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Textiles, grids help build Seattle park

Case Studies | April 1, 2007 | By:

Seattle’s Olympic Sculpture Park is a visionary architectural achievement that blends building and site design, including a strollable park on Seattle’s steep waterfront.

A visitor’s journey proceeds down a continuously sloping, 2,200-ft.-long Z-path, revealing artwork along the way.

For the architect’s Z-path vision to be successful, a 50-ft. elevation change had to feel effortless, and two bridge crossings needed to virtually disappear into their surroundings. There was only one problem: the entire length of the proposed path hovered in mid-air, up to 32 ft. above the existing grade.

Some 215,000 yds.3 of dirt (equivalent to a 100-ft.-deep, full-city-block excavation) had to be imported to create the path and park. To keep that dirt from spilling onto adjacent streets and railroad tracks, more than 50,000 ft.2 of retaining walls up to 36 ft. high were required.

The underlying soils were settlement prone, so the Seattle engineering firm MKA (Magnusson Klemencic Associates) answered with a mechanically stabilized earth (MSE) system, employing layers of geotextile fabric to strengthen earth fills, with small precast concrete fascia units forming the finished face. The system was decoupled, leveraging the cost-effective benefits of mechanically stabilized earth while covering it with artistic, custom-designed, full-height precast panels instead of small units.

The MSE walls have steel containment baskets holding aggregate with engineered geogrid structural reinforcement laid between each layer of fill, stabilizing the retaining system. Some of the layers are as deep as 20 ft. and are stacked with up to 18 separate geogrid layers. Wire mesh layered atop geotextile fabric created a ‘basket’ for the drainage rock face of the MSE system.

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