Abstract

The soil around the pile foundations of offshore wind turbines (OWTs) would suffer from earthquakes which are widely believed to undermine the bearing capacity and serviceability of foundations. The non-intermittent lateral environmental loads in the ocean (e.g., wave, wind, and current) continuously act on OWTs. However, the seismic response of pile foundations and the soil around is less clear when considering the OWTs are subjected to lateral environmental loads. This paper presents two sets of centrifuge modelling tests on single piles, with a prototype diameter (D) of 1.5 m and a first-order natural frequency highly comparable to that of a prototype wind turbine. Two model piles with the same dimension and stiffness, but one with a lateral load on the pile head, were both installed in a dry sand ground and a saturated sand ground. Owing to the fact that the lateral load increased the initial static shear stresses of the soil in front of the pile, the development of excess pore pressure was inhibited and the permanent ground lateral displacement was accumulated during shaking. The existence of the lateral load led to a pile head displacement as much as 34 cm and increased the bending moment along the pile up to 6 MN·m. Moreover, the seismic response of piles and soils were compared between the dry sand ground and saturated sand ground to clarify the influence of excess pore pressure. It was also found that the residual bending moment after unloading the pile was still very large up to 17 MN·m because of the rebalanced soil-pile interaction. These findings highlight the necessity to consider the lateral load effect in the seismic design of pile foundations for OWTs.

摘要

海上风力涡轮机 (OWT) 桩基周围的土壤会遭受地震，人们普遍认为地震会破坏地基的承载能力和适用性。海洋中的非间歇性横向环境载荷（例如波浪、风和洋流）持续作用于 OWT。然而，当考虑到 OWT 受到横向环境载荷时，桩基础和周围土壤的地震响应不太清楚。本文介绍了两组单桩离心机建模试验，原型直径为（D) 的 1.5 m 和与原型风力涡轮机高度可比的一阶固有频率。两个具有相同尺寸和刚度的模型桩，但一个在桩头上有侧向荷载，分别安装在干燥的沙地和饱和的沙地中。由于侧向荷载增加了桩前土体的初始静剪应力，抑制了超孔隙压力的发展，并在震动过程中积累了永久的地面侧向位移。侧向荷载的存在导致桩头位移高达 34 cm，并使沿桩的弯矩增加至 6 MN·m。此外，通过比较干砂地和饱和砂地的桩和土的地震反应，明确超孔隙压力的影响。还发现卸载后的残余弯矩仍然非常大，高达 17 MN·m，因为重新平衡了土 - 桩相互作用。这些发现强调了在 OWT 桩基础抗震设计中考虑横向荷载效应的必要性。