Insight into Soil-Pile-Structure Interaction Including Inertial and Kinematic Effects

Abstract

The important role of soil-pile-structure interaction on the seismic response of pile-supported structures has been widely established by several theoretical and experimental studies. However, due to the complex nature of the physical phenomenon, the identification of the key parameters that affect the interaction mechanism remains a crucial task. Along these lines, the frequency content of the seismic motion constitutes an important parameter that affects the intensity of soil-pile-structure interaction phenomena and consequently the seismic response of pile-supported structures. In this paper, soil-pile-structure interaction is numerically examined in the frequency domain in order to obtain an insight on the effect of the natural frequencies of the system on pile and structural dynamic response. Kinematic soil-pile interaction is initially investigated under harmonic excitation applied at the base of the soil profile, emphasizing on the effect of the soil fundamental frequencies on the pile bending moments. Within the framework of the validation of the adopted soil-pile model, additional analyses were performed implementing pilehead loading in order to obtain pile impedance functions and compare them to existing analytical formulas. In a second stage of analysis the coupled soil-pilestructure system is examined, adopting single pile-supported structures with different dynamic characteristics. Soil-pile-structure interaction effects are discussed in terms of the fundamental frequency of the superstructure, the bending moments generated along the pile shaft and the pile head motion. The analysis results indicate that for certain soil-pile cases, the kinematic peak pile bending moments may occur at frequencies higher than the fundamental frequency of the soil deposit. On the other hand, the investigation of the coupled soil-pile-superstructure system revealed that structural oscillations transmit large bending moments on the pilehead when the modified frequency of the structure due to SSI effects is close to the fundamental frequency of the input motion. Furthermore, the combined effect of inertial and kinematic interaction may under certain conditions result in a significant amplification of the pilehead horizontal motion at the fundamental frequency of the pilestructure system.