Estimating mechanical properties of natural siliceous offshore sands

Large area civil engineering projects, such as offshore wind farms, require extensive soil investigations for detailed soil characterisations. Site-wide geotechnical soil units are commonly defined for simplification due to budgetary constraints. Consequently, practitioners rely on a limited number of costly laboratory tests and a set of semi-empirical CPT correlations, predominantly established based on research sands, for deriving sand parameters. A recent publication by the authors highlights some valid concerns about currently often applied idealisation when deriving strength parameters of natural sands and presents some possible pathways to address the limitations with a grading curve parameter (d10+d30). In the current paper, the size of the original laboratory test database is increased to improve the robustness of the methods. In addition, the database is used to also explore the potential of the d10+d30-parameter to improve estimations of drained stiffness parameters. However, since the current database mainly consists of relatively fine sands with varying fines content, a previously published database of much coarser clean sands is applied to investigate the limitations of the presented methods. Finally, a new independent trial database is collected to demonstrate the performance of the new methods for estimating drained strength and stiffness parameters compared with commonly applied industry-acknowledged methods. Even though limitations of the presented methods are identified for coarser clean sands, significantly improved reliability is demonstrated when deriving drained strength and stiffness parameters of relatively fine and slightly silty to very silty siliceous offshore sands.