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Reservoir Bottom Absorption

Dam-water interaction effects can be visualized as an added mass, an added damping, and an added force. Such added hydrodynamic terms can significantly affect dynamic response of concrete dams to earthquake loading. The added hydrodynamic mass tends to lengthen resonant periods of the dam. The added force presents additional seismic inertia load acting on the dam. The added damping term arises from the transmission (absorption or loss) of energy at the reservoir boundaries and from propagation of pressure waves in the upstream direction. The energy loss or transmission at the reservoir boundaries is usually approximated by a wave reflection coefficient known as "alpha". An alpha=1 corresponds to a total reflection (i.e. no transmission) and alpha=0 represents total transmission into the boundary materials. If the reservoir boundary materials are relatively soft, an important fraction of the reservoir water energy can be transmitted, leading to a reduction in hydrodynamic pressures and thus dynamic response of the dam.

Quest Structures has developed and applied three different geophysical techniques to measure in-situ values of the reservoir-bottom reflection coefficient (alpha). These include seismic reflection, seismic refraction, and acoustic reverberation techniques that have been employed at two dams in China and seven dams in the United States.

National Science Foundation Sponsored Projects
- Dongjiang Dam, China
- Longyangxia Dam, China

US Army Corps of Engineers and US Bureau of Reclamation Sponsored Projects
- Monticello Dam, California
- Pine Flat Dam, California
- Hoover Dam, Nevada-Arizona
- Glen Canyon Dam, Nevada
- Morrow Point Dam, Colorado
- Crystal Dam, Colorado
- Folsom Dam, California




 

Reflection and refraction at a plane interface

Reflection off a sediment layer with finite depth of d

Variation of reflection coefficient with frequency and sediment depth

 

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