Cyclic Capacity of Plate Anchors in Loose Sand-Paper

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The study used 50g centrifuge tests to examine the drained monotonic and irregular cyclic capacity of a vertically installed plate anchor in dry loose sand. The rectangular anchor was embedded at five times its width and loaded horizontally at the mudline. Tests included two monotonic trials and three cyclic trials with peak cyclic load ratios of 1.0, 1.25 and 1.5.<br /><br />Under monotonic loading, the anchor rotated as it was pulled, reaching a peak rotation before reversing direction. This keying behaviour was similar to that observed in dense sand. However, the loose-sand anchor had a softer load–displacement response and required about 60% more line displacement to reach ultimate capacity. Its monotonic capacity was approximately 445 kPa—about 60% of the capacity measured in comparable dense-sand tests. At ultimate capacity, the anchor had rotated more in loose than in dense sand.<br /><br />Cyclic loading increased capacity by 3% at a peak load ratio of 1.0 and by 7% at 1.25, relative to the monotonic reference. These gains were smaller than the 13% increase reported for dense sand. At a ratio of 1.5, the anchor failed during cyclic loading, although its capacity was still 5% above the monotonic reference. Higher cyclic load ratios also produced greater line displacement.<br /><br />The results indicate that plate anchors in loose sand may be less able to meet both strength and serviceability requirements than anchors in dense sand. Their lower capacity, softer response and larger displacements are important considerations for offshore mooring design.

Keywords

plate anchor

loose sand

50g centrifuge tests

monotonic loading

cyclic loading

anchor rotation

drained capacity

mudline loading

offshore mooring

load-displacement response