How we use ground-penetrating radar to devise the most suitable solution

In ground-penetrating radar (GPR) surveys, electromagnetic waves of frequencies between 50 MHz and 2.6 GHz are transmitted into the ground or a structure. Because of the wide range of antennae available, GPR can be applied to numerous geological, environmental and engineering applications.

GPR is widely used for a host of applications within the engineering and construction industry, in the archaeology and forensic sectors, in geological and environmental science and for utility detection and concrete inspection. It is an intrinsically safe technique for evaluating concrete and has the highest resolution of any non-invasive subsurface imaging method. GPR collection is rapid, undertaken at walking pace, and can be used in the majority of situations, including the evaluation of walls, roads, fields, car parks, basement areas and brownfield or greenfield sites.

The GPR systems we deploy are highly portable and comprise a handheld control unit connected by a cable to the antenna. The equipment operates at a range of frequencies that vary according to the target type and depth of penetration required. At higher frequencies, smaller, as well as more closely spaced, targets such as reinforcing bars, pipes or voids are more readily detected than when using alternative detection techniques.

Below is a table of antennae we use to meet many requirements within a broad range of applications (depths may vary depending on ground conditions)

Frequency Typical depth of penetration (bgl) Common applications
2600 MHz Up to 0.4 m (12 in) Concrete evaluation
1500 MHz Up to 0.7 m (20 in) Concrete evaluation and void detection
900 MHz 0–1 m (0–3 ft) Concrete evaluation and void detection
400 MHz 0–3 m (0–9 ft) Utility, engineering and environmental and void detection
200 MHz 0–6 m (0–20 ft) Utility, geological, engineering and environmental
100 MHz 0–12 m (0–40 ft) Geological, engineering and mining
50 MHz 0–25 m (0–75 ft) Geological

 

Large areas up to 1 ha can be covered in a single day using portable carts. In urban areas with many buried obstructions and services, the scan line spacing is reduced in order to provide a more detailed study.

Limitations to the technique include clay-rich ground (the signal attenuates more readily, so the scan depth is restricted), concrete with very dense reinforcement (multiple layers with bars less than 100 mm apart) and significantly vegetated or uneven ground (the antenna requires a good coupling to the ground in order to transmit quality signals).

Advantages of GPR

  • Versatile: detects both metallic and non-metallic objects non-destructively
  • Cost effective: typically requires a single operator, making surveys fast and reducing field and project time
  • Speed: high-speed and real-time data interpretations minimise traffic disruption and blocked access to facilities

Other geophysical survey techniques

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RSK Geosciences is part of the RSK group of companies

The RSK group is a leading integrated environmental, engineering and technical services business offering bespoke end-to-end solutions to a variety of sectors. Headquartered in the UK but with an established presence throughout Europe, Africa, the Middle East, Asia and Australia, RSK helps organisations around the world achieve their business aspirations in a sustainable and efficient manner.