ODOT hurdles bridge replacement challenges

November 2012 » Features » SUCCESS STORIES
An Interstate 5 Willamette River Bridge replacement project case study.
Karl Wieseke
This photo provides an aerial view of the original Interstate 5 Willamette River Bridge and temporary detour bridge in Eugene-Springfield, Ore.

Most any weekend during the spring in Eugene, Ore., known widely as Track Town USA, you can find a track meet going on. During some events, athletes jump over a series of hurdles as they race to the finish line. Just down the road, a similar event is taking place: Teams are overcoming the construction hurdles of delivering a massive project while taking into account public involvement and environmental protection issues as they race toward their finish line – the completion of the Interstate 5 Willamette River Bridge.

Let the games begin: An overview
Nearly 50 years ago, the Oregon Department of Transportation constructed the original I-5 Willamette River Bridge. Located in Eugene-Springfield, the newly constructed bridge formed a vital link in the nation's West Coast interstate highway system.

In 2002, the bridge showed its age. During an inspection, ODOT engineers identified shear cracks severe enough to require the agency to place weight limits on the bridge. Heavy-haul trucks had to be rerouted on a 200-mile detour. As part of the Oregon Transportation Investment Act III State Bridge Delivery Program, ODOT's 10-year, $1.3 billion program to repair and replace hundreds of bridges across Oregon, the agency erected a temporary detour bridge over the Willamette River to keep freight and other vehicles moving while it began the $204 million replacement project.

Starter's gun is fired: CM/GC benefits the largest bridge program project
With a construction budget of $157 million, the Willamette River Bridge is the largest replacement project in the bridge program and one of its most complex: it's located between two cities with highly engaged citizens; it crosses a set of railroad tracks, a four-lane boulevard and a river; it's flanked by two parks; and it's massive in scope. Once completed, the bridge will be approximately 1,759 feet long – larger in length than the Empire State Building.

Because of the project's size and complexity, the agency set its sights on a new, versatile delivery method. Instead of using traditional contracting methods – design-bid-build or design-build – ODOT chose to use construction manager/general contractor, or CM/GC, for the first time. While this approach is well established in vertical construction, it's uncommon in bridge construction.

CM/GC also allows for an accelerated timeline. In comparison with design-bid-build, where the process is linear – design, permits and right-of-way all need to be complete and acquired before a project is put out for bid – a CM/GC project can be fast-tracked. Project elements with completed design can be constructed while design continues on others.

The project team hosted informational sessions in the park area surrounding the bridge to inform community members about the project and solicit their input on design.

While design-build would have allowed for accelerated construction, the drawback is the cost of limited flexibility to make design changes after the contract is awarded. With CM/GC, the agency's prime contractor, Hamilton Construction, provides input on design as the project evolves. The architecture and engineering firm, OBEC Consulting Engineering, benefits from Hamilton's construction insights, which results in fewer changes once the design packages are approved.

For this project, CM/GC helps the agency control costs, schedule and design, manage risks and resolve and adjust outcomes as the project proceeds. The partnership and constant collaboration among the three partners have already proven its value.

Overcoming a series of hurdles
Public input drives project
One challenge for ODOT was to design and construct the bridge within the physical constraints of the river and the adjacent parklands, but another was to ensure the look of the new bridge met community values. For local residents, it was important that the new bridge enhance the area's natural beauty.

Working with local citizens, community stakeholders, public agencies, and artists and architects, ODOT integrated the community's input into the design. The dynamic public involvement process required immediate responses about construction impacts and pricing. CM/GC allowed Hamilton to provide ODOT with feedback about cost, schedule and feasibility quickly and accurately, while OBEC modified the design based on the community's input.

The collaborative effort led to the project's defining feature: its graceful deck-arch design. These structures – side-by-side north- and southbound spans 16 feet apart – are a landmark for the community and complement the scenic area while addressing environmental challenges.

Single-pier design improves river habitat
As the team designed the bridge, they had more to consider than aesthetics. It was equally important to protect nearby habitats and safeguard the river below at this ecologically sensitive stretch of the Willamette River.

To prevent interruption of water flow and backwater, and to minimize disturbances to river dwellers such as salmon and Oregon chub, the team designed each arch to touch down in the water only once in the middle of the river. In comparison, the previous structure required five support piers in the water and obstructed the site's beauty with a bulky, bulb-type I-beam structure. The new bridges will provide open vistas for drivers and a sleek profile to passing bike riders and river paddlers.

Work bridge serves multiple functions
The single-pier design was not the only environmental solution for the river below. The project team went even further to protect the river during demolition of the old structure. Demolishing the original 2,000-foot-long, 50-foot-high bridge had the potential to be highly disruptive to water quality while generating a large amount of construction waste. ODOT's project team spent months planning and preparing a demolition process that greatly minimized impacts to surrounding parks, roads and the river below.

When demolishing the original Willamette River Bridge, crews had to consider the railroad and river below.
To muffle noise from pile driving in the river, crews used an innovative "bubbleator."

The team ultimately decided that excavators should pull the obsolete structure apart from a work bridge built below the existing structure. The wood and steel work bridge – stretching across the river about 10 feet above the high-water mark – supported the crew and the machines used for demolition. The work bridge also doubled as a containment structure to prevent all construction debris from entering the water.

Innovative techniques protect wildlife during construction
While ODOT protected the habitat from falling debris, it also protected surrounding habitat in other ways. During construction, fish populations must be protected from construction noise that can affect communication and migratory patterns negatively. To muffle the noise from underwater pile driving, the contractor placed a noise attenuator (or "bubbleator") around each pile template, designed for two piles. The bubbleator is a custom-made circular device constructed of sheet metal and lined with high-density polystyrene foam. Aluminum pipes frame the piles to produce a thick wall of frothy bubbles, thus dampening sound from pile strikes. Due to its large size, the frame of these devices also serves as a safe, sturdy work platform for crews during pile driving. To date, hydro-acoustic monitoring on the project has shown attenuators are maintaining noise levels below required thresholds.

The agency also used the new bridge to provide habitat for the local Myotis bat populations, which are declining at a rapid rate across the Northwest. Bridges are exactly the type of structure in which bats roost. Even with construction already underway, OBEC was able to design bat habitats to be placed on the new bridge. Each roosting site is roughly 6 feet wide, 6 feet deep and 12 feet long and made of concrete, wood and steel. By the time the project is complete, ODOT will build eight bat habitat structures on the new bridges.

Halfway to the finish line: Southbound structure opens early
In August 2011, almost two years to the day after the team broke ground, ODOT opened the southbound bridge – two months ahead of schedule. To commemorate the project's halfway point, community members, elected officials and media gathered as spectators, admiring the completed bridge, both from the construction work bridge below and the structure's deck above.

What looks like an effortlessly graceful bridge today was once a construction event with complicated challenges that ODOT and its contractors embraced and overcame. Now, ODOT is jumping the last few hurdles to finish its race as the project team works to cross the finish line in 2013 – when the northbound bridge opens to traffic.

Crews install rebar cages that will help shape the bridge's columns.

Karl Wieseke is a project manager with the Oregon Department of Transportation.

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