purchased in Wisconsin. The tire chip test sec-
Chunkwood
Chunkwood is a product developed by the
tions were approximately 30 cm (12 in.) thick. As
USFS as a replacement for granular material. It is
was the case with the chunkwood, traffic was
produced by chopping trees in a "chunker," a
applied directly on the tire chip surface.
large shredder that cuts trees into particle sizes
ranging from a few centimeters to 20 cm (8 in.),
Geosynthetics
depending upon the diameter of the trees put
Several types of geosynthetics, some of which
into the machine. The wide range in sizes of the
were development products or products newly
angularly shaped wood promotes particle inter-
on the market, were tested in pretests to rank
lock. High permeability makes chunkwood a good
their relative resistance to damage incurred by
replacement for gravel in wet areas. It also biode-
tank trafficking. Geosynthetics are listed in Tables
grades slowly. Some chunkwood roads had been
2 and 3.
in place with no improvements to them for over 8
Products that sustained the least amount of
years (Arola et al. 1991). Chunkwood is typically
damage in the pretest (see App. D) were used
used as a base course. However, for expediency,
during the field demonstration in the stabilized
no cover was placed on the chunkwood, and it
test sections without any cover. These were the
was tested as a wear surface. Chunkwood was
double-sided geonet and the nonwoven polyes-
mixed with sand to increase the grain size range
ter. An additional geotextile section of polypropy-
a n d improve interlock. Thickness of the
lene was used with minimal gravel cover (less
chunkwood sections ranged from 20 to 40 cm (8
than 10 cm [4 in.], primarily in ruts) on the
to 16 in.). In addition to the chunkwood test sec-
wooded trail and with 30 cm (12 in.) of gravel
tions, chunkwood served as the mainstay of the
cover on the pentagonal loop trail test section. It
trail improvement program, replacing gravel
was also used beneath sections of tire chips,
wherever additional fill was required.
chunkwood, and slash on the wooded trail. In
these sections the geotextile was used to prevent
intermixing of the fine-grained subgrade with the
Tire chips
Tire chips are produced by shredding old tires
fill material and in construction of chunkwood
in pieces that will pass through a 5-cm (2-in.)
"pillows" to prevent lateral spreading of the
sieve. Although the tire chips were ordered to be
chunkwood. The pillows were 6.5 m (20 ft) long.
cut with fresh blades to reduce the amount of
Prior to the pillow construction, the chunkwood
exposed metal, metal pieces protruded from many
migrated into an adjacent depression. The pillow
chips, and tire bead steel was prevalent. Prior to
was constructed by laying out the geotextile (trans-
the field demonstration, a small section of tire
verse to trail direction), covering it with 30 cm (12
chips was spread and compacted with a front end
in.) of chunkwood and wrapping the remaining
loader, and trafficked with a CJ5 to determine if
geotextile over the chunkwood. The pillow was
tire damage would be a major problem. The tires
then covered with chunkwood as a wear surface.
of the CJ5 were punctured by the steel after only a
few passes, but the larger tires of the front end
Tree slash
loader did not suffer, even though some small
The slash consisted of branches of trees placed
pieces of steel were stuck in the tire. Later the
at angles to the direction of travel. The technique
bead steel caused flat tires on a jeep and grader.
is commonly used in Alaska to provide a base for
Tire chips without bead steel can be produced by
a rock fragment surface course for timber access
removing the bead steel before shredded the tires
roads. The best method of placing the slash was to
or reduced by using only automobile tires, which
use the trunks to fill in ruts and hollows and to lay
have less bead steel than truck tires.
branches no bigger than 8 cm (3 in.) in diameter in
a herringbone pattern at 45 angles to the direc-
Like chunkwood, tire chips are very permeable
and can replace granular fill material. In recent
tion of travel. More slash was added during traf-
years, tire chips have been used in road bases
ficking to replenish the existing surface.
because of their high permeability and good insu-
lating properties (to reduce detrimental effects of
Tire mats
frost action) and to efficiently recycle old tires
The commercially available tire mats are con-
(Humphrey and Eaton 1995). Commercially avail-
structed of two layers of truck tire tread perpen-
able tire chips can be obtained throughout the
dicular to each other with a layer of truck tire
United States. The chips used in this project were
sidewalls on top. These mats are designed to with-
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