March/April
2002
Stone-Walling
in Arkansas
by
Laurin
R. Lineman
Imagine
a quaint gravel road leading through the Ozark National Forest. The
road parallels the Mulberry River, part of the National Wild and Scenic
Rivers System, and the view is spectacular, either driving along the
road or looking up at the bluffs from a canoe on the river.
The
road was adequate in the past to meet the access needs of the residents
along the river, but it no longer meets highway safety standards.
In addition, the number of visitors to the Ozark National Forest is
increasing, and many of the visitors are traveling in large recreational
vehicles.
The
Arkansas State Highway and Department of Transportation (AHDT) faced
a significant challenge to improve the quality of the road and some
bridges without disturbing the beautiful vista. AHDT was joined in
this effort by the Eastern Federal Lands Highway Division (EFLHD)
of the Federal Highway Administration (FHWA) and the U.S. Forest Service.
AHDT
planned to reconstruct almost 15 miles (24 kilometers) of Forest Highway
65 from Cass to Oark in several phases. AHDT designed,managed,
and took responsibility for the inspection of the first phases of
the reconstruction and will maintain the improvements for the entire
project when it is completed. AHDT invited EFLHD to be a partner to
design and supervise the reconstruction of the remaining phases.
EFLHDs
first project was a section of the highway that did not have guardrails;
was not wide enough for two-lane traffic, especially the recreational
vehicles used by hikers, campers, and hunters; and could not physically
accommodate the increased demand for accessibility to the scenic area.
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The
Eastern Federal Lands Highway Division of the Federal Highway
Administration took on the project to widen a portion of Forest
Highway 65 in the Ozark National Forest in Arkansas. A special
part of the project was the natural stone retaining wall.
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Due
to the increased traffic, there also was a need to pave the gravel
surface. The dust and sediment from the gravel measurably degraded
the water quality of the river below.
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The
project called for the installation of guardrails and a retaining
wall.
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The
basic plan included widening almost a mile (1.47 kilometers) of the
existing gravel road to accommodate two 10-foot- (3-meter-) wide paved
travel lanes with 2-foot- (0.6-meter-) wide shoulders, and designing
functional and aesthetic retaining walls for the project. The project
also included drainage improvements, curbs and gutters, and minor
realignments.
Because
of the rivers designation [as part of the National Wild and
Scenic Rivers System], views from both the roadway and the river are
a major concern to the U.S. Forest Service, said Dave Weber,
the project manager for EFLHD.
The
environmental assessment for the project described four key concerns:
(1) to protect the river by controlling erosion during and after construction;
(2) to protect the free-flowing
character of the river by not encroaching with permanent improvements
into its jurisdictional waters; (3) to protect the view from
the river; and (4) to maintain the unique physical relationship
of the sheer bluffs [near the river], the natural scenery of the Mulberry
Valley, and the scenic experience this provides for viewing from the
river and road.
The
most difficult design issue was the composition of the retaining wall
because the EFLHD team did not want any adverse visual or structural
impacts on the road or natural bluff.
The
solution to the problem was a stones throw away.
Based
on design, architectural, landscape, and aesthetic considerations,
the team chose to construct a natural rock retaining wall, made with
stones quarried just a half-mile (0.8 kilometers) from the construction
site.
Jack
Van Dop, the environmental specialist on the team, wanted the wall
to look natural and to fit in with the surroundings. Using natural
stone was lower in cost than some traditional systems and much cheaper
than a masonry face. Although the cost of using natural stone was
more expensive than using a manufactured facing, the team believed
the aesthetic benefit was worth the increase in cost.
Many
people thought that the design would not work. Placing quarried stones
along the short 3- to 4-foot (1- to 1.3-meter) walls poses no engineering
problem because the stones can be stacked without reinforcement, just
with occasional chinking to stabilize the stacking.
But
what about the higher walls? EFLHD had to resolve the engineering
problem of building and reinforcing 18-foot- (5.5-meter-) high walls
along the embankment and to resolve the aesthetic problem of making
the taller walls look like the shorter walls.
The
team chose a mechanically stabilized earth (MSE) wall system, using
geogrid reinforcements for the taller walls, which were then covered
by the locally quarried stone. This type of construction requires
no special equipment or specialized labor. The construction is generally
rapid, plus the wall system is flexible and can accommodate
relatively large total and differential settlements without distress,
according to the FHWA Geotechnical Engineering Circular No. 2 (February
1997).
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The
stone used for the retaining wall came from a quarry just a
half-mile (0.8 kilometers) from the construction site.
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The
natural stone facing provides an additional advantage — natural
water drainage — and that makes it more conducive to fluctuation
in the water level of the adjoining Mulberry River. Engineers often
use concrete for retaining walls. However, if concrete were used for
this project, water would seep into concrete walls when the Mulberry
River flooded, and then when the river receded, the wall would retain
the water. Engineers are able to correct for this problem with man-made
solutions, but this was not necessary for the retaining walls planned
for this project.
With
this design, the smaller walls, built from jointed natural rock without
mortar in between the stones, and the taller walls, covered by the
natural stone, are free-draining, eliminating the need for a human-engineered
drainage system. In addition, all of the slopes, including those that
are reinforced, are to be revegetated with grass mixtures of native
plant material.
The
process for such a sensitive design naturally included public involvement.
Comments from the public included concern about pedestrian safety
due to the anticipated increase in traffic and a suggestion to augment
the improvements to include a bicycle path.
Keeping
in mind the environmental concerns, EFLHD proposed a more basic plan
that included sufficient improvements to make the roadway safe and
to preserve the view from the river but did not include suggested
enhancements that would have required serious road-widening construction.
Janice
Dewberry Shelton, whose parents live along Forest Highway 65, commented
on the proposal, writing, You are proposing progress, but preservation.
That is the key to progress.
We need this road.
Jimmie
and Doris Dewberry commented
in favor of the project, Although it would be tempting to feel
that the beauty of that area should be kept exclusively for those
of us who live here, we really think that it should be shared with
others.
However,
homeowner William G. Rue opposed the project, expressing concerns
that the road-widening would irreparably damage the primitive
atmosphere of the area, adversely affect the Mulberry River,
increase traffic, and be a danger to anyone traveling on the road.
He also expressed concern about the cost to taxpayers.
In
response to these concerns, Gary L. Klinedinst, who at the time was
the division engineer for EFLHD, emphasized in a written response
that federal construction projects are keenly sensitive to the surrounding
environment and are designed to minimize disturbance and be
as unobtrusive as practical. As a matter of fact, the construction
project will reduce the adverse affects that the dust and sediment
from the unpaved road currently have on the river, and the project
is designed to protect the river during construction.
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Supervisors
inspect the retaining wall.
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Acknowledging
that the project may result in increased traffic, Klinedinst said
that the project upgrades the existing roadway to provide an
adequate, safe roadway for current and future traffic.
Klinedinst
also noted that the U.S. Department of Transportations Forest
Highway Program provided funds for the improvements. The project is
eligible for such funds because it is a public road, connects the
Ozark National Forest to nearby roads, and serves local residential
and commercial needs as well as those of visitors to the forest.
The
road was kept open throughout the project, and thus, there was minimal
disruption of traffic.
The
local residents were impressed with the results. Mrs. Ken Byrd, a
homeowner affected by the project and the owner of a canoe rental
company, initially expressed concern that the project would diminish
the scenic view for her clients on the river. After viewing the finished
wall, she said, Why did you build such a beautiful wall for
canoeists and not for drivers?
EFLHD
came through for their partners at AHTD, for local residents, and
for visitors to the Ozark National Forest. EFLHD made a portion of
the roadway safer for all users and, by using natural stone retaining
walls, enhanced the already spectacular view for nature enthusiasts
traveling in canoes along the river.
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The
results were both functional and aesthetically pleasing. On
the right is a section of the slope that has been revegetated
with native grasses.
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Laurin
R. Lineman
is the division materials engineer for the Eastern Federal Lands Highway
Division. He was previously a geotechnical and pavements engineer
for EFLHD. Lineman joined FHWA in 1991, and his career has included
assignments in design, construction, and geo-technical areas. He has
a bachelors degree in civil engineering from The Pennsylvania
State University, a masters degree in civil and environmental
engineering from The George Washington University, and he is a registered
professional engineer in Virginia.
For
more information about this project, please contact Laurin Lineman
by e-mail at Laurin.Lineman@ fhwa.dot.gov or by telephone at (703)
404-6268.
Other Articles in this issue:
"Stone-Walling"
in Arkansas
Arkansas
Combines Best Practices for an Innovative Insterstate Rehabilitation
Program
Small
Investment, Dramatic Dividends — Saving Lives in "Blood
Alley"
National
Review of the Highway Safety Improvement Program
Weather:
A Research Agenda for Surface Transportation Program
Highway
Quality Awards
FHWA
Model Predicts Noise Impacts
Synergy
in Action: FHWA's Transportation Pooled-Fund Program