How Ground Penetrating Radar (GPR) works

by

kavinusa

Ground Penetrating Radar is a cutting edge non destructive technology which is extensively used in various fields like construction, locating utilities and pipes underground, bridge and road inspection, concrete inspection, geology, archaeology etc. It can be used over variety of media such as rock, ice, soil, water, concrete, pavement and structures as well as to locate all types of underground substances. It is more recently coming into popularity for concrete and bridge inspections as well as for construction to locate underground pipes and electric before digging

How it works

GPR or Ground Penetrating Radar uses high frequency Radar pulses or electromagnetic waves which usually fall into the range of 10 MHz to 2.6 GHz to scan the subsurface. Radar (Radio detection and ranging) is a technology used to detect the target in free space and determine its range.

A GPR setup consists of a transmitting and receiving unit, control unit, display console and power supplies. It sends electromagnetic pulse through an antenna which penetrates the surveyed surface and portion of energy deflect back to the receiving end when the wave encounters any obstacle under the surface.

The returned signal is then stored digitally so that the computer can calculate the travelling time of the signal to and from the target. This assessment helps in indicating the depth and location of the target. The result is displayed on the console unit.

Data collection on different surfaces

GPR is used on the ground to find the depth and location of buried objects. The radar unit can send and receive signal up to 1000 times per second. The field operator checks the reflected signals and stores it in the system so that it can be used for further analysis.

It is used on concrete surface to locate targets like rebar, conduits and post tension cables. A high frequency signal is used to scan the concrete structure. The data is depicted in form of grid format to generate a map of objects located in concrete while line scan is used for determining the thickness of it. It is used in creating the 3D maps of the target and determining the depth as well.

Data interpretation

Since the GPR signals traverse through different types of material like concrete, soil, debris etc. therefore the resultant data is quite complex. Although, the result is illustrated in graphical form but It still requires high expertise to interpret the findings.

The accuracy of the GPR is based on elements beneath the surface and frequency of waves used to emit and receive signals from the antenna. For example, while evaluating targets in concrete structure like rebar or conduit, higher frequencies like 1000 MHz is required for producing high resolution illustrations. It can provide details of the depth up to 24 inches.

On the other hand, If deep penetration is required on subsurface like soil then low frequency wave ranges from 12.5 MHz to 500 MHz is used.

Advantages

It is non destructive, non intrusive, fast and extremely accurate technology. It doesn’t require any drilling or digging of the surveyed surface which saves money as well as time. It is safe, user friendly and can store complex data in short time for further analysis. The detailed result in form of high resolution image helps in generating accurate condition assessment report.

Ground Penetrating Radar Use In Bridge Inspections

There are many companies that use gpr for Bridge inspections but most of them are not professional services companies and do not have the technology or know how to properly interpret the results. Infrastructure Preservation Corporation is a professional services non-destructive testing and robotic engineering company that developed a patented process that interprets the information for bridge inspections and can assesses bridge decks and bridge deck approach ways. The process goes well beyond just using gpr (Ground penetrating radar) alone. Ground penetrating radar is a great tool but will not provide the level of detail that IPC’s GPR or patent pending process named BridgeScan can deliver.

In order to properly repair and maintain our bridges the current bridge inspection process needs to change. The current requirement only requires bridge inspection companies to visually assess the bridge deck and drag a chain across suspect areas while traffic is driving by at 70mph. The current inspection methods are the reason why our infrastructure and bridges are failing. It is time that the department of transportation utilize modern technology and robotics to update current inspection services.

How can we continue to justify using current manual subjective inspection methods when companies like IPC have the technology to provide the asset owners (department of transportation) real quantitative data that can be recorded and monitored for any deterioration progression over time and to keep our public safe. For more information contact www.infrastructurepc.com or info@infrastructurepc.com

To know more about please follow this link:

Ground Penetrating Radar

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Concrete Crack Inspections

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