Determination of depth-of-fixity point for laterally loaded vertical offshore piles: A new approach

Abstract

Offshore piles are used as foundations for various marine structures such as quay walls, dolphins, and offshore platforms. Offshore piles are primarily subjected to lateral loads from wind, waves and currents, which is particularly challenging for piles with substantial free length above the seabed. This paper presents a new approach to determine the depth-to-fixity and the depth of the apparent plastic hinge of offshore piles considering the pile head condition, type of soil below, and the soil nonlinearity employing the p-y curve method. A comprehensive numerical investigation was conducted covering a wide range of key parameters governing the lateral response of offshore piles. The results of the parametric analysis were used to establish numerical equations to determine the depth-to-fixity and the depth of the apparent plastic hinge for free and fixed head piles embedded either in sand or in clay. In addition, a closed form solution has been developed utilizing the equivalent cantilever fixed-base model to estimate the lateral capacity of an offshore pile at specified lateral deflection and the corresponding maximum bending moment. The new approach was verified by field load test results conducted on partially embedded piles in sand and clay.