Boardwalk Site Conditions: Wetlands, Grasslands and Floodplain
If you have experience designing projects for park & recreation clients, trail systems or greenways, I’m sure you can appreciate how much site conditions influence your design concepts.
For architects and engineers with boardwalks or pedestrian bridge projects in their portfolios, delicate environments come up often – including wetlands, grasslands or floodplain areas. Designers are hired for their expertise in specifying a boardwalk or pedestrian bridge product through these types of natural environments in order to provide a safe walkway for visitors, an “outdoor classroom”, or simply a connection to another part of the trail system. These project locations dictate the design and specification of an elevated structure; a traditional gravel or asphalt surface simply won’t suffice.
So how do the site conditions relate to designing boardwalk foundations through a wetland area? Out of all of the potential places to engage in boardwalk construction, wetlands are among the more fragile ecosystems. The level of wetland disturbance during boardwalk construction is obviously very important for permitting purposes, not to mention the implications for maintaining an environmentally friendly design approach.
Shallow Foundations: PermaTrak’s Precast Concrete Pier System
When designing a boardwalk system through an area like this, if Step 1 involves understanding site conditions, budget and your goals for the project, Step 2 is determining which foundation type is right for your project. Taking the boardwalk through a wetland area as an example, where is the tipping point when a deep foundation must be used?
On certain boardwalk construction projects, PermaTrak supplies a precast concrete pier foundation system to complement our precast concrete beams and treads. These piers are composed of a base, riser(s) and a cap. Each of these components is a nominal 6’’ high, and additional risers are added if the designer wishes to elevate the boardwalk. Typically 42’’ is the maximum total height for a precast pier.
Can PermaTrak Precast Concrete Piers Be Used in This Type of Wetland Environment?
Compared with driving a pile foundation, shallow foundation systems such as precast piers can allow for fewer disturbances to the sub grade, if they can be used.
First of all, know that you don’t have to go through this process alone! Our engineering team provides free support in order to help you pull together a set of detailed construction documents that can be included directly in the project’s bid documents.With this approach, we’ve partnered with hundreds of landscape architects and engineers to design foundation systems suitable for their boardwalk and pedestrian bridge projects.
One of the first steps in designing a boardwalk foundation system is to gather any pertinent geotechnical data. A geotechnical report can provide useful soil history for a project site, and many times includes specific footing recommendations.
PermaTrak’s precast concrete piers (base, riser(s) and cap) start with the fixed 2’ diameter of the base component. These shallow foundations are best suited for dry soils and require sufficient soil bearing capacity. Practically speaking for the average commercial boardwalk project, you will probably need ~2000 psf bearing pressure to make the pier work structurally. Otherwise the piers will likely settle, leading to an uneven foundation system.
Boardwalk Construction with Precast Concrete Piers
Even more significant than determining allowable bearing pressure, the constructability of a precast pier system for a wetland boardwalk will be the primary factor in determining whether a project can utilize PermaTrak’s concrete piers.
From a boardwalk construction standpoint, a wetland typically doesn’t lend itself well to excavating a hole and setting a pier into it, because the hole will probably cave once open. The biggest drawback would be the time and cost associated with the installing contractor trying to brace the hole and keep it in the dry. Therefore, excavation becomes challenging for this stackable precast pier system.
Great...so where do we go from here?
Using these precast concrete piers for a wetland boardwalk situation would be a rare scenario, but it is possible. Depending on the boardwalk size, designers need some minimum sub grade requirements in order to utilize these piers.
Our engineering team would be happy to take a look at your project’s geotechnical report or any other available soil information. If no geotechnical report or soil information is available yet, we can discuss your project site over the phone to gather more details and make a recommendation on foundation types that would make for a cost-effective boardwalk system.
Every boardwalk project site is different, regardless of the desired boardwalk dimensions and technical specifications. While there isn’t a one-size-fits-all boardwalk foundation system, there are several options available that should be considered. Best of luck, let us know if we can help!
Take a look at PermaTrak’s boardwalk design considerations.