Soil failure mechanisms during installation and inclined pullout of stiffened suction caisson in calcareous silt

Soil failure mechanisms of stiffened suction caisson during installation and inclined pullout in calcareous silt have been investigated through centrifuge model tests and small strain finite element analyses (FEA). In the tests, a model half-caisson was installed followed by loading at a 45° inclination. Digital images were captured and subsequently analysed using particle image velocimetry (PIV), allowing soil failure mechanisms to be observed. The FEA were carried out to study the effects of pullout angles for caissons with and without internal suction. The PIV results revealed that during suction assisted installation, localised shear strains develop surrounding the skirt. As the stiffeners penetrated into the soil, the particles filled up the gaps between the inside wall and soil plug. During inclined pullout, a double wedge type failure was observed at the front and rear sides that extended to 1.5 caisson diameter at the soil surface. A pure shear type failure was observed around the skirt tip. The FEA results showed that, for caissons without internal suction, a wedge failure mechanism was prevalent. The size of the wedge decreased with increasing pullout angle. For caissons with internal suction, a rotational failure mechanism was apparent.