GPR (Ground Penetrating Radar) Awareness

Ground penetrating radar (GPR) uses electromagnetic pulses to detect buried objects, voids, and services.
GPR complements CAT and Genny surveys by detecting non-metallic services such as plastic pipes and ducts.
The equipment is pushed or dragged across the ground surface, scanning beneath without any excavation.
GPR interpretation requires specialist training — results are displayed as radargrams that need expert analysis.
GPR performance is affected by soil type, moisture content, surface material, and the depth of the target.
Clay soils and waterlogged ground significantly reduce GPR penetration depth and data quality.
GPR does not replace the need for service plans, CAT and Genny surveys, or trial holes.
The survey must be carried out by a competent operator certified to PAS 128 standards where required.
GPR is also used for structural surveys, void detection beneath roads, and locating reinforcement in concrete.
Survey results should be recorded, marked on site, and included in the excavation permit documentation.

Detect non-metallic services	CAT and Genny cannot detect plastic pipes or non-metallic ducts — GPR provides additional detection capability.
Reduce service strikes	Using GPR alongside other methods reduces the risk of striking buried services during excavation.
Informed decisions	GPR data helps engineers and operatives make safer decisions about where and how to dig.

Do

Don't

Use GPR surveys as part of a combined approach with CAT, Genny, and service plans
Ensure the GPR operator is trained and certified to the appropriate PAS 128 level
Mark GPR-detected services and anomalies on site using spray paint or markers
Include GPR survey results in the permit to dig documentation for the excavation
Request GPR surveys on sites where non-metallic services are known or suspected
Brief the excavation team on the GPR findings including any uncertainties
Use GPR in combination with trial holes to confirm the identity of detected features
Consider ground conditions — request GPR early before wet weather reduces performance
Record the GPR survey coverage area, date, and operator on the survey report
Retain GPR survey records for future reference when further works are planned

DON'T rely on GPR alone — always use it alongside CAT, Genny, and service plans
DON'T assume GPR will detect everything — soil conditions affect its performance
DON'T interpret GPR data without specialist training — radargrams require expertise
DON'T excavate without marking GPR findings on the ground surface clearly
DON'T skip GPR on sites with known non-metallic utilities such as plastic gas pipes
DON'T treat a clean GPR result as a guarantee that no services are present below
DON'T use GPR equipment that has not been calibrated and maintained correctly
DON'T carry out GPR surveys on heavily reinforced concrete without adjusting settings
DON'T ignore anomalies in the GPR data — investigate with trial holes if uncertain
DON'T allow untrained operators to perform or interpret GPR survey results

See also: CAT and Genny Safe Use | Permit to Dig Process

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