Soil failure mechanism and capacity of stiffened caisson anchors in calcareous silt

This paper describes centrifuge modelling of installation and inclined loading of stiffened caissons in calcareous silt. Two series of tests have been carried out in a beam centrifuge. In the first series, for the first time, a half-model caisson was installed and loaded laterally against a transparent window at an enhanced gravity of 100g. Digital images during installation and inclined 45 degree pullout were captured and later analysed using the particle image velocimetry (PIV) technique. PIV allowed accurate visualisation of the evolving soil failure mechanisms inside and outside of the caisson skirt. During suction installation, significant inward soil flow resulted heaving of the inner plug surface. At the base of the skirt and bottom stiffener, an end bearing failure was mobilised. During inclined loading (at 45°), a double sided wedge mechanism, extending from the skirt tip to the outer soil surfaces, was observed with a pure base shear mobilisation at the tip level. This is different from the combined wedge and flow around mechanism at the sides and the scoop type general end bearing mechanism at the tip used in the guidelines and analytical solutions. In the second series, a full-model caisson was tested under cyclic loading. An onerous cyclic loading episode was found to augment the monotonic capacity by 23%.