200
results indicate that seismic velocity (or the dy-
namic elastic moduli calculated from the velocity
Density (kg m 3 )
data and the density) is a potential index prop-
350
erty.
420
480
SNOW HARDNESS
Hardness, as indicated by a penetrating cone
(e.g., Swiss Rammsonde, Russian AARI penetrom-
100
eter), flat plate penetrometer (Kragelski 1949) or
by the hand-hardness scale (de Quervain 1950),
has been used for many years as an index param-
eter in a semi-quantitative sense. Quantitative in-
terpretations have been hampered by difficulties
in interpreting the results of measurements with
these devices because the results depend on the
shape of the penetrometer, the size of penetrom-
eters of the same shape (Kragelski 1949) and other
0
20
40
60
variables. Abele (1963) attempted to derive a quan-
Blade Penetration Force (N)
titative correlation between Rammsonde hardness
Figure D3. Uniaxial compressive
and the uniaxial compressive strength of snow
strength of snow samples vs. blade
but was not successful. Later, Waterhouse (1967)
penetrating force (from Fukue 1979).
reanalyzed Abele's data using alternative ap-
The linear relationship indicates the
proaches but was still not able to establish a reli-
potential value of the blade penetrating
able correlation. He concluded that his inability
force as an index property.
to account for the structure of the snow was a
major reason for the lack of success. In fact, Gubler
analogy, that it might be useful to experiment
(1975) concluded that it is not possible to define a
with penetrometers in the form of thin-walled
unit of hardness that is independent of the in-
hollow tubes.
strument used to measure it. However, if it is
Kuvaeva et al. (1967) described another pen-
possible to establish a relationship between the
etration technique but, unfortunately, without giv-
nature of the bonding in a range of snow samples,
ing the dimensions of the equipment. They pushed
and the hardness of those samples as measured
a small spherical penetrometer into snow samples
by any particular instrument, then the hardness
up to some value of a parameter they define as
values as determined by that instrument could be
the hardness, H (see Fig. D4). They then allowed
useful as an index parameter.
the penetrometer to settle further under its own
Snow hardness is relatively easy to measure in
weight and calculated H at a series of later times,
the field and for that reason it is worth seeking a
using the weight and dimensions of the penetrom-
measurement of that type that can be quanti-
eter and assumptions about the manner in which
tatively related to the snow structure. A test that
the displacement was partitioned between differ-
may be useful for the purpose is the measure-
ent mechanisms. Eventually, the hardness became
ment of the blade penetration force as suggested
asymptotic to some value, designated as H∞, which
by Fukue (1979). He measured the force required
was presented in a table along with the tensile
to push a thick blade into a snow sample at a
and shear strengths of the samples and informa-
constant rate and then showed that the results
tion on grain sizes and bonding. The samples
were related to both the bonding between grains
were of different densities and grain sizes, and
and the uniaxial compressive strength (Fig. D3).
the temperatures varied through the tests. How-
Similarly, Kovacs (1976 and pers. comm.*) noted
ever, the plot of H∞ against the values for the
that the resistance to driving hollow piles in polar
strength measurements (Fig. D4) shows that the
snow was closely correlated with the uniaxial com-
relationships may be linear, which suggests that
pressive strength of the snow. This suggests, by
this technique should be investigated further as a
possible index test.
*A. Kovacs, CRREL, personal communication 1992.
34
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