砂土中裙式吸力基础水平循环承载特性的影响因素分析

吸力基础作为海上风电工程的基础主要受到风、波浪和洋流等产生的水平循环荷载作用，因此提高其水平循环承载力和控制侧移是保证风机正常运行的关键。采用有限元分析软件Z_SOIL对饱和砂土地基中的裙式吸力基础开展水平循环加载数值分析；考虑到土体小应变阶段刚度增大的特性，土体选用刚度与应力相关的小应变硬化模型（HSS模型）；重点分析和讨论了循环荷载比、加载高度、加载方式和加载顺序对基础循环累积位移和刚度的影响。研究发现：当循环荷载比小于0.5时，基础累积位移很小，基础循环割线刚度随循环振次变化不明显；当循环荷载比大于0.5时，循环加载过程中基础周围砂土地基被挤密实，导致基础循环割线刚度随循环振次增加而增大，卸荷后基础残留较大塑性变形。裙式吸力基础的循环割线刚度随循环荷载比和加载高度的增加呈线性关系减小，基础水平及竖向累积位移则逐渐增大。3种加载方式下，基础水平累积位移从大到小排序为单向荷载、不完全对称荷载、双向对称荷载；竖向累积位移从大到小排序为双向对称荷载、单向荷载、不完全对称荷载。当循环荷载由大到小变化时，基础的水平和竖向累积位移均大于荷载由小到大时的情况，说明前期加载历史对基础后期变形有重要影响。

Analysis of Influence Factors on Cyclic Bearing Behaviors of Skirted Suction Caissons

The suction caisson can be used in offshore wind farms. Due to the long-term horizontal cyclic loadings caused by wind, waves and currents, the offshore wind turbine foundation is required to provide high horizontal bearing capacity and limit the deflection. To better meet these needs, the skirted suction caisson, consisting of an internal caisson in an external short-skirted structure, was put forward. Numerical studies were conducted with the finite element software Z_SOIL to investigate the cyclic behavior of skirted suction caissons in sand, and the influence of cyclic load ratio, load eccentricity, loading way and loading order on the accumulated displacement and stiffness were analyzed. It was found that the soil stiffness increases at the small strain stage, the hardening small strain stiffness model was adopted. Results showed that the cyclic secant stiffness does not change significantly with the number of cycles when the cyclic load ratio is less than 0.5. However, it increases with the increase of cycles when the cyclic load ratio is larger than 0.5 due to the fact that the sand around the caisson is compacted during cyclic loading. As the increase of cyclic load ratio and load eccentricity, the cyclic secant stiffness of the skirted suction caisson reduces linearly, resulting in an increase of both horizontal and vertical displacement. It was also found that one-way cyclic loading produces the largest horizontal displacement while the two-way loading produces the largest vertical displacement. Moreover, a decreasing cyclic loading causes both the largest horizontal and vertical displacement of the caisson, which indicates that the previous cyclic loading has an important influence on the bearing behavior of the caisson.