Geomechanics and Engineering

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Investigation on the responses of offshore monopile in marine soft clay under cyclic lateral load

  • Fen Li (School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology) ;
  • Xinyue Zhu (School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology) ;
  • Zhiyuan Zhu (School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology) ;
  • Jichao Lei (School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology) ;
  • Dan Hu (School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology)
  • Received : 2023.09.04
  • Accepted : 2024.05.02
  • Published : 2024.05.25
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Abstract

Monopile foundations of offshore wind turbines embedded in soft clay are subjected to the long-term cyclic lateral loads induced by winds, currents, and waves, the vibration of monopile leads to the accumulation of pore pressure and cyclic strains in the soil in its vicinity, which poses a threat to the safety operation of monopile. The researchers mainly focused on the hysteretic stress-strain relationship of soft clay and kinds of stiffness degradation models have been adopted, which may consume considerable computing resources and is not applicable for the long-term bearing performance analysis of monopile. In this study, a modified cyclic stiffness degradation model considering the effect of plastic strain and pore pressure change has been proposed and validated by comparing with the triaxial test results. Subsequently, the effects of cyclic load ratio, pile aspect ratio, number of load cycles, and length to embedded depth ratio on the accumulated rotation angle and pore pressure are presented. The results indicate the number of load cycles can significantly affect the accumulated rotation angle of monopile, whereas the accumulated pore pressure distribution along the pile merely changes with pile diameter, embedded length, and the number of load cycles, the stiffness of monopile can be significantly weakened by decreasing the embedded depth ratio L/H of monopile. The stiffness degradation of soil is more significant in the passive earth pressure zone, in which soil liquefaction is likely to occur. Furthermore, the suitability of the "accumulated rotation angle" and "accumulated pore pressure" design criteria for determining the required cyclic load ratio are discussed.

Keywords

Acknowledgement

This article was funded by National Natural Science Foundation of China (No. 52178353).

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