2001 – Estimation of the Probability of Failure Embankment Dams by Internal Erosion and Piping Using Event Tree Method

M.A. Foster, R. Fell, R. Davidson, C.F. Wan

The probability of failure of embankment dams by internal erosion and piping can be estimated using historic performance, and event tree methods. Event tree methods are preferred for all except preliminary assessments, because they can better model the characteristics of the dam. This paper provides guidance on how to estimate the conditional probabilities within the event tree based on an understanding of the process involved, the historic performance of dams, and experience in recent risk analyses. This includes methods for representing the reservoir water level; assessing the likelihood that piping initiates; assessing the likelihood that erosion will be controlled by the filters or transition zones; and assessing the likelihood of development of a pipe and breach. The paper will be useful for those carrying out risk analyses and will also have relevance to those who are assessing piping of dams using traditional methods.