Burdekin Bridge

The Burdekin Bridge (known as the Burdekin River Bridge or Silver Link) spans the Burdekin River between the towns of Ayr (locality of McDesme) to the north and Home Hill to the south, both in the Shire of Burdekin, Queensland, Australia. Located on the Bruce Highway which is part of Highway 1, it is an important link in the national road network. It is a road-rail bridge which provides high flood immunity link between north and south Queensland.

The Bridge was completed in 1957. Construction began 10 years earlier in 1947. At 3,620 feet (1,103 m) in length, it is one of the longest multi-span bridges in Australia and longer than Brisbane's Story Bridge or New South Wales's Hawkesbury River Railway Bridge. It is 46 metres shorter than Sydney's Harbour Bridge. It is the only bridge in Australia to be built on sand.

Prior to the construction of the high-level Burdekin Bridge, there were two low-level bridges over the Burdekin River, one for road and one for rail. These bridges were frequently impassable due to flooding of the river. Remnants of the old rail bridge can be seen immediately downstream of the present bridge.

Originally, it was thought that the bridge could not be built in its present location. No trace of rock could be found on which to build the bridge foundations. In 1946, two high-ranking Government engineers visited India to inspect a number of bridges built on sand foundations. The same technique was used for the Burdekin Bridge and it is the only bridge in Australia not built with a firm foothold.

The bridge rests on 11 huge, hollow, concrete caissons sunk into the river bed. The caissons are 17 metres across the top (measured parallel to the stream) and vary in width from 5.5 to 7.6 metres. The caissons were sunk into the river bed to a depth of about 30 metres. Add to that the approximately 20 metres that the caissons rise above the bed and the result is some very massive pieces of concrete. Each weighs about 4,000 tons. The caissons were fitted with steel "cutting edges" to help them sink. The steel used in the cutting edges weighed 238 tons.

Construction of the first caisson started in 1947 after the "wet season". As each caisson rose in height, sand was removed from the centre of the caisson to make it sink into the sand bed. To get such a tremendous mass to sink gradually and evenly was difficult. To add to the difficulties, often a caisson became stuck and a diver had to be sent down to find the problem and remedy it. Another difficulty was that each caisson had to be sunk to a secure depth before the "wet season". If a caisson was not firmly anchored deep enough, a flood could have swept it away.

Because the bridge does not have rock foundations but is entirely supported by sand, it is sometimes described as a floating bridge. It is not a true floating bridge as it does not float on water.

The metal bridge spans were bolted together with high-tensile bolts instead of being riveted. At the time, no other Australian bridge had ever been constructed this way.