Influence of humidity on granular packings with moving walls

Laboratoire FAST, UMR CNRS 7608, Bât. 502, Université Paris XI 91405 Orsay Cedex, France

Received: 28 January 2004
Accepted: 27 July 2004

Abstract

A significant dependence on the relative humidity H for the apparent mass () measured at the bottom of a granular packing inside a vertical tube in relative motion is demonstrated experimentally. While the predictions of Janssen's model are verified for all values of H investigated (), increases with time towards a limiting value at high relative humidities (), but remains constant at lower ones (). The corresponding Janssen length λ is nearly independent of the tube velocity for but decreases markedly for . Other differences are observed on the motion of individual beads in the packing: for , they are almost motionless, while the mean particle fraction of the packing remains constant; for the bead motion is much more significant and the mean particle fraction decreases. The dependence of these results on the bead diameter and their interpretation in terms of the influence of capillary forces are discussed.