Lateral Pile Group Effect: Literature Review and a Numerical Study-Paper

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The paper reviews lateral pile-group effects and presents a numerical study of a two-pile group in clay. Although pile groups are common in offshore platforms, design standards provide limited guidance, and much of the underlying research is decades old. Existing approaches modify single-pile response using either displacement-based (y-) or resistance-based (p-) multipliers, but these can combine several distinct influences into a single factor.<br /><br />The literature review finds that most physical tests concern larger, regularly arranged groups, leaving limited evidence for offshore groups of two to four piles. Group loading direction has also been relatively understudied.<br /><br />The numerical study models a horizontal soil slice under plane-strain conditions using the NGI-ADP clay model. It examines pile spacings of 2D–5D and loading angles of 0°, 25°, 45°, and 90°. Results show that group interaction is generally strongest when piles are close and the load acts along the line joining them (0°), because their soil failure zones overlap. Increasing spacing reduces this negative interaction, bringing the p-multiplier closer to 1. Loading angle matters most at small spacings. At 90°, very closely spaced piles (about 2D or less) can act as a single larger foundation, mobilising more soil and producing a positive group effect; at wider spacing, interaction diminishes. The y-multiplier was relatively insensitive to spacing but varied with loading angle.<br /><br />The authors conclude that pile spacing and loading direction should be considered in offshore design. The study is limited to two piles and flow-around failure; wedge failure and other group configurations remain to be investigated.

Keywords

pile group

lateral loading

offshore platforms

clay soil

two-pile group

pile spacing

loading angle

p-multiplier

y-multiplier

NGI-ADP model