Skirted foundations in calcareous soil

Exploitation of oil and gas reserves in deep water off Australia's North-West Shelf has provided the impetus for expensive research into offshore foundation systems for the seabed calcareous sediments. Significant performance and installation problems associated with traditional piled foundations for the North Ranking A and Goodwyn A platforms have prompted investigations into shallow foundations, such as caissons and skirted rafts, where centrifuge modelling has played a key role in exploring potential designs. This paper provides an overview of modelling undertaken for industry for three separate foundation systems, namely a single caisson group and a skirted raft foundation, in two different areas of the North-West Shelf. Attention is focused on simulation and characterization of the in situ seabed conditions, in addition to the measured foundation response. A key aspect of the latter is the performance under cyclic loading due to cyclonic storm conditions, giving rise to cumulative settlement and potential instability caused by partial liquefaction of the soil.