Research On Lateral Bearing Capacity Of Pile Foundation Of Wind Power

Wind power is currently one of the world’s fastest growing,most commercialized and large-scale developed renewable energy.With the energy structure reformation in China,more and more attention is concentrated on the offshore wind power.For the convenience in construction and cheap in cost,the monopile foundations are widely used in offshore wind farms.For a single monopile,during the design working life,it will subjected to the long term cyclic lateral loads induced by the wind,wave and current etc.,and the deformation behaviour of the monopile will become extremely complicated.For analysis of laterally loaded piles,p-y curve method is widely being used in academic and engineering applications.Various p-y curves have been proposed based on field tests,such as Matlock p-y curve for clay(1970),Reese p-y curve for sand and Reese&Welch p-y curve for stiff clay.However,most of the existing p-y curves are on the basis of small-diameter piles,it causes a big problem whether they can be applied in large-diameter piles or not.This thesis mainly investigates the influence of diameter on p-y curves through theoretical analysis,numerical simulation and field test analysis,and then comes to a conclusion that p-y curve method may introduce great errors when applied in large-diameter piles.Besides,based on the soil modulus degradation model,the accumulated deformation of monopile for energy applications is investigated via the developing of the user subroutine inFLAC3 D.This thesis mainly completed the following research works:(1)The three-dimensional finite element models are established to simulate the field tests of clay and sand whose numerical results are compared with the measured displacements and bending moments,and then the fundamental features of p-y curves are summarized by analyzing the numerical results.(2)The influence of diameter on p-y curves is investigated through theoretical analysis,numerical simulation and field test analysis.The three-dimensional finite element models of different diameters are established and then the initial subgrade modulus and limit force profile are obtained from the numerical results,meanwhile,the curves of diameter vs the initial subgrade modulus and diameter vs the limit force profile are ploted.(3)Based on the fundamental features of p-y curves,the new p-y curve is proposed for clay and the p-y curve for sand is also replaced by a more reasonable formula.The limit force profile of clay is based on elastoplastic model while it is simplicated as for sand.(4)Based on the finite difference method,the nonlinear solution of p-y curves were derived,and the solution processs were coded in Matlab to calculate the bearing capacity of the horizontal loaded pile.Besides,the influences of initial subgrade modulus and limit force profile in p-y curve on the bearing capacity of lateral loaded pile were investigate based on the Matlab codes.(5)The cases of laterally loaded piles are calculated with the above two different p-y curves,and then the better is picked out.Meanwhile,equivalent depth method is presented for large-diameter piles in layered soils and its feasibility is also verified.(6)Based on the soil modulus degradation model,the detailed implementation procedures in finite difference code FLAC3 D were explained.The accumulated deformation of monopile for energy applications is investigated via the developed user subroutine,and the influence of load amplitude on the accumulated deformation is also analyzed.A prediction model of cyclic accumulation deformation is proposed for the monopile embedded in the sandy seabed,and the model is calibrated with the other models published in literatures.