CSi—a joint industry project into CPTUs in silty soils

The CPTU constitutes the main in situ offshore investigation tool for geotechnical site characterisation and provision of soil input for the design of wind turbine foundations. CPTUs are typically performed at all foundation positions. Thus, all obtained results of supporting geotechnical in situ, model and laboratory testing need to be confidently correlated to the CPTU parameters. Most of the interpretation methodologies available for industry practice consider the soil behaviour around the cone either as fully drained or undrained, and acknowledged and well-proven correlations between CPTU parameters and classification and engineering properties exist for sand and clay. However, for transitional soils, e.g. silty soils, which may exhibit partial drainage during standardized cone penetration, such robust interpretation schemes do not exist. This paper presents the background, the objectives, setup and early field results of a joint industry project into CPTUs in silty soils for developing schemes for planning, execution and interpretation.