非共面循环荷载联合激励下吸力锚在软土地基中的失效机制及承载特性研究

With the successful deployment of the innovative point absorption oscillating float type of wave energy converters (WEC), the vitality of the wave energy as a new reliable form of renewable energy source has been demonstrated. The key geotechnical engineering challenge is associated with the design and operating of tensile mooring and anchoring structures, as to provide sufficient supports for the WEC to remain high performance in the complex ocean environment. The geotechnical condition of seabed along the coastal area in China is characterised as soft clay, where the suction caisson is thought to be qualified as a supporting structure. Therefore, the project will (1) propose the numerical model, representing the variations in soil strength of soil clay sediments with time, with the consideration of the effect of the remolding softening, consolidation hardening and cyclic shearing; (2) illustrate the dynamic out-of-plane loading transferring mechanism on the tensile mooring and anchoring systems, during the operation time of the WEC; (3) interpret the failure mechanism and bearing capacity of the suction caisson under cyclic uplift loading and multi-directional horizontal loadings; (4) propose the failure envelope to quantify the soil property-soften shear strength- cyclic out-of-plane combined loadings, based on the study on the cyclic softening mechanisms of the soil strength of soil clay sediments. And finally, a systematic prediction method will be proposed to interpret the life-time bearing capacity of the suction caisson, qualitatively and quantitatively. It provides the scientific methods and engineering tools to optimise the anchoring type, and fills in the knowledge gap in the softening theory of the soft clay sediments under cyclic out-of-plane combined loadings.

随着高效能大型点吸收振荡浮子式海浪换能技术的成功研制，波浪能潜在地成为了一种新型的替代能源。该项技术的核心问题是如何利用锚固系泊结构使上层浮式换能系统在复杂海况条件下安全运行。由于我国沿海海域表层常为软质黏土，特别适合吸力锚基础，因此本项目通过深入研究软黏土扰动软化、扰动后固结硬化及循环剪切和扰动软化特性，提出土体强度演化数值模型；揭示波浪能发电系统运行时锚链多向非共面动力传力机制；洞察吸力锚在抗拔和多向水平非共面复合动荷载作用下的失效机理及承载特性；最终结合对软黏土的循环软化规律的研究，构建关联“土体工程参数-软化强度-非共面循环复合承载力”的量化破坏包络面模型，据此提出对吸力锚全寿命周期的承载特性评价方法，为新型吸力锚固系统的设计提供理论依据和工程对策，以填补非共面复合循环荷载下软黏土软化理论的空白。

本项目面向海洋清洁能源开发领域系泊锚固技术的重大工程需求，聚焦于应用推广潜力巨大的吸力锚海洋基础安装及承载性能评价关键问题，通过理论、数值模拟及试验等手段，从以下四个方面开展研究并取得了相关的研究成果：（1）通过高级土工试验研究软黏土的静、动力工程特性，开发了可反映软黏土应变软化及结构性损伤的本构模型，评估了土体的固结应力、超固结度、灵敏度等因素对软黏土不排水抗剪强度的影响规律；（2）通过二次开发的大变形有限元技术，厘清了吸力锚基础沉贯过程中侧壁土体的软化发展机理，揭示并量化安装扰动引起的软黏土扰动范围、扰动程度及其对沉放后的短期承载性能影响；（3）基于研发的黏土软化本构模型，洞察了吸力锚基础受锚链动力拉拔荷载作用下的锚土相互作用机理，并考虑锚体被动区的开槽效应，提出了锚链系泊点的优化设计方法；（4）通过高重力离心机模型试验和数值模拟相结合，揭示了单向、双向及多向循环荷载作用下吸力锚的抗滑承载性能演化规律，并结合承载包络面理论，提出了可关联“黏土软化强度–地基承载力 ”的循环荷载作用下的吸力锚复合承载力计算方法。基于项目研究，完善了吸力锚基础在黏土海床中的承载性能评估理论，建立了一种可指导工程实践的吸力锚岩土设计方法，可为其在深远海能源开发中的推广应用提供关键理论和技术支撑。