SEISMIC RESPONSE OF GRAVITY DAMS .2. EFFECTS OF SEDIMENTS

The finite element technique developed in the companion paper is applied to the analysis of an idealized concrete gravity dam interacting with the water, sediment, and foundation. Of interest in the study is the evaluation of the effects of fluid-filled poroelastic sediment on the response of the dam to harmonic ground motion. Since specific information on the sediment behind dams is not currently available, the sediment properties are developed on the basis of measurements near river deltas. The results indicate that the effects of fully saturated sediment are limited to a slight decrease in the maximum acceleration of the dam and the maximum hydrodynamic force. However, if the sediment is only partially saturated, there is a significant decrease in the fundamental frequency along with a substantial reduction of the peak acceleration under horizontal ground motion. These findings hinge on the assumed sediment properties and suggest that the latter be measured in actual dam sites before any definitive conclusion is reached regarding the importance of sediment effects.