【作者】 王鑫；

【导师】 赵学亮； 刘益平；

【作者基本信息】 东南大学 ， 岩土工程（专业学位）， 2020， 硕士

【摘要】 筒型基础作为一种新型深水基础结构型式,弥补了单桩基础和重力式基础的诸多缺点,逐渐广泛应用于近海工程。在海上风电工程中,由于复杂的海上水文气候条件、土体条件及荷载条件等因素,传统基础设计方案仅凭设计人员经验未必达到资源合理配置,对吸力式筒型基础的研究还需要进行大量的工作。目前筒型基础研究成果很多集中在黏土中单筒基础的力学特性分析,对于砂土地基中的多筒基础的受力特性和破坏机理研究尚不充分。针对以上存在的问题,本文借助小比尺模型试验对吸力式三筒基础在水平和弯矩荷载作用下的破坏模式与承载特性进行分析,并通过PLAXIS有限元软件对试验的结果加以验证和扩展。在此基础上,利用数学计算方法对三筒基础尺寸进行优化,为实际工程提供优化设计方案。论文主要工作包括以下内容:(1)采用模型试验、数值模拟和理论分析等手段,针对水平和弯矩荷载作用下的三筒基础的承载力与失稳破坏模式展开深入研究。经试验和数值计算方法比较发现,砂土中三筒基础极限承载力可通过荷载—位移曲线中的特征点来确定。在相同的水平和弯矩荷载下,随着长径比的减小,三筒基础水平位移量越小。基础在水平和弯矩作用下的失稳破坏模式表明,加载前期,基础主要发生转动加平动的运动趋势,到了破坏阶段,基础发生整体倾覆破坏。三筒基础失稳时,整体结构的转动中心位于受压筒中轴线附近,并随着长径比的减小发生下移规律。针对复合加载模式下三筒基础承载力特性,通过PLAXIS有限元平台,采用固定荷载比方法搜寻M-H应力空间内的破坏包络线。讨论了吸力式三筒基础的水平和弯矩承载力的理论计算公式,并在原有的理论基础上提出了适合本文的承载力效率系数和承载力计算修正系数。(2)通过模型试验、数值模拟计算,系统地讨论了不同承载力影响因素下的三筒基础承载特性。研究了相同筒重条件下,长径比的改变对三筒基础水平承载力的影响。针对水平和弯矩荷载的不同作用方向,确定了三筒基础水平承载力最有利及最不利方向。讨论了相同尺寸和荷载方向下,不同筒间距对吸力式三筒基础承载力结果的影响,引入承载力增长效率系数概念确定最优筒间距。(3)结合三筒基础承载力特性研究结论,建立数学优化模型,对已有的工程案例基础进行尺寸优化重设计,通过有限元方法验证优化后基础结构的稳定性,优化方案大幅度节省了工程材料。更多还原

【Abstract】 The bucket foundation,as a new type of deep-water foundation structure,has been gradually developed and applied in offshore engineering field,which makes up for the shortcomings of single pile foundation and gravity foundation.In offshore wind turbine projects,due to the complicated hydrologic and climatic conditions,soil conditions and load conditions,the traditional foundation design scheme only depends on the designer’s experience may not achieve the reasonable allocation of resources,a lot of work needs to be done to study the suction foundation.At present,the research of bucket foundation mainly focus on the analysis of the mechanical properties of single type,but the research on the mechanical properties and failure mechanism of multi-bucket foundation in sand foundation is not enough.In view of the above background,this thesis analyzes the failure mode and bearing characteristics of tripod-bucket foundation under horizontal and bending moment loads by means of small scale model test,and verifies and expands the test results by PLAXIS finite element method.Finally,the size of the tripod-bucket foundation is optimized by mathematical method,which provides the optimal design scheme for an actual project.The main work of this thesis includes the following contents:The bearing capacity and failure mode of tripod-bucket foundation under horizontal and bending moment load are studied by means of PLAXIS and model test.It is found that the ultimate bearing capacity of tripod-bucket foundation in sand can be determined by the characteristic points in the load-displacement curve.Under the same horizontal and bending moment load conditions,with the decrease of the ratio of length to diameter,the horizontal displacement of the tripod-bucket foundation is smaller.The failure mode of foundation under horizontal and bending moment shows that in the early stage of loading,the main movement trend of foundation is rotation and translation.At the failure stage,the whole foundation is overturned.When the tripod-bucket foundation trends to rotate,the rotation center of the whole structure is located near the axis of the compression tube,and moves down with the decrease of the length to diameter ratio.According to the bearing capacity characteristics of tripod-bucket foundation under combined loading mode,the failure envelope in the M-H stress space is searched by using the fixed load ratio method with the finite element PLAXIS.This thesis discusses the theoretical calculation method of horizontal and bending moment bearing capacity of tripod-bucket foundation,and proposed the efficiency coefficient of bearing capacity and the correction coefficient for bearing capacity calculation s on the basis of the existing theory.Through numerical simulation and model test,the bearing characteristics of tripod-bucket foundation under different bearing capacity factors are systematically discussed.The influence of the change of the ratio of length to diameter on the horizontal bearing capacity of the tripod-bucket foundation under the same caissons’ weight is studied.According to the different action directions of horizontal and bending moment load,the most favorable and unfavorable directions of horizontal loads on the tripod-bucket foundation are determined.The influences of different bucket spacing on the bearing capacity of tripod-bucket foundation under the same size and load direction are discussed,and the concept of bearing capacity growth efficiency coefficient to determine the optimal spacing between buckets are introduced.Based on the research conclusion of the bearing capacity characteristics of the tripod-bucket foundation,the mathematical optimization model is established,and a practical project of offshore wind turbine is redesigned for size optimization.The stability of the optimized structure is verified by the finite element method.The results show that the optimization scheme results in a greatly saving of materials and so cost.更多还原