Influence of Reservoir Water Levels on the Protective Performance of Concrete Gravity Dams Subjected to Underwater Explosions

Abstract

Blast loads would cause serious damage to concrete gravity dams, and a possible dam break can lead to a catastrophe in downstream populated areas. Preventing damage to dam structures is of great interest in the blast-resistant design of dams. This paper investigates the influence of reservoir water levels on the protective performance of a typical concrete gravity dam under blast loads. For that purpose, five different reservoir water levels are considered in this study. Because the dam structure may undergo both air and underwater blast loads near the free water surface with the drawdown of the reservoir water level, comparison analyses of the shock wave propagation characteristics of an underwater explosion and an air blast near boundaries are first carried out. The results show that shock wave peak pressures from an underwater explosion near the free water surface are much higher than those from an air blast near the free water surface. To further compare the damage characteristics of concrete gravity dams in these two blast scenarios, a fully coupled numerical approach with combined Lagrangian and Eulerian methods is performed to model the dam-reservoir-foundation system. For a dam subjected to an air blast near the free water surface, there is almost no damage and hence an underwater explosion is mainly investigated. The influence of detonation positions on the degree of damage to a dam subjected to underwater explosions is investigated. The effect of reservoir water levels on the protective performance of a dam is discussed and identified. The results show that protective performance is greatly improved when the reservoir water level is below the change in downstream slope of the dam, which also reduces the loss of downstream areas even when the breaching of the concrete dam occurs.