Geosynthetics for Trails in Wet Areas: 2008 Edition

Geosynthetic Product Information

The following manufacturers and products were included in the "Specifier's Guide for Geosynthetic Materials" published by Geosynthetics Magazine, available from the Industrial Fabric Association International Resource Center, 1801 County Road B.W., Roseville, MN 55133-4061 (800-225-4324). The recommended minimum physical properties listed are from the Forest Service's "Standard Specifications for Construction and Maintenance of Trails" (1996). The recommended physical properties are typically on the low end of those available because trails applications are much less demanding than geosynthetic applications in road construction where heavy machinery and large, angular boulders require stronger products.

This edition of "Geosynthetics for Trails in Wet Areas" does not recommend specific products. Hundreds of suitable products are available from manufacturers and even home improvement centers. Most manufacturers and geotechnical or materials engineers can help you select products if you provide details on soil and moisture conditions and expected loads (trails generally have light loads).

No prices are listed. Prices may change quickly because of changes in the price of the petroleum (the raw material). Call the listed phone numbers for current prices delivered to your area or to contact the local sales representative. Manufacturers may provide prices by the square meter, square yard, square foot, or for full rolls. Unit costs decrease as the amount ordered increases. All geosynthetic products can be cut in the field or cut by the manufacturer to meet your requirements.

Geotextiles

Critical physical properties for geotextiles used in trail construction:

• Material structure: Nonwoven
• Polymer composition: Polypropylene
• Apparent opening by ASTM D 4751-87: Less than 0.297 millimeter (mesh larger than No. 50)
• Permittivity by ASTM D4491-92: More than 4,060 liters per minute per square meter (more than 100 gallons per minute per square foot)
• Puncture strength by ASTM D4833-88: More than 0.110 kilonewton (more than 25 pounds)
• Mullen burst by ASTM D 3786-87: More than 900 kilopascals (more than 130 pounds per square inch)
• Trapezoid tear strength by ASTM D4533-91: More than 0.110 kilonewton (more than 25 pounds)
• Grab tensile at 50 percent elongation by ASTM D4632-91: More than 0.355 kilonewton (more than 80 pounds)
• Ultraviolet degradation: More than 70 percent retained strength at 150 hours

Notes: The products that work best for trail applications typically are the nonwoven, felt-like materials that are easier to work with rather than heat-bonded or slit-film products that have a slick surface. Physical property requirements are minimum average roll values where applicable. Compare your desired widths with standard roll widths and consult with manufacturers when deciding whether it's best to cut the fabric in the field or have the manufacturer cut it.

Geonets

Critical physical properties of geonets used in trail construction:

• Polymer composition of core (net or mesh): Medium- or high-density polyethylene.
• Geotextile: Must be attached to both sides of the core and meet or exceed the requirements of AASHTO M 288 Subsurface Drainage Class B with permeability greater than 0.0001 centimeter per second, and an apparent opening size less than 0.297 millimeter (larger than the No. 50 U.S. Standard Sieve).
• Core thickness: Thicker than 5 millimeters by ASTM D5199.
• Compressive strength of core: Stronger than 500 kilopascals by ASTM D1621.
• Transmissivity with gradient of 0.1 and pressure of 10 kilopascals: More than 0.0009 square meter per second (more than 4 gallons per minute per foot).

Notes: Discuss the roll width and length requirements for your project with manufacturers.

Geogrids

Critical physical properties of geogrids used for trail applications:

• Polymer type: High-density polyethylene, polypropylene, or polyester with acrylic or PVC coating
• Mass per unit area by ASTM D5261-92: 175 grams per square meter (more than 5.5 ounces per square yard)
• Maximum aperture size: Machine direction (MD): 100 millimeters (4 inches). Cross direction (XD): 75 millimeters (3 inches)
• Wide-width strip tensile strength at 5-percent strain by ASTM D4595-86: Machine direction (MD): 8 kilonewtons per meter (550 pounds per foot). Cross direction (XD): 6 kilonewtons per meter (410 pounds per foot)

Notes: Specify desired product widths and lengths for the project application.

Geocells

Critical physical properties of geocells used for trail construction:

• Composition: Polyethylene or high-density polyethylene.
• Geocell weight expanded: Heavier than 1.7 kilograms per square meter (heavier than 50 ounces per square yard).
• Minimum cell seam peel strength by U.S. Army Corps of Engineers Technical Report G:- 86-19, Appendix A: 800 newtons (180 pounds).
• Expanded dimensional properties: As specified by the designer--see the manufacturer's dimensions.

Notes: Specify the desired product widths for the project application. The 100-millimeter (4-inch) cell depth should be adequate for trails--depths from 50 to 200 millimeters (2 to 8 inches) are available. Consult manufacturers for the availability of different section widths and alteration of standard section widths to fit your project needs.

Geocomposites--Sheet Drains

Critical physical properties of sheet drains for trail construction:

• Structure: Single- or double-dimpled core
• Core polymer composition: Polystyrene or polypropylene
• Attached geotextile: Nonwoven on one side if the core is solid, on both sides if the core is perforated. Geotextile must meet or exceed the requirements of AASHTO M 288 Subsurface Drainage Class B with permeability more than 0.0001 centimeter per second and an apparent opening size less than 0.297 millimeter (larger than the No. 50 U.S. Standard Sieve)
• Core thickness by ASTM D5199: Thicker than 10 millimeters (thicker than 0.40 inch)
• Core compressive strength at yield by ASTM D1621: More than 650 kilopascals (more than 95 pounds per square inch)

Notes: Compare desired width with standard sheet width and consult with manufacturers to learn whether the material can be cut easily in the field and how much it would cost to have it cut at the factory. Sheet drains with cores made from thicker materials usually have greater bending strength, limiting the amount of settling in soft soils and reducing the amount of fill material needed. Various core thicknesses are available.

Geo-Others--Turf Reinforcement

Erosion Control

Identification of Unsuitable Tread Fill Material

Soils from wet areas are normally not suitable for use as tread fill because they are too moisture sensitive and lose strength easily when they become wet. It's important to avoid spending scarce dollars to excavate and haul fill that will fail when wet. Poor materials can be identified by several methods.

Organic Soils: Identified by musty odor when they are damp, and they are dark in color.

Other Unsuitable Tread Fill Materials: The stability of tread fill material is influenced primarily by the amount of silt or clay. If the fill is more than 20 percent silt and clay, the fill will probably become unstable when wet. Rough evaluations for suitability can be done by the following methods.

Method A--Field Comparison

Compare proportions of gravel, sand, and fines in existing trail tread materials with the proportions in borrow sources. Individual "fine-size" material particles are not visible to the naked eye and are classified as silt or clay. If the proportions of gravel, sand, and fines are similar, you can expect the borrow materials to perform as well as the existing trail tread materials. If the borrow source has a lower proportion of fines, you can expect better performance.

Method B--Laboratory Test

Take a 5-kilogram (10-pound) sample of the proposed tread fill material to a materials testing laboratory for a washed sieve analysis to determine the percentage of minus No. 200 material. The minus No. 200 material represents the amount of silt or clay. If the sample has more than 20 percent minus No. 200 material, it is not suitable for fill. A washed sieve analysis typically costs $50 to $100.

Method C--Geotextile Field Test

Build a short section of a small-scale trail over a wet area with a 2-meter (6-foot) square piece of geotextile and the proposed tread fill material. The depth of tread fill should be at least 150 millimeters (6 inches). Saturate the section with as much water as would be expected under the worst conditions. Evaluate the stability of the tread material by stepping onto the tread repeatedly, mimicking traffic.

Case Studies

The following case studies show how geosynthetic materials were used to solve problems on trails. One of the studies points out problems that can arise if geosynthetic materials are installed improperly.

Geoblocks for ATV Trails

The Francis Marion National Forest in South Carolina had serious erosion problems on all-terrain vehicle (ATV) trails. The ATVs were causing ruts. Water collecting in the ruts compounded the problem (figure 16). The forest reinforced the trail with Geoblocks, solving the problem (figure 17). Other national forests and national parks now use turf reinforcement products to reduce erosion and reinforce ATV trails.

Figure 16--An ATV trail in South Carolina
before Geoblocks were installed.

Figure 17--The finished trail after Geoblocks were
installed in the Francis Marion National Forest.

Geocells for Trail Bridge Approaches

The Tongass National Forest in Alaska is using geocells to build approaches for trail bridges (figure 18). In the past, approaches have sloughed off because of the steep embankments and wet conditions there. The geocells have worked wonders and are highly recommended for trail bridge approaches in the Tongass (figure 19).

Figure 18--Using geocells to construct
a trail bridge approach.

Figure 19--A finished trail bridge approach
in the Tongass National Forest.

Geotextiles for Underdrains

The Bureau of Land Management in Oregon had trouble with water going over a trail (figure 20). Large rocks were used to create an underdrain (often referred to as a French drain). The large rocks were placed on the ground and a geotextile fabric was laid over the rock (figure 21). The geotextile fabric was used as separation to keep the trail's surface material (crushed rock) from migrating down into the larger rocks. The finished trail (figure 22) allows water to flow through the underdrain.

Figure 20--An ATV Trail on BLM land in
Oregon before geosynthetics were used
to construct an underdrain.

Figure 21--Constructing an underdrain from
large rocks, with geotextile serving as
a separator between surface material
and large rocks.

Figure 22 --A finished rock and
geotextile underdrain.

Geocell Problems

Trail maintainers had the right idea when they decided to install geocells at the approaches to this bridge (figure 23). The geocells would provide a stable approach to the bridge and keep the fill material from soughing. Unfortunately, they did not install the geocells deep enough to allow 2 to 3 inches of gravel cover above them. The geocells were exposed to traffic and gradually unraveled, creating an unsightly and unsafe approach.

Figure 23--Geocells placed too close to the surface
may unravel. The top of the geocell should be 2
to 3 inches below the surface of compacted tread fill.

References

Bathurst, R.J. [no date]. Geosynthetics classification. International Geosynthetics Society. Available electronically at: http://geosyntheticssociety.org/source_documents/Classification.pdf.

Bathurst, R.J. [no date]. Geosynthetics functions. International Geosynthetics Society. Available electronically at: http://geosyntheticssociety.org/source_documents/Functions.pdf.

Geosynthetic Materials Association (GMA). 2002. Handbook of geosynthetic materials. Roseville, MN: Geosynthetic Materials Association. Available electronically at: http://www.gmanow.com/pdf/GMAHandbook_v002.pdf

Industrial Fabrics Association International. 2008. Geosynthetics specifier's guide: 2008. Roseville, MN: Industrial Fabrics Association International.

Koerner, Robert M. 2005. Designing with geosynthetics, 5th ed. Upper Saddle River, NJ: Pearson/Prentice Hall.

McKean, J.; Inouye, K. 2000. Field evaluation of the longterm performance of geocomposite sheet drains. Tech. Rep. 0077-1804-SDTDC. San Dimas, CA: U.S. Department of Agriculture Forest Service, San Dimas Technology and Development Center. 22 p.

Meyer, Kevin G. 2002. Managing degraded off-highway vehicle trails in wet, unstable, and sensitive environments. Tech. Rep. 0223-2821-MTDC. Missoula, MT: U.S. Department of Agriculture Forest Service, Missoula Technology and Development Center. 48 p.

Monlux, Steve; Vachowski, Brian. 2000. Geosynthetics for trails in wet areas: 2000 edition. Tech. Rep. 0023-2838- MTDC. Missoula, MT: U.S. Department of Agriculture Forest Service, Missoula Technology and Development Center. 18 p.

Shukla, Sanjay K.; Yin Jian-Hua. 2006. Fundamentals of geosynthetic engineering. London, UK: Taylor & Francis Group. 410 p.

U.S. Army Corps of Engineers. Engineering use of geosynthetics. 1995. Available electronically at: http://www.army.mil/usapa/eng/DR_pubs/dr_a/pdf/tm5_818_8.pdf

U.S. Department of Agriculture Forest Service. 1996. Standard specifications for construction and maintenance of trails. Eng. Man. EM-7720-103. Washington, DC: U.S. Department of Agriculture Forest Service.

Web Sites

Geosynthetic Institute
http://www.geosynthetic-institute.org/

Geosynthetic Materials Association
http://www.gmanow.com/

Industrial Fabrics Association International
http://www.ifai.com/

International Geosynthetics Society
http://www.geosyntheticssociety.org/guideance.htm

About the Authors

James "Scott" Groenier, professional engineer, began working for MTDC as a project leader in 2003. Scott earned a bachelor's degree in civil and environmental engineering from the University of Wisconsin at Madison and a master's degree in civil engineering from Montana State University. He worked for the Wisconsin and Illinois State Departments of Transportation and with an engineering consulting firm before joining the Forest Service in 1992. He worked as the east zone structural engineer for the Eastern Region and as a civil engineer for the Ashley and Tongass National Forests before coming to MTDC.

Stephen Monlux is an engineering consultant in materials and pavement engineering, contract administration, and technology transfer for several federal agencies, state Local Technical Assistance Program centers, and numerous counties in the Northwest. He was the Northern Region materials engineer for the Forest Service in Missoula, MT, for 26 years.

Brian Vachowski was a project and program leader at the MTDC from 1993 until his retirement in 2008. He received a bachelor's degree in forestry from the University of Massachusetts and a master's degree in outdoor recreation from Utah State University. He has worked for the Nez Perce, Bighorn, Winema, and Routt National Forests.

Produced by:
USDA Forest Service
Missoula Technology and Development Center
5785 Hwy. 10 West Missoula, MT 59808-9361
Phone: 406-329-3978
Fax: 406-329-3719
E-mail: wo_mtdc_pubs@fs.fed.us

For additional information about geosynthetics, contact James "Scott" Groenier at MTDC:
Phone: 406-329-4719
Fax: 406-329-3719
E-mail: jgroenier@fs.fed.us

Electronic copies of MTDC's documents are available on the Internet at: http://www.fs.fed.us/eng/t-d.php

Forest Service and Bureau of Land Management employees can search a more complete collection of MTDC's documents, CDs, DVDs, and videos on their internal computer networks at: http://fsweb.mtdc.wo.fs.fed.us/search/

You can order a copy of this document using the order form on the FHWA's Recreational Trails Program Web site at:
www.fhwa.dot.gov/environment/recreational_trails/publications/trailpub.cfm

Fill out the order form and either submit it electronically, fax it to 301-577-1421, or mail it to: FHWA R&T Report Center
9701 Philadelphia, Ct, Unit Q
Lanham, MD 20706