the sinkage (volume of compacted snow) there
means used to routinely generate strong snow
has yet to be a reliable mathematical description.
pavements. Using additives has always been
Richmond et al. (1995), Richmond et al. (1990),
popular; however, these rarely provide a long-
and Blaisdell et al. (1990) have tried many empiri-
term benefit (Lee et al. 1989) Studies of snow
cal and analytical possibilities but acknowledge
pavement technology at the time of those reports,
no better than 25% accuracy on average. Some
and continuing to now, were largely empirical.
vehicle types show much larger divergence be-
Since Abele's review, there have been a few
tween measured and predicted resistance. Mobil-
advances. A successful experimental effort was
ity measurements can even differ widely for snows
completed to build a snow runway on deep snow
that have the same density and similar physical
at the Australian Antarctic base Casey (Russell-
characteristics. Closer inspection usually shows
Head and Budd 1989). Compaction in layers was
that these differences are the result of differences
used to build up a pavement of snow that with-
in the internal strength of the snows brought on
stood proof rolling by a cart that simulated a
by variable compaction or sintering histories. Pen-
loaded C-130 Hercules aircraft. A prototype snow
etrometer and direct shear tests have occasionally
runway was also produced in the Ross Sea area
been used in an attempt to document snow
of Antarctica using sequential compaction efforts
strength. However, these are isolated attempts
governed by seasonal ambient temperature
and none have been shown by themselves to ac-
changes (Blaisdell et al. 1992). This group took
curately determine expected snow/vehicle behav-
advantage of warming temperatures to place in-
ior. Thus, numerical models have begun to ap-
creasing loads on thin (10-cm) snow layers via a
pear (Mohamed et al. 1993 and Xu et al. 1993).
heavy pneumatic tire roller (glacial ice provided
These models hold promise for greater accuracy
a rigid reaction base for the roller). Rest periods
and insight in describing mechanical interaction
of at least 24-hours were interspersed between
between the snow and a vehicle's running gear.
compaction rolling to allow new interparticle
bonds to form. Densities of about 600 kg m3 were
However, these models are currently limited by
the need for complex snow load response data
the maximum attained and strengths adequate to
that in general does not exist. For use, sophisti-
support a test landing by C-130. Lack of near-
cated and case-specific tests are performed to ob-
melting temperatures and the ever-present strong
tain these data. No systematic library of these test
temperature gradient limited bond development
data is maintained.
and thus the ultimate strength of the snow.
Lang et al. (in press) performed a series of tests
using a variety of snow processing tools. They
Snow roads and runways
The most practical, and perhaps widespread
used snow tillers, of the type used by the ski
application of snow mechanics is for the creation
industry for reconstituting ski slopes, and a snow
of snow roads and runways. Animal herds pro-
blower. Minimal compaction was done, in con-
duced the first snow "roads," having recognized
trast to the emphasis in all prior studies. This
the reduced energy expenditure associated with
study appears to be the first to attempt to identify
traveling along narrow compacted paths. Humans
the intergranular processes occurring as a result
traveling over snow-covered terrain followed this
of processing and subsequent aging. Using stere-
approach and, using snow shoes, skis, or boots,
ology and mechanical index tests (penetrometer),
packed trails to increase travel efficiency. Me-
Lang et al. (1996) tried to correlate intergranular
chanical techniques were sought by humans to
bond and grain size changes with strength
produce robust snow roads beginning when beasts
changes. They also correlated these changes with
were harnessed to conveyances and continuing
ambient temperature changes.
when mechanical locomotive devices evolved.
The study by Lang et al. (in press) was success-
Upon the refinement of motor vehicles and the
ful in producing some of the strongest snow pave-
advent of aircraft, the focus moved from modify-
ments ever recorded. However, snow strength
ing the snow to removing the snow. Today, only
was difficult to quantify, owing to the difficulty
persons interested in off-road travel and polar
in using a penetrometer in hard, dense snow.
operators still required snow roads and runways.
Larger scatter in the data were apparent, and oc-
Abele (1990) produced a thorough review of
casionally, the penetrometer could not be forced
the topic of snow roads and runways. His review
into the snow. In addition, it was found that the
highlights the fact that compaction and snow mill-
current state of stereological software is inad-
ing (with snowblowers) were the only successful
equate for making determinations of snow's me-
9
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