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A first in India: Mumbai Trans-Harbour Link to have special decks to make longer-span bridge

'Orthotropic' steel decks allow for 6 times longer spans, accelerated construction, and are more economical. Technology is coming to India for the first time.

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Mumbai: From December, engineers working on Mumbai’s showpiece under-construction Sewri-Nhava Sheva trans-harbour link will enter a phase of complex construction activity.

The 22-km-long Mumbai Trans Harbour Link (MTHL), touted as India’s longest sea link, is set to see the installation of the first of multiple special steel decks, known as ‘orthotropic steel decks’, which will enable spans that are up to six times longer than usual, ThePrint has learnt.

According to the Mumbai Metropolitan Region Development Authority (MMRDA), the technology, while popular in Europe along with some countries in Asia, South America and the United States, is being used for the first time for any infrastructure project in India.

The distance between two piers of a bridge is referred to as a span, and while regular girders allow for a span of about 30 metres, the orthotropic steel decks enable spans of up to 180 metres, MMRDA Commissioner S.V.R. Srinivas told ThePrint. 

“From December, we will start some complex works on the MTHL. We will start launching special steel decks that will be used in India for the first time. Each of these decks weighs more than a thousand tonnes,” Srinivas said.

Read also: Mumbai’s Rs 14,262 crore trans-harbour link may get more expensive over design changes, delays

Orthotropic decks

Orthotropic decks are fabricated decks that have a structural steel deck plate that is stressed longitudinally and transversely to become dense enough for bearing a high load. 

MMRDA officials said the bridge design was chosen as the most preferable for a portion of the 22-km MTHL, as it not only provides for longer spans, but does so while helping accelerate construction and promises a longer bridge life at a relatively economical cost.

Longer spans also mean there is minimum disturbance to the navigation channels in the water.

Orthotropic steel decks accelerate construction by reducing the activities required on site, officials said. Only the bridge modules need to be assembled and field-welded on site.

“The fabrication of the decks is happening in different countries such as Japan, Taiwan, Burma, Vietnam. We have to bring the steel fabricated material, assemble them and launch. These decks have longer spans of more than 150 metres, up to 180 metres,” Srinivas added.

Access to mainland, Navi Mumbai development 

Once ready for use, the trans-harbour link will be a key connector to the proposed Navi Mumbai International Airport, the construction of which is also underway. The link is also likely to provide easier access to mainland Maharashtra from the island city of Mumbai, and speed up development in Navi Mumbai. 

The MMRDA was originally hoping to complete the project by 2022.

“We have put in place an acceleration plan to complete the construction by September or October 2023. We have multiple work fronts, additional machinery and manpower,” Srinivas said.

“We are also constructing more barges so that launching of girders can happen simultaneously at multiple locations,” he added.

Overall, the cost of the MTHL, which is being made in three packages, is pegged at Rs 17,843 crore, of which the total cost of construction is Rs 14,262 crore. The project, which is being implemented with a loan from the Japan International Cooperation Agency, is among India’s costliest infrastructure projects.

Contractors in charge of the three packages have claimed a 5-15 per cent escalation in construction cost, citing additional components such as extra barges and delays due to the Covid-19 pandemic.

(Edited by Saikat Niyogi)

Also read: Metro, coastal road, sea link — migrant exodus leaves Mumbai’s major transport plans hanging


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