Incorporating Shank Resistance into Prediction of the Keying Behavior of Suction Embedded Plate Anchors

Abstract

The suction embedded plate anchor (SEPLA) is a promising deepwater anchoring solution that uses a suction caisson to install a plate anchor vertically to a precise depth within the seabed. The plate anchor is then rotated from its vertical position toward an inclination approximately normal to the load applied by the mooring line in a process known as keying. This configuration reduces the embedment depth and, in typically increasing strength with depth soils, diminishes the installed capacity of the anchor. Therefore, an accurate prediction of the keying behavior of SEPLAs is crucial for offshore operations. Recently, plasticity approaches that combine a yield surface written directly in terms of the applied loads on the anchor with an associated flow rule have been suggested. However, the combined loading yield surface has been defined only for a flat square or rectangular plate. None of these approaches directly account for the resistance of the relatively large anchor shank used to attach the mooring line. The results described in this paper show (1) the impact of the joint plate and shank on the size and shape of the combined loading yield surface and (2) the subsequent impact on predicting the keying behavior of SEPLAs using the plasticity approach. The influence of anchor thickness and shank height on the capacity of an idealized plane-strain anchor is first defined through two-dimensional finite-element (FE) studies. Then, the yield surface parameters for a typical plate and anchor size are provided from three-dimensional FE analysis. The keying behavior of this anchor when subjected to pullout loading from an anchor chain is simulated using the plasticity approach and the results are compared with keying paths for a simple plate anchor without a shank. The predictions using parameters derived from a plate anchor with a shank significantly outperform those using parameters derived from a plate anchor without a shank.