Capacity of dynamically embedded plate anchors as assessed through field tests

Abstract

A dynamically embedded plate anchor (DEPLA) is a rocket-shaped anchor that penetrates to a target depth in the seabed by the kinetic energy obtained through free-fall and by the anchor’s self-weight. After embedment, the central shaft is retrieved leaving the anchor flukes vertically embedded in the seabed. The flukes constitute the load bearing element as a plate anchor. This paper presents and considers field data on the embedment depth loss due to the plate anchor keying process and the subsequent bearing capacity factor of the plate anchor element. The loss in plate anchor embedment was significantly higher than that reported from corresponding centrifuge tests and is reflected in the larger padeye displacements required to mobilize peak capacity in the field tests. Measured plate capacities and plate rotations during keying indicate that the end of keying coincides with the peak anchor capacity. Experimental bearing capacity factors are in the range Nc = 14.3–14.6, which is appreciably higher than existing solutions for vanishingly thin circular plates. The higher Nc for the DEPLA is considered to be due to a combination of the cruciform fluke arrangement and the fluke (or plate) thickness.