Seismic Hazard Analyses and Risk Classification for Large Embankment Dams in Turkey

Turkey is one of the most seismically active regions in the world. Major earthquakes with the potential of threading life and property occur frequently. In the last decade over 50 000 residents lost their lives, commonly as a result of building failures. For dams, structural damage was significantly developed at a number of dams, but there was no failure in any case. The most well-known earthquake damage to an embankment dam in Turkey occurred during the 1986 Dogansehir earthquake with Ms of 5.8. The epicenter of earthquake was very close to the dam. It was believed that the dam damages were resulted by the strong motion of fault zone, which is very close to the embankment. There are so many dams, which are under the effect of near-source zones in Turkey. Therefore, the use of meaningful seismic parameters is needed to perform a satisfactory evaluation of the earthquake safety of dams. In general, strong ground shaking can result instability of the dam and strength loss of foundation. Active faults within the foundation of the dam have the potential to cause damaging displacement of the structure. To obtain rational solution to the problem such as catastrophic release of water from the reservoir, appropriate design measure should be considered to resist earthquake loads. State Hydraulic Works, which is responsible to design and construct dams in Turkey, began a program about reanalyzing embankment dams. This program is still continuing, but it seems that some dams are poor to earthquake loads and needed to be improved. This paper discusses the guide for the selection of parameter to be used in the seismic design, analysis and safety evaluation of dams and introduces the analyses performed for 25 large dams, which are within three basins at the central part of Turkey. For the dams with a height ranging from 45 to 205 m, located on very active seismic zones, the seismic hazard rating of the dam site and the risk rating of the complete structures were determined and possible modes of failure were estimated. As a result of this study, 85 percent of dams has high or extremely high of risk class and 38 percent of dam are under the influence of near seismic source. 9 pp., 3 tables, 2 figures, 13 references.