Lateral vibration and internal forces of grouped piles in layered soil

Simplified analytical models are developed for the lateral harmonic respons e of single piles and pile groups in layered soil. File-to-soil interplay i s represented by a dynamic Winkler formulation based on frequency-dependent springs and dashpots. For pile-to-pile interaction, the wave field origina ting from each oscillating ("source") pile and the diffraction of this fiel d by the adjacent ("receiver") piles are considered. The response of single piles and pile pairs is evaluated both numerically (through a transfer-mat rix formulation) and analytically (introducing an efficient virtual-work ap proximation). Closed-form solutions are obtained: (1) for the impedance of single piles; (2) for the dynamic interaction factors between two piles; an d (3) for the "additional" internal forces ("distress") developing in group ed piles because of pile-to-pile interaction, a phenomenon frequently ignor ed in current methods of analysis. Both swaying and rocking vibrational mod es are considered. The effect of pile length and soil layering on the imped ances 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.