Erosion Resistance and the Impact of Water Content

Often plasticity, water content, and percent compaction are key variables specified to ensure an embankment material is well constructed. However, do these specifications ensure that the embankment is erosion resistant? Intuitively, density may be seen as one of the critical factors for erosion resistance. Reclamation has completed several large-scale erosion tests and several index tests to understand factors that influence an embankment’s erodibility and density was found to be misleading when considering erosion resistance. This paper focuses on the influence water content has on an embankment’s erodibility and methods designers could use to increase erosion resistance. During the large-scale testing, compaction effort was maximized for each test, and as expected, the higher water content tests had significantly lower densities. However, these higher water content, low density tests were found to be more erosion resistant compared to the lower water content, higher density companion tests. Specifically, the research found erosion resistance increased when water content was greater than the typically specified two percent wet of optimum. For critical features, such as penetrations through an embankment or at foundation contacts, increasing the water content beyond the typical two percent wet of optimum has potential to significantly increase a material’s erosion resistance. This paper looks at the impact higher water content has on erodibility and discusses what embankment dam designers should consider when specifying compaction in areas where erodibility is a concern.