Embankment breach research: Observed internal erosion processes

Authors: ALI, ABDELFATAH - Orise Fellow; Hunt, Sherry; Tejral, Ronald; TEMPLE, DARREL - Retired ARS Employee

Submitted to: State Dam Safety Officials Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/11/2018
Publication Date: 9/13/2018
Citation: Ali, A.K., Hunt, S.L., Tejral, R.D., Temple, D.M. 2018. Embankment breach research: Observed internal erosion processes. In: Dam Safety 2018. Proceedings of the Association of State Dam Safety Officials Annual Conference, 09/09-13/18, Seattle, WA. 4 p.

Interpretive Summary: The two most common causes of earthen dam or levee failure are water spilling over the top of a dam or the unintended release of water through an opening in the dam. An unintended release of water through an opening in the dam occurs when water flows through a cavity, crack, and/or opening within the dam. These openings may be caused by drought conditions, earthquakes, animals digging, and/or tree roots creating a flow path. Having knowledge about the soils in earthen dams is key to knowing how fast a dam may erode or in some cases fail. Scientists at the USDA-Agricultural Research Service Hydraulic Engineering Research Unit in Stillwater, Oklahoma conducted research on small earthen dams. Scientists observed the release of water through an opening in the dam until the dam failed. This research was conducted to provide data to assist in the development of computer software to predict dam failures.

Technical Abstract: Internal erosion and embankment overtopping are among the most common causes of embankment dam and levee failures and incidents. Internal erosion occurs when water flows through a cavity, crack, and/or other openings within the embankment. Internal erosion initiation may be caused by vulnerabilities (e.g. inadequate compaction during construction, earthquakes, differential settlement, desiccation, burrowing animals, or/and vegetation roots) 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. Because the breach formation process and breach timing can vary due to soil materials (e.g. soil gradation, density, moisture content), it is important to study this phenomenon to improve prediction of dam incidents and potential for breach failure. 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. 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 erosion and failure observed in these tests varied by several orders of magnitude. The objective of this research was to document the observed rates of failure for the internal erosion tests and to compare the influence soil materials have on the erosion processes.