Effects of cubic container's wall or floor on random packing structures of spherical particles

By computer simulation, we examined how a wall or a floor of a container affects the random packing structure of a cubic aggregate of spherical particles. We constructed a model of the aggregate by sequential accumulation of spheres in a cubic box using (A) cyclic boundary conditions only in the y-direction together with random ups and downs of the box floor to estimate the wall effect and (B) the conditions in both of the horizontal directions to extract the floor effect. Using the obtained packing data, we estimated the "area porosities" and cumulative frequencies of the diameters of circles appearing on some cross sections created by cutting the aggregate at different levels, both as functions of distance from the wall/floor. From these results, we found that the surface effect seems to extend as deep as 2.5 particle diameters from the wall and approximately 4.5 diameters from the floor.