Pile Foundation Optimisation for Rail Bridge: A Case Study From Dodson Road, Bunbury, Western Australia-Paper

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The Dodson Road rail bridge replacement in Bunbury, Western Australia, required a foundation solution suited to variable ground conditions and confirmed acid sulfate soils (ASS). Investigations found alternating clay and sand layers, with a very dense sand layer over clay at the East Abutment. ASS testing showed significant potential acidity, making excavation and spoil handling environmentally challenging.<br /><br />The initial design specified driven steel tubular piles. The team compared these with 400 mm square precast concrete displacement piles, considering capacity, drivability, durability, cost and environmental impacts. Concrete piles were selected as a lower-cost option; a durability review confirmed their suitability for ASS conditions when designed with appropriate sulfate-resistant concrete.<br /><br />Drivability analysis identified possible refusal in the East Abutment’s dense sand. A trial pile was therefore driven and dynamically tested. It reached the target depth without pre-drilling, achieved capacities well above the required design capacity, and remained within allowable stress limits. Production piles were then installed, with pile-driving monitoring and PDA testing on half the piles at each abutment.<br /><br />All tested piles exceeded the required design capacities. Results also confirmed different load-transfer behaviour: East Abutment piles generally mobilised more end bearing, while West Abutment piles relied more on shaft resistance. Although subsurface variability caused some measured capacities to differ from predictions, the design requirements were met.<br /><br />The case demonstrates how supplementary investigation, comparative design, trial installation and field testing can manage geotechnical and environmental risks while improving constructability. Switching to precast concrete piles also produced estimated savings of approximately AUD 800,000–1 million.

Keywords

Dodson Road

rail bridge replacement

Bunbury

Western Australia

acid sulfate soils

geotechnical investigation

precast concrete piles

drivability analysis

dynamic pile testing

construction cost savings