Volume 34, Issue 4 (July 2011)
A New Technique to Measure the Trajectory of Drag Anchors in Soils
Drag anchors, including the vertically loaded plate anchors, play a very important role in deepwater mooring systems. However, the behavior of the anchor has never been clearly known, especially the trajectory of the anchor in soils when pulled into the seabed. Positioning in seabed soils is especially important for drag anchors because the working performance of the anchor is closely related to the embedment depth and orientation of the anchor and the properties of the surrounding soils. Hence, studying the trajectory by analytical and experimental methods is critical for the further application of drag anchors in offshore engineering. An overview of the present trajectory measurements demonstrates that there has not been an acceptable measurement technique for laboratory model flume experiments. In this paper, a contact measurement technique, which is based on the knowledge of the motion characteristic of the drag anchor in soils, is developed and applied in measuring the trajectory of the anchor models. This technique is easier to perform and has little effect on the behavior of drag anchors in soils. The measurement precision and applicability of the technique are verified through specially-designed experiments. Being an important application, the measurement technique can be adopted to detect the movement direction of the anchor with an arbitrary fluke section. The present work has demonstrated that through model tests and employing the developed technique, the movement direction of any type of drag anchor can be effectively and easily determined.