| Summary: | The behavior of laterally loaded pile groups is usually accessed by beam-on-nonlinear-Winkler-foundation (BNWF) approach employing various forms of empirically derived <i>p-y</i> curves and <i>p</i>-multipliers. Averaged <i>p</i>-multiplier for a particular pile group is termed as the group effect parameter. In practice, the <i>p-y</i> curve presented by the American Petroleum Institute (API) is most often utilized for piles in granular soils, although its shortcomings are recognized. In this study, we performed 3D finite element analysis to develop <i>p</i>-multipliers and group effect parameters for 3 × 3 to 5 × 5 vertically squared pile groups. The effect of the ratio of spacing to pile diameter (<i>S/D</i>), number of group piles, varying friction angle (<i>φ</i>), and pile fixity conditions on <i>p</i>-multipliers and group effect parameters are evaluated and quantified. Based on the simulation outcomes, a new functional form to calculate <i>p</i>-multipliers is proposed for pile groups. Extensive comparisons with the experimental measurements reveal that the calculated <i>p</i>-multipliers and group effect parameters are within the recorded range. Comparisons with two design guidelines which do not account for the pile fixity condition demonstrate that they overestimate the <i>p</i>-multipliers for fixed-head condition.
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