· · · Repository Hydraulic Engineering Reports

This paper has two main objectives: (1) to describe the experimental work carried out in order to verify the theoretical method from Martin (1995) for the calculation of wave forces on crown walls and (2) to show some results from field and lab measurements and compare these data to calculations from several analytical methods. The Principe de Asturias Breakwater at Port of Gijon has been taken as the reference structure in this study. The experimental work (prototype and scale models) has been carried out over the same cross section, corresponding to this breakwater. Three scales have been used here: scale 1:1 (prototype measurements), scale 1:18..4 (tests done at Laboratorio de Ingenieria Maritima, UPC, Barcelona) and scale 1 :90 (tests done at Laboratorio de Ingenierfa Oceanogratica, Universidad de Cantabria). Therefore, data from the same phenomena in three different scales are available, which will provide the basis to analyse scale effects in the lab. The main part of the experimental work was carried out from 1995 to 1998 .. Due to the large costs of such a long experimental project, several organisations (referred in the acknowledgements section) were asked for financial support to the study. This is a good example of long-term project which was possible by the joint effort of, several institutions (public and private) within the European Research Framework. In the paper, forces from the tests are compared to calculations done from the method proposed by Martin (1995). The comparison shows good agreement between the calculations and the measurements from the lab, and not-so-good agreement to prototype data. From these results, it can be stated that the method is working well as it was developed from lab data From this study, it can be stated that differences to prototype forces are due to scale effects between lab and prototype measurements.

Research on rubble mound breakwaters when confronted with waves. The rapport covers the flow characteristics and mound stability under regular waves and under oblique wave attack. The authors find a formula for rough, permeable slopes, flow characteristics under the action of a regular wave train by a function of the type. Furthermore they conclude that the distribution of flow characteristics in sea state can be obtained on the basis of interaction curves and joint probability density function of wave heights and periods. The conclusions on the mound stability of breakwaters are: -Stability conditions of an undefined, rough, permeable slope are governed by the stability function. -The stability function depends only on Iribarren's number. -Randomness can be accounted for by using confidence bands for the stability function. -For each type of armour unit, an optimum slope of maximum stability exists. The greater the interlocking among armour units the steeper the optimum slope and the more peaked the stability maximum. -Given a rubble mound breakwater a minimum sea state exists which produces a significant failure probability. If a sea state is presented which is the same or higher than this minimum, failure of the structure is only a question of the duration of the sea state. Conclusions on the characteristics and stability of rubble mound breakwaters under oblique wave attack: -There is a dangerous lack of experimental data on the subject. -Run-up and run-down under small oblique incidence of waves (angle lower than 45 degrees) are function of Ir.cos(theta). For higher incidence angles the hypothesis is unreliable. -The stability of steep slopes under oblique wave attack is not worse than under perpendicular wave incidence. For milder slopes the opposite may be true. -The failure of probability of a rubble mound breakwater under a sea state with oblique incidence, can be calculated by taking into account the breaking limit, the interaction curve and a joint distribution of wave heights and periods.

Experimental research to the influence of the air pressure on the impact pressure cause by breaking waves. The research shows that there are three factors which load the structure during the breaking of waves: the water layer over the structure, the shock due to the impact of the water jet from breaking and the air pocket entrapped in the water mass. The influence of all of the factors is determined.