Field Testing of Suction Anchors for Mooring Applications: Fid-Bau Portal

Field Testing of Suction Anchors for Mooring Applications

Ravichandran, Vijaya / Maji, V. B. / Gandhi, S. R.

Abstract Suction anchors are among the popular type of anchors used for mooring/position keeping of floating vessels in deep waters. It comprises a cylindrical anchor, closed at the top and achieves penetration into the seabed by applying vacuum pressure inside the anchor. In order to arrive at guidelines for design of such anchors, field tests have been conducted on suction anchors with varying diameters and lengths for evaluating the pullout behaviour under various loading conditions. The tests have been carried out in marine conditions within breakwaters where the impact of environmental loadings from winds and waves is low. Since suction anchors are subjected to cyclic loading in the offshore areas due to effect of waves and winds, tests for static and cyclic pullout have been carried out and comparison has been made. It is found that anchor geometry, angle of pullout and nature of pull (static/cyclic) have a significant influence on the response to pullout. As angle of pullout changes from vertical to horizontal the reaction offered by the suction anchor changes from skin friction to passive soil resistance. Resistance offered by the internal plug of soil is found to vary according to dimension of the anchors. Theoretical estimates are found to reasonably predict static mooring capacity of suction anchor. A reduction of 35 % in mooring capacity is observed under dynamic response for a frequency of 6 s.