On the statics of silos

The distribution of vertical pressures in a silo filled with grains has been described long ago by Janssen, with two basic assumptions, one on. internal behavior; and one on wall friction. The phenomenological coefficient K-J of Janssen, describing the internal behavior; has been estimated, using apr elastic description of the compression (P. E.). We discuss here ii the precise definition of material displacements ii) the wall function: this is fully mobilised only if the local displacement is larger than a certain 'anchoring length' Delta (of order one micron). From this, we define a characteristic height H*(Delta), between which the Janssen picture fails. (C) Academie des Sciences/Elsevier, Paris.