Abstract: 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.

Key words: three-dimensional axisymmetry, construction disturbance, complex stiffness transfer model, viscous damping, dynamic impedance