Iowa DOT Expands Council Bluffs Interstate System
The Iowa Department of Transportation continues upgrading the aging Council Bluffs Interstate System, with three segments, valued at $1.2 billion under way and engineering for additional projects in design.
"It's to update the interstate system and bring it to a modernized condition," says Troy Jerman, Iowa DOT, District 4 Engineer. "The structures and pavement were reaching their age, and we needed some added capacity."
The interstates in the area were built in the 1960s to the standards of that time. Interstate-80 currently carries twice its original design capacity, and by 2030, estimates are that it will carry more than 130,000 vehicles daily, as more planned developments become reality. During the 1980s and 1990s, Iowa DOT performed routine maintenance, but this is the first significant investment in the system. The entire 18-mile interstate project is valued at $2 billion and aims to make the corridor safer and resolve traffic congestion on Interstate-80, Interstate-29 and Interstate-480.
"For the Iowa DOT, this is the largest single project we have undertaken," Jerman says.
Thirteen projects and $442 million worth of work have been awarded. Twelve projects remain, with $571 million programmed and $360 million planned. In 2016, $146 million has been allocated, with $110 million planned for 2017.
The department prioritized projects based on the highest traffic volume and benefits in regard to safety, capacity and traffic management.
As of the end of 2015, seven of 32 bridges, one of 15 interchanges and 26 lane miles of 135 planned, had been completed. The work to date has consumed 4,200 tons of structural steel for the bridges, 1,800 tons of reinforcing steel, 75,000 square yards of concrete and 8,400 linear feet of pipe.
Replacement of the 24th Street Bridge on I-80/I-29, completed in 2008, received funding from the Highways for Life and Innovative Bridge Research and Development programs and freed up state funding for other projects. The work was condensed into one season. Precast concrete deck panels helped speed the job. Well-planned staging and intelligent transportation systems helped keep traffic moving during the construction.
The construction on the I-80 Missouri River Bridge began in January 2008. That project received funding from both the Iowa DOT and Nebraska Department of Roads. Iowa has completed its work, but some tasks remain on the Nebraska side, after Iowa DOT finishes the West System Interchange.
The first major area of work, on the south portion of the project, is nearly complete. It rebuilt I-29 and the U.S. 275/Iowa 92 interchange. This $172-million interchange is scheduled for completion in summer 2017.
The west portion of the project, includes the $26-million, three-level West System Interchange and paving of the I-80 westbound lanes. Two projects in this segment, valued at $50 million, were completed already. The west interchange will eliminate left-hand entrances and exits from I-29 to I-80, increase the number of travel lanes, and reduce the need for lane changes. It is scheduled for completion in 2017.
Iowa DOT started on the eastern portion of the project, in 2013. The work includes the $13-million railroad consolidation project, moving five rail lines into one common corridor. It required a master agreement with two railroads and features grading and track work.
"That work allows us to clean up the corridors around Council Bluffs and allows us to lower some of our structures and the grade," Jerman says.
Above the railroad, construction continues on I-29/I-80.
The East System Interchange includes a $103 million project that was let in October and started in November 2015. Another $24 million portion of the East System Interchange is scheduled to start this summer and will not wrap up until 2018. The East System Interchange includes three bridges totaling 8,200 feet in length and a section of I-80, which will be straightened through the interchange. It will eliminate left entrances and exits and require fewer lane changes. The road is elevated above the rail line.
The roads and bridges are paved with concrete.
Traffic Management and Utilities Create Challenges
Maintenance of traffic on the truck and cross-country route presented challenges as has been the coordination and relocation of utilities, says Keith Quernemoen, Project Manager of the Council Bluffs Interstate System Improvement Program.
Throughout the work, soil conditions have required mitigation. The project runs through the Missouri River floodplain, necessitating ground improvements. The department worked with the Army Corps of Engineers to maintain the levees and the city's line of protection. Within levee critical zone, Iowa DOT used rigid inclusions. In some sections the levee needed rebuilding due to a ramp. Outside of those areas, it used wick drains.
For rigid inclusion, "they use a drill rig operation and push a steel pipe into the ground," Quernemoen explains. "You are not actually taking soil out. You are displacing the soil."
Once the steel pipe reaches the designated depth, crews fill the void with concrete while pulling the steel casing out.
"It tightens up the underground soil and forms a foundation for the embankment to bear on," Quernemoen explains.
For the wick drains, crews push a fabric sock into the soil until it reaches a layer with water. As the embankment is loaded, the water wicks up the fabric and comes out at the surface, allowing the area to settle.
Segment 4 includes the I-480 and I-29 interchange, which is primarily at street level. This will allow movement to a major city street that does not exist today, so Iowa DOT will correct that.
"We're working on the documents for segment 4," Jerman says.