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Title: DETERMINATION OF MATERIAL RATE PARAMETERS FOR HEADCUT MIGRATION OF COMPACTED EARTHEN MATERIALS

Author
item Hanson, Gregory
item COOK, KEVIN - USDA-NRCS

Submitted to: State Dam Safety Officials Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/1/2004
Publication Date: 9/30/2004
Citation: Hanson, G.J., Cook, K.R. 2004. Determination of material rate parameters for headcut migration of compacted earthen materials. In: Dam Safety 2004. Proceedings of the Association State Dam Safety Officials, September 2004, Phoenix, Arizona. 2004 CDROM.

Interpretive Summary: Predicting downstream floodwaters that may occur as a result of an earthen dam failure is of extreme interest to dam safety officials as well as the general public. One of the key components to predicting the timing and extent of these floodwaters is the rate at which the materials within an earthen dam erode as water is released from a failing dam. This paper describes large-scale flume and embankment failure tests that have been conducted and material erosion rates that have been determined from these tests. Results from these tests have shown the importance of the construction practices and materials used. These tests and the rate relationships that have been developed are essential in predicting the impact of downstream floodwaters as a result of an earthen dam failure.

Technical Abstract: The timing and formation process of a dam embankment breach due to flood overtopping can dramatically impact the rate that water is released from a reservoir. This rate of water release directly impacts the hazard to life and property downstream of a breached dam. Therefore, dam embankment erosion and breaching from overtopping events is important to both engineers and planners alike, who must predict impacts on local communities and surrounding areas affected by flooding. Based on observations from overtopping tests the erosion process has been described as a four-stage process. A key erosion feature has been observed to be headcut formation and migration. Therefore, determination of the material parameter for predicting rate of headcut migration is important to modeling embankment erosion. An equation for predicting the material parameter based on results from a flume study is compared to results from embankment overtopping tests. Flume tests were conducted on 2 soil materials and embankment-overtopping tests were conducted on 3 soil materials. The flume tests and overtopping tests were compacted using similar compaction efforts. It was concluded that the headcut migration parameter was primarily dependent on compaction water content. A 4% change in compaction water content caused an order of magnitude change in the headcut migration parameter. The results of this study will have an impact on the prediction of the potential rate of failure of overtopped embankments and extent of floodwaters downstream.