Numerical analysis of group effects of a large pile group under lateral loading

Abstract

Large pile group (≥100 piles) foundations supporting liquified natural gas (LNG) storage tanks and high-rise buildings are subjected to significant vertical and lateral loads, where foundation design can be governed by the required lateral resistance. A typical approach for design of laterally loaded pile groups uses the beam on Winkler foundation method, where nonlinear p-y curves are reduced by a p-multiplier to account for the group effects. Alternatively, an average p-multiplier known as a group reduction factor (GRF) can be used. There is no published guidance on these topics for large pile groups (≥100 piles) as existing design standards are premised upon smaller pile groups (<25 piles). This study uses 3D continuum finite element models to study the group effects in large pile groups using p-multipliers and GRFs. The study also looked at the effect of the circular configuration of pile groups used in LNG tank foundations. The design standards and prevailing methods are shown to overestimate trailing row p-multipliers for large pile groups, particularly with larger pile spacing. Based on the study data and published data, a predictive equation is proposed for estimating GRF of a laterally loaded large pile group.