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Piles in a group experience additional displacements in soil due to pile-to-pile interactions apart from those resulting from the external loading. The effect of these interactions determined assuming soil as an elastic and/or viscoelastic material on pile head impedance functions of the pile group is studied by relating the group stiffness to the static stiffness of a single pile. However, the prevailing elastic solutions may misestimate the resulting pile group response due to the lack of consideration for either soil (material) and/or soil-pile interface nonlinearities. It is well established that soil behaves nonlinearly under moderate-to-high loading amplitudes, and besides, the soil-pile interface nonlinearity can exist even at small loading amplitudes. This study addresses the effects of these nonlinearities on the vertical impedance functions of a 3×3-pile group using numerical methods by direct analyses and superposition using pile-to-pile interaction factors. The numerical results are validated using scaled model tests under 1 g conditions. The results highlight the overestimation of pile-to-pile interactions in the pile group when assuming elastic soil conditions. The cases either by direct analyses or superposition approach involving soil and soil-pile interface nonlinearities agree well with the experimental pile group responses under close-to-elastic and nonlinear conditions. [ABSTRACT FROM AUTHOR]

Physical-scaled model testing under 1 g conditions is carried out in obtaining the vertical response of fixed head floating-inclined single piles embedded in dry sand. Practical pile inclinations of 5° and 10° besides a vertical pile (0°) subjected to static and dynamic vertical pile head loadings are considered. To account for the effects of soil nonlinearity as well as the soil–pile interface nonlinearity on the response of piles, a range of low-to-high magnitude of pile head displacements is considered for the static case while a varying amplitude of harmonic accelerations for a wide range of frequencies is considered for the dynamic case. Experimental results are obtained in the form of pile head stiffnesses and strains generated in the pile under both the static and dynamic loadings. Results suggest that the nonlinear behavior of soil as well as the nonlinearity generated at the interface between the soil and the pile as the result of applied loading considerably affect the response of piles. The soil–pile interface nonlinearity that governs the slippage of pile shows a clear influence on the pile head stiffnesses by providing two distinct values of stiffnesses corresponding to the push and the pull directional movement of piles; the two values are significantly different. Axial and bending strains generated in the piles show expected dependency on the amplitude of applied loading; the pile head-level bending strain increases almost linearly with the increase in the angle of pile inclination. [ABSTRACT FROM AUTHOR]

The effects of soil nonlinearity on the dynamic behavior of fixed-head floating inclined pile groups are investigated experimentally in the form of horizontal impedance functions (IFs) and internal forces in piles. A 2 X 2 model of inclined pile groups embedded in dry cohesionless soil and subjected to a broad range of lateral harmonic loadings at the pile-cap level are examined. Piles with a spacing-to-the-diameter ratio (s/d) of 5 with practical pile inclinations of 0, 5, and 10° along the direction of loading are reported. Results show a profound impact of local nonlinearity and resonance of soil on the horizontal impedance functions. The inclined pile groups show higher values of horizontal IFs than the vertical pile group, in accordance with the general understanding. Influence of pile inclinations on the horizontal IFs is further examined through the variation of soil reactions along the depth of the piles. Semiempirical expressions for estimating the soil reactions, as a function of pile inclinations, are proposed. As for the internal forces in piles, bending strains for the inclined piles are smaller than the vertical pile; the axial strains show an opposite behavior. [ABSTRACT FROM AUTHOR]

In recent years, Japan has experienced an increasing number of short-period-dominated, high-acceleration earthquake motions. These strong motions, however, have caused only a limited damage to structures founded on piles. Among the possible reasons for the limited damage is the earthquake motion filtering effect of pile foundations. This filtering effect has been amply examined in numerous studies, most of which are based on an assumption that both the soil and piles behave linearly. This linearity-based approach, however, cannot be fully applied to strong earthquake motions as they essentially involve nonlinearity of both the soil and piles. With such considerations, the current work assesses the impact of nonlinear behavior of soil and piles on the filtering effect of pile foundations. As a first step, the filtering effect produced by a lumped mass model is examined for validation against the closed-form solutions. Secondly, dynamic analysis is conducted considering nonlinear behavior of soil and piles on the filtering effect. Finally, the impact of the filtering effect on the response of structures is examined using short-period-dominated earthquake motions. • Evaluated of kinematic interaction by analytic solution of lumped mass model. • Dynamic analysis is conducted considering nonlinear behavior of soil and piles on the filtering effect. • Filtering effect is assessed through the comparison of the lateral interaction factors. • Response spectra for short-period-dominated earthquake motions considering the filtering effect. [ABSTRACT FROM AUTHOR]