Pressure distribution under a two-dimensional sandpile

In the experiments about a pressure distribution under a sandpile, an interesting phenomenon was previously found. Just under the apex of a pile, a vertical pressure minimum, called a dip, may be seen. Whether a dip appears or not depends on the way grains are poured. Dip is reproduced in our numerical experiment with a distinct element method (DEM) that is a kind of molecular dynamics simulation. We choose two different methods of supplying grains and compare the results (e.g., the distributions of the resulting contact force direction, Coulomb angle distributions) as well as the pressures in order to recognize the difference between the piles with two different histories. We made sure that the Coulomb angle distribution is thought to be connected with a dip.