Destruction Mechanism of Seawalls by Typhoon Faxai in 2019

Typhoon Faxai passed through eastern Japan along with strong winds in 2019. This typhoon destroyed a wide range of seawalls and caused wave-induced inundation in Fukuura and Honmoku in Yokohama. Considering the design method of Japanese parapets against wave pressure has not yet been established, it is important to clarify the factor of damage caused by this typhoon. In this study, we performed large-scale hydraulic experiments and numerical simulations to examine the mechanism of this disaster. As a result, we found that the wave pressure acted on parapets during this typhoon was unexpectedly larger than the one calculated by the formula normally used for the seawall design because of the configuration of seawalls; parapets was located behind the front of the caisson. This phenomenon could be reproduced by both hydraulic experiments and numerical simulations. We also showed that the wave overtopping from parapets with setbacks from caisson front could be unexpectedly larger than that from parapets in front due to its collapse.