Bearing capacity of pile groups under generalized loading conditions-Paper

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The paper proposes a practical method for assessing pile-group bearing capacity under combined vertical, horizontal, and moment loading. Existing design approaches can be overly conservative because they may treat failure of one pile as failure of the whole group. Conversely, simplified methods that neglect interaction between horizontal force and moment can overestimate capacity when the piles’ cross-sectional moment resistance is significant.<br /><br />The proposed method uses limit equilibrium to construct interaction diagrams in the horizontal-load–moment plane for a given vertical load. The diagram is defined by a small number of points calculated from pile axial and lateral capacities in compression and uplift, together with the piles’ yielding moments. These parameters are generally already available in routine design, allowing the approach to be applied with limited computation. The authors also present a simplified procedure for ultimate limit-state checks using plots of vertical load against moment and vertical load against horizontal force.<br /><br />A case study of a railway viaduct foundation illustrates the design implications. For the analyzed nine-pile foundation, conventional design required 36 m piles. The proposed framework indicated that a 29 m design could satisfy vertical-load checks, but its reduced reinforcement did not meet the more complete combined-load assessment. A revised option using 31 m piles and greater reinforcement was assessed as suitable. Overall, the method accounts more consistently for group ductility and load-component interaction, helping avoid both unnecessary conservatism and unsafe overestimation of capacity.

Keywords

pile-group bearing capacity

combined loading

vertical load

horizontal load

moment interaction

limit equilibrium

interaction diagram

ultimate limit state

pile foundation design

load interaction