Measurements and analysis of full-scale avalanche impact pressure at the Vallée de la Sionne test site

Abstracts pressures of eight snow avalanches measured at the Swiss avalanche test site Vallée de la Sionne are reported. Avalanche typologies varied between dense and powder. Measurements were performed on obstacles of different shape and dimension. High-frequency pressure sensors were mounted on a 20 m high tubular pylon and on a 5 m high steel wedge. To interpret the influence of sensor dimension on impact pressure measurements, the total pressure exerted on the steel wedge was recorded using two bi-axial sensors and compared to the pressure recorded by the high-frequency sensors. On a small concrete wall, a 1 m2 pressure plate mounted with 4 load-gauge bolts measured normal and tangential forces. Along the tubular pylon (between 1–6 m above ground) optoelectronic sensors recorded the avalanche flow velocity. Flow depths were measured by mechanical sensors. Analysis of high resolution impact forces in combination with velocity measurements allowed us to reconstruct the flow structure. We combined impact pressure with observation on avalanche structure to obtain load distribution and size effects for different avalanche typologies. Measured pressures are compared to the existing Swiss calculation procedure. It is shown that actual calculation formulas are not able to properly reproduce the measured pressure values and the load distribution.