Interparticle Grain Size Relationships Resulting from Flocculation

Abstract

Past studies of microfabrics resulted in a considerable body of information on the internal arrangement of individual grains in a sediment. A number of workers have published their conclusions with diagrams illustrating the conceptual models they have formulated. These illustrations are a useful synthesis of observations not easily summarized by other methods of presentation due to the qualitative nature of the observations. Casagrande (1932), based partly on an earlier illustration by Terzaghi (1925), showed a honeycomb structure of smaller grains connecting larger silt particles (Fig. 12.1). A noteworthy feature is that similar sized grains everywhere appear to be separated from one another by linkages formed by grains of a different size. Pusch’s well known sketches (Fig. 12.2) also show similar sized grains within a floc never touching each other (Pusch, 1962, 1970). When several flocs come together they are joined by the smallest grains, implying that these form the strongest bonds. These drawings also bring out the fact that each relict aggregate unit or floc is composed of a large range of grain sizes. The intergrain arrangement in these diagrams is such that the effect of dividing one or a series of flocs along a random line would be to produce two parts with constituent size distributions similar to that of the whole.