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Commercial Helical Pier Installation for Southwest Bible Church in Beaverton, Oregon
TerraFirma provided commercial foundation support for a major nursery school and daycare addition in Beaverton, adapting the underpinning system after unexpected groundwater conditions affected the original construction approach.
Foundation Support for a Three-Story School and Daycare Addition
Southwest Bible Church in Beaverton planned a 31,000-square-foot nursery school and daycare addition consisting of three stories and a basement.
Before excavation for the addition could proceed, one corner of the existing church required underpinning. The new basement excavation would extend approximately 12 feet below the existing footings, creating a significant foundation-support requirement beside the existing structure.
Subsurface exploration identified soft to medium-stiff clay and silt to approximately 30 feet, with progressively stiffer material below. Conditions encountered during construction ultimately required the project team to modify the original underpinning approach.
Unexpected Groundwater Changed the Underpinning Strategy
The original concept called for a drilled and grouted micropile and tieback system because the existing building was believed to sit over a dense layer of compacted gravel.
Deep Excavation
Construction required excavation approximately 12 feet below the existing footing elevation.
Variable Soil Conditions
Soft to medium-stiff clay and silt extended to approximately 30 feet before transitioning into stronger material.
Artesian Groundwater
Groundwater encountered during installation made effective grout injection difficult for the planned micropile system.
Construction Requirements
An alternate commercial piering solution was needed to maintain foundation capacity while allowing the excavation work to continue.
Helical Piers, Tiebacks and Staged Shotcrete Construction
Further evaluation showed that the dense gravel layer did not extend beyond the footprint of the existing structure, allowing the project team to transition to a helical pier foundation-support system.
The revised commercial piering design incorporated 11 helical piers and 22 grouted tiebacks. Excavation and construction of the shotcrete wall were completed in two approximately six-foot stages to achieve the required 12-foot depth.
- 11 Supportworks Model 288 helical piers installed beneath the existing structure.
- Helical piers installed approximately 40 to 50 feet below the existing footings.
- Minimum installation torque of approximately 5,200 ft-lb.
- External sleeving provided additional lateral support during excavation.
- 22 grouted tiebacks supported the reinforced shotcrete excavation wall.
Commercial Piering and Foundation Support in Beaverton
The project required close coordination between underpinning, excavation, tieback installation, reinforcement and shotcrete construction beside the existing building.
How the Commercial Foundation Support System Was Installed
The revised installation approach allowed foundation support, excavation and wall construction to proceed in controlled stages while supporting the existing church structure.
Underpin the Existing Footings
Helical piers were installed beneath the existing foundation to transfer structural loads to stronger soil at depth.
Complete the First Excavation Stage
Excavation proceeded approximately six feet while the underpinning system maintained support for the existing structure.
Install Tiebacks and Shotcrete
Grouted tiebacks and reinforced shotcrete provided excavation support along the new basement wall.
Complete the Final Excavation
A second excavation stage brought the project to the required depth and completed the approximately 12-foot support wall.
Shotcrete and Commercial Foundation Work in Action
See how shotcrete and foundation-support techniques are used during structural and excavation projects. These videos provide a closer look at the methods TerraFirma uses to construct durable foundation-support systems.
Shotcrete Timelapse
Watch TerraFirma’s shotcrete installation process and see how sprayed concrete is placed to form reinforced structural walls during foundation and excavation work.
TerraFirma Foundation Project
Take a closer look at TerraFirma’s field work and the foundation-support methods used during structural construction projects.
A Revised Foundation System That Kept Construction Moving
Adapting from the original micropile concept to commercial helical piers allowed the project team to respond to unexpected groundwater conditions while maintaining the structural-support requirements of the existing church and the new excavation.
Engineering and Construction Partners
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