By Jenny Jones
The state is employing geosynthetic reinforced soil-integrated bridge system technology to speed construction and reduce costs.
Pennsylvania is reconstructing many of its deficient small bridges using a time- and money-saving geosynthetic reinforced soil-integrated bridge system. The technique enables a small crew of workers to build robust and attractive on reinforced-soil foundations using hand tools and minimal heavy equipment. G. Randy Albert
January 13, 2015—The majority of its bridges more than 50 years old, Pennsylvania has the largest number of structurally deficient bridges in the nation. But the state and its municipalities are working to change that in part by using a recent technology that makes constructing small bridges faster and less expensive.
The geosynthetic reinforced soil-integrated bridge system (GRS-IBS) is a technology that uses multiple layers of geotextile fabric and compacted stone to form bridge abutments that are then integrated with the superstructure and approach roadway. Unlike traditional concrete abutments that require formwork and specialized equipment, a small crew of workers can construct GRS-IBSabutments on reinforced-soil foundations using hand tools and minimal heavy equipment.
As a result, GRS-IBS can lead to significant cost savings, and construction time can be reduced from months with traditional construction methods to weeks or even days, says G. Randy Albert, P.E., the municipal services supervisor for the Pennsylvania Department of Transportation (PennDOT) District 2-0. "It's relatively easy," he says. "There's no formwork, there's no waiting for concrete to cure, and it's work that local forces can do without a lot of in-depth training."
Pennsylvania's first GRS-IBS bridge was completed in Huston Township, in Clearfield County, in October of 2011. Located on a secondary road and carrying roughly 50 vehicles a day, the 18 ft long bridge was closed and needed to be replaced. But with funding limited for the relatively insignificant structure, the municipality had to find a quick, economical solution that would serve the community for years to come.
With technical direction from the Federal Highway Administration (FHWA), the PennDOT Municipal Services Unit and the township used GRS-IBS technology to construct the new bridge in just 30 days, a third of the time it would have taken with conventional methods, at a cost of just $102,000. "Thirty days was pretty amazing to me, especially using local forces and a minimally trained crew," says Albert, whose department has developed specifications for constructing local and state-owned GRS-IBS bridges across Pennsylvania.
Since then, other Pennsylvania municipalities, the PennDOT, and some private owners have used GRS-IBS on more than a dozen bridges statewide, and the technology is expected to be used on several more bridges there in the future. "It allows bridges that may not be an immediate priority on some major funding lists to be replaced quickly and relatively inexpensively," Albert says. "Additionally, it moves bridges off our structurally deficient, functionally obsolete list."
While Pennsylvania is just beginning to use GRS-IBS, the FHWA has been touting the benefits of the technology for single-span bridges up to 140 ft long for some time. "We would like transportation departments to consider this type of structure during the structure-type selection process," says Daniel Alzamora, P.E., M.ASCE, a senior geotechnical engineer for the FHWA. "We have found that there is a potential to save time and money [with the technology]." In 2005, the FHWA teamed with engineers in Defiance County, Ohio, to complete the world's first GRS-IBS bridge. The administration reports that the 80 ft long Bowman Road Bridge was completed in just six weeks for $226,000, 25 percent less than it would have cost using conventional pile cap abutments.
When engineers learn about GRS-IBS, they often have questions about scour and the stability of the abutment facing units. Scour is an important design consideration with GRS-IBS, just as it is with conventional construction, but it can be mitigated using standard design and construction procedures, Albert explains. Concrete masonry units (CMU) are typically used as facing for GRS-IBS abutments and typically provide suitable stability; however, alternatives are also available. "There have been some minor construction issues because people are not familiar with the technology, but it's nothing that you can't solve in the field while it's being constructed," Albert says.
Constructed nearly a decade ago, the Bowman Road Bridge has held up well. Since that bridge's completion, Defiance County engineer Warren Schlatter, P. E., S.E., and his team have used GRS-IBS on more than 30 other bridges in their county. Schlatter and his team have become so knowledgeable about the process that they can construct a GRS-IBS bridge in a week, when prefabricated elements are used and the site is properly staged, Albert says. "Initially contractors are curious about the new construction methods, but as they become more familiar with the technology, you start to realize even more savings," he explains. "Federal highway claims you can save 25 to 60 percent using the technology, and that is proving to be true in most situations."
The FHWA gives presentations about GRS-ISB to municipalities and agencies across the country as part of its Every Day Countsinitiative. States nationwide are now dabbling with the technology, and Dave Hoglund, P.E., a project manager for RETTEW, a Lancaster, Pennsylvania-based engineering firm that used the technology to construct a state road bridge for a private client in northeastern Pennsylvania, expects GRS-IBS to become even more common in the coming years. "I foresee its use increasing due to the economy of these structures and diminished funding options [available to states for infrastructure improvements]," he says.
While GRS-IBS works for many bridges and is expected to be deployed more often, Albert notes that it is not the definitive solution to the nation's infrastructure challenges. "It's not the answer for every situation, but it's another tool you can use to leverage your money and your resources more wisely," he says.