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51.
Determination of critical shear stress of non‐cohesive soils using submerged jet test and turbulent kinetic energy
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Laboratory tests using Jet Erosion Testing (JET) apparatus, impinging normally on a horizontal boundary, were conducted to determine the critical shear stress (τc) of non‐cohesive soil samples. A three‐dimensional (3D) SonTek/YSI 16 MHz Micro‐Acoustic Doppler Velocimeter (MicroADV) was used to measure turbulent kinetic energy (TKE) at a radial limit of entrainment in the wall jet zone and the measurements were used to calculate τc of the samples. The results showed that TKE increases exponentially with increasing particle size. The τc from this study were comparable (R2 = 0.8) to the theoretical τc from Shields diagram after bed roughness scale ratio (D/ks), due to the non‐uniform bed conditions, was accounted for. This study demonstrated that JET and TKE can be used to determine τc of non‐cohesive soils. The use of JET and TKE was found to be faster and easier when compared to the conventional approach of using flumes. A relationship of TKE at the onset of incipient motion (TKEc) and samples’ D50 developed in this study can be used to predict τc of non‐cohesive soils under similar non‐uniform conditions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
52.
Lake Houston is a man-made reservoir located northeast of Houston, Texas. The purpose of this investigation was to document
suspended sediment transport, sedimentation, and resuspension in the lake with a view towards estimating the influence of
sedimentation on water quality. Sediment traps were placed in strategic locations in the lake to collect suspended sediments.
Samples were analyzed for bulk density, grain size, organic carbon, and a number of trace elements. These data were analyzed
along with meteorological data to examine those factors which regulate suspended sediment input and dispersal, and the role
of suspended sediments in controlling water quality within the lake.
Sediment input to the lake depends primarily on the intensity of rainfall in the watershed. Sediment movement within the lake
is strongly influenced by wave activity, which resuspends sediments from shallow areas, and by wind-driven circulation. The
increased residence time of suspended sediments due to resuspension allows greater decomposition of organic matter and the
release of several trace elements from sediments to the water column.
Virtually all samples from sediment traps suspended between 1 and 5 m above the lake bottom contain medium to coarse silt,
and even some very fine sand-sized material. This implies that circulation in Lake Houston is periodically intense enough
to transport this size material in suspension. During winter, northerly winds with sustained velocities of greater than 5
m/sec provide the most suitable condition for rapid (<1 d) transport of suspended sediment down the length of the lake.
Fluctuations in current velocities and the subsequent suspension/deposition of particles may explain variations in the abundance
of coliform bacteria in Lake Houston. 相似文献