Turning Skeptics Into Adopters
Bridges using geosynthetic reinforced soil–integrated bridge system technology are popping up everywhere. The innovation’s popularity continues to increase, and for good reason.
Geosynthetic reinforced soil–integrated bridge system (GRS-IBS) technology enables transportation agencies to build durable structures quickly and cost effectively. However, before the Federal Highway Administration’s Every Day Counts (EDC) program began promoting the innovation in 2011, only a few projects employed the technology. Cautious about the novel design, some engineers dismissed it at first because there was a general feeling of “that’s not the way we build bridges.”
EDC and other champions shined a spotlight on GRS-IBS, providing opportunities for the transportation community to learn about the benefits and expanding its use to more than 200 known bridges. Deployment through EDC also demonstrated the technology’s versatility and applicability to a range of types of bridge structures, project sites, and construction materials.
GRS-IBS technology can reduce construction time from months to weeks, cutting work zone congestion, saving motorists time, and enhancing safety. Construction costs can be 25 to 60 percent lower than for conventional bridges, enabling agencies to stretch limited resources while building and replacing the Nation’s bridge infrastructure.
An Established Innovation
Developed by FHWA’s Turner-Fairbank Highway Research Center, GRS-IBS is a rapid-construction, high-quality method of bridge support that blends the roadway into the superstructure. The technology consists of three primary components: the reinforced soil foundation, the abutment, and the integrated approach. Alternating layers of compacted granular fill and geosynthetic reinforcement create a composite material with predictable properties that can provide support for the superstructure, which rests directly on the GRS-IBS substructure to create a smooth, seamless transition. More information on design and construction is available in the Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide (FHWA-HRT-11-026). An updated manual, Design and Construction Guidelines for Geosynthetic Reinforced Soil Abutments and Integrated Bridge Systems (FHWA-HRT-17-080), is slated for release in mid-2018.
Time and cost savings from the technology result from the simple design and construction procedures and materials, compared to traditional concrete abutments on deep foundations. GRS-IBS uses standard, readily available materials such as geosynthetic reinforcements and facing blocks to build a structure to support bridge loads. Construction crews can place fill with minimal effort while achieving the required strength and stiffness when using the recommended open-graded fill (a uniformly graded durable coarse aggregate) material. The properties of recommended reinforcement materials enable the efficient use of a single product, reducing material waste and complexity.
Because of the many benefits, FHWA selected the technology for promotion through EDC. FHWA supported deployment by providing technical assistance through EDC and funding projects and implementation activities through the Accelerated Innovation Deployment (AID) Demonstration and State Transportation Innovation Council (STIC) Incentive programs. The multidisciplinary EDC team leading the deployment collaborated with States, localities, tribes, and the FHWA Office of Federal Lands Highway to generate awareness through demonstration projects, presentations, webinars, videos, reports, and case studies.
Those efforts proved effective. By the end of the third round of EDC in December 2016, more than 200 bridges were built in 44 States in a variety of environments, demonstrating that GRS-IBS is a practical, cost-effective solution to replacing the Nation’s aging infrastructure. Eleven States had adopted the technology as a standard practice. An additional 25 States, the District of Columbia, Puerto Rico, and Federal Lands Highway were demonstrating or assessing the technology for deployment in their bridge programs.
“EDC is a great tool to thoroughly educate bridge owners on the benefits of this technology. It allows the experts to have an open dialogue with owners who may be skeptical,” says Michael P. Culmo, chief technical officer at CME Engineering, which helps the Connecticut Department of Transportation manage its bridge program and has designed GRS-IBS structures for the agency. “You really need to dig into the technology and give it careful thought. The more you look at it, the better it looks.”
Deployment of GRS-IBS through EDC has produced many success stories that demonstrate the technology’s flexibility and value for widespread use. In addition to accommodating various combinations of materials and bridge elements, GRS-IBS is applicable for a range of site conditions and geometries. For example, these bridges have been built on low- and high-volume roadways and across streams and railroads. In addition, these structures have been used in seismically active regions.
Promotion through EDC broadened understanding of the technology among transportation stakeholders. Many of those who deployed GRS-IBS continue the information exchange by discussing their experiences and lessons learned at project showcases, workshops, conferences, and professional society meetings. What follows is a closer look at the innovation’s flexibility and current uses across the country.
Materials and Superstructure Types
GRS-IBS can use a variety of abutment materials to satisfy project design criteria. Wall facings can consist of concrete masonry units, segmental retaining wall units, precast panels, or sheet piles. Backfill types may vary based on factors such as drainage, strength requirements, and availability. Geosynthetic reinforcements are specified based on the requirements of the project design. With reinforcement spacing of 12 inches (30 centimeters) or less, many geosynthetic reinforcement products meet the material specifications, providing flexibility and reducing project cost. More information on design criteria and material selection is available in FHWA’s Interim Implementation Guide and Design and Construction Guidelines.
This technology can support several superstructure types. The most common is prefabricated, prestressed concrete box girders, which Federal Lands Highway and Crook County, WY, used on four of the six Sand Creek Road bridges replaced in the Black Hills National Forest. The project used GRS-IBS technology because of its cost-effectiveness, rapid construction, and suitability for the site conditions. FHWA organized an EDC showcase in July 2016 at which transportation professionals from 10 States observed the GRS-IBS construction at the Sand Creek site.
Use on Low-Volume Roads
The Nation’s first GRS-IBS bridge was built in Defiance County, OH, in 2005. The technology enabled Defiance County to cut costs on replacement of the Bowman Road Bridge by about 25 percent compared to costs using traditional techniques. Defiance County now has 36 GRS-IBS bridges—10 percent of the county’s bridge inventory—built mostly with its own workers and local funds.
As Defiance County engineers built more GRS-IBS bridges and gained experience with the innovation, they shared their knowledge at EDC events and conferences, and with neighboring counties. Engineers in Hamilton County, IN, sought more information and guidance from Defiance County and FHWA in replicating the successful application. Hamilton County built its first four GRS-IBS structures in 2015 and 2016.
“We were interested in GRS-IBS because of its flexibility to adapt to any project site and blend into the environment’s aesthetic,” says Faraz Khan, Hamilton County Highway Department engineer. “Construction knowledge and expertise can be easily infused into [a] skilled or unskilled workforce in minimum time, and [a] limited amount of construction equipment is needed onsite.”
Hamilton County also chose the innovation to speed up construction and reduce costs, applying the savings from each project—about $55,000 to $75,000 per bridge on the county’s first four projects—to future bridge projects. Among the solutions engineers developed to lower costs was using locally available, segmental retaining wall units for constructing abutments. On two bridges, crews built the abutment walls with rounded corners instead of 90-degree corners, which eliminated the need to cut blocks to fit the corners, reduced construction time, and minimized material waste.
“Approximately 20 to 30 minutes were being spent on custom fitting corner blocks on each GRS-IBS layer,” says Khan. “Our onsite solution expedited construction time [on erection of] the GRS-IBS abutment wall and eliminated any cutting of the blocks.”
Huston Township, PA, used its own crews and equipment and economical materials to construct Pennsylvania’s first State-funded GRS-IBS bridge on Mount Pleasant Road in 2011. Interest spread among other Pennsylvania municipalities and resulted in the construction of an additional 24 GRS-IBS bridges on low-volume State and local roads. To help municipalities plan and build projects, the Pennsylvania Department of Transportation (PennDOT) developed design guidance. The guidance has been instrumental in deploying the technology throughout Pennsylvania.
“The process was placed into a specification for low-volume roads after the first couple of projects were completed,” says G. Randy Albert, supervisor of PennDOT’s municipal services. “It was then adapted for PennDOT use, and we are refining the specification to allow it to be used on more bridges. As more projects are completed and the process proves its merit, I believe it will be more widely adopted as a viable alternative for bridge construction.”
On the National Highway System
After early deployment on low-volume local roads, use of the technology expanded to the National Highway System (NHS). The I–84 bridges over Echo Frontage Road near Salt Lake City, UT, were the first GRS-IBS structures constructed for higher average daily traffic (ADT)—8,300 vehicles, including 40 percent trucks. The project also was the first to combine the innovative technology with slide-in bridge construction, an accelerated method in which a construction team builds the new bridge on temporary supports next to the existing bridge and then slides it into place during a road closure.
From 2013 to 2015, 20 GRS-IBS bridges were built on NHS roads including interstates with ADTs ranging from 2,000 to 34,000. The early performance of these structures demonstrates how well the system manages traffic loads.
Over Streams and Railroads
A project in Dodge County, WI, to replace two bridges over streams was one of several that demonstrated the feasibility of the technology for water crossings. The project highlighted the resilience of the system when flooding of a cofferdam during abutment construction immersed the half-finished abutment on one bridge. No damage occurred to the constructed section, and construction resumed quickly.
During an EDC showcase on the project, participants observed the construction of the wall facing at one bridge site and placement of the pavement overlay on top of the concrete girders at the other bridge.
As of early 2018, two States have built GRS-IBS bridges over railroads, which typically require taller walls and longer spans to accommodate trains passing beneath. The Minnesota Department of Transportation coordinated with the Rock County Highway Department to build their first on County Route 55 over Minnesota Southern Railway tracks in Rock County, MN, in 2013. The project included abutment walls up to 26 feet (8 meters) high built with concrete masonry blocks and a 78-foot (24-meter) span with precast concrete girders as the superstructure. A unique feature was the 5.3-percent grade required to provide clearance for passing trains.
The second was the State Route 7A Bridge over the Housatonic Railroad in Sheffield, MA, which featured the maximum skew for a GRS-IBS bridge at the time of the 2014 project. The bridge required a single 105-foot (32-meter)-long span with a 30-degree skew and abutments that provide clearance up to 28 feet (8.5 meters) in height to accommodate passing trains. FHWA instrumented and monitored the bridge for 36 months after construction to determine the effect of the skew and found that the bridge performed as intended. The project, which was featured in an EDC demonstration showcase and earned several national awards for its innovative techniques, is one of the largest constructed with GRS-IBS and cost nearly 50 percent less to build than the alternative design.
In Seismically Active Areas
Several implementers have designed and constructed GRS-IBS structures for seismic loads, including the I–84 bridge over Echo Frontage Road in Utah and the PR–2 Bridge in Yauco, Puerto Rico. Federal Lands Highway also has used the technology on projects in more active seismic regions, including the Disney Bridge in Sequoia National Park and a bridge on Beckwourth Genesee Road over Crocker Creek in Plumas National Forest, both in California.
The Daniel K. Inouye Highway GRS-IBS underpass on the Big Island of Hawaii was the first GRS-IBS bridge designed for a relatively high (0.58g) peak ground acceleration (PGA), the horizontal acceleration represented as a fraction of Earth’s gravity. Because guidance did not exist at the time for seismic design of GRS abutments subjected to 0.58g PGA, the design team developed the procedures, advancing design guidance for future GRS-IBS structures in seismic zones.
Analyzing the Cost Benefits
Lower cost is one of the chief reasons the technology is succeeding as a bridge construction method. In many cases, agencies select the technology because of limited funds. Across the country, States and localities report that using the innovation can save 25 to 60 percent on projects, enabling agencies to build and replace more bridges with available funds using their own labor forces.
PennDOT collected and analyzed the costs of its GRS-IBS bridges, comparing them to conventional bridge projects with similar geometry and site conditions. The comparisons showed that GRS-IBS technology generated savings of as much as 50 percent. Communicating the results of the cost analysis to transportation stakeholders contributed to the spread of the technology in Pennsylvania. By the end of 2017, Pennsylvania municipalities, PennDOT, and the Pennsylvania Department of Conservation and Natural Resources had built nearly 30 of these structures.
“In my experience, with a well-planned, well-executed, and closely monitored project, there is no reason that up to 50 percent savings cannot be achieved,” says PennDOT’s Albert.
The St. Lawrence County Department of Highways in New York also found that using GRS-IBS reduced bridge costs by about 50 percent compared to conventional construction methods. In addition, the technology shortened average project duration by 5 or 6 weeks. The department, which designs and builds most of the county’s bridges, attributes its ongoing success with the innovation to applying lessons learned from past projects. Between 2009 and 2016, the department built 19 of these bridges and 2 bridge-style culverts in St. Lawrence County at a rate of 3 per year. In addition, the county has identified about half of the 194 bridges it owns as eligible candidates for replacement with the innovative technology. Plans are in place to replace those structures using GRS-IBS.
A Versatile Solution for Bridges
GRS-IBS technology is one solution among many to support bridge projects. When used on appropriate projects, the technology can save time and money. Bridge owners should review the specific site conditions—including hydraulic, environmental, and geotechnical—when considering the technology for a project.
Shining the EDC spotlight on this innovation proved to be an effective way to promote the technology and broaden its use. The EDC deployment team’s efforts exposed transportation practitioners to the advantages of GRS-IBS and its many applications, significantly increasing the number of projects implemented across the country. With each deployment, increased knowledge about the technology highlighted its versatility and applicability to various project types and site conditions. As a result, GRS-IBS is helping agencies stretch limited resources and build and replace more bridges at lower costs, which will continue to benefit transportation agencies and the taxpayers they serve.
Daniel Alzamora, P.E., is a senior geotechnical engineer at the FHWA Resource Center. He led the EDC team promoting deployment of GRS-IBS technology. Alzamora earned a master’s degree in civil/geotechnical engineering from the University of Colorado and a bachelor’s degree in civil engineering from the University of Connecticut.
For more information, see www.fhwa.dot.gov/innovation/everydaycounts/edc-3/grs-ibs.cfm or Deployment of the Geosynthetic Reinforced Soil–Integrated Bridge System From 2011 to 2017 Synthesis Report (FHWA-HIF-17-043), which is slated for release in mid-2018. Or contact Daniel Alzamora at 720–963–3214 or firstname.lastname@example.org.