familiar (e.g., International Classification of Seasonal
problem, locate information on the expected de-
Snow on the Ground [Colbeck et al. 1990]), and
formational behavior for the conditions of the
measures of mean grain size, grain size distribu-
problem, and have access to numerical values of
tion, snow crystal morphology, bulk snow struc-
the parameters for constitutive relationships that
ture, and density are appropriate. To categorize
are applicable. Our suggested approach to filling
snow types by their deformational behavior, the
this need is given in the next section.
classification should also include information on
microstructure and bonding that most influence
deformational processes. Unfortunately, there are
AN APPROACH TO SNOW
no suitable variables that provide unambiguous
MECHANICS RESEARCH
microstructural information (App. C) so it will be
necessary to use index properties that depend on
Introduction
microstructure instead. These are not true prop-
We believe that for the present, the goal of
erties of the material, but are the numerical re-
engineering snow mechanics research should be
sults of simple tests that are correlated with the
to develop a comprehensive source of data on the
deformational behavior of interest.
mechanical properties of interest and analytic tools
that can be used to solve engineering problems.*
Once a classification is established, the
deformational behavior of each class of snow can
This would make it possible for investigators to
be characterized. This would involve collecting
1) identify the types of snow involved in a par-
representative stressstraintime-strength data for
ticular problem, 2) anticipate the response of that
samples of snow from each class in different load-
snow to applied loads under the conditions of the
ing modes and rates. When available over a suffi-
problem using various measures or indices of the
cient range of conditions, the data would be use-
mechanical property of interest (see Abele 1990),
ful for selecting constitutive relationships and
3) guide the selection of an appropriate constitu-
determining their parameters. Initially, the test-
tive relationship and test its usefulness, 4) find
ing might be restricted to a representative range
numerical values of the parameters of that rela-
of conditions to demonstrate the styles of defor-
tionship, and 5) determine the strength of snow
mation for each class of snow.
in different loading modes if that is relevant to
the problem. This clearly requires new data on
snow in a format that currently does not exist in
Establishing independent
the literature. To provide it requires that a classi-
variables or index properties
fication of snow be developed relating the physi-
for snow microstructure
Index properties are the results of simple tests
cal characteristics of snow (e.g., grain size, grain
that are correlated with the deformational behav-
size distribution, grain shape, density and other
ior for snow. According to Salm (as cited in
measures) to specific deformational behavior (e.g.,
Oakberg 1982) in order for the results of some test
compressive strength and deformation under
to be useful as an index property it is necessary to
load) that operate over known ranges of en-
establish the following:
vironmental conditions. The data on the defor-
1. The results of the test depend on the micro-
mational behavior will be needed to select appro-
structure of the snow, although it is not
priate constitutive relationships and their
necessary to know exactly how that depen-
parameters for various snow types under the con-
dence arises.
ditions of specific problems.
2. The results are repeatable and can be done
The classification must be based on features
in a field setting, either in-situ or with por-
that can be determined objectively and repeatably
table equipment that minimizes the need to
by direct observation or by simple measurements.
handle the snow.
The physical characterization of snow should be
3. The numerical range of the test results is
large enough to discriminate across the
scope of possible seasonal snow types as
*A mechanical property of interest is defined as that property
they appear in various environmental con-
most relevant to a particular snow mechanics application (e.g.,
high rate uniaxial compaction for impact and explosive prob-
ditions.
lems, compaction and shear deformation for mobility and ava-
4. The test results can be shown to vary sys-
lanche release studies, creep deformation behavior to deter-
tematically with the mechanical properties
mine loads on snow fences and structures, and other data useful
by demonstrating, for example, that they
in dealing with a particular engineering problem).
11
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