The present investigation considers the seismic behaviour of rubble-mound breakwaters by taking into account the coupling between the hydrodynamic loading and the shaking of the mound. To this end a boundary element code was developed that predicts the hydrodynamic pressures on the faces of the breakwater. This was coupled with a geotechnical code providing the accelerations along the height of the structure. Shaking-table experiments were carried out to verify the model. The methodology was then applied to real-life structures. It is found that the quality of the foundation soil directly and decisively affects the pressures and induced accelerations. Weak foundations can trigger large structure deformations. In tall structures the pressures and accelerations of the mound increase with frequency. Far from resonance, the maximum pressures on the slopes occur at 40% of the water depth from the bed. The total hydrodynamic force can be high under resonance conditions. It is also found that Westergaard's expre...

Coupled seismic response analysis of rubble-mound breakwaters

Experimental study on the seismic behavior of composite breakwaters located on liquefiable seabed

Rubble-mound breakwaters are subject not only to wave action but, also, to other types of environmental loading, such as earthquakes. High seismic activity combined with soft foundation soil can lead to large settlements and even to failures of these structures. This paper reports on the experimental investigation undertaken to study the behaviour of rubble-mound breakwaters under seismic loading. Two models were built: the first one was designed to sit on a rigid bed, and the second on a yielding base of loose sand. Input earthquakes were of horizontal acceleration with increasing magnitude at consecutive tests. Measurements of hydrodynamic pressures and accelerations were taken. It was found that in general rubble-mound breakwaters resting on rigid bed are quite seismic resistant structures. Careful placement of the armour units provides extra strength to the armour layer as well as to the whole mound. The hydrodynamic forces on the faces of the break water, although small compared to the inertia effect on the structure, should be taken into account since they tend to modify the fundamental period of oscillation of the rubble-mound. Extra care should be taken during the design phase whenever rubble-mound breakwaters are to be placed on soft soil in areas of high seismicity.

C. D. Memos

Papers

Experimental investigation of the seismic reponse of rubble-mound breakwaters