Principle of superposition for assessing horizontal dynamic response of pile groups encompassing soil nonlinearity

Model tests on fixed-head floating piles embedded in dry cohesionless soil (Gifu sand) are carried out under 1- g conditions on a shaking table, to investigate the effects of local soil nonlinearity on the dynamic response of pile groups. Results obtained from these tests are employed to assess the applicability of Poulos' superposition method in determining the pile group response under different levels of material nonlinearity. A wide range of head loading amplitudes inducing low-to-high levels of soil strain are employed for a broad range of frequencies. Utilizing the aforementioned superposition method, horizontal impedance functions of a closely spaced 3×3-pile group are computed based on: (1) experimentally-measured values of horizontal impedance functions for a single pile, and (2) experimentally-measured pile-to-pile interaction factors. Comparisons between computed and measured impedance functions show good agreement for low to intermediate loading amplitudes, suggesting that the superposition method is valid even under moderately nonlinear conditions.