Suction pile relocation, a numerical study

Abstract

Suction pile anchors are large diameter hollow cylinders used as offshore foundations mostly on deep water Oil and Gas developments. Their variety of applications and ease of installation make them a competitive solution. Installation tolerances have to be met in terms of tilt (vertical inclination) and heading (plan view misorientation) to meet their design requirements. If these requirements are not met at the end of penetration, the pile will have to be retrieved and installed again. However the extraction process might damage the soil inside the anchor, thus reducing its strength. Reinstallation has to be done far enough from the original position to ensure that this will not affect the anchor. In congested areas, respudding at the closest possible distance can be of major interest. The aim of this study is to assess the minimum distance at which a suction anchor can be relocated after a failed attempt, without impeding its holding capacity. 3D Finite elements calculations have been conducted for a number of anchor geometries and loads, and for varying respudding distances. Results indicate that for most applications, the impact of relocation on suction anchors capacity becomes negligible at three pile diameters away from the original position. The distance can be less for instance for flowline anchor application.