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Crack in a caisson of the First Hawkesbury River Railway Bridge
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Date11th August 2012
PhotographerRobert GreenDescriptionThis photo shows a crack in one of the bridge caissons.
The real difficulty in constructing the first Hawkesbury River Railway Bridge in 1889 was firmly placing six piers in what was the deepest bridge foundations in the world. There was no technology to reach the rock bed of the river 90 metres below the water line.
An iron tube called a caisson was driven into the silt by increasing its weight and filling it with concrete. However, as the caissons sank they tilted and moved away from their intended positions. One caisson was so far out of alignment that a secondary one had to be sunk next to it, but it collapsed. One caisson sank to be four feet (1.2m) away from where it should have been and so the bridge span had to be lengthened to reach it.
Within the 12 months warranty, divers found concrete had been washed away with the tide, making it impossible to repair at that depth. The bridge's pin-jointed design precluded strengthening of the main structure.
On 13th June 1937 after 50 years of monitoring the bridge, a crack developed suddently in No. 4 pier. Within two months a second crack developed. The 4th pier had two rolling bearings supporting both spans that became locked through corrosion and dirt. As the steel trusses moved, they tore the pier apart and a third and fourth crack was found.
An investigation found that the iron tubes of the deep foundations had not been filled with concrete but merely river gravel and the question in engineers' minds was how could this have been allowed to happen.
The eastern end of the track was closed and all trains reduced to a speed limit of 10 mph. Drilling revealed the caissons to be of unreliable strength. The whole concrete mass was found to be riddled with open water passages, large voids apparently filled with nothing more than mud and the concrete was so weak that it would not stay together to provide a core sample. The only solution left was to build a new bridge.
The bridge structure was dismantled but the piers were left in place.Physical FormatHawkesbury RiverDimensionsRobert Green Collection
PhotographerRobert GreenDescriptionThis photo shows a crack in one of the bridge caissons.The real difficulty in constructing the first Hawkesbury River Railway Bridge in 1889 was firmly placing six piers in what was the deepest bridge foundations in the world. There was no technology to reach the rock bed of the river 90 metres below the water line.
An iron tube called a caisson was driven into the silt by increasing its weight and filling it with concrete. However, as the caissons sank they tilted and moved away from their intended positions. One caisson was so far out of alignment that a secondary one had to be sunk next to it, but it collapsed. One caisson sank to be four feet (1.2m) away from where it should have been and so the bridge span had to be lengthened to reach it.
Within the 12 months warranty, divers found concrete had been washed away with the tide, making it impossible to repair at that depth. The bridge's pin-jointed design precluded strengthening of the main structure.
On 13th June 1937 after 50 years of monitoring the bridge, a crack developed suddently in No. 4 pier. Within two months a second crack developed. The 4th pier had two rolling bearings supporting both spans that became locked through corrosion and dirt. As the steel trusses moved, they tore the pier apart and a third and fourth crack was found.
An investigation found that the iron tubes of the deep foundations had not been filled with concrete but merely river gravel and the question in engineers' minds was how could this have been allowed to happen.
The eastern end of the track was closed and all trains reduced to a speed limit of 10 mph. Drilling revealed the caissons to be of unreliable strength. The whole concrete mass was found to be riddled with open water passages, large voids apparently filled with nothing more than mud and the concrete was so weak that it would not stay together to provide a core sample. The only solution left was to build a new bridge.
The bridge structure was dismantled but the piers were left in place.
Physical FormatHawkesbury RiverDimensionsRobert Green CollectionLocation
Building NameHawkesbury River Railway BridgeHawkesbury RiverBridgesStreet:StreetView:&enabled=0&fov=90&heading=0&pitch=0&zoom=15
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Crack in a caisson of the First Hawkesbury River Railway Bridge (11th August 2012). Hornsby Shire, accessed 19/03/2026, https://hornsbyshire.recollect.net.au/nodes/view/2735