9 minute read
CONSTRUCTION
About Bridges
Retrofits, repairs, and construction for this critical infrastructure
By Isaac Stone Simonelli
With about 365,000 miles of river and thousands more miles of streams and other waterways—not to mention 6,640 miles of coastline—bridges are vital infrastructure for keeping Alaskans moving along the state’s roadways.
“You’ve got to understand the geography of Alaska: to get from point A to point B, there are rivers, streams, and creeks. Everything that is fish-bearing and things of that nature has to have a bridge over it,” says Bud Courtright, a senior project manager for Swalling General Contractors, which specializes in bridge building. “In the old days, they drove across them; I think we’ve finally grown out of that mindset.”
And while some smaller, fragile stream systems might have once been crossed without a bridge, there are many water crossings in Alaska where such attempts are unimaginable without a bridge—or a boat.
More than $80 million has been spent on bridge retrofits, repairs, and construction in the Last Frontier since 2019, explains Richard Pratt, chief bridge engineer for the Alaska Department of Transportation & Public Facilities (DOT&PF).
A number of bridge projects will be under construction in 2021, including the replacement of two bridges along the Chena River, the replacement of the bridge on Old Sterling Highway over Anchor River, and the replacement of five bridges on the Seward Highway.
“Replacements are typically condition and cost-based decisions,” Pratt says. “If we have a bridge within the limits of a highway rehabilitation project, we will compare the life cycle cost of rehabilitation versus replacement. We also include some consideration of improving the anticipated performance of a bridge designed to meet current standards versus a lower cost rehabilitation strategy.”
A new bridge—instead of a replacement—is often required due to expanding highway systems.
“For example, we need new bridges on the Sterling Highway because we’re constructing several miles of new alignment for the Cooper Landing Bypass. We also build new bridges to improve safety such as replacing an at-grade railroad crossing with a grade separation structure,” Pratt says.
Cool—But Not Record Setting
The new Juneau Creek Bridge for the Cooper Landing Bypass Project on the Sterling Highway, which has been more than forty years in the coming, sits at about 30 percent design as of March, with expectations that geotechnical exploration will provide the necessary information to take it to 75 percent by the fall.
The bridge, which has inaccurately been identified in the media as what would be the longest single span bridge in the state, will come to a total of 776 feet, including the end spans.
“There are already several bridges over 2,000 feet in length; however, Juneau Creek Bridge will be a significant structure, and its design and construction offer many challenges,” Pratt says. “This bridge will cross a canyon, and the project’s environmental document limits the amount of work that can be performed within the canyon walls.”
Jonathan Tymick, DOT&PF project manager for the bridge, points out that the project—though impressive in many ways—will not set any state bridge records.
“I was hoping to have a fun fact, like it might be the largest single span bridge in the state, but it's not,” Tymick says. “We should probably try to kill that rumor. It’s on track to be the third or fourth largest single span bridge in the state of Alaska.”
But the project will include the State of Alaska’s first wildlife overcrossing, which is a broad term for any structure that allows wildlife to cross manmade structures. They have been proven effective in both the Lower 48 and in Canada. The project has been studying wildlife movements for several years and working with experts to help provide input during design and make sure it’s successful.
According to the Juneau Creek Bridge Record of Decision, “The purpose of the project is to bring the highway up to current standards and to efficiently and safely serve through-traffic, local community traffic, and traffic bound for recreation destinations in the area. FHWA identified three needs for the project: to reduce highway congestion, meet current highway design standards, and improve highway safety.”
Though the project is designed to bypass Cooper Landing, Tymick says he doesn’t expect it to have a negative economic impact on the community.
“From a local point of view, I think a lot of folks will be happy they can cross the old highway safely with their children, whereas it's pretty hard to do that in the busy month of July,” Tymick says.
The entire Cooper Bypass project is estimated to cost upward of $500 million, Tymick says, with the bridge itself originally slated to cost $50 million to $60 million.
“The bridge has some global stability concerns,” Tymick says, noting that mitigating those with strand anchors will add a significant amount of work.
The need for an estimated 200 strand anchors could increase the project’s cost by $10 million to $20 million.
“Bridge access is the critical path for us right now,” Tymick says. “We need to get up to the bridge site to better determine how many strand anchors will be required.”
Tymick’s team is still operating under a land-use permit, though once it has access they will begin a geotechnical investigation to get a better idea of what challenges lay ahead.
A geotechnical investigation includes identifying the water table, seismic activity, ground movement, and fracture critical surfaces. Once complete, the team will better know how deep the strand anchors need to go to provide overall stability to the structure.
“By drilling, we're able to basically interpolate the data from multiple drill holes to find where those failure planes are located,” Tymick explains.
Bud Courtright, Senior Project Manager Swalling General Contractors
Spanning the Unexpected
But bridge building isn’t always a perfect science.
Swalling General Contractors was in charge of executing plans for replacing the Indian Creek Bridge in 2020, with the project slated to be wrapped by September. However, during
construction, the team uncovered an abandoned foundation of a previous bridge from the ‘40s or ‘50s that there was no record of.
“One thing about driving pile is that you can find any obstruction or utility faster than you can find them with a locating device,” jokes Paul Swalling, co-owner and senior project manager of Swalling General Contractors.
Swalling is a third-generation bridge builder in Alaska. His grandfather moved to Cordova in 1929 to work on the region’s narrow gauge railroad as a carpenter and ended up on a bridge crew. In 1947, he started the original entity that is now Swalling General Contractors.
Courtright adds that with every project there seems to always be something a little different than expected when construction starts.
The team of seasoned bridge builders all agreed that nothing beats experience when it comes to troubleshooting.
“Sometimes the best thing to do is find the oldest guy in the room and ask him what he sees,” says Steve Rowe, co-owner and operations manager at Swalling.
For the Indian Creek Bridge project? The solution is to divert the water and remove the original foundation, which pushed its finish date back to this year.
Seasonal Considerations
Bridge builders and DOT&PF design teams face an assortment of challenges in Alaska, from working in remote locations and material appropriation logistics to adjusting for weather and wildlife.
Because of the sensitivities of migratory birds, anadromous fishes, and marine mammals, construction in vital habitat can be paused for windows of time during the summer to protect those natural resources, explains Brian Van Abel, a co-owner of Swalling General Contractors.
Working in critical spawning habitat requires additional levels of permitting through the Alaska Department of Fish and Game, Van Abel says.
“If you have pile foundations in the water, you have to get those in late in the fall and then come back and build the rest of the substructure and the superstructure,” Courtright explains of working around salmon spawning windows.
Swalling General Contractors crew on the Chatanika Bridge. The team usually takes on about five bridge projects a year.
Hook, LLC
In addition to working around windows for wildlife and harsh weather conditions, contractors have to navigate the logistics of material procurement.
“You can’t go down the street and buy a piling,” Swalling says. “You’re looking at three to four weeks to get it wherever it’s needed, and if you're going to the North Slope or out west, that could be a three month delay to get that material up there.”
Such logistical issues are mitigated by buying extra materials, having a stash of backup materials, or working out a trade with other contractors, Swalling explains.
While construction season (April to October) in the past has been a limiting factor for projects, Swalling says that slight changes in technology are now allowing them to operate nearly year-round.
On the North Slope, there is still a limited construction season, though the situation is almost the opposite of what people from Outside might expect.
“The bridge work up there is predominantly done in the winter months,” Swalling says.
The deep cold on the North Slope requires contractors to use a more expensive concrete mixing process, and the permitting process for such work usually prohibits work until the winter.
Seismic activity in the state also presents challenges when building stable bridges in Alaska.
“Since the ‘90s, we have worked with universities in Alaska and across the country to develop analysis tools and structural detailing to enhance anticipated bridge performance under seismic loading. Soil liquefaction during earthquakes results in the need for deeper and more robust foundations,” Pratt explains.
Swalling says that within even the last decade he has seen the size of pilings increase.
“In situations where a 10-inch pile was being used, now engineers are calling for a 36- or 48-inch piling,” Swalling says. “The steps are still the same, but it requires different equipment and tools.”
While bridge designs are being adjusted to meet changes in regulations and demand, there is a steady demand for work in the sector. Swalling—one of several contractors bidding on bridge projects in the state—handles between three and five major bridge projects per year.
Unlike in the Lower 48, where some bridge projects can close a section of road, forcing motorists to use detours, the situation is more complicated.
Because of Alaska’s limited road system, shutting down a road or bridge completely is in most cases not possible at all or would result in a detour hundreds of miles long. Instead, it’s necessary to construct temporary alignments or develop creative and safe ways to allow access through the project area.
For instance, Swalling recalls replacing a bridge pier and bearings over the Nenana River for the Alaska Railroad without interrupting scheduled train traffic.
Despite the hardships and challenges bridge builders in Alaska face, Swalling says the views during construction are hard to beat.
“You are in some of the most picturesque places in the world when you're building a bridge,” Swalling says.
