In the case of coastal dikes and seawalls, since big waves break before reaching these structures, the frequency in which they are broken directly by strong wave force is low. On the other hand, with continuous impact of middle waves, scour arises in these fronts. Before long, incident waves infiltrate into these bodies, backfilling materials flow out, and caves in these bodies become big. Owing to these phenomena, the frequency of destruction of these dikes and seawalls becomes high. Therefore, the development of methods for predicting scour rates in these fronts and sand outflow rates of backfilling materials is useful. Regarding scour rates in these fronts, there are already some accurate methods that specialists can use under various conditions. However, for sand outflow rates of backfilling materials, there are some prediction methods limited to simple types of dikes and seawalls. In this research, the authors develop a numerical model that calculates the flow velocity and pressure in the dike or seawall with arbitrary form using "CADMAS-SURF." The model can predict the time change in the sand outflow rate and the development of the cave. First, for a sand outflow rate simulation, the authors propose empirical equations to modify the pressure calculated by CADMAS-SURF using hydraulic experiment data. Then, they confirm the practical feasibility of the numerical model by applying it to field cases on sand outflow damage in Japan and Thailand.
In a beach or a shallow area, there are a few cases that coastal dikes were destroyed directly by strong wave force. On the other hand, a lot of field cases show that scour and suction caused by the continuing action of waves bring their destruction gradually. Therefore, it is important for us to establish prediction methods of suction rate from within the coastal dikes. In this paper, we improve Ioroi et al.'s formula so that the suction rate is gotten with high accuracy by using the settling velocity of Rubey. Then, we reveal the influence of coefficient of uniformity and dry density to the suction rate using experimental data. Moreover, we examine how to get the suitable values of the flow velocity and the excess pore pressure using CADMAS-SURF, and confirm that the calculated values agreed with experimental values.
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