Effect of Best-Estimate Clay P-Y Curves on Performance of Offshore Structures

Abstract

Abstract Fixed offshore platform pile foundation design and assessment in the Gulf of Mexico (GOM) has been based on API RP 2A [1] and current (2014) API/ISO RP 2GEO 1st edition [2] recommendations. Over the years, post-hurricane observations of the platform performance in the GOM have shown that these standards tend to underestimate soil lateral stiffness and capacity. Research work has been carried out for years to understand this conservatism and define the best-estimate soil lateral reaction for pile foundation design. These efforts culminated in a proposed draft of API/ISO RP 2GEO 2nd edition, which re-defines the clay soil lateral reaction formulations (p-y curves) for piles under monotonic, cyclic, and fatigue loads. This paper summarizes a study performed to determine the effect of the new clay soil p-y curves on the structural responses of offshore platforms. In this study, three (3) featured fixed offshore platforms in the GOM were selected as representative structures for structural analysis and comparison. The selected platforms are actual platforms in operation in the GOM. The predicted platform responses from analyses were directly compared with measured and observed platform performance in field, including platform damage in hurricanes. Analysis results demonstrate that structural models using the soil reaction formulations of the proposed 2GEO 2nd edition (draft), in combination with the best-estimate soil profiles interpreted based on the standard direct simple shear (DSS) tests, adequately predicted the platform responses observed in field. The clay soil p-y reaction formulations (monotonic, cyclic, and fatigue) proposed for the update of 2GEO, as included in Appendix A, show significant improvement over the formulations in older editions of 2GEO and RP 2A, and are endorsed and recommended for pile foundation design and assessment. Complete documentation of the study can be found in [3].