Anyone who’s spent any time at all on a construction site knows what can be seen above the ground is only half the problem, but could pose significantly more than half the risk. For thousands of years, people have struggled with the problem of detecting subsurface buried objects in the earth: how to find them, how they can be identified, and how to avoid them so as to minimize ancillary damages to the site or injury to workers.
The history of the science of locating buried utilities and objects in soil is varied, checkered, sometimes amusing, and horrifying in equal parts.
Some methods verge on the bizarre, such as the use of dowsing rods depicted in figure studies and drawings dating back as far as ancient Egypt as a sort of antenna for scrying out water and buried metal deposits. Others are outrageous to modern sensibilities, such as the heedless plunder and untold destruction of necropolises (cemetery developments) and their contents across the ancient world in the name of archaeology by people of dubious qualification. Some of the best-known “luminaries” of this latter type are Howard Carter and Lord Carnarvon, the English figures behind the excavation of the tomb of the pharaoh Tutankhamen and the men most frequently associated with the so-called Pharaoh’s Curse.
Fortunately, in the 2020s there’s a better, more affordable, and more accurate way than these distinctly analog and haphazard methods for locating underground objects, and Safe2Core has it!
Known as ground-penetrating radar (GPR) and sometimes referred to as ground probing radar or “georadar,” this technology has been used in data acquisition and location mapping for sciences ranging from geology and environmental geophysics to forensics and even search and rescue operations after avalanches, where there is very little margin for error and getting precise information and accurate locations quickly could literally be a matter of life and death.
Of course, we hope our GPR systems will never be needed for stakes quite that high when using ground-penetrating radar for construction sites, but if they are, Safe2Core is proud to say we have the right equipment and GPR training for the job!
Some common GPR applications for construction sites include:
- 3D imaging
- Bridge deck asphalt and concrete inspection in situ
- Data collection
- Concrete scanning
- Nondestructive testing
- Concrete structural examination
- Public and private utility locating
- Subsurface structure location
- Subsurface utility identification, such as sewer lines
- Surveying subsurface objects and unknown/anomalous targets
- Underground utility mapping
- And more!
To learn more about how Safe2Core’s ground-penetrating radar systems can help you get faster results with less expense and better coverage for your construction project, click here to contact us for your job. Also, be sure to check out our Frequently Asked Questions for more information about ground penetrating radar on construction sites!
Frequently Asked Questions about Ground Penetrating Radar on Construction Sites
Safe2Core gives you the real talk you need to know if ground-penetrating radar on construction sites is the right answer for your job. Spoiler: It almost always is!
Question: How does ground penetrating radar work? –Ravi, Menlo Park, CA
Answer: At its most basic, GPR works on essentially the same principle as sonar. It sends electromagnetic waves into the material to be tested and measures the speed and rate of return. By doing this, the unit detects the dimensions and shape, also known as the footprint, of many obstructions or voids in the material and produces an image of what lies below.
The longer, more complex answer: Modern GPR scan technology works on the principle of dielectric permittivity.
In layperson’s terms, the dielectric constant is the degree of electrical conductance, or lack thereof, in a given material.
The technician sets probes into the ground which set up an electromagnetic induction field. By measuring the difference in electric properties between areas of higher or lower density in a given material and the variance in electromagnetic energy return, the locating equipment translates the GPR signal into an image which allows technicians and engineers trained in interpreting GPR data to locate variances in the electromagnetic properties of the material and create maps of the varying material properties for precise subsurface imaging.
Question: What are the applications of GPR? –Cedric, Los Angeles, CA
Answer: From detecting areas of dry sand and gravel versus silty clay versus limestone to differentiating between rebar and electrical lines, case studies of mobile GPR surveys have consistently demonstrated their efficiency and efficacy at finding hidden hazards, obstructions, and anomalies that warrant further investigation.
Dual-borehole GPR can be used to identify the precise GPS coordinates of pilings, footings, and other structures on both lateral and vertical trajectories. Multi-channel GPR, which uses multiple antennas at high and low frequencies, gives the most complete picture possible of a flat area.
By varying the antenna frequency range from high frequency to low frequencies and their inverse low to high definition, the depth ranging and depth penetration properties are enhanced, as is the overall picture. Basically, if it has mass and/or takes up space, and assuming it’s not made of PVC or a material with similar dielectric properties, modern GPR systems can detect it—saving companies time, money and risk!
Question: Are there advantages to a digital GPR system over analog systems? –Beverly, Anaheim, CA
Answer: In most cases, absolutely there are. A digital GPR system generally delivers a more comprehensive picture, in a more compact unit, with less downtime and greater accuracy. There are some circumstances where an analog system may be a better choice, but this is very circumstantial and needs to be evaluated on a case-by-case basis. Please contact Safe2Core to determine whether digital or analog GPR is going to be best for your specific site and situation!
Question: Can ground-penetrating radar detect through concrete? –Buddy, Tucson, AZ
Answer: Honestly, it depends. High-frequency GPR scans can deliver more accuracy, but they also have a lower depth penetration. Conversely, low-radio frequency GPR has greater depth penetration but lower accuracy. Slab depth, the mix design, the material underneath, utilities and electromagnetic fields in the area, and other factors can all impact the accuracy and penetration of the GPR systems and the resolution of the overall readings. However, a multi-channel GPR can overcome these limitations and give a comprehensive picture of what’s embedded within and below the slab.
Question: How are GPR methods better for concrete inspection than other NDT methodologies like X-ray? –Enrique, Littlefield, AZ
Answer: For starters, unlike other geophysical methods, GPR methods have far more customer testimonial and field study evidence, as well as more companies relying on it, to demonstrate they work well. X-ray examination is limited mainly to walls because there have to be two plates, one on each side of the surface, to achieve the optimum results. In cases where two plates can’t be placed, everything beneath the scanner becomes a scientific wild guessing game. More to the point, X-ray cannot deliver the same clarity or precision as a general rule, and you have to shut down all operations within a prescribed range of the unit or risk getting images that are mangled or wholly unusable. GPR also has the advantage of superior data processing capabilities in most cases, meaning it delivers a clearer and more accurate picture faster, with less downtime. Even better, you can use GPR equipment without having to shut down significant areas of the site in order to get a clear picture. This gives you the information you need to help you decide how, when, and where the ideal place is to make cuts, core samples, and perform other operations without risk of damage to subsurface utilities.
Question: What is subsurface imaging? –Millicent, Phoenix, AZ
Answer: Subsurface imaging is the science and art of scanning the material below a surface, such as soil, concrete, or asphalt, and detecting the obstructions, imperfections, and voids within the material which might not be visible to the naked eye. Until recently, this was usually accomplished by using X-rays and trying to match them up with the site drawings, assuming they were reasonably accurate. With the advent of ground-penetrating radar and GPS, along with the accuracy of as-built site drawings, the sensitivity, and accuracy of subsurface imaging have increased exponentially. As of this writing, as long as the less conductive conduits and pipes under the surface are marked with conductive tape, which they have been as a standard practice since around 2003, the images produced by ground-penetrating radar scanning can produce a mapping of the area below the surface.
Question: Does GPR work to detect underground utilities? –Bill, Austin, TX
Answer: For metallic and solid utilities, such as electrical lines and septic tanks or other subsurface structures, yes. Since 2003, pipes and conduits made of PVC or materials with similar electroconductive properties which may not show up on a scan on their own are generally marked with conductive tape or a guidewire that traces the length, depth, and direction of the pipe. As long as we can match up the relative depth of the utility with its meter and placement on the drawings, we can give your crew precise locations with a very small margin of error and help assure your excavation or placement project is exactly located to avoided utilities.
Question: What is the penetration depth for ground-penetrating radar? –George, New Braunfels, TX
Answer: The depth for GPR scans depends on the frequency and power of the scan, the density of the intervening material, the concrete or asphalt mix design, and so on. High-frequency scans show a greater resolution, but can’t penetrate more than a few inches. At lower frequencies, you get less resolution but higher overall penetration. A combination of high-frequency antennas with frequencies into the high megahertz (MHz) to gigahertz (GHz) range and lower-frequency antennae can give a more comprehensive picture deeper into the material. However, the material beneath the concrete or asphalt makes a difference as well. The dry sand will give a clearer return than silty clay, for example. Using a combination GPR unit can overcome this to a degree. For the best results, we’ll have to see the site, the thickness of the slab on grade, the characteristics and the material underneath as well as the as-builts to ensure we can deliver the most accurate picture possible and the maximum safety for your crew.
Question: Is GPR scanning safe? –Derek, Taos, NM
Answer: GPR scanners use radio waves, which move at the speed of light. Unlike X-rays or other types of radiation such as the kind nuclear density gauges rely on to give soil and asphalt and are particulate and based on radioactivity, radio waves are simply electromagnetic energy that permeates the entire universe. You’re surrounded by these waves all day, every day, when you use Bluetooth, your car radio, your cell phone, or just standstill. The only risk GPR scanning involves is to the technician if they handle the unit carelessly.
Question: Are GPR emissions going to put my crew at risk of health problems? –Bobby, Las Vegas, NM
Answer: Absolutely not! GPR requires no special safety precautions either for the technician or surrounding personnel, unlike a nuclear density gauge which requires a radiation badge and generous space between people and the unit. Because of this, GPR is one of the safest and most comprehensive ways of performing nondestructive testing quickly and effectively!
Question: Will the GPR signal interfere with other instruments operating in the area? –Deanna, San Mateo, CA
Answer: In general, no. Modern technology is sophisticated enough and GPR scanners are self-contained enough to prevent cross-interference. Any interference other receivers, such as GPS location and site radios, can pick up should be minimal to nonexistent. As long as the equipment is not parked directly on top of the scanner, or vice versa, there shouldn’t be any interference on either side. However, a direct examination of the equipment will tell us if there are any special considerations we need to take into account to ensure there are no issues either with your communications and location equipment or our scanners.