Evaluating The Controls On The Physical Properties Of The Dogger Bank Formation

The Dogger Bank is a large shallow topographic feature in the Central North Sea with water depths of 18 – 63m. As one of the proposed round 3 windfarm licence areas an extensive siteinvestigation was undertaken during 2010 and 2011 across Tranche A including extensive 2Dultra high resolution reflection seismic surveys, over 100 geotechnical boreholes, cone penetration tests, 15 wireline log boreholes and more. To adequately plan the location, type and cost of foundation installation an understanding of the physical and geotechnical property distribution of the area is necessary. This thesis demonstrates that these properties, whilst complex and often times difficult to tease out of the data, can be linked to geological processes and thus predicted with some confidence away from control points.

During relatively recent geological history (100 – 19 kyrs BP) The Dogger Bank was dynamically shaped by the Eurasian Ice Sheet, and at least two hypothesised glacial cycles led to deformation, deposition and post‐depositional modification of the sediments. Of these processes, the consolidation and deformation of The Dogger Bank Formation exerts the strongest control on the present day measured properties. The signal of consolidation can be correlated to the geophysical data through well to seismic ties and correlated on a regional scale across Tranche A. When the two data types are brought together and analysed using a novel mechanical modelling approach it is possible to not only explain the reason for the degree of consolidation, but also predict the likely thickness of the ice that was present at The Dogger Bank.

This thesis additionally outlines a series of recommended practices for future offshore site investigations for windfarm foundations. These are synthesised from identified shortcomings of the Tranche A dataset, and a reflection of the time that passed between data collection and the work presented in this thesis.