FAQ’s for GPR

What is Ground Penetrating Radar (GPR) ?

GPR is the process by which a radar wave is directed into the structure or the ground and the resulting reflection is collected and analysed by the technician. The latest powerful software processes the collected data into either 2D or 3D images which can then inserted into reports or presentations.

What can be located?

Under ideal conditions, almost anything can be located providing the object is large enough and close enough to the surface in relation to the frequency of the antenna and that there is sufficient contrast between the electrical properties of the object and its surrounding material. Unfortunately however, ideal conditions are generally rare, with the most common problems occurring on site being dense reinforcing cover over shadowing lower level low amplitude signals from services or tight survey areas that do not allow for adequate data to be collected for proper analysis.

Is it Safe ?

GPR generates less power than a standard mobile phone and at similar frequencies and can therefore be used in any environment deemed safe for mobile phone operations. Unlike X-Ray which requires evacuation of people within a 20 metre radius around and below, GPR causes little or no disruption to other people working within the vicinity

Where can it be used?

GPR can be used anywhere providing the surface over which the survey is being conducted is reasonably flat and has no surface water. Our equipment is light and versatile enough to allow surveys to be conducted almost anywhere, whether it be floors, walls, ceilings, roads or fields. Sizes of surveys are tailored to the Client’s needs.

How deep can we see?

Depth of surveys are dependent on antenna frequency and attenuation of the transmitted radar wave. Antennae which have higher frequencies will give an image with better resolution but lack the penetrating depth of lower frequency antennae. Attenuation is the ability of the material being surveyed to absorb the radar wave. The greater the rate of attenuation, the lower the ability of the radar wave to penetrate the material. Test surveys may need to be done in order to assess the penetrability of the radar signal. Our (Services available) page lists the depth capabilities of various antennae frequencies under ideal conditions.

Can GPR determine the diameter of reinforcing?

No. There is currently no equipment available that can determine reinforcing diameters accurately, under all conditions. Given the right conditions, GPR does have the ability to estimate reinforcing diameters. For the purpose of determining diameters for engineering calculations, invasive inspection is still required to give accurate information. Should the need for this type of investigation arise, it should always be achieved as discreetly as possible.

Can GPR penetrate Bondek ?

No. Bondek or similar, is a structural metal formwork base onto which the concrete is cast and which remains in place for the life of the floor. As GPR cannot penetrate metal, surveys requiring the locating of services, reinforcing and Post Tension Cables from the underside of the slab are not possible.

Can GPR tell the type of service?

Unless there is some form of visual reference as to the nature of the service being traced, GPR has no real ability to distinguish between targets. A metal pipe carrying water, gas or air will reflect the same signal as a reinforcing bar of a similar size. Even a conduit containing multiple conductors will be difficult to differentiate from reinforcing. There may however be tell tale signs that a trained technician may pick up on to indicate which target the service may be.

Can GPR tell whether an electrical service is active or not?

GPR does not register electrical current, however some GPR units do have EMF (electro motive force) detectors built into the search head of the GPR antenna. Two important factors must be understood about these detectors. 1: the circuit being surveyed must be “Alive” (active) and 2: the circuit must have sufficient load using the electricity to produce a magnetic field strong enough to be detected. Numerous problems are associated with this. The magnetic field produced by live cables has the ability to jump onto metal objects such as reinforcing causing the reinforcing to emit the same frequency as the electrical service, creating confusion as to what is service or reinforcing. Weak EMF signals can be shielded by reinforcing making them undetectable. These inbuilt EMF detectors only register mains voltage. Video, voice, data or fire services etc. cannot be detected.

Should the same Company be used to do the scanning and coring?

To create transparency, it would be wise to separate the two services. Mistakes in analysing GPR data can create serious & costly consequences to structural elements if damaged through coring or sawing. Unscrupulous operators may take advantage and hide mistakes such as damage to Post Tensioning, critical reinforcing or services, leaving you with the consequences and a costly repair when the problems emerge later .

I have more questions!

Please feel free to contact us either direct by phone or send us an email. Either way, we will endeavour to answer all your questions as clearly and simply as possible.