Project Name: Rogue Credit Union
Location: Coos Bay, OR
Project Overview
S+B James Construction recently completed the new Rogue Credit Union branch in Coos Bay, Oregon. The KSW Architects design addressed subsurface challenges commonly found in coastal areas, where the ground conditions required a foundation approach that could support the slab without placing excessive additional weight on the soils below.
As part of the engineered design, KSW Architects specified geofoam fill in place of a deep-pier foundation system. The lightweight material allowed the required elevation to be achieved while reducing the load placed on the underlying soils.
Challenge
Coastal soil conditions can create added complexity for foundation design and construction. At the Rogue Credit Union site, the project required fill beneath the slab, but using traditional materials would have added significant weight to the subgrade.
The team needed a solution that would:
- Reduce loading on the underlying soils
- Support the slab and foundation design
- Limit the need for heavy fill placement and compaction
- Maintain constructability in the field
- Help keep the project on schedule
Solution
Geofoam was specified by KSW Architects as a lightweight fill material that could occupy the required space beneath the slab while significantly reducing the load placed on the subgrade. This approach provided an alternative to using deep piers and allowed the foundation system to respond to the site’s challenging soil conditions.
S+B James constructed the foundation assembly in accordance with the design through the following sequence:
- Excavate and import 4 feet of new subgrade soils
- Form and pour the base slab
- Form and pour the raised slab walls
- Install utilities
- Place the geofoam
- Form and pour the finish slab
Once the finish slab was poured, the geofoam was fully encapsulated within the foundation assembly, protecting it from exposure and allowing it to serve as a permanent lightweight fill material. Although geofoam is commonly used in roadway, culvert, and infrastructure applications, it is less frequently used on local commercial building projects.
Installation and Coordination
The geofoam blocks were large and somewhat awkward to handle, but their light weight made them much easier to move, place, and adjust than conventional fill materials. This helped reduce the labor and equipment demands typically associated with placing and compacting heavier materials.
Successful installation required close coordination with the engineered foundation design and the planned construction sequence. Key considerations included establishing the new subgrade, sequencing the base slab and raised slab walls, coordinating utilities before foam placement, accurately placing the geofoam blocks, and protecting the material through the finish slab pour.
By eliminating the need to place and compact large volumes of heavier fill, the team improved constructability while reducing the overall load on the foundation soils.
Results
The use of geofoam helped the project team:
- Reduce soil loading beneath the slab
- Improve field efficiency and constructability
- Avoid extensive placement and compaction of heavier fill
- Support the foundation design in challenging coastal soil conditions
- Maintain momentum in the project schedule
With favorable field conditions and strong coordination among the project team, the Rogue Credit Union branch was completed approximately one month ahead of schedule.
Benefit to Owner
For the Rogue Credit Union project in Coos Bay, geofoam provided a smart, cost-effective solution that matched the technical requirements of the site. Its lightweight properties helped address challenging soil conditions, while its ease of placement supported an efficient construction process.
The result was a successful project outcome that demonstrates how alternative fill materials can help solve site-specific challenges on commercial building projects.
