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Ground Penetrating Radar F.A.Q.
Q: Can Ground Penetrating Radar determine the difference between rebar and electrical conduit? A: Although it is true that rebar and electrical conduits produce similar reactions on the data screen, in most cases, yes, we can determine the difference. We are able to differentiate between the two materials by determining the rebar pattern (spacing and elevation). If the pattern is broken, in all likelihood, the rupture is from the presence of a conduit. We have an extremely high success rate in applications in which we are asked to find electrical conduits in supported slabs or in slabs-on-grade prior to saw cutting or core drilling. Additionally, GPRS now has the capability of using electro-magnetic induction to determine the location of conduits in the concrete. If we are able to “induct” a tone onto the metal conduit we can locate it with pinpoint accuracy. We can also locate the conduit if it has “live” electrical power or telecommunications running through it. With both GPR and EM Induction we provide one of the most comprehensive and accurate conduit locating services available. Q: Can Ground Penetrating Radar tell me the size of a void cavity below ground? A: GPR can tell the area where the void is occurring as well as clearly identify its boundaries. Ground Penetrating Radar System cannot, however, determine the depth from the top of the void to the bottom of the void. Q: In a post-tensioned slab, how are you able to differentiate the tendons from the rebar? A: In post-tensioned structures, we typically find one mat of support bar near the base of the slab. This mat of support bar is generally consistently spaced and remains at a constant elevation. When we use the Ground Penetrating Radar to determine the location of post-tension cables, we usually find them above the mat of support bar, and they usually are "draped" through the slab. The elevation of the cable is usually high near the beams and column lines and drapes lower through the span between beam and column lines. Our ability to accurately and consistently locate post tension cables comes from a combined 50+ years of experience with GPR. The GPRS technician will leave you feeling confident in the survey findings and in your ability to drill or cut without issue. Q: When you find underground utilities, can you determine what type of utility it is? A: No, we cannot. We can generally find the utility without much difficulty, but we cannot determine if the piping is gas, or water, etc. We can often trace the utility to valve, meter, control box, or other type of signifying marker, thereby determining the utility. Additionally, we have the ability to provide the elevation of the utility and can cross check it with as-build plans to confirm the plans are without error. Q: How quickly can you respond to an emergency need? A: In most circumstances, we can have a technician on your site within 24 hours. Q: What is the maximum distance Ground Penetrating Radar System will travel to perform your work? A: GPRS provides nationwide Ground Penetrating Radar services with offices in over 50 different geographic locations from coast to coast. Simply put, we are willing to do what it takes to accomplish your project goals, including travel. Q: Why would I choose Ground Penetrating Radar over another similar company? A: You would be hard pressed to find a similar company. Most companies providing Ground Penetrating Radar System services use Ground Penetrating Radar as a supplemental source of revenue. GPRS uses it as its only source of revenue. We are using the technology on different projects every single day, and we have established a reputation for providing a reliable and value-added service. Q: What type of training do your technicians go through? A: Each of our technicians goes through a training course provided by our supplier, GSSI, Inc. We also pair each trainee with an experienced technician until the trainee has demonstrated the consistent ability to work on a comparable level to an experienced technician providing technical expertise and the ability to get through difficult Ground Penetrating Radar applications. Q: Can your Ground Penetrating Radar equipment be used to scan vertical surfaces or could it be used on a ceiling? A: Yes. We regularly use our equipment to scan for the location of rebar in concrete columns and walls. On occasion we are also asked to scan from the underside of a floor to mark out the reinforcing steel and any embedded conduits. This is most common when a customer wants to set anchors into a floor for large piping. Q: Does Ground Penetrating Radar Systems buy used equipment? A: Yes, we buy used equipment from other GPR companies. Contact us today as we would be happy to see the equipment and negotiate a deal. Q: What type of “output” do you provide for mapping utilities? A: Our typical survey output is to simply paint and pin flag our findings directly on the surface. For most applications this is sufficient as the excavation/digging will commence within a few days of our service. However, for some this may not be enough. GPRS now has the capability to provide you with a GPS map of your utilities. We can output our survey results directly into a Google Earth image or provide you with a CAD file overlay. Please contact us to discuss pricing and mapping options that your project may need. Q: Can you locate unmarked grave sites? A: Yes, Ground Penetrating Radar can be used to determine the precise location of unmarked graves for site planning purposes. While older grave sites can be harder to locate because of material deterioration, in most cases we can accurately map where these grave sites are found. Q: How deep can your Ground Penetrating Radar “see”? A: This answer depends on the type of application in which you are interested. For concrete applications we can typically penetrate to a depth of 18-24”. We use a 1500/1600MHz antenna for concrete scanning applications. For utility locating needs on grass, asphalt or concrete we can generally penetrate anywhere from 6-10’. For these types of applications we use a 400MHz antenna. Because GPRS is committed to providing the most accurate and comprehensive GPR surveying services, we also have the ability to use larger antennas for greater depth penetration. Please contact your local GPRS representative for more information. Q: How accurate are the results when using ground penetrating radar? A: Extremely accurate! Again, our accuracy is dependent upon the type of application in which you are interested. We have found that when scanning with the 1500/1600 MHz antenna (most concrete applications) we are +/- ¼” to the center of the object we are locating and ½” +/- to the actual depth. We have found that when surveying with the 400 MHz antenna (most utility locating applications) we are +/- 6” to the center of the object we are locating and +/- 10% to the actual depth. Soil moisture conditions and other factors affect the accuracy for the 400 MHz antenna, and these accuracy results are based on over 50+ years of GPR experience. Q: Is GPRS available to work at night or on the weekend? A: We, at GPRS, pride ourselves on customer service and our ability to meet your inflexible scheduling needs. We are willing to work nights and weekends, or any other time, in order to help you accomplish the goals of your project. Please contact your local GPRS representative for rates and schedule availability.
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