Over a decade ago, the Cass Street bridge was refurbished and a second bridge was installed.
Together, the two have become a symbol of La Crosse.
I remember driving over the project at the time thinking, “How do they do that?”
I understand paving roadways. I can get my head around the idea of framing up large office buildings. I can see the basics of house construction.
However, with bridges, we are talking about negotiating tons of steel and concrete amidst untamed waterways. One does not have to be an engineer to appreciate the intricacy and large scale of bridge construction.
A few miles upriver from the Cass Street bridge, construction of the Interstate 90 bridge is now under way. Here, I thought, is an opportunity to investigate my question, so I did some digging and learned some of the basics.
First and foremost, a project of this magnitude requires a great deal of forethought, assessment and planning.
In 2016, we’ll have two new bridges — one two-lane bridge for each direction, east and west — and a new interchange with U.S. Hwy. 61 on the Minnesota side, for a total cost of $187.5 million.
“This is a major project that rivals pretty much anything we’ve seen in the Twin Cities metro area, in terms of size and complexity,” said Terry Ward, project manager with the Minnesota Department of Transportation.
With so much work and money involved, officials take care to follow all protocols. Preliminary studies for the new bridges and interchange began in 2006.
MnDOT, in conjunction with the U.S. Fish and Wildlife Service, the Department of Natural Resources and the Federal Highway Administration, completed an extensive environmental assessment, as well as evaluations of the existing bridge, which is in significant disrepair.
From an environmental perspective, the bridge project demands careful attention.
Governmental agency officials, designers and construction crews must protect natural resources during all phases of construction and left no river rock unturned during preliminary studies.
“A project like this is really a delicate balance between the environment that we’re working within and delivering the project,” Ward said.
The environmental assessment is the overarching document that includes all of the studies and construction plans as they relate to the natural environment.
Suffice to say, this document is large and detailed, and took several years to complete.
In creating the environmental assessment, officials consider impacts on land, water and the river bottom.
General efforts to preserve the environment include sediment control, reforestation and erosion control, but some interesting specific practices are implemented, too.
For example, one aspect of the assessment considers how man-made lighting will affect migratory birds. Thus, a special ambient lighting will be used so as not to disrupt their flight patterns.
Also, a “bubble wall” will be placed down into the depths of the river and will be used to protect fish during demolition of the original I-90 bridge.
Fish are not merely expected to hear the commotion and hightail it out of there like one might think.
A bubble wall is composed of compressed air that is organized to release into the water and repel fish away from the immediate demolition area. It essentially creates a force field of air that blows fish toward safer waters.
Overall, construction crews follow a strict containment plan.
As concrete decking is sectioned, steel pieces are dismantled and concrete piers are demolished with explosives and hydraulic hammers. Cranes and barges will haul the rubble away for proper disposal.
Once demolition is complete, construction crews numbering in the hundreds begin the process of installing the new bridge.
Eric Breitsprecher, an engineering specialist with MnDOT, explained that once all of the blueprints are reviewed and found to meet the proper specifications, it is time to take on the river.
Crews start by driving huge metal tubes down through the water column and past the river bottom another 50 feet.
Next, workers pump out all of the water and sediment caught within the tubes, which creates a space for pouring concrete.
From there, barges carry cement trucks out onto the river and workers begin the process of pouring concrete into the tubes, which act as forms. Ultimately, this will create all of the piers on which the steel bridge components and roadway will rest.
Each pier takes about 45 days months to complete due to multiple pours and curing time. Piece by piece, year by year, the new bridges will take shape. Suffice to say, this is no ordinary job.
Mother Nature demands careful, creative engineering to fashion new projects over her wild lands and waterways.
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