Seismic response of jacket wind-turbines: Dimensional analysis of foundations and SSI

Abstract

The paper introduces a cost-effective and ‘easy-to-install’ foundation concept to be used for the seabed support of jacket wind-platforms. The concept, commonly termed as ‘suction caisson’ is a skirt foundation (i.e. a stiff cylindrical shell with an open bottom and a top slab) that is particularly advertised for the ease of installation and the minimization of installation noise compared to piles. Aiming to reduce the barriers towards their implementation, the paper initially illustrates the key parameters controlling the response of suction caissons in non-liquefiable clayey soils under dynamic loading, by means of a dimensional analysis and a subsequent parametric study. The caissons are shown to behave excellently when subjected to pure dynamic loading, displaying only minimal permanent displacements. Alarming issues for their performance arise when a non-zero steady force is superimposed to the subsequent dynamic loading. In the case of concurrent static and seismic loading, analyses results reveal that the rate and amplitude of the irrecoverable caisson deformation is controlled by the amplitude of the initially imposed static action and the intensity of the earthquake motion. Subsequently, an 8MW jacket-supported offshore wind-turbine (OWT) installed at a water depth site of 60m in the seismically active region of North-Western Adriatic is used as benchmark example to examine suction caisson behavior within the soil-structure system. The dynamic response of the benchmark OWT is numerically explored by exciting the system with a regional seismic record from the L’ Aquila earthquake. As expected, the jacket is shown to behave excellently when subjected to pure earthquake loading, displaying minimal permanent foundation rotation. When earthquake loading is combined with a co-seismic wind action, jacket legs settle unevenly while the OWT tower builds-up rotations at an increasing rate. © 2019, National Technical University of Athens. All rights reserved.