Knife River Midwest Tackles Unstable Soil and Tight Work Spaces to Rebuild I-29 Through Sioux City
As the Iowa Department of Transportation (DOT) works to transform 10 miles of I-29 from an outdated, four-lane facility to a modern, six-lane highway near Sioux City, Iowa, they've dealt with unstable soil and accessibility issues as the highway hugs the banks of the Missouri River without any shoulders for a cushion.
The $400 million project includes 22 new and reconstructed bridges and five interchanges. In addition, "To keep traffic flowing, one of the principles we've worked from is not closing successive interchanges, but our staging has been complex due to the lack of alternative routes," said Dakin Schultz, Iowa DOT District 3 Transportation Planner.
With the northern and southern portions of the project finished (see "Construction by Segment" sidebar for details), work now focuses on the complex section through downtown Sioux City. Once Knife River Midwest of Sioux City (General Contractor for the current phase of construction) rebuilds the northbound lanes and bridges, the Iowa DOT will bid downtown's southbound lanes and bridges. After over a decade of carefully staged construction, the Iowa DOT anticipates mainline completion by the end of 2019.
Originally opened in 1961, this stretch of I-29 had undergone just two resurfacing projects before the current improvement plan. Funded by state and federal transportation dollars (with local funds for much of the utility relocation), the work that started in 2008 adds a lane in each direction to improve safety and update the roadway infrastructure for durability and better traffic flow.
So far the three segments of the project involved 91 contractors. Knife River served as prime contractor for over half of the main contracts and provided paving as a subcontractor on another. The current two-year, $63.4 million contract awarded to Knife River includes seven bridges and covers three-and-a-half miles of downtown Sioux City roadway. Work began in March 2016 and is scheduled for completion by Thanksgiving of this year.
According to Chris Winkel, Knife River's Concrete Construction General Manager, the biggest challenge has been coordinating the work in the limited space. To overcome the difficulties, the team employed multiple strategies. For instance, "We used a lot of dump trucks because they're smaller than tractor trailer units," he said. "A lot of times the vehicles had to drive in, then back out because there wasn't room to turn around."
In addition, "Some of the reinforced soil slopes we're building using fabric," Winkel said. "That allows us to build the slope a little steeper and gain more room for traffic."
The design also includes a large number of walls, since they take less space than slopes. Knife River's subcontractor, Linhart Construction of Omaha, Nebraska, is installing almost 85,000 square feet of MSE walls and 24,000 square feet of precast fascia wall panels.
Cutting and Sliding 200-Pound Blocks
Throughout the three segments of the I-29 improvement, "Due to our soil conditions and proximity of the roadway to the Missouri River, we used various foundation treatments, including geopiers, drilled shafts, lightweight concrete fill, and expanded polystyrene (EPS)," Schultz said. "We've got the largest drilled shaft in the state on one of our bridges. The average depth of our drilled shafts was 165 feet and they utilized about 200 yards of concrete in each one."
Because of the unstable soil in the downtown section, Knife River is installing 66,000 cubic yards of EPS foam blocks under the roadway. "Each block weighs over a couple hundred pounds," Winkel said. "They need to be placed by hand, one block at a time, because we can't have any equipment on top of them."
To increase efficiency, Knife River uses telehandlers and cranes to get the blocks as close as possible, then crews slide them into place. "It's very labor-intensive, with eight to 10 guys working most of the time when we're placing the blocks," Winkel said.
Some of the areas with the EPS blocks add an extra challenge. "They're very intricate shapes, almost like puzzle pieces going together," Winkel explained. "We had to cut a lot of the blocks to fit around bridge abutments, piling, and the bridge slope protection. We cut them with hot wire; there's a rheostat switch that puts resistance through the wire, then it's almost like a large cheese cutter."
To avoid running equipment on top of the EPS, telebelts transfer material in tight areas and pumps frequently place concrete on the load distribution slabs over the blocks.
Knife River also worked with their subcontractor, Peterson Contractors of Reinbeck, Iowa, to build geopiers for intermediate foundation improvements. After stabilizing the soil through the various efforts, Knife River's crews install polymer grid, covered by 12 inches of special backfill (totaling more than 70,000 tons), 6 inches of granular sub-base (22,000 tons), and 11 inches of concrete pavement (30,000 cubic yards).
The special backfill contains the original pavement. "We recycled 100 percent of the removals," Winkel said. "Because of the lack of room, though, we had to haul everything to our yard in Sioux City, crush it there, then bring it back."
In another effort to help the environment, as crews build a bigger channel next to the highway to carry storm water, they incorporated wetland plugs, limestone blocks, boulder veins, prairie seed mixes, wetland plants, and native grasses. Those features protect the Missouri River by filtering out impurities before the storm water enters the river.
Scheduling Around the River
Since the overall project began nine years ago, construction weathered many storms - both literally and figuratively. For instance, segments one and three were under construction during the severe Missouri River flood of 2011.
Last year the Missouri River behaved itself. "We didn't have any trouble with groundwater; we were fortunate with all the pipe work we did," Winkel said. This spring, wetter weather presented more challenges. "We've been doing some channel work and fighting the river a little. We've been pumping water or building dike areas, or many times just having to wait for the water to go down and things to dry out."
In 2014, the Iowa DOT needed to adjust their schedule because of staging issues in building multiple bridges near the Missouri River. "When we put out the original bid package for the section near Bacon Creek and the Floyd River channel, we had several contractors say, "˜There isn't room to build it and maintain traffic,' so we ended up having to go back and reconfigure our plans," Schultz said. "We essentially lost a construction season, in that we did a package for just the Bacon Creek bridge one year, then put the other southbound bridge into the package with the two northbound bridges and made that a two-year project."
That delay pushed the original schedule back a year, but the Iowa DOT maintained their commitment to keep traffic moving throughout construction. Dakin expects work underneath I-29 to continue into 2020, but when mainline construction finishes in 2019, the highway will run as a modern, six-lane facility from south of Sioux City to the South Dakota border.