Mandurah Estuary Bridge Duplication â€“ Sustainable Geotechnical Design-Paper

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The Mandurah Estuary Bridge Duplication project required a new 400 m incrementally launched bridge across the estuary, supported by piled abutments and piers. During detailed design, the team reassessed the reference design using targeted site investigations and historical records from construction of the existing bridge.<br /><br />For foundations, the original bored-pile proposal was replaced with driven piles: precast concrete piles for abutments and nearshore piers, and concrete-filled, closed-ended steel piles for river piers. Seismic CPT results, historic pile records and dynamic pile testing supported the revised ground model and pile design. Predrilling through limestone at the western abutment mitigated refusal risk and was verified by pile testing.<br /><br />For approach embankments, conventional earthwork preloading replaced the reference design’s controlled modulus columns. Back-analysis of historical settlement monitoring informed ground parameters and preloading periods of one month at the eastern abutment and three months at the western. Construction monitoring confirmed that settlement stabilized sufficiently for preloading release, embankment stability was adequate, and impacts on the existing bridge were acceptable.<br /><br />The detailed design reduced estimated concrete use by about 2,500 m³ for piling and 5,300 m³ for ground improvement, while simplifying construction and avoiding extensive temporary works. These changes delivered cost, schedule and sustainability benefits through more efficient material use and reduced embodied carbon.

Keywords

Mandurah Estuary Bridge

bridge duplication

incrementally launched bridge

driven piles

precast concrete piles

steel piles

pile testing

ground improvement

preloading

embodied carbon