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Etude microstructurelle du transport par charriage de mélanges bidisperses à forte pente

Abstract : Bedload transport remains poorly understood partly due to the polydispersity of particles and resulting segregation. Experiments were carried out at the particle scale to compare the motion of spherical 4~mm and 6~mm glass beads and to analyze the segregation of two-size mixtures. Particles were entrained by a turbulent supercritical flow down a steep two-dimensional channel with a mobile bed under bedload equilibrium conditions. Flows were filmed from the side and analyzed by image processing to determine the particle trajectories, their state of motion (rest, rolling, saltation), and flow depth. Contrasting with the 6~mm uniform case where rolling was frequent, saltation was dominant for 4~mm beads and the two-size mixtures. Our one-size data support the erosion-deposition model of cite{Char06}. The velocity profiles exhibit three segments (exponential, linear, logarithmic). As well as concentration profiles, they are similar to profiles in sheet flows and dry granular flows. Our two-size experiments also revealed a phenomenon of segregation comparable to the kinetic sieving process.
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Virginie Hergault. Etude microstructurelle du transport par charriage de mélanges bidisperses à forte pente. Sciences de la Terre. Université de Grenoble, 2011. Français. ⟨NNT : 2011GRENU022⟩. ⟨tel-00684258⟩

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