Abstract: Based on the theory of saturated porous media, the dynamic characteristics of vertical vibration of an end-bearing pile in a stratified saturated viscoelastic soil layer was investigated. The dynamic impedance of the soil to vertical vibration of the pile was obtained firstly with the Novak’s layer method. Then, regarding the pile as a Rayleigh-Love rod, the general analysis method for the vertical vibration of the end-bearing pile in the stratified saturated viscoelastic soil was presented; and the analytical expression of the complex dynamic stiffness at the pile top was obtained. The dynamic characteristics of vertical vibration of an end-bearing pile in a two-layer saturated viscoelastic soil were analyzed specifically; and the variations of the dynamic stiffness factor and equivalent damping of the pile top with respect to the frequency were given in figures. The influences of the physical and geometry parameters on the dynamic stiffness factor and equivalent damping were examined in detail. It is revealed that the length-radius ratio of the pile, the modulus ratio of the soil layers and the modulus ratio of the pile-soil have remarkable influences on the dynamic stiffness factor and equivalent damping of the pile top. Compared with pile in a uniform soil layer, the amplitudes of the dynamic stiffness factor and equivalent damping of the pile are increased as the elastic modulus of the upper soil layer is increased or the elastic modulus of the lower soil layer is decreased; and changes of the dynamic stiffness factor and equivalent damping with frequency are in form of the oscillation for large radius pile. Furthermore, the influences of the interaction coefficient between soil and pore water and the pile’s Poisson ratio are trivial relatively. The results can provide data base of pile design for dynamic foundation and dynamic detection of pile.

Key words: saturated porous medium, pile-soil interaction, transversal inertia effect, vertical vibration