Abstract: The modified Poulos method is universally used in design of laterally-loaded pile groups of platforms in current ocean engineering practices. However, given that increasing engineering cases have jack-up rigs with large-diameter spudcan foundations operating near a platform, the effects of spudcan penetration on the adjacent pile group should be evaluated. A pile group analysis method which is able to evaluate the effect of spudcan penetration on the pile group interaction is proposed in this paper. Single pile head deflections under the combined loading of spudcan penetration and the pile head load are firstly analyzed using the nonlinear foundation beam method. Then combining the effects of pile group interaction and nonlinear soil-pile interaction, the additional pile response due to the group effect is calculated through an elastic analysis. Finally, the pile group interaction Y-modifier is obtained by several pilot modifications of p-y curves of the single pile, whose variation during spudcan penetration indicates the effect of the spudcan penetration on the pile group interaction. Centrifuge model tests are conducted in sand to study the effect of spudcan penetration on adjacent a single pile and a pile group, respectively, and the proposed method is verified by comparison with predicted pile head deflections at different stages. In this case, the Y-modifier tends to decrease during spudcan penetration, and it can be inferred that the factor determined in the active loading stage is conservative enough in pile group analysis when considering spudcan penetration.

Key words: modified Poulos method, pile group analysis, Poulos analysis method, spudcan penetration, Y-modifier