Effect of CPT profile resolution on minimum required size of monopile for ultimate limit state design

Cone penetrometer tests (CPTs) provide high-resolution data on soil resistance at the location of testing, which is then used to inform the design of various offshore structures including monopiles for offshore wind turbines. Emerging techniques allow for the generation of synthetic CPTs at any spatial location on a site, based on geophysical data and machine learning, eliminating issues of interpolation between physical CPTs, and offering improved layout flexibility of the wind farm in the design process. Synthetic CPTs however have lower resolution than physical CPTs, which may affect geotechnical design outcomes. This paper investigates the impact of CPT profile resolution on the minimum required monopile size for ultimate limit state design. For example, as resolution decreases, less economical designs may be predicted due to smoothing effects, or be required by the certifier to compensate for the greater uncertainty. In this study, CPT profiles with a prescribed degree of vertical resolution were used for monopile sizing, and plots of CPT resolution against monopile dimensions are presented and discussed. The broader purpose of this work seeks to provide design guidance on the minimum synthetic CPT resolution that generates reliable monopile designs, i.e. with dimensions equal to that predicted from the full resolution CPT design. The purpose of the study presented in this paper is to explore the effect of CPT resolution on minimum required monopile dimensions to assure ultimate limit state.