| In recent years,offshore wind power with many development advantages,gradually into people's vision.The marine environment of offshore wind turbine foundation is quite different from that of onshore pile foundation,especially the performance of foundation structure under the large-scale wave load directly affects the stability of the whole structure,and all kinds of wind turbine foundation forms are faced with the problem of ground foundation stability.Therefore,it is necessary to systematically study the mechanical characteristics of typical marine soil under cyclic load,such as stiffness weakening and strength reduction,and to carry out accurate numerical simulation.In order to guarantee the accurate and rigorous dynamic design of the foundation of offshore wind power engineering in the later stage,and to predict its dynamic response and ensure its safe and stable operation,the failure mode of soil under the special condition of large number of wave cyclic load is studied by means of experiment and numerical value.This paper focuses on the study of marine mucky clay in Laizhou Bay,taking the mucky soft soil of a offshore wind farm in Changyi City,Weifang City,Shandong Province as an example.Affected by the alluvial action of the Yellow River,the mucky clay in Laizhou Bay has poor engineering properties,such as high water content,high compressibility,large void ratio and low strength.It has obvious softening characteristics under the cyclic wave load,which is easy to cause foundation damage.Therefore,in this paper,laboratory test and numerical simulation are used to study the softening characteristics of the mucky clay in Laizhou Bay under cyclic load.The influence of dynamic stress ratio and depth of soil on the deformation and strength characteristics of soft clay is discussed through the dynamic cyclic loading tests of different dynamic stress ratio and depth of soil in this area.The research results are of great significance for the optimal design and stability analysis of foundation of offshore wind turbine under large-scale cyclic loading.The main research work and achievements are as follows:(1)Based on the GDS dynamic triaxial apparatus and the method of stress-control,the failure laws and dynamic responses of the samples under different dynamic stress ratio and buried depth are studied systematically,and the cumulative strain and pore pressure development model of the soft soil in this area are put forward to describe the development trend of the dynamic characteristics of the marine soil under different buried depth.(2)Based on the analysis of stress-strain and stress path development of samples under different working conditions,the change of internal stress state of samples under cyclic load is studied,and the failure mechanism of marine soil in Laizhou Bay under cyclic load is revealed.(3)Based on the dynamic triaxial test,the critical CSR under each buried depth is proposed,and the change curve of critical CSR with the buried depth is drawn.The failure state and the un-failure state are distinguished,and the judgment basis of dynamic failure and bearing capacity instability of foundation is proposed.(4)This paper summarizes the commonly used constitutive model of soil materials,determines the boundary interface model suitable for the study of soil dynamics,demarcates the boundary interface model parameters by consolidation compression and other tests,and accurately simulates the sample stiffness attenuation and stress state transition under cyclic load.The boundary interface model is used to predict the dynamic characteristics and failure law of marine soft soil under different cyclic load at any buried depth. |
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