This paper discusses selected results from 3-dimensional model tests conducted by researchers from University of Naples, University of Sheffield, and HR Wallingford in the UK national Coastal Research Facility (CRF). The purpose of the work was to extend to composite walls previous analysis performed by Allsop & Calabrese to predict, in presence of directional seas, the reduction in the total load exerted by breaking waves on vertical walls. Experimental results on the load decay have been linked to a parametric characterisation of breaking wave sea states proposed by Calabrese which permits to discriminate the wave modes in front of the structures into three different categories (pulsating waves, impact waves and broken waves). The analysis appears to indicate a stronger effect of wave impacts on the force reduction in comparison with the influence of wave multi-directionality.
Recent research studies and case histories have demonstrated that hydrodynamic pressures on vertical and composite breakwaters due to the impact of breaking waves can yield not only localised effects but can also cause cumulative sliding and eventually the failure of the structure (Oumeraci, 1994). Much research has been conducted to improve understanding of interactions between waves and vertical breakwaters. Results have highlighted the complexity and the integrated nature of the problems related to breakwater stability including the uncertainties associated with the prediction of occurrence of impact pressures from breaking waves as well as the importance of the three-dimensional nature of the processes involved in the wave-structure-foundation interactions. Among the most recent contributions, under the Research Project "PROVERBS" ('Probabilistic design tools for vertical breakwaters'), included in the European Programme "Marine Advanced Science and Technology" (MAST III)
