  We investigate the effects of lateral walls on the angle of movement and on
the angle of repose of a granular pile. Our experimental results for beads
immersed in water are similar to previous results obtained in air and to recent
numerical simulations. All of these results, showing an increase of pile angles
with a decreasing gap width, are explained by a model based on the redirection
of stresses through the granular media. Two regimes are observed depending on
the bead diameter. For large beads, the range of wall effects corresponds to a
constant number of beads whereas it corresponds to a constant characteristic
length for small beads as they aggregate via van der Waals forces.
