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September 11, 2003
Photo courtesy of Parsons Brinckerhoff
A giant steel girder — among the heaviest ever to be transported on a Washington highway — is slowly eased onto a concrete column. The series of steel sections that make up the girder had to be pieced together at a steel plant in Vancouver and then shipped north as a unit to the project site.
Two years after ground was broken in Issaquah, the Interstate 90 Sunset Interchange is a reality.
Politicians, construction workers and consulting engineers all shared the podium at the recent opening of the Sunset Interchange — a testament to the number of significant design and construction obstacles that were overcome to deliver the largest and most complex interchange project undertaken in Washington in the last decade.
According to the Census Bureau, Issaquah is the fastest growing city in the state. With plans to build the Issaquah Highlands urban village and a Microsoft campus atop the Sammamish Plateau, transportation improvements are greatly needed. The new interchange will alleviate congestion, improve safety and better connect this rapidly growing city to the Sammamish Plateau.
Running into boulders the size of small automobiles during foundation drilling was just one of challenges the team faced, but the interchange was delivered on time and with many unique features.
The project required transporting a massive steel girder across the state, protecting the environment during construction, blending concrete structures into art forms, and facilitating a team of public and private agencies. This was also one of the first major transportation projects in the region built under the new Endangered Species Act requirements.
Partnering for the project
Perhaps the most challenging, yet most valuable, aspect of the project was the formation of the Sammamish Plateau Access Road (SPAR) executive committee. This committee — a unique partnership between the city of Issaquah, King County, state Department of Transportation and Port Blakely Communities — provided coordination, core funding and momentum. It was the most celebrated topic at the grand opening, and its cohesiveness was the key to avoiding roadblocks.
Parsons Brinckerhoff, the project’s lead engineering design firm, worked closely with the partners to ensure each of their priorities was reflected in the process and in the project.
Karl Winterstein, project manager for Parsons Brinckerhoff, said the biggest challenge of all was delivering a project of this size and complexity in six years instead of eight or 10.
“The spirit of cooperation and desire to build this facility had to be balanced against financial, regulatory and institutional constraints,” Winterstein said. “Keeping the project moving in a streamlined fashion was the executive committee’s real value.”
The SPAR executive committee also helped leverage local funding to match other federal and state sources, including the transportation improvement board.
The partnership’s impact reverberated at the opening ceremony.
“I’m sad today,” said James Warjone, Port Blakely Communities chief executive, in a bittersweet address at the opening. “I’m happy that we have completed the project, but I’m sad that this partnership has come to a close.”
The heaviest girders ever to ride Washington highways now carry traffic up to the Issaquah Highlands and away from previously clogged arterials below. The girders, two 116-ton, 132-foot-long pre-assembled bridge segments, were shipped 180 miles from Vancouver to Issaquah at maximum speeds of 30 mph.
A special rig was custom-built to make the trek: a tractor-trailer that spanned 253 feet and rolled on 86 tires. The lengthy bridge span was needed to avoid disturbing the salmon-filled East Fork Issaquah Creek below.
“Because the creek and the bridge alignment were nearly parallel, the span had to be long enough to keep the bridge foundations away from the creek and its banks,” said Yuhe Yang, a senior structural engineer at Parsons Brinckerhoff. “We worked closely with WSDOT and environmental teams to come up with a design that had minimal disruption to the environment and was still feasible from a logistical standpoint.”
The series of steel sections that comprise the girder had to be pieced together at the Universal Structure steel plant in Vancouver, and then shipped as a whole unit to the project site.
Once the girders arrived, two cranes lifted them off the trailer and gingerly set them onto waiting concrete columns. The girders were bolted to other steel bridge segments and covered with a layer of concrete to form the bridge deck.
The largest girder now comprises the off ramp from eastbound I-90 to East Sunset Way.
The steel bridges also use an innovative seismic isolation system on the curved structures. The system includes placing a large isolation bearing between the bridge deck and the columns on which it rests. The top of the bearing is connected to the underside of the bridge deck and the bottom is connected to the column. In the middle, a friction-reduced, bowl-shaped plate provides a flexible, movable surface.
Maintaining the environment
Protecting the delicate environment at the project site, coupled with ESA requirements, was another major challenge for the project team.
The project required minimizing wetland impacts and working carefully in and around the East Fork Issaquah Creek, where endangered Chinook salmon come to spawn.
Osborn Pacific Group, working on the environmental program requirements, teamed with the city of Issaquah to locate a feasible wetland mitigation site. They also worked with design engineers and regulatory agency representatives at the outset of the project to devise specifications that allowed construction in adjacent sensitive areas without any in-stream staging areas or the introduction of sediment materials into the creek. This involved trapping any muddy run-off produced from soil boring activities and pumping it out of the area.
Since two of the bridge structures crossed directly over the East Fork Issaquah Creek, significant care was taken to ensure that neither the foundations, nor their construction, caused any impacts to the creek.
Sections of the creek needed to be restored to accommodate sockeye salmon, which also inhabit the creek. Osborn Pacific Group’s staff designed and specified the construction of in-stream fisheries habitat structures and a series of log weirs to modify the slope of the channel bottom. Osborn Pacific Group also designed and specified the construction of 500 feet of bio-stabilized creek bank to restore natural functions to former residential recreational structures along the creek.
This in-stream work, required by the state Department of Fish and Wildlife, could only be completed in a dry creek bed, requiring the re-routing of creek water into pipes and its release back into the channel downstream of the work area.
Kirk Hackler, of Osborn Pacific Group, found the permitting process and its timing the most challenging aspect of the project. At least 14 different federal, state and local permits were required.
“We worked with state, local and federal agencies to ensure all of our applications and everything they were going to need was in place,” Hackler said. “So when we received approval from the federal agencies, the other agencies could move forward with their approvals without any delay.”
Art of concrete walls
Photo courtesy of Parsons Brinckerhoff
Artist Peggy Gaynor designed 2-inch-deep leaf imprints to decorate the project’s concrete walls. The leaf patterns — poplar, willow, cedar and Douglas fir — are intended to reflect the natural and human environment around the interchange.
When looking at the number of walls and sheer volume of concrete that would eventually comprise the structures, landscape architect/artist Peggy Gaynor saw an opportunity to propose something different. She recognized that this immense project was considered the gateway to the Cascades and knew that with all of the structures involved — bridges, ramps, flyovers, walls — the natural aesthetics could be lost.
“The challenge was not to have nature totally overwhelmed by the structures,” Gaynor said. “This could all become total visual clutter in what is a very natural gateway heading up to the Cascades.”
Gaynor began working with WSDOT, the city of Issaquah and Parsons Brinckerhoff to develop a number of alternative designs for nearly 20 of the project’s concrete walls.
Selling the idea of original artwork to design and construction engineers proved a bit daunting. A series of open houses were held, with full-size paper mock-ups, clay models and poured concrete samples.
After more than a year of examining alternatives, a final design was approved for construction: the now signature “leaves” design.
The 2-inch-deep imprints of various leaf patterns along the walls were not randomly selected. The symbolism of the patterns reflects the natural and human environment around the interchange.
There are four different leaf patterns: poplar leaves, to reflect the city of Issaquah and its farming community history; willow leaves for East Fork Issaquah Creek; cedar leaves for the bordering forest; and a single seed from a Douglas fir cone to represent the idea that seeds of the forest are everywhere. Not only are the patterns selected to represent the area, they are also arranged according to where the actual leaves can be found.
“Part of the art is not just the patterns but how they are arranged,” Gaynor said. “The way they flow on the walls. They’re closer together as you slow down and further apart as you pick up speed. There were a lot of factors involved in their placement: their surroundings, the wind pattern and the speed of travel as you’re going by them.”
“They’re not just leaves,” Gaynor said. “They’re gestures of movement. That’s what this project is all about — moving things!”
Project in use
Secretary of Transportation Doug MacDonald, master of ceremonies at the opening event, acknowledged the challenges and construction budget overruns but he also emphasized that the project is no longer just a dream, but a reality.
“We wanted to show the taxpayers that we could indeed deliver projects,” he said. “This is a symbol of our ability to put projects into use.”
The true victory for the Sunset Interchange is that it was delivered, with unique public-private collaboration that is a model for others to follow. The result is reflected in the vastly improved access onto the Sammamish Plateau for cars, transit, cyclists and pedestrians.
Mark Pendolino is the graphics and editing group manager at Parsons Brinckerhoff, a multidisciplinary engineering organization. The firm’s Seattle staff provides planning, architectural, engineering, communications and construction services throughout the Northwest.