Movement direction of drag anchors in seabed soils

The movement direction of drag anchors is an important property of the anchor and plays a key role for the anchor penetrating seabed soils. However, the generally accepted assumption for the movement direction is too vague to be adopted for a precise analysis. The former work both in numerical and experimental studies demonstrates that there has not been a clear knowledge of the movement direction for the drag anchor with a complicated fluke section. In this paper, an analytical method that is capable of predicting the movement direction of the drag anchor with an arbitrary fluke section is developed. In the analytical study, based on a rational mechanical model for drag anchors and the knowledge of the mechanism that the anchor penetrates and moves in soils, an analytical model that can predict the movement direction of drag anchors with an arbitrary fluke section both in cohesive and noncohesive soils is established. The analytical model is applied to predicting the movement direction of the anchor with rectangular and wedge-shaped sections, and clear prediction results are obtained. Some important features of the movement direction are revealed, especially the step change of the movement direction from the unstable to the stable penetration stages due to the anchor weight. In the experimental study, specially designed model flume tests in saturated sand are performed to detect the movement direction of four anchor models with different fluke sections. Being verifications of the analytical model, the experimental data are employed to compare with the theoretical predictions and the agreement is satisfactory. The present work proves that the movement direction of the drag anchor with an arbitrary fluke section can be reasonably determined by the developed analytical method.