Bill & Melinda Gates Foundation Headquarters, Geotechnical Services
GeoEngineers’ geotechnical solutions help create a major Seattle green development project
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GeoEngineers collaborated with the project team to identify the most cost-effective foundation and shoring solutions.
Expertise
  • Geotechnical

Market
  • Development

Location
  • Seattle, Washington

Overview

This private family foundation funds education, health and development programs around the world. The family envisioned building a new world headquarters for the foundation on urban land in Seattle, Washington. GeoEngineers was fortunate to be involved from the very beginning—long before a site was selected—and remained on the project through the environmental cleanup, building design and construction phases.

GeoEngineers’ geotechnical engineers collaborated with the integrated project team from the conceptual phases to final design for the foundation’s campus development. The final design for the 12-acre site consisted of a parking garage and three six-story office buildings that will offer a combined 1.3 million square feet of office space once the third building is finished.

The project presented an array of complicated geotechnical problems for GeoEngineers’ geotechnical experts to solve:

  • Highly variable groundwater conditions and the presence of compressible fill and clay soils across the site.
  • Two immense water tanks—one to hold rainwater and the other to optimize cooling—were called for in the sustainable design, each requiring detailed geotechnical analyses to meet stringent performance requirements.
  • A 6-foot-diameter, 100-year-old brick sewer lay beneath the planned basement level and was not to be disturbed by the excavation or building loads.
  • Geotechnical designs had to accommodate GeoEngineers’ significant environmental remediation plans for the site.

GeoEngineers’ environmental studies, analyses, and extensive experience with brownfields projects were also a critical part of the site-selection and design process. For a full discussion of the GeoEngineers’ environmental work on the Foundation project, see the related project profile.

Approach

  • Collaborated with the project team throughout design to identify the most cost-effective foundation and shoring solutions
  • Provided sophisticated geotechnical analyses for unique design issues to provide the team with a detailed understanding of the anticipated loads and structural response
  • Developed design recommendations for temporary shoring systems that consisted of both soil nail walls and soldier pile and tieback walls
  • Created sophisticated shoring and foundation designs to accommodate the two water tanks
  • Assessed impact on the sewer and nearby area with extensive modeling of the excavation sequence
  • Provided full-time special inspection of shoring systems and part-time observation of foundations and site earthwork to confirm compliance with plans and specifications and to provide practical solutions to unique construction conditions

A Closer Look at the Geotechnical Solutions

The Fifth Avenue North garage—encompassed a full city block and extended 45 feet below existing site grades. Excavation was shored with an innovative temporary soil nail shoring system.

The Phase I campus below-grade excavation—required a soldier pile and tieback temporary shoring system comprised of more than 335 soldier piles and more than 600 tiebacks. These extended to depths of 50 feet below existing site grades. The foundation design was tailored to the variable soil conditions present at the site. Our efforts resulted in a design in which the campus facilities all bear on cost effective shallow foundations.

The 100-year-old, 6-foot-diameter brick sewer—was located 40 to 50 feet below the planned basement level of the buildings. In order to assess the potential impact to the sewer, GeoEngineers used sophisticated numerical modeling of the planned excavation sequence to estimate how much the sewer would rebound during the deep excavation for the campus basement. This modeling was used by the project team to assess the potential impact to the sewer and to facilitate permitting of the project.

A 1 million gallon rainwater storage tank—allows rainwater harvesting for landscape irrigation and non-potable reuse within the building. The rainwater storage tank was situated in an area with soils of variable compressibility and above a settlement-sensitive storm sewer. GeoEngineers developed foundation solutions for the rainwater storage tank that limited differential settlements to tolerable levels and protected the underlying storm sewer from localized settlement.

The thermal energy storage (TES) tank—optimizes the campus cooling system and required a cylindrical excavation 70 feet deep and 50 feet in diameter. GeoEngineers collaborated with the project structural engineers to develop a highly efficient compression ring shoring system (without ground anchors) to construct the tank. GeoEngineers completed the geotechnical design of the TES tank using a three-dimensional finite element model that modeled structural elements of the tank, soil and groundwater and construction sequence. The tank was constructed top-down in a series of 6-foot-high permanent reinforced shotcrete lifts. GeoEngineers monitored tank displacements throughout construction, using highly sensitive geotechnical instrumentation to confirm that the tank was performing as anticipated.

Awards


  • ACEC-Washington Engineering Excellence Gold Award, 2014

Results

  • Created highly efficient foundation and shoring systems
  • Kept project on budget and schedule with daily operational plan and integration with contractor
  • Facilitated effective communication and collaboration with the project team during both design and construction
  • Made recommendations that helped the general contractor protect existing infrastructure from adverse impacts during construction
  • The foundation campus was awarded LEED©-NC (Leadership in Energy and Environmental Design for New Construction) Platinum certification from the United Stated Green Building Council, and is the largest, non-profit LEED©-NC Platinum building in the world.
  • The project also provided GeoEngineers with the opportunity to advance the understanding of soldier pile and tieback shoring systems through a full-scale demonstration project that identified opportunities for significant cost savings on future projects along with improved performance of below-grade basement walls. See the related news story for more information about the soldier pile and tieback demonstration project.