Do you know what Ground Penetrating Radar can be used for? Do you know how it works? Can it help you? This article will help you understand. It’s all about informing you how Ground Penetrating Radar could help you.

GPR basic principles

Ground Penetrating Radar (GPR) uses pulses of high-frequency radio waves to detect and map changes in the sub-surface. It is a non-intrusive survey technique and there are no harmful emissions.

The velocity of the waves through the sub-surface depends on the permittivity of the scanned material — a change in the velocity results in a reflection in the GPR data. The difference in the permittivity of the two materials governs the strength of the reflection; therefore, a pulse travelling from limestone into a void generates a much stronger reflection than a pulse travelling from limestone into sandstone.

By moving the survey equipment over the surface, the GPR equipment records a series of pulses. This makes up a scan. A series of scans, typically collected on a regular grid, can be combined to survey an area. A skilled GPR surveyor can interpret a series of scans and understand what is in the subsurface.

GPR radargram showing changes in floor-slab construction. On the left we have a reinforced slab and on the right clay pot construction
GPR scan showing changes in floor-slab construction

You can find a more detailed explanation in our article What is Ground Penetrating Radar, and how does it work?

What can Ground Penetrating Radar detect?

GPR detects changes; therefore, it can detect most things. It is most commonly used to locate features in the ground, concrete, masonry, and asphalt.

Examples of uses include the location of metal, plastic, voids, and timber; in fact, any material as long as it is sufficiently different from the surrounding media. The higher the difference in the permittivity between the adjacent materials, the better GPR can see it.

So what can Ground Penetrating Radar be used for? GPR is probably best known as a utility location technique; however, at Sandberg, we specialise in the use of GPR for the Civil Engineering and Construction industries. Our surveys include rebar location and mapping, concrete floor slab surveys, chimney flue location, location of voids blow concrete slabs, detecting embedded metal in mason, and much more. Find out more about our GPR surveys. You may be surprised what Ground Penetrating Radar can be used for!

Three GPR surveyors marking-up reinforcement in platform slab in London railway station.
Insitu markup of reinforcement in station platform by three GPR surveyors

GPR – Points for consideration

If you are assessing different investigation and survey techniques to improve productivity but reduce overall costs, the following are the main factors to consider:

Reliability

Although GPR is a relatively new survey technique in Civil Engineering and Construction, it has been around for a long time. Originally, it was developed and used for archaeological surveys. Nasa saw its potential and developed and used it in its space exploration programme, initially on the moon and, more recently, on Mars. Continual technological advances mean that GPR continues to improve and offer higher resolution and better detection of sub-surface features.

So, Ground Penetrating Radar has been tried and tested and is reliable—however, a word of caution. A survey is only as good as the GPR surveyor and the equipment used. Beware of survey companies with limited experience and a single GPR system who claim to be able to undertake any kind of GPR survey.

GPR surveyors should be suitably experienced, use the most suitable equipment for a given survey type, know how to plan and conduct a GPR survey, and last, but by no means least, know how to process and interpret the data.

Safety

The Health and Safety at Work Act (1974) states that businesses have a duty of care to provide a safe working environment for their employees.

Ground Penetrating Radar is a non-intrusive survey technique without any harmful emissions. It poses no safety risk to the surveyor or other workers/general public in the area. Furthermore, it can locate hidden hazards, such as services and buried objects, so that any intrusive or excavation works can be planned and undertaken safely. Indeed, a GPR survey is often specified as a requirement before a contractor can undertake excavation or intrusive works,

Although GPR itself is safe, due care and consideration must be given to the environment where it is used. For example, when working at height or in a confined space, suitably trained operatives should be used, and a safe system of work followed.

Efficiency

For the right survey type, GPR can offer increased efficiency and cost savings. For example, GPR can locate buried objects or determine construction details without needing trial pits or opening up works; this means significant savings!

GPR also lends itself to scanning large areas. Even a single antenna system can scan a large warehouse very quickly. Multiple antenna systems can further improve speed and efficiency, either by using different antenna frequencies (to provide a range of penetration depths and resolutions) or the same frequency to collect several scan lines with one pass.

GPR scanning of warehouse floor slab
GPR scanning of warehouse floor slab – large areas can be scanned relatively quickly

As GPR makes no noise and doesn’t emit any harmful radiation. We can conduct the surveys in occupied buildings if required, keeping disruption and inconvenience to an absolute minimum.

A Sandberg GPR survey

At Sandberg, we aim to deliver the highest standard of GPR survey possible. We individually assess each assignment to ensure that we meet the client’s expectations.

  • Sandberg is licensed to undertake GPR surveys.
  • We train all our GPR surveyors in-house to the highest standards.
  • We have a wide range of GPR equipment, which is suitable for most surveys.
  • All surveyors hold CSCS cards.
  • We have appropriate insurance and professional indemnity insurance.

We usually collect the GPR data on regular grids and save it electronically for off-site processing, analysis and interpretation. In most cases, this produces the best possible results. However, we can undertake site markup if this is required.

Our interpretation and results are presented in a clear factual report, with CAD drawings, sketches and photographs as required.

CAD plot of located chimney flues
CAD plot of located chimney flues (click image for larger version)

Can we help you?

To find out more about our GPR services and if they could help you, please contact our knowledgeable staff, who will be happy to discuss your requirements in detail:

Tel: 0207 565 7056
Email: gpr@sandberg.co.uk