Failure loci of piled foundations under vertical load-biaxial moment

This paper presents a novel exact solution for the failure locus of pile groups subjected to axial load and biaxial moment, derived from limit analysis theorems. The failure mechanism involves a rotation about a line connecting two piles, uniquely determined by the load path in the force space. For foundations with few piles, the proposed method enables straightforward hand calculation of the failure locus. For large pile groups, a new algorithm is introduced that evaluates the complete set of kinematically admissible solutions. Ready-to-use charts are provided for the most recurrent pile layouts found in Italian highway bridge infrastructure. Previous theoretical and experimental studies on the failure loci of pile groups under planar loading are revisited and discussed. Finally, a case study of a highway bridge built in south Italy in the 1960s demonstrates the potential advantages of the proposed framework.