Coupled seismic response analysis of rubble-mound breakwaters

Abstract

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 expression overestimates pressures, except in cases of rigid base and shakings of small acceleration and high frequency. The coupling of the hydrodynamic loading and the shaking of the mound, as well as the frequency dependence of the model, represent advances over the conventional Westergaard's relation.