Avalanche impact pressure on an instrumented structure

Full-scale experiments have been conducted on the Lautaret avalanche test site (France, Hautes-Alpes) to quantify avalanche impact pressure. A structure with a flat surface is used as a large sensor and an inverse analysis procedure is developed to reconstruct the pressure applied on this obstacle. This method is validated by numerical simulations and in-situ impact hammer tests are performed to acquire the frequency transfer function of the sensor. Experimental measurements are carried out with the device during an avalanche and are processed to quantify the impact pressure. Results show that the loading rate can reach up to 100 kPa/s with a nominal pressure of 35 kPa for an avalanche with a front velocity of around 17 m/s and a density of around 100 kg/m3. The nominal impact pressure of this avalanche, with a Froude number of around 5, is roughly consistent with the kinetic pressure estimation. Interactions between the flow and the structure form a dihedral snow deposit upstream of the obstacle (stagnation zone), modifying the shape of the obstacle and reducing the hydrodynamic drag pressure, which is nevertheless mainly depending on the velocity of the flow. Results are discussed on the basis of the drag coefficient, Cr, to the Froude number, Fr, relationship which can be expressed as Cr = 10.8 Fr− 1.3 from the data.