Wed July 31, 2013
Solid foundations: new technique used in Utah bridge construction
A first-of-its-kind road construction project is underway in Summit County where crews are building a new freeway overpass atop piles of dirt instead of concrete. UPR’s Matt Jensen reports.
The Utah Department of Transportation is replacing an aging pair of bridges near Echo Junction on Interstate 84 with a new road deck that won’t be supported by columns of steel or concrete. Instead the roadway will sit on piles of soil compacted between layers of a specialized fabric.
Engineers say the process saves time and money because crews don’t have to pour concrete and wait for it to dry. The new bridges will sit between abutments of this layered earth that can be built up faster compared to building abutments with concrete.
According to the European company that supplies the geotextile fabric that holds the dirt together, this is the first structure of its kind to be used on an interstate highway.
UDOT engineer Matt Zundel says most bridge abutments are constructed using steel piles and large cast-in-place concrete structures that requires specialized labor, heavy equipment and steps that can take up to a month to complete. Using Geogrid Reinforced Soil, or GRS, builders can eliminate much of the substructure of the bridge.
The abutments are built by stacking layers of soil sandwiched between the fabric. The process is repeated until the abutments reach the specified height of the bridge.
Once the abutments are ready, builders will slide a conventional concrete bridge deck into place. Construction started April 22, and Zundel says he expects the deck to be ready for installation on Aug. 16. The project has gone so smoothly, he says it’s likely UDOT will adopt the process to replace bridges statewide.
In past years, Zundel says overpass bridges could take a year or more to complete. Today’s bridges go up much quicker, and using the GRS method, Zundel says it’s possible new bridges can be built in two to three months or less.
Zundel said using the reinforced soil method for the I-84 project shaved $200,000 off the total cost of building the two bridges.