Effects of Layer Thickness and Core Material on Stability of Wave Dissipating Concrete Blocks

Horizontally composite breakwaters covered fully with wave-dissipating concrete blocks have been widely employed in Japan because of the efficiency in rapid construction. However, in recent years, due to economical advantage, layered covered types having the core material beneath the primary cover layer have increasingly been constructed. Hudson and Van der Meer pointed out the influence of layer thickness and permeability of core material on the stability of armor units used for rubble mound breakwaters. Although these factors also affect the stability of armor blocks in horizontally composite breakwaters, such influences have not yet been evaluated quantitatively. In this paper, the results of a series of hydraulic model experiments are described. First, stability tests were conducted under several combinations of layer thickness and core material. Second, the velocity fields on the breakwater were measured to correlate the wave force with the stability test results. Finally, an assessment methodology of the interlocking force in the armor layer based on possible displacement length is proposed and applied to dolos armor layer.