海洋结构性软土中风机桶形基础的变频多向水平循环承载特性

Shared anchoring wind farm connects multiple floating wind turbines to a shared anchor, forming an integrated turbine array that can significantly reduce wind power costs. As an excellent candidate for shared anchors, the bucket foundation will sustain multidirectional varying frequency lateral cyclic loading. When the foundation soil is marine soft clay, the lateral deformation and capacity of the bucket foundation will also be affected by the soil structure and viscosity, i.e. cyclic degradation of the soil strength/stiffness and the rate-dependent accumulation of deformation, respectively. This project aims to establish the relationship between the basic mechanical properties of the soil and the response of the foundation structure and to form a multidirectional lateral cyclic resistance model for bucket foundation considering the soil structure and viscosity. Specifically, the project will study the cyclic degradation and rate-dependent behavior of structured clays through laboratory soil tests, and form a cyclic constitutive model considering soil structure and viscous property. The deformation accumulation of the bucket foundation under multidirectional cyclic loading and the softening of lateral capacity were studied by geotechnical centrifuge test. Based on the new constitutive relationship and centrifuge test observations, this project will establish a finite element model for predicting the deformation of bucket foundation under multidirectional lateral cyclic loading, and construct a yield envelop for bucket foundation under multidirectional lateral static loading that accounts for the cyclic softening of soil strength.

基于“共享锚点”的悬浮式风电场将多台风机连接于同一海底锚点，形成可大幅降低风电成本的集成风机列阵。桶形基础作为优秀的共享锚点结构形式，将承担多方向变频率水平循环荷载。当地基土为海洋软土时，桶形基础的水平变形及承载力将受到土体结构性和粘滞性的共同影响，分别表现为土体强度及刚度的循环软化和加载速率相关的变形累积。本项目旨在建立土体基本力学特性与风机基础响应之间的联系，形成考虑土体结构性和粘滞性的桶形基础多向水平承载的分析方法。本项目将通过土单元体试验研究结构性软土循环软化特性和粘滞效应，建立考虑结构性及粘滞性的循环本构关系。通过离心模型试验研究桶形基础在多向循环荷载下的变形累积以及承载力软化规律。基于新本构关系和离心试验观测，本研究将建立考虑土体结构性和荷载速率效应的桶形基础多向水平循环变形分析有限元模型，并利用三维极限分析构建考虑土体强度循环软化的多向水平静力承载包络线模型

桶形基础设计理论的优化对海上风电降本增效具有重要作用，对“碳中和、碳达峰”国家战略具有重要意义。风浪环境荷载具有多方向性，且位于不同方位的风机会系泊于同一共享锚固基础。这些因素导致海上风电桶形基础需要承担不同方向的水平循环荷载。多向、往复荷载下桶形基础的承载力及正常服役主要由循环作用下土体强度刚度弱化及变形累积所控制。针对海洋软黏土，其循环加载响应更受到黏滞性的显著影响。桶形基础独有的负压沉贯及其引起的土层变形也可影响基础的承载特性。针对海洋环境荷载下桶形基础承载变形的预测分析，既有本构模型较少全面反映小应变刚度非线性、强度各向异性、循环弱化及应力路径相关黏滞变形等软土核心力学特性。现有海上风机基础设计理论往往针对单向荷载工况，且负压沉贯分析忽略土体变形及内部侵蚀。本项目综合应用本构理论、数值方法及模型试验，对软黏土循环特性与黏滞效应的本构模拟、桶形基础负压沉贯过程物理模拟及考虑土体应力-渗流耦合和内部侵蚀的沉贯设计方法、软土中桶形基础多向承载变形和稳定性分析方法等关键性问题进行了研究。. 首先，结合颗粒间应变弹性方法和塑性运动硬化理论，建立了反映路径相关小应变刚度和各向异性强度的不排水黏土循环加载总应力本构模型，基于土单元及离心模型试验，从单元体和边值问题尺度上验证了模型。其次，提出了多粘塑机制和热敏性流变本构模拟框架，再现了加卸载复杂应力路径及变温条件下黏土的黏滞变形响应。再次，研发了桶形基础临界沉贯负压模型试验系统，揭示了负压作用下土体变形模式及破坏机理，建立了考虑应力-渗流耦合和土体内部侵蚀的负压沉贯分析的数值及简化方法。最后，基于不排水黏土总应力本构模型，建立了桶形基础多向加载数值计算模型，获得了多向水平加载相互作用承载包络线，提出了多向单调及循环荷载下桶形基础变形分析的简化方法。