Evaluating prEN 1991-1-8 for a mound breakwater from a coastal engineering perspective

In Europe, there are design codes for public works called Eurocodes. These codes provide technical regulations on how to design structures. The Eurocodes focus on how loads and uncertainties should be incorporated into the design of a structure. Each member state of the European Union must accept designs based on the Eurocodes. Currently, a new Eurocode (prEN 1991-1-8) is being developed for coastal structures. The goal of this report is to get an insight into how the new Eurocode prEN 1991-1-8 proposed way of working, compares to the deterministic approach within Van Oord. These insights are currently unknown, as only one other case study has been performed with an older version of prEN 1991-1-8. Meaning that the effect of changes within prEN 1991-1-8 is still unknown. The main research question is: ’What are the consequences on design steps and parameters of the semi-probabilistic design approach [DA1] in prEN 1991-1-8 in comparison to the deterministic design approach, tested with a physical modelling study for a mound breakwater design case study?’ The sub-questions are: • In which steps are there differences, in design approach and parameters, between the semi-probabilistic design approach and the deterministic design approach in prEN 1991-1-8? • In which steps are there similarities, in design approach and parameters, between the semi-probabilistic design approach and the deterministic design approach in prEN 1991-1-8? • How do the results for the final breakwater from both design approaches compare to a 2D and 3D physical modelling study? These questions will be answered by the use of a case study. The results of the semi-probabilistic design approach, proposed by prEN 1991-1-8 are on average 68% bigger in dimensions than the van Oord design. This is due to that prEN 1991-1-8 prescribes different values that are stricter for the acceptable damage parameters and higher for return periods, which leads to the difference in the final design. All other design steps and parameters are similar between both design approaches, as well as the required data and methods for the wave studies. Due to the bigger final design dimensions, the semi-probabilistic design is not comparable to the outcome of the physical model testing. The deterministic design only differs for the toe dimensions from the outcome of the physical model testing. So in conclusion the semi-probabilistic design approach does contain a lot of similarities with the deterministic design approach together with a physical modelling study for a mound breakwater design. This means that the way of working within van Oord will only slightly change during the design criteria set-up for the return period and acceptable damage factors but further stay the same.