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Title: Internal erosion and impact of erosion resistance

Author
item Hanson, Gregory
item Tejral, Ronald
item Hunt, Sherry
item TEMPLE, DARREL - Retired ARS Employee

Submitted to: United States Society on Dams Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2010
Publication Date: 4/13/2010
Citation: Hanson, G.J., Tejral, R.D., Hunt, S.L., Temple, D.M. 2010. Internal erosion and impact of erosion resistance. Proceedings of the 30th U.S. Society on Dams Annual Meeting and Conference, April 12-16, 2010, Sacramento, California. p. 773-784. CDROM.

Interpretive Summary: The two most common causes of earthen embankment and levee failures are embankment overtopping and internal erosion. Internal erosion occurs when water flows through a cavity, crack, and/or other opening within the embankment. These openings may be a result of inadequate compaction during construction, settlement, drying, earthquakes, burrowing animals, and/or vegetation roots. One of the challenges in predicting failure due to internal erosion is characterizing the material properties relevant to how fast the soil material in the embankment erodes. Large scale earthen embankment internal erosion tests have been conducted at the USDA-ARS Hydraulic Engineering Research Unit in Stillwater, Oklahoma, to evaluate how embankments erode and how fast they fail. These tests are being conducted to provide engineers with data to validate the computer models they are developing to predict dam and levee failures. Information of this nature is essential to make sure that the models are correct.

Technical Abstract: The two most common causes of earthen embankment and levee failure are embankment overtopping and internal erosion. Internal erosion occurs when water flows through a cavity, crack, and/or other opening within the embankment. These openings may be a result of inadequate compaction during construction, differential settlement, desiccation, earthquakes, burrowing animals, and/or vegetation roots. One of the challenges in predicting failure due to internal erosion is characterizing the material properties relevant to the rate of failure. A series of four large scale earthen embankment internal erosion tests have been conducted at the USDA-ARS Hydraulic Engineering Research Unit in Stillwater, Oklahoma, to evaluate how soil properties influence the erosion rate, timing, and geometry of an embankment breach as well as outflow from an embankment breach. The embankments were constructed of homogeneous soils to a height of 1.3 m with a 40-mm diameter, continuous steel pipe placed through the embankment for purposes of initiating internal erosion. Three different materials were used in the tests ranging from an SM to a CL material. The embankment materials were characterized by water content, density, texture, strength, and erodibility. Erodibility was measured using a jet erosion test (JET). The rate of internal erosion and failure observed in these tests varied by several orders of magnitude. This paper documents the observed rate of failure for two of the internal erosion tests P1 and P4 which represent the two extremes in field and laboratory erodibility measurements and in embankment erosion rates.