Effects of misalignment on the undrained HV capacity of suction anchors in clay

Suctions anchors are widely employed to connect offshore floating structures to the seabed, and in particular to withstand the horizontal-vertical (HV) loads transmitted through inclined moorings. Imperfections during suction installation may cause anchor misalignment (or misorientation): this term denotes the line of action of the applied force not passing through the vertical axis of the anchor, and thus resulting in additional torsion during operations. The outcomes of a finite element (FE) investigation on the effects of misalignment are reported, with specific reference to the undrained HV capacity of suction anchors in soft clay. The changes in HV failure envelopes due to spurious torsion are described over a large misalignment range, in combination with varying geometrical/ mechanical factors. Based on fundamental understanding of “misaligned” soil-anchor interaction, new algebraic expressions are provided for practical capacity assessment. A further simplified methodology is also proposed for the most common case of low misalignment.