The effectiveness of countermeasures to improve the tenacity of coastal dikes against tsunami overflow is investigated numerically in terms of local scouring at its landward toe and wave force acting on armor blocks. Numerical results show that protection blocks and filter units covering the foundation around the landward toe of the dike move the scouring area landward and reduce its maximum depth, suggesting that these countermeasures would be effective to extend the time before beginning the damage of the body of the dike. It is also revealed that air vents created at the armor blocks reduce an increase in air pressure inside the dike, improving the stability of the armor blocks. Furthermore, it is found that there is no effect of a sheet pile against liquefaction during an earthquake on the local scouring and wave force.
