U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000


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Geotechnical Laboratory

 

Geotechnical Laboratory

The Geotechnical Laboratory is used to study the material properties of soil and the interactions between soil and structural elements such as steel, concrete, geosynthetics, or timber that are used for bridge foundations and retaining wall systems. Testing is also performed to calibrate numerical models for finite element modeling.

The Geotechnical Laboratory consists of a standard indoor testing facility and several unique outdoor testing facilities. New materials and methods of design and construction are tested and evaluated in both indoor and outdoor environments to determine their applicability and to identify opportunities for improvement.

Indoor Laboratory

This is a photo that shows a large-scale direct shear device under operation. The bottom box is displacement allowing some of the aggregate being tested to show in the figure.
Figure 1. Large-Scale Direct Shear Device.
The indoor facility is capable of conducting basic index tests for characterizing soil and aggregate materials for both research studies and production projects. Unique capabilities include a 12-inch direct shear device, a 6-inch diameter triaxial unit, and a 20-kip universal testing machine. The laboratory 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.

The photo shows a geotextile that is clamped on the top and bottom. The geotextile has been ripped in the middle due to tensile testing in a universal testing machine.
Figure 2. Strength Testing of
Geosynthetics.

This photo shows a sample being tested in a large 6-inch diameter triaxial chamber within a load testing device equipped with a load cell. The device is connected to two water pumps through clear plastic tubes and controlled with a data collection computer.
Figure 3. Large Diameter Triaxial Device.

This is a photo showing a side view of frictional connectional testing. Concrete masonry units are stacked with a layer of geotextile sandwiched in between and attached to a clamp that is attached to a worm gear. Dead weight and lead ingots are placed on top of the concrete masonry units.
Figure 4. Frictional Connection Testing: Side View.

The photo shows hollow core concrete masonry units (CMU) infilled with No. 57 stone.  A layer of geotextile extends out from between the CMU blocks. The geotextile is clamped to the metal bar and connected to the worm gear driven with an electric motor.  The displacement and pullout force of the frictionally connected geotextile is measured with 2 linear variable differential transformers and a load cell, respectively.
Figure 5. Frictional Connection Testing: Top-Down.

This is a photo showing a calibration reaction assembly with two courses of concrete masonry blocks stacked up and an inflated airbag pressed against them from the top.
Figure 6. Calibration Reaction Assembly.

This is a photo showing a tactile pressure sensor between a layer of geotextile and concrete masonry units.
Figure 7. Evaluation of Pressure-Sensor Technology.

This is a photo showing a front view of a standard direct shear device. There are controllers on the bottom with the shear box on the top, connected to a motor and a load cell.
Figure 8. Standard Direct Shear Device.

Outdoor Laboratories: Test Pits

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.

Top-down view showing into the outdoor geotechnical sand pits. A mechanically stabilized earth (MSE) shoring wall is on one side and a green lightweight vibratory compactor is shown on top of the sand.
Figure 9. Mechanically Stabilized Earth (MSE)
Shoring Wall Experiment

The image shows two men working in a sand pit. To the left of the pit is a piece of heavy equipment that is drilling steel anchors into the pit.
Figure 10. 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 in these locations to illustrate the capabilities of Turner-Fairbank Highway Research Center (TFHRC) to lead the advancement of the state of the art.

This is a photo showing a tested geosynthetic reinforced soil pier. Vegetation is growing out from the top. A trailer and trees are shown in the background.
Figure 11. Geosynthetic Reinforced
Soil (GRS) Test Pier

Photo. Long-range view of the FHWA prototype geosynthetic reinforced soil integrated bridge system. The facing modular block is decorative with FHWA inscribed and a road shown. A tunnel through the bridge and underneath a staircase is also depicted.
Figure 12. Prototype Geosynthetic Reinforced
Soil -Integrated Bridge System (GRS-IBS)

This photo shows four GRS piers with concrete masonry units (CMUs) on a concrete pad. Two large concrete I-beams are positioned on top of the GRS piers.  The beams have salt spray catch barriers attached to them.
Figure 13. 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 feet by 3 feet, each with a 300 kip capacity—similar to the Structures Laboratory—for the capability of a variety of load fixtures and arrangements.

This is a photo showing the outdoor concrete strong floor. A pallet of concrete masonry units and some helical anchors lie on top.

Figure 14. Outdoor Strong Floor

This photo shows a GRS abutment experiment built with a concrete masonry units (CMU) facing element on the outdoor strong floor. The CMU blocks have a zigzag pattern in different colors.  A concrete footing is positioned on top near the edge of the face of the GRS abutment with five hollow core hydraulic jacks on top. The hydraulic jacks are connected to load cells. Scaffolding flanks both sides of the GRS abutment experiment and reference beams are supported on the scaffolding to measure vertical deformations.
Figure 15. National Cooperative Highway Research Program
(NCHRP) 12-59 Experiment on the Strong Floor

Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101