GPR is used in many industries around the world, including utility locating, construction, engineering, road and building maintenance, law enforcement, mining, archaeology, UXO detection, geophysics and environmental assessment projects. The ability of GPR to locate metallic and non-metallic utilities, such as plastic, PVC and concrete, makes it a particularly valuable tool for many users. We’ll look at more about the GPR in this article.
GPR survey – What is GPR?
GPR (ground-penetrating radar) is used in many areas to observe man-made and natural features. GPR detects metallic and non-metallic pipes, power lines, conduits, water pipes, rebar and post-tensioning cables inside concrete. GPR’s waves are equal to those of a cell phone or Wi-Fi network, while X-rays require a clearance of 50 feet before being used for safety reasons. In general, ground-penetrating radar is the most cost-effective option and the fastest method of testing the concrete.
GPR survey – How does GPR work?
GPR works by transmitting very high frequency radio wave pulses (electromagnetic microwave energy) into the ground through a transducer (also called an antenna). GPR’s antenna (transducer) is pulled across the ground by hand or from behind an ATV or vehicle. The transmitted energy is reflected by various buried objects or by distinct contacts between different ground materials.
The antenna then receives the reflected waves and stores them in the digital control unit. The control unit records the reflections as a function of travel time in both directions in nanoseconds and then amplifies the signals. The voltage peaks of the output signals are plotted on GPR profile as different colored bands by the digital control unit.
What surfaces can GPR penetrate?
GPR can be applied very successfully for numerous applications, it can also be very limited for many reasons: clay soils, saturated soils, saline groundwater, no penetration past/through metal objects, or alkali on the soil surface.
The radars can come in a variety of sizes, ranging from hand-held devices to those that travel on a cart. Smaller units can be placed on a wall or floor to detect cracks or voids in non-metallic surfaces. Larger units can be pushed or pulled along a property by an operator.
Is GPR effective on CMU walls?
Yes, GPR is effective on CMU walls. GPR is very effective for concrete scanning and can be used on manufactured concrete blocks (MBC) and concrete floors. For manufactured concrete blocks, this can help you determine if there are vertical reinforcing bars and joints in the structure.
The use of GPR on vertical surfaces or ceilings
It is possible to perform a ground penetrating survey on vertical surfaces or ceilings. In fact, GPR is regularly used to analyze concrete columns and walls in order to identify the reinforcing bars. Lately, it has also been used on certain infrastructures such as bridges and viaducts in poor condition that need to be repaired or rehabilitated. Thanks to GPR, workers can avoid accidents and collapses. As far as the ceiling is concerned, it is possible to perform GPR detection of steel reinforcements and embedded pipes before starting any construction work.
What is the depth of GPR?
What is the depth of GPR? This is the most common question asked of the surveyor’s suppliers. The majority of new GPR users are not aware that there are fundamental physical limitations. Many people believe that the depth of penetration of the surveyor is limited by the instrumentation. This is true in a way, but the depth of exploration is essentially determined by the material itself and any improvements in instrumentation will not overcome the fundamental physical limitations.
The limits of GPR
GPR is a powerful tool, but it has its limitations. Its effectiveness is site-dependent and changes considerably depending on the location: concrete soil, soil conditions and weather are just some of the limiting factors that exist. To date, the main limitation of GPR results is in highly conductive materials such as clay and contaminated soils.
In addition, the performance is also limited by the scattered signal in heterogeneous conditions (rocky soil). Changes in soil type, such as density and water content, also contribute to limited performance since the antenna cannot penetrate properly, resulting in erroneous results. Detection of buried objects is also problematic as it can be difficult to identify the desired target.
You can’t do GPR survey through the plates and the fine metal mesh. So it’s essential to do the subsurface GPR as close to the site as possible to see what’s underneath.
Conclusion
GPR survey or detection is a very effective method for many surfaces. GPR can help in the detection of voids and concrete homogeneity, evaluation of slabs on the ground, evaluation of road and bridge structures, detection of environmental and natural structures such as sinkholes, soil structures, water tables, salt water seepage, ground water channels, etc.