The baymouth breakwater is to protect the port area from tsunami. It narrows the bay mouth and prevents tsunami from flowing in the port area. A submerged breakwater is built at the central opening section of the baymouth breakwater (Tsunami breakwater) to close the bay mouth as much as possible. Because of narrowness, it is expected strong current is generated at the opening section of the breakwater when tsunami occurs. The submerged breakwater consisting of a rubble mound foundation and a submerged caisson must have stability against the strong current.
The estimation method of the stability against sliding of the submerged caisson and armor block was proposed on the result of experiments. However, using a numerical simulation calculates velocities and pressures at all points and examines the mechanism of the stability against sliding of the submerged caisson and armor block more exactly.
　The purpose of this study is to examine the stability of the opening of the breakwater on the basis of the result of numerical wave tank (CADMAS-SURF/3D: Arikawa el at. 2005). Thus, conducting the experiments of the stability of the opening of the breakwater in large flume confirms the validity of results of CADMAS-SURF/3D (called CS3D). The main conclusion is shown below.
1) CS3D calculates velocities and water surface elevations around the opening section of the baymouth breakwater within 20% error of the value of experiments in most cases. CS3D reproduces pressures on the submerged caissons in some cases.
2) By using CS3D, the horizontal pressure acting on submerged caisson is calculated within 10% error of the value of experiments in most cases, and the lifting pressure acting on submerged caisson is calculated within 30% error of the value of experiments in most cases. By using CS3D, the validity of the stability against sliding of the submerged caisson is confirmed from the result of the sliding experiments of the submerged caisson.
3) By applying a velocity calculated by CS3D and Isbash’s constant to Equation of CERC(1977) and calculating the weight of the armor blocks on sliding limited condition, it is cleared the armor blocks where CS3D predicts that armor blocks slide slide at first in experiment. The average of weight ratio correlates with the rate of the sliding of armor.