Study On Laws Of Transport For Non-uniform Sediment

The transport character of non-uniform sediment is one of the most important problems in the field of sediment mechanics and river dynamics. It is still a challenge problem because of the unsteady and random characteristics in its physical process. On the basis of the comprehensive review of the study achievements for this problem, the transport characters of non-uniform sediment has been studied systematically by combination theory with experiments. By means of the analyses of the instantaneous velocity of flow, the incipient motion criteria of sediment, the relative exposure degree of the particles of bed material lying on the surface of river bed, as well as the concept and mathematical expression of the additional mass force or equivalent diameter, etc., the analyses and experiment study on laws of incipient and transport for non-uniform sediment has been conducted, and the main results are as follows:In consideration of the fluctuation of flow, the relative degree of exposure of the bed material, and the standard of incipient motion, the concept and its expression for additional mass force and equivalent diameter for single particle lying on the river bed have been put forward according to method of mechanics and geometry. The formula for calculating the dimensionless critical shear stress of non-uniform sediment has been established by using the method of combining the classical mechanics with statistics. And then transformed to the formula for calculating the critical flow velocity for incipient motion, which contains parameters such as standard of incipient motion and relative degree of exposure ofbed material, so it is more reasonable for the formula in its application for practical calculation.The absolute exposure degree A and relative exposure degree, ,, of bed material have been defined, and the determination of their value has been analyzed. The result indicates that the value of , is not a constant, but located in a domain with a range of from zero to one. The determination of the value of coefficient in the formula for calculation the criteria of incipient motion for non-uniform sediment is mainly by means of theory analysis and related calculation but not by the regression analysis. The minimum dimensionless critical shear stresses of non-uniform sediment at weak motion status and at middle motion status have been established as 0.020 and 0.029 respectively. According to the concept of the equivalent diameter, a kind of calculating procedure for the bed roughness dimension k*. in the formula for calculation the flow velocity has been obtained.The formula for calculating the transport rate of bed load of non-uniform sediment has been proposed. The transport rate is decrease with the increase of ?relative exposure degree, of bed material at the same incipient motion status. And it is decrease with the decrease of flow condition while the flow shear stress is bigger than that of the maximum diameter at the critical incipient motion condition. The condition and formula for calculating the maximum diameter, dCmax of incipient motion, as well as the method for calculating the size distribution of bed load for equilibrium condition based on the probability of the duration rested on river bed for particles of bed material less than dcmax have been put forward.The general formula for calculating the size distribution of stable armoring layer has been presented. Difference methods are obtained according to the values of index of the general formula. The method for calculation the size distribution using this formula is simple, and the formula can calculate the bed armoring material according to the original bed material size-distribution and its water condition.Results above mentioned have been verified with field or laboratory experiment data.