密砂地基上海上风机吸力式桶形基础承载力研究

Bearing Capacity of Suction Bucket Foundations for Offshore Wind Turbines in Dense Sand

海上风机吸力式桶形基础在服役过程中经常承受高力臂水平荷载.对于密砂地基上海上风机吸力式桶形基础的水平承载特性进行了比较系统的三维有限元分析.通过二次开发,对于有限元软件ABAQUS中的Mohr-Coulomb弹塑性本构模型进行了改进,从而可以考虑砂土中变形模量随平均主应力变化的压力相关性.首先对已有的现场原位试验进行了模拟,数值计算得到的荷载—位移曲线与现场试验结果比较吻合.进而通过变动参数研究,系统的探讨了加载高度、长径比对吸力式桶形基础承载力及其变形破坏机理的影响,结果表明:水平荷载相对桶顶中心的弯矩承载力随加载高度的增加而逐渐增大,但不同加载高度下水平承载力相对桶底中心的力矩大致相等.与黏土地基情况相比,密砂地基中吸力式桶形基础在水平荷载—力矩构成的荷载平面内的破坏包络曲线曲率较小.基于有限元模拟结果,给出了基础失稳时桶壁土压力的简化分布模式,进而发展了密砂地基上直径在10m范围的大直径桶形基础水平承载力的极限平衡计算方法.

Suction bucket foundations for offshore wind turbines are usually subjected to a high arm lateral loading.The lateral bearing response of suction bucket foundations in dense sand is explored through three-dimensional finite element numerical analyses.The Mohr-Coulomb elaso-plastic constitutive model in ABAQUS is improved by redevelopment through user subroutine interface,so that the pressure dependence of modulus of sand with the variation of average principal stress can be modeled.The finite element model is validated against published loading test in situ of bucket foundation in Frederikshavn.The load-displacement curves obtained from numerical analyses agree well with those from the in situ tests.The effect of loading height of lateral load and aspect ratio of foundation is investigated through parametric studies,on the bearing capacity and failure mechanism of suction bucket foundation.The results show that the moment capacity with respect to the center of the bucket lid increased with the increasing loading height,however the moment calculated in respect of the center of the bucket bottom almost did not change with the loading height.Compared with the case of clayey soil,the curvature of failure locus of bucket foundation in the load plane composed of horizontal load and moment in dense sand is smaller.According to the numerical calculation results,the simplified distribution mode of earth pressure on bucket wall is introduced,and a limit equilibrium method is developed to predict lateral capacity of bucket foundations with diameter of 10 m order of magnitude in dense sand.