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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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|Publication Number: Date: March/April 2002|
Issue No: Vol. 65 No. 2
Date: March/April 2002
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.
EFLHD's 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.
|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.|
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.
|The project called for the installation of guardrails and a retaining wall.|
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 river's 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 stone's 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).
|The stone used for the retaining wall came from a quarry just a half-mile (0.8 kilometers) from the construction site.|
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.
|Supervisors inspect the retaining wall.|
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 Transportation's 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.
|The results were both functional and aesthetically pleasing. On the right is a section of the slope that has been revegetated with native grasses.|
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 bachelor's degree in civil engineering from The Pennsylvania State University, a master's 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.