Cyclic behaviour of an over consolidated marine clay

Abstract

Performance of offshore wind turbine foundations under cyclic loading is one of the most important issues in designing these structures because they are constantly subjected to cyclic loads from winds and waves. This paper investigates the cyclic behaviour of an overconsolidated marine clay from the Bolders Bank Formation (one of the four main soil units) found at the Sheringham Shoal offshore wind farm in the North Sea. The clay samples are tested in both cyclic undrained triaxial and cyclic direct simple shear apparatuses under various combinations of average and cyclic shear stresses. The result shows that the number of cycles to failure decreases with increasing cyclic shear stress but can change in either direction as the average shear stress increases. The failure modes experienced by the samples tend to depend on the relative magnitude of the two shear stresses applied during testing. This cyclic behaviour of the clay is found to be relatively consistent with the notion represented by the cyclic contour plot framework for designing offshore foundations (developed by the Norwegian Geotechnical Institute). Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE).