Validity of the Janssen law in narrow granular columns.

We have performed experiments on narrow granular columns to test the validity of the Janssen law under such conditions. The weight at the bottom of the cylinder and the compression and movement of the packing have been measured. The apparent mass dependence on height is not in good agreement with the Janssen law using a one-parameter fit. A two-parameter fit yielded good results for the apparent mass during upward and downward movement at constant velocity of the granular column inside the enclosing cylinder. The dependence of the apparent mass on the diameter of the column does not follow the Janssen law. Rather, it depends strongly on details of the packing. A slow force relaxation was observed when stopping the translational stage after upward motion.