台风海况下海床液化与近海风机桩基础动态响应

The safety of pile foundation during extreme sea environment is a chanlenge for the offshore wind farm. The liquefaction mechanism of seabed under the composited loadings from storm surge and rocking piles, and its influence to the deformation and dynamic response of pile foundation is the key issues. Due to the multi-cycle and long-period nature of wave loading, and the consideration of the interaction between wave, seabed and structure, current numerical method can not be applied directly. In this study, the long term cyclic hollow cylinder torsional shear tests are carried out to obtain the liquefaction properties of sands under composited loading conditions. A non-coaxial constitutive model that takes into consideration the number of cylic loading is proposed. The numerical wave tank and the u-p format paralleled dynamic FEM with the non-coaxial constitutive model are integrated as a 3D wave-seabed-pile foundation interaction model. Model tests on wave-induced and swaying pile-induced liquefactions around pile foundation are performed. Combined with numerical analysis, the build-up of excessive pore water pressure and deformation of pile are examined to get an understanding of the mechanism of liquefactions under two types of loadings.Result outcomes can be applied to the research and design of other marine strucutres, enchancing the development of offshore wind farm industry in China.

极端海况下基础结构物的安全问题是我国发展海上风电面临的重大挑战。台风风暴潮和结构物振动的复杂荷载组合作用下桩周土的液化机理，以及桩基础的受力变形及动态响应规律是需要解决的关键科学问题。 本项目采用动态空心圆柱扭剪试验获得不同荷载组合持续作用下的砂土液化机理，开发考虑复杂应力组合和循环次数效应的非共轴砂土液化本构模型。然后进行风暴潮与桩振动引起桩周土液化的水槽模型试验，获得不同荷载组合下土体孔压变化与桩基础动态响应数据。最后集成台风波浪模型与并行动态有限元，形成一套高效的波浪～海床～桩基础共同作用分析方法，并与试验数据进行对比验证。结合模型试验和数值分析，深入揭示台风海况的复杂荷载组合作用下桩周土的液化机理，明确土体液化对桩基础受力变形及动态响应的影响规律，并探讨最不利工况与提出相应控制措施。研究成果可应用于海洋结构物的理论分析及工程设计，为我国海上风电建设作出贡献。

极端海况下基础结构物的安全问题是我国发展海上风电面临的重大挑战。台风风暴潮和结构物振动的复杂荷载组合作用下桩周土的液化机理，以及桩基础的受力变形及动态响应规律是需要解决的关键科学问题。本项目首先针对原有仪器仅有扭矩或轴力可以实现动态控制的限制，自主研发了四向控制动态空心圆柱扭剪仪。进行了砂土的应力主轴固定和应力主轴旋转的试验，获得了偏应力、相对密实度和旋转起点对砂土力学特性的影响规律。改进了砂土液化弹塑性本构，基于该本构和水土耦合数值计算算法，形成了一套可以模拟波浪～海床～桩基础共同作用的数值分析方法。进行波浪作用下海床液化的圆筒模型试验，获得不同波浪作用下土体孔压变化和土体位移响应。最后基于所开发的数值分析方法，分析波浪和桩晃动复合荷载作用下桩周土的孔压和位移响应，指出了桩晃动将加剧桩周土的液化。相关研究成果发表论文19篇，其中SCI检索论文13篇、中文EI论文2篇，培养博士生1名，硕士生4名。研究成果可应用于海洋结构物的理论分析及工程设计，为我国海上风电建设作出贡献。