Speaker
Description
Design of gravel beds for offshore wind turbines gravity foundations is commonly constrained by the lack of laboratory testing methods capable of representing the true mechanical behaviour of coarse granular materials. Standard tests are often unsuitable due to particle size and scale effects, boundary conditions, and installation challenges leading to significant uncertainty in material parameters used in foundation design. This paper introduces a conceptual large-scale testing approach developed to bridge the gap between conventional laboratory testing and field-relevant behaviour of gravel beds. At a scale where particle size effects and specimen fabric are more realistically represented, the current concept provides insights that are otherwise difficult to obtain for coarse gravel materials. Conceptual testing typically requires a significantly larger and costlier effort than conventional testing; hence, the campaigns are often small. The present concept is thus demonstrated on a campaign including 3 monotonic, and 9 cyclic, large-scale consolidated anisotropically drained triaxial tests conducted in a 50 × 50 cm triaxial cell. The cell of this size is allowing testing of very coarse gravels and stone or blasted rock materials typically used under large foundations for their large bearing capacity and large permeability. The testing setup enables realistic specimen reconstitution, stable installation of coarse gravel, controlled anisotropic stress paths, and reliable measurement of axial and volumetric strains under both monotonic and cyclic loading. Monotonic tests are used to establish mobilized shear strength and stress–strain behaviour across a wide strain range and define a reference shear stress for cyclic testing. Cyclic tests capture stiffness degradation and strain accumulation under loading regimes relevant to offshore wind turbines. The paper demonstrates how representative parameters can be measured. Furthermore, the applicability of hypothesis confirmation testing in place of full investigative programs is addressed in the light of reducing uncertainty in parameters and improving confidence in the assessment of gravel beds supporting offshore wind gravity-based foundations. The paper concludes that large-scale conceptual testing offers a practical and scalable pathway for the offshore wind industry to better characterize gravel foundation behaviour, supporting more robust and efficient design of gravity-based foundations under combined monotonic and cyclic loading.