Foundation and Retention Solutions in Geology Susceptible to Lateral Soil Movements Impacting Sensitive Wharf Structures-Paper

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A high-rise residential development in Melbourne’s Docklands required deep foundations beside a historic timber wharf and a newly constructed seawall. The reclaimed site contained very soft, normally consolidated Coode Island Silt over variable Fisherman’s Bend Silt and Moray Street Gravels, with a basalt tongue across part of the site and deeper siltstone bedrock. These conditions made pile installation capable of causing damaging lateral ground movement.<br /><br />Finite-element modelling and prior local experience showed that movements—particularly from continuous flight auger (CFA) piling—could threaten adjacent structures and impose bending forces on the new piles. Equipment access and ground-bearing limits also varied across the site. The design therefore used different methods in different zones: CFA piles in the central area; predrilled, driven precast concrete piles beside the northern wharf, with predrilling through the upper 12 m of soft clay; and open-ended steel circular hollow section piles near the southern seawall, installed using a specially designed guide frame and low-bearing-pressure support system. Sheet piles confined ground movements around the building cores and provided excavation retention.<br /><br />Modelling indicated that installation-induced bending could not be resisted by plain concrete pile sections, so reinforcement was extended to 30 m depth. Inclinometer monitoring confirmed the predicted movement mechanism, though movements were somewhat greater than forecast; the installed reinforcement remained adequate. Dynamic load testing and CAPWAP analysis verified the capacities of CFA, precast and steel piles under variable founding conditions.<br /><br />The project demonstrated that combining piling techniques, movement modelling, staged construction controls, monitoring and close coordination among the design and construction teams can protect sensitive neighbouring structures while delivering an efficient foundation solution on constrained, soft-ground sites.

Keywords

Melbourne Docklands

deep foundations

soft ground

CFA piling

precast concrete piles

steel circular hollow section piles

lateral ground movement

finite-element modelling

inclinometer monitoring

sheet piles