Installation and inclined loading of a suction caisson anchor in calcareous sand

This paper reports a series of centrifuge tests conducted on a stiffened suction caisson anchor in a medium dense calcareous sand. The aims were to provide insight into the behaviour of the anchor during installation and under operational monotonic loadings, and to propose corresponding design approaches to be used in practice. The sand was collected from the Pluto field of Australia's North-West Shelf and characterised through consolidated-drained triaxial compression tests and cone penetration tests (CPT). For assessing caisson installation resistance, a conventional shear resistance method and a CPT-based method were calibrated hinging on the measured caisson installation resistance, effective radial stress, cone tip penetration resistance and friction angle of the sand. Under inclined loadings, with reducing loading angle at the padeye (and hence mooring angle at the mudline), the ultimate capacity increased and the rotational failure mechanism changed to a more lateral translational mechanism. For assessing ultimate capacity, an extended analytical model was presented and verified against the centrifuge test data capturing stress and dilatancy with a simple yet robust systematic approach to include particle breakage. Particle breakage under inclined loading was shown to increase with reducing loading angle. The anchor vertical-horizontal failure envelope was approximated by a parabolic expression.