Research On Horizontal Bearing Capacity Characteristics Of Large Diameter Mono-pile Of Offshore Wind Power

China’s offshore wind energy resources are rich with a potential capacity exceeding 500 million k W.Wind energy has become an important direction for the development of renewable energy.Mono-pile is the main foundation type of offshore wind power with advantages of simple structure and clear stress analysis.With the continuous increase of the capacity of the offshore wind generator,the maximum diameter of mono-pile foundation for offshore wind power in China has reached 10 m with a pile length of over 100 m and pile weight nearly 2000 t.With the increase of diameter,the original bearing mode of mono-pile with small diameter is no longer suitable.Therefore,the investigation of bearing performance for large diameter pile is necessary.In this paper,the characteristics of horizontal bearing capacity of large diameter mono-pile are studied.The main research contents and results are as follows:(1)The plastic behavior of the soil is described by introducing the kinematic hardening model.The rationality of the model is verified based on the triaxial test results.The influence of the diameter-length ratio of the pile foundation,the wall thickness and the undrained strength of the soil on the horizontal bearing capacity of mono-pile are analyzed by adopting API specification method and finite element method.The results indicate that the horizontal bearing capacity of the pile foundation is mostly affected by the diameter-length ratio.The horizontal bearing capacity has positive correlations with the diameter-length ratio,wall thickness,and undrained strength of the soil.(2)Based on the results of finite element analysis,the criterion of the critical length of flexible long piles and rigid short piles is obtained according to the deformation characteristics of flexible long pile and rigid short pile under horizontal load.The method is compared with the identification described in Design Code for Wharf Structures.The results indicate that for mono-pile with diameter less than 2m,the critical pile length identification method in Design Code for Wharf Structures can accurately define rigid short piles and flexible long piles.But as the pile diameter increases,the results of the method in Design Code for Wharf Structures are different from the situations in finite element models.Theoretical derivation and numerical analysis reveal that when the pile foundation diameter increases from 2m to 6m,the criterion of rigid short piles is close to 2.2T,and the criterion of flexible long piles criterion is close to 3.7T.(3)Based on the non-linear kinematic hardening criterion,the weakening model of saturated clay is established.The influences of the weakening of the foundation soil on the horizontal bearing capacity under cyclic load,foundation stiffness and the overall natural frequency of the offshore wind power pile foundation are studied.The research results indicate that when the load cycles are identical,the bending stiffness and flexural bearing capacity of the pile-soil system attenuates more than the horizontal stiffness and the horizontal bearing capacity.Within a certain number range of cycles,the influence of the cyclic amplitude is greater than the number of cycles,and the overall natural frequency of the turbine is positively correlated with the stiffness of the pilesoil system.