دانلود رایگان مقاله جنبه های ایمنی پایدار سدهای ذخیره و ایمنی زلزله سدهای موجود

Abstract

The basic element in any sustainable dam project is safety, which includes the following safety elements: ① structural safety, ② dam safety monitoring, ③ operational safety and maintenance, and ④ emergency planning. Long-term safety primarily includes the analysis of all hazards affecting the project; that is, hazards from the natural environment, hazards from the man-made environment, and project-specific and site-specific hazards. The special features of the seismic safety of dams are discussed. Large dams were the first structures to be systematically designed against earthquakes, starting in the 1930s. However, the seismic safety of older dams is unknown, as most were designed using seismic design criteria and methods of dynamic analysis that are considered obsolete today. Therefore, we need to reevaluate the seismic safety of existing dams based on current state-of-the-art practices and rehabilitate deficient dams. For large dams, a site-specific seismic hazard analysis is usually recommended. Today, large dams and the safety-relevant elements used for controlling the reservoir after a strong earthquake must be able to withstand the ground motions of a safety evaluation earthquake. The ground motion parameters can be determined either by a probabilistic or a deterministic seismic hazard analysis. During strong earthquakes, inelastic deformations may occur in a dam; therefore, the seismic analysis has to be carried out in the time domain. Furthermore, earthquakes create multiple seismic hazards for dams such as ground shaking, fault movements, mass movements, and others. The ground motions needed by the dam engineer are not real earthquake ground motions but models of the ground motion, which allow the safe design of dams. It must also be kept in mind that dam safety evaluations must be carried out several times during the long life of large storage dams. These features are discussed in this paper.

8. Conclusions

In the seismic design and seismic safety assessment of dams, the following items are of main concern: (1) Seismic hazard is a multi-hazard for most dam projects. Ground shaking is the main hazard considered in all earthquake guidelines for dams. However, rockfalls and fault movements could be more critical than ground shaking. (2) Movements of active faults in the footprint of a dam, or movements at discontinuities (faults, joints, and bedding planes), which can be activated during strong nearby earthquakes, are the most critical seismic hazard for concrete dams. If no other site can be selected, then a conservatively designed earth core rockfill dam with wide filter and transition zones would be the best solution. (3) Today, the seismic safety of a large storage dam includes the following safety elements: ① structural safety, ② dam safety monitoring, ③ operational safety and maintenance, and ④ emergency planning. All items are equally important. (4) Dams are not inherently safe against earthquakes. However, technology is available for designing and building dams and appurtenant structures that can safely resist the effects of strong ground shaking. (5) The earthquake load case has evolved as the critical load case for most large dams. Since safety is the main prerequisite for sustainability, managing the various safety aspects of the earthquake (and flood) hazard is a basic requirement for sustainable dams. (6) The assumption that a civil structure that is safe at the time of construction remains safe during its whole service life is not realistic. During the life span of a dam, several seismic safety assessments will be needed if new information on the seismic hazard becomes available, when new design and safety criteria are introduced, if the seismic risk increases due to development in the downstream valley, and so forth.