Measurements on Skier Triggering

Abstract

The skier's impact is measured with load cells buried' the snow cover. The dimension of each of the five identi cal load cells is 0.5 x 0.5 m, giving an area of 0.25 m2, th thickness is 5 cm and the density about 400 kg/m3 (Schweizer et al., 1995a). Within the load cell four canti lever type transducers measure the normal and shear force Additionally, temperature and cell inclination are re corded. We presently use a data acquisition system with scan frequency of 2 kHz, giving a time resolution of O. ms (Camponovo, 1995). We started the experiments during the winter 1993-9 and up to now we performed about 60 experiments. Th measurements were realised in the.flat terrain of the study plot of the Swiss Federal Institute for Snow and Avalanch Research (SFISAR) at Weissfluhjoch, 2540 m a.s.1., abov Davos, Switzerland. To measure the skier's impact in th flat terrain is reasonable, because we are primarily inter ested in the snow cover response. The best way to ensure realistic measuring condition is to put the load cell onto the snow surface just before a The skier's load was introduced in the evaluation of th stability index by Fohn (1987). The numerical modelin by Schweizer (1993) showed that the layering of the sla seems to be crucial for skier triggering. Schweizer et al (1995a,b) studied the stress distribution in the layere snow cover and in particular the response of the sno cover in the case of dynamic loading. Since field meas urements strongly depend on weather and snow can' tions during the course of the winter, measurementshav to be done over a couple years to meet different snow cove conditions. This article represents a su=ary and updat of the previous results (Schweizer et al., 1995a,b). 5