Abstract
FPSO [Floating Production Storage and Offloading] structures have been accepted as a sustainable economic solution for deepwater development projects. Short to medium length (typically 15 to 25m) large diameter driven piles are often used to anchor FPSOs. The loading in such piles during a storm can be resolved into two components: (a) Lateral load, which is one-way cyclic; (b) Tensile (upward) load, which is typically only a few percentage of the lateral load. The greatest uncertainty in the analysis is the load carrying capacity of the pile, since the cyclic storm loading results in progressive degradation of the soil (sand or clay) supporting the pile. Thus understanding the degradation of the supporting oil is critical, for a safe, economic design. This paper thus hastwo aims: (a) to propose criteria and considerations for design of such piles; (b) to set out simple modifications in the p-y formulation that will provide a safe working envelope for the full range of ground conditions likely to be encountered at different sites. A parallel is also drawn to the approach routinely used by the geotechnical earthquake engineering profession, and reported centrifuge tests have been used to validate the proposed modification.