Hydrodynamic Isolation of Concrete Dams

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This is a project supported under the "Expedited Awards for Novel Research" (NSF 87-90). The method of hydrodynamic isolation to protect concrete dams against earthquakes is studied. A dam is isolated, not from the ground motions, but from the dynamic water pressure by means of either anchoring gas-filled balloons in the reservoir, attaching a closed-cell foam material to the upstream face, or continuously injecting bubbles into the reservoir. Thus, the significant increase in response of the dam which may occur when the reservoir is full or nearly full is eliminated. All three schemes will be evaluated for potential benefit as well as cost. It has been shown that a strong earthquake represents a severe loading of a large concrete dam with full or nearly full reservoir, causing extensive cracking with unknown consequences. Isolating a concrete dam from hydrodynamic effects avoids the increase in dynamic response. This increase becomes significant as the water level is raised from about the three-quarter height of the dam to the crest. The study has potential to impact retrofit of existing dams with seismic deficiencies and the design of new dams.