The settling properties of cohesive particles in still water and non-cohesive particles in suspensions of ocr hesive particles are studied by experiments. Only cohesive particles decanted from the sediment of the Yellow River depotted at Huayuankou is used throughout the experiments. When the concentration of cohesive particles is less than a certain critical value. discrete floes form during the settling process. The settling velocities of these flocs tend to be equalized to a common value. On the bests of this fact. the equivalent diameter and density of flocs are determined by measuring the settling velocities. In a certain range of concentration, an anomalous distribution of concentration along the depth is oh served. When the non-cohesive particles settle in a suspension of cohesive particles. different settling properties will result for different combinations of the two concentrations. Accordingly. five different Settling zones may by delineated. When non-cohesive particles settle through the flocculated network. with the concentration of the non-co- hesive particles less than that of the cohesive particles. then non-uniformization of the settling velocities of the non-cohesive particles is oberved. A tentative explanation has been given. Besides. when the concentration of suspension ramains unchanged. the settling velocities of the non-cohesive particles will at first increase and then decrease as the concentration of non-cohesive particles increases incessantly.
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