| Nearly all granular flow models have a maximum value for the friction
and therefore predict that flows on steep slopes will accelerate at a
constant rate until the interaction with the ambient fluid becomes
important. This prediction has not been tested by previous work, which
has focused on relatively low slope angles where steady, fully
developed flows occur after short distances. We report on experiments
where we investigating flows over a much greater range of slope angles
30-50 degrees and flow depths 4-130 particle diameters with up to
20kg/s of sand flowing steadily. The data suggests that friction can
be much larger than the mu(I) rheology or kinetic theories predict
and suggest and that there may be constant velocity states above the
angle of vanishing hstop. |