Influence of Characteristic-Soil-Property-Estimation Approach on the Response of Monopiles for Offshore Wind Turbines

Different approaches to estimation of the characteristic undrained shear strength of soil are discussed, based on 12 cone penetration tests (CPTs) carried out within a soil volume representative of an offshore monopile foundation. The paper is focused on the statistical treatment of the data, and pile–soil interaction is modelled by the Winkler approach with nonlinear p–y curves for the soil resistance. The 5MW NREL reference wind turbine is employed for load estimation, utilizing the aeroelastic code FAST. The study includes comparison of monopile capacities based on a single CPT as well as multiple CPTs. Comparisons are made between results obtained from a single CPT and those from all the CPTs at the site. The influence of assuming few or many layers in the deterministic soil model is assessed, and different assumptions regarding the statistical distribution of the data are compared. Finally, based on findings of the analyses, guidelines for the estimation of the characteristic soil strengths are proposed.