Modes of Failure for Suction Caissons Under Vertical Pull-Out Loads

Suction caissons have a fair base in the offshore industry, however, prediction of their behaviour and capacities still need extra attentions. Understanding their modes of failure is crucial for any analytical solutions. In this paper, failure mechanisms noticed in a numerical study of the suction caissons behaviour under vertical pull-out loading are reported. The employed finite element models have been calibrated by and verified against different available experimental data. In principal four distinctive modes of failure have been recognized. The first mode corresponds to a shear sliding failure in the soil plug along the caisson’s wall interior. This mode of failure has been mainly found in drained but comparatively weak soils. The second mode of failure noticed under drained conditions in soils with enhanced strength characteristics is a local tension failure occurring in the bottom of the soil plug. In this case the detached soil plug accompanies the caisson in its movement upward. The third mode corresponds to a restricted shear failure outside the caisson. It develops to a local wedge initiating halfway through the caisson walls and extending out to the soil surface. This failure mode has been mostly noticed with clays under undrained conditions. The foruth mode has been found to be a general shear failure in the soil underneath and around the caisson. It occurs in a wider spread body of the soil and has been noticed with the undrained sands. The load-displacement curves present a virtually bi-linear behaviour.