Assessment of Synthetic CPTs in Monopile Design for Offshore Wind Turbines: A Case Study

Summary Synthetic cone penetrometer tests (CPTs) enable profiles of geotechnical resistance to be derived from 2D or 3D geophysical seismic survey data at any location across a wind farm site, alleviating dependence on interpolation between geotechnical CPTs. However, the lower vertical resolution of synthetic CPT data compared with in situ geotechnical CPT data introduces uncertainty in design outcomes. To explore the effect of synthetic CPT resolution on design outcome, this study applies co-located in situ geotechnical and geophysical data from the TNW wind farm site investigation, to calculate the required minimum volume of monopiles to assure ultimate limit state under lateral loading. Comparison between the two datasets and design outcomes has demonstrated that with synthetic CPTs, it is possible to obtain minimum monopile dimensions within 3% of those calculated with the in situ geotechnical CPT, corresponding to within 7% of the required capacity. This study highlights the potential for the use of synthetic CPTs in pile design to facilitate the expansion of offshore wind by reducing the time required for geotechnical site investigations and uncertainty in design outcome from interpolating between in situ geotechnical CPTs.