ARS | Publication request: Breach Widening Observations from Earthen Embankment Tests

Submitted to: American Society Of Agricultural Engineers Meetings Papers
Publication Acceptance Date: July 1, 2004
Publication Date: August 1, 2004
Publisher's URL: http://www.asae.org/pubs/index.html
Citation: Britton, S.L., Hanson, G.J., Cook, K.R., Kadavy, K.C. 2004. Breach Widening Observations From Earthen Embankment Tests. In: American Society Of Agricultural Engineers/canadian Society For Engineering Annual International Meeting, August 1-4, 2004, Ottawa, Canada. Paper No. 04-2080. 2004 Cdrom.

Interpretive Summary: In recent years, interest has risen in the occurrence and effects of overtopping on earth embankments due to the number of dams that have reached the end of their design life. The embankment failure process due to overtopping may begin with vegetation failure or in areas where the soil is vulnerable to the concentrated flow overtopping the structure. Soil properties such as soil type (i.e. soil particle size) and compaction water content can greatly influence how a soil erodes and the rate at which it erodes. The research discussed in this document provides a summary of two large-scale embankments tested to failure at the USDA-ARS Hydraulic Engineering Unit. Researchers hope to gain a better understanding of how an embankment breach develops over time and what variables influence its development. The primary erosion process of interest during testing was breach widening. The results from these two tests as well as widening data from previous embankment overtopping tests conducted at the laboratory are compared. Rates of breach widening were strongly influenced by the soil compaction water content. Measured soil properties are promising in characterizing the development of a breach. This research may lead to the development of future warning systems for dam failures and may impact breach modeling and dam safety.

Technical Abstract: In recent years, interest has risen in the occurrence and effects of overtopping on earth embankments due to the number of dams that have reached the end of their design life. The embankment failure process due to overtopping includes several aspects of erosion including failure of the vegetation; concentrated flow; headcut migration; and breach timing, formation, and widening. Research using large-scale physical models is on-going at the USDA-ARS Hydraulic Engineering Unit to provide a better understanding of how a breach develops over time and what variables influence breach development. Soil properties such as particle size, compaction effort, compaction water content, bulk density, and soil erodibility can greatly influence how a soil erodes; and therefore, influence the embankment erosion processes including breach widening. The objective of this paper is to evaluate the time rate of breach widening of two large-scale earthen embankment tests. The embankments were of a homogeneous, non-plastic SM silty sand material 1.3 m in height with a 0.30 m notch through the center of the embankment. The primary erosion process of interest during testing was breach widening. The results from these two tests as well as widening data from previous embankment overtopping tests conducted at the laboratory are compared to soil properties including particle size, water content, bulk density, and soil erodibility. Rates of widening were strongly influenced by the compaction water content. A 5% increase in compaction water content is observed to decrease widening rate more than 2 orders of magnitude. Prediction of widening using a hydraulic stress based approach is consistent with observed results.