Is GPR efficient for detection of underground ducts?

GPR (Ground Penetrating Radar) 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.

Underground duct detection – What is GPR?

GPR is used in many areas to observe man-made and natural features. GPR detects metallic and non-metallic pipes, power lines, conduits, water lines, rebar and post-tensioning cables within concrete. GPR 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, GPR is the most cost-effective option and the fastest method of testing concrete.

GPR meets wider needs

Over the past two decades, surveyors and engineers have increasingly embraced GPR utility locating equipment. Already using electronic equipment throughout the construction process, surveyors and engineers have successfully used ground-penetrating radar to modify the 811 process in United States.

In recent years, engineers and project managers for underground utility engineering contracts have begun to specify that contractors must take extra steps to avoid unknown problems associated with buried underground utilities. GPR service providers have carved out a niche serving electricians, plumbers, and contractors responsible for detecting utility locations.

Now, with the wider availability of many powerful, high-quality, and less expensive GPR devices for locating utilities, inspectors, electricians, plumbers, and utility contractors are wondering why they have to pay to use GPR scanner when they can just buy one for themselves.

How deep can GPR penetrate?

The answer to this question is usually a range between 2 to 10 feet or up to 18 inches. However, for a client’s specific study area and objectives, these answers are often unsatisfactory and can be misleading. When detecting underground reservoirs, the depth of penetration of GPR is affected by the individual layers of the subsurface, making it more difficult to estimate the actual depth until you are on site.

Just as a sheet of paper placed directly in front of your eyes can totally block your view, a thin layer of electrically conductive material can totally block the view of GPR. For example, sandy and loamy soils are relatively good for GPR, while clay soils are not. You can say that the soils on the site are mostly sand and silt, but a thin layer of clay only a few centimeters thick at a shallow depth could severely block the view of GPR and make the rest of the good soils irrelevant.

Underground detection by GPR – GPR limitations

GPR is a powerful tool, but it has limitations. Its effectiveness is site-dependent and changes dramatically depending on the location: concrete floors, soil conditions, and weather conditions are just a few of the limiting factors that exist. To date, the main limitation to GPR results is in highly conductive materials such as clay and contaminated soils.

In addition, 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 (impossible to find the individual tree in a forest).

We can’t perform an underground detection by GPR through the plates and the fine metal mesh. So it’s essential to do an underground detection by GPR as close to the site as possible to see what’s underneath.

Are GPR results accurate?

The level of accuracy will always depend on the difficulty of your target. If you want to detect underground pipes, pipelines, landmines, buried cables, etc. it is possible to get a very accurate detection (approximately 90%). On the other hand, detection of damaged areas, cracks, etc. is not very accurate. You won’t get much better than GPR. In environmental applications such as searching for oil leaks in reservoirs, polluted areas, GPR can be effective.

Conclusion

GPR is an effective tool for the detection of underground tanks. It can assist 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, groundwater channels, etc.

In general, GPR is one of the most advanced technologies that can be used to get a more accurate picture of the composition of underground areas. To learn more about underground tank detection, or to see how it can improve your construction techniques, contact us or call us today.