Europhys. Lett.
Volume 67, Number 6, September 2004
Page(s) 955 - 961
Section Electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics
Published online 01 September 2004
Europhys. Lett., 67 (6), pp. 955-961 (2004)
DOI: 10.1209/epl/i2004-10157-x

Influence of humidity on granular packings with moving walls

Y. Bertho, Th. Brunet, F. Giorgiutti-Dauphiné and J.-P. Hulin

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

(Received 28 January 2004; accepted in final form 27 July 2004)

A significant dependence on the relative humidity H for the apparent mass ( $M_{\ab{app}}$) 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 ( $25\%\leq H\leq
80\%$ ), $M_{\ab{app}}$ increases with time towards a limiting value at high relative humidities ( $H\ge 60\%$), but remains constant at lower ones ( $H=25\%$). The corresponding Janssen length $\lambda$ is nearly independent of the tube velocity for $H\ge 60\%$ but decreases markedly for $H=25\%$. Other differences are observed on the motion of individual beads in the packing: for $H=25\%$, they are almost motionless, while the mean particle fraction of the packing remains constant; for $H\ge 60\%$ 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.

45.70.-n - Granular systems.
68.08.Bc - Wetting.

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