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Managing Degraded Off-Highway Vehicle Trails in Wet, Unstable, and Sensitive Environments

Trail Management—Responding to Trail Degradation

Management Components

The task of trail management ranges from planning, designing, and constructing trails to maintaining them. In an ideal world, every trail would have a formal, well thought-out management plan and a staff dedicated to its implementation. Unfortunately, that is not the case. In Alaska, the term 'orphan trail' has been coined to describe active trails that receive no management oversight at all. Trail management should include elements from these five basic building blocks:

Trail Location Documentation

Trail location documentation is plotting the location of the trail in a geographic database. A simple sketch of a trail location on a U.S. Geological Survey topographic map is better than no location data, but documenting the alignment with a mapping-grade global positioning system (GPS) unit is best. The GPS unit can record geographic coordinates of a trail alignment that can overlay digital topographic maps or be downloaded into a geographic information system (GIS). The GIS allows trail locations to be plotted over other geographic databases such as land ownership, soils, and terrain. Accurate trail location information is also critical for obtaining a legal right-of-way easement for a trail alignment.

Trail Condition Assessment

Condition assessment is an inventory of the physical character of a trail alignment. It documents conditions and problems and provides a baseline for monitoring changes over time. This assessment can be used to set priorities for trail prescription mapping (next section) and provide general information for future trail improvement work.

The assessment should evaluate the entire trail length, not just problem sites. This ensures that the assessment will provide a basis for evaluating condition trend during future monitoring efforts. Condition assessments can be conducted with manual data collection using a measuring wheel, tape measure, or odometer in the traditional "trail log" approach. The author has developed a simple alphanumeric system to classify individual trail segment conditions (table 3).

Table 3—Trail impact classes.
Impact class Subclass Description
A 1 Minor loss of original surface vegetation (over 80 percent remaining)
2 Moderate loss of original surface vegetation (40 to 80 percent remaining)
B 3 Most original surface vegetation stripped away (less than 40 percent remaining)
4 Exposed roots on trail surface
C 5 Almost total loss of root mass
6 Only exposed mineral or organic soil at surface
7 Erosive loss of less than 2 inches of soil, or compaction and subsidence less than 2 inches deep
D 8 Erosive loss of 2 to 8 inches of soil, or compaction and subsidence 2 to 8 inches deep
F 9 Erosive loss of 9 to 16 inches of soil, or compaction and subsidence 9 to 16 inches deep
10 Erosive loss of more than 16 inches of soil, or compaction and subsidence more than 16 inches deep
11 Trail segment intermittently passable during dry conditions
12 Trail segment impassable at all times

For quick assessments, trail segments can be classified using classes A to F. For more detailed assessments, the numeric subclass designators can be used.

Trail segments with class A impacts have yet to experience significant degradation. Class B segments are generally new trails or lightly traveled routes. Segments with class C impacts display the beginnings of detrimental impacts, but have not yet been seriously degraded. Monitoring these sites should be a high priority. Segments with class D impacts display degradation due to poor site conditions or excessive use. Mitigation may be needed to stabilize impacts. Segments with class F impacts are seriously degraded trails, probably with significant environmental impacts. These sites should receive a high level of management attention. Methods to respond to the degradation of classes D and F trail segments are detailed later.

While table 3 presents a classification system for manual assessment, a much more powerful and descriptive assessment can be made by using a mapping-grade GPS receiver that attaches line, point, and area descriptors with collected trail alignment coordinates. The author has developed a trail condition mapping legend (table 4) that can be used with standard mapping-grade GPS software and equipment. The legend contains a fairly complete list of trail condition attributes, and it can be used as the starting point to develop a customized legend appropriate for any specific trail system. When the data elements in table 4 are loaded into a menu-driven GPS mapping system, they can be collected easily during trail condition mapping.

Table 4—Trail condition mapping legend (bold text identifies the more important data fields).
Feature element Menu selection options
Trail segment type (feet) Single track, double track, or multibraid 6 to 20, 21 to 40, 41 to 80, 81 to 160, 161 to 320, 321 to 480, wider than 480
Trail track type Main, secondary, abandoned, access, cutoff, spur
Trail surface grade (percent) Zero to 6, 7 to 20, 21 to 40, steeper than 40
Side slope (percent) Less than 20, 21 to 60, 61 to 100, steeper than 100
Trail surface Vegetated, native organic, wetland vegetated, floating organic, native fine mineral, mixed fines and gravel, sand, gravel, cobble, imported gravel, gravel over geotextile, wood chips, timbers/planking, corduroy, paved, porous pavement panel, rock, water crossing, other
Trail impact rating None
Loss of surface vegetation
Exposed roots
Less than 2 inches erosive loss or surface subsidence
2 to 8 inches erosive loss or surface subsidence
9 to 16 inches erosive loss or surface subsidence
17 to 32 inches erosive loss or surface subsidence
33 to 60 inches erosive loss or surface subsidence
More than 60 inches erosive loss or surface subsidence
Mud-muck index None, muddy, extremely muddy, muck hole, multiple muck holes, seasonally impassable, impassable at all times
Trail drainage Well drained, moderately well drained, poorly drained, saturated, ponded, water running across surface
Stone hindrance (percent) None, less than 10, 11 to 25, 26 to 75, 76 to 100
Track width (feet) One to 3, 4 to 6, 7 to 12, 13 to 20, 21 to 30, 31 to 40, 41 to 60, over 60
Vegetation stripping Single track, wheel track only, full width of trail
Type of use Multiuse, foot only, motorized only
Season of use Multiseason, winter only, thaw season only
Road type Access, primary, secondary, subdivision, unimproved, other
Road surface Paved, gravel, dirt
Road width (feet) 8 to 12, 13 to 16, 17 to 20, 21 to 30
Line type Text entry
Type Water bar, grade dip, rolling dip, round culvert, box clvert, open drain, sheet drain, check dam, ditch
Condition Serviceable, poor
Culvert size (inches) Numeric entry
Type Unimproved ford, improved ford, bridge, culvert
Stream name Text entry
Stream width (feet) Numeric entry
Approximate flow
(cubic feet per second)
Numeric entry
Frame/reference No. Numeric entry
Bearing (degrees) Numeric entry
Type Beginning, middle, intersection, angle, end
Type Milepost, trailhead, trail marker, survey marker, property marker, road crossing, junction, gate or barrier, other
Mileage Numeric entry
Type Scenic vista, pullout, shelter, campsite, cabin, structure, powerline, fence, staging area
Type Text entry
Type Informational, directional, regulatory, warning
Text Text entry
Type Text entry

Figure 6 displays a GPS plot of a complex trail system with a large number of braided trail segments. Note the highlighted trail segment at the top of the image. The 'Feature Properties' data frame to the right of the screen lists the characteristics of that trail segment as it was mapped in the field. Similar data detail can be extracted for every line segment, point, or area feature displayed on the screen. The 'Feature Properties' box shows the location, date of data acquisition, and precision of the data collected.

Image of a computer mapping program showing a trail map and dialog boxes for position properties and feature properties.

Figure 6—This computer screen display shows the mapping
legend for a complex trail system with a large number of
braided trails. The feature properties (data box on the right)
relate to the bolded trail segment at the top of the display.
For a larger image click here.

Data collected with this level of sophistication should be downloaded into a GIS system. While a GIS requires a relatively high level of technical support, it can have tremendous payoffs for trail management. Once downloaded, the data can be subjected to a wide variety of map and tabular analysis, including overlay with other geographic information such as soils and terrain. Attribute values can be used to generate trail segment impact ratings and to identify critical problem areas. The length and area of trail segments can be calculated to help estimate mitigation and maintenance costs. When the condition inventory is incorporated into a GIS, it provides a baseline of trail conditions that can be used to plan and track monitoring efforts, evaluate trail performance across varying soils and landscape units, and plan future work.

Based on the author's experience and some limited contract work conducted by the Bureau of Land Management in Alaska, about 8 miles of trail can be mapped per day by a two-person crew mounted on OHVs using the GPS-based system. Production rates vary depending on trail conditions, weather, access, staff experience, and equipment performance. Office support work is required in addition to the field work. Allow about twice as much time in the office as in the field to set up equipment, load data dictionaries, download data, edit data, and integrate the data into a GIS.

Trail Improvement Prescriptions

Trail prescriptions focus on identifying locations for specific treatment applications, such as surface improvements, ditches, brush control, water management, and water-crossing structures.

The crew preparing trail prescriptions needs to be knowledgeable of the treatments available for specific trail ailments. Unlike condition mapping, which requires just a basic knowledge of field inventory technique, prescription mapping requires expertise in trail planning, construction and maintenance, and knowledge of the trail construction and maintenance resources that are available.

Prescription mapping can be greatly assisted by GPS/GIS technology. Table 5 is a prescription mapping legend developed by the author. It identifies a wide range of treatments and can be adapted readily for use on any trail systems.

Table 5—Trail prescription mapping legend (bold text identifies the more important data fields).
Feature element Menu selection options
Trail type Active, inactive, new segment, access, water crossing, other
Surface Treatment No treatment, light water management, heavy water management, grading/leveling, gravel cap, gravel/geotextile, porous pavement, corduroy, turnpike, puncheon-boardwalk, abandon—no treatment,
abandon with light rehabilitation, abandon with heavy rehabilitation
Gravel cap depth (inches) None, 2 to 4, 5 to 8, 9 to 12, 13 to 18, deeper than 18
Trail width (feet) Numeric entry
Surface treatment priority High, medium, low
Ditching None, left (outbound), right (outbound), both
Ditching priority High, medium, low
Brush control None, left, right, both
Brushing priority High, medium, low
Root removal None required, required
Cut-and-fill section (percent side slope) None, less than 15, 16 to 45, 46 to 100, more than 100
Type Text entry
Type Beginning, middle, intersection, angle, end
Type Milepost, trailhead, trail marker, survey marker, property marker, road crossing, junction, gate or barrier, other
Mileage Numeric entry
Type Water bar, grade dip, rolling dip, culvert (diameter in inches, less than
8, 9 to 16, 17 to 36, larger than 36), check dam, open drain, other
Type (feet) Unimroved ford, improved ford, bridge (shorter than 12, 13 to 24, longer than 24)
Reference number Numeric entry
Bearing Numeric entry
Type Scenic vista, pullout, shelter, campsite, cabin
Type Tree removal, stump removal, rock removal, guardrail, fill hole, other
Type Informational, directional, regulatory, warning
Text Text entry
Type Switchback center point, climbing turn center point

A prescription inventory collected with a GPS system provides an excellent basis for cost and labor estimates, but it does not have the familiar '1+00' trail log references typically associated with trail inventory work. Therefore, ground location reference points should be established before or during the inventory. Markers every one-quarter mile—or every 1,000 feet—are not too close for detailed surveys. Measuring wheels and OHV odometers are common measuring devices for establishing approximate milepost locations. Labeled flagging, lath, or metal tags should be placed at these standardized reference points. The more permanent the markers, the better.

Trail Improvement Implementaion

Improvement implementation is planned trail maintenance, stabilization, or mitigation based on a trail improvement prescription. Improvement actions should be based on standard design specifications or commonly accepted management practices. Commonly accepted practices are best described in the following Federal and private publications:

Building Better Trails. 2001. International Mountain Bicycling Association, P.O. Box 7578, Boulder, CO 80306. Phone: 303–545–9011; e-mail:; Web site: May be purchased both in HTML and PDF formats from the Web site or the IMBA office. 64 p. in printed book format.

Installation Guide for Porous Pavement Panels as Trail Hardening Materials for Off-Highway Vehicle Trails. 2001. Kevin G. Meyer. USDI National Park Service—Rivers, Trails, and Conservation Assistance Program Technical Note, 2525 Gambell St., Anchorage, AK 99503 (attached as appendix B).

Lightly on the Land—The SCA Trail Building and Maintenance Manual. 1996. Robert C. Birkby. The Mountaineers, 1001 SW. Klickitat Way, Seattle, WA 98134.

Off Highway Motorcycle & ATV Trails Guidelines for Design, Construction, Maintenance and User Satisfaction. 2d Ed. 1994. Joe Wernex. American Motorcyclist Association, 13515 Yarmouth Dr., Pickerington, OH 43147. Phone: 614–856–1900; fax: 614–856–1920, e-mail:; Web site:

Trail Building and Maintenance. 2d Ed. 1981. Robert D. Proudman and Reuben Rajala. Appalachian Mountain Club, 5 Joy St., Boston, MA 02108.

Trail Construction and Maintenance Notebook. 2000. Woody Hesselbarth and Brian Vachowski. Tech. Rep. 0023–2839–MTDC. United States Department of Agriculture, Forest Service, Missoula Technology and Development Center, 5785 Hwy. 10 West, Missoula, MT 59808–9361.

Wetland Trail Design and Construction. 2001. Robert T. Steinholtz and Brian Vachowski. Tech. Rep. 0123–2833–MTDC. United States Department of Agriculture, Forest Service, Missoula Technology and Development Center, 5785 Hwy. 10 West, Missoula, MT 59808–9361.

In addition to these references, supplementary information is available from the Missoula Technology and Development Center. Call 406–329–3978 to request the latest list of recreation publications and videos. Many of these are available through the Federal Highway Administration's Recreational Trails Program. To obtain a list of publications and an order form, go to Web site:

Each of these documents provides valuable information on trail design, construction methods, maintenance, or general trail management. While some may be regional in nature or focus on specific types of trails, their basic concepts can be adapted to OHV trails.

Trail Maintenance and Monitoring

Each trail alignment should receive regular maintenance at least once a year, preferably early in the season of use. Primary activities should include maintaining water-control structures, ditches, and culverts, and clearing fallen timber.

Periodic inspections also should be made of bridges, especially after spring breakup or floods. Maintenance crews also should report on problem areas and maintenance concerns. In many cases, periodic, systematic maintenance can head off major trail degradation.

Monitoring to detect changes in trail conditions, including a complete condition assessment, should be conducted about every 5 years, depending on levels of use and a trail's soil and terrain characteristics. This frequency could be increased if significant environmental values are at risk, but enough time should pass between assessments to filter out changes due to seasonal effects, weather effects, or the subjectivity of inventory crew personnel. The same inventory classification system should be employed during each monitoring with key components such as trail surface character, trail impact rating, trail drainage, mud-muck index, and track width recorded from identical menu selection options.

Management Response to Severely Degraded Trails

Managing severely degraded trails presents a formidable challenge to resource managers. Severely degraded trails tax traditional trail management techniques and sometimes force managers to investigate and test innovative management methods, refining them for local conditions. No single set of responses can meet every situation, but a framework can help guide the process.

The trail degradation issue must be addressed on several fronts. The National Off-Highway Vehicle Conservation Council (NOHVCC), a nonprofit OHV advocacy group, uses an approach they call the Four Es. They are:

  • Education
  • Evaluation
  • Engineering
  • Enforcement

Education is needed to teach users about responsible riding and appropriate environmental ethics. In addition, resource managers and technicians need to be educated about effective trail management practices. Evaluation is necessary to develop methods to document use, assess impact, and evaluate mitigation methods. Engineering is necessary to develop trail improvement techniques and equipment modifications to reduce impacts. Enforcement is necessary to manage use within acceptable impact limits. In many locales, enforcement isn't a viable option. In those areas, enforcement may be implemented as "encouragement," encouraging users to conduct their activities in a sustainable manner. This might best be achieved by providing trail location maps that direct users to sustainable trails and trail signs that encourage appropriate use.

I would also add a fifth E: 'Enculturation' (the process of modifying human behavior over time). Enculturation can best be accomplished by the steady application of education, appropriate evaluation techniques, progressive engineering, appropriate enforcement, and encouragement.

The five Es show how broadly the issue of degraded trails must be addressed. Unfortunately, this report addresses a only a few of the five Es. It is intended as a tool to help educate trail managers and users about OHV trail degradation. In addition, the section on trail condition inventory presents an important evaluation component, and the following section identifies engineering solutions within a range of management options. These options include:

By evaluating these options and developing a forum with users, advocacy groups, and the environmental community, trail managers can resolve many of the conflicts between degraded trails and environmental resources.

Trail Rerouting

Few OHV trails are planned trails where a full range of environmental considerations was carefully weighed before construction. In fact, few trails are specifically constructed for OHV use. Most OHV trails developed as individual riders followed game or foot trails or passed through natural corridors to remote fishing, hunting, or cabin sites. In Alaska, many OHV trails develop along routes that originally served as dogsled or snowmobile trails.

Because of the unplanned nature of OHV trails, many of them cross soils and sites poorly suited for the level of use occurring on them today. For example, a trail that originally developed from a game trail may not be suitable as a primary access route into a heavily used recreation area. A winter route across snow-covered wetlands doesn't necessarily provide a good alignment for a summer OHV route.

When numerous segments of a trail have been significantly degraded by the level of use, trail managers need to ask the following questions:

  • Do opportunities exist to reroute the trail onto better soils and terrain?

  • If yes, what is the cost of stabilizing the existing route com-pared to constructing a new trail alignment and rehabilitating the old one?

In some cases, moving a trail or segment may be an effective method of responding to trail degradation. For example, moving a trail from a foot slope to a side slope may significantly reduce trail wetness. Moving a trail from an open wetland to an adja-cent woodland may stop trail braiding. Figure 7 shows an example where rerouting should be considered.

Photo of a heavily used OHV trail.
Figure 7—A heavily used OHV trail
in Alaska crosses two distinct soil
types. In the foreground, the trail passes
through a mixed forest ecosystem where
the soils support use along a single track.
In the background, the trail crosses degraded
wetland soils where users have created a
braided trail. Managers should consider rerouting
the trail to stay within the forest system.

A rerouting assessment should follow this process:

  • Obtain and evaluate aerial photography of the trail alignment.

  • Obtain soils data for the area surrounding the trail. Soil survey reports are available from the USDA Natural Resources Conservation Service.

  • Conduct a site visit. Take available aerial photography and soils data with you. Visit the site during the primary season of use. Evaluate the trail conditions on the ground to identify relationships between vegetation communities, terrain, soil conditions, and trail performance. Table 1 may be of some assistance. Use aerial photographs to identify adjacent areas that might support trail use. Identify alternative trail routes on aerial photographs and flag those routes on the ground.

  • Identify the long-term benefits of the new route compared to continued use of the existing route.

  • Develop a trail design for the alternative route. Develop a detailed construction plan. Identify any stabilization or reclamation work that is needed on the abandoned trail alignment. Identify methods to redirect use onto the new alignment using barriers, markers, or signs.

Decisionmakers and environmental groups may object to constructing new alignments where existing trails have failed, so it is important to have photos documenting the difference between trail segments on degraded sites and trail segments on more suitable sites. Illustrate the sustainability of the pro-posed new location to build consensus for the reroute option.

Seasonal or Type-of-Use Restrictions

Seasonal-use restrictions are another option for responding to trail degradation. Because soils are most sensitive to impact when they are wet, restricting use of sensitive trails during spring breakup or periods of high rainfall may significantly reduce trail degradation. Also designating winter-season trails that cross wetlands as 'WINTER ROUTES ONLY' would significantly reduce impacts on sites that are extremely sensitive to impact by motorized vehicles during summer months.

Type-of-use restrictions limit the kind of equipment allowed on trails. For example, restricting gross vehicle weight to less than 1,500 pounds could significantly reduce the size of equipment operating on a trail. This would allow managers to build trails to a much lower design specification than when weight is unlimited.

In general, the potential of trail activities to create impacts ranges from slight to heavy as shown in table 6.

Table 6—Activities that have the potential to impact trails.
Impact Use
Nonmotorized Motorized
down arrow (Minimum snow cover 6 inches) (Minimum snow cover 12 inches)
Skiiing/snowshoeing Snowmobiling
down arrow Dog sledding
Nonmotorized Motorized
down arrow Hiking Light, tracked vehicles
Mountain biking Motorcycle riding
down arrow Horseback riding OHV riding (less than 1,500 pounds gross vehicle weight)
Potentially heavy Unlimited off-higway vehicle use

Reducing the types of use would lessen the potential for impact. Successfully restricting trail use requires user cooperation and enforcement. Signs, gates, and barriers aren't enough to discourage some users, so public education and development of alternative routes on more resilient trails are needed to encourage compliance.

Controlled Use (Traffic Volume Restrictions)

Controlled use is another management option when responding to trail degradation. Trail degradation occurs when use exceeds the ability of the trail surface to resist impact. Controlling the level of use can be a powerful tool in reducing impacts. Determining the appropriate level of use can be difficult, especially since a trail's resistance to impact can change with weather and type of use. Good decisions require knowledge of existing trail conditions, patterns and levels of use, and trail condition trends. If trail conditions are stable under existing loads, no volume restrictions may be necessary. If trail conditions are deteriorating, traffic volume may have to be decreased or trail surfaces may need to be modified to support the increased use.

Managing trails through controlled use is complicated because there may not be a linear relationship between use levels and impact. Typically, after a certain level of impact is reached, trails will continue to degrade without any further use. This is clearly the case when vegetation stripping exposes soils to erosion. Finding the balance between appropriate levels of use and acceptable impacts is a resource management art form, ideally backed up with good monitoring of the level of use and resource damage.

Controlled use also requires an authorized and determined enforcement presence. This may not be readily available. But where it is, monitoring impact and setting the allowable use may be a good management approach to controlling degradation problems.

Trail Hardening

Another management option is trail hardening. Trail hardening is a technique of modifying trail surfaces so they will support use without unacceptable environmental impacts to vegetation, soils, hydrology, habitat, or other resource values. Trail hardening should be considered under the following conditions:

  • Existing trail impacts are causing or are projected to cause unacceptable onsite or offsite impacts, and

  • More suitable alternative trail locations are not available, or

  • Alternative trail locations are not environmentally acceptable or economically feasible.

Trail hardening provides the following benefits:

  • Defines a single trail alignment for vehicle travel.

  • Stabilizes surface soil conditions along the hardened trail section.

  • Provides a stable, durable trail surface for OHV traffic.

  • Halts trail widening and the development of braided trail sections.

  • Allows formerly used trail alignments to naturally stabilize and revegetate.

  • May provide for vegetation growth (or regrowth) within the hardened trail surface that helps to reduce visual impacts, maximize site stability and increase site productivity.

Trail hardening seeks to improve trail surfaces by one of three methods:

The goal of trail hardening is to reinforce soils so they will support a specified level of use under all environmental conditions. Because of the range of trail-hardening methods available, a trail manager must select a method that provides maximum utility for the investment in time, labor, and cost. Utility includes site stabilization, resource protection, and suitability for use as a surface for OHV traffic (figure 8).

Aerial photo of a hardened OHV trail.

Figure 8—This aerial image shows a recently installed
section of hardened trail crossing a wetland in southcentral
Alaska. The new trail alignment defines a single route of travel
that will prevent the continued development of braided trails.

The following section introduces a number of trail-hardening techniques.

Trail Hardening—Replacing or Capping Unsuitable Soils

Replacing unsuitable soils is the most intensive, trail-hardening technique. Problem soils are excavated and removed until a subbase of competent subsoils or gravel has been exposed. High-quality material is placed over the subbase to bring the trail surface up to the trail's original level. This process is appropriate for trails with a suitable subbase close to the surface and a convenient source of high-quality fill. The work generally requires heavy equipment. It is most appropriate near trailheads and along highways where heavy equipment can be used to good advantage.

Where a suitable subbase is not close to the surface or excavation work needs to be minimized, geotextile fabrics may be used to provide a base for surface capping. The use of geotextile materials extends the application of capping to many areas where removal of substandard surface soils is impractical.

Geotextiles, also known as construction fabrics, are widely used in roadways, drains, embankments, and landfills. They are constructed of long-lasting synthetic fibers bonded by weaving, heat, extrusion, or molding. They come in a wide variety of types including fabrics, sheets, or three-dimensional materials. They can be pervious or impervious to water passage.

Geotextiles provide four important functions in road and trail surface construction:

  • Separation
  • Stabilization
  • Reinforcement
  • Drainage

These functions are illustrated in figures 9a, 9b, and 9c. Geo-textiles work as separation fabrics when they are placed between gravel caps and underlying soils to prevent the materials from mixing. The geotextile serves to maintain the original thickness and function of the gravel cap as a load-bearing layer. Geotextiles increase soil stabilization by maintaining the load transfer capability of the gravel cap. This increases effective bearing capacity and prevents subsoil pumping. Geotextiles reinforce soils by providing a structure to bond the gravel cap and underlying soils.

The geotextile fabric locks the two materials together and allows the soil to receive a load across a broader footprint. Geotextiles also help maintain the drainage characteristics of the gravel cap. In addition to use in trail tread, geotextiles can have important applications in erosion control, drainage interception (sheet drains), and ditch liners.

Cross-sectional drawing of the directional forces from a tire on a gravel surface without geotextile with points labeled: Aggregate cap, Shear force, Cross contamination leads to impacts from shear stress, ground surface, Aggregate migration, Upward movement of soil, and Substandard soil base.

Figure 9a—Gravel cap without geotextile. The
aggregate cap will lose strength as the gravel is
contaminated by the subbase.

Cross-sectional drawing of the components of a tire on a gravel surface with geotextile with labels: Aggregate cap, Ground surface, Drainage, Separation, Geotextile layer, and Substandard soil base.

Figure 9b—Gravel cap with geotextile. The
geotextile layer prevents the migration and
contamination of the surface gravel cap by
underlying poor-quality soils.

Close-up cross-sectional drawing of the directional forces from a tire on a gravel surface with geotextile.Points labeled on the drawing are: Ground surface, Shear force contained within gravel cap, Increased stabilization, Improved drainage, Separation, Distributed load, Geotextile acts as a soil reinforcement layer, and Aggregate carries load.

Figure 9c—Gravel cap with geotextile. Using a
geotextile enhances trail performance through
separation, stabilization, reinforcement, and drainage.

Site conditions such as soil texture, moisture, depth to foundation materials, and the type of use indicate when a geotextile fabric should be used. Because gravel is difficult and expensive to deliver onsite, the use of a separation fabric makes good economic sense to protect the function of the gravel cap. The use of a geotextile fabric requires adequate capping (a minimum of 6 inches) and regular maintenance to maintain the cap. Regular maintenance prevents the geotextile fabric from being exposed at the surface.

The National Park Service experimented with the use of geo-textile and gravel placement during the summer of 1999 on degraded trail segments of a former mining road connecting two administrative sites in the Yukon-Charley Rivers National Preserve (Meyer 1999a). About 678 feet of geotextile with a 4- to 6-inch gravel cap was installed over soils in areas that crossed melted permafrost soils. Using this technique, the road alignment was reclaimed as an OHV trail.

Geotextile and gravel placement is relatively simple. The Yukon-Charley approach was adapted from Forest Service methods (Monlux and Vachowski 1995, figure 10). This technique provides a rim structure to minimize the loss of cap material (figures 11 and 12). A local source of suitable gravel was identified. One-half-cubic-yard belly dump trailers, loaded by a skid-steer loader and towed by 4x4 OHVs, transported gravel to trail construction sites.

Cross-sectional drawing of a layer of gravel fill over a layer of geotextile spaced 6 feet apart and bordered by two rim poles.

Figure 10—Adapted geotextile installation design.

Photo of the author placing geotextile around a rim pole at an installation.

Figure 11—The author installing woven geotextile
around a rim log in the geotextile gravel-capping test
installation at the Yukon-Charley Rivers National Preserve
in Alaska. The rim log held the gravel cap on the installation.

Photo of the gravel fill being spread over an insallation of geotextile.

Figure 12—A geotextile and gravel-cap installation
over permafrost-degraded soils in Yukon-Charley
Rivers National Preserve in Alaska. Use of geotextile
and a gravel cap on this trail allowed the National Park
Service to construct a 6-foot-wide OHV trail over a 3- to
4-foot-deep muck hole.

About 45 labor days and 80 cubic yards of gravel were required to construct 678 linear feet of 6-foot-wide trail, roughly 45 work hours per 100 feet of hardened trail. Construction efficiency dropped considerably when construction sites were more than one-quarter mile from the gravel source because of the small size of the transport vehicles and the round-trip travel time. The loaded trailers, weighing about 2,000 pounds gross vehicle weight, also seriously degraded marginal trail segments along the haul route. Future operations at the site will use larger haul vehicles operating over frozen soils during the winter months.

The geotextile used on the project was AMOCO 2000, a light-grade woven synthetic fabric. The material cost about 5 cents per square foot, quite inexpensive, considering all other costs. Overall construction costs for the project were estimated at $3.60 per square foot using a labor rate of $18 per hour.

Cellular Confinement Systems—Cellular Confinement Systems (CCS) are three-dimensional, web-like materials (figure 13) that provide structural integrity for materials compacted within the cell. They are engineered so cell walls limit the transfer of shear forces within the soil. Employed worldwide for a wide variety of uses, cellular confinement systems are a well-accepted soil engineering tool (Ron Abbott 2000). In Alaska, these systems have been used with success on military runways and remote radar sites, Arctic tank farms, construction sites, and boat ramps (Joseph Neubauer 2000). The systems also have been used when constructing shallow-water fords in the contiguous 48 States (Forest Service 1987).

Photo of gravel fill being spread into a cellular confinement system.

Figure 13—A cellular confinement system being
installed on an experimental trail in southcentral
Alaska. Four-inch-deep cells were formed by
expanding the cellular product accordion style, then
backfilling and compacting with a suitable fill material—
in this case, sandy gravel. The sides of the installation
were confined by a 6-inch-deep trench.

A cellular confinement system consists of a surface-aggregate wear surface, the cell membrane, fill material, and an optional separation fabric (depending on site characteristics). Fill material is usually imported gravel, but onsite material can be used in some circumstances (the use of onsite fill will be covered later). Installation of the system is labor intensive. The smallest cell commercially available is 4 inches deep. A minimum of 6 inches of fill material is required to fill the cells and provide a 2-inch wear surface, about 1 cubic yard of loose material per 6 linear feet of a 6-foot-wide trail. While the cell material alone costs about 70 to 90 cents per square foot, installation costs include the costs of any separation fabric, the fill, cap material, transportation of materials, cell panel connectors, and excavation of a trench or the construction of a curb or rim to confine the materials.

Test installations of cellular confinement systems for trail use in the contiguous 48 States have shown mixed results (Jonathan Kempff 2000). While the systems provided excellent structural reinforcement for soils, maintaining the surface wear cap to protect the cell membrane has been difficult. Without adequate curbing, capping material tends to erode from the cell surface. This is particularly true on sloped surfaces. With the loss of capping material, the cell membrane becomes exposed to damage by trail users. Although such damage usually doesn't significantly affect the cell's strength, exposed cells are unsightly and create a tripping hazard.

A somewhat similar problem occurred in the Bureau of Land Management's White Mountains District in Alaska. The agency reported mixed to poor results using cellular confinement systems on roadways in the Fairbanks area (Randy Goodwin 2001). Cellular confinement systems were used to cap four culvert installations on the Nome Creek road. The systems were installed in 50- to 200-foot segments to provide a stable fill road surface. Spring melt of overflow ice (aufeis), that typically plugs the culverts, scoured fill material out of the web cells each year. Replacing the fill without damaging the cell structure was difficult and time consuming.

Also in Alaska, about 900 feet of cellular confinement systems, with recycled asphalt fill and cap, were installed in 2000 on an access trail in the Turnagain Pass area by the Forest Service (Doug Blanc 2001). Based on the success of that installation, the Forest Service is planning another 3-mile installation adjacent to a visitor center. Both trails were designed to meet the requirements of the Americans With Disabilities Act and are not representative of remote OHV trails. A more representative installation is a 20-foot test installation at Palmer Hay Flats State Game Refuge (figure 13). Since its installation in August 2000, the trail surface has been performing well, but the capping material has begun to show signs of erosion (Colleen Matt 2001).

Cellular confinement systems are manufactured under a variety of trade names, including Geoweb, Envirogrid, and TerraCell.

  • Geoweb is available from Presto Plastic Co., phone: 800–548–3424.

  • Envirogrid is available from AGH, phone: 713–552–1749.

  • TerraCell is available from WEBTEC, phone: 800–438–0027.