ABSTRACT
Weight measurements at the bottom of a quasi-bidimensional vertical sheet of cohesionless static grains are reported. The grains are held between two concentric cylinders, which allows us to set boundary conditions for the sheet to either periodic or fixed ones. Weight saturation is examined as the height of the piling increases. In case of fixed boundary conditions, measurements exhibit huge relative fluctuations. Such a level of fluctuations is consistent with the hypothesis that friction forces acting on grains at the boundary are not necessarily oriented in the upward direction but can also be oriented downwards. A modified Janssen description is presented. Our argument allows us to justify why fluctuations of weight measurements in our bidimensional system are much larger than those usually observed in three-dimensional granular systems.
