployed in India, will be used for a 3.45-km twin undersea tunnel from Girgaum Chowpatty to Malabar Hill for Mumbai’s 29.2-km Coastal Road project.

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Which country dominates the TBM business?

The global TBM market is at present dominated by China. As per vendors, nearly 90 per cent of the TBMs deployed across India have a Chinese connection. China has a dominating presence in the heavy equipment machinery segment, and officials claim it is not possible to replace the sources of these types of equipment overnight.

With Indian firms like BHEL and BEMP still in early stages of producing TBMs, the need to procure the machines from outside India will continue for quite some time.

Is the stuck TBM in Mumbai of Chinese make?

The stuck TBM has been built by the German Company Herrenknecht, which, however, has manufacturing units in China.

How did the TBM get stuck?

The TBM had got stuck last August during tunneling for a 4.4-km stretch from Powai to Ghatkopar, after drilling about 1.2 km of length and 90 m depth. The tunnel was flooded with a slush of soil and rainwater. The soil at the location is soft and extricating the machine has proved to be an impossible task so far.

The portion where the TBM was drilling the soil strata is pyroclastic ash, which is very loose in nature. Such soil strata is not found anywhere in Mumbai, which predominantly has basalt rock strata. There are cavities near the TBM and during the rains last year, the tunnel was flooded. The TBM is now surrounded by slush, making its movement difficult. 📣 Express Explained is now on Telegram

What happens now?

The TBM’s diameter is about 2.8 m and its length is less than 50 m. In the last one year, the civic body has approached several TBM experts in the country as well as across the world, including those in Germany, seeking help for removal of the machine, but the efforts have been in vain.

The BMC has also formed an expert committee under the chairmanship of a professor from IIT-Mumbai to decide on the further course of action. BMC officials and members of the expert committee are set to meet next week.

Is it normal for TBMs to get stuck?

There have been no instances in India of TBMs being stuck for such a long period of time. Across the world, too, it is rare for a TBM to get stuck. In 2013, the world’s then biggest TBM, ‘Bertha’, which was drilling for a highway project, was stuck under Seattle city in the US after a technical snag. It was removed after four years.

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