U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
Through its unique capabilities and expertise, the Geotechnical Laboratory (GTL) supports the FHWA Geotechnical Research Program, other disciplines, laboratories, and offices throughout the agency, as well as other organizations and agencies within the transportation community. The core mission of the GTL is to advance the state-of-the practice and develop innovative solutions for applied transportation issues.
The GTL currently evaluates the material properties of soils and structural backfills; studies the interaction with structural elements such as steel, concrete, geosynthetics, or timber that are used for bridge foundations and retaining wall systems; and assesses geostructural aspects related to pavements. Testing is also performed to calibrate numerical models for finite element modeling.
Recent Accomplishments and Contributions:
The GTL contributes to transportation agencies through material testing and technical assistance. In addition, research conducted by the Geotechnical Research Program has recently led to the development of the following key accomplishments:
The GTL consists of an indoor testing facility, several unique outdoor testing facilities, and a numerical modeling station. The indoor facility can conduct basic and specialized index tests for characterizing soil, aggregates, nontraditional backfill materials, and geosynthetics for both research studies and field production projects. The outdoor facilities consist of two test pits to perform large-scale foundation experiments and a strong floor to test earth-retaining structures. In addition, the laboratory functions extend throughout TFHRC with several full- and large-scale GRS structures primarily to evaluate their long-term performance under load conditions. For field work, the GTL has the ability to prepare and install remote automated field instrumentation to monitor and evaluate performance of bridges, pavements, and slopes.
Some of the basic and specialized laboratory services include, but are not limited to:
Current activities and services performed by the GTL are to: 1) study the material properties of soil and structural backfills for earth-retaining structures and geostructural aspects of pavements; 2) advance the state-of-the-practice of geotechnical instrumentation and remote automated systems; 3) assess the long-term performance of geotechnical assets; and 4) perform load and resistance factor design (LRFD) calibrations.
|Figure 1. Large-Scale Direct Shear Device.|
|Figure 2. Strength Testing of
|Figure 3. Large Diameter Triaxial Device.|
|Figure 4. Frictional Connection Testing: Side View.|
|Figure 5. Frictional Connection Testing: Top-Down.|
|Figure 6. Calibration Reaction Assembly.|
|Figure 7. Evaluation of Pressure-Sensor Technology.|
|Figure 8. Standard Direct Shear Device.|
One of the outdoor laboratory facilities consists of two test pits that are 18 feet wide, 23 feet long, and 18 feet deep. The pits can be filled with various soil types for modeled shallow or deep foundation experiments and have also been used to conduct full-scale wall experiments and to test the tension capacity of ground anchors. The pits have reinforced concrete walls, sump pumps to control water-table levels, and anchorage systems to provide reaction loads for experiments.
The pits have a separate building to store the load-test equipment and a control room for the data-acquisition systems.
|Figure 9. Mechanically Stabilized Earth (MSE)
Shoring Wall Experiment
|Figure 10. Helical Anchor Tensile Tests|
The laboratory includes two additional outdoor test sites where full-scale bridge piers, abutments, and retaining wall structures were constructed for research and testing purposes. The following are a few examples of full-scale experiments in these locations to illustrate the capabilities of Turner-Fairbank Highway Research Center (TFHRC) to lead the advancement of the state of the art.
|Figure 11. Geosynthetic Reinforced
Soil (GRS) Test Pier
|Figure 12. Prototype Geosynthetic Reinforced
Soil -Integrated Bridge System (GRS-IBS)
|Figure 13. Long-Term Performance of GRS Test Piers|
The Geotechnical Laboratory has an outdoor strong floor that is also available for the construction and testing of full-scale geotechnical features on a rigid concrete platform. The spacing of the anchorage locations is 3 feet by 3 feet, each with a 300-kip capacityâ€”similar to the Structures Laboratory–to allow a variety of load fixtures and arrangements.
Figure 14. Outdoor Strong Floor
|Figure 15. National Cooperative Highway Research Program
(NCHRP) 12-59 Experiment on the Strong Floor
|Figure 16. Long-Term Performance of GRS Abutments with Various
Geometries on the Outdoor Strong Floor.
The geotechnical laboratory also calibrates many different types of typical and advanced geotechnical instrumentation and develops data acquisition systems for installation in the field. Recent installations have included pressure cells, strain gauges, tactile pressure sensors, in-place inclinometers, and survey targets. Various projects, including evaluation of bridge abutments and monitoring of pavement and slope conditions, are currently underway.
|Figure 17. Pressure cell installation in Sheffield, MA.|
|Figure 18. Installation of automated MEMS-based accelerometer
sensors and piezometers in Denali National Park, AK.
|Figure 19. Solar powered remote data acquisition system in
St. Lawrence, NY.
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Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101-2296
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