Large deformation numerical modeling of the short-term compression and uplift capacity of offshore shallow foundations

Large-deformation finite-element analysis has been used to model the undrained response of skirted shallow foundations in uplift and compression. Large-deformation effects involve changes in embedment ratio and operative local soil shear strength with increasing foundation displacement—either in tension or compression. Centrifuge model testing has shown that these changes in geometry affect the mobilized bearing capacity and the kinematic mechanisms governing failure in undrained uplift and compression. Small-strain finite-element analysis cannot by definition capture the effects of changing foundation embedment ratio and variation in local soil strength with foundation displacement. In this paper, load-displacement relationships, ultimate capacities, and kinematic mechanisms governing failure from large-deformation finite-element analyses are compared with centrifuge model test results for circular skirted foundations with a range of embedment between 10 and 50% of the foundation diameter. The results show that the large-deformation finite-element method can replicate the load-displacement response of the foundations over large displacements, pre- and postyield, and also capture differences in the soil deformation patterns in uplift and compression. The findings from this study increase confidence in using advanced numerical methods for determining shallow skirted foundation behavior, particularly for load paths involving uplift.