Onkaparinga Valley Bridge, Australia

The Seaford Rail Extension Project involves the construction of 5.7 kilometres of dual electrified track on Adelaide’s southern suburban railway line.

Aurecon was engaged to design the 1.2 kilometre Onkaparinga Valley Bridge which is an elevated rail bridge, and a key element of the rail extension. Aurecon was responsible for the concept through to detailed design which included a complex geotechnical assessment in liquefiable soils, piled foundations, piers and superstructure.

Our role also included lighting and provision of earthing and bonding, along with noise assessment of the entire route. The bridge is an incrementally launched, post-tensioned, box girder bridge with multiple 52-metre spans.

The unusual articulation accommodated the complex behaviour of rail track associated with long ballasted deck bridges. The abutment and launch bay structures were employed as the main anchors against massive braking and earthquake loads.

Aurecon’s preferred design required fewer piers, with a single span across the river and confinement of construction equipment away from the sensitive valley floor. A launched medium span bridge proved the most cost-effective design and minimised environmental impacts compared with a conventional super tee option.

The project is being delivered as a joint venture between Thiess and McConnell Dowell, who are currently constructing the bridge for the South Australian Department of Planning, Transport and Infrastructure. Construction commenced in 2011 and is expected to be completed in 2013.

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