Influence of spontaneous percolation on apparent mass at the bottom of a Janssen granular column

The effect of spontaneous percolation on apparent mass at the bottom of granular assemblies has been investigated experimentally. Bi-layered arrangements of two types of granules which differ in size are poured in a vertical silo. In this configuration, the smaller grains are layered at the top of larger grains in order to realize percolation. Contrary to the description that apparent mass decreases for denser granular packing [L. Vanel, E. Clement, Pressure screening and fluctuations at the bottom of a granular column, Eur. Phys. J. B 11 (1999) 525-533], we find that apparent mass increases due to the increase in packing density by spontaneous percolation. This behavior may be the consequence of the development of a stronger force network in bigger particles after percolation is achieved. Furthermore, due to inhomogeneous force chains in grains, we find that the value of the product of the friction coefficient by the Janssen coefficient decreases with the increasing of saturation mass.