A Sound Solution to Seattle's Airport Traffic

The South 200th Link Extension transit project will extend the existing light rail system by 1.6 miles through the use of an elevated guideway adjacent to Sea-Tac International Airport. The new guideway extension will offer patrons an additional means of traveling to and from the airport and provide an alternative form of transportation to transit-dependent communities in South King County. This project is unique in that both PCL’s Transportation Infrastructure Group and its Seattle Buildings division are aiding in the project’s successful execution. PCL’s Transportation Infrastructure Group is the prime contractor on this project and will construct the guideway and light rail expansion, while PCL’s Seattle Buildings division is constructing the new South 200th Street Station. Utilizing the span-by-span and balanced cantilever erection methods, PCL will erect close to 1,200 precast-concrete segments.

Close to 1,200 precast-concrete segments made
their way from an off-site casting yard to the project

Coordination between the Washington State
Department of Transportation and PCL was
essential to ensuring timely delivery of these
massive pieces.

The project team used a collaborative mobile
application to define and track deficiencies within
each precast-concrete segment.

A Wild Ride

To minimize traffic disruptions at the jobsite, the project team produced and stored the noted concrete segments at an off-site casting yard located in Enumclaw, Washington. To fabricate these elements, the project team placed concrete into a variety of segment bed molds: four typical segment beds, a pier segment bed, a constant depth bed, and a variable depth bed. A high-strength concrete mix yielding 6,500 pounds per square inch of pressure in just 24 hours was used to pour the segments. This quick turnaround time was essential to starting the casting cycle again the next day. Trucks then transported the 35-ton segments more than 30 miles from the casting yard to the primary jobsite for installation.
Wide-load restrictions set by the Washington State Department of Transportation (WSDOT) made coordination between project teams and jobsites critical to the successful and timely delivery of the precast-concrete bridge segments. Such restrictions prohibited travel times during morning and evening commutes, reduced speed limits, and limited load-bearing on particular roads and highways. To comply with WSDOT regulations, trucks transporting the massive elements were shipped from the casting yard between two and three o’clock in the morning and arrived at the jobsite by four in the morning.
“Fabricating the precast-concrete segments off-site and delivering segments ‘just-in-time’ for span-by-span assembly has significantly reduced the project construction and traffic impacts at the airport and for the Sea-Tac community,” said Sound Transit project director Miles Haupt.

Weathering It All

If you’ve ever visited Seattle, you know that rainy days are a way of life there, and the Pacific Northwest’s wet conditions created unique challenges for the casting yard project team. In order for the concrete segments to cure correctly, the temperature had to be above 40° Fahrenheit, and conditions dry. To mitigate exterior conditions, the project team implemented tent system at the casting yard.

To define and track deficiencies within each precast-concrete segment, the project team used Building Information Modeling 360 Field, a collaborative mobile application that allowed PCL to manage construction through the entire life cycle of a project. Despite the trials imposed by Mother Nature, the project team maintained strict internal and client quality specification and compliance requirements and enthusiastically delivered a high level product.

“It feels great to know that we’ve put in this structure that will last for many generations to come,” said PCL casting yard project manager Geren Shankar. “I’ll miss the people, the challenge, and the enthusiasm that the laborers and carpenters put into their work every day.”



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