Six piers constructed as part of a $23-million interchange upgrade in Iowa will have to be modified as a result of a contractor’s measurement error that left them too tall for a planned flyover bridge.
The brick veneer-clad cast-in-place piers, ranging in height from 22 ft to 36 ft and designed by Parsons, were built for the Interstate 35/U.S. Route 30 interchange near Ames by Minnowa Construction of Harmony, Minn. Recent field surveys conducted in preparation for adding a 1,690-ft-long continuous steel deck bridge showed the piers deviated from the specified heights by 3 in. to 6 in., according to Iowa Dept. of Transportation engineers.
While the agency and contractor have not publicly identified a reason for the error, IDOT District Engineer Scott Dockstader speculated that anchor sleeves may have become misaligned during concrete pours.
Minnowa Construction did not respond to requests for comment. Local media reported that Minnowa vice president and co-owner Keith Breuning characterized the problem as “a major mistake.”
According to IDOT, the contractor has begun removing the top 30 in. of concrete on the piers using smaller chipping hammers to protect the reinforcing steel. Hydro-demolition will also be used to expedite the concrete removals.
Next, “the contractor will ensure reinforcing steel is in compliance with contract requirements and that the existing concrete is sound,” says Jesse Tibodeau, IDOT engineer. “They will then install forms and the anchor bolt sleeves before pouring the top of the piers.” Minnowa will pay for all rework. The first piers are to be repoured by early August, IDOT says.
Construction of the flyover bridge, originally scheduled to take 240 days, has encountered difficulties from the outset. Last summer, improper concrete settlement in the first pier required that structure to be demolished and rebuilt at the contractor’s expense, according to IDOT.
The agency did not estimate how long the current rework will take, though it will likely push the two-year interchange project past the originally scheduled completion date of later this year. Minnowa’s contract with IDOT calls for liquidated damages of $5,500 for each day past the deadline.
Highway improvements and embankments for the structure are already in place. Once the piers are repaired, Dockstader says, “it’s just a matter of setting the beams and pouring the flyover bridge deck.”
Built in the mid-1960s, the I-35/U.S. Route 30 interchange currently handles 40,000 vehicles a day, a figure that IDOT projects could nearly double over the next 20 years. It also has highest crash rate of Iowa’s six cloverleaf interchanges, with an IDOT study citing short weaving segments between the loop ramps. The flyover structure is intended to provide a safer transition from northbound I-35 to westbound Route 30.