轴对称径向非均质土中单桩纵向振动特性研究

为了分析径向非均质土中单桩纵向振动特性，基于复刚度传递径向多圈层并采用黏性阻尼模型描述桩周土材料阻尼，建立了三维轴对称径向成层非均质土体中桩基纵向振动简化分析模型。采用Laplace变换和复刚度传递方法，递推得出桩周土体与桩体界面处复刚度，进而利用桩-土完全耦合条件推导得出桩顶动力阻抗解析解，并将所得解退化到均质土情况，与已有解答进行比较验证其合理性。在此基础上对桩基纵向振动特性进行参数化分析，计算结果表明：桩周土体阻尼系数、桩底土阻尼因子仅对桩顶动力阻抗曲线振幅有较明显的影响，而桩底土刚度因子对桩顶动力阻抗曲线振幅及共振频率均有显著影响；桩周土软（硬）化程度越高（低），桩顶动力阻抗曲线振幅越大（小）；桩周土软（硬）化范围越大，桩顶动力阻抗曲线振幅水平越高（低）；但桩周土软（硬）化程度、软（硬）化范围对桩顶动力阻抗曲线共振频率影响则可忽略。

Dynamic impedance for vertical vibration of a single pile in axisymmetrically surrounding soil considering radial inhomogeneity

For the aim to analyze the vibration characteristics of a single pile surrounded by radially inhomogeous soil, a simplified mechanical model for vertical vibration of a single pile embedded in a radially inhomogeneous viscoelastic soil is proposed by employing the viscous damping and three-dimensional axisymmetric continuum model with annular transferred complex stiffness. Firstly, the complex stiffness at the interfaces between soil and pile is derived using Laplace transform and complex stiffness transfer method. Secondly, an analytical solution for dynamic impedance at the pile head is obtained by using the compatibility condition of pile and radially inhomogeneous surrounding soil. Furthermore, the obtained analytical solution for dynamic impedance at the pile head is reduced to verify its validity by comparison with an existing solution. Extensive parametric analyses are performed to investigate the effects of the parameters on the vibration characteristics at pile head. The computational results show that the viscous damping coefficient and the damping factor only have significant influence on the amplitude of dynamic impedance at pile head, while the stiffness factor has significant influence on the amplitude and resonance frequency of dynamic impedance at pile head. The higher the degree of softening (hardening) of the surrounding soil, the larger (smaller) the amplitude of the dynamic impedance at pile head. The larger the range of softening (hardening) of the soil around the pile, the higher (lower) the level of the dynamic impedance at pile head. However, the influences of the degree of softening (hardening) of the soil around the pile and the range of softening (hardening) on the resonance frequency of the dynamic impedance at pile head can be neglected.