A numerical study on the lateral loading behaviour of offshore tetrapod piled jacket foundations in clay

摘要

Jacket foundations for offshore wind turbines, typically having three or four latticework legs, are mainly subjected to lateral loads induced by winds, waves and currents during their service life. An accurate assessment of the bearing capacity of these foundations is of great importance in the design. This paper presents a study into the monotonic lateral loading behavior of tetrapod piled jacket foundations in undrained clay, with the complex lateral loads being simplified to an equivalent lateral load acting at a certain height of the jacket. A centrifuge testing programme was undertaken to provide high-quality validation data for the development of a three-dimensional finite element model established using ABAQUS. The key parameters investigated are the spacing and embedment of the piles, the height to which the equivalent lateral load acts and the angle between the direction of this load and the orthogonal line of the jacket in the horizontal plane. The parametric study aims to provide guidance to the optimal design of jacket piled foundations: for instance, to examine the critical pile embedment beyond which limited improvement of the bearing capacity of the foundation can be achieved and to define the most unfavorable lateral loading direction. In addition, the limitations of the commonly assumed constant p-multiplier, regardless of the lateral deflection of the pile and the depth along it, are critically discussed. Then an improved analytical model is proposed, based on the existing model used in design and the parametric study results, to quantify the variation of p-multiplier with depth and with pile deflection.