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Lecture tip | Does it make a difference who hits the compression test?

News from the ÖGSL online lecture series

by Lea Hartl 01/13/2022
Silke Griesser wrote her master's thesis on force measurements in compression tests (CT) and presented the results as part of the monthly ÖGSL lectures. As usual, you can watch the video of the lecture and the subsequent Q&A session on YouTube.

The aim of stability tests is to obtain information about the fracture behavior in weak layers: Where in the snowpack does the block break and at how many impacts? Does the fracture extend through the entire block or is it only an irregular partial fracture? We then use the test results to draw conclusions about the avalanche risk, even if the interpretation is not always easy or clear.

It seems reasonable to assume that a 190cm tall person weighing 100 kilos will hit the block differently than a smaller, lighter person. But how do you quantify this? Developing a measurement system was the first part of Griesser's work, details of which can be found in the video.

Presentation:

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Results

For a more comprehensive explanation of the results, we recommend watching the presentation. Here are just a few key points noted:

  • In principle, the measured stresses in the snowpack increase if you follow the usual steps "blow from the wrist", "blow from the elbow", "blow from the shoulder". Anything else would be very surprising.

  • The tensions not only increase when switching to a different type of blow, but also within a step. This means that higher values are measured on the 10th stroke from the elbow than on the 1st stroke. This is presumably due to the fact that the snow becomes more compact as a result of the strikes and this changes the transmission of force.

  • Figures from the literature suggest that a strike from the shoulder is roughly comparable to a skier in terms of the forces acting, although there is little data that is suitable for comparison.

  • The measured stress is dependent on the depth at which the measurement is taken. The voltages become lower the deeper the sensor is in the snow. (The sensor is inserted horizontally in the CT snow block at a certain height from the ground.)

  • People with longer arms and higher body weight tend to cause higher tension when hitting the block than people with shorter arms and lower body weight. However, there are outliers and the fluctuation range is relatively high. In other words, even smaller people sometimes hit the block very hard.

  • The lower the sensor, the smaller the differences. The tension increases less with weight and arm length at greater measuring depths than further up in the snowpack.

  • The arm length and the weight of the arm have a correspondingly smaller effect if you only move your wrist. The dispersion is therefore smaller for hits from the wrist than for hits from the elbow or shoulder.

Conclusion

These results are not yet very helpful for the practical assessment of the situation on the slope, but they form an exciting basis for further investigations in this direction. The answer to the title question is yes. Griesser also emphasizes that the spatial variability of the snowpack may be a much greater uncertainty factor for the test result than the stature of the person striking the snow.

This article has been automatically translated by DeepL with subsequent editing. If you notice any spelling or grammatical errors or if the translation has lost its meaning, please write an e-mail to the editors.

Show original (German)

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