Sub-Nappe Air Cavity Pressure During Overflow of a Vertical Structure

Abstract

Megathrust earthquakes cause tsunamis that can destroy coastal structures and damage buildings, resulting in injuries and deaths. To prevent these consequences and reduce the risk of failure of coastal structures, it is essential to understand the exact mechanism of structure failure. Sub-nappe air cavity pressure during overflow of a vertical structure, which is the main topic of this research, can increase the risk of failure of structure, but had not yet been quantified. In this research, hydraulic experiments were conducted to reveal the relation among the air cavity pressure, overtopping flowrate, and tailwater depth for aerated and non-aerated overflow cases. For the aerated case, we found that air cavity pressure is almost equal to the atmospheric pressure regardless of flowrate and downstream weir height. On the other hand, for the non-aerated case or a partially-aerated case, air cavity pressure is inversely proportional to overtopping flowrate. The relation between air cavity pressure and tailwater depth could be interpreted in different ways based on the flow condition downstream.