Future climate change will possibly cause high storm surges and high waves larger than the design level. In such severe conditions, unexpected failures of coastal structures can occur. Gravity seawalls with parapets are commonly used in coastal areas. Above all, a caisson type seawall is one type of gravity seawall used in deep coastal areas, especially in artificial islands. In this study, we conducted a series of hydraulic experiments to clarify the wave overtopping and wave force acting on a caisson type seawall with parapets during severe storm surges. The experiments examined high tides and high waves larger than the design level. As a result, the following events were observed. When the water level is higher than the crest level of the seawall, not only wave overtopping but also water overflowing occurs. The overflowing rate is 20–50 times larger than the wave overtopping rate at a storm surge level larger than the crest level of the seawall. The pore pressure inside the backfill stone almost equals the wave pressure in front of the caisson. Moreover, high water level induces water to flow out from the backfill stone opening.
Future climate change could cause high storm surges and high waves larger than the design level. In such severe conditions, unexpected failures of coastal structures could occur. Gravity seawalls with parapets are commonly used in coastal areas. Above all, the caisson type seawall is a type of gravity seawall used in deep coastal areas, especially in artificial islands. Recently, failures of gravity seawalls have been caused by storm surges and high waves. Takahashi et al. (2000) has reported that the destruction of parapets by breaking wave force during storm surges caused a large inundation of Yamaguchi Airport.
Martinellia et al. (2018) conducted experiments on wave force acting on parapets of different shapes. Van Doorslaer et al. (2017) also examined the strong wave force to the facility behind the seawall by wave overtopping. Castellino et al. (2018) conducted a 2-dimensional numerical simulation of recurved parapet and examined that the wave power acting on the parapet differs depending on its shape.
