What is it?

Ground Penetrating Radar (GPR) is an accurate, non destructive form of scanning. While GPR is not a new technology, it's application the construction industry is still fairly new. Today, some of the more common applications of GPR are concrete scanning and utility locating.

 

How Does it Work?

GPR works by emitting radar waves into a surface and measuring the the time it takes for the wave to bounce off an object and return to the receiver. The radar waves interact with different objects in varying ways to produce data signatures that allow the GPR analyst to interpret what the composition of the hazard is.  As the application changes, so does the frequency needed for the scan.

For concrete scans, a higher frequency wave (1600 MHz) is emitted from a handheld control unit. This small system allows scans to be completed in tight quarters. While unusually heavy concentrations of steel may distort data below,  the higher frequency wave typically displays clear data down to depths of about 16".  With post tension cables being installed in most elevated slabs, GPR has become a popular tool to ensure all concrete coring goes smoothly.

Since utilities are buried in the ground at greater depths, the GPR frequency wave needed (400 MHz) is lower than the one used for concrete scans. The 400 MHz antenna system is larger, and sends a signal down to depths between 8'-12'. As the depth of the scan increases, clarity is lost. A general rule of thumb is to know that for a target to be located by GPR, it's diameter in inches must be equal to the depth that it is buried in feet. For example, in order to clearly see a target that is 4 feet below the surface, it must have a diameter of at least 4 inches. Besides the radar signal traveling deeper, the technology is exactly the same as concrete scans. Unique signatures are given for different compositions, and hazards are able to clearly marked. One of the great traits about GPR is its ability to find non metallic utilities. No locate is complete without a GPR scan.

GPR vs X-Ray

	GPR	X-Ray
Cost?	$150 per hour, average 4-5 scans/hour	$750 per scan
Scan Size?	2’x 2’	1’x 1’
Interpretation Needed?	Yes	No
Available for slab on grade use?	Yes. GPR only needs access to one side of a slab	No. XRay needs access to both sides of a slab
Radiation?	GPR emits 1% of the radiation of a cell phone, making it a very safe option.	X-Rays produce harmful radiation. Because of this job sites need to be cleared before scans begin.