Pile-Seabed Interaction Behavior And Long-Term Response Under Wave Loads Considering The Rocking Effect Of Mono-Pile

In recent years,with the rapid development of ocean engineering,much attention has been paid to the construction of onshore and offshore structures.Mono-pile is the main foundation forms of offshore wind turbine and offshore platform,and the mechanism research of its interaction with seabed soil under dynamic wave loading has been one of the key points of ensuring load capacity and security in mono-pile application.In actual marine environment,besides the dynamic wave loading,the mono-pile foundations are also subject to wind load and effect of upper structures which result in pile rocking effect and make influence on seabed response in the vicinity of mono-pile.Up to now,the researches on pile rocking effect is relatively rare and further analysis should be conducted on the response of pile and seabed under long-term wave load and pile rocking effect.Based on numerical simulation,a 3-D integrated model is established to conduct research on coupled response of seabed and mono-pile under different forms of wave loads.In addition,the rocking effect of mono-pile is taken into consideration to do further analysis on the pile-seabed interaction.Furthermore,the present calculation method of residual pore pressure in 2-D form has been extended to the case of 3-D model.Correspondingly,studies has been conducted on the response of residual pore pressure in seabed with monopile.The main research content of this paper contains the following parts:1.The integrated numerical model containing wave,seabed and monopile is proposed to conduct research on wave-seabed-pile interaction.The wave-pile and seabed-pile sub-models are one-way coupled on the seabed surface.User-defined PDE module is adopted to simulate the response of mono-pile and pile-seabed coupled interaction.The wave model is governed by Navier-Stokes equations together with turbulence effect.The seabed is treated as an homogeneous isotropic porous media and simulated by Biot's quasi-static(QS)equations.The mono-pile model is solved based on elastic theory and identical displacement is considered between pile and soil.Main results of pore water pressure distribution in seabed and the displacement and bending moment of mono-pile under linear and cnoidal wave loading are obtained.The results show that the pore pressure along depth in seabed is largest at the seabed surface.The vertical distribution of pore pressure decreases along seabed depth.The peak value of mono-pile displacement under linear wave appears subjected to the effect of wave balance position,while pile displacement is relatively small under wave crest and trough.For cnoidal wave,the pile displacement is almost zero because of the characteristic of wave surface.2.Based on response research of the coupled pile and seabed,further studies are conducted on pile-soil interaction under pile rocking effect by the method of imposed periodic displacement on pile head.The characteristic of seabed and mono-pile dynamic response under pile rocking is obtained.With the consideration of disadvantageous load combination,the response of pore pressure and liquefaction distribution in seabed together with displacement and bending moment of mono-pile under pile rocking are discussed.In addition,parametric studies are conducted on the main characteristics of wave,seabed soil and mono-pile.The results show that the phenomenon of local pressure enlargement appears near the seabed surface in pile rocking model and the trend of pore pressure decrease along vertical direction is slower in the vicinity of mono-pile.Furthermore,the pile rocking effect makes the seabed liquefaction around mono-pile more obvious.The variation of parameters of wave,seabed and mono-pile has influence on the interaction and response of mono-pile and seabed.3.The 3-D model of residual pore pressure based on instant oscillatory shear stress is obtained by extention of present 2-D model.The long-tem effect of pile-seabed interaction is discussed by means of nonlinear residual pore pressure response in seabed soil.Comparison with available experiment and numerical results shows that the proposed 3-D model can accurately simulate residual response of seabed with mono-pile.Analyses show that the residual pore pressure accumulates with time development and the buildup of residual pore pressure has oscillatory characteristic in small amplitude.For seabed with mono-pile,the phenomenon of shear stress concentration appears near the mono-pile surface.In addition,the pileseabed-wave interaction affects seabed soil around the mono-pile in nonlinear way.The effect of pile rocking and wave loading leads to difference in residual pore pressure development at different positions around mono-pile.