Author(s): L. G. Bierawski; S. Maeno
Linked Author(s): Shiro Maeno
Keywords: Submerged breakwater; Reef breakwater; Water exchange process; Water and pore water pressure fluctuations; Velocity field
Abstract: A laboratory small-scale experiment in a two-dimensional wave tank is conducted in order to investigate the interaction between the reef breakwater, the sandy bed beneath it and the surrounding wave field for several combinations of various: the water depth, the wave height and the stone diameter of the rubble mound. The water and pore water pressure fluctuations throughout the breakwater and the bottom as well as the velocity field by Acoustic Doppler Velocitymeter in the vicinity of the structure is clarified. Additionally, the significance of different rates of the permeability coefficient for the interaction is discussed. As the main result of this research, the water exchange process is proved to be a crucial factor in the wave propagation inside a highly permeable porous medium. The influence on the velocity distribution of the wave field in front of the structure is also explained. Finally, considering construction safety precautions, it is proved that if the permeability of a submerged structure becomes lower, high pore water pressure gradients may cause seepage force inside the sandy bed below the structure and subsequently lead even to serious damage even without any increase in the wave parameters. The paper provides a wide view into the reef breakwater operation and is a sufficient base to develop and verify a numerical model to get remaining parameters presently unreasonable or impossible to measure in the laboratory.
Year: 2003