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Industrial/Commercial

Project

Name: Fifth and Yesler Building
Client: Martin Selig Real Estate
Location: Seattle, Washington

Client Benefits

By offering unique insight and solutions to the project’s complex problems, the client understood the value of Kleinfelder and the firm’s desire to understand their business.

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Martin Selig Real Estate has emerged as one of the largest privately held commercial real estate development companies in Seattle. Among their 25 significant office buildings in Seattle is the 76-story Bank of America Tower, the city’s tallest building. When Martin Selig began planning for a 300,000 square foot, 17-story office high-rise at Fifth and Yesler in the historic district of Seattle, he came to Kleinfelder for both geotechnical and environmental engineering services. The proposed building will include several levels of below-grade parking extending some 65 feet below the ground surface on the uphill side of the site.

Several elements had a significant impact on the geotechnical aspects of this project. The site has a history of landslides dating back to the early 1900s. The need for deep below-grade construction into the hillside of a known landslide area was one challenge. Below-grade construction would result in unbalanced wall pressure across the building that the structure could not easily resist. In addition, upslope of the site was both a narrow city of Seattle alley easement and an adjacent parcel of land to be developed by King County in the near future. Thus, the project had to consider these adjacent properties and the likely sequence of future hillside development. The conventional approach to supporting the construction excavations would be a soldier pile and tieback wall, with the tiebacks de-stressed as the floors are poured. Due to dense soils at the foundation levels, spread footings would be feasible.

Based on the landslide history, Kleinfelder could have assumed that a deep-seated slide plane underlay the site. This assumption would have resulted in more conservative and costly design and construction criteria. However, by carefully examining historical documents, particularly old photographs and topographic maps, Kleinfelder determined that the historic landslides were related to the steep topography of the bluff above Fifth Avenue. These conditions were aggravated by groundwater seepage likely discharging at the contact between the upper sandy soils and the clays.

The steep bluff may have been natural or a result of grading to create the level areas adjacent to Fifth Avenue for development. It appears that after a portion of the steep bluff failed, the slide debris was partially removed and the area re-leveled, leaving the site underlain by slide debris mixed with fills. In the 1960s, as part of the Interstate 5 construction, the area was regraded and the rock rib drains were installed. The structural engineer determined that it would be difficult to resist the high uphill basement wall pressures through the building structure as is normally done. These structural design issues threatened the feasibility of the project.

Working with the design team, Kleinfelder proposed to support the uphill wall with permanent tiebacks located under the city and county properties. The concept required a careful assessment of strain compatibility between the building and the tiebacks, particularly related to seismic loads. More importantly, it involved obtaining permanent tieback easements from the city and the county. Kleinfelder developed a design that would satisfy the current conditions and the likely future conditions after development of the county’s site.

Since future development will require some of the upper rows of permanent tiebacks to be removed, Kleinfelder had to demonstrate that development, including the Fifth and Yesler buildings’ two basement levels, would reduce the pressures on walls satisfying both current and future conditions.

By offering unique insight and solutions to the project’s complex problems, the client understood the value of Kleinfelder and the firm’s desire to understand their business. Kleinfelder currently is working with the design team to obtain permits and develop final design plans and specifications and will be involved as geotechnical engineer of record during construction.