US Department of Agriculture, USDA Forest Service, Technology and Development Program Banner with Logos.
Images from various aspects of the T&D Program.
HomeAbout T&DT&D PubsT&D NewsProgram AreasHelpContact Us
  MTDC > MTDC Pubs >Innovative Foundations for Boardwalks and Viewing Platforms T&D Publications Header

Recreation Tech Tip.
February 2013
2300 Recreation
1223-2310P-MTDC
Print this pub
Innovative Foundations for Boardwalks and Viewing Platforms

Jerry D. Barrow, Civil Engineer and James Scott Groenier, Project Leader

Several methods are used for constructing elevated boardwalk foundations across areas with standing water. Digging holes or driving piles into swampy ground and building up stone and log cribbing are two conventional techniques. The tech report "Wetland Trail Design and Construction, 2007 Edition" (0723–2804P–MTDC), <http://www.fs.fed.us/eng/pubs/htmlpubs/htm07232804/index.htm> provides information on traditional techniques for constructing elevated boardwalk foundations.

This tech tip focuses on two less commonly used techniques:

  • Helical piles to support the superstructure.

  • Prefabricated concrete foundations, such as curbs placed on a bed of geocells filled with gravel and wrapped in geotextile fabric.
Highlights...
  • Digging holes or driving piles into swampy ground and building up stone and log cribbing are conventional techniques for constructing elevated boardwalk foundations.

  • Driving helical piles to support the boardwalk superstructure and placing prefabricated concrete foundations are less common but useful techniques.

  • Helical piles cause minimal ground disturbance. Prefabricated concrete foundations resist movement during floods and are well suited for areas with rocky or thin soils.

The U. S. Department of Agriculture, Forest Service, Trails Unlimited enterprise team used these foundations on three projects. Trails Unlimited designed and/or installed:

  • Helical piles for a viewing/fishing platform as part of an accessible trail on the U. S. Department of the Interior, U. S. Fish and Wildlife Service, Okefenokee National Wildlife Refuge in Georgia (figure 1)

  • Helical piles to support an elevated boardwalk on the Town Creek Off-Highway Vehicle (OHV) Trail system at the Chattahoochee-Oconee National Forest in Georgia (figure 2)

  • Precast concrete with 3-inch steel pipe posts to support a stout, high-elevation boardwalk (250-poundsper- square-foot snow load) over a seasonally wet meadow (figure 3) on the Snake Creek Trail at the Inyo National Forest in California

Photograph of a fishing platform over a pond in the woods.
Figure 1—Helical piles support this viewing/fishing platform
at the Okefenokee National Wildlife Refuge in Georgia.

Photograph of an elevated boardwalk supported by helical piles.
Figure 2—This elevated boardwalk on the Town Creek Trail
system at the Chattahoochee-Oconee National Forest
in Georgia is supported by helical piles.

Photograph of boardwalk in a meadow with a atv next to it.
Figure 3—Precast concrete barriers on top of geogrid filled with
stone provide solid footing for this Snake Creek Trail boardwalk
at the Inyo National Forest in California.

Helical Anchors and Piles

A helical anchor, pile (figure 4), or pier is a foundation system consisting of round or square steel shafts with one or more helical bearing plates welded to it. These versatile earth anchors are used in highway retaining walls; for supporting building foundations, power lines, and streetlight bases; and for supporting elevated boardwalks. Pile installation depth is limited by soil density and economic practicality. Additional lengths are bolted on as depth increases.

Photograph of specialized equipment installing helical piles for a platform with a man standing behind the equipment.
Figure 4—Specialized equipment is needed to install helical piles.
For this installation, Trails Unlimited installed 12 helical piles for 4
viewing platforms in 4 hours.

Several companies manufacture helical piles. A helix (one pitch of a screw thread) provides the bearing surface. Choosing the correct size and quantity of helical piles for a specific project involves calculations based on the supported load, soil structure, and soil density. These calculations often are determined by a certified installer or under the guidance of a geotechnical or structural engineer.

Advantages and Disadvantages

Helical piles have some advantages and disadvantages when compared with conventional techniques.

Advantages

  • Helical piles cause minimal ground disturbance in wet and sensitive soil environments.

  • Helical piles are cost effective in wet/swamp/marsh environments with soft or clay soils.

  • Galvanized helical piles resist corrosion, unlike wood piles that may rot.

  • Helical piles do not leach wood preservative into the surrounding environment.

  • Helical piles can be installed rapidly when proper equipment is used.

Disadvantages

  • Helical piles require professional sizing and soil measurement expertise.

  • Installation often must be contracted, or at least requires special screw heads and hydraulics for the mini-excavator or other power source.

  • Helical piles may require ingenuity for "install-as-yougo" build sequencing when installing piles in deep standing water.

  • Helical piles are not a good option for rocky soils or where bedrock is close to the surface.

-Continued-

Top

Next