problems introduced by the presence of free wa-
Plan of the report
In the following sections we review the litera-
ter. For brevity, we have not considered friction
ture on descriptive and experimental studies of
between snow and other materials, acoustic prop-
snow mechanics and snow deformation, and give
erties, properties of snow in motion, and shock
our view of the current state of the subject. We
waves in snow.
conclude that the field is relatively static at present,
particularly in the area of applications to engi-
neering problems. We then argue that there is
REVIEW OF PREVIOUS WORK
little hope for improvement in the near future,
unless special efforts are made to make data on
Background
the deformational behavior of snow available to
Most of the literature on snow mechanics has
potential users in an accessible format. A prime
been summarized in reviews by Bader (1962a),
source of difficulty is that data on mechanical
Mellor (1964, 1975, 1977) and Salm (1982). We
properties and deformational behavior* have usu-
used these extensively. For discussion, we sepa-
ally been organized and presented as functions of
rate the field into two areas. The first area in-
the snow density. However, we will show from
cludes the descriptive and experimental studies
the literature that snow density is not a reliable
that established the basic ideas about snow defor-
indicator of these properties. Instead, for a given
mation and snow as a material, and efforts to
temperature and loading condition, the response
establish constitutive relationships for snow. In
to load depends primarily on the bonding and
much of this work, the objectives were to describe
microstructure, and the geometric characteristics
how snow responds to applied loads, to measure
of the grains. This was recognized in early studies
the strengths of various types of snow under dif-
of snow deformation, but developing a method of
ferent loading conditions, and to find numerical
using microstructural properties as an indicator
values of the parameters required by the various
of deformational response to load still remains to
constitutive relationships. Early experiments and
be done. We propose that this can be done by
constitutive relations were based on measure-
building a classification of snow based on a com-
ments of macroscopic deformation. Later, recog-
bination of microstructural properties and physi-
nition of the importance of snow microstructural
cal characteristics, with the classes then corre-
influences on deformational behavior led to the
lated to characteristic deformational behavior. We
second area of research: studies of microstruc-
argue that the critical microstructural properties
tural scale processes that operate during defor-
cannot be established by stereologic work (App.
mation. The purpose of these studies has been to
C). Instead, we suggest that index properties (the
describe and quantify the changes in grain and
results of tests designed to be sensitive to the
bond relationships that occur during deforma-
state of the microstructure) are the best way to
tion as the grains rearrange, fracture, recrystallize
represent the critical microstructure. We describe
or sinter, and then to use the results as the basis
several possible index tests, but suggest that a
for developing constitutive relationships for snow.
modification of a blade penetration measure of
snow hardness (Fukue 1979) may be most useful.
Constitutive equations
With a classification established, tests can be run
and parameters
to obtain stressstraintimestrength data to es-
Most of the descriptive and experimental stud-
tablish the characteristic deformational behavior
ies were done between 1930 and 1980 and are
for each class of snow.
described in the reviews by Bader (1962a), Mellor
We have limited this report to the properties
(1964, 1975) and Salm (1982). The early studies in
of dry snow in order to avoid dealing with the
western Europe were primarily motivated by the
need to understand and predict the occurrence of
avalanches, and to mitigate their hazards. Simi-
larly, the problems posed by the heavy seasonal
*We use "mechanical properties" to refer to parameters such
snow cover in parts of Japan provided the incen-
as the constants of the familiar stressstrain relationships of
tive for the systematic studies of snow properties
elastic, viscous and viscoelastic materials, or the strength in
various loading modes. The expression "deformational be-
by researchers at the Institute of Low Tempera-
havior" is intended to mean the nature of the response to
ture Science at the University of Hokkaido. In the
load in a general sense. For example, Young's modulus is a
U.S.A., the work by SIPRE and CRREL in-
mechanical property, while deformational behavior is the
vestigators between the late 1940s and continuing
bulk deformation of the material.
2
Previous Page
