Holding Capacity of Suction Anchors with Trench - Centrifuge Test Results and Interpretation-Paper

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The study investigates how seabed trenches affect the holding capacity of suction anchors in soft Gulf of Guinea clay. Centrifuge tests at 75–80g examined vertical and inclined pull-out, using anchors with and without trenches. Tests measured anchor movement and pore-water pressures to assess reverse end bearing (REB), the suction-supported resistance beneath the anchor. Finite-element analyses were also used to interpret the results.<br /><br />For vertical pull-out, the trench had little apparent effect on capacity. REB was a major contributor to resistance, and measurements indicated that trenching caused, at most, a limited reduction in this contribution.<br /><br />For inclined loading at 30–40°, the trench reduced holding capacity by approximately 15–21% for the tested anchor and trench geometries. In the equal-angle comparison, capacity fell by 15%. Suction beneath the anchor was lower than in vertical tests because inclined failure involved both backward rotation and forward translation, limiting full REB mobilisation. The observed failure mechanism did not involve detachment at small or moderate displacements; instead, soil behind the anchor showed shear failure.<br /><br />The results suggest that suction behind and beneath the anchor limits the loss of capacity caused by trenching. Finite-element predictions using measured soil strength and a strain-rate correction generally agreed reasonably with the tests, though performance varied between test series.<br /><br />Overall, trenching can meaningfully reduce capacity under typical inclined mooring loads, but its effect on vertical capacity is small when REB is mobilised. These conclusions apply to the specific anchor and trench configurations tested.

Keywords

suction anchor

seabed trench

holding capacity

soft clay

Gulf of Guinea

centrifuge tests

inclined pull-out

reverse end bearing

finite-element analysis

soil failure