PRELIMINARY RESULTS OF EARTHEN EMBANKMENT BREACH TESTS

Authors: Hanson, Gregory; Cook, Kevin; HAHN, WILL - OKLAHOMA STATE UNIVERSITY

Submitted to: American Society of Agri Engineers Special Meetings and Conferences Papers
Publication Type: Proceedings
Publication Acceptance Date: 7/13/2000
Publication Date: 7/13/2000
Citation: Hanson, G.J., Cook, K.R., Hahn, W. 2000. Preliminary results of earthen embankment breach tests. American Society of Agricultural Engineers Meeting. Paper #002007. 12 p.

Interpretive Summary: Interest in the occurrence and effects of water flowing over the top of earthen embankments by rising floodwaters has existed for years. There are about 57,000 dams on the national dam inventory that have the potential for overtopping. Even though dam overtopping failures are rare, the impact to people and property downstream of a reservoir is important to engineers, and planners alike, who must evaluate the hazards of local flooding. Recen outdoor laboratory overtopping studies have been or are being conducted on relatively large-scale models, earthen embankments with test sections made up of a different soil. The test soils varied from a silty sand to a lean clay. The soil type had a significant effect on the timing and rate of water released from the upstream reservoir during the overtopping tests. Overtopping tests on the silty sand material resulted in a breach, erosion through the embankment releasing water at a rate greater than the rate coming into the reservoir, 35 minutes after overtopping began. The outflow peaked 6 minutes later, with peak outflow 7 times greater than the inflow. In contrast, overtopping tests on the lean clay material did not produce a breach even after 1200 minutes of overtopping. These studies add insight into the nature of embankment overtopping erosion and failure. These observations will be essential in updating earthen embankment failure models and adding to the safety and well being of people and property.

Technical Abstract: Interest in the occurrence and effects of overtopping events on earthen embankments has existed for years. There are about 57,000 dams on the national dam inventory that have the potential for overtopping. Even though dam overtopping failures are rare, the impact to people and property downstream of a reservoir is important to engineers, and planners alike, who must evaluate the hazards of local flooding. Recent outdoor laboratory overtopping studies have been or are being conducted on relatively large-scale models, earthen embankments 2.3 m and 1.5 m high. Each embankment has three test sections with each test section made up of a different soil. The test sections are 7.3 m wide for the 2.3 m high embankment and 4.9 m wide for the 1.5 m high embankment. The test soils vary from a silty sand to a lean clay. The soil type had a significant effect on the timing and rate of water released from the upstream reservoir rduring the overtopping tests. Overtopping tests on the silty sand material resulted in a breach 35 minutes after overtopping began. The outflow peaked 6 minutes later with peak outflow 7 times greater than the inflow. In contrast, overtopping tests on the CL material did not produce a breach even after 1200 minutes of overtopping. These studies add insight into the nature of embankment overtopping erosion and failure. These observations will be essential in updating earthen embankment failure models and adding to the safety and well being of people and property.