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.