Novel aspects on the segregation in quasi 2D piles

We present the results of an experimental study of granular segregation on a large number of rectangular grain piles built by dropping simultaneously glass beads of two different sizes. During the construction process, we control the height of the injection point, the amplitude and velocity of its displacement and the injection flow rate for each kind of grain. The final spatial distribution of the grains is determined by a quantitative image analysis. A phase diagram of the mixing state as a function of the experimental parameters is presented along with a quantification of the different types of segregation patterns. Contrary to the assertions of other authors, we clearly demonstrate here, that stratification phenomena may be observed even for beads with the same round shape but a different size. We also find that the free fall height of the grains, the ratio between the discharged masses of the different types of grains and the amplitude of the horizontal motion have the greatest influence on segregation.

We study experimentally the segregation of piles built by dropping beads of two sizes. A wide range of parameters is evaluated. A state diagram for segregation -mixing is determined. Suitable indices are measured to study segregation vs. mass ratio, mLS and height, h. State diagram for the grain size ratio 3:1.M, mixture; B, bands; SM, segregation-mixture; SB, segregation-band.Figure optionsDownload as PowerPoint slideHighlights
► Systematic study of segregation patterns in piles with two different grain sizes.
► Injection point and mass ratio can be varied through a versatile experimental set-up.
► Determination of a state diagram for segregation–mixing.
► Definition and measurement of two suitable segregation indices.
► Stratification is present although the grains only differ in their sizes.