Abstract
For over three decades, emergency planners have used numerical models to predict breaching in earthfill dams due to extreme events such as overtopping. However, current models neglect the role of the unsaturated zone present within the downstream face of an earthfill dam. This leads to an incorrect estimation of the time and space evolution of the breaching process, as such models often oversimplify governing geotechnical aspects such as the presence of the unsaturated soil medium in the vicinity of the breach channel. The stress state in the soil due to matric suction acts as a stabilizing force for the breaching mechanism and influences the erosion of the breach channel, especially during the initial phases of the breaching. The side-slope failure mechanism observed along the breach channel is also influenced by the negative pore-water-pressures in the soil. Based on a comprehensive experimental research program carried out in the Hydraulics Laboratory at the University of Ottawa, Canada, several new concepts are proposed to incorporate geotechnical factors and techniques which must be considered during the construction of earthfill dam models for laboratory testing. Two main findings emerged from this experimental work. First, the installation of a drainage mattress at the downstream toe of the dam depressed the phreatic surface through the earthfill dam body, which caused a lag in the breaching process due to the infiltration and reduced erosion occurring in the breach channel. Second, it is essential to control compaction during the construction of the earthfill dam model, since this significantly influences the erosion, as well as the side-slope failures which occur in the breach channel. Future studies are under way by the authors with the purpose of scaling of parameters such as the matric suction and soil erodibility.
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Acknowledgments
This work was possible through the support of the National Science and Engineering Research Council (NSERC) Discovery Grant. We also wish to thank Professor Sai K. Vanapalli and Dr. Won-Taek Oh from the Geotechnical Laboratory at the University of Ottawa for their advice and support during the experimental program. The authors are also grateful for the support and assistance of undergraduate civil engineering students Philippe St-Germain from the University of Ottawa, Canada and Sihame Mimid, Pierre Moreels, Claire Doerrer and Yann Boscher from Université de Limoges, France, who helped during this experimental work in 2008 and 2009.
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Al-Riffai, M., Nistor, I. Impact and analysis of geotechnical processes on earthfill dam breaching. Nat Hazards 55, 15–27 (2010). https://doi.org/10.1007/s11069-010-9586-6
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DOI: https://doi.org/10.1007/s11069-010-9586-6