Numerical Analysis of Inclined Uplift Capacity of Suction Caisson in Sand

Three-dimensional finite element (FE) analyses are conducted to calculate the pullout capacity of a suction caisson subjected to oblique loadings. Two sets of FE analyses are performed using Abaqus FE software. In the first set, the sand around the caisson is modeled using the built-in Mohr Coulomb (MC) model available in Abaqus where constant values of the angle of internal friction phi' and dilation psi are defined. The effects of key variables, such as loading angle, mooring position, and aspect ratio, on pullout capacity and rotation of the caisson are examined. A comparison between FE and centrifuge test results is also shown. The second set of analyses are performed using a modified Mohr Coulomb (MMC) model where the prepeak hardening, postpeak softening, and effects of density and confining pressure on stress-strain behavior of dense sand are implemented via a user subroutine by varying phi' and psi as a function of plastic shear strain and confining pressure. By comparing the failure surface development in the soil with increase in loading for two different models (MC and MMC), it is shown that the mobilized phi' and psi vary along the failure planes if the MMC model is used, although the capacity of the caisson could be obtained even if appropriate values of constant phi' and psi are used in the MC model.