泥沙的群体沉降—两种典型情况下非均匀沙沉速计算

Settling of Particles in Suspension-Two Typical Cases in Calculating the Settling Velocity ot Nonuniform Sediment

本文讨论了泥沙群体沉速的计算公式、着重分析了非均匀沙沉速确定的两种典型情况:即水流挟沙力计算中非均匀沙的沉速确定,及浆体浓缩或浑水澄清中非均匀沙沉速计算.对于前者颗粒组成中较粗部分对沉速起主要作用,对于后者,颗粒组成中的细颗粒对沉降起主导作用.企图从非均匀沙中找出平均粒径或中值粒径作为代表粒径来计算群体沉速,往往难以符合实际.本文从实际应用角度出发,分析了上述两种典型情况下非均匀沙沉速的确定方法,并有实例验证说明.

In this paper the formulas of settling velocity for particles in suspension are dicussed. Two typical cases in determining the settling velocity of non-uniform sediment are analyzed: the settling velocities of nonunifprm sediment in calculating the sediment carrying capacity of the flow and that in the concentrated slurry or muddy water. In the former case the coarse par- tides in composition play an important role to mean settling velocity, and in the later case the fine particles in composition are important to the settling property. The parameters of ∑△pidi2 and ∑△pi/di as the characteristics of nonuniform sediment in calculating the settling velocity for above mentioned cases are presented in the paper. It is indicated that determining settling velocity of nonuniform sediment by means of d56 or d as characteristic particles will lead to noticeable errors. The critical conditions of settling by discrete floes and by flocculated network are also analyzed in the paper.