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August 18, 2011
Drivers have been enjoying the benefits of the Westbound Nalley Valley viaduct project, a new connection between state Route 16 and Interstate 5 in Tacoma, since late June.
Guy F. Atkinson Construction rebuilt the interchange for WSDOT to increase safety, improve mobility and reduce congestion. Now that the westbound project is complete, a separate construction project will build a new eastbound Route 16 connection to I-5.
It’s the perfect time for a retrospective on the challenges and successes of the westbound project. Kathleen Wilcox, Nalley Valley project manager for Atkinson, described several major challenges Atkinson encountered and overcame during construction.
Wilcox said Atkinson delivered the project on time and saved taxpayers and WSDOT more than $20 million.
First, Atkinson’s bid for the project came in at $119.9 million, nearly $20 million under the WSDOT engineer’s estimate. In addition, Atkinson developed two innovative methods for construction, saving nearly $1.5 million, split equally between WSDOT and Atkinson. These were “mini-design-build” projects: a temporary bridge and a segmental bridge.
First segmental bridge
One of the most remarkable aspects of the project is that it included a segmental bridge one built in segments and assembled on top of a column, building outward. From a drivers’ perspective, during construction there were times when the bridge seemed to extend unsupported into the air.
Atkinson proposed a segmental bridge to replace WSDOT’s plan for a steel tub bridge, with bathtub-shaped pieces of steel supporting the bridge deck. A segmental bridge, built with concrete, would save the company and state money at a time when steel costs were high.
In Washington state, most bridges are built with concrete or steel girders spanning separate columns.
“This was the first time a segmental bridge was built for WSDOT,” Wilcox said.
Since it was the first time, there was no place set up to build the pieces.
“We cast all the segments ourselves,” Wilcox said.
Crews built individual segments at a five-acre construction yard in an industrial area in south Tacoma and assembled them above the freeway overnight. Coordination between day shift and night shift added to the complexity. So did the fact that each segment was different, with slightly different dimensions and specifications, and required custom work. But it was all worth it.
“They have a beautiful bridge. It’s a signature bridge,” Wilcox added.
Weather hampers construction
The end result came after surmounting a number of challenges, including the weather. WSDOT awarded the contract to Atkinson in the fall of 2008 and construction began in 2009. A large part of the work took place this year, when the region had record rainfall and low temperatures.
“There are certain construction activities that you can’t do in the rain and when it’s cold,” Wilcox said. The weather delayed three or four activities into the spring, and crews had to do them all at the same time.
“That was a huge challenge,” she said.
Work that was delayed included pouring the concrete for the bridge decks and the barrier, and digging drainage ponds at the bases of the columns. Crews couldn’t finish the ponds until the bridges were done, because they would be in the way of equipment (such as huge cranes) needed to finish the bridges.
The delays meant that crews ended up finishing several bridges at the same time, which cost the company more and prevented the project from being completed early.
Soft soils stretch schedule
The contract included widening and realigning both the east- and westbound lanes of Route 16.
Before the highway was built, a gorge angled from what is now the Allenmore Public Golf Course, across the future Route 16 alignment, and emptied down into Nalley Valley. When crews built Route 16, they filled the gorge with a mixture of dirt, concrete rubble, bricks, and whatever else was available. No pipe was installed to help direct the existing creek drainage through the fill.
At the time, this was common practice when leveling out the terrain.
The Westbound Nalley Valley project plans identified two locations, approximately 500 feet apart, as unsuitable material. When crews excavated this area for the alignment shift, Atkinson learned that the unsuitable material stretched across all lanes of traffic.
“We had to dig all the way across the highway,” Wilcox said. This added a month to the schedule.
Cramped work zones
The project includes 10 bridges, three of which loom high above the ground. The new bridge from northbound I-5 to eastbound Route 16 stands more than 100 feet above the valley floor. The new bridge from southbound I-5 to westbound Route 16 is more than 80 feet tall. The segmental bridge is 60 feet up.
Building structures at such a height magnified the need for safety precautions and presented logistical challenges. Even the weather is different 100 feet in the air. Wind in the work zone caused problems even when there was no wind at ground level, Wilcox said.
Workers were scaling scaffolding that was eight to 10 stories high just to get to the work zone. If they forgot something, they’d have to climb down and back up. Of course, all workers used safety harnesses.
The company had to think of innovative ways to get material and supplies to the work zone.
“You need large equipment to lift material up that high,” Wilcox said. “And large equipment takes up lots of room on the ground.”
Space was one commodity in short supply.
The project’s towering bridges weave over each other through tight quarters. At the north ends of the bridges, where the ramps exit to Sprague Avenue, the bridges come within 10 feet of each other. One Sprague ramp rises up and over the new I-5 southbound to westbound Route 16 bridge. New stormwater detention ponds are shoehorned between and under the new bridges and off ramps. The Tacoma Screw Products parking lot is wrapped in and around the base of the new bridges.
Add in bundles of lumber and plywood, other construction materials, manlifts, cranes and equipment, and storage containers, and there was barely room for construction vehicles to turn around. During the construction phase, the tight quarters made planning and staging the work even more critical.
Design error headaches
The project made headlines when crews discovered a million-dollar design error caused by WSDOT. Atkinson crews had to remove a ramp they had just built, and rebuild it in a different alignment.
Wilcox acknowledged this was a challenge and a public relations headache for WSDOT, but wasn’t a major one for Atkinson.
“We were able to fix it at the time, rather than put it into the next stage,” Wilcox said. “It didn’t affect our schedule.”
Like a typical engineer, Wilcox is matter-of-fact when describing all the challenges Atkinson overcame during construction. But there’s a glimmer of pride when she looks back at what she and the company accomplished. As she said, “it’s a signature bridge.”
Barbara Ramey is an Accredited Business Communicator with more than 20 years of experience. More than half of her career has been in the transportation sector, for both public and private industry. She is a public information officer for Guy F. Atkinson Construction.