Ground Penetrating Radar (GPR) is widely accepted to be one of the most reliable methods of detecting and mapping underground utilities.
Why use GPR to detect and map underground utilities?
Ground Penetrating Radar can detect most types of utility, including metal, plastic, clay and concrete pipes, cables, and utilities for which there might be no manhole access, which could be difficult to trace using Electromagnetic Location (EML) methods without the ability to clamp on and induce a signal. GPR is also able to detect and map the extents of underground rebar and other features such as basements, culverts, voids, and recover structural information.
How a GPR utility survey is performed?
A GPR utility survey is usually performed using one of two methods: on site mark out, or post processing. In either case the equipment will be brought to site, assembled, and then multiple passes of the GPR will be made across the surface until it has been covered in a series of regularly spaced scans in both directions. Typical spacing between scans could be 0.5m or 1m, but is sometimes closer.
In the case of on-site mark out, the GPR data will be interpreted on-site and the results marked on the ground using chalk, crayon, or temporary paint. In the case of a post processed GPR survey, the data will be collected with the locations of each scan accurately recorded using grids, GPS or Total Station, and then post processed and interpreted in the office to produce a drawing.
(See our page On Site Detection vs. Post Processing for further information.)
Ground Penetrating Radar vs. Electro Magnetic Location
Electromagnetic locators (EML) are relatively cheap with respect to Ground Penetrating Radar and require less skill to operate. For that reason, EML is more established as a technique for detecting underground utilities.
However, based on our experience and controlled experiments, GPR is able to recover more information about the below ground environment and detect more features and utilities with respect to EML, when deployed without manhole access. GPR is therefor an important and integral part of the underground utility survey procedure and should be included as part of a survey.
(See our page Ground Penetrating Radar vs. Electromagnetic Location for further information.)
PAS128 provides guidance for the specification of a utility survey, how it should be performed, and the deliverables which should be produced. Most utility surveys within the UK are specified in accordance with PAS128.
In order to be compliant with PAS128, all utility surveys should incorporate GPR. At KB GPR Surveys we are specialists in GPR, we offer a GPR utility survey service where we provide the GPR portion of the survey to which you can add your own EML results.
(See our page What is PAS128 for further information about PAS128.)
GPR Utility Survey Results
The deliverable from a GPR utility survey will usually take the form of a drawing and a report. For smaller surveys, it can be more appropriate to detect the locations of utilities on site and mark them on the ground using temporary paint.