The New ISO/API P-Y Curves in Clays and their Reconciliation with the PISA Framework

Abstract

Abstract ISO will soon issue the Draft International Standard (DIS) ISO 19901-4 to its members for comments and ballot. This DIS document includes major updates to the present state of the practice, including new p-y curves that will replace the long-standing API Matlock p-y curves for clays. The new p-y framework for offshore piles and well conductors results from comprehensive and extensive research that has successfully been tested against numerous field load tests and monitoring data. It covers monotonic, cyclic and fatigue loading conditions and uses fundamental soil properties to generate the p-y curves applicable to the loading scenario. The release of this DIS document coincides with a significant industry momentum to develop offshore wind energy, which often includes the use of large diameter monopiles. Significant research, including the PISA project, has been conducted to provide design guidance for the offshore wind sector. This paper achieves two objectives: First, it presents a detailed discussion and context behind the exact formulations of the new p-y framework as it appears in the ISO DIS document, without repeating the underlying development, calibration and verification processes that are already published. Second, it demonstrates that the new ISO p-y curve framework and the PISA distributed lateral load resistance curves in clays are entirely consistent with each other. This is done by de-normalizing the published PISA curves for the Cowden site, re-normalizing them in the ISO format, and comparing the bearing capacity factors and the shape of monotonic p-y curves obtained with the two methods for the Cowden site conditions. The second objective is an important factor in understanding the overlap and alignment between the techniques used in the offshore oil and gas sector and those used in the offshore wind sector.