Numerical investigation on the lateral loading behaviour of tetrapod piled jacket foundations in medium dense sand

Wen, Kai, Wu, Xiaofeng and Zhu, Bin (2020) Numerical investigation on the lateral loading behaviour of tetrapod piled jacket foundations in medium dense sand. Applied Ocean Research, 100, [102193]. (doi:10.1016/j.apor.2020.102193).

Abstract

Recently tetrapod piled jacket (TPJ) foundations are considered as a promising solution for offshore wind turbines in waters with depths ranging from 20 m to 50 m. This paper presents a numerical study into the monotonic lateral loading behaviour of TPJ foundations in medium sand, in terms of overall load-displacement responses of TPJ foundations and internal force within individual corner piles as well as pile-soil interaction. The results of previous centrifuge model tests are used to provide high-quality verification for the development of a 3D finite element model established by ABAQUS. A series of parametric studies is then carried out to look into more detailed response of TPJ foundations subjected to lateral loads, including the influence of spacing and slenderness ratio of piles, loading height as well as soil friction angle. The numerical results show that there are two various deformation models of TPJ foundations during lateral loading. One is shearing dominated deformation model under smaller loads, while another one is overturning dominated model under larger loads. Moreover, the lateral soil-pile interaction is found to be greatly influenced by enhancing/weakening effects of the axial forces of individual piles. The cause of this phenomenon is primarily due to the change in soil stress induced by pile vertical movement and radial deformation. To quantify this effect on pile-soil interaction of TPJ foundation, an enhancement factor Γs, defined as the ratio of the soil resistance on downwind piles to that on upwind piles, is proposed. Consequently, the relationship between Γs, depth of influence zone zc and four parameters are carefully investigated. For simplicity, the Γs is assumed constant and independent with pile lateral deflection as well as soil depths, based on which the values for Γs and zc are recommended for practical design uses. It is highlighted in the present study that these values should be chosen based on the specific loading conditions to provide much safer and more robust design for TPJ foundations.

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Contributors

Author: Kai Wen

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