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Geotechnical Laboratory Overview

Laboratory Purpose

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.

Laboratory Description

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:

  • Design and Construction Guidelines for Geosynthetic Reinforced Soil (GRS) Abutments and Integrated Bridge Systems (IBSs) (FHWA-HRT-17-080) (In production).
  • Deep Foundation Load Test Database, version 2.
  • Risk Assessment for Mechanically Stabilized Earth (MSE) Walls.
  • Protocols for the use of high-speed inertial profilers to quantify the bump at the end of a bridge.
  • Strength Characterization of Open-Graded Aggregates for Structural Backfills (FHWA-HRT-15-034).
  • Methodologies to measure super-substructure thermal interaction for integral and semi-integral abutments.
  • Inaugural Geo-Structural Aspects of Pavements for Highways, Railways, and Airfields Conference (GAP-2018).
  • Constitutive soil model for crushed, manufactured open-graded structural backfills.
  • Field monitoring programs and training for the Federal Lands Highway Division.

Laboratory Capabilities

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.

Laboratory Services

Some of the basic and specialized laboratory services include, but are not limited to:

  • Forensic analysis
  • Material testing
  • Technical assistance
  • Research advice
  • Compaction testing
  • Automated data collection system development and installation
  • Large- and small-scale load tests for structural foundations
  • Soil constitutive model development
  • Risk assessment
  • Numerical analysis
  • Quality assurance

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.

Laboratory Equipment

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 has equipment to characterize soil and aggregate materials for both research studies and production projects. Special equipment includes 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.

Figure 2. Strength Testing of Geosynthetics
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 to allow 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.

Field Instrumentation

Figure 1. Long-Term Performance of GRS Abutments with Various Geometries on the Outdoor 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 2. Pressure cell installation in Sheffield, MA.
Figure 17. Pressure cell installation in Sheffield, MA.

Figure 3. Installation of automated MEMS-based accelerometer sensors and piezometers in Denali National Park, AK.
Figure 18. Installation of automated MEMS-based accelerometer sensors and piezometers in Denali National Park, AK.

Figure 4. Solar powered remote data acquisition system in St. Lawrence, NY.
Figure 19. Solar powered remote data acquisition system in St. Lawrence, NY.

Updated: Thursday, October 25, 2018