Installation and capacity of dynamically embedded plate anchors as assessed through centrifuge tests

A dynamically embedded plate anchor (DEPLA) is a rocket or dart shaped anchor that comprises a removable central shaft and a set of four flukes. Similar to other dynamically installed anchors, the DEPLA penetrates to a target depth in soft seabed sediments by the kinetic energy obtained through free-fall in water and the self-weight of the anchor. In this paper DEPLA performance was assessed through a series of beam centrifuge tests conducted at 200 times earth's gravity. The results show that the DEPLA exhibits similar behaviour to other dynamically installed anchors during installation, with tip embedments of 1.6-2.8 times the anchor length. After anchor installation the central shaft of the DEPLA, termed a follower, is retrieved and reused for the next installation, leaving the DEPLA flukes vertically embedded in the soil. The load-displacement response during follower retrieval is of interest, with mobilisation of frictional and bearing resistance occurring at different rates. The load required to extract the DEPLA follower is typically less than three times its dry weight. The vertically embedded DEPLA flukes constitute the load bearing element as a circular or square plate. The keying and pullout response of this anchor plate is similar to other vertically embedded plate anchors, with an initial stiff response as the anchor begins to rotate, followed by a softer response as the rotation angle increases, and a final stiff response as the effective eccentricity of the padeye reduces and anchor capacity is fully mobilised. For the padeye eccentricity ratios considered (0.38-0.63 times the plate breadth or diameter), the loss in plate anchor embedment is between 0.50 and 0.66 times the corresponding plate breadth or diameter. Finally, the bearing capacity factors determined experimentally are typically in the range 14.2-15.8 and are higher than numerical solutions for flat circular and square plates. This is considered to be due to the cruciform fluke arrangement which ensures that the failure surface extends to the edge of the orthogonal flukes and mobilises more soil in the failure mechanism. (C) 2014 Elsevier Ltd. All rights reserved.