砂土循环累积变形规律与显式计算模型研究

海洋基础在上部结构风和波浪等长期循环荷载的作用下产生累积变形,易影响海上风电机组等构筑物的正常服役性能,其本质是基础周边土体的循环累积变形问题。针对该问题,开展了一系列饱和砂土在排水条件下的循环剪切三轴试验,研究了动应力比、初始密实度、初始平均应力和初始静应力比等土性和应力参数对循环累积变形的影响,发现随动应力比、初始平均应力和初始静应力比的增大及初始密实度的减小,饱和砂土的轴向循环累积应变增大。从试验数据分析来看砂土轴向循环累积应变和循环次数之间近似存在双对数线性关系。将砂土轴向循环累积应变与第一次循环轴向应变归一化能消除上述土性和应力参数的影响,进而分析了第一次循环轴向应变与土性和应力参数之间的关系,通过引入与密实度相关的砂土抗剪强度计算表达式,建立了饱和砂土在排水条件下的循环累积变形显式计算模型,适合海洋基础长期循环累积变形分析。

Cyclic accumulative deformation of sand and its explicit model

The foundation of offshore wind turbines subjected to cyclic loads derived from wind and waves tends to produce cyclic accumulative deformation, which affects the turbines' normal operation. Its essence is the accumulative deformation of soils around the foundation. A series of cyclic triaxial compression tests on saturated sands under drained conditions are carried out to study the influence of soil and stress parameters, such as dynamic stress ratio, initial density, initial mean stress and initial static stress ratio, on the accumulative deformation of sands. It is found that when the dynamic stress, initial mean stress and initial static stress ratio increase and initial density decrease, the cyclic accumulative deformation of sands becomes severer. A double logarithmic linear relationship between the axial accumulative strain and the number of cycles is obtained from the analysis of cyclic triaxial tests. The influence of soil and stress parameters is eliminated by normalizing the axial accumulative strain with the first cyclic axial strain, and relationships between the first cyclic axial strain and soil and stress parameters are analyzed after that. By introducing a density-related strength formula for sand, an explicit model for cyclic accumulative deformation of sand under drained conditions is established, which is suitable for analyzing the cyclic accumulative deformation of foundation of offshore wind turbines.