Scaling issues in centrifuge modelling of monopiles

Abstract

This paper deals with three different and important issues for centrifuge testing on monopiles for offshore wind turbines. A series of centrifuge model tests has been conducted on cylindrical stiff model monopiles that were installed at 1g and in-flight before being loaded laterally as well as on conical model piles installed in-flight. All model tests were performed in normally consolidated dense dry sand, simulating drained conditions. The tests confirmed three important issues for centrifuge modelling of monopiles for offshore wind turbines. First, to avoid any noticeable grain-size effect, the geometric ratio between average grain-size in poorly graded soils and pile diameter has to be larger than 88. Second, the non-linear stress distribution with depth, which is often neglected, has to be taken into account in the analysis of the lateral response. Finally, the pile lateral load–displacement tests confirm that both stiffness and strength increase following in-flight installation and that in-flight installation is needed to avoid any scale effects. This paper illustrates how these three issues are important factors in achieving reliable centrifuge modelling, which is capable of scaling model observations to prototype.