Measurement of Fracture Mechanical Properties of Snow and Application to Dry Snow Slab Avalanche Release

Summary

Snow specimen before and after a three-point-bending test. With this test it was possible to determine the fracture toughness of snow in mode I. (Specimen dimensions: 50 cm x 20 cm x 10 cm). Click on image to enlarge.

Cutting along the weak layer of an isolated snow block on a slope. Based on this experiment, the critical energy release rate for fracture propagation in a weak layer was determined. Click on image to enlarge.

A dry snow slab avalanche is released by a sequence of failure processes in the snow cover. When a weak layer in the snow cover is damaged over a certain area, the weak layer starts to fail progressively in slope parallel direction. This shear failure disconnects the overlaying slab from the basal layer. Finally, a tensile fracture occurs in slope normal direction across the layering which releases the slab. For a better understanding of these mechanisms a well founded understanding of the fracture mechanical properties of homogeneous and layered snow is essential.

The aim of this work was to investigate the fracture mechanical properties of snow under tension (mode I) and under shear (mode II) with homogeneous and layered snow samples on the basis of experiments in the cold laboratory and in the field and to relate the results to dry slab avalanche release. The experimental work was structured in three groups of fracture experiments: experiments in mode I with homogeneous snow samples in the cold laboratory, experiments in mode II with layered snow samples in the cold laboratory and mode II experiments with in-situ snow beams in the field.

By applying new test methods to snow and acquiring a considerable data set of fracture mechanical properties of snow in laboratory and field tests, it was possible to improve the knowledge and the understanding of the fracture mechanical behaviour of snow.

Download

• PhD thesis of Christian Sigrist, July 2006 (PDF, 5.33 MB)

Participants

• Christian Sigrist (phD student)
  
• Dr. Jürg Schweizer (Co-Supervisor)
• Prof. Dr. Jürg Dual, IMES / Mechanics, ETH Zürich, Zürich, Switzerland (Supervisor)
• Dr. Hans-Jakob Schindler, Mat-Tec AG, Winterthur, Switzerland (Co-Supervisor)

Contact

• Jürg Schweizer