BREACH WIDENING OBSERVATIONS FROM EARTHEN EMBANKMENT TESTS

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 planned service life. The embankment failure process due to overtopping includes several aspects of erosion: 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 have been observed to greatly influence how a soil erodes and therefore influence the embankment erosion processes, including breach widening. The objective of this article is to evaluate the time rate of breach widening of three large-scale earthen embankment tests. The embankments were constructed of homogeneous materials ranging from silty sand to lean clay, 1.3 m in height with a 0.30 m notch through the center of the embankment. The primary erosion process of interest during these tests was breach widening. The results from these tests as well as widening data from previous embankment overtopping tests conducted at the laboratory are compared in relation to the compaction water content of the soils used to construct the embankments. Rates of widening were strongly influenced by the compaction water content. Measured soil properties are promising in characterizing the development of a breach.