Retarding avalanches in motion with net structures

Steel wire rope nets have become a common protection measure against snow avalanches in Europe, as they can prevent a release in potential starting zones. A novel approach in this context, is to retard the movement of an avalanche after it has been initiated. A full scale structure, the so-called Snowcatcher, was installed and instrumented with several load measuring pins, which record the dynamic loads caused by an avalanche. The motivation of the measurements is to observe the influence of net structures on snow avalanches. In the lab, scaled granular experiments were performed in two set-ups, investigating the influence of i) the net barrier angle and ii) the mesh size of the net. For both set ups various experiments with different chute inclinations were performed. The results from measuring the front velocities and flow depths showed that higher chute angles are accompanied with both, higher flow velocities and Froude numbers. Experiments with different net barrier angles showed that the effectivity increases with higher chute inclinations. Furthermore the results indicate that different barrier angles slightly influence the effectivity, e.g. for small chute inclinations, nets perpendicular to the flow direction lead to lower effectivities than inclined nets. Experiments with different mesh sizes indicate a velocity dependency of the effectivity corresponding to a certain ratio of mesh to grain size. Smaller mesh sizes in the range of the maximal particle grain size lead to an obstruction of the net, acting as a solid barrier and therefore reaching best effectivity, notwithstanding overflows. For large mesh sizes the effectivity of the net barrier increases with a higher velocity of the flow.