DETERMINING THE ERODIBILITY OF COMPACTED SOILS FOR EMBANKMENT DAMS

Authors: Hanson, Gregory; Hunt, Sherry

Submitted to: United States Society on Dams Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/30/2006
Publication Date: 5/1/2006
Citation: Hanson, G.J., Hunt, S. 2006. Determining the erodibility of compacted soils for embankment dams. Proceedings of the 2006 U.S. Society on Dams Annual Meeting and Conference, San Antonio, Texas. p. 311-320.

Interpretive Summary: Soil type and construction practices used in embankment dams and levees play a key role in both the process and rate of failure which ultimately affects flooding. Laboratory erosion tests were conducted in this study on two soils, a sandy soil and a clay soil, compacted at various water contents and densities. The results from the erosion tests showed that: 1) the proportions of sand, silt, clay; and 2) the compaction water content at a standard compaction effort have an important impact on the rate of erosion. The rate of erosion of the clay soil tested at optimum conditions for the same compaction effort was observed to be 100 times less than the sandy soil. The rate of erosion of either soil was also observed to change more than 10 times by changes in the compaction water content. The laboratory results were consistent with results from embankment erosion tests in the field for the same two soils. Conducting laboratory tests on compacted samples can provide guidance in determining compaction specifications as well as aid in determining the likelihood and rate of embankment dam failure.

Technical Abstract: Embankment overtopping is one of the main causes of failures and incidents in embankment dams and levees. The erosion of the embankment soil material plays a key role in both the process and rate of failure. A battery of jet erosion tests were conducted on laboratory compacted samples of two soils, a SM and a CL material, prepared with standard laboratory compaction energy at various water contents and dry densities. The jet erosion test (JET) was conducted to measure the affects of compaction on erodibility. Test results showed that: 1) soil gradation is an important parameter in determining erodibility; 2) compaction water content plays a major role; and 3) erodibility decreased with increases in dry density but at a faster rate on the dry side of the optimum water content than on the wet side. Erodibility was observed to vary over several orders of magnitude. Laboratory tests also showed consistency with field results from embankment erosion tests on breach widening for the same two soils. Conducting laboratory tests on compacted samples, may potentially aid in determining compaction specifications as well as the likelihood and rate of embankment dam failure.