Abstract Large-diameter monopiles are the most commonly used foundation to support offshore wind turbines. Early designs usually adopted pile diameters (D) between 4 and 6 m, which is recently extended to 8 m and will target 10 m in the future. It is increasingly evident that the existing design method (i.e., API's p-y model) can significantly under-predict the lateral stiffness and capacity of large-diameter monopiles in soft clay, due to ignoring the soil resistances from base shear and base moment which become more pronounces as L/D reduces. In this study, a two-spring approach is proposed, aiming to predict the lateral behaviour of monopiles with varied L/D ratios in a unified manner. In light of the soil flow mechanisms around monopiles, the pure lateral soil resistance above the rotation point (RP) is quantified using a p-y model, while the resistances below the RP including the base shear and base moment are integrated into a moment-rotation spring (characterized by a MR-θR model) at the RP. It can naturally recover to a p-y model while analyzing flexible piles, where θR = 0 at RP. Formulations of the ‘p-y + MR-θR’ model (including diameter-related p-y and MR-θR models, and the depth of the RP) are proposed based on the results of a series of well-calibrated 3D numerical models. The proposed model has satisfactorily reproduced a number of field and centrifuge test results on laterally loaded monopiles with a wide range of L/D ratios (including flexible, semi-rigid and rigid piles), using a unified set of parameters. Compared to the standard p-y model, the adoption of the proposed ‘p-y + MR-θR’ model is shown to substantially reduce design conservatism.

中文翻译：

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考虑各种长径比（L/D）的软粘土中单桩统一横向土壤反应模型

摘要 大直径单桩是海上风力发电机最常用的支撑基础。早期的设计通常采用 4 到 6 m 之间的桩直径 (D)，最近扩展到 8 m，未来将达到 10 m。越来越明显的是，现有的设计方法（即 API 的 py 模型）可以显着低估软粘土中大直径单桩的侧向刚度和承载力，因为忽略了来自基础剪切和基础力矩的土壤阻力，这些阻力变得越来越大。当 L/D 减小时发音。在这项研究中，提出了一种双弹簧方法，旨在以统一的方式预测具有不同 L/D 比的单桩的横向行为。根据单桩周围的土壤流动机制，旋转点 (RP) 以上的纯侧向土壤阻力使用 py 模型量化，而低于 RP 的阻力，包括基础剪力和基础力矩，在 RP 处被整合到一个力矩-旋转弹簧（以 MR-θR 模型为特征）中。它可以在分析柔性桩时自然恢复到 py 模型，其中 RP 处的 θR = 0。基于一系列经过良好校准的 3D 数值模型的结果，提出了“py + MR-θR”模型（包括与直径相关的 py 和 MR-θR 模型，以及 RP 的深度）的公式。所提出的模型使用一组统一的参数，令人满意地再现了具有宽范围 L/D 比的横向加载单桩（包括柔性、半刚性和刚性桩）的大量现场和离心机测试结果。与标准 py 模型相比，采用所提出的“py + MR-θR”模型可以显着降低设计保守性。