The U.S. Army Corps of Engineers (USACE) has gradually implemented risk assessment into its Dam and Levee Safety programs over the last 10 years. This has resulted in a focused effort to better understand potential failure modes. A common assessment by engineers is that the presence of sand boils indicates a high risk condition. It is often assumed that if sand is eroding from the boil and no flood fighting actions are implemented, it will continue to erode horizontally under the dam or levee and will ultimately lead to failure of the structure. Although it is prudent to treat the presence of sand boils with caution, we have found that field observations and laboratory studies indicate that not all boils will progress to failure. This paper will discuss our current knowledge of the factors that influence the progression of sand boils to embankment failure, field observations of boils that did not lead to failure, and the current approach we are using to estimate risk associated with backward erosion piping (BEP).
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