Dynamic response of pile embedded in unsaturated soil under SH waves considering effect of superstructure

Soil is usually treated as one-phase or two-phase media in previous soil-pile dynamic studies. However, the air inside the soil pores can induce strong matrix suction to the skeletons, which would significantly affect the propagation of the shear horizontal waves within the soil. In addition, the superstructure's effect on the soil-pile system's dynamic response is often neglected. This can result in the underestimation of the dynamic impedance of a pile, which would further lead to the overdesign of the pile dimensions. In this study, a novel unsaturated soil-pile-superstructure model induced by vertically propagating shear horizontal waves is established to investigate the seismic performance of a pile under the influence of superstructures. The analytical solutions of the kinematic amplification and interaction factors (I-U and A(U), respectively) are derived using the Laplace transform and variable separation method. The developed solution is verified by comparing results from the hybrid boundary element method and the dynamic Winkler model in previous studies. Based on the obtained solutions, a parametric study is conducted to investigate the effects of pile and soil properties on the system's seismic response. The main conclusions can be drawn as follows: (1) When 0.2 < a(0) (normalized frequency) < 0.7, I-U and A(U) decrease with the increase of soil water saturation. This trend becomes extremely evident when the saturation is above 0.95. (2) Resonance appears at 0 < a(0) < 0.7, and the resonance frequency decreases with the increase of the superstructure mass. (3) The vibration of the free-field soil has a non-negligible effect on reducing the system's seismic response.