软黏土中桶形基础竖向循环加载超重力离心模型试验研究

Study on suction caisson foundations in soft clay under vertical cyclic loading based on centrifuge tests

桶形基础越来越广泛应用于海洋油气平台、海上风机、输电塔、防波堤等构筑物,研究其循环承载特性对以上构筑物服役安全性具有重要意义。通过在软黏土中开展单桶循环上拔以及小间距群桶循环上拔和循环下压超重力离心模型试验,发现循环上拔地基破坏模式为整体破坏,裂隙均呈现圆弧形,循环下压呈现渐进式整体破坏模式,下压过程的挤压作用可明显减小桶周泥面高度,导致其承载力降低。模拟双向受荷工况的循环上拔试验在5次加载后荷载弱化系数开始趋于稳定,远早于单向受荷工况;单向和双向受荷工况循环上拔荷载弱化系数残余稳定值分别为0.31和0.32,循环下压荷载弱化系数最小值为0.35,表明不同加载方式竖向循环荷载作用下,此三者大小均可用软黏土地基灵敏度倒数预估。

Suction caisson foundations have been widely used in offshore structures such as oil and gas platform,offshore wind turbine,transmission tower,and breakwater,and their bearing characteristics under cyclic loading have significant influence on the whole-life safety of the offshore structures.In this study,the centrifuge tests are carried out to investigate both the single caisson and caisson groups with small spacing under tensile and compressional cyclic vertical loading in soft clay.The results show that the surrounding soil of caissons is of global failure,and the cracks are arc-shaped in tensile cyclic tests,whilst the surrounding soil of caissons presents progressive global failure in compressional cyclic tests,and the height of soil reduces significantly due to the extrusion effect,which results in the capacity decreasing.The load weakening coefficient tends to be stable after 5 cycles loading in the two-way cyclic tests,which is much earlier than that of one-way cyclic tests.The residual stability values of load weakening coefficient are 0.31 and 0.32 respectively in one-way and two-way tensile cyclic tests,whilst the minimum value of load weakening coefficient is 0.35 in compressional cyclic tests,which indicates that these three values can be predicted by the inverse sensitivity of soft clay under different vertical cyclic loadings.