A new method for probabilistic risk analysis of earth dams

This paper presents a novel methodology for probabilistic failure risk analysis of earth dams based on the use of event trees. This approach is designed to eliminate low-relevance failure risks, thereby enabling engineers to concentrate on the detailed characterization of critical risks. The proposed methodology integrates probabilistic load characterization, reliability analyses of dam subsystems, and consequence assessments. The application of the method to a dam under construction on the Camanducaia River (São Paulo, Brazil) demonstrated its effectiveness; the filtering process reduced the number of analyzed risks by 67% (from 9 to 3). The quantitative results indicate that piping is the predominant failure mode, exhibiting a failure probability of 9.81×10-6, under standard operating conditions. The probability of overall failure was determined to be 1.02×10-5 for dry weather and 1.12×10-5 for rainy conditions. The number of incremental fatalities ranged from 29 to 51 depending on the reservoir level and failure mode. A review of international guidelines revealed notable discrepancies. Specifically, risks were deemed acceptable under the guidelines of the USBR (2011) and USACE (2014), yet were not permitted under ANCOLD (2003). These findings underscore the notion that low failure probabilities do not invariably align with acceptable risk levels, thereby reinforcing the need for a comprehensive risk evaluation.