DOI QR코드

DOI QR Code

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

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).

References

  1. Achmus, M., Kuo, Y.S. and Abdel-Rahman, K. (2009), "Behavior of the monopile foundations under cyclic lateral load", Comput. Geotech., 36(5), 725-735. https://doi.org/10.1016/j.compgeo.2008.12.003.
  2. Abhinav, K.A. and Saha, N. (2019), "Effect of stiffness degradation of clay in the dynamic response of monopole-supported offshore wind turbines", Geotech. Appl., 13, 331-339. https://doi.org/10.1007/978-981-13-0368-5_35.
  3. Barari, A., Zeng, X.W., Rezania, M. and Ibsen, L.B. (2021), "Three-dimensional modeling of monopiles in sand subjected to lateral loading under static and cyclic conditions", Geomech. Eng., 26(2), 175-190. https://doi.org/10.12989/gae.2021.26.2.175.
  4. Broms, B. (1964), "The lateral response of piles in cohesionless soils", J. Soil Mech. Found. Eng. Division ASCE, 90(3), 123-156. https://doi.org/10.1061/JSFEAQ.0000614
  5. Charlton, T.S. and Rouainia, M. (2021), "Cyclic performance of a monopile in spatially variable clay using an advanced constitutive model", Soil Dyn. Earthq. Eng., 140, 106437. https://doi.org/10.1016/j.soildyn.2020.106437.
  6. Cuellar, P., Baessler, M. and Rucker, W. (2013), "Relevant factors for the liquefaction susceptibility of cyclically loaded offshore monopiles in sand", Poromechanics V: Proceedings of the Fifth Biot Conference on Poromechanics, 1336-1345. https://doi.org/10.1061/9780784412992.160.
  7. Cui, H.N. and Liu, X.L. (2019), "Effect of shear stiffness degradation on accumulation of pore water pressure in marine sediments", J. Mar. Environ. Eng., 10(3), 165-180.
  8. Cui, Z.D., Zhang, L.J. and Zhan, Z.X. (2023), "Dynamic shear modulus and damping ratio of saturated soft clay under the seismic loading", Geomech. Eng., 32(4), 411-426. https://doi.org/10.12989/gae.2023.32.4.411.
  9. Depina, I., Le, T.M.H., Eiksund, G. and Benz, T. (2015), "Behavior of cyclically loaded monopile foundations for offshore wind turbines in heterogeneous sands", Comput. Geotech., 65, 266-277. https://doi.org/10.1016/j.compgeo.2014.12.015.
  10. Feizi, S., Arnesen, K., Aaslid, A. and Bergan-Haavik, J. (2023), "Validation of earthquake analysis methodology of a suction-caisson foundation-structure through model testing", Mar. Struct., 88, 103368. https://doi.org/10.1016/j.marstruc.2023.103368.
  11. Gao, Z.T., Feng, X.Y., Zhang, Z.T., et al. (2022) "A brief discussion on offshore wind turbine hydrodynamics problem". Journal of Hydrodynamics 34(1), 15-30. https://doi.org/10.1007/s42241-022-0002-y.
  12. Guth, S., Katsidoniotaki, E. and Sapsis, T.P. (2023), "Statistical modeling of fully nonlinear hydrodynamic loads on offshore wind turbine monopile foundations using wave episodes and targeted CFD simulations through active sampling", Wind Energy, 27(1), 75-100. https://doi.org/10.1002/we.2880.
  13. Gerolymos, N. and Gazetas, G. (2005), "Constitutive model for 1-D cyclic soil behaviour applied to seismic analysis of layered deposits", Soils Found., 45(3), 147-159. https://doi.org/10.3208/sandf.45.3_147.
  14. Gotschol, A. (2009), "Veranderlich elastisches und plastisches Verhalten nichtbin-diger Boden und Schotter unter zyklischdynamischer Beanspru-chung", Herausgegeben im Eigenverlag, Kassel, Hessian, Germany.
  15. Hu, A.F., Zhang, G.J. and Jia, Y.S. (2014), "Application of degradation stiffness model in analysis of cumulative lateral displacement of monopile foundation", J. Zhejiang Univ. (Engineering Science), 48(4), 721-726. https://doi.org/10.3785/j.issn.1008-973X.2014.04.023.
  16. Huang, M.S., Li, J.J. and Li, X.Z. (2006), "Cumulative deformation behaviour of soft clay in cyclic undrained tests", Chinese J. Geotech. Eng., 28(7), 891-895.
  17. Huurman, M. (1996), "Development of traffic induced permanent strain in concrete block pavements", Heron, 41(1), 29-52.
  18. Idriss, I.M., Dobry, R. and Singh, R.D. (1978), "Nonlinear behavior of soft clays during cyclic loading", J. Geotech. Eng. Division, 104(12), 1427-1447. https://doi.org/10.1061/AJGEB6.0000727.
  19. Kishore, Y.N., Rao, S.N. and Mani, J.S. (2009), "The behaviour of laterally loaded piles subjected to scour in marine environment", KSCE J. Civil Eng., 13(6), 403-408. https://doi.org/10.1007/s12205-009-0403-2
  20. Kuo, Y.S., Achmus, M. and Abdel-Rahman, K. (2012), "Minimum embedded length of cyclic horizontally loaded monopiles", J. Geotech. Geoenviron. Eng., 138(3), 357-363. https://doi.org/10.1061/(ASCE)GT.1943-5606.0000602.
  21. Lei, J., Wang, Y., Zhang, B, Li, F. and Liu, C. (2022), "Cyclic and post-cyclic characteristics of marine silty clay under the multistage cycling-reconsolidation conditions", Ocean Eng., 258. https://doi.org/10.1016/j.oceaneng.2022.111803.
  22. Liu, J.M., Fu, H.Q. and Guo, T.T. (2020), "Comparative experimental study on dynamic characteristics of soft clay under different cyclic loads", China Earthq. Eng. J., 42(4), 973-981. https://doi.org/10.3969/j.issn.1000-0844.2020.06.973.
  23. Matasovic, N. and Vucetic, M. (1995), "Generalized cyclic-degradation-pore-pressure generation model for clays", J. Geotech. Eng., 121(1), 33-42. https://doi.org/10.1061/(ASCE)0733-9410(1995)121:1(33).
  24. Shi, Y.X., Cheng, Y.Z. and Huang, X.Y. (2022), "Numerical simulation of unsteady flow field around monopile under the combined influence of wave and vibration", Ocean Eng., 276, 114238. https://doi.org/10.1016/j.oceaneng.2023.114238.
  25. Thiers G.R., Seed H.B. (1968), "Cyclic stress-strain characteristics of clay", J. Soil Mech. Found. Division, 94(2), 555-569. https://doi.org/10.1061/JSFEAQ.0001110.
  26. Tuladhar, R., Maki, T. and Mutsuyoshi, H. (2008), "Cyclic behavior of laterally loaded concrete piles embedded into cohesive soil", Earthq. Eng. Struct. D., 37(1), 43-59. https://doi.org/10.1002/eqe.744.
  27. Werkmeister, S. (2003), "Permanent deformation behaviour of unbound granular materials in pavement constructions", Technischen Universitat Dresden, Dresden, Germany.
  28. Wang, Y., Lei, J., Gong, X., Wang, Y. and Yang, P. (2018), "Post-cyclic undrained shear behavior of marine silty clay under various loading conditions", Ocean Eng., 158:152-161. https://doi.org/10.1016/j.oceaneng.2018.03.081.
  29. Wang, Y., Qi, Z., Wei, T., Bao, J., Zhang, X. and Zhou, Y. (2023), "Numerical study on the responses of suction pile foundations under horizontal cyclic loading considering the soil stiffness degradation", J. Mar. Sci. Eng., 11(12), 2336. https://doi.org/10.3390/jmse11122336.
  30. Yasuhara, K., Yamanouchi, T. and Hirao, K. (1982), "Cyclic strength and deformation of normally consolidated clay", Soils Found., 22(3), 77-91. https://doi.org/10.3208/sandf1972.22.3_77.
  31. Yu, D.W., Ye, J.H. and Yun, C.Q. (2023), "Dynamics of offshore wind turbine and its seabed foundation under combined wind-wave loading", Ocean Eng., 286, 115624. https://doi.org/10.1016/j.oceaneng.2023.115624.
  32. Zhao, C.Y, Zhou, S.H. and Li, Z. (2012), "Cyclic accumulative pore pressure model of soft clay in the Shanghai region", J. China Railway Soc., 1,77-82. https://doi.org/10.3969/j.issn.1001-8360.2012.01.014.