Impacted Penetration Progress Researches Of Large-diameter Open-ended Steel Pipe Pile Applied In Offshore Wind Farm

With the development of offshore wind farm,large diameter steel pipe open-ended piles(LDSPOed pile)are applied widely that is installed by impact driving.During progress of installation,pile hammer strikes pile top,and then striking energy propagates along pile shaft as stress wave to overcome soil resistance so that penetrates pile into more depth.The pile-soil relationship during impacted penetration is a large deformation and dynamic nonlinear progress,and dynamic response of soil after installation need more researches.A finite element method,‘Pile hammer-Pile-Soil',is built systematically to analyze LDSPOed pile-soil response by impact force in offshore engineering.This method is based on RITSS(Remeshing and Interpolation Technique with Small Strain)method,and a LDSPOed pile impact penetration numerical model is built to simulate relationship between pile and soil in the progress of penetration.More than,a numerical model is also established to reveal the trends of pore pressure dissipation and set-up effect.The main researches are shown as follows:(1)A total stress analysis MCC model is built to implement the nonlinear response of pile impacting penetration into saturated soil in ABAQUS.The pore pressure matrix is inosculated into elastic-plasticity soil constitutive to build this model.A related UMAT subroutine is developed and complied to complement the model.The complied model is contrasted to MCC model in ABAQUS to validate its rationality and robustness.(2)A pile-soil contact constitutive is built to eliminate pore pressure value of pile-soil friction stress when compiled MCC model is applied in the numerical analysis.New contact model is complied in FRIC subroutine and compared to Coulomb friction in ABAQUS to validate the constitutive rationality.(3)The soil pluging condition of LDSPOed pile during dynamic penetration is created,and a displacement solutions of soil core and pile are proposed.(1)Based on open-ended pile and its soil core mechanical property under static loading,inertia force and friciton of dynamic factor,DRF,are brought in and dynamo-statics method are applied.And then,limit mechanical balance relationship is built and soil pluging condition is formulated.(2)A displacement calculation formula of soil core is derived under static loading,and displacement solution of soil core under dynamic loading is derived by appending inertia force and its effect factors are analyzed.(3)A partial differential equation of open-ended pile is built based on wave equation,and displacement of open-ended pile is described under dynamic loading by Fourier formula and its factors are compared.(4)A LASPOed pile dynamic penetration numerical model is created and RITSS is applied.A series of impact loading-time curves are plotted,which is borrowed ideas from researches of Randolph et al.These curves are verified to GRLWEAP its curves.The dynamic penetration numerical model is validated with a literature data.(5)A LDSPOed pile driving formula is proposed.The modelling work is conducted to analyze effects of different diameters and ratio between wall thick and pile diameter of LDSPOed pile.The results of soil resistance during pile driving are compared with various present driving formulas to validate numerical results.Then,a new pile driving formula is built.(6)A new pore pressure calculated formula is put forward and effect scope of excess pore pressure is analyzed during LDSPOed pile driving.The formulas are built to describe soil pore pressure of inner/outer of pile and below its tip.More than,the effect radius/scope of excess pore pressure is derived and validated with numerical results.(7)A set-up effect calculated formula is presented to analyse capacity of LDSPOed pile with time.The analysis numerical model after penetration work is built to simulate pore pressure dissipation of soil and set-up effect of LDSPOed pile.And,its validity and robustness is analyzed by a close-ended pile penetration field case.The initial distribution of pore pressure is contrasted to two theoretically distribution model,which initial pore pressure is mapped.The Q-s curves are plotted after various dissipation days.The capacities of LDSPOed piles from Q-s curves are validated with that from home and abroad codes.A new set-up effect formula of LDSPOed pile is created,which considers the pile diameter.To sum up,an analysis method of the LDSPOed pile impact penetration progress is developed systematically,in which the mechanical property of open-ended pile and soil core is analyzed by theoretical method,and numerical models are created.A displacement solution of LDSPOed pile and soil core under dynamical loading is presented separately.A new LDSPOed pile driving formula,pore pressure during pile driving formula and a set-up effect calculated formula are proposed.These researches could offer technical supports to analyze pile capacity and size design during LDSPOed pile penetrating saturated soil.