Earth Dam Design. New Safety Criteria
VII Lição Manuel Rocha, 1990
DOI:
https://doi.org/10.14195/2184-8394_62_1Abstract
The traditional approach based on safety factors does not attempt to explicitly quantify all significant risk factors for a dam, nor does it explicitly determine the degree of safety which can be justified for a particular structure considering the potential consequences with respect to life and property of a sudden release of the contents of a reservoir following dam failure. Basic principles of safety are discussed to show the importance of the methods which use the probability of dam failure and its consequences. A probabilistic measure of risk costs is presented for the possible hazard scenarios. The risk involved with each failure scenario allows the selection of risk aversion measures. The concept of "figure of merit" is presented so as to permit the best safety criteria to be used. The safety of dams can be improved by the existence of a reliable warning system, but signals can be missed or false alerts can be issued, and thus obtain insufficient safety. Because the majority of the probability risk criteria and of the "figures of merit" are only recently used and few examples are available in the literature, it was considered that an illustrative example was needed to show the importance of such a safety criterion. The M'Jara dam in Morocco was chosen because of the importance of the works and of the associated risks. The dam was designed with the traditional approach on safety factors, but for seismic events a "fail-safe" technique was used to assess the permanent seismic displacements as a safety criterion. It was expected, before the illustration with the M'Jara dam case, that the seismic scenarios would be the most critical. Unexpectedly the worst loading scenario for the dam is the interna erosion. Important risk aversion measures should be implemented during the present construction of the dam. The practical example is an exercise made for this lecture, beeing the first trial of the author, and no experience is available to check some of the inconsistencies that were detected. The conclusions of this
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