Geotechnical Offshore Site Investigation And Reclamation Design At Port Kembla

Port Kembla is an active seaport situated approximately 90 kilometres south of Sydney. The majority of the current port activities are focussed in the Inner Harbour area of the Port. However, as this is reaching capacity, the port authority is turning its focus onto the planning of the development of the mostly undeveloped Outer Harbour. Stage 1 and 1A (Phase 1) development of the Port Kembla Port Corporation (PKPC) Outer Harbour master plan would create one additional bulk cargo berth and approximately 10 hectares of reclaimed land. In February of 2010, PKPC awarded Snowy Mountains Engineering Corporation (SMEC) the contract to undertake Phase 1 detailed geotechnical site investigation works, and the associated reclamation and berth designs.

The Outer Harbour has been subjected to deposition of materials from five previous disposal campaigns, whereby dredged sediment from the Inner Harbour was disposed of within the Outer Harbour. Underwater containment bunds of uncrushed blast furnace slag were constructed for one of the disposal campaigns, and the contained areas were filled with spoil that typically consists of unconsolidated, very soft, compressible clay. This is consistent with geotechnical interpretation based on site investigation data which found that unconsolidated dredged fill, up to eight metres thick, underlies the majority of the Stage 1A and 1B development, generally thickening towards the east and southeast.

Phase 1 geotechnical design for the Outer Harbour development includes the design of containment bunds and land reclamation design associated with subsequent infilling with appropriate select fill material. Various design options were considered for both the bund and reclamation construction. Instrumentation and monitoring were proposed as part of the detailed design in order to confirm design assumptions and monitor the performance of the reclamation.

As the detailed design progressed, PKPC made the decision that the conforming design, which satisfied the original scope of works and settlement criteria, would not be constructed. Their preference instead was for a reclamation design that eliminated the need for removal of any of the underlying dredged spoil and did not utilise ground treatments other than passive preloading and surcharging techniques. The developed design has since been issued for tender and a constructor selected with construction about to commence.