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Friday, May 07, 2021

Chenab bridge: A future icon of Indian Railways heritage

Upon completion, it will be the world’s highest railway bridge

Written by Bibek Debroy |
Updated: April 15, 2021 8:58:33 am
The world’s highest railway bridge, over river Chenab. (Courtesy: Afcons/Northern Railway)

This figure is a few years old. Indian Railways (IR) has 1,47,523 railway bridges, classified under heads of important bridges, major bridges and minor bridges. About 700 of those bridges are “major” ones. Usually, when we think of IR heritage, we have in mind steam locomotives such as the 1855-built “Express” and “Fairy Queen”, numbered EIR-21 and EIR-22 respectively (EIR stands for East Indian Railway). Housed respectively in Perambur and Rewari, both are remarkably still in working order. But heritage isn’t only about locomotives (steam or otherwise), coaches and wagons. It is also about buildings, stations, bridges and tunnels and much else.

IR’s heritage inventory includes several bridges. Many bridges are old and when constructed, they were marvels of engineering. For figures on old bridges in IR, people generally quote a 2015 CAG report: 36,470 are more than 100 years old and 6,680 more than 140 years old. Some of these must be phased out, rehabilitated in some fashion or completely reconstructed. Because of the way “heritage” is defined, not every old bridge is listed in IR’s inventory. The old Yamuna bridge in Delhi (known as Lohe-ke-Pul) is an example. For years and years, people remembered these bridges — Jubilee Bridge between Hooghly Ghat and Garifa, Yamuna Bridge in Naini, the bridge across the Mahi in Bhairongarh, Netravati bridge near Mangalore, Old Godavari bridge (Havelock bridge) in Rajahmundry, Pamban bridge, Abdul Bari bridge across Sone, Aryankavu bridge near Punalur, Dapoori viaduct near Pune and Nanjangud bridge across Kabini. That one, across Kabini, was constructed in 1735. Originally used as a road bridge, from around 1889, railways started using this bridge. With some cheating, one can say this is the oldest surviving railway bridge in India. To place this in perspective, the oldest surviving railway bridge anywhere in the world is Causey Arch in England, built in 1725-26.

Heritage bridges are old marvels of engineering. There are new marvels of engineering, too. People might talk about these railway bridges 150 years from now. For instance, there is the world’s tallest pier bridge across the river Irang in Manipur, part of the Jiribam-Tupul-Imphal broad gauge network. The pier height is 141 metres, two metres more than the present world record, held by a viaduct in Montenegro. There is the new Pamban bridge, India’s first vertical lift bridge, replacing the old Pamban bridge. There is Bogibeel bridge, connecting Assam and Arunachal Pradesh. However, when one hears the expression new engineering marvel, I suspect most people will not think of Irang, Pamban or Bogibeel, but Chenab. Since the arch closure happened in early April, the Chenab bridge has also recently been in the news.

Construction wasn’t easy, given the terrain. That’s the reason the timeline for completion kept getting postponed, from an initial 2009 to 2015. (The official timeline for completion probably remains December 2021.) A similar bridge, the Anji Khad bridge, could not be pursued because of geological issues. That doesn’t mean the Anji Khad bridge won’t be built. It will be built, but it will be a different kind of bridge. The Chenab bridge is an arch bridge. The Anji Khad bridge could have been an arch bridge. But it will now be a cable-stayed bridge, which means cables from towers will support the bridge.

Not all railway bridges are the same. Materials used can be different, but so can the design — truss, cantilever, trestle, arch, beam, suspension and cable-stayed. One must be careful, though. Design doesn’t occur in silos. Modern bridges often splice one design idea with another, such as suspension with cable-stayed, or cantilever with truss. The Bogibeel bridge is a truss bridge. The old Pamban bridge is cantilever. The Vembanad bridge, the second-longest bridge in India, is probably the most recognisable beam bridge. There are several iconic suspension bridges (Howrah bridge, Vidyasagar Setu, Bandra-Worli), but these aren’t railway bridges. Chenab is an arch bridge. There is a certain majestic quality about long arch bridges. Think of the Godavari arch bridge in Rajahmundry. When completed, the Chenab bridge will also be majestic. It will be 1,315 metres long, with an arch span of 467 metres, certainly the longest span for any Indian railway bridge.

But it has also been described as the world’s highest railway bridge. There is a difference between the tallest bridge and the highest bridge. A bridge may have tall towers. When we talk about the tallest bridge, we mean distance from the highest portion of the bridge to the surface of the water (that is, the exposed portion of the bridge that is above water). Engineers call this structural height. Unlike the tallest, highest is defined in terms of deck height, the deck being the surface of the bridge along which trains and vehicles travel. Deck height is the distance between the deck and the surface of the water. Deck height is used to define the highest bridge and the Chenab bridge has a deck height of 359 metres. Several bridges are higher. Most are in China. There is one in Papua New Guinea and one in Mexico. But all those are road bridges. As a railway bridge, the Chenab bridge will be the world’s highest. The present record is held by Najiehe Railway Bridge in China, with a deck height of 305 metres. That’s also an arch bridge. With an arch span of 467 metres, will the Chenab bridge have the longest arch span in the world? No, because of Sydney Harbour bridge. IR is adding quite a few bridges for a future heritage list.

This column first appeared in the print edition on April 15, 2021 under the title ‘Heritage on track’. The writer is chairman, Economic Advisory Council to the Prime Minister. Views are personal

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