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The Coronado National
Forest seems to fit almost precisely into the southeast corner
of Arizona, but up-close, these 1.7 million ac. of public
land are actually a wild mix of hot, arid desert juxtaposed
with "sky islands" vaulting mountains rising directly
from the desert floor. In less than an hour's travel, one
can pass from hot desert to cool mountain forests: a characteristic
of this land that Apache leaders Cochise and Geronimo knew
well and used repeatedly to escape a pursuing cavalry more
than a century ago. Within this jumble of landscape managed
by the US Department of Agriculture's Forest Service are 10
well-developed recreation areas, more than 1,100 mi. of trails,
and four fishing lakes that provide a wide variety of recreational
opportunities.
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There are also
eight wildernesses, each with its own unique history, wildlife,
and structure. More than 200 threatened and endangered species
frequent the area. The Chiricahua Wilderness occupies 87,700
ac. in the Chiricahua Mountains located at the southeastern
boundary of the Coronado National Forest, immediately adjacent
to the town of Portal. There is a well-developed trail system
through the dense brush and timber, steep slopes, and precipitous
canyons of this one-time Apache hunting ground, which makes
this historical wilderness area popular with novice hikers
as well as devotees. Also, there are many Forest Service campgrounds
and picnic areas within hiking distance just outside the wilderness,
in addition to a number of nonforest facilities. As one might
expect, this ease of access to a site with considerable historical
interest has made the Chiricahua Wilderness extremely popular
with visitors. The presence of several world-class bird-watching
sites-within the wilderness and nearby-contributes another
measure of popularity and another important reason for visitors
to choose this area. The South Fork Trail and Picnic Area
and the Silver Peak Trail provide birding opportunities: more
than 300 species, including the elegant trogons, blue-throated
hummingbirds, and the Montezuma quail, are on display.
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An increasing number
of visitors and associated traffic have made road maintenance
a high priority for the tightly budgeted Forest Service. Roads
in this high (5,000-ft.-plus) mountain area are subjected
to snow and rain in the winter as well as regular summer rains.
When it became necessary to rebuild a 2-mi. section of Portal
Road, an essential access road for the Chiricahua wilderness,
Cave Creek Canyon, South Fork Trail, and neighboring attractions,
planners took a hard look at traffic requirements and costs
to find a realistic compromise. The old road had once been
partly paved and partly chip sealed, but even the paved sections
were badly potholed. The need for major reconstruction was
clear. The strategy adopted was one of "incremental construction";
that is, fund and build the road in two stages: (1) realign
the road, correct drainage problems, and construct a stabilized
crushed aggregate surfacing during the first year and (2)
pave over the stabilized base two years later.
Incremental, or
staged, construction in itself is not unusual, but the Coronado
National Forest engineering and road construction staff brought
in two road construction innovations on this project to reduce
costs, improve the quality of the road structural section,
and provide road users with a safe and functional running
surface during the two-year increment before the permanent
pavement surfacing could be placed. This area is approximately
70 mi. "uphill" from the nearest commercial aggregate
sources. Creek-run gravel with cobbles up to 12 in. in diameter
was the only local source practical if the Forest Service
was going to avoid the tremendous trucking costs. Historically
the oversize creek-run material was used in the area to build
up the road system. With the population of threatened and
endangered species, it was no longer possible to develop nearby
borrow pits, so the material resource was limited to the old
roadbed, which they ripped up, as well as oversize material
collected from shoulders and ditches. This material was windrowed
on the road in adequate quantity after crushing to produce
a 4-in.-thick surface course.
What made use of
the creek-run material feasible was availability of new mobile
rock-crusher equipment technology. The FAHR Forester C-2000,
manufactured in Canada, mounts on the front of large front-end
loaders. Rocks are crushed between rotating hammers and steel
anvils. Materials with up to 16-in. cobble and boulder rocks,
angular or rounded, can be fed in the windrow into the mobile
crusher to produce crushed aggregate materials with a maximum
rock size of 2 in.
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The Coronado National
Forest rented the mobile rock crusher in 1995 as part of a
demonstration project that was written up the following year
by the Forest Service's Technology & Development Center
in San Dimas, CA, (Forester C-200 Demonstration Project).
After eight weeks of operation, the calculated cost for this
"crushed-on-the-road" aggregate material was $3.86/ton,
a very economical cost at this remote site considering commercial
sources are more expensive to purchase at the production location
with no transportation costs included.
The only complication
involved the quality of this aggregate. With fines content
(minus No. 200 sieve) ranging from 3% to almost 20%, much
of the aggregate would be highly moisture- and frost-susceptible
and the road, during the interim without paved surfacing,
would be subject to damage and erosion by heavy rains, occasional
flooding, and snow-removal operations. A low-cost method to
stabilize the aggregate was needed to maintain a functional
running surface and protect the adjacent riparian areas from
sedimentation. Project engineers selected the EMC Squared
System, a concentrated liquid stabilizer technology from Soil
Stabilization Products Company Inc. of Merced, CA. They based
their selection on the product's history of effectiveness
with this range of aggregate material gradation and with its
service history in treatment of unpaved roads for the Forest
Service and other public agency projects in severe cold-climate
areas.
The construction
operation included the frontloader/mobile-crusher unit, two
motor graders, compaction equipment, and three water trucks
to supply the diluted solution of concentrated liquid stabilizer.
The graders ripped the existing road and gathered all available
material into two windrows, then spread and graded behind
the mobile crusher as it progressed down the road. The project
was constructed in August. After first being short of water,
the construction operation was then hit by the heavy monsoon
rains moving up from the Gulf of Mexico, which are typical
to this area during summer. Compaction equipment also broke
down, further compounding the difficulties of working at the
remote site. With improvement in the weather and equipment
repairs, the aggregate surfacing work was completed.
Preparation for
placement of the pavement surface began in late summer 1997.
The stabilized aggregate proved to be solid, and the Forest
Service engineers abandoned any idea of ripping it up and
recompacting. Extruded curbs were placed on both sides of
the road for lateral confinement in the narrow road easement
and for protection of the pavement surfacing during the occasional
flooding of the canyon. Aggregate was added as needed to increase
the elevation of the base course, and paving operations were
completed late that fall.
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