Physical modelling of the interaction between powder avalanches and defence structures

In order to better understand the interaction between powder snow avalanches and defence structures, we carried out physical experiments on small-scale models. The powder snow avalanche was simulated by a heavy salt solution in a water tank. Quasi two-dimensional and three-dimensional experiments were carried out with different catching dam heights. For the reference avalanche, the velocity just behind the nose in the head was greater than the front velocity. For the 2D configuration, the ratio Umax/Ufront was as high as 1.6 but depended on the height. For the 3D configuration, this ratio differed slightly and was even greater (up to 1.8). The vertical velocity rose to 87% of the front velocity for the 3D simulation and 66% for the 2D simulation. The reduction in front velocity due to the presence of dams was an increasing function of the the dam height. But this reduction depended on topography: dams were the more effective on an open slope avalanche (3D configuration). The ratio Umax/Ufront was an increasing function of the dam's height and reached a value of 1.9. The obstacle led to a reduction in vertical velocity downstream of the vortex zone.