The axial capacity of tubular steel piles for offshore installations is often based on the recommended practice of the American Petroleum Institute (API, 2007, 2011). In the Commentary, API includes four CPT-based methods for predicting the axial pile capacity in sand. The paper compares the axial capacity of largediameter piles in sand as predicted by the four CPT methods with the capacity as predicted by the API method. The calculated capacity and unit shaft friction are shown for different pile diameters and sand densities. The results highlight the wide range in predicted capacity, and the dependency of the unit skin friction on pile diameter for some of the methods. However, the measured average unit skin friction from the available static pile load tests, albeit on smaller diameter and short piles, do not show such trend.

1. Introduction

Four cone penetration test (CPT) based methods for calculating the axial capacity of piles in sand are included in the American Petroleum Institute (API) RP 2GEO commentary. The API/International Organization for Standardization (ISO) committee is currently discussing reducing the number of CPT method(s) and placing those in the main text instead. Before a decision is made, it is important to understand the implications of each method, especially when the methods are to be applied beyond the range of available verification data. This paper provides a partial evaluation of the methods through an examination of the statistics of the methods and a parametric study of piles in medium dense to very dense sand. The study highlights the predicted dependency of the unit skin friction on pile diameter for some of the CPT methods. This study is part of a larger effort to document the adequacy and reliability of axial capacity calculation methods for piles in sand.

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