FRACTAL DIMENSIONS AND SETTLING VELOCITIES OF COHESIVE SEDIMENT FLOCS

摘要

The fractal dimension of the cohesive sediment floc in suspension is a measure of the complexity of its microscopic structure, and has a great influence on floc characteristics, such as size, density, settling velocity and breakup strength. In this study, we employed several kinds of microscopes to observe the microscopic structures of floes formed during flocculation-settling process. The sediment samples were collected from the mudflats at Huayuankou hydrometric station on the Yellow River in Henan Province, China. The experiments were carried out by three groups of different sediment concentrations(1.0, 8.0 and 12.0 kg/m~3). Digital images for the microscopic structures of the floes were obtained in the experiments and then were processed and analyzed by means of a Box counting technique to determine the fractal dimensions. The group settling velocities of the floes were estimated on the basis of the recorded data, and then were compared with the theoretical values which were calculated according to a modified Stokes formula in which the effects of the fractal structure were considered. Comparison results were discussed further in the paper as well.