Table 1. Data on TVIM ruts
that we measured.
Site
Rut name
No. of passes
C
T-2
2
T-4
4
TURN 1
2
TURN 2
1
E
T-2
2
T-8
8
TURN 1
1
TURN 2
1
TURN 3
1
All ruts formed in April 1995, except
E T-8 which was formed in July
1994. Soil water at time of tracking
at T-8 was 05% (by volume); for all
Figure 3. Site C.
others it was 15%.
(6 and 5 replicates, respectively). At site E, we
a 03% slope, and dominated by big sagebrush
measured profiles across straight ruts formed by
(Artemisia tridentata) (Daubenmire 1970, Jones and
2 or 8 tank passes (6 replicates each) and across 3
Bagley 1997). Site C (Fig. 3), at about 900-m alti-
turning ruts formed by 1 pass (9 replicates in all).
tude, has lower temperatures and about 30 cm of
We established transects perpendicular to sin-
annual precipitation. Soils are Colockum-Ben-
gle tank ruts (each tank track is composed of two
way, fine loamy, mixed, mesic Calcic and Aridic
such ruts). We drove a 1-m length of steel rebar
Calcic Argixerolls on a 13% slope. The dominant
into the soil outside the tank rut at both ends of a
vegetation is perennial bunchgrass such as blue-
profile location to serve as a stable foundation for
bunch wheatgrass (Elytrigia spicata) or Poa secunda.
repeated measurements with a profile meter, such
Further details about vegetation at both sites are
as described in McCool et al. (1981) (Fig. 5).
reported by Jones and Bagley (1997).
The profile meter is composed of a 1.83-m alu-
Tank ruts examined during this study were
minum frame that supports 145 free-sliding, ver-
formed by one to eight passes of an M1A2 Abrams
tical aluminum-alloy pins arranged in a line on
combat tank in July 1994 or April 1995 as part of
the TVIM study (Table 1). Jones and Bagley (1997)
1.27-cm spacing. The frame is held perpendicu-
provide more details on site layout. The M1 has a
lar to the soil surface by folding aluminum arms
listed vehicle weight of about 63,000 kg (69.5
that also house a camera. To measure the rut, the
tons), yielding a ground pressure of 1.08 kg/cm2
profile meter is placed onto the rebar, and the
frame is leveled using a bubble level so that the
(15.4 psi) (General Dynamics 1997). We concen-
pins point directly down. The aluminum pins are
trated most of our measurements on ruts formed
carefully lowered onto the soil surface taking care
in April 1995 when soil water content was about
that each is in contact with the soil surface. The
15% (by volume) in the top 10 cm (moist), because
details of the soil surface are shown by the height
we observed little surface rutting in locations
of the 145 aluminum pins against a scaled back-
where tracks were formed in July 1994 when soil
drop on the aluminum housing frame, which is
water was 05% (dry) (see also Thurow et al. 1993).
photographed (Fig. 6).
Each rut profile was photographed three times,
MEASUREMENT AND
8 December 1995, 27 March 1996, and 16 July 1996.
ANALYTICAL METHODS
Each photo was digitized using SprintScan 35 (Po-
laroid) at a resolution of 1021 dots per inch (dpi)
Rut profiles
and archived as tagged image file format (TIF)
We established 23 rut surface profile locations
files. Digitized images of pin heights were pro-
across ruts at site C and 21 at site E (Fig. 4). At site
cessed to correct for picture angle and exposure,
C, we measured profiles across straight ruts
and pin height measured using Sigmascan
formed by 2 or 4 tank passes (6 replicates each)
3.02.035 (SPPS Inc. 1997a). We judged 46 data
and across turning ruts formed by 1 or 2 passes
3
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