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

PPT Presentation

Pdf Summary

The Fitzroy River Bridge in Western Australia was severely damaged by Tropical Cyclone Ellie in January 2023. Floodwaters reached an estimated 60,000 m³/s, scouring foundation piles and washing away around 80 metres of embankment near the eastern abutment. The damage cut the only sealed road between Western Australia and the Northern Territory, disrupting transport and isolating remote communities.<br /><br />The replacement bridge was designed and built on a fast-track schedule despite limited recent geotechnical information and uncertainty about riverbed conditions. Initial pile penetration tests suggested dense sand and gravel, possible boulders, and deeper weathered bedrock. Engineers used the test data to estimate pile resistance, adopting conservative values for preliminary design while assessing higher values for pile installation.<br /><br />Scour was a major design concern: the previous event had removed up to eight metres of material, while the new bridge had to account for a much rarer flood and up to 15 metres of scour. The design also considered how scour could loosen soils below the eroded riverbed.<br /><br />Key construction risks included whether piles could be driven with available hammers, potential obstructions, and the time required to splice pile sections. Mitigations included avoiding old pile locations, using a purpose-designed construction causeway and driving shoes, allowing for rock drilling, and limiting pile sections to two 21-metre lengths. Geotechnical investigations continued during detailed design, progressively refining the ground model and pile design.<br /><br />The bridge was opened to traffic on 10 November 2023—nine months after the project was awarded and six months ahead of schedule.

Keywords

Fitzroy River Bridge

Western Australia

Tropical Cyclone Ellie

flood damage

scour

geotechnical design

pile foundations

bridge replacement

construction risks

remote communities