Lateral vibration and internal forces of grouped piles in layered soil

Simplified analytical models are developed for the lateral harmonic response of single piles and pile groups in layered soil. Pile-to-soil interplay is represented by a dynamic Winkler formulation based on frequency-dependent springs and dashpots. For pile-to-pile interaction, the wave field originating from each oscillating ('source') pile and diffraction of this field by the adjacent ('receiver') piles are considered. The response of single piles and pile pairs is evaluated both numerically (through a transfer-matrix formulation) and analytically (introducing an efficient virtual-work approximation). Closed-form solutions are obtained: (1) for the impedance of single piles; (2) for the dynamic interaction factors between two piles; and (3) for the 'additional' internal forces ('distress') developing in grouped piles because of pile-to-pile interaction, a phenomenon frequently ignored in current methods of analysis. Both swaying and rocking vibrational modes are considered. The effect of pile length and soil layering on the impedances and interaction factors is studied. The predictions of the model are in agreement with earlier results, while its simplicity offers a versatile alternative to rigorous solutions.