International Symposium on Frontiers in Offshore Geotechnics, (DFI)
On the Triaxial Testing of Sand for Offshore Wind Turbine Foundation Design
Lewis Jones, Jonathan White and Truong Le
As the size of offshore wind turbine generators (WTGs) continues to increase, significantly larger foundations are being employed, which has led to a need to review previously established design assumptions and the laboratory testing regime associated with these assumptions. For example, the assumption of fully drained conditions in sand is increasingly not considered valid across the full range of WTG foundation loading rates, which can result in unreliable predictions of foundation response depending on the sand classification and in situ state. In addition, the use of triaxial compression tests alone to calibrate parameters for design analysis may not adequately represent the stress path variations induced around large foundations. Despite these known limitations, drained triaxial compression tests are almost exclusively used to parameterise sands for offshore WTG foundation design. This paper considers the results of drained and undrained triaxial compression and extension tests which were performed for recent offshore WTG foundation design. Results from several different sands at a range of densities and stress states are presented. Common issues associated with the performance and interpretation of the tests are highlighted, and practical recommendations to overcome these issues are discussed. Comparison of strain- and stress-controlled tests is presented to demonstrate the effect of shearing mode on the test sands. Results from constant volume (pseudo-undrained) direct simple shear tests are also provided for comparison. The test results provide a useful experimental dataset for a range of typical North Sea sands. It is shown that careful consideration of test procedures is required to ensure the most appropriate results are obtained for geotechnical design of offshore WTG foundations.
|article #3522; publication #1069 (IC-ISFOG21)|