Oblique shocks in rapid granular flows -: art. no. 077101

The interaction between rapid, free-surface granular flows and deflecting dams is investigated by laboratory experimentation and by the formulation and analysis of a shallow-layer model of the motion. It is found that uniform, downslope flows of grains are deflected to flow parallel to the barrier and that upstream of the barrier, the flow state undergoes an abrupt transition whereby its depth, velocity, and direction of motion change. These oblique shocks are investigated for a range of Froude numbers and for a range of angles between the deflector and the direction of steepest descent. The experimental results are found to be in good agreement with predictions from the shallow-layer theory. Experiments were also conducted with rapid, free-surface flows of water. They reveal not only similarities between the steady deflection patterns of the water and grain flows, but also some differences in the nature of their initial interaction. A simple interpretation for this is given in terms of the relatively high pressures that develop during the initial impact of the incompressible water with the impermeable barrier. Deflecting dams are deployed to defend against large-scale snow avalanches and these results are applied to this situation. (c) 2005 American Institute of Physics.