Implications of Complex Seismotectonic Site Conditions on Seismic Design of Large Dams

Abstract eng:
The implications of complicated seismotectonic site conditions on the selection of the dam type and the seismic design are discussed. As a case study the proposed Rudbar Lorestan dam in Iran is used. The dam is located at a distance of ca. 1.6 km from an active fault, which is capable to produce earthquakes with a maximum magnitude of up to 7.5. The site is at a narrow gorge with almost vertical abutments and there are several faults and other discontinuities in the footprint of the dam, which can experience movements during strong earthquakes. The discontinuities (old faults, joints, bedding planes etc.) in the dam foundation are short and are not seismogenic. The following dam types are discussed: RCC gravity dam, earth core rockfill dam, and concrete-face rockfill dam. Due to the topography a concrete dam would be the obvious solution. For sites with active faults embankment dams are recommended by ICOLD. At such a site, foundation movements acting at several discontinuities and ground shaking act together. The peak ground acceleration of the horizontal component of the safety evaluation earthquake at the dam site is estimated as 0.7 g. Fault movements in the footprint of a dam are probably the most severe conditions a large dam may experience and may cause severe cracking in concrete dams. Therefore, the seismic analysis must be carried out for the cracked dam, which is a difficult task.

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