Study On The Characteristics Of Un-uniform Bed Load Movement

Sediment is rich in resources, also can become hazard factor. With the increase of population,the development of economy, environmental variation, the greenhouse effect, etc., the disasters(mainly geological disasters and flood disasters)，caused by the sediment directly or indirectly, aredrawing more and more human attention. A correct understanding of sediment and sedimentdisaster type and its formation mechanism, has a great significance for safeguarding thesustainable development of the regional economy.The content of sediment movement theory is very much, this study only around of thesediment movement basic issues, namely: bed load motion form, incipient motion and transportrate of non-uniform sediment. On the basis of theoretical study, combined with a large number ofexperimental data, the characteristic of bed load movement has carried on the preliminarydiscussion and analysis, the main contents and results are as follows:(1) Establish the contact-type bed load (rolling) movement theoretical model, give a briefanalysis on the movement characteristics.Depending on sediment particle force model, the sediment particles rolling motion equationsis obtained, using the numerical method, obtain the particle motion trajectory, and study thevariation characteristics of sediment motion state.(2) Establish the sediment saltation kinematic model, analysis the characteristics of saltationmotion parameters and bed load transport rateA numerical calculation method is used to solve the motion equation, this paper analyzes thesaltation parameters (saltation high, length, and velocity) statistical properties, also gain themathematical expression of movement parameters, and the bed load transport rate calculationformula. Comparing with other formulas, indicates it can reflect actual sediment motion.(3) Improve the determination method for non-uniform sediment additional resistance andincipient velocity, obtain the incipient velocity formula, which can fully reflect the characteristicsof non-uniform sediment.This article briefly explains the non-uniform sediment movement mechanism from itscharacteristics. The additional resistance coefficient was determined by the flume experiment data.The incipient velocity formula, which can reflect the non-uniform sediment coarsening, refiningprocess and exposure of bed material, was obtain by the rolling balance equation, compared withexisting formulas, it show the formula can be used to study the non-uniform sediment problems. (4)Discuss the non-uniform sediment transport law, put forward a new method to calculatethe non-uniform sediment transport rate.Based on theoretical analysis for bed load movement equation, a mathematical expression ofShields parameter is obtained. Thereby explains the difference between non-uniform sandthreshold motion and uniform sand threshold motion theoretically. The incipient velocity of coarseparticle is lower than that of uniform sand, the incipient velocity for fine particle in non-uniformsand mixture is higher than that of uniform sand.At the same time, we also get the fractional transport rate formula under the equilibriumcondition of sediment transport, the calculated value and the measured data are in good agreement,which can be applied to calculate the bed load transport rate of non-uniform sediment and uniformsand also.