Evaluation of Dynamic Soil-Pile Interaction Based on Back Calculated P-Y Curves

Abstract

Soil-pile interaction constitutes an important parameter in predicting the seismic response of pilesupported structures. Towards a computationally attractive investigation of the interaction mechanism, the p-y method, where the soil is represented as a series of independent springs distributed along the pile shaft, has been extensively used. Along these lines several p-y curves for different soil-pile systems have been proposed which are mainly based on in-situ pile tests under static or low frequency cyclic loading conditions. However, soil-pile interaction under seismic excitation becomes more complex due to the incident seismic waves scattered by the pile, thus modifying the p-y relationship and introducing an additional damping mechanism at the soil-pile interface. In this paper, dynamic soil-pile interaction is estimated based on back-calculated p-y curves, disregarding in a first stage any potential soil-pile gapping mechanism. Pile displacements and soil reactions are derived through double integrating and differentiating respectively the bending moments obtained along the pile shaft. The p-y curves generated at each depth are utilized to derive frequency dependent springs and dashpots, which may then be implemented within the framework of a Beam on Dynamic Winkler foundation modeling of the soil-pile system. The proposed procedure is validated through centrifuge tests results of a coupled soil-pile-structure system under real earthquake excitation and is also compared to existing analytical formulas of frequency dependent springs and dashpots under steady state harmonic excitation applied on the pile head. Analysis results reveal that for each one of the loading scenarios considered, soil-pile interaction mechanism is adequately captured while utilizing existing analytical expressions for the computation of dynamic soil spring supports may under certain conditions lead to an overestimation of pile and structural response when the coupled soil-pilestructure system is analyzed.