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There is a paucity of systematic experimental studies on the group effect of dragloads in pile foundations. This paper reports on a series of 1-g model tests that were conducted on single piles as well as 2 × 2 and 3 × 3 pile groups with various pile spacings to investigate the influence of soil compressibility, pile installation method, pile end constraint, and pile spacing on dragload development in the piles. The results indicate that soil compressibility significantly influences the magnitude of dragloads developed in single piles and piles in a group. However, the effect of soil compressibility on the group effect (a measure of dragload reduction) is negligible. Pile spacing is the most significant factor that influences group effect, followed by the number and position of piles. The group effect can reach 50% for a spacing of 3D (where D denotes pile diameter), but becomes negligible for a spacing of 7D. The influence of pile end constraint and pile installation method on group effect is comparatively insignificant. Although group effects of the suspending piles are marginally lower than those of end-bearing piles under otherwise identical conditions, the dragloads on the suspending piles correspond to tensile forces and are detrimental to concrete piles.