软土中吸力式桶形基础倾覆承载性能离心模型试验

输电杆塔和风电机组基础主要承受上部结构倾覆弯矩荷载，倾覆承载性能是该类基础设计中的关键问题。针对饱和软黏土地基中的杆式结构桶形基础，通过开展位移控制循环加载、位移维持加载、力控制循环加载和单调静力加载离心模型试验，研究其倾覆承载能力。试验发现，当桶形基础达到极限承载力时其转动中心位置约在桶盖正下方0.8倍桶裙高度处；当循环倾覆弯矩幅值与极限抗弯承载力比值小于3/5时，桶形基础在循环过程中转角的累积难以持续增长，并逐渐趋于稳定；循环加载作用下土与结构相互作用刚度出现明显弱化，所获得的桶形基础循环弱化因子阈值约为0.15；位移维持加载的峰值荷载-位移曲线与单调静力加载的荷载-位移曲线较为一致，位移维持加载的谷值荷载-位移曲线对应的承载力较峰值荷载-位移曲线对应的承载力明显偏小，减少约30%～40%。

Centrifuge model test on suction caisson foundation in soft clay subjected to lateral loads

The foundations of power transmission towers and offshore wind turbines are prone to huge overturning moment loading from the super structure; therefore the overturning bearing capacity is crucial for the design of such foundations. To investigate the overturning bearing capacity of suction caisson foundation, four centrifuge model tests including a displacement controlled cyclic loading test, a displacement maintained loading test, a load controlled cyclic loading test and a monotonic loading test were carried out in saturated soft clay. The test results show that the instantaneous rotation center of model caisson can be simplified to be at the depth of about four fifths of the skirt length right below the lid center, when the ultimate capacity was reached. When the amplitude of the cyclic moment is smaller than three-fifths of the bearing capacity moment, the rotation of the caisson cease to accumulate, and gradually become stable. The stiffness of the soil-structure interaction significantly softened under cyclic loading, and a threshold of cyclic degradation factor t = 0.15 can be obtained from the peak stiffness curves of the caisson. The moment-rotation curve of peak value of maintaining tests is universally quite in accordance with that of monotonic loading test. The capacity of the model caisson corresponding to the moment-rotation curve of the valley values is much lower than that corresponding to the moment-rotation curve of the peak values in maintaining tests, and a 30%-40% reduction is needed when considering the maintaining overturning capacity of the caisson foundation in design.