| Summary: | 碩士 === 國立中央大學 === 土木工程研究所 === 100 === Mountain floods accompanied with landslides, slope avalanches and debris
flows often cause tremendous disasters to downstream residents and
infrastructures. The dynamic process and deposit mechanism of alluvial fans by
torrential flows is experimentally explored in this study. An acrylic flume
experiment is adopted to observe the deposit progress of granular flows, deposit
angle of foreset and topset, and flow patterns with a high-speed camera. The
particle size (D), water discharge (Q w ), and sediment discharge (Q s ) dominates
the flow patterns, and the slopes of foreset and topset mainly depend on
sediment concentration (i.e., the ratio of sediment discharge to water discharge).
The slope of topset increases with increasing sediment concentration. The
velocity profiles of the flowing layer are explored by using particle image
velocimetry (PIV). The velocity profiles in the flowing layer depict SSH
rheology when the free surface is equal to or slightly higher than granular-flow
surface. When the free surface is substantially higher than granular-flow surface,
the lower part of the velocity profile in the flowing layer still obey SSH
rheology. The upper part of velocity profiles near the free surface follow the
Bagnold-type velocity profiles instead.
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