Modelling drag anchors in a drum centrifuge

The design of large offshore drag anchors remains relatively primitive, relying on design charts that cover broad categories of soil type, and with no direct link to specific shear strength profiles at a given site. Physical modeling offers one way to improve the design framework, and the drum centrifuge, offering essentially unlimited drag distance, has obvious advantages. This paper describes a series of scale model drag anchor tests performed in the drum centrifuge at The University of Western Australia (UWA) in a soil sample comprising normally consolidated clay. A special loading arm was developed in order to circumvent problems in modelling the anchor chain in the curved g environment of the drum. Measurements of the vertical and horizontal components of load at the anchor pad-eye during installation allowed validation of the Neubecker-Randolph analytical approach for drag anchor embedment and holding capacity. The two design parameters needed for this approach were evaluated for model Vryhof Stevpris anchors in soft clay, and the resulting anchor performance was shown to be consistent with published design charts.