The foundations here have a smaller diameter in their top part, in order for the transition piece to be lowered on top of them and around them. The two parts are then grouted together (a special concrete is injected between the two pieces, this is done on site, naturally, and under water).
Some offshore wind farms use a different connection between foundation and transition piece, with the transition piece snuggling inside the foundation. One European wind farm has quality issues on the grouting in that configuration, and there are worries that the turbines could slip lower into the foundations (which is not that important) and lose their horizontality (which is a big problem). With the design here, this is less of an issue as the wider diameter below acts as a stop should the grouting fail.
"Ovality" is also an issue for foundations as the transition pieces need to fit on top of them, and it needs to be checked carefully.
As you can see, the foundation in the photo at right has a serious problem: It's really not round. In that case, it is not a manufacturing problem: That foundation sank during the transport to site and hit the seabed. The project company, together with the insurance companies, is investigating the best way to deal with this problem: replace it completely, try to improve its roundness by squeezing it back into shape (the giant steel "pinch" for that was being prepared on site when we visited) or, quite possibly, use it as it is (by luck, it is the bottom part which was damaged, ie. the part that goes in the sand, so ovality is less of an issue there as long as the vertical penetration in the soil can still be controlled).
The reason the foundation sank is that it was transported to site by floating it — plugs were installed on each end and the foundation could simply be pulled on the water.
But the design of a plug was found (after a number of trips) to be slightly faulty and water seeped in, leading to the incident. The foundation was recovered, and the design flaw was identified and has now been corrected. Transport of the foundations to the site was of course interrupted during the investigation, but by luck the weather was poor at that time so no work could have been done in that period. The pictures at right show the new improved plug system, which includes a more comprehensive set of sensors to warn of any risk of infiltrations.
This is a fairly typical offshore construction incident, in that it was unexpected, hitting a system that had worked fine previously and had not altogether minor consequences.
It was a technical problem, to which a technical solution could be found reasonably easily. It had an impact on the schedule, which could be absorbed by the buffers put in place (and indeed in this case did not require more buffers than were required because of bad weather anyway). In terms of financial impact for the project, it will be fairly minor as this can be largely minimized by repairs or covered by insurance.
It goes to confirm that the goal cannot be to expect a flawless project, but to have teams which are able to deal with problems as they appear, because they — inevitably — will appear at some point, and to have a budget and scheduled which include contingencies and are able to withstand such incidents. Resiliency is the key word here.