Centrifuge modelling of cyclic loading of shared ring anchors in fine-grained soil

As water depth increases, floating offshore structures supported by subsea anchors become increasingly attractive from an economic feasibility standpoint. New alternatives have been proposed to decrease costs, including anchor sharing and new anchor types. This investigation characterises the cyclic loading behaviour of ring anchors in kaolin through centrifuge tests. Load tests were performed on shared anchors (three lines) and single-line anchors (one line) with different line inclination angles. Different load packets were applied to the anchors to simulate typical storm events. The results show an increase in anchor and line displacement as the mean and cyclic loads increase, while an increase in cyclic loads leads to a reduction of stiffness. The principal anchor failure mode is loss of embedment, which is accentuated more in shared anchors than in single-line anchors due to the direction of the resultant load being closer to vertical and the rotation of principal stresses. Local instrumentation shows the dissipation of excess pore pressures during cyclic loading, leading to increases in strength, which were evidenced by a reduction in the rate of displacement accumulation and an increase in monotonic capacity after cyclic loading. The implications of the results in terms of the expected behaviour of shared anchors in the field are discussed.