On the statics of silos

The distribution of vertical pressures in a silo filled with grains has bee n described long ago by Janssen, with two basic assumptions, one on. intern al behavior; and one on wall friction. The phenomenological coefficient K-J of Janssen, describing the internal behavior; has been estimated, using ap r elastic description of the compression (P. E.). We discuss here ii the pr ecise definition of material displacements ii) the wall function: this is f ully mobilised only if the local displacement is larger than a certain 'anc horing length' Delta (of order one micron). From this, we define a characte ristic height H*(Delta), between which the Janssen picture fails. (C) Acade mie des Sciences/Elsevier, Paris.