Through its unique capabilities and expertise, the Geotechnical Laboratory (GTL) supports the Federal Highway Administration (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 of geotechnical engineering in transportation and develop innovative solutions for practical transportation issues.
The GTL currently evaluates the material properties of soils and structural backfills; studies the interaction with the environment (e.g., temperature, moisture) and structural elements (e.g., steel, concrete, geosynthetics, timber); assesses geotechnical aspects of pavements; performs advanced numerical modeling of foundation and retaining wall systems; and engages in the instrumentation and remote monitoring of bridges constructed with innovative designs and construction practices. The laboratory partners with various transportation agencies in advancing innovative technologies and solutions.
Recent Accomplishments and Contributions
The GTL currently has many ongoing large-scale and long-term experiments, some dating back to the 1990s, that have formed the basis for many reports, publications, and presentations. These experiments are aimed at improving the code of practice of foundations in transportation structures. The laboratory has provided technical assistance to a number of transportation agencies on a variety of issues, and is currently spearheading a roundrobin program for the evaluation of large-scale direct shear devices. Some key accomplishments and contributions include the following:
- Report: Instrumentation and 5-Year Performance Monitoring of a GRS-IBS in St. Lawrence County, NY (FHWA-HRT-20-040).
- TechNote: Geosynthetic Reinforced Soil-Integrated Bridge System—Bid Price Analysis and Cost Comparisons with Alternative Foundation Systems (FHWA-HRT-19-024).
- TechNote: Impact of Initial Density on Strength-Deformation Characteristics of Open-Graded Aggregates (FHWA-HRT-18-048).
- Report: Design and Construction Guidelines for Geosynthetic Reinforced Soil (GRS) Abutments and Integrated Bridge Systems (IBSs) (FHWA-HRT-17-080).
- Development of the FHWA Deep Foundation Load Test Database, Version 2 (DFLTD v.2).
- Report: Strength Characterization of Open-Graded Aggregates for Structural Backfills (FHWA-HRT-15-034).
- Report: FHWA LTPP Guidelines for Measuring Bridge Approach Transitions Using Inertial Profilers (FHWA-HRT-16-072).
- Partnership with the Federal Aviation Administration (FAA), Federal Railroad Administration (FRA), and the U.S. Army Engineer Research and Development Center (ERDC) to sponsor the inaugural Geo-Structural Aspects of Pavements,Railways, and Airfields Conference (GAP-2019).
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 soils, 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 Turner-Fairbank Highway Research Center (TFHRC) with several full- and large-scale geosynthetic reinforced soil (GRS) structures constructed to evaluate their long-term performance under realistic loading 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:
- Forensic analysis
- Materials characterization
- Technical assistance
- Research guidance
- Compaction testing
- Automated data collection system installation and monitoring
- Large- and small-scale load tests for structural foundations
- Soil constitutive modeling
- Risk assessment
- Numerical analyses
- Quality assurance
Current activities and services performed by the GTL are to: 1) study the material properties of soil and structural backfills for pavement and earth-retaining structures; 2) study drainage of pavement bases and subbases; 3) study geotechnical aspects of pavements; 4) evaluate erosion resistance of stream beds based on soil characteristics; 5) advance the state of the practice of geotechnical instrumentation and remote automated systems; 6) assess the long-term performance and resilience of geotechnical assets; 7) evaluate and advance innovative testing methods; and 8) perform load and resistance factor design (LRFD) calibrations.
Figure 1. Large-Scale Direct Shear Devices.
The indoor facility has equipment to characterize soil and aggregate materials for both research studies and demonstration projects. Special equipment includes two 12-inch direct shear devices, a 6-inch diameter triaxial unit, a 6-inch resilient modulus device, an Erosion Function Apparatus, and a 20-kip universal testing machine. The indoor facility also has a variety of fixtures and auxiliary equipment to conduct a variety of specialized tests to include the evaluation of innovative instrumentation for geotechnical applications.
Figure 2. Strength Testing of Geosynthetics.
Figure 3. Large Diameter Triaxial Device.
Figure 4. Resilient Modulus Device.
Figure 5. Frictional Connection Testing: Side View.
Figure 6. Frictional Connection Testing: Top-Down.
Figure 7. Calibration Reaction Assembly.
Figure 8. Evaluation of Pressure-Sensor Technology.
Figure 9. Standard Direct Shear Device.
Figure 10. Constant/Falling Head Permeameter.
Figure 11. Walk-in Environmental Chamber.
Outdoor Laboratories: Test Pits
One of the outdoor laboratory facilities consists of 2 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 12. Mechanically Stabilized Earth (MSE) Shoring Wall Experiment.
Figure 13. Helical Anchor Tensile Tests.
Outdoor Laboratories: Full-Scale Test Sites
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 at these outdoor test sites to illustrate the capabilities of TFHRC to lead the advancement of the state-of-the-art and state-of-the-practice.
Figure 14. Geosynthetic Reinforced Soil (GRS) Test Pier.
Figure 15. Prototype Geosynthetic Reinforced Soil - Integrated Bridge
Figure 16. Long-Term Performance of GRS Test Piers.
Outdoor Laboratories: Strong Floor
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-by-3 feet, each with a 300-kip capacity similar to the Structures Laboratory to allow a variety of load fixtures and arrangements.
Figure 17. Outdoor Strong Floor.
Figure 18. National Cooperative Highway Research Program (NCHRP) 12-59 Experiment on the Strong Floor.
Figure 19. 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, piezometers, water content reflectometers, and survey targets. Various projects, including evaluation of bridge abutments and monitoring of pavement and slope conditions, are currently underway, some for as long as more than 5 years.
Figure 20. Pressure cell installation in Sheffield, MA.
Figure 21. Installation of automated MEMS-based accelerometer sensors and piezometers in Denali National Park, AK.
Figure 22. Solar-powered remote data acquisition system in St. Lawrence, NY.