Dynamical Janssen effect on granular packings with moving walls
  Apparent mass measurements at the bottom of granular packings inside a vertical tube in relative motion are reported. They demonstrate that Janssen's model is valid over a broad range of velocities v. The variability of the measurements is lower than for static packings and the theoretical exponential increase of the apparent mass with the height of the packing is precisely followed (the corresponding characteristic screening length is of the order of the tube diameter). The limiting apparent mass at large heights is independent of v and significantly lower than the static value. 
Yann Bertho, Frederique Giorgiutti-Dauphine and Jean-Pierre Hulin