January 18, 2007

Sculpting an oasis from a blighted landscape

  • 300,000-pound art installation rounds out a project filled with challenges
    Sellen Construction


    A new civic landmark has been created with the opening of the Seattle Art Museum’s Olympic Sculpture Park.

    What was once a fuel transfer and storage facility, and a blight on the downtown Seattle waterfront, has been made into an 9-acre oasis.

    Construction began in August 2005 and is slated to finish this month. The park showcases 21 art installations, an 11,000-square-foot pavilion and amphitheater with a café, exhibition spaces and 22,000 square feet of underground parking. The complex construction process included numerous challenges, from soil remediation to art placement.

    Soil cap

    Photo by Paul Macapia
    Richard Serra’s ‘Wake’ required a 300-ton crane to place its 10 component panels. The identical panels are each 14 feet tall, 50 feet long and weigh 30,000 pounds.

    Due to the site’s slope and contaminated soils, there was a need for a soil “cap” that required importing 200,000 cubic yards of fill and 15,000 cubic yards of topsoil.

    Because of site topography and the challenges associated with importing and placing fill material during winter and spring months, a critical schedule element was to get this material placed, graded and sealed during the dryer months for it to be cost effective, and to manage temporary erosion control measures during the wetter months.

    Retaining walls

    Bordered by Broad Street and Western and Elliott avenues, the site slopes 56 feet to Puget Sound and required an innovative design to traverse a busy truck route and the Burlington Northern Santa Fe railroad tracks.

    Although more commonly seen on highway projects, a mechanically stabilized earth (MSE) retaining wall system was built to support the Elliott Avenue and BNSF bridges.

    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 feet and are stacked with up to 18 separate layers.

    Utilities had to be installed at several different depths and directions within the fill environments, which also complicated the construction.

    The entire project was modeled in AutoCAD and the information was downloaded to robotic total station survey equipment to ensure accuracy and precision.

    Building the bridge

    Once the mechanically stabilized earth walls were constructed, the bridge abutment construction and steel erection could begin.

    Since the abutments were built within 25 feet of the railroad tracks, an agreement with BNSF was executed stipulating the rules of the work, including track protection, safety training, special insurance provisions and personnel to signal the arrival of trains. In some instances, Sellen was required to stop all work as trains passed.

    Concrete deck pours and other significant work on the bridge were scheduled on weekends when train traffic was less frequent. The trapezoidal geometry and wall heights of the BNSF bridge abutments created some significant formwork and concrete consolidation challenges. Both abutments required corbelled support of bridge beams, with one wall thickened to 42 inches to create a pocket for beam support.

    The heaviest beam on the BNSF bridge was 100,000 pounds and 145 feet long. Complex recesses were built into the walls to receive handrails and precast panels. Concrete, soil and throw fence loads were carefully engineered in order to accommodate the high degree of precision required for a glass art installation that serves as the canopy across the bridge.

    Unique panels

    A unique precast panel design was selected to hide the mechanically stabilized earth walls in order to enhance the overall appearance of the park from the street level.

    Of the 305 precast panels installed, 263 of them were one-of-a-kind sizes to help create a staggered look. Besides its aesthetics, this functional precast panel system also serves as the guardrail structure.

    This approach was used in lieu of installing expensive conventional steel guardrails. It took careful coordination between design disciplines, engineering and construction teams to ensure 42-inch guardrail height requirements were met at all locations.

    Another challenge for the team was managing the potential settlement of the fill material behind the walls. By utilizing an overlapping connection between precast panels — as opposed to a more conventional butt-jointed alignment between panels — the team was able to provide another, more cost-effective solution.

    Installing the art

    Installing each of the sculptures throughout the park required a unique approach. The team used a variety of creative construction strategies — including flying in one piece using a helicopter — and strong coordination with SAM staff, artists and subcontractors.

    The “vivarium” by Mark Dion houses a 60-foot, 55,000-pound nurse log from the Green River watershed that provides an opportunity to watch the natural decaying process of a tree and to see the mutual interdependence of insects, slugs and snails, and nature.

    Concrete foundations and walls were first installed to accommodate the nurse log and the greenhouse foundation requirements. The log was then trucked in and placed into the tree pit. The greenhouse was erected around it, more cautiously than normal to ensure the nurse log wasn’t damaged.

    Another sculpture piece, Richard Serra’s “Wake,” required a 300-ton crane to place the 10 individual panels that are 14 feet tall and 50 feet long, and each weighing 30,000 pounds, creating five identical wave shapes. Since the art pieces were being installed concurrently with the park’s completion, specific construction plans were made to ensure their safety and security.

    Bill Badger, senior vice president and senior project manager at Sellen, has been with the company for 20 years providing estimating, budgeting, scheduling and planning support.

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