Vertical vibration and additional distress of grouped piles in layered soil

Analytical solutions are developed for calculating the harmonic steady-state axial stiffness, damping, and internal forces of pile groups embedded in multi-layered soil. Pile-soil interaction is represented through a dynamic Winkler model, with frequency-dependent spring and dashpot moduli. Pile-to-pile interaction is taken into account analytically by considering the wave field originating along an oscillating ("source") pile and the diffraction of this field by an adjacent ("receiver") pile. In the case of uniform and two-layer soil profiles, closed-form expressions are derived for both pile impedances and dynamic interaction factors between piles. A solution is finally presented for the additional axial forces developed in piles due to pile-to-pile interaction. The predictions of the model compare well with results of earlier studies, while its simplicity offers a versatile alternative to complicated numerical solutions.