A singular case of development of deep soil expansions in the vicinity of pile groups supporting bridge pillars motivated the analysis. A semi-analytic procedure, which uses some available fundamental solutions for cavity expansion and the presence of concentrated loads in an elastic half-space, has been developed. The analysis requires an estimation of the soil displacements under the combined action of the stresses induced by the pile, the external loads and the volumetric deformations imposed by the soil expansion. “In situ” measurements provided an estimation of the deep volumetric deformations. The pile cap was also monitored and the evolution of its rotations and displacements was available. The analysis shows that all the piles of a group develop considerable bending stresses, which explain the cracking observed in the contact between the pile and the pile cap. The procedure developed predicts reasonably well the displacements and rotations experienced by the pile cap of the pile group.