When avalanches hit objects

Ever since avalanche research began, scientists have been investigating the pressure that avalanches exert on obstacles. Until now, calculations have been based on models. While these accurately represent fast, dense flow avalanches, they can underestimate the pressure from slow-flowing wet snow avalanches. However, in practical applications – designing suitable protective measures for buildings, for example – it is important to consider a range of avalanche flow types. SLF researchers therefore set about investigating the processes that occur in the interaction between obstacles and avalanches with different flow types, and have developed a new method for calculating avalanche pressure on obstacles. To do this, they had to consider a range of factors influencing avalanche pressure, such as the avalanche's behaviour during the flow process and the cohesion of the avalanche snow. With the new method it should now be possible to determine pressure values more precisely.

The physical processes involved in the interaction between avalanches and obstacles were investigated using the discrete element method (DEM). An avalanche is modelled as a granular flow that has very different flow properties depending on its composition and temperature. A slow-moving wet snow avalanche builds up more pressure near the ground than at the surface because the pressure depends on the weight of the snow above. Furthermore, avalanche pressure increases proportionally to the square of the velocity, which is a particularly relevant factor in faster avalanches. The researchers used computer simulations to model collisions between numerous virtual avalanches and obstacles of different shapes. From these simulations they derived pressure calculation methods, which they then compared with measurements from real-life avalanches hitting obstacles.