Risk Analysis Perspectives on the Camara Dam Failure

摘要

The June 2004 breach of Camara Dam, Brazil, is one of the few documented failures involving a Roller Compacted Concrete (RCC) Dam. The details of the failure, as well as the aftermath of the flooding, have been previously discussed, and many of the original source documents are available. From the risk analysis perspective, however, estimators continue to struggle with the mechanisms that could result in an RCC dam underperforming, and there is often a sense that RCC structures are more forgiving than those built of conventional concrete. While the case history literature suggests that a concrete dam is only as good as the underlying rock, it is important to'question the idea that an RCC design is ideally suited for every geologic setting, and that the Camara Dam failure was exclusively the result of a problem with the foundation. This paper advances, in the form of a site-specific potential failure mode (PFM), an alternative conceptual model for what happened, discusses whether such a process could have been reasonably anticipated using risk analysis, and argues that a well-known concrete dam case history could have been recognized as a prototype. With the benefit of hindsight, conditional probabilities are estimated for the events that comprise the PFM, and the life loss consequences of the breach flood are compared to what might have been predicted using the Reclamation consequence estimating methodology (RCEM). The results of the evaluation are used to highlight the actions that can be taken, both during and after construction, to address the types of problems experienced at Camara Dam. The paper also provides an overview of the engineering geology and discusses opportunities to improve geologic design data collection in the interest of preventing a similar occurrence.