饱和砂土中裙式吸力基础水平循环特性和累积转角变化规律

Bearing behavior and accumulated rotation of modified suction caisson(MSC)in saturated sand under cyclic loading

裙式吸力基础是一种新型海上风电工程吸力基础形式。采用模型试验研究水平循环荷载作用下,传统和裙式吸力基础的累积转角变化规律和影响因素,循环加载方式包含单向循环加载和变幅循环加载。试验结果表明:传统和裙式吸力基础循环累积转角主要发生在前200次循环,循环累积转角随循环荷载幅值和循环次数增加逐渐增大,累积转角增长速率随循环次数增加逐渐减小。基础累积转角与循环次数之间的关系可用幂函数进行表达。采用Leblanc方法和Miner准则,对长期变幅循环加载下基础累积转角转化为等幅循环荷载进行分析,预测了基础累积转角,发现循环荷载的顺序和循环荷载幅值对基础累积转角有一定的影响。荷载幅值逐级增大条件下,预测的基础累积转角略高于实测值。另外,研究了循环加载过程对基础水平极限承载力的影响,基础水平承载力较循环加载前有一定提高。研究成果能为海上风电吸力基础的设计提供依据。

Skirted suction caisson is a new type of suction foundation for offshore wind power engineering.Model tests were carried out to investigate the variation of cumulative rotation angle and its influencing factors of the regular suction caisson(RSC)and skirted suction caisson(SSC)under horizontal cyclic loading.The cyclic loading mode includes one-way cyclic loading and variable-amplitude cyclic loading.The experimental results showed that the cumulative rotation angle of the RSC and SSC under horizontal cyclic loading mainly occurs within the first 200 loading cycles.The cumulative rotation angle was found to increase with the increase of cyclic loading amplitude and the number of loading cycles.However,the increasing rate of cumulative rotation angle decreases with the increase of loading cycle number.The relationship between the cumulative rotation angle and the number of loading cycles can be well fitted by a power function.By using Leblanc method and Miner’s rule,the cumulative rotation angle of the suction caisson foundation under long-term variable-amplitude cyclic loading was transformed into that under constant amplitude cyclic loading and then can be estimated.It was found that when the loading amplitude increases step by step,the predicted cumulative rotation angle of the RSC and SSC obtained by using the Leblanc method and Miner’s law is slightly higher than the measured model test results,indicating that the sequence and amplitude of cyclic loading have a certain influence on the cumulative rotation angle of the suction caisson foundation.In addition,the influence of cyclic loading on the ultimate bearing capacity of suction caisson foundation was studied and it was found that the ultimate bearing capacities of the RSC and SSC after cyclic loading are higher than those before cyclic loading.The research results can provide a basis for the design of the suction caisson foundation of offshore wind power.