Sediment particle movement for different packing patterns under varying channel slope and discharge conditions
Loading...
Files
Date
2018-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
Sediment particle movement depends on not only the discharge and surface topography but also on the inherent properties of sediment particle including its shape, size, specific weight apart from their orientation. The shear force exerted on a sediment particle by flowing water plays a dominant role in deciding the rate of movement. The movement of sediment particles starts only when the shear stress acting on the particle is more than the critical shear stress. A number of studies have been conducted to study initiation of particle known as the condition of incipient motion and critical shear stress. Mostly, these studies have been conducted considering sediment particle as uniform and spherical which are never met in practice. In case of non-spherical and irregular shaped particles their orientation becomes a deciding factor for the shear force acting on the particle as it varies with changing orientation under similar conditions. Similarly, in case of non-uniform sediment material, the packing pattern of the sediment particles also plays a dominant role in deciding the magnitude of acting shear force and their movement behaviour. This study was conducted to study the effect of sediment particle packing pattern on their movement speed under varying discharge and channel slope conditions. Laboratory experiments were conducted using 6 m long slope adjusting hydraulic tilting flume on artificially constructed regular shaped sediment particles. For this purpose, sediment particles of three different sizes were constructed in the laboratory and designated as P, Q and R. These particles were arranged in different packing patterns on the bed of the flume and particle movement speed were observed for selected packing patterns with five different discharges i.e.11.1 l/s/m, 15.3 l/s/m, 19 l/s/m, 23 l/s/m, and 26.7 l/s/m, and three different channel bottom slopes of 1%, 2% and 3%. In this way the experiment was conducted in total for 405 runs for different packing patterns, slope and discharge conditions. On the basis of the analysis of observed data, it was observed that in case of patterns 1R3, 2R3 and 3R3, the maximum movement of 78.61 cm/s was observed in 1R3 pattern at 3% land slope and the minimum movement was found to be 30.14 cm/s for 3R3 pattern at 1% channel slope. The maximum movement of Q particle was found to be 68.32 cm/s for 2Q3-2P3 pattern and 62.27 cm/s for 2P3-2Q3 pattern with a discharge of 26.7 l/s/m at 3% land slope. Similarly, the maximum movement speed of R particle was observed to be as 81.56 cm/s for 2 (1R3-1P3-1Q3) pattern which came down to 79.09 cm/s for 2P3-2Q3-2R3 and 78.14 cm/s for 2(1Q3-1R3-1P3) patterns at 3% channel bottom slope for a discharge of 26.7 l/s/m. In general, however, the magnitude of shear force, increased with increase in discharge for a particular packing pattern at a slope. Similarly, for a given discharge, the shear force increased with increase in channel slope. However, it was observed that for a given discharge by changing packing pattern of particles, the exposed area changed and the shear force and particle movement changed accordingly.
Description
Keywords
null