悬移质挟沙能力水槽试验研究

Experimental studies on carrying capacity of suspended load

利用0.03 mm黄土和卵石碾成粉末制成的0.03 mm人工沙,0.06 mm黄土,0.13 mm黄沙,共计4种沙样,在槽长33 m,宽1.25 m,深0.5 m,可以调节坡度的钢板水槽内按系统试验方法进行饱和含沙量试验.进槽含沙量较高,含沙量沿程降低,底部泥沙淤积,形成沙波,待水流中含沙量在1～2 h内保持不变时,定义为极限或饱和含沙量.每次试验测定含沙量、流速、水深、水面比降、悬沙颗粒级配、槽底泥沙淤积比降、槽底泥沙颗粒级配等数据,探求细粒泥沙在一定条件下的饱和悬沙含量,即悬移质挟沙能力.试验观测及理论分析表明,在恒定均匀水流条件下,浑水悬沙饱和含沙量取决于悬浮泥沙的沉速、水流流速、水深、水力半径、水面比降、底部淤沙粒径各水沙因子.在寻求挟沙能力经验公式中,除水流本身紊动挟沙外,还应考虑底部含沙量,淤沙粒径,包括糙率(沙波高度)和底沙运动,对输沙的影响,所求得的经验公式包括Velikanov公式诸因子以及底沙受水流剪力流速和底沙粒径的比值的因子.天然渠道资料检验说明了公式的适用性.

Experiments on the carrying capacity of suspended load were conducted in a flume,33 m long,1.25 m wide,and 0.5 m deep,with adjustable bed slopes.The objective of the experiment is to determine the suspended sediment carrying capacity under specific flow regime and sediment conditions.Four sediment samples of loess and silicon powder（d50=0.03 mm）,sand of d50=0.06 mm and 0.13 mm were used in the tests.Systematic test methods were adopted for arranging the test runs.For each run with specific fluid regime,the inflow with excess sediment concentration was introduced into the flume and the sediment concentration was decreasing with time until an extreme sediment concentration in steady state was maintained at least for one to two hours.This sediment concentration is defined as the limit or saturation concentration of suspended sediment in sediment-laden open channel flow. During each run of the tests,flow discharge,velocity,water depth,water surface slope,bed deposit slope,mean sediment concentration,sediment particle size distribution,sand wave height of deposited sediment on the bottom,particle size distribution of bottom deposits were measured.Also,vertical profiles of sediment concentration and vertical profiles of sediment particle size were measured for several runs. Analysis indicated that under the steady uniform flow laden with suspended load,the magnitude of limit concentration varied with velocity and water depth,particle size of sediment in transport and bed deposit characteristics. To determine the suspended sediment carrying capacity formula,the mean concentration in weight per cent was selected as a nondimensional number,and the flow regime with turbulence intensity was considered as a main factor to carry sediment,together with the boundary conditions of the suspended load and bed load movement within the layer over the deposit bottom. Empirical formulas of the suspended sediment carrying capacity were developed by adopting the Velikanov parameter and the correlation parameter between shear velocity and mean diameter of sediment deposits on the bottom,as shown in Eq.（19） and Eq.（20）.The former empirical formula was calibrated by the field data measured in an irrigation channel.