Embankment breach research: Observed internal erosion processes

Authors: ALI, ABDELFATAH - Oak Ridge Institute For Science And Education (ORISE); Hunt, Sherry; Tejral, Ronald

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2020
Publication Date: 1/1/2021
Citation: Ali, A.K., Hunt, S.L., Tejral, R.D. 2021. Embankment breach research: Observed internal erosion processes. Transactions of the ASABE. 64(2):745-760. https://doi.org/10.13031/trans.13701.
DOI: https://doi.org/10.13031/trans.13701

Interpretive Summary: Dams and levees serve many purposes with the primary purpose often described as flood control. Many dams and levees are made of soil and can be prone to erosion during extreme weather events. While these earthen dams and levees are mostly safe, these structures can fail. The two common causes of earth dam and levee failure are overtopping and internal erosion. Overtopping is described as water flowing over the top of the dam, and internal erosion is described as an internal opening created by water flowing through a cavity, crack, and/or continuous void within the earth dam or levee. Internal erosion may be caused by lack of compaction of the soil during construction, settlement in the dam, soil materials becoming extremely dry, earthquakes, animals digging into the dam or levee, and/or woody roots constructed in the dam become decayed over time. This research found that the erosion of an internal opening in a dam and/or levee is affected by the soil properties. These soil properties include the percentage of soil clay, silt, and sand; the amount of water in the soil when the dam and/or levee is constructed; and the resistance to soil erosion. Quality control at the time of construction can also play a role in the erosion rate. This research is intended to assist engineers to prioritize aging dams for upgrades, policymakers to make decisions on zoning regulations, and emergency managers to develop improved emergency action plans.

Technical Abstract: Internal erosion and embankment overtopping are the two most common causes of embankment dam and levee failures and incidents. Internal erosion is the removal of soil material by the flow of water through a continuous defect, cavity, or crack within a compacted fill and/or its foundation. Internal erosion initiates from vulnerabilities within the embankment. The embankment soil material plays a key role in both the erosion process and rate of failure, but characterizing soil properties and how they relate to the rate of failure can be challenging. Soil properties such as texture, density, strength, moisture content, and erodibility can vary greatly; thus, it is important to study the effects of these properties on the breach formation process and breach timing. The USDA Agricultural Research Service performed internal erosion breach experiments on four intermediate-scale homogeneous earthen embankments constructed of soils ranging from a silty sand to a lean clay material. The embankments were constructed to a height of 1.3 m, a top width of 1.8 m, and upstream and downstream slopes of 3(H):1(V). The embankment materials were characterized by water content, density, texture, strength, and erodibility. Erodibility was measured using a jet erosion test (JET) apparatus. A 40 mm diameter, continuous steel pipe was placed through each embankment during construction and removed to form an open-ended void through the embankment connected to the upstream reservoir. The removal of the pipe initiated internal erosion. The objectives of the experiments were to observe the development of the internal erosion process over time and to examine the influence of soil properties on the erosion rate, breach timing, geometry of the breach opening, and breach outflow. The rate of erosion and failure observed in these tests varied by several orders of magnitude, with the silty sand embankment eroding most rapidly and the lean clay embankment with a mean moisture content of 18% dry basis at standard compaction eroding the slowest. These observations were indicative of the soil textures. Although the two lean clay embankments were constructed of similar soils, the difference in erosion rates speak to the importance of quality control (e.g., compaction moisture content) during construction. Soil properties including soil texture, erodibility, and compaction moisture content are key predictors of erosion rate and observed failure.