The identification and integration of geological and geotechnical units in ground model development

1. Home
2. Publications
3. Online Library
4. The identification and integration of geological and geotechnical units in ground model development

Offshore wind energy is a globally growing technology critical to meet climate targets, with the North Sea a key development region. The dynamic glacial evolution of the North Sea has resulted in a complex morphology and subsurface, with several glacial cycles recorded in the sediments of the uppermost 10s to 100s of meters. Subsurface models are at first guided by the regionally established geological formations, defining the main geological units. However, as these formations do not represent discrete single depositional and post-depositional events, the geological and geotechnical properties within most formations are both vertically and laterally highly variable. These heterogeneities lead to challenges in the design of offshore-windfarm foundations.

Here, we discuss the use of ultra-high-resolution 2D seismic profiles, and analyses from boreholes and cone penetration tests to demonstrate data integration practices to establish a robust link between the geological and geotechnical units. We focus on the properties of glacial meltwater channels and their infill (Coal Pit and Forth Formations) to discuss the variability of sub-units belonging to the same geological formation. We use the integrated knowledge from geological, geophysical and geotechnical data to identify units that are consistent in both geological and geotechnical behaviour.

Subglacial meltwater channels within the same geological formation, and identified in close vicinity (<1 km) and at the same stratigraphic level, can be infilled by a variety of sediments. These sediments range from dense sand to gravelly clay, and with a wide range of geotechnical properties. Changing sedimentary environments have resulted in a heterogenous facies of the units, and a separation of the channel infill (here Coal Pit Formation) into at least eight sub-units for that particular formation. In total, the subsurface of a windfarm site might easily include >20 soil units or sub-units, reflecting the complex geological and sedimentological history. Although often highly challenging, this unitisation is crucial for the development of a robust integrated ground model, and subsequently geotechnical or soil parameter predictions, especially in areas with limited geotechnical data.

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

4 - Ground models