Horizontal vibration characteristics of pile groups in unsaturated soil considering coupled pile–pile interaction

The horizontal vibration responses of pile groups are critical in pile engineering. However, the majority of existing research has regarded soil as a single-phase medium and ignored the coupled pile–pile interaction that cannot elaborate on the features in practical engineering. An analytical framework for investigating the horizontal vibration characteristics of pile groups in unsaturated soil was developed in this study. The poroelastic theory and Euler–Bernoulli beam theory were utilized to simulate soil and pile vibrations, respectively. Subsequently, the dynamic pile–pile interaction factor and lateral dynamic impedance of the pile groups were determined considering the boundary conditions of the pile–soil system. After verifying the existing results, a systematic discussion was conducted to analyze the effects of soil porous properties and secondary waves. The main conclusions are as follows: (1) Secondary waves mainly affected the dynamic pile–pile interaction factor in the low-frequency range, and the influence gradually weakened as the frequency increased. (2) The influence of soil porosity and saturation could be neglected in the low-frequency range, but it became significant with increasing frequency. (3) Secondary waves amplified the effect of soil porosity on the pile group dynamic impedance.