COMPARISON AND COMPLEMENTARITIES OF AVALANCHE PRESSURE MEASUREMENTS: PIEZO-ELECTRIC LOAD CELLS AND DEFORMATION BASED PRESSURE DECONVOLUTION

ABSTRACT. The impact pressure of snow avalanches have been measured at the Vallée de La Sionne experimental test site using two different types of sensors. The first sensors consist of traditional piezo-electric load cells, with area of 80 cm2 (diameter 10 cm), installed on the hillside of an instrumented pylon. A second “mechanical ” type of sensors consist of a 125 cm2 (5 x 25 cm2) steel cantilever beams installed to the side of the pylon at different heights and extending into the avalanche flow. The beams are equipped with high precision strain gages to record the deformation histories during the loading by the avalanche. Pressure is extracted from measured deformations by deconvolution and the cantilever’s frequency response function (FRF). The FRF is calculated from an Euler-Bernoulli beam model and validated by impact hammer in-situ tests. Pressures measured in the same avalanche by both sensors are compared and discussed in terms of sensor form, location and some other relevant parameters. As the two sensors are located at the same elevation and pair-wise close to each others having their “force sensing ” surfaces differently oriented with a deviation angle of 23 degrees, it turned out that the two measurements can be combined to retrieve a rough estimate of average resultant force vector acting on a avalanche-snow control volume in the vicinity of the sensors. We estimate the modulus and the orientation of the force and discuss changes in these variables for different flow regimes