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On August 13 – just in time for the 75th anniversary of Indian Independence – India’s Chenab Bridge was officially inaugurated, and became the highest rail bridge in the world.

It marked the conclusion of a near 20-year civil engineering project that faced an enormous number of challenges, many summed up in two words: The Himalayas – a region full of geological surprises, extreme winters, torrential rain and boiling summers.

More than 60km of tunnels lead to the steel and concrete arch bridge itself, which spans the Chenab River in a remote and mountainous part of northern India. It lofts above the riverbed at a height of 359m (it would clear the Eiffel Tower by an easy 30m), and is not just the world’s highest rail bridge, but also boasts the longest broad-gauge railway span and the longest arch for rail traffic (467m).

Konkan Railway Corporation announced the completion of the ‘golden joint’ at the centre of the deck of the bridge high above the River Chenab. Source: https://www.bridgeweb.com/

The crossing was envisioned as part of an ambitious scheme to create a 272km railway line through Jammu and Kashmir. However, though approved in 2003, work was paused in 2008 when the complexity of the geology bedevilled the bridge’s stability. With reservations assuaged, it was restarted two years later, but even so, the hostile nature of the location has continued to nudge back the completion date from 2015 to 2022. (It opens for rail traffic in December.)

Construction involved inching the bridge superstructure together from each side of the river valley, until it met in the middle and was linked by the final 5.6 metre ‘golden joint’ (the centrepiece of the official inauguration).

Source: Indian’s Ministry of Railways

High winds and terrorist attention

Of the bridge’s 18 piers, four sit on the left abutment and 14 on a long approach on the right abutment. The two-ribbed arch is built from steel trusses, where the chords of the trusses are sealed steel boxes, internally stiffened and filled with concrete to resist wind speeds of up to 260kmh. Considering the violent history of the area, the bridge is even toughened against terrorist attack, and can withstand up toa 40kg of TNT blast.

During the build, Indian Railways used drones to develop a reality model to check on construction, plan project resources and identify potential issues. This approach is estimated to have reduced construction inspection time by around 80%.

Without the drones and high precision 3D mesh modelling of very minute details of the bridge structure – supported by Bentley Systems ContextCapture – many of the locations would have been almost impossible to inspect using traditional methods. (Bentley’s OpenRail Designer was also used to help the team transition the bridge rail alignment from straight to curved.)

In conclusion, a few statistics. It’s estimated that 3200 people worked on the construction; that the arch weighs 10,600 tonnes; it should last for 120 years; and cost Rs 1486 crore – around $185m.

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