沙中横向加载海上风力单桩的性能

R. Gilbert, Yunhan Huang, K. Stokoe, S. Wang, J. Munson, Jonas Bauer, R. Hosseini, Ahmed Hussien, H. Fadaifard, Daniel P. O'Connell
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摘要

API RP 2GEO(2014)和DNV(2018)这两种传统的砂中横向加载海上基础设计方法,并没有针对在使用过程中经历横向载荷施加相对较小横向位移的风力涡轮机单桩开发。本文对现有的小位移单桩横向荷载设计指南的适用性进行了评价,并对改进单桩基础设计方法提出了建议。研究包括应用现有技术测量小剪切应变下砂土的非线性刚度,利用包含砂土非线性刚度的三维有限元方法(3-D FEM)模型来预测单桩的横向响应,并在实验室中通过基础模型测试测试所提出的方法。并将所建议的方法应用于1966年在野马岛进行的横向荷载试验,该试验为当前的设计方法提供了原始基础。研究得出以下主要结论:模型试验和现场试验一致表明,目前设计实践中传统的p-y曲线往往低估了侧向荷载桩的初始刚度,不能反映小侧向位移时刚度的非线性。三维有限元模型结合本构模型来表征砂的小应变特性,包括极小应变下的最大剪切刚度以及剪切刚度与剪切应变和有效围应力之间的关系,能够在模型和现场尺度上预测侧向加载桩的响应。这些结论对砂土中横向加载单桩的设计提出了以下建议:在使用常规的砂土p-y曲线来预测海上风力涡轮机单桩的性能时要谨慎。目前设计实践中使用的传统p-y曲线不能充分预测与海上风电单机桩相关的小侧向位移处的横向荷载桩的刚度和非线性。直接测量或经验建立原位最大(“小应变”)剪切模量、剪切模量与剪切应变的关系、剪切模量与有效围压的关系。需要这些小应变特性来预测小侧向位移下水平荷载桩的刚度和非线性。利用小应变下现场砂土的代表性特性,通过三维有限元分析建立改进的p-y曲线,直接用于设计。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Behavior of Laterally Loaded Offshore Wind Monopiles in Sands
The conventional design methods for laterally loaded offshore foundations in sand, API RP 2GEO (2014) and DNV (2018), were not developed for wind turbine monopiles that experience lateral loads imposing relatively small lateral displacements in service. This paper presents the results of research to evaluate the suitability of existing guidance for the design of laterally loaded monopiles at small displacements and to provide recommendations for improving design methods for monopile foundations. The research included applying existing techniques to measure the non-linear stiffness of sand at small shear strains, utilizing a three-dimensional finite element method (3-D FEM) model that incorporates the non-linear stiffness of sand to predict the lateral response of a monopile, testing the proposed approach with foundation model tests in the laboratory, and applying the proposed approach to the lateral load tests conducted on Mustang Island in 1966 that provided the original basis for current design methods. The following major conclusions are drawn from this research: Model tests and field tests consistently show that the conventional p-y curves from current design practice tend to underestimate the initial stiffness for laterally loaded piles and fail to capture the non-linearity of the stiffness at small lateral displacements. A 3-D FEM model that incorporates a constitutive model to characterize the small-strain properties of sand, including the maximum shear stiffness at very small strains and the relationships between shear stiffness and both shear strain and effective confining stress, is capable of predicting the response of laterally loaded piles both at model and field scales. These conclusions lead to the following recommendations for the design of laterally loaded monopiles in sand: Exercise caution in using conventional p-y curves for sand to predict the performance of offshore wind turbine monopiles in service. The conventional p-y curves used in current design practice do not adequately predict the stiffness and non-linearity of laterally loaded piles at the small lateral displacements relevant for offshore wind turbine monopiles in service. Measure directly or empirically establish the in-situ maximum ("small-strain") shear modulus, the relationship between shear modulus and shear strain, and the relationship between shear modulus and effective confining pressure. These small-strain properties are needed to predict the stiffness and non-linearity of laterally loaded piles at small lateral displacements. Establish improved p-y curves to be used in design directly from 3-D FEM analyses using representative properties of the sand in-situ at small strains.
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