Interaction domains of pile groups in cohesive soils under generalised loads

This work focuses on the undrained bearing capacity of pile groups subjected to combined vertical, moment and lateral loads. Advanced three-dimensional (3D) finite-element analyses were used to identify the possible plastic mechanisms occurring within the soil–foundation system, as well as the most relevant factors affecting its limit behaviour. The numerical results show a strong coupling between the lateral capacity of the group and the applied vertical/moment loads, resulting from a different degree of mobilisation of the axial and bending capacity of the piles. Based on the numerical findings, a new theoretical lower bound solution was developed to compute the 3D failure domain of pile groups in clay, overcoming limitations and inconsistencies of theoretical solutions recently proposed in the technical literature. The method accounts for the combined effect of group geometry, structural and geotechnical capacity of the single piles, and loading direction on the actual plastic mechanism occurring within the group and the corresponding failure envelope.