Experiments of the wave impinging forces on seawalls reefs were conducted in the large wave flume of the Tianjin Research Institute of Water Transport Engineering. Wave forces, including the horizontal and uplift pressures, on seawalls were measured at different water levels and wave conditions. The force values were compared with those obtained by empirical equations. The experimental results show that the wave force on seawalls was determined by the incident wave height, the wave setup on reefs and the wave-induced flow after breaking. A rectangular distribution for the horizontal pressure and a triangular distribution for the uplift pressure were found. Correction coefficients were proposed based on the relative distance between the seawall and reef edge and the relative water depth at the reef. The calculated correction values were demonstrated to be in good agreement with the experimental results.
The water depth around coral reefs is generally a few hundred metres or kilometres. The terrain of the coral reefs is similar to a hill, and when waves reach the reef flat from the deep water, they will inevitably pass a large gap in the reef edge with a strong non-linear characteristic. Coral reefs are exposed to harsh marine environments with variable water depths, tropical cyclones and prevalent monsoons. Under the effect of typhoon waves, storm surges and other extreme waves, the reef wave-protection structures will be strongly affected. The wave forces on seawalls directly affect the safety of the wave-protection structures. Although the current equation of wave force on a seawall of a rubble-mound breakwater was given in the Code of Hydrology for Harbour and Waterway (JTS145–2015), its application conditions clearly stipulate the following: "The slope of the bottom is i<1/10, and the water depth of the structure is 1.5~5.0 H; the fore slope of the structure is i<1/50." However, the steep slopes of coral reefs are often 1:10~1:0.5; then, the existing norms about water depth and the bottom slope do not satisfy the special topographical conditions of coral reefs. Therefore, the relevant norms are no longer applicable.