Geotechnical characterisation of faulted Paleogene clays

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Paleogene clays constitute the substrate for the foundation of several offshore wind farms which are built or planned in the North Sea. In some of these clay layers, intense faulting and other deformations (often referred to as Clay Tectonics) were reported in several studies since the 1980s. Several hypotheses were put forward to explain the occurrence of these deformations. However, high-resolution geophysical surveys in the Princess Elisabeth Zone (Belgian Part of the North Sea) shed a new light on the genesis of these large-scale faults in the Paleogene clays of the Kortrijk Formation. It is put forward that the presence of these faults may influence the installation and operational response of foundations. An investigation into the mechanical properties of these deformations in the Kortrijk Formation is reported in this contribution.

Undisturbed push samples were taken at an onshore site where the Kortrijk Formation occurs close to the surface and which is considered as a valid analogue for the offshore clay material. CT scanning of the samples reveals that in addition to the large-scale faulting observed in the geophysical surveys, intense fissuring on a smaller scale occurs throughout the sediment. Drained direct shear tests with a re-shear stage were undertaken to characterise the intact strength and the strength on a previously sheared sample. The index properties and drained shearing properties are compared to other studies from France and the United Kingdom and reveal consistent trends for the entire sedimentary basin.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

2 - Site characterization, in-situ and laboratory testing, measurement