2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference

Experimental study on the effect of dike geometry on the breach outflow and erosion rates during overtopping of non-cohesive homogeneous embankment

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Mr. AMANJ RAHMAN, university of Ottawa (Presenter)
Dr. Ioan Nistor, University of Ottawa
Dr. Julio Angel Infante Sedano, University of Ottawa

The paper will present the results of a comprehensive experimental program conducted to obtain the effect of downstream slope on the planar breaching progress and outflow hydrograph of homogenous non-cohesive embankments due to overtopping. Visualizing flow by injecting fluorescent dye and using LED UV Blacklight in a light controlled room combined with high-speed cameras provided high-accuracy data of high temporal and spatial resolution of the processes investigated. Downstream slopes of  (1:2, 1:3 and 1:4) were tested with the initial overtopping head of  5 and 10 cm respectively. The time-history of the pore-water-pressure (PWP) during overtopping flow on the downstream face were recorded using micro-tensiometer-transducer probe assemblies (MTTPA), assembled and calibrated conducted in the Geotechnical and Hydraulic Engineering Laboratories at the University of Ottawa, Canada. Styrofoam balls (2-3) mm size painted with fluorescent paint were used as a seeding particle to measure surface velocity, in combinations with a high-speed Phantom 410L (HSPC) camera with a recording capacity of 1000 fps. The image processing and tracking particles velocity were achieved using Davis@ commercial software.

The authors overcame significant difficulties in measuring outflow hydrograph due to the shallowness of the flow and the highly unsteady state flow. Past researchers used different methods to estimate breach hydrographs such as v-notch weir installed at the downstream end of the experiment, or hydrologic routing of the reservoir or most common one is broad-crested weir formula. The element of novelty of this work is the deployment of recent technology and image processing tools made possible to use particle tracking velocimetry (PTV) in measuring overtopping flow hydrograph.

The hydrographs computed for the three embankment configurations indicated that erosion rate for steeper slope under the high initial overtopping head is quite faster due to the acceleration of flow and high shear stress applied on the bed material. In contrast, with the low initial overtopping head (5cm), the downstream slope has less impact on peak-flow rather than delaying the erosion progress.