Lunda Construction Keeps New Mississippi River Bridge Ahead of Schedule Despite Flooding
To replace the outdated Highway 24 bridge over the Mississippi River in Clearwater, Minnesota, Prime Contractor Lunda Construction Co. of Black River Falls, Wisconsin, paired two huge cranes to set 46 large beams - 30 of which weighed more than 110 tons each - as traffic continued to move on the original bridge just a few feet upstream. Because barges can't navigate that stretch of the river, the cranes worked from a causeway rimmed in metal sheeting but often flooded by ice jams and rain. Despite the many weather-related delays, the new bridge opened to traffic in August, slightly ahead of the original construction schedule.
Huge Beams, Constrained Space
Started in August 2015, the $17.4 million Highway 24 bridge project increases safety and capacity by replacing the original 59-year-old structure with a new seven-span, two-lane bridge that features wider lanes and shoulders and a multipurpose trail separated by a concrete barrier. The new bridge sits south, or downstream, of the old bridge. From fall 2015 to fall 2016, crews constructed the bridge abutments and six piers - two inland and four in the river - working from sheet pile cofferdams.
One of the biggest challenges of the project came last winter in setting six huge beams in each of the spans across the river. "The beams were quite large and quite heavy - the biggest girders they make," said Bruce Reihl, Lunda's Vice President of Minnesota Field Operations. Each of the 30 pre-stressed concrete girders weighed 110.3 tons and measured 96 inches deep and 178 feet long.
Oversized semi-trailers delivered the beams one at a time. "We were able to pick the beams off the existing bridge, which helped quite a bit access-wise," Reihl said. "Getting those beams down to the river elevation would've been very tough."
Lunda rented a 300-ton capacity 2250 Manitowoc Crane from Vic's Crane & Heavy Haul Inc. in Rosemount, Minnesota, to complement their own 2250. They positioned the cranes on each side of the piers so they could work together to lift the large beams.
During the setting operation, "We flagged traffic on the original bridge the whole time and stopped traffic from the time we picked the girder off the truck until we got it swung away from the bridge," Reihl said. The traffic stoppages lasted no more than 10 minutes, two to four times per day.
Space constraints prevented placing every beam on the new structure immediately after lifting them off the truck. "Once we set three girders on the new bridge, the cranes couldn't reach the old bridge any longer," Reihl explained. "We had to store half the beams for each span down on the causeway behind the cranes and pick them up again to set them."
Because the work space experienced frequent flooding, "We didn't want to leave girders sitting on the causeway when the water came up," Reihl said. "If it rose high enough it could've tipped them over, so we had to carefully plan."
In addition to the 110-ton beams, "We also had two spans of smaller, 63-inch girders," Reihl said. "There were 16 of those. They were at a higher elevation at the west end so we didn't need to work off the causeway to set those." In total, crews installed 7,566 linear feet and 4,280 tons of bridge beams.
To give all the equipment an area to work, the Minnesota Department of Transportation (MnDOT) specified construction of the causeway, with a design intended to protect the waterway. "It's the first time we had a full causeway enclosed in sheeting," Reihl said. "MnDOT required that mainly for environmental reasons, to keep from causing any kind of siltation in the river when we put in the causeway and removed it."
To build the causeway, "We started up on the river bank and had a 165-ton Terex crane," Reihl explained. "The operator reached out and placed sheeting as far as he could, then we hauled in the riprap. The banks were fairly high so we cut a road down to the riprap elevation after the sheeting was put in. The crane just kept walking and reaching out further, and we brought the riprap out as he went."
Eventually the road extended to the river elevation and ran parallel with the bridge. "At each of the new piers we put in what we called a "˜finger,' perpendicular to the main causeway," Reihl added. "The cranes used those to walk alongside the new piers to the old bridge and pick up the beams."
To support the large cranes, "The fingers had to be designed with tie-backs so the sheeting wouldn't collapse," Reihl said. "When the cranes picked up the heavy loads, that's when the most stress was put on the sheet piling so we tied them together with Williams or DYWIDAG rods."
MnDOT's specifications for the causeway included a maximum elevation to avoid backing up the flow of the river. Unfortunately, that created construction challenges. "When we had rains as we built the piers, we were shut down quite often," Reihl said. "The causeway provided our only access to the work and it was underwater a lot more than we would've liked. When we could work, we put in some extra hours to stay on schedule."
Similar issues occurred during the winter when ice jams downstream raised the river level and brought ice and water onto the causeway. Lunda began setting the bridge beams in the first half of December. "The first jam-up came fairly early, around Christmas," Reihl said. "That slowed us down and we didn't get done setting the beams until March. We were hoping for about a month maximum."
Weather continued to interfere this spring as the flooded causeway delayed crews pouring concrete for the bridge deck. Once the water receded, concrete pumps worked from the causeway to finish the deck pours in June.
Beating the Schedule
Despite the setbacks, Lunda finished the bridge deck and subcontractors completed the new roadway approaches this summer. After traffic transferred to the new bridge in August - ahead of the original fall schedule - Lunda began the process of removing the old bridge.
To accommodate equipment for that last phase of work, "We're moving the causeway over alongside the old structure," Reihl explained. "For construction, the causeway was south of the new structure, so we're moving portions over north of the old structure. We'll dig out the riprap as far as the crane will reach, then pull the sheeting and keep working our way back, then we'll use the same process to put it alongside the old structure."
As they demolish the old bridge, crews will saw cut the deck and pull the pieces out with a Kenco Slab Crab. Beams will be cut and picked down. Complete removal of the old bridge and road connections is scheduled to finish by June 30, 2018.