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

Appendix B--Installation Guide for Porous Pavement Panels as Trail-Hardening Materials for Off-Highway Vehicle Trails

The following discussion provides information on methods of installing GeoBlock and SolGrid porous pavement panels based on the author's experience in Alaska during the 1996, 2000, 2001, and 2002 summer field seasons.

Preplanning-The size of individual porous pavement panels (19 by 39 inches) lends them to constructing trail in 4.8-, 6.5-, and 8-foot-wide configurations (see figure B1 for panel layout configurations).

Figure B1--Typical panel layouts.

Table B1 provides information for ordering material, based on typical installation configurations.

Table B1--Material layout specifications. (All prices depend on volume and are subject to change.)

A typical installation requires the following:

Supplies

• 3/4- to 1-inch No. 8 or 10 Phillips-head screws, galvanized or stainless steel (No. 8, 1-inch truss-head screws are generally the least expensive.)
• Quik Drive screws (TRSD34S) 2,500 screws per box (for use with Quik Drive system)
• Zip ties, 11-inch, 120-pound test (Catamount L-11-120-0-C or equivalent)
• One 1/2-inch sheet of CDX plywood to help join panel sections (cut down to 24 inches wide and 1 foot longer than the installation width)
• 3/4-inch CDX or all-weather plywood for joints (cut into 8-inch-wide strips the width of the installation)
• One 2 by 4 by 8 piece of lumber
• One 2 by 6 by 8 piece of lumber

Equipment

• At least two 400 cc or larger ATVs for transporting workers and equipment
• At least one flatbed or large-box ATV trailer for hauling panels
• At least one small-tub ATV trailer for hauling equipment and supplies
• Miscellaneous straps and tiedowns for trailers
• 5-gallon gas can
• Chain saw with chain oil and mix gas, or a portable circular saw for cutting panels
• Gas-powered weed trimmer with blade option
• Shovels, pulaskis, and rakes
• At least three portable drill drivers with extra battery packs (18 volts recommended)
• One Quik Drive automatic screw gun (modified No. PHD18R with head for 3/4- to 1-inch screws)
• Utility knife
• Leatherman tool for clearing screw jams
• Tool belts, knee pads, drill holsters, and waterproof tool storage containers
• 100-meter tape measure, lath, flagging, marker pens
• First-aid kit, communications equipment, water, sunscreen, insect repellent, rain gear, and similar items

Labor

• Calculate 3 to 6 hours per 100 square feet for onsite installation. The actual time will depend on site conditions, logistics, and installation design.
• Ideal crew size, two to four teams of three; one supervisor, one runner

Here is an example of the supplies and labor needed for a 4,800-square-foot installation, 6.5 feet wide by 800 feet long:

• About 850 GeoBlock panels
• About 140 SolGrid panels
• Four boxes of Quik Drive screws (TRSD34S, 2,500 screwsper box)
• 2,000 screws
• 1,500 zip ties Catamount, L-11-120-0-C
• 5 days labor with an eight-person crew

Supplemental geotextiles and membranes are required in some locations to increase the flotation of installations in extremely muddy conditions, to support installations over long expanses of weak ground, or to help contain fill material. Table B2 lists the most commonly used materials and their purpose.

Table B2--Supplemental geotextiles and membranes.

The author has used Polynet PN-3000 (or equivalent) as a suitable open-cell drainage mat. It decreases the size of openings to less than 1/4 inch and also reduces the total opening by roughly 30 percent. This increases the flotation of the panels on extremely muddy sites and still allows for vegetation regrowth. A nonwoven separation fabric in an 8-ounce material weight can be used to completely eliminate openings when flotation needs to be maximized. Nonwoven fabric delays vegetation regrowth unless cells are filled with a growth medium. Vegetation regrowth helps anchor and stabilize the installation, integrate it into the environment, and improve site productivity. Tensar BX 1100 (or equivalent) has been used as a geogrid under-layment for installations longer than 100 feet in ponded areas. The geogrid provides a lateral membrane that helps prevent joint failure. Because the panels are neutrally buoyant and will float just below the surface in pooled areas, they should be filled with aggregate as a ballast when the trail crosses long ponded sections. A separation fabric should be used to contain the ballast gravel within the cells. In many cases, cells do not have to be filled because the grid cell provides an adequate traffic surface for most applications. Fill can increase regrowth in some cases, help integrate the installation, and provide a buffer for thermal contraction and expansion of the panels. High-quality fill is not required because the cell walls carry the load. Any readily available growth medium can be used. Gravel fill may also be necessary where tracked vehicles or snow machines with cleats will operate on panel surfaces. The gravel will help protect the soft plastic grid cell walls from crushing and abrasion.

Site Preparation--New trail locations should be cleared of trees, shrubs, rocks, and large tree roots. Tussocks and thick clumps of grass should be sheared off at ground level. It is generally not necessary to strip the site to mineral soil because vegetation growth through the open cells is desirable. For existing trails, the surface should be leveled to the extent practicable and center humps between wheel tracks and along trail edges should be roughly level to the depth of wheel ruts. Potholes should be filled to the extent that is practical. The installations handle variations in terrain along the course of the trail better than across the trail. An undulating surface is okay, but there shouldn't be more than a 4-inch variation across the surface. The smoother and more nearly level the surface, the cleaner the installation will look and the better the panels will be able to transfer load from one to another. Simple handtools such as shovels and grubbing tools (such as pulaskis) can be used for site preparation. Small backhoes, bulldozers, and/or tillers and weed trimmers may have application at some sites.

Staging--After the pallets of panels have been delivered to the trailhead, they can be broken down and shuttled to the staging areas with ATVs and small ATV trailers. Using double-axle ATV trailers to haul larger loads will increase the efficiency of shuttle operations and minimize trail impacts between the trailhead and staging areas. Machines that are 400 cc or larger are recommended for these operations.

Staging areas should be located along the identified alignment every 500 feet or so. Trail conditions may require that the trail be hardened before heavy loads can be shuttled to distant staging areas. If so, only stage enough panels to construct trail to the next staging area. Stock the staging areas as the trail extends to them. The staging areas should be relatively level and large enough to accommodate stacked panels and assembly areas. An area 20 by 30 feet is usually adequate. If a helicopter will be used to stage the panels, be sure to site the staging areas with clear approaches and leave extra room for drop zones.

Subsection Assembly--It helps to assemble panels into subsections before installing them. Stack panels neatly to the outside of the trail corridor, leaving room to assemble subsections on the trail side of the staging area. With the GeoBlock panels upside down on a flat, level surface, assemble the panels (refer to figure B1 for the panel layout configurations). For a 4.8- or 6.5-foot-wide trail, six panels will form a subunit. For an 8-foot-wide trail, 10 panels will form a subunit. Assembling the panels upside down places the edge tabs closer to the surface, making it easier to screw the panels together.

Either screw the panels together using individual screws or use a automatic-feed screw gun. A Quik Drive No. PHD18R (figure B2) with Quik Drive 3/4-inch TRSD34S screw strips has been used successfully in Alaska. The Quik Drive gun has limited capability to countersink screws, so the panels must be upside down when using this tool. The tool must be slightly modified to allow it to countersink an additional 1/8 inch. To do this, grind off the small raised area on the base collar to increase the depth of drive. Screws should be driven through the center of the overlapping tabs between panels (figure B3). It is not usually necessary to place screws in every tab, but tabs should be fastened in adjacent pairs to pin the panels. At a minimum, a pair of tabs should be fastened on each side of a joint and along the outside edge. Along interior joints, screw a pair of tabs together along every 6 inches of the panel's length.

Figure B2--The Quik Drive automatic-feed
screw gun speeds assembly of the panel
subsections.

Figure B3--Illustration of the tab-fastening
screw pattern at panel joints.