Abstract: Group effect in a pile group under eccentric lateral loading is much more complicated than that in a pile group under lateral loading because the grouped piles have different motion directions due to the twist of the pile cap. The purpose of this study is to develop new p-multipliers quantifying group effect in pile groups subjected to eccentric lateral loading. Motions of two individual piles in a pile group under eccentric lateral loading were first studied and concepts of the leading pile and the trailing pile were defined to characterize the relative positions of the two piles. Then centrifuge model tests, numerical analysis, and theoretical analysis were carried out to study the interactions between two piles. It is found that the angles between the motion directions of the leading and trailing piles and the line through both piles, denoted as η and θ, vary in the ranges of 0°–90° and −90°–90°, respectively. The reduction factors of the leading and the trailing piles are both nonlinearly changed with η and θ. The reduction factor of the leading pile is larger than that of the trailing pile if interaction exists. There exist regions on the η-θ plane where the interaction between the two piles is negligible. A concept of critical angle θ₀ was introduced to define the boundary with and without interaction for a given η. Finally, empirical equations of reduction factors and a procedure to calculate p-multiplier were proposed and examined using existing test results.

Key words: Pile foundations; Pile groups; Lateral loads; Eccentric lateral loading; Pile-soil-pile interaction; Pile tests

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