Soil Characterization
Special soil bins were prepared for each soil moisture series, and characterization measurements
were obtained both to verify similarity between C and FT soils prior to freezing and quantify differences
after the FT cycle. Penetration resistance was measured with an ELE International Proctor Penetrometer,
and these pre-freeze compressive strengths were essentially identical in each bin, both within and outside
the rill. Additional post-thaw measurements included in-rill and out-of-rill shear strength with a Pilcon
handheld vane tester, and constant head infiltration time with a 5-cm-interior-diameter cylindrical
infiltrometer. We calculated porosity, % soil water by volume, % saturation, and moist and dry unit
weights of soil cores taken with an Eley volumeter. The post-thaw data are summarized in Tables 2, 3,
and 4 for the low, mid, and high soil moisture conditions, respectively. In-rill penetrometer compressive
strengths were higher than those outside the rill at low soil moisture, but this difference diminished for
wetter soils. Mid-moisture compressive strengths were highest, decreasing at both lower and higher soil
moistures. Reductions in compressive strength due to FT were either minor or negligible. Both the
magnitude of and the difference between in-rill and out-of-rill vane shear measurements peaked at the
lowest soil moisture and diminished as moisture increased. Vane shear strength measurements following
FT were, at most, slightly reduced relative to the controls. Contrary to the results of Formanek et al.
(1984) and Van Klaveren (1987), neither the penetrometer nor the vane shear data indicated a significant
effect of FT on soil strength.
Infiltration rates diminished significantly with increasing soil moisture over the range of these
experiments. At low moisture the infiltration rates outside the rill were much greater than those in the rill,
and FT produced an even larger increase in all the rates. Mid soil moisture infiltrations were all
significantly slower, but relatively rapid rates were more frequently found outside the rill. The value in
parentheses following >3600 (Table 3) indicates the number of very slow infiltration results. At mid
moisture the FT bin infiltration was not more rapid than that in the C bin. At high soil moisture all
infiltrations were negligible. Infiltration into Hanover silt diminished significantly as soil moisture
approached a saturated condition.
Cores taken in each bin from within and outside the rill completed our soil characterizations.
With the exception of high soil moisture, the porosity in the rills was slightly less than that outside.
Porosity diminished significantly between the low and mid moisture bins, and then was unchanged at
high moisture. There was no measurable porosity difference between the FT and C bins at any soil
moisture. Soil moisture data from the cores were largely in agreement with the probe measurements.
Differences in soil moisture inside and outside the rills were not evident. Near-surface soil moisture in
the FT bins after thaw was generally higher than that of the C bins, though differences diminished at high
soil moisture. The saturation data largely follow the same trends as the soil moistures. The moist and dry
unit weights in the rills are greater than those outside at low and mid soil moisture. However, this
difference diminishes with increasing soil moisture, and is not evident at high moisture. Unit weights
increase between the low and mid moisture bins, and then stay the same or decrease slightly at high soil
moisture. There were no significant differences in the unit weights between the FT and C bins at any soil
moisture.
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