【作者】 贺琼；

【导师】 邹新军；

【作者基本信息】 湖南大学 ， 土木工程， 2019， 硕士

【摘要】 随着我国基础建设的快速发展,海上风力发电厂、钻井工作平台及跨海大桥等工程不断兴建。桩基础由于具有承载力高、便于施工等优点而成为这些工程的常用基础形式,且此类桩基大多受力复杂,除静力荷载（上部结构及基础自重等）外,还不可避免地要承受动力荷载如机器运转荷载、风荷载及波浪荷载等,从而导致复杂的桩-土动力相互作用问题。目前桩土动力问题中的扭转振动研究大多假定桩周土为均质各向同性介质,而实际工程中地基土多呈现出非均质性,因此,本文基于已有研究基础并结合国家自科基金项目（NO:51578231&51378197）,针对非均质地基中的桩基扭转振动问题进行理论分析,主要工作如下:首先,考虑地基土的径向非均质与竖向成层特性,基于连续介质模型理论和弹性动力学原理,分别建立土和桩的扭转振动平衡方程,采用分离变量法由内到外、从下至上求解土体动力方程,通过引入桩土接触面应力位移协调条件,导得桩周土对桩身的环向剪应力,再将其带入桩身动力方程,并结合相应边界条件求解获得桩顶复刚度解析表达式。为验证该解答的可行性,将其分别退化为均质地基模型和径向非均质地基模型,并与已有研究结果进行了对比分析。其次,根据所获得的双向非均质地基中动力受扭桩的桩顶复刚度解析表达式,基于Mathematica编写桩顶复刚度计算程序,并据此分析了桩周土的径向非均质性、竖向非均质性、桩土剪切波速比V_p/V_s及桩身长径比H/r₀等参数对桩顶复刚度的影响规律。最后,假定地基土体剪切模量随深度呈指数函数非线性分布,基于Biot固结理论与弹性动力学原理,建立出竖向非均质饱和地基内部作用简谐扭转荷载时的动力平衡方程,通过Hankel变换与逆变换求解获得土体应力位移解答,并通过进一步的参数分析,得到荷载频率、荷载埋深、剪切模量非均匀系数及土体渗透系数对饱和地基扭转动力响应的影响规律。更多还原

【Abstract】 With the rapid development of infrastructure in China,major projects such as offshore wind turbines,offshore work platforms and bridges across ocean continue to be constructed.The pile foundation is widely used in the above projects due to its advantages such as high bearing capacity and convenient for construction.Most of these pile foundations are subjected to both static loads(weight of upper structure and foundation,etc.)and dynamic loads such as running loads of machine,wind loads and wave loads,which results in complex dynamic problems of pile-soil system.At present,the research of torsional vibration mostly assumes that the surrounding soil is homogeneous and isotropic,while the actual foundation soil tends to be inhomogeneous.Therefore,based on the existing research results and supported by the National Natural Science Foundation of China(NO:51578231&51378197),this study investigated torsional vibration of an elastic pile embedded in inhomogeneous soil and subjected to a time-harmonic torsional loading.At first,considering the radial inhomogeneous of layered foundation,dynamic equilibrium equation of soil and pile were established based on three-dimensional continuum model and the dynamic elastic theory.Using the variables separation method to solve the equation of soil from inside to outside and from bottom to top,the circumferential shear stress on the pile generated by surrounding soil is then obtained by considering continuity conditions of stress and displacement on the contact surface.Then putting the circumferential shear stress into the equation of pile,and the analytical expression of the complex stiffness at pile head is obtained due to solving the equation of pile and the corresponding boundary conditions.In order to verify the feasibility of the solution,the above inhomogeneous foundation model was degenerated to homogeneous foundation model and radial inhomogeneous foundation model respectively,and compared with the existing research results.Secondly,the calculation program by Mathematica was completed based on above solution and used to analyze the influence of radial and vertical inhomogeneous of soil,shear wave velocity ratio V_p/V_s and length-diameter ratio H/r0 on the complex stiffness at pile head.Finally,assuming a nonlinear distribution of the shear modulus of soil with the depth defined by the exponential function,the dynamic equilibrium equation of soil under a time-harmonic buried torsional loading was established by using the Biot’s consolidation theory and the dynamic elastic theory.The expressions of stress and displacement then were acquired by solving the soil equation with the method of Hankel transform.Then,the influence of load frequency,load depth,non-uniform distribution factor of shear modulus and permeability coefficient of soil on the dynamic response of saturated soil are analyzed.更多还原