<p>In this study, unlike most previous investigations for the vertical dynamic interaction of pipe piles in unsaturated soil, an improved solution for the pile dynamic responses is established for involving the incomplete bonding contact behavior between the soil plug and the pipe pile. Based on the potential function method, operator decomposition technique, and separation of variables, the vertical vibration responses of the pile surrounding soil and the soil plug are solved separately. The Kelvin interface model is employed to describe the small-deformation slippage behavior between the soil plug and the pipe pile, enabling the derivation of analytical solutions for the complex impedance function and velocity admittance at the pile-top in the frequency domain. A semi-analytical solution for the pile-top velocity response in the time domain is constructed using the inverse Fourier transform. The effects of Kelvin model parameters, soil saturation, viscous damping coefficient, porosity, and pile radius on the vertical dynamic characteristics of the pipe pile are systematically investigated. The results show that the partial bonding model more accurately reflects the dynamic response of pipe piles in unsaturated soil compared to the complete bonding model. Increases in the dynamic damping coefficient of the Kelvin model and the soil viscous damping coefficient, as well as decreases in soil saturation or porosity effectively reduce the oscillation amplitude at the pile-top.</p>