Author(s): Gang Xie; Xingnian Liu; Shuyou Cao; Er Huang
Linked Author(s): Xingnian Liu
Keywords: Sediment; Non-uniform sediment; Threshold condition; Incipient shear stress
Abstract: The threshold of motion of sediment is a very important problem in river dynamics and sediment engineering. It is the foundation of theoretical researches and studies on actual project problems. Because the sizes of sediment at bed are not uniform, the forces acting on a single grain are complex. Many researchers suggest there is another force on a grain that is related to interaction of grains, in addition to submerged weight, lift force and drag force. This paper analyses flow state near bed, composition of bed materials and forces on grain, and presents the formula of grouping initial shear stress of non-uniform sediment according to equilibrium equation of rolling grain. An additional force G on a single grain is introduced in the formula, which is related to non-uniformity of bed materials. By comparison with experimental data, the formula agrees with the data well, and the comparison between the calculated results of this formula with that of Egiazaroff formula indicates that this formula is better than Egiazaroff formula. In addition, according to this formula of grouping initial shear stress of non-uniform sediment, a formula of incipient velocity of uniform sediment is established.