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.

中文翻译：

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中密砂四足桩套管地基侧向荷载特性数值研究

摘要 最近，四脚架桩式导管架 (TPJ) 基础被认为是深度为 20 m 至 50 m 水域的海上风力涡轮机的有前途的解决方案。本文根据 TPJ 地基的整体荷载位移响应和单个角桩内的内力以及桩土相互作用，对中砂中 TPJ 地基的单调横向荷载行为进行了数值研究。之前的离心机模型测试结果用于为 ABAQUS 建立的 3D 有限元模型的开发提供高质量的验证。然后进行了一系列参数研究，以研究 TPJ 基础在承受侧向荷载时的更详细响应，包括桩间距和长细比、荷载高度以及土壤摩擦角的影响。数值结果表明，TPJ地基在横向加载过程中存在两种不同的变形模型。一种是较小载荷下的剪切支配变形模型，另一种是较大载荷下的倾覆支配模型。此外，横向土桩相互作用被发现受单个桩的轴向力的增强/减弱影响很大。造成这种现象的原因主要是由于桩身垂直运动和径向变形引起的土应力变化。为了量化这种对 TPJ 地基桩土相互作用的影响，提出了一个增强因子 Γs，定义为顺风桩与逆风桩的土壤阻力之比。因此，仔细研究了Γs、影响区深度zc 和四个参数之间的关系。为简单起见，Γs 被假定为常数且与桩侧向挠度以及土壤深度无关，在此基础上，Γs 和 zc 的值被推荐用于实际设计用途。本研究强调，应根据特定的载荷条件选择这些值，以便为 TPJ 基础提供更安全和更稳健的设计。