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Stability and scour analysis, new design Arc Marine structure

Background
In a previous study, (WaterProof, 2020), WaterProof has looked into the stability of structures, designed by Arc Marine at these two locations. To this end, first the extreme MetOcean boundary conditions (waves, flow) were identified. Next, the expected scour in the vicinity of the structures was calculated considering the local morphological circumstances (soil composition, bedforms, depth, etc.). Finally, using both flow flume experiments and analytical calculations the stability of the structures was determined, both for the failure mechanism turning over as well as sliding.

The result of the study was that (1) scour protection should be applied, to prevent the structures from sinking into the bed and (2) additional measures needed to be taken to prevent the structures against turning over / sliding, as for both locations the stability of the structures was not sufficient to be able to withstand a 1/100 year storm.

Based on these findings, Arc Marine has updated the design, in order to meet the stability requirements. As the form of the structures changed significantly, so do the total forces on the structures themselves. Therefore, the Rich North Sea has asked WaterProof to perform another analysis into the stability of this new design, for both locations. Additionally, WaterProof was asked to re-evaluate the scour that can occur and what degree of scour protection is needed in the case that the structures are placed at the Borssele OWF location.

Conclusions
Bed protection should be applied under the foreseen structures to guarantee no scour hole formation. Due to the changes in the new design shape (more like a pyramid), and considering that the lower layer of the structure partially functions as an armour layer, the required volume of scour protection is significantly lower than calculated in the previous study (WaterProof, 2020).

Author: Waterproof Marine Consultancy & Services BV.

Date: 18/09/2020

Keywords: Ecological structures, North Sea, stability, scour, scour protection, Arc Marine

Reference: WP2020_1218_M1r1

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