Fast-track Pile Design and Construction for the Fitzroy River Bridge Replacement, Western Australia-Paper

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The Fitzroy River Bridge in Western Australia was destroyed by severe flooding caused by ex-Tropical Cyclone Ellie in January 2023, severing the Great Northern Highway, a vital freight and community link. The replacement bridge was delivered on an accelerated schedule and opened in December 2023, six months ahead of plan.<br /><br />Because modern geotechnical data were unavailable at the start of design, engineers used 1972 pile penetration test records to estimate soil and rock resistance through driveability back-analysis. These preliminary estimates informed conservative foundation design and hammer selection while a staged investigation was completed. The investigation identified variable alluvial deposits, local cobbles and boulders, and low-strength siltstone bedrock.<br /><br />The 270 m bridge is supported by 1,200 mm diameter open-ended steel piles driven 30–40 m into the riverbed, then drilled out and filled with reinforced concrete. Design considered extreme loading, potential scour of up to 15 m, and other geotechnical hazards. A large-capacity hammer was selected to reduce the risk of premature refusal and inadequate embedment.<br /><br />During construction, geotechnical staff monitored pile driving, logged ground conditions, and checked installation and concreting. Dynamic pile testing and CAPWAP analysis verified capacity; restrike tests also measured capacity gains from pile setup. Results generally supported the design, with shaft resistance providing most axial capacity and end bearing contributing significantly. Scour assessments were essential because scour had caused the original bridge’s failure, although reduced flood loading in the enlarged channel meant scour cases did not govern the final design.<br /><br />The project demonstrates how historical data, conservative assumptions, staged investigation, and continuous verification can manage uncertainty on an urgent infrastructure project. Adaptive design and construction practices enabled the bridge to meet its performance requirements despite a compressed schedule and challenging river conditions.

Keywords

Fitzroy River Bridge

Western Australia

severe flooding

ex-Tropical Cyclone Ellie

Great Northern Highway

geotechnical investigation

pile driving

scour assessment

CAPWAP analysis

bridge reconstruction