We also need laboratory-based experiments to
CONCLUSIONS
provide basic information about the impacts of
Data collected from 8 December 1995 to 16 July
soil moisture on soil compaction, freezethaw
1996 document the general smoothing of tank rut
deformation, and the effects of thawing on soil
geometry over the seven-month period. How-
erodibility. In light of the results of this pilot study,
ever, large variation in the amount of smoothing
future work at the YTC should be directed
observed between individual tank ruts suggests
towards testing the hypothesis that amelioration
that the initial degree of soil compaction by tanks
of compacted soil in ruts occurs at different rates
is variable, and subsequent impacts of freeze
in the soil profile and its corollary that the rates
thaw cycles vary from rut to rut with greatest
of soil change are not linear.
smoothing observed in deepest ruts.
The degree of compaction by tanks seems to be
LITERATURE CITED
related to soil moisture content at the time of
tracking. We observed comparatively more soil
Anderson, G., J.D. Pidgeon, H.B. Spencer, and
penetration resistance, higher bulk density, and
R. Parks (1980) A new hand-held recording pene-
lower hydraulic conductivity inside ruts at depths
trometer for soil studies. Journal of Soil Science, 31:
greater than about 2.55 cm when the tracks had
279-296.
been formed on moist soil. In contrast, we observed
Buchkina, N.P. (1997) Impacts of tracked vehicles
little difference between rutted and uncompacted
on properties of tundra soils. In Proceedings of the
soil when tracks were formed in dry soil.
International Symposium on Physics, Chemistry,
Our findings also imply that soil is less com-
and Ecology of Seasonally Frozen Soils, Fairbanks,
pacted by tanks at the surface than deeper in the
Alaska, June 1012, 1997 (I.K. Iskandar et al., Ed.).
profile or that surface compaction does not persist.
USA Cold Regions Research and Engineering
Less compaction may occur at the soil surface, if
Laboratory, Special Report 97-10.
water content is relatively low compared to deeper
Daubenmire, R. (1970) Steppe vegetation of
in the profile at the time of tracking. Alternatively,
Washington. Washington Agricultural Experi-
compacted soil near the surface may be more
ment Station, College of Agriculture, Washington
strongly affected by forces such as wind, and wet-
State University, Pullman, Washington, Technical
tingdrying and freezethaw cycles that fluctuate
Bulletin 62.
with higher frequency and amplitude at the soil
Elliot, W .J., and J.M. Laflen (1993) A process-
surface.
based rill erosion model. Transactions of the Amer-
Variation in the degree of compaction through-
ican Society of Agricultural Engineers, 36: 6572.
out the soil profile has important implications for
Foltz, R.B. (1993) Sediment processes in wheel
potential erosion and its prediction, because sur-
ruts on unsurfaced forest roads. Ph. D. Disserta-
face conditions will not resemble the compacted
tion, University of Idaho.
soil beneath it. Site managers might underestimate
Formanek, G.E., D.K. McCool, and R.I. Papen-
environmental damage or potential erosion based
on the condition of the surface soil. Alternatively,
on strength of a wet silt loam. Transactions of the
the relatively uncompacted top few centimeters
American Society of Civil Engineers, 27: 17491752.
may significantly offset some of the impacts of
Gatto, L.W. (1997a) Freezethaw effects on the
compaction on water infiltration and runoff.
hydrologic characteristics of rutted and com-
pacted soils. In Proceedings of the International Sym-
posium on Physics, Chemistry, and Ecology of Sea-
FUTURE RESEARCH
sonally Frozen Soils, Fairbanks, Alaska, June 1012,
Future research efforts should focus on sever-
1997 (I.K. Iskandar et al., Ed.). USA Cold Regions
al issues. We need to expand our basic knowledge
Research and Engineering Laboratory, Special
about the particulars of soil freezing and thawing
Report 97-10.
at the Yakima Training Center, including charac-
Gatto, L.W. (1997b) Ground freezing effects on
terization of the number and degree of freeze
soil erosion of army training lands. Part 1: Initial
thaw events, the relative importance of freeze
test results. USA Cold Regions Research and
thaw events compared to other soil modifying
Engineering Laboratory, Special Report 97-15.
processes such as rainfall, and the spatial and tem-
General Dynamics (1997) General Dynamics
poral variability of freezethaw as affected by
Land Systems home page. URL: http://www.
microclimate, landscape position, or soil depth.
gdls.com/
.
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