Influence of soil plug effect on vertical dynamic response of pipe piles

Based on the additional mass method, the vertical vibration of pipe piles embedded in layered soils is theoretically studied by taking into account the soil plug effect. Firstly, allowing for the stratification of pile surrounding soil and pile end soil, the pile-soil system is divided into finite segments. By means of the fictitious soil pile method and the additional mass method, the vertical dynamic governing equations for pile-soil system are established. Then, by virtue of the Laplace transform technique and the impedance function transfer method, the analytical solution of velocity response at pile head in frequency domain is derived, and the corresponding semi-analytical solution of velocity response at pile head in time domain is also obtained when there is vertical half-sine pulse excitation force acting on the pile head. Finally, the sensibility intervals of the parameters of Voigt model in additional mass method are analyzed, and the influence of soil plug effect on the vertical dynamic response of pipe pile is also investigated. The rationality of the proposed theoretical solution is validated by means of model tests. The results show that: (1) with the increase of parameters of Voigt model, the interaction of pile and soil will be strengthened; (2) as shown in the time-domain curves of velocity response at pile head, there are reverse reflection signals at the upper surface of soil plug. It looks like there are expanding neck pile segments at the upper surface of soil plug; (3) due to the presence of soil plugs, the integrated velocity of the pile section filling soil plug is less than the elastic longitudinal wave velocity of pipe pile, and the higher the height of soil plug is, the smaller the integrated velocity of the pile section filling soil plug is.