Threshold Probability And Transport Laws Of Bed-load Sediment Based On Statistical Theory

The threshold probability and transport law of bed load sediment is one of the basic problems in the theory of sediment movement and the study of river dynamics,which has been studied deeply by domestic and foreign scholars.Meanwhile,sediment incipient is widely used in practical water conservancy engineering,such as scour of downstream scour pit of discharging building,scour around bridge pier,reservoir sedimentation,riverbed evolution,numerical simulation of water and sediment,etc.On the basis of previous studies,this paper studies the shape coefficient,full probability,the 3-D exposure degree of sediment particles,the distribution probability of surface sediment particles,the incipient motion velocity of on arbitrary slope and the formula of bed load transport.And the main work has been carried out in the following areas:(1)On the basis of the sediment shape coefficient proposed by Han Qiwei,the gravel material of Weihe River is selected.The four groups of sediment particle sizes are 5-10mm?10-15mm?15-20mm?20-25 mm,respectively.Each group of sediment particles is divided into three types: spherical,ellipsoid and long strip.The distribution law of sediment shape coefficient is obtained and its probability density function is approximately obeys normal distribution.Then,the influence mechanism of sediment shape on the incipient motion velocity is obtained by flume test.(2)Through theoretical analysis,and adopting sliding model,the formulas of incipient motion velocity are obtained under the conditions of arbitrary slope,curve bank slope,straight bank slope,positive and negative slope and flat slope by introducing two-dimensional sediment particle exposure degree and threshold probability.On this basis,the law of sediment incipient motion under seepage is obtained,which provides a theoretical basis for studying the mechanism of slope erosion and seepage stability.The influence of sediment particle shape coefficient and relative exposure distribution on the initial velocity of sediment was considered.(3)For bed surface sediment,the flow randomness and the relative position of bed sediment particles are mainly affected by two factors in the starting process,in which the relative position of bed sediment particles is expressed by the relative exposure degree.On the basis of(1)and(2),and the randomness of water flow and the relative position of sediment were took into account in the study of threshold probability,the full probability formula of sediment incipient motion is deduced theoretically by using the sliding starting model.Then,according to Einstein's assumption and the definition of unit width sediment transport rate,introducing the full probability of sediment,the formula of bed load transport on bed surface are obtained.(4)In view of the fact that the 2-D exposure degree and the exposure angle of sediment are based on the 2-D "round cake",and it different from the three-dimensional shape of the sediment.Therefore,the sediment particle is simplified as a 3-D sphere and a self-designed test device is used.The exposure degree and exposure angle of sediment particles in 3-D model were measured by high resolution camera and post processing software.Then a series of post-processing software,such as MATLAB,EXCEL are used to compare and analyze the test data,and the range and distribution of exposure degree and exposure angle are obtained.A new concept of the probability of sediment particle distribution in three dimensional bed surface is presented.(5)The distribution law of exposure degree and exposure angle in 2-D,3-D model are compared and analyzed,and the formula of sediment incipient motion velocity on arbitrary slope based on 3-D exposure degree and threshold probability is obtained.Adopting the theoretical analysis and experimental observation,the formula of uniform bed load transport is established based on the 3-D characteristics and the full probability of sediment incipient motion.