Centrifuge modelling of monopiles in dense sand at The Technical University of Denmark

The pile-soil interaction is of great importance in the design of monopiles supporting offshore wind turbines. Especially the predication of accumulation of rotations, change in stiffness and damping is difficult. The design tools used today cannot in a proper way take the effects from cyclic, lateral loading into account. In order to develop simple design tools for cyclic lateral loading, a large centrifuge test series is ongoing at the Technical University of Denmark (DTU). This paper presents the main conclusions found from centrifuge testing over the last 4 years and gives indication where research is going. From monotonic tests \u93modelling of models\u94 has been performed to identify scaling errors. It appears that the non-linear stress distributions occurring in centrifuge tests should be taken into account when dealing with stiff monopiles. Also the effect from load eccentricity has been investigated and initial results indicate that the normalised initial stiffness is unaffected but the ultimate capacity is increased by increasing load eccentricity. Accumulation of rotations and increase in secant stiffness has been seen from cyclic, load-controlled tests. One initial test has been used to generate cyclic p-y curves and is here presented. This is the first step in the development of a cyclic spring element which can be used as a simple engineering tool in the prediction of accumulation of rotations, change in stiffness and damping