This paper describes the use of 3D finite element analysis (FEA) to compute the undrained capacity of a suction anchor in clay. A particular issue that this study focused on was use of interface elements to model the possibly reduced strength and slippage along the soil-structure contact surface.

The suction anchor was first analyzed as a plane strain problem followed by full three dimensional analyses of a 5 m diameter suction anchor. The studies included an evaluation of the effects of the wall interface strength and comparisons with approximate hand calculations. The holding capacity computations were for pure horizontal loading and also for varying loading angles. The load was attached at the optimal load attachment point to produce a failure mode corresponding to pure translation.

These studies have shown that 3D FEA can be used to estimate the capacity of suction anchors. The strategic use of mesh refinement procedures, interface elements and symmetry greatly reduce the discretization error associated with FEA. Isoparametric interface elements are required to accurately model the soil-anchor slippage along curved surfaces and minimize overshoot for this benchmark problem.