Reinforcing or Augmenting Soil Structure—Reinforcing or augmenting existing soil structure is a method that adds material to existing soil to improve its engineering characteristics. Unlike excavating and replacing substandard soils, this method works with the native in situ soil material. The two major types of material are soil binders and structural additives.
Binding agents come in two forms: chemical binders and physical binders.
Chemical Binders—The EMC SQUARED system is an example of a chemical binder. EMC SQUARED is a concentrated liquid stabilizer formulated to increase the density, cementation, moisture resistance, frost-heave resistance, bearing strength, shear strength, and stability of compacted earth materials. The highly concentrated product is diluted in water and applied as soil materials are mixed and compacted. The product is activated by biological catalyst fractions. According to the manufacturer, it is an environmentally friendly product. The system is supposedly effective with a wide range of aggregate and recycled materials, as well as clay and silt soils.
The primary binder in the EMC SQUARED system is Road Oyl, which has been used extensively as an aggregate binder for resin pavement mixtures. Road Oyl has demonstrated considerable success on urban and accessible trails for the Forest Service, National Park Service, and other governmental and private organizations. Paul Sandgren, superintendent of the south unit of the Kettle Moraine State Park in southeastern Wisconsin, reports good success with Road Oyl in binding aggregate-capped mountain bike trails. The park's south unit, which receives heavy mountain bike use from surrounding urban areas, found annual applications of the binder worked well in reducing the displacement of a surface cap of ¾-inch crushed limestone (Paul Sandgren 2001).
Test applications of chemical binders in Alaska have proved disappointing. The municipality of Anchorage experimented with the use of a chemical binder on an urban access trail with poor results. The material failed to set up properly. In areas where the material set up, the surface was very slick. Whether the problem was caused by climate or improper installation was never resolved (Dave Gardener 2001). Denali National Park and Preserve has also experimented with a variety of chemical binders as dust suppressants on a gravel road that serves as the primary access for the park. To date, results have been disappointing (Ken Karle 2000).
Chemical binders such as Road Oyl have the greatest potential application in urban areas and at trailheads where high-quality gravel or recycled materials are available. They have yet to be tested on degraded OHV trails in remote locations where unsuitable soil materials, high moisture levels, inability to use heavy equipment, and severe climatic conditions would present challenges for this technique.
The EMC SQUARED system and Road Oyl are available from Soil Stabilization Products Company, Inc., of Merced, CA. Phone: 209–383–3296 or 800–523&3150;9992. Other chemical binders available on the market include:
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Stabilizer (4832 East Indian School Rd., Phoenix, AZ 85018. Phone: 800–336–2468).
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Soil-Sement (Midwest Industrial Supply, Inc., P.O. Box 8431, Canton, OH 44711. Phone: 800–321–0699).
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Pennzsuppress D (John Snedden, National Sales Manager, Pennzoil Products Co., 100 Pennzoil Dr., Johnstown, PA 15909).
Physical Binders—Fine-textured native soil is an example of a physical binder. It can be used where trails are constructed with coarsely textured aggregate or washed gravel. Soil material containing high sand- and silt-sized fractions is used to fill voids between gravel- and cobble-sized material. The fine materials help "bed" the larger material, reducing displacement, improving the quality of the travel surface, and helping vegetation to become established.
Structural Additives—Another method of augmenting an existing soil structure is to add a physical component to the soil body. This can be as an internal structural member or as a surface feature.
Internal Structural Member—The use of cellular confinement systems to reinforce sandy soils is an example of adding a physical component to an existing soil structure. The original soil is excavated and used as fill and cap material. The cells of the cellular confinement system add a structural component to the sand that prevents shear force transfer and soil failure. This method was tested by the U.S. Army Corps of Engineers (Webster 1984; Purinton and Harrison 1994) and applied during Operation Desert Storm to construct sand roads capable of carrying heavy military traffic. The technique has also been applied by an American oil company to build roads through the Algerian Sahara Desert (Presto 1991). Using a cellular confinement system would be an excellent method to stabilize trails that cross sandy soils.
Another method used by the Forest Service (Kempff 2000) and recommended by the American Motorcyclist Association (Wernex 1994) is to embed concrete blocks in the body of the soil. The concrete block, installed with the block walls in a vertical position, provides a hardened wear surface. The open cell structure of the block prevents shear force from being transferred. This method may have applications where blocks can be readily transported to degraded trail sites, but has limited application in remote locations. Blocks are available that are specially designed for OHV trails. They are not as thick as normal construction blocks, and have a different grid pattern.
Surface Feature—The geosynthetics industry has developed a class of materials known as 'turf reinforcement' materials. These products are designed for installation at or near the surface to reinforce the surface vegetation mat. The Park Service experimented with one of these materials in a series of test plots established as part of an OHV trail mitigation study conducted in the Wrangell-St. Elias National Park and Preserve in Alaska. In 1996, the Park Service installed four 40-foot test sections of a combination of a drainage mat (Polynet) with a turf reinforcement mat (Pyramat) over moderately degraded OHV trails. Polynet is a 1/8-inch-thick polyvinyl chloride (PVC) material, resembling expanded metal decking. Pyramat is a ¾-inch-thick, finely woven polypropylene product in a pyramid-shaped microweave pattern (figure 14).
Figure 14—Polynet over Pyramat was used in this
National Park Service installation to test the addition
of a synthetic turf reinforcement mat. The Polynet,
with its more durable wear surface, was installed
over the less durable Pyramat.
The manufacturer had extensively tested Pyramat as a soil-reinforcement product. The company had documented significant increases in resistance to erosion and shear stress after vegetation regrowth (Synthetic Industries 1999). The National Park Service tested both turf reinforcements to see whether they would support existing roots and cushion soil bodies from direct impact. Polynet provided a wear surface, while the open weave of Pyramat allowed for active plant growth and eventually was integrated into the soil surface layer.
The Park Service field tests were encouraging because the materials appeared to protect the underlying soils from impact. They stabilized degradation and provided a durable wear surface for OHV use. Vegetation regrowth on the sites increased from 54-percent cover at installation to 79.5 percent 3 years later (figure 15). On sites with a high percentage of sedge and cotton grass, the materials were well integrated into the root mass by the end of the second year.
Figure 15—A Park Service Polynet/Pyramat test
installation after 3 years in a wetland area with a
high percentage of sedge. By the third year, sedge
had become well established and its roots well
entwined with the Pyramat matting.
The products worked fairly well to stabilize trail degradation, but were difficult to install and maintain. They had a poor appearance. The material installation cost of the two products was $4 per square foot. It took 26 hours to install 100 linear feet of a 6-foot-wide trail. The full results of the test are detailed in the report, All-Terrain Vehicle (ATV) Trail Mitigation Study: Comparison of Natural and Geosynthetic Materials for Surface Hardening (Allen and others 2000).
Pyramat has also been used to reinforce foot trails and provide erosion control at a portage on Jim Creek, a tributary of the Knik River in the Matanuska Valley near Palmer, AK. Nancy Moore, who works for the Alaska Center for the Environment, coordinated the installation of a 90-foot-long by 8-foot-wide strip of Pyramat at the site in the summer of 2000. The mat was laid on the soil surface, capped with pit-run gravel and topsoil, and seeded to reestablish vegetation. According to Moore, the installation was successful in stemming erosion and improving trail conditions (Moore 2001).
Appendix A identifies the attributes of the Polynet/Pyramat combination and compares the combination with other products tested by the Park Service. While this combination of products may have utility in other applications, it is not considered suitable for hardening OHV trails because of the difficulty of installation and the limited durability of the wear surface.
Trail Hardening—Providing a Wear-and-Carry Surface Over Unstable Soils
The final method of trail hardening is to provide a wear-and-carry surface over unsuitable soils. Typically, this is accomplished by installing a semirigid structural component on the soil surface that provides a durable wear surface while distributing weight over a broad soil area. In this manner, the material "carries" the weight of the load, rather than directly transferring it to the underlying soil.
The methods of wear-and-carry, trail-hardening techniques for OHV trails discussed in this document include:
These methods are expensive and labor intensive. It is not practical to use this method to harden the entire length of a trail. It should only be used to harden those segments that cannot be rerouted to more suitable locations or managed to reduce impacts.
Much of the following discussion is drawn from the author's personal experience with trail hardening tests conducted in Alaska. This experience includes a formal study conducted in Wrangell-St. Elias National Park and Preserve, mentioned in a previous section (Allen and others 2000), data obtained from other test installations, independent research, and conversations with other professionals.
Corduroy—Corduroy has been commonly used to harden trails in Alaska. Many of the first wagon trails in the State were constructed as corduroy roads. It is not uncommon to see corduroy being excavated during roadwork today. In traditional road construction, the corduroy logs were covered with soil or a gravel cap to provide a smooth and durable road surface. Burying the poles beneath the surface cap also served to preserve them. This was especially true when the poles remained water-saturated under acidic soil conditions.
For most trail applications, corduroy is not covered with a surface cap. This is primarily due to the scarcity of quality cap material and the expense of hauling the material to installation sites. When corduroy is exposed to the air with frequent wet/dry cycles, its longevity is significantly shorter than if it was buried. Fastening the individual poles together is another challenge. Poles can be secured by weaving them with line, spiking them to sill or rail logs, or threading them with rope or cable. Corduroy provides a suitable, if somewhat rough, surface for OHV and foot traffic. Also, woven or threaded corduroy floats on water so it does not provide a stable surface for ponded areas.
The Park Service tested corduroy as one trail-hardening technique in the Wrangell-St. Elias study (Allen 2000). Although corduroy was somewhat labor intensive to install, the expense of installation was mitigated by the low cost of materials. The Wrangell-St. Elias study identified a material installation cost of about $1.75 per square foot. About 25 hours were required to install each 100-foot section of 6-foot-wide trail (figure 16).
Figure 16—Spruce pole corduroy laid across
permafrost soils in Alaska. These poles were
imported to the site and secured by weaving
them with three strands of 3/8-inch nylon line.
Corduroy may also have an environmental cost if trees are harvested in sparsely timbered areas. Three to four poles are required for every linear foot of 6-foot-wide trail. The management tradeoff of harvesting trees to mitigate trail impacts needs to be evaluated for each installation site. Appropriate thinning methods can mitigate impacts of timber harvesting. Harvesting poles offsite can also mitigate impacts.
Appendix A has more detailed information about the benefits and drawbacks of corduroy. Corduroy is considered a suitable trail-hardening material for relatively short sections of trail when timber is available locally.
Wood Matrix—Wood matrix was another trail-hardening method tested by the Park Service in the Wrangell-St. Elias study (figure 17). The wood matrix was a wooden grid structure constructed of rough-cut, 2- by 4-inch timbers that were notched and fitted to form an 8- by 8-inch open grid. The surface of the grid formed the wear surface. The interlocked timbers carried and distributed the load across the soil surface. The technique was adapted from an approach developed in Britain (Shae 2000).
Figure 17—Wood matrix after installation in the
Wrangell-St. Elias National Park and Preserve in
Alaska. The wood matrix provided a suitable surface
for OHVs, but had several characteristics that limited
its suitability for future field applications.
The grid formed a rigid unit that had excellent load transfer characteristics, but was too inflexible to conform well to terrain. Although raw materials were cheap, preparing and fitting the joints was very labor intensive. The green, untreated lumber warped, was difficult to fit together in the field, and was subject to breaking at the joints. It was also subject to rot and showed visible signs of deterioration within the first year.
The installation cost for the wood matrix was $2.90 per square foot. About 70 hours were required to install a 100-foot section.
Additional information on the suitability of wood matrix for trail hardening is included in appendix A. Because a wood matrix installation entrapped wildlife in one case, it was removed from the Wrangell's test plots during the second season of the study. That concern and other factors of the material limit its suitability for future trail-hardening applications.
Puncheon—Constructing puncheon (a type of elevated boardwalk) for wet and muddy footpaths has been a standard trail construction technique for many years. Recently, its use in providing a hardened trail surface for ATVs has been pioneered by John Coila, an Alaska homesteader in the Kachemak Bay area of southcentral Alaska. Coila developed an installation similar to a standard Forest Service design called puncheon with decking (figure 18). Coila used locally available beetle-killed spruce and a portable bandsaw mill to produce the decking onsite.
Figure 18—Forest Service Standard Drawing 932-2
of a puncheon with decking boardwalk trail.
This design is similar to the one developed
by an Alaskan homesteader to provide hardened
trails for OHVs. For a larger version of the Figure click here
Typically, Coila cuts timber adjacent to the trail from standing or recently fallen, beetle-killed spruce trees. Coila's slab-plank design uses two size classes of beetle-killed timber. Smaller diameter timber provides sills and stringers (figure 19). Larger diameter timber provides logs for planking. Sill timbers are 12 feet long and stringer timbers are 24 feet long. The minimum top diameter of logs used for sills and stringers is 7 to 8 inches. Bark is not typically stripped off the logs, nor are the sill or stringer logs milled in any fashion. The plank log diameter is controlled by the size the mill can accommodate. Plank logs are cut to 6-foot lengths to ease handling and are milled into 2-inch-thick slabs. Planks are not square edged. All round-faced slabs are discarded. Each plank provides an average of 1 linear foot of boardwalk (figure 20).
Figure 19—Rough layout of the sill and stringer
timbers for puncheon trail construction over a
wetland area in southcentral Alaska. Stringers are
laid with tops meeting tops and butts meeting butts.
Figure 20—A finished puncheon trail. Note the
placement of the plank taper to accommodate
the curves along the trail.
Coila estimates the expense of the installations at about $5 per linear foot, with a construction rate of 50 to 100 feet a day for a three-person crew when timber is close at hand. Installations have been in active service for longer than 15 years with the occasional replacement of a surface plank. An installation guide for the technique has been prepared and is available from the author (Meyer 2001a).
Porous Pavement Panels—Porous pavement panels (PPP) are three-dimensional, structural geotextiles designed to provide a durable wear surface and a load distribution system for driveways, parking areas, fire and utility access lanes, golf cart paths, and approaches to monuments, statues, and fountains. The panels are intended to be installed over a prepared subbase and filled with soil. They are designed to support grass growth and provide a reinforced turf surface for light or intermittent heavy traffic. In contrast to asphalt or concrete pavements, these porous pavement systems reduce surface runoff, increase infiltration, resist erosion, and enhance groundwater recharge.
The standard industrial installation technique is modified for hardening OHV trails. After surface leveling, the panels are installed directly over the existing trail surface. The grid cells are not backfilled unless fill material is readily available. After installation, the panel's surface provides a tread surface for vehicles, and the panel's structure distributes their weight. The open structure of the panels allows vegetation to grow through the panel after installation. On extremely muddy or boggy sites, a supplemental geotextile layer may be placed beneath the panels to increase flotation. Polynet PN3000, an open-grid drainage mat, has been used for that purpose in a number of test installations in Alaska.
One advantage of the panel system is the light weight of the panels (about 2 pounds per square foot). The panels do not add any significant weight load to wetland surfaces and have little impact on surface hydrology. Their use can dramatically reduce the need for culverts or other water transfer structures along the trail.
Two porous pavement panel products have been the subjects of extensive field testing in Alaska. They are GeoBlock (figure 21) and SolGrid (figure 22).
Figure 21—A GeoBlock panel. Note the edge
tabs used to connect the panels and
transfer loads between them.
Figure 22—Two SolGrid panels. Note the U-shaped
flex connectors between panel subsections.
GeoBlock is a commercially developed porous pavement system manufactured by Presto Products of Appleton, WI. GeoBlock has been on the market, in one form or another, since the early 1990s and was specifically tested in two earlier configurations by the Park Service in the Wrangell-St. Elias National Park and Preserve. Its primary industrial applications are emergency vehicle lanes, light service roads, and auxiliary parking areas.
SolGrid is a commercial porous pavement system developed by SolPlastics, of Montreal, Canada. SolGrid is a newer product. It has a unique configuration that makes it suitable for irregular terrain and sloped areas. Its primary industrial applications are walkways, bikeways, golf cart paths, and driveways.
Both products are partially recycled polyethylene plastic panels about 39 inches long, 19 inches wide, and 2 inches thick. GeoBlock has also been manufactured as a 1 ¼-inch-thick panel. The panels are stabilized with carbon black to help them resist degradation by ultraviolet light. Both GeoBlock and SolGrid are constructed with an open grid surface and interlocking edges. The GeoBlock products have a 3- by 3-inch-tall vertical grid reinforced by a base sheet perforated with 2 ¼-inch-diameter holes on a 3 ¾-inch spacing. About 44 percent of the base is open. The GeoBlock products form a rigid panel with good weight transfer between panels.
The SolGrid product has a 2 ½- by 2 ½-inch-tall vertical grid pattern with an 8- by 8-inch subpanel. When assembled, subpanels form 16- by 16-inch weight-transfer panels. Flexible U-shaped connectors join the subpanels. There is no base sheet. About 85 percent of the grid surface is open for vegetation regrowth. Weight transfer between panels is poor because of the integrated flexible connectors. This can be mitigated somewhat by the use of supplemental geosynthetics underneath the panel. Polynet-PN3000 has been used for that purpose in Alaska and has demonstrated some benefit.
The flexibility of the SolGrid panels increases their utility on irregular surfaces and on slopes. It also provides an integrated buffer for thermal expansion and contraction.
In 1996, earlier configurations of GeoBlock 1 ¼- and 2-inch panels were tested by the Park Service in the Wrangell-St. Elias trail mitigation study. The test demonstrated that the panels perform very well as trail-hardening materials. They provided a suitable wear surface for foot and OHV use and were easy to install. In addition, they readily facilitate vegetation regrowth.
Vegetation cover along two hardened trail segments increased on average from 70 to 90 percent and from 48.5 to 77.5 percent respectively, within the 4-year study period.
In 1996, the total installation costs for 100 feet of 6-foot-wide trail were:
| 1 ¼-inch Geoblock | 2-inch Geoblock |
|---|---|
| • $6.67 per square foot | • $8 per square foot |
| • Installation, 32 hours | • Installation, 36 hours |
| • Panel costs with shipping, $3.14 per square foot | • Panel costs with shipping, $4.50 per square foot |
Since 1996, GeoBlock panel costs have fallen to about $2.15 per square foot for the 2-inch panel, depending on volume. Presto no longer manufactures the 1 ¼-inch GeoBlock.
SolGrid costs about $1.60 per square foot, depending on volume. In some areas, SolGrid would require the use of a supplemental geotextile, such as Polynet PN-3000. This would add 15 to 25 cents per square foot to installation costs.
Both products have been tested in Alaska on OHV trails during 2000, 2001, and 2002. In 2000, two 100-foot test sections were installed on a dedicated recreation OHV trail in the Forest Service Starrigaven Recreation Area near Sitka. Several test sections of GeoBlock and one section of SolGrid were installed in cooperation with the Alaska Department of Fish and Game at the Palmer Hay Flats State Game Refuge near Palmer (figures 23 and 24). The Forest Service reports that the installations were more economical than the standard gravel cap placement and may be applied more widely in the future (LaPalme 2001).
Figure 23—Test installation of 2-inch GeoBlock
at the Palmer Hay Flats State Game Refuge
in Alaska. This configuration of panels provided
a 4.8-foot-wide trail. Note the interlocking tabs
along the panel edges. These tabs transfer weight
between panels. In this test, GeoBlock was installed
over Polynet PN-3000.
Figure 24—Test installation of SolGrid at the
Palmer Hay Flats State Game Refuge in Alaska.
Note the U-shaped flex joints between sub-panel
sections. The SolGrid was tested without Polynet
PN-3000 to test the characteristics of the product
when installed on a soft, silty substrate.
The 2000 test project on the Palmer Hay Flats Game Refuge was successful enough for the department to install an 800-foot section in 2001. That installation included a 600-foot-long shallow underwater section that was supported by a base layer of geogrid and a gravel cap infill to ballast the installation to the pond floor. Also in 2001, the Bureau of Land Management sponsored test installations in the White Mountains National Recreation Area north of Fairbanks, AK, and the Tangle Lakes Archeological District west of Paxson, AK. More than 400 feet of hardened trail was installed at those two sites. In addition, a 300-foot test section was installed in the Caribou Lakes area on the lower Kenai Peninsula in Alaska. Average material costs ranged from $3 to $3.50 per square foot. Among the four sites, trail surfaces were constructed in 4.8-, 6.5-, and 8-foot-wide configurations. Labor requirements varied from 6.5 to 14 hours per 100 square feet, depending on site conditions, logistics, and layout configurations.
In the contiguous 48 States, GeoBlock was tested on the Wambaw Cycle Trail in the Francis Marion National Forest near Charleston, SC. Sections of the trail had extensive trail braiding due to wet soils. Fifty-five feet of GeoBlock was installed with a clay-sand fill and a 2-inch cap over a geofabric layer. The installation completely stabilized the soils at the site. More than 3,500 passes had been made over the installation by endurotype motorcycles within the first 3 months of installation. According to the project manager, not one vehicle has ventured off of the hardened trail to further impact the wetland site. Except for minor rutting of the surface cap, there has been no noticeable wear to the surface of the GeoBlock panels (Parrish 2001).
Appendix A provides an evaluation of the two products. GeoBlock is highly suitable for use as a trail-hardening material. The 1 ¼-inch product, if available, would be suitable for most installation sites, while the 2-inch product could be used for extremely degraded segments, for crossing large ponded areas, and possibly for shallow water fords. SolGrid, which is still undergoing field tests, is suitable for irregular terrain and sloped areas, but is not as suitable for extreme conditions because of its limited ability to transfer lateral loads.
GeoBlock is available from Presto Plastics, Inc., P.O. Box 2399, Appleton, WI 54913. Phone: 800–548–3424; Web site: http://www.prestogeo.com
SolGrid is available from SolPlastics, 1501 des Futailles St., Montreal, PQ, Canada H1N3P. Phone: 888–765–7527.
Appendix B provides an installation guide for these products.
Matting—Matting is another method of wear-and-carry trail hardening. Metal matting was used extensively during World War II to reinforce soft soils during airport construction on tropical islands and at remote sites in Alaska. Some of those installations are still in place. The military stopped stocking metal matting in the 1950s and it is no longer manufactured. Its availability as a surplus material is very poor; therefore, it is not considered a viable material for trail hardening.
Matting available in the commercial market today is typically plastic decking or industrial antifatigue matting made from PVC or rubber. Plastic decking costs too much for trail hardening and is not discussed further. Rubber and PVC matting are somewhat more cost effective and are readily available. In contrast to the rigid porous pavement systems, matting is generally thinner and more flexible. It drapes across the terrain and provides an excellent wear surface, but has a limited ability to transfer lateral loads.
PVC Matting—Safety Deck was a commercially available PVC mat tested in the Wrangell-St. Elias mitigation study. Safety Deck is a high-density, semirigid, open-grid PVC mat that is ¾-inch thick. It was supplied in 20-inch-square tiles that were laced together with parachute cord (figure 25). Safety Deck was installed on moderately impacted trail surfaces so the need to transfer lateral loads wasn't too extreme. In this less demanding condition, Safety Deck provided an excellent surface for all forms of use. However, it was expensive to procure and time consuming to install. Safety Deck had good vegetation regrowth values with an increase from 69 to 91 percent mean cover over the 4-year study period.
Figure 25—Safety Deck installed across a tundra
surface in Wrangell-St. Elias National Park and
Preserve in Alaska. Individual 20- by 20-inch tiles
were lashed together with parachute cord and
fishnet line. This time-consuming task drove up
installation costs. The material performed very well
on moderately degraded trails and provided an
excellent surface for most uses.
Safety Deck was the most expensive material tested in the Wrangell-St. Elias study. Costs were $7.50 per square foot, including shipping. Forty-three labor hours were required to install a 100-foot-long, 6-foot-wide section of trail, for a total cost of $5,274 per 100 feet.
Appendix A shows the positive attributes of PVC Safety Deck. Although Safety Deck is a strong performer for moderately impacted sites, its high cost limits its use for most OHV trail-hardening applications. It may have excellent application on foot or horse trails where the volume of material is much reduced, or in providing a surface for accessible trails where the costs might be better justified.
Safety Deck is no longer commercially available. It was originally purchased from The Mat Factory, Inc., of Costa Mesa, CA, phone: 800–628–7626. The company carries a similar product called Dundee Grass Retention & Erosion Control Mat. That product sells for about $5.33 per square foot. Other PVC matting products may also be available.
Rubber Matting—Rubber antifatigue matting is commonly available in discount and hardware supply stores. Rubber mats are typically available in 3- by 3-foot panels, are ¾-inch thick and have an interlocking system along their edge (figure 26).
Figure 26—A section of rubber antifatigue mat
undergoing preliminary field trials at the Palmer
Hay Flats State Game Refuge in Alaska. The large
panels install quickly, but the rubber's flexibility
limits the panels' ability to transfer lateral loads.
Omni Grease-Proof Anti-fatigue Mat (manufactured by Akro Corp. of Canton, OH) and Anti-fatigue Mat (manufactured by Royal Floor Mats of South Gate, CA) were tested in a preliminary field trial in the spring of 2000 by the National Park Service and the Alaska Department of Fish and Game at the Palmer Hay Flats State Game Refuge. The mats protected the soil surface and conformed well to surface terrain, but provided no lateral load transfer. The wheel track was noticeably lower after 10 passes by an OHV on a silty substrate. The low rigidity of the rubber products and their inability to transfer load across the mat's surface limit their application for all but the lightest of impact areas.
A typical rubber mat sells for about $3.20 per square foot. Estimated installation time would be about 14 hours per 100 linear feet of 6-foot-wide trail.
Appendix A identifies a number of positive attributes of the rubber matting. Rubber matting is not suitable for trail-hardening applications on degraded trails because of its extremely low ability to transfer lateral load. Rubber matting would not prevent shear impacts on wet, finely textured soils. The material may have some limited applications before sites become degraded or could provide a temporary wear surface for special events.
Cost Comparisons for Trail-Hardening Techniques—Table 7 compares installation materials and labor costs for the trail-hardening methods discussed. The costs and hours of labor were developed for data in the Wrangell-St. Elias OHV mitigation study and other Park Service projects. These figures are rough estimates to assist in project scoping. Actual cost and the hours of labor depend on site conditions, logistics, and project design.
The test installations were small scale. Larger projects would benefit from volume discounts on materials and labor efficiencies. This is especially true when considering shipping costs of raw materials. The unit cost of shipping large quantities of bulky materials, such as the porous pavement products, can be much less than the cost of shipping small quantities.
Another important consideration is the cost of labor. The figures presented use an $18 per hour labor rate. This represents the cost of a typical government wage-grade seasonal maintenance worker in Alaska. The installation of trail-hardening materials is well suited for summer field crews, such as fire crews, Student Conservation Association crews, or volunteer crews. The work is relatively simple and doesn't require extensive use of power equipment. Fire crews filling in between fire calls or seeking early season training would be excellent sources of labor. The availability of cheaper labor could significantly reduce installation costs.
| Material | Cost per square foot ($) | Cost per 100 linear feet¹ ($) | Hours to install per 100 linear feet¹ | Labor costs per 100 linear feet¹ at $18 per hour | Installation cost per square foot ($) | Installation cost per 100 linear feet¹ ($) |
|---|---|---|---|---|---|---|
| Corduroy | 1.00 | 600 | 25 | 450 | 1.75 | 1,050 |
| Wood matrix | 0.80 | 480 | 70 | 1,260 | 2.90 | 1,740 |
| Onsite puncheon | 0.83 | 500 | 24 | 432 | 1.55 | 932 |
| Gravel/geotextile | 2.25+² | 1,350+² | 45 | 810 | 3.60+² | 2,160+² |
| GeoBlock, 1 ¼ inch | 2.75 | 1,650 | 38 | 684 | 3.89 | 2,334 |
| GeoBlock, 2 inch | 3.50 | 2,100 | 40 | 720 | 4.70 | 2,820 |
| SolGrid | 2.25 | 1,350 | 40 | 720 | 3.45 | 2,070 |
| PVC matting | 7.50 | 4,500 | 43 | 774 | 8.79 | 5,274 |
| Rubber matting | 3.50 | 2,100 | 14 | 252 | 3.92 | 2,352 |
| ¹ Trails are 6 feet wide. ² Depends on gravel source and haul distance. |
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Trail Closure
The final management option to be discussed is trail closure. As a last resort, resource managers may close a trail to protect threatened resources. This would halt direct trail impacts, but might not halt secondary impacts, such as erosion and sedimentation. A trail identified for closure needs to be assessed and stabilized or reclaimed as necessary.
Closing a trail is seldom popular with trail users. Before the action is taken, the proposed closure should be discussed at a public forum. Alternatives to the closure—such as reroute options, seasonal or type-of-use restrictions, controlled use, trail hardening, or other surface improvements—should be addressed and evaluated. Agency budgetary and workforce limitations that may restrict implementation of alternatives should be discussed. User groups may offer to accept some of the responsibility of maintaining or implementing necessary trail improvements to avoid losing access.
In the contiguous 48 States, user advocacy groups such as the American Motorcyclist Association and National Off-Highway Vehicle Conservation Council have often been able to help facilitate projects that protect trail access while assuring resource protection. These on-the-ground projects have rallied a large response from volunteer groups and individuals who develop a certain "ownership" of the trail resources they are working to protect. Often the energy generated by a resource conflict has been harnessed by land management agencies to generate support for work that has prevented trail closure.
