Boardwalks rely on robust foundations to ensure stability and longevity. Whether used for public recreation or private developments, the durability of a boardwalk depends on the foundation system the structure is supported upon.
Each foundation type has general construction tolerances that define acceptable deviations in measurements from plan. These include the foundation’s location, elevation, and alignment, which are crucial for ensuring the structural integrity of the foundation.
This article outlines the various types of foundations used in boardwalk construction, the specific tolerances associated with each, and the importance of adhering to these tolerances during the construction phase of a project.
Importance of Foundation Tolerances in Boardwalk Construction
Foundation tolerances are critical in ensuring that the boardwalk is installed and performs as intended per the project plans and specifications. Establishing acceptable foundation tolerances in the project specifications is vital to provide clear expectations for the installer adherence.
Ensuring that foundation elements are installed within allowable tolerances helps to optimize the installation time of the boardwalk, provide consistency, avoid delays/costly change orders, distribute loads evenly and allow for optimal constructability of the superstructure that will be installed on top of the foundation system.
Types of Boardwalk Foundations and Their Tolerances
The choice of foundation for a boardwalk depends on soil conditions, environmental factors, the intended design, and aesthetic appeal. Each foundation type has its own specific construction tolerances to ensure its effectiveness.
One important item to note for all foundations is that the vertical elevation of a foundation should never be installed higher than the elevations specified on the plans. Installing a foundation slightly lower than plan (within tolerance) allows the installer to easily adjust the superstructure in the field, as opposed to installing a foundation too high which causes constructability issues while installing the superstructure.
Below are the most common foundation types used for boardwalks and their corresponding tolerances.
1. Shallow Footings
Plan position tolerance: ±2” to ±3” in horizontal placement.
Elevation tolerance: -½”to -1” of elevation specified on plans.
PermaTrak precast shallow footing being installed/leveled:
2. Driven Pile and Micropile Foundations
Plan position tolerance: ±2” to ±3” in horizontal placement.
Vertical alignment: Pile should be plumb within 1–2% of total length.
Elevation tolerance: -½”to -1” of elevation specified on plans.
Driven pile being installed:
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Micropile being installed:
3. Drilled Shafts
Plan position tolerance: ±2” to ±3” in horizontal placement.
Vertical alignment: Deviation from vertical within 1–2% of shaft length.
Elevation tolerance: -½”to -1” of elevation specified on plans.
Drilled shaft hole being augered prior to casting concrete for shaft:
4. Helical Piles
Plan position tolerance: ±2” in horizontal placement.
Vertical alignment: Pile shall be installed with a variation of no more than ¼” per foot from the vertical of from the batter line indicated.
Elevation tolerance: -½”to -1” of elevation specified on plans.
Helical pile lead section being installed:
Consequences of Not Meeting Foundation Tolerances
When foundation installation tolerances are not adhered to, this can result in having to install additional foundations, requiring a redesign to the superstructure and/or increase constructability issues for the installing contractor, which all increase the overall project cost and cause delays to construction.
- Superstructure Redesign: The design of a boardwalk superstructure is performed with foundation tolerances in mind. However, if foundations are installed outside of the specified installation tolerances, this can require the original superstructure design to be reevaluated and potentially redesigned. This results in additional time for the engineer of record and installing contractor, which results in a higher installed project cost to the owner.
- Contructability Issues: Even if a redesign is not required, installing foundations outside of tolerance can result in difficulties in constructability of the boardwalk superstructure. More difficulties for the installer generally results in additional time spent on the job site than originally intended, which tends to result in unwanted change orders back to the owner.
- Aesthetics: Whether the field fix for an out of tolerance foundation is addressed with a redesign, installer modification or both, any change from the original design runs the risk of affecting the uniformity and aesthetics of the completed structure.
Examples of As-Built Field Repairs for Out of Tolerance Piles
Field repair for out of tolerance pile Example 1 – Pile Encasement:
Field repair for out of tolerance pile Example 2 – As-Built Pile Cap:
Whether using shallow foundations, helical piles, drilled shafts, driven piles or micropiles, maintaining precise tolerances in boardwalk construction is essential for ensuring that the structure is constructible, as well as matches the original design performance and aesthetics as originally intended.
As a result, careful planning and quality control during the construction phase are critical to achieving these tolerances and delivering a durable, safe boardwalk structure.
