I am using GrainGeo to creat different homogeneous solid packings, each consisting of ideally spherical particles. One pack only consists of particle spheres of one diameter. I use the Pile-Mode and drop the particles one after the other until they have a stable position and the process ends when the pack is filled to the rim. This procedure works well in principle. However, it turns out that the porosity increases with the particle diameter. I am not yet able to understand this result. In theory, the porosity should be the same for ideal spheres regardless of the particle diameter (densest sphere packing). Otherwise, I could still understand that the porosity decreases with the particle diameter because with larger particles the weight force prevails over interparticle forces. I have so far explained it to myself as being due to the pack size, as wall effects play a greater role with larger particles. Accordingly, for larger packings, the porosity should converge to the densest packing regardless of the diameter.

Which effects are considered for the stable minimum? Are forces such as gravity and Van der Waals forces included? Or are only geometric factors taken into account?

Thanks in advance!

Alex