Situated within the Boston Mountains and Springfield Plateau subregions of the Ozarks, the region of Northwest Arkansas (NWA) has more than doubled in population over the last two decades and is currently the 22nd fastest-growing metropolitan area in the country.
In order to meet the infrastructure needs of a growing population, extensive efforts have been made in recent years to increase the capacity of the north-south corridor of I-49, NWA’s only major thoroughfare. But with the continued growth and nearly 80,000 ADT along I-49, a need arose for an east-west expansion as well, the first phase of which included the 4.5 miles of construction on the Highway 412 Bypass.
Work on the expansion project included over 5.5 million cu yd of earthwork, 2.3 miles of drainage pipe, 167,000 tons of aggregate base, 14 bridges, 16 structural retaining walls, 132,500 sq yd of 11-in. PCC paving and 35,000 tons of asphalt paving. To make matters complicated, the work had to be scheduled around 200 existing utilities in conflict with the proposed improvements in excess of the nearly 100 documented in the contract documents. All of this work had to be completed without impeding traffic flow through I-49 and the seven county roads throughout the project.
The Ozark landscape and geology proved to be a challenge as far as building bridges and moving dirt were concerned. Of the 14 bridges constructed on the project, four of them were built over protected waterways. “Two bridges were constructed in an area where underground springs had to be effectively controlled for multiple footings, plus a potential cave discovery delayed excavation for investigation by the U.S. Fish and Wildlife Service,” Casey Taggart, senior project manager/estimator for Eutaw Construction, told Roads & Bridges. Engineering and constructability means and methods were heavily deliberated prior to construction as a portion of the roadway was built adjacent to an active limestone quarry with 100-ft vertical walls.
An additional challenge encountered during the project was a 100-year flood that struck the region halfway through the peak of construction season, delaying the project by more than three weeks due to extensive cleanup and replacement efforts of damaged materials.
In terms of traffic management and safety, construction of the I-49 tie-ins proved to be a challenge as well. The Highway 412 Bypass ties in at four locations along I-49 for access onto the new highway. Also, two bridges had to be constructed over live traffic with minimal lane closures and less than 10 total nighttime traffic shutdowns for hanging beams.
With the help of of more than 13 bridge/structure crews, 10 earthwork/drainage crews and more than 20 subcontractors, Eutaw was able to successfully complete the project a year ahead of schedule.
Location: Springdale, Ark.
Owner: Arkansas Department of Transportation
Designer: Arkansas Department of Transportation
Contractor: Eutaw Construction
Cost: $104.3 million
Length: 4.5 miles
Completion Date: April 29, 2018