The $119.9-million Nalley Valley project is designed to fix a pickle of a traffic bottleneck where Interstate 5 meets State Route 16 in South Tacoma.
Contractor Guy F. Atkinson Construction, Renton, Wash., is replacing the original road structure that travels over the valley named for Nalley Inc., a Northwest food manufacturer that produces chili, pickles and other canned food.
Increasing traffic from I-5 to the Key Peninsula made the interchange a dangerous area with frequent slowdowns.
The road couldn’t be expanded using traditional methods because it was supported by a tetrapod – a foundation system with four support structures coming out of a single underground column.
This project is the first of three to rebuild the I-5/SR 16 Nalley Valley interchange and includes building a new westbound viaduct, new ramps between SR 16 and Sprague Avenue and new ramps from I-5 to westbound SR 16.
Atkinson demolished those structures and the roadway it supported last year. Now it’s drilling shafts and building columns for the new roadway.
“Atkinson chose to demolish the existing structures using excavator-mounted breakers and shears,” says Jon Deffenbacher, WSDOT project manager. “In order to support that demolition method, they’ve had to manage work around the various traffic stages of the project and implement protection methods for drainage ponds, city streets and existing buildings. The bridges were demolished either in their entirety or to an existing joint in the bridge where you can have a clean break. In cases where we want to widen an existing structure, the contractor sawcut the bridge deck at the demolition limit to ensure a clean connection point.”
Once the structures were dropped, crews processed the debris to separate the concrete and reinforcing steel. Steel was sent to a recycling facility, and the concrete rubble can either be used onsite for construction roads or disposed at offsite facilities.
Crews have completed 69 of 84 shafts, 59 of 77 columns, 18 of 34 caps and installed four spans of the girders that will comprise the west bound roadway, says Deffenbacher.
“The most difficult thing about the project is the size of everything,” says Kathleen Wilcox, Atkinson project manager. “Everything is so high and so big it takes a lot of preplanning and scheduling.”
Another planning puzzle is how to build the bridges. Atkinson submitted a Cost Reduction Incentive Proposal to build a precast concrete segmental bridge instead of the planned steel tub girder bridge. Estimated cost savings is $500,000.
Atkinson is operating an offsite facility where it will cast 114 bridge segments that will later be transported to the main project site. Although precast segmental bridges are not new to the Puget Sound area, this is a first for WSDOT.
“It’s the same type of bridge design used to replace the Interstate 35 bridge that collapsed in Minneapolis and the same as the elevated structure built for the Sound Transit Light Rail, except that we’re using traditional cranes instead of a gantry,” Wilcox says.
The next phase of the project will be to built the east roadway that connects eastbound SR 16 with I-5.
“We try to limit risk by having Atkinson complete all elements in their entirety instead of leaving partially completed elements for another contractor to finish,” Deffenbacher says. “There is also a significant coordination effort between WSDOT construction staff and the designers of the next project to manage change and ensure success of the overall interchange. Ultimately, these are separate contracts that will not take place concurrently, but we still face a big challenge to develop contract documents that seamlessly connect with the preceding project.”
General Contractor: Guy F. Atkinson Construction
Consulting Engineer: McNary Bergeron
Total Project Cost: $183.7 million
Average daily viaduct traffic: 131,000 cars
Number of bridges: 10 Steel used: 10.4 million lbs.
Concrete poured: 48,000 cu. yds.
Workers at peak: 200
Depth of piers: 50 - 70 ft.
Height of old viaduct: 64 ft.
Height of new viaduct: 94 ft.
Linear storm drainage: 3.14 miles
Capacity of permanent stormwater retention ponds: 22.4 million gal.