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Photo for visual interest. This image is made up of two photos. In the top photo, a ground-penetrating radar (GPR) antenna is mounted to the front of a white Texas Transportation Institute van (shot from the front). In the bottom photo, shot from the interior of the van, one man drives while another man monitors testing equipment.

Ground Penetrating Radar (GPR)

Ground penetrating radar (GPR) is a nondestructive geophysical method that "sees" underground and produces a record of subsurface features—without drilling, probing, digging, or coring. Since 1988, researchers at TTI have been developing, testing, and implementing GPR technology for TxDOT to use in its road repair and maintenance activities.

GPR operates by transmitting pulses of high-frequency radio waves (electromagnetic energy) into the ground through a transducer or antenna. The transmitted energy is reflected from various buried objects or distinct contrasts between different earth materials. The antenna captures the reflected waves and stores them for subsequent analysis. TTI-developed software (COLORMAP) then converts these signals into information meaningful to engineers. GPR can monitor changes in layer thickness of pavements and detect areas of either trapped moisture or air voids beneath the roadways.

On a national level, the American Association of State Highway and Transportation Officials is beginning efforts to implement use of GPR across the country. Currently, TTI is continuing research and development of GPR use on the state's highways. Researchers have delivered training courses in numerous TxDOT districts, as well as created analysis software and interactive CD-ROM and web-based training tools for TxDOT personnel. TTI is working with Texas A&M University's Department of Electrical Engineering to develop and implement more specialized antennas that can provide detail at varying depths. With three GPR systems operating and active, TxDOT and TTI plan to continue supporting the research and working to add more units to the current stock.

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A single use of GPR in the Ft. Worth area illustrates the value of GPR technology. On a 14.2-mile, two-lane strip of FM 917, the submitted repair estimate was $3.1 million before GPR was brought in to test the section. "The GPR analysis showed us air voids under the pavement," says TxDOT Ft. Worth engineer Andew Wimsatt. "Knowing that allowed us to change our rehabilitation strategy." The new repair solution came to only $2.55 million, saving the state around 15 percent—$550,000 in this single instance.

Recently GPR was used to test a section of I-35 in downtown Austin following a major water main break under the freeway. Testing indicated the presence of a major washout beneath the asphalt surface layer. Traffic was routed around the problem area, and repairs were scheduled for the following day. However, the roadway collapsed by itself overnight. In this case, the timely use of GPR prevented a possible major accident on this interstate.

For More Information

Tom Scullion
CE/TTI Building, Room 503
TTI/Flexible Pavements
Texas A&M University System
3135 TAMU
College Station, TX  77843-3135
ph. (979) 845-9913 · fax (979) 845-1701
t-scullion@tamu.edu

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