Comparing measurements of snow mechanical properties relevant for slab avalanche release

Benjamin Reuter,Alec Van Herwijnen,Henning Löwe,Martin Proksch,Jürg Schweizer

doi:10.1017/jog.2018.93

Abstract

ABSTRACTSnow properties relevant to the fracture processes involved in dry-snow slab avalanche release include weak layer specific fracture energy, slab elastic modulus and density. Various techniques exist to determine these snow mechanical properties, but it is presently unclear how values determined with different methods compare. In the laboratory, the 3-D microstructure of cm-sized snow samples is reconstructed by micro-computed tomography (μCT) so that density and elastic modulus can be computed. In the field, fracture energy and modulus are estimated based on particle tracking velocimetry (PTV) of the displacement field observed during propagation saw tests. Snow stratigraphy is measured with the snow micro-penetrometer (SMP) in either, field or laboratory. We compared SMP-derived properties to correspondingμCT- and PTV-derived values. Values of snow density related well toμCT results and so were SMP-derived elastic moduli related to PTV-derived values. By taking into account snow anisotropy a good relation between SMP- andμCT-derived moduli resulted suggesting the SMP-derived modulus characterizes the components of the modulus perpendicular to the axis of penetration. SMP- and PTV-derived values of fracture energy were correlated. The SMP can provide a bridge between scales and techniques, yet further improvements in signal interpretation are still needed.

Highlights

Fracture energy and modulus are estimated based on particle tracking velocimetry (PTV) of the displacement field observed during propagation saw tests
Dry-snow slab avalanche release involves a sequence of fracture processes, most importantly failure initiation and crack propagation, which eventually leads to the detachment of the snow slab (e.g. Schweizer and others, 2003)
The snow micro-penetrometer (SMP)–μCT dataset included snow density and elastic modulus calculated from μCT images; the propagation saw test (PST)–SMP field dataset comprised the elastic modulus of the slab and the specific fracture energy derived from the PTV technique (Table 3)

Summary

Introduction

Dry-snow slab avalanche release involves a sequence of fracture processes, most importantly failure initiation and crack propagation, which eventually leads to the detachment of the snow slab (e.g. Schweizer and others, 2003). The critical crack length integrates slab and weak layer properties and can be modelled using the density and the elastic properties of the slab and the specific fracture energy of the weak layer, which is the resistance to crack propagation (Sigrist and Schweizer, 2007). It is, well-known that measuring snow mechanical properties is intricate and different techniques commonly yield different results, with obvious implications for predicting snow instability

Objectives

Methods

Results

Conclusion