GPR Survey FAQ’s

Below are a list of questions that we are asked on a regular basis about GPR Surveys for Utility Mapping:

What is a GPR survey for?

A Ground Penetrating Radar (GPR) Survey is used to detect changes in ground density.

These changes may relate to:

Buried Services & Utilities – we utilise GPR every day as part of our utility surveys and it is an integral tool in detecting plastic gas and water, as well as other services such as drainage.

Voiding and Unconsolidated Ground – voiding such as tunnels, cavities or disturbed / looser ground.

Significant buried features such as tanks, foundations or other substantial obstructions. 

Saturated ground conditions – this is identified by a significant degradation of radar data.  When paired with a utility survey, this may identify where leaks could be present. Voiding may be associated with wash.

How much does a GPR survey cost in the UK?

The cost of a survey depends on a number of factors:

1. Objective of the survey
2. Depth survey needs to penetrate
3. Size and nature of the survey area
4. Geographical location of the site
5. Whether any out-of-hours working or traffic management measures are required.

How accurate are GPR surveys?

Utility Mapping Surveys have a tolerance of the 10% of the depth down to 2m below the ground surface.

This tolerance increases significantly beyond 2m.

A number of factors affect the accuracy of the Ground Penetrating Radar, such as ground conditions.  For example, dry sand is the best medium for getting the most from a GPR system, whilst wet sand is the worst!

What are the disadvantages of GPR survey?

Ground Penetrating Radar on its own cannot tell you what a specific feature or anomaly may relate to.    Use of radio frequency detection or excavation can assist in identifying what anomalies or unidentified linear targets may be.

GPR cannot be used where vegetation or obstructions are present and is not practical where long grass or uneven ground is in situ.

The presence of reinforced concrete also limits the effectiveness of GPR.

How deep can GPR survey go?

Ground Penetrating Radar is a versatile tool which can be tailored for a range of applications.

We use a handheld GPR system which has a depth penetration of 400mm below the ground surface for concrete analysis and locating anomalies in small, often, internal spaces including underfloor heating pipes and voids.

There are antennas which offer high resolution at shallow depths.

Next, we have dual antenna systems which provide high resolution output at a shallow depth and a deeper depth.

Our standard set up consists of a 350MHz hyper-stacking digital antenna or 400MHz antenna designed for detecting buried services and utilities.

We can then use 200, 270 or 100MHz GPR antenna for deeper depth penetration up to 10m, subject to ground conditions.

The smaller the feature, the harder it is to detect. The deeper we penetrate the larger the feature has to be for it to be picked up in the radar data. This is displayed by the below graphic:

Vehicle-mounted GPR surveys are designed to cover large area or highways quickly. This is completed using a multi-array or multi-channel system.