Serviceability and ultimate limit state checks for pile groups via the equivalent pier method

The representation of a pile group by an equivalent pier involves significant simplifications, but nevertheless provides a very useful check on the results of more complex analyses of the group. In this paper, previous work on the vertical and lateral responses of an equivalent pier under serviceability limit state (SLS) loadings have been extended to the consideration of the overall stability of the pier under ultimate limit state (ULS) loadings. Approximate expressions for the ultimate axial, lateral and moment resistances of the pier have been adopted, and the stability of the pier has been assessed in terms of a published criterion for foundation failure under combined axial, lateral and moment loads. For this assessment, the computed ultimate resistances have been factored down by a geotechnical reduction factor while various load combinations have been applied to the load components.

For practical application of the equivalent pier approach, some correlations for the estimation of the various geotechnical parameters for both SLS and ULS states has been summarized.

The simplified equivalent pier approaches, for both SLS and ULS loads, have been applied to the foundation system for the Incheon Tower, for which more complex 3-dimensional analyses were undertaken. The simplified approach gives outcomes that are generally consistent with those from the more complex analysis.