US Peace Arch Port of Entry Redevelopment
GeoEngineers’ geotechnical solutions supported an award-winning design.
GeoEngineers was part of the design team that undertook an ambitious, complex redesign of the US/Canada border crossing at Peace Arch Port of Entry in Blaine, Washington. The US General Services Administration (GSA) undertook the expansion project to accommodate more traffic at the Port of Entry and to improve the Interstate 5/Blaine interchange at this busy international crossroads.
The project’s design elements included a new administration building, retaining structures to support a 20-foot deep excavation for the building, and an expanded parking and car inspection area covered with a “green” roof. Due to the limited land available for expansion near the building, architects Bohlin, Cywinski and Jackson designed new parking and 10-lane car inspection areas to be located on the opposite side of the freeway. This approach necessitated building a new, taller freeway bridge over the site.
Project Challenges Included
- Addressing soft-clay soil conditions throughout the 15-acre site
- Excavating the 20-foot deep cut below previous grade
- Completely reconstructing a section of Interstate 5 (I-5) freeway
- Raising the I-5 embankment height by six feet in a manner that would stand up to the site’s soft clay soils
- Developing recommendations for effective soil-retaining solutions
- Designing parking surfaces and roof supports suitable over soft clay subgrades
- Designing the I-5 bridge foundation with consideration of the area’s soil characteristics
The completed Port of Entry facility was dedicated at a March 2011 ribbon-cutting ceremony. Washington State Department of Transportation (WSDOT) completed the new I-5 bridge and interchange improvements in September of 2010. The new facility has won acclaim that includes a GSA Design Excellence Honor Award for subtly balancing functionality, landscape, architecture, roadways and the adjacent Peace Arch State Park.
The site design called for lowering the overall site grades around the new building and parking area, including excavating below the elevation of the existing northbound lanes of I-5. However, the soft clay soils that underlay the site would not allow for conventional excavation, retaining walls or foundations.
GeoEngineers conducted extensive testing at the site, including a series of explorations as deep as 200 feet below grade, to explore subsurface conditions. The project team employed finite-element modeling and other test methods to predict how project components would be affected by the challenging conditions. The team also performed soil tests to determine soil strength and character and to predict soil-structure interaction for the project’s components.
GeoEngineers recommended deep-drilled shafts for the bridge foundation to achieve the desired load capacity. Using Plaxis computer modeling, the team predicted how much load the shafts could support at varying depths.
Guided by test results, GeoEngineers provided geotechnical excavation, shoring and foundation solutions and designs that effectively addressed the potential for settling and shifting soil:
- Created a foundation design for the Port of Entry building that hindered settlement between the two-story and one-story sections
- Incorporated sheet-pile walls with tiebacks to resist slope instability and support cuts up to 20 feet deep below grade
- Designed large-diameter drilled shafts that supported the I-5 bridge foundation while restricting settlement between new building and adjacent piers
- Designed I-5 bridge elements to WSDOT standards
- Used Geofoam blocks in the new roadway embankment construction that limited new loads and avoided long-term settlement
- Designed paving and lightly loaded canopy foundations for parking and inspection areas that worked effectively with the site’s soft-clay soils