Boundary effects on dynamic centrifuge testing of onshore wind turbines on liquefiable soils

Centrifuge modelling is an effective tool to assess the response of reduced-scale structures subjected to earthquakes under increased gravity. Space limitations, however, force the model to be contained within relatively small boxes, whose boundaries may affect the seismic performance of the structure under consideration. In this paper, the influence of the proximity of the boundaries of an equivalent shear beam (ESB) container during dynamic centrifuge tests of an onshore wind turbine resting on liquefiable soils is evaluated. To this end, numerical modelling of the ESB box was implemented in the finite-element framework OpenSees, to replicate the results observed in the experiment. The hydraulic and mechanical soil parameters were calibrated against far-field centrifuge results only. From this calibration, the seismic performance of the raft foundation turned out to be in good agreement with the experimental results for a seismic input capable of triggering liquefaction. A larger numerical model, where boundaries do not play any role, was then built, to compare its outcomes with those of the small model, thus allowing the effect of ESB boundaries to be assessed.