The forces depend on the weights, pressure and space available. You can predict how fast things will move through fluids with such as this work on sand settling through water. But the real forces and particle sizes will likely be different in nature. The best way to test such effects is to measure them. The main ingredient is silica for all glass.
Softer glass has soda lime and potash, the later acts as a flux.
See my other web site below. So based on this, the 200 sieve is 75 microns wide. Of course you could refine these numbers by measuring numbers of grains in a square inch say pressed up against the side of a glass then taking the square root for the average length of a grain. I finally found a sight on sand-it was not easy to find but it is very helpful. I am doing a science fair project on whether the size of the sand particle used to make a brick will affect the brick's strength.