Advertisement
"It's kind of a marvel, something you don't do every day," said Gary Snyder, bridge project supervisor. "For me, it's very exciting being down there. You look up and see blue sky, knowing the water is surrounding you."
More than 200 steel pilings were driven into the river bed with a crane and mechanical hammer to create a box about the size of a basketball court. Sand, rocks and mud were scooped out, then a hose was dropped to the river bed to pour a concrete seal at the bottom of the cofferdam.
Next, the water was pumped out over 24 hours and the river was effectively parted.
Water still trickles in through cracks in the steel pilings, but a pump remains at work to ensure the cofferdam doesn't flood. Other layers of concrete are added around steel beams and rods that reinforce the concrete.
Once the hole is filled, workers can start building a pier's stems. A cofferdam is in place for about two months, while the entire pier construction itself takes about another month.
The new Mississippi River bridge, which is scheduled to open in the fall of 2004, will have 10 support columns, three of which require cofferdams for construction.
Lunda Construction Co. of Black River Falls, Wis., was contracted to build the piers and cofferdams. Safety measures are a huge priority as cofferdams elsewhere in the world have been known to collapse when not built properly, killing people, Snyder said.
The bridge, which will span the river between La Crosse and Minnesota, is being built at a cost of nearly $40 million.
It will be one-way from Barron Island near La Crescent, Minn., while the existing bridge will be one-way from La Crosse heading west. The project is intended to improve traffic flow and provide safer and more efficient access on both sides of the river.
When water is pumped from a cofferdam, workers said they see a lot of walleye and other fish.
"They caught them and released them," said Josh Blum of the state Department of Transportation.
When the river bed was dug up prior to concrete seals going in, the odd bottle was found among the sand and muck, but little else, workers said.
Unfortunately, people interested in peering into a huge hole in the river are out of luck due to safety issues. Even the south side sidewalk on the existing Cass Street Bridge has been closed to the public because of cranes swinging loads as well as the fact the pavement needs replacing.
Ed Hoskin can be reached at ehoskin@lacrossetribune.com or (608) 791-8226.
