Damping of Horizontal and Uplift Forces on Horizontally Composite Breakwaters

Innovative structures like horizontally composite breakwaters or so-called ‘Japanese-type' are increasingly used to reduce loading on and hydraulic responses from vertical breakwaters leading to a reduction of the dimensions and costs of the structure. Horizontally composite breakwaters consist of a protective layer in front of the vertical breakwater which is made of armour blocks. Large-scale hydraulic model tests were conducted to measure wave-induced horizontal and uplift forces on a vertical model breakwater. Comparisons of these force time series were performed for a structure with and without a protective layer made of tetrapods. Tentative formulae to calculate damping ratios of wave forces were then derived and compared to standard design formulae.