Abstract
This paper describes new physical model tests aiming at measuring both wave overtopping and wave induced forces on rubble mound breakwater crown walls. The physical model and the equipment used for the measurements are described in detail. For the completed tests, a detailed analysis is reported, by evaluating the properties of the incoming waves at the toe of the breakwater and some statistical parameters to describe the wave induced forces and pressures on the crown wall. Careful analysis is also carried out to evaluate how the distribution of the pressures changes with time. It is found that the upper part of the wall is subjected to the first large quasi-impulsive action of the wave; the lower part of the wall is afterwards flooded and a quasi-hydrostatic pressure develops along the height of the wave wall. As far as the pressures on the base of the crown wall are concerned, they develop after a quite large time lag after the maximum of the horizontal force. First attempts to correlate the maximum horizontal force with some explanatory variables such as the ratio of the crest freeboard and of the significant wave height of the incoming waves indicate a promising correlation, also in agreement with the existing literature on the topic. The overtopping rate are also measured and compared with empirical formulas. The correlation between the wave induced forces and the average overtopping discharge on the breakwater is also investigated.
Highlights
The crown wall, often installed on the crest of rubble mound breakwaters, guarantees safe accessibility of the breakwater and can be used to increase the crest freeboard, avoiding too large use of quarry material
While a large amount of information, data and design methods are available for other hydraulic responses, like for example the wave reflection coefficient (Zanuttigh et al, 2013) and the average overtopping discharge (EurOtop, 2016), it is widely accepted that design methods for estimation of the wave forces on crown walls can still be improved
The aim of this paper is to present the results of new small scale 2D physical model tests on a rubble mound breakwater, with measurements of wave overtopping and wave forces on the crown wall
Summary
The crown wall, often installed on the crest of rubble mound breakwaters, guarantees safe accessibility of the breakwater and can be used to increase the crest freeboard, avoiding too large use of quarry material It should withstand the forces applied by the waves, that may induce sliding and overturning of the whole structure, as it behaves monolithically, and local damages such as the failure of the wave wall or part of it. Very recently, Molines et al (2018) have analyzed new experiments on crown wall wave forces and overtopping and have discussed the importance of many possible explanatory variables of the phenomena They have found that a strong correlation exists between the wave induced forces and the average overtopping discharge on the breakwater. Conclusions and future developments of the research are reported in the final Section 5
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