Impact and analysis of geotechnical processes on earthfill dam breaching |
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| Authors: | Mahmoud Al-Riffai Ioan Nistor |
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| Institution: | (1) Department of Civil Engineering, University of Ottawa, 161 Louis Pasteur, Ottawa, ON K1N 6N5, Canada |
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| 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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