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Boardwalk Design: Foundations

Engineers and landscape architects have plenty of material options in designing a foundation system, including:

  • Timber (pressure treated piles)
  • Composite
  • Concrete (precast piers, cast-in-place, caissons, precast piles, etc.)
  • Steel (helical, H-pile)

Continue to read through the information below if you're looking to find the answers to any of the following questions:

  • I have a boardwalk project through a wetland area; what are my foundation options?
  • Which foundation types are most cost effective?
  • Can I use timber piles with your PermaTrak system? If so, how do the piles connect?

As always, our professional engineering team is available to discuss boardwalk design and engineering team is ready to assist landscape architects and engineers who are researching their boardwalk materials options. We offer engineering and CAD support details for PermaTrak projects that range in foundation type from precast pier to driven pile.

Foundation Types Used with PermaTrak Boardwalk System: Timber, Concrete and Steel

1. PermaTrak Abutment Component

abutment component

The precast concrete abutment is an “L-shaped” shallow foundation component, much like a conventional bridge beam seat. It is typically used at the beginning or ending of the boardwalk run. Sections are produced in 3’-9” sections and butt-jointed together to form longer abutments. They are designed for lateral earth pressure against one side and for the load transferred from the beam and tread combination from the first span.

This abutment component will rest on a bed of compacted stone or an unreinforced cast in place pad (aka "mud mat") so that load can be transferred uniformly to the insitu soil. These abutments contain a horizontal reveal positioned to receive the first groove on the adjacent tread. The beam seat of the abutment has a semi-circle shaped valley for proper seating of the precast beams. 

permatrak_abutment

2. Precast Concrete Pier System (supplied by PermaTrak)

Precast piers are advantageous to engineers and designers for many reasons. First, these relatively-light components are easily handled in the field by laborers or small lifting equipment such as a Bobcat®. Taller piers are achieved by adding risers to the precast pier. Typically 42'' is a maximum total height for a precast pier. Second, precast piers allow for fewer disturbances to the sub grade and surrounding areas than driving deep foundations. Read about projects (specifically Mellow Mushroom, Judaculla Rock, Robertson Park, Kaiki Trail) that have taken advantage of using this low-impact foundation system here.  

If feasible, we recommend using this precast concrete pier system; it is the most cost-effective foundation option for a commercial boardwalk. See the step-by-step boardwalk construction process here

  • Shallow footing option
  • Most cost-effective
  • Stackable components consisting of base, riser(s), and cap 
  • Can stack additional risers up to 3.5' in height above grade before additional bracing is required

precast concrete piers

3. Cast-in-Place Concrete Shallow Footings (Sonotube)

cast in place concrete pier

Cast-in-place concrete shallow footings are typically circular or square, and commonly formed with a Sonotube form. The Sonotube (or equal product) acts as a stay-in-place form. The advantages associated with concrete piles (durability & longevity) are realized with this method. Once constructed, the precast caps are then attached to the top of the pier with a steel dowel and epoxy connection, allowing proper alignment of the beams via the pin connectors. Shallow footings are preferred over deep footing options as they contribute to a lower boardwalk construction cost. See the step-by-step installation process of a concrete boardwalk on CIP shallow footings here.

  • Shallow footing option
  • Typically more cost-effective than a deep foundation option
  • Circular or square 

concrete boardwalk shallow footing

4. Timber Piles

Throughout the Gulf Coast region of Alabama, Mississippi and Louisiana, Pressure Treated timber piles (aka timber poles) are the most common deep foundation option for commercial boardwalks. 12’’ diameter piles are often specified.

Several variables will impact the price of timber pile installation: site access, diameter of pile required, required driven depth, geographic region, total number of piles, soil conditions, etc. The PermaTrak precast cap is then affixed to the top of the timber pile with a lag screw. See the step-by-step timber pile installation process here
  • Deep foundation option
  • Typically on the cheaper end of all deep foundation types
  • 12'' dia. most common
  • Typically 10' to 40' total pile length
  • PermaTrak cap secured to top of pile transitions from foundation to PermaTrak system
timber pile boardwalk foundation

5. Composites - Fiberglass Piles

  • Deep foundation option
  • Durable
  • Lightweight
  • Shapes similar to conventional deep foundation options (circular
  • Cost ranges between timber piles and precast concrete driven piles

composite pilings

6. Drilled Shaft or Concrete Caisson

This type of deep foundation is a reinforced, concrete member typically formed by advancing a temporary or permanent casing. Once a hole is cased, reinforcing is placed and concrete is poured inside. Sizes typically vary from 12’’ to 42’’ in diameter for PermaTrak boardwalk applications. The PermaTrak cap attaches similarly to the that of a cast-in-place concrete foundation, via a steel dowel and epoxy connection.

When designing a boardwalk on cast-in-place caissons, designers will consider site conditions, industry standard casing sizes, and finished boardwalk elevation (height above grade). All of these factors influence the structural engineer’s design for diameter and depth of the caissons. The photo to the right from a multi use path project shows a walking surface at roughly 5-6’ above grade.

  • Deep foundation option
  • PermaTrak cap secured to top of pile transitions from foundation to PermaTrak system

concrete caisson boardwalk foundation

7. Driven Steel Piles (H-pile, Pipe, Helical)

This type of foundation is a driven steel member.  These piling systems offer durability and potential long-term cost savings for harsh environments such as floodplains or over bodies of water. Common shapes are H-piles, open members such as pipes and helical piers (“screw piles”).

beam on steel pile

boardwalk_foundations_steel_h_pile_boardwalk_400.jpg

Steel piles may provide several distinct advantages over timber or concrete foundations for your project site. Helical “screw” piles may also provide a solid foundation option. Helical "screw" piles may provide a solid foundation option. These piles are typically advanced in sections, allowing for much lighter driving equipment to be used. For example, this type of foundation lends itself well to a wetland boardwalk application where top-down construction is required.

  • Deep foundation option
  • PermaTrak cap component eliminated
  • PermaTrak beams bolted to top of steel cap plate
boardwalk_foundation_helical_pile_top_plate.jpg
helical_piles_permatrak_boardwalk_adams_park.jpeg

8. Driven Precast Concrete Piles 

Similar to driven steel piles, precast concrete piles are less commonly used for lightly loaded boardwalk applications. Typically manufactured in circular or square shapes, they provide a durable deep foundation option. The PermaTrak cap attaches similarly to other concrete options with a steel dowel and epoxy connection.

  • Deep foundation option
  • Durability and longevity
  • Higher cost than most foundation systems

You can also read more on finding the right foundation type for your project by viewing this blog article - "Boardwalk Foundation: Which Type is Right for My Project?"

How much does a concrete boardwalk cost? Lean more here » 
engineer_architect_guide_boardwalk_design
download concrete boardwalk installation guide