Study On Combined Bearing Characteristics Of Tripod Bucket Foundations And The Effect Of Earthquake Liquefaction

Offshore wind power is a clean and renewable energy source with unlimited resource potential and stability,and has been gaining attention and developing rapidly in recent years.Offshore wind turbines are the basic equipment for offshore wind power development and are fixed to the sea bed by the foundation structure to resist the harsh marine environment.Therefore,the design and research of the foundation structure is particularly important.The tripod bucket foundation is a new type of foundation type,which has a strong bearing capacity and high stability and can be used on different types of seabed,and has good applicability to future large wind turbine structures.The environmental load on the superstructure of the wind turbine is transferred to the bottom foundation structure through the pile foundation or anchor chain.At this time,the foundation is subjected to vertical load（V）and at the same time,it is also subjected to huge horizontal load（H）and moment load（M）,which causes vertical displacement（w）,horizontal displacement（u）and corner displacement（θ）of the foundation,and this is the combined loading mode.The combined loading analysis of tripod bucket foundation is beneficial to understand the ultimate bearing capacity of the foundation under a certain bearing environment,so as to judge whether the foundation can carry normally in advance.Most of the coastal areas in southeast of China are sandy soil or silt zone,and are in the Pacific Rim seismic zone,so the earthquakes are frequent and the soil is prone to liquefaction.The liquefaction areas of different soils are also different,and the bearing capacity is greatly reduced after liquefaction,which greatly affects the bearing performance of the foundation and foundation.The seismic liquefaction analysis of tripod bucket foundation is beneficial to analyze its effect on the bearing performance of foundation and foundation.In this thesis,the effects of combined bearing capacity and seismic liquefaction of tripod bucket foundation are investigated by using large finite element analysis software ABAQUS.Based on the structure-soil-foundation interaction,a three-dimensional finite element model is established,and the foundation bearing envelope of the tripod bucket foundation under the combined loading mode and under the influence of seismic liquefaction is calculated and analyzed in detail for the tripod bucket foundation applicable to floating and stationary wind turbines,considering both upward and downward vertical loading conditions.Firstly,based on the combined bearing capacity analysis model,the uniaxial ultimate bearing capacity V_ult,H_ultand M_ultof the tripod bucket foundation and the foundation failure envelopes of V-H,V-M,H-M and V-H-M loading spaces under the combined loading mode were calculated,the failure modes of the soil around the pile perimeter were studied,the damage mechanisms of the soil around the tripod bucket foundation under different uniaxial loads were compared,and the systematic comparison The range,shape and characteristics of the H-M envelope under different vertical loads（V）are compared.Then,based on the theory and numerical model of liquefaction of seabed soil,this thesis calculates the anti-liquefaction shear stress of tripod bucket foundation in pulverized sand and pulverized soil under seismic load,divides the soil into multiple soil layers by using grid,discriminates the liquefaction area of foundation soil,studies the displacement and stress state of foundation and foundation soil before and after liquefaction,systematically analyzes the liquefaction area of liquefied soil layer and the bearing performance of foundation after liquefaction.The effect of seismic liquefaction effect on the bearing characteristics of tripod bucket foundation is discerned by the study of foundation failure envelope under combined loading mode.Finally,in this thesis,the influence of geological conditions and the height-to-diameter ratio of the barrel foundation on the bearing performance of the tripod bucket foundation is comprehensively analyzed by comparing the foundation failure envelopes of V-H,V-M and H-M loading spaces under the combined loading mode,considering the soil parameters and the height-to-diameter ratio of the foundation.The research results of this thesis can be applied to the structural design and foundation bearing capacity assessment of the tripod bucket foundation,which provides an optional foundation design solution for the continuous large-scale offshore wind turbine,and has a certain reference value for the applicability analysis of the tripod bucket foundation on the seismic zone liquefaction-prone seabed.