GPR (Ground Penetrating Radar) Survey
Ground Penetrating Radar (GPR) is a tool used to provide pavement construction information using a non-destructive process. The procedure is split into two distinct parts, survey and analysis.
How it works:
GPR operates by transmitting a pulse of electromagnetic radiation from an antenna into the pavement. At the interfaces between different materials, part of the signal is reflected back. By collecting and interpreting this signal the type and thickness of the pavement layers can be ascertained.
What it's used for:
GPR surveys on pavements tend to be employed for two main reasons. More often than not it is used as an initial scheme specific survey in order that more detailed surveys can be identified and targeted. It is also used as a network level survey where the reults are utilised to aid with network modelling and the production of deterioration trending and life cycle costing.
What it identifies:
- GPR can confidently identify the following pavement features:
- Construction changes
- Bound and unbound layer thickness and profiles
- Voids and wet patches, particularly beneath concrete slabs
- Depth and gross misalignment of joint dowel bars, and reinforcement detail
- Variation of sub-base moisture content
It can also act as a guide in identifying:
- Delamination between bituminous layers
- Debonding between cementitious layers
- Average depth of cover to reinforcement
- Condition of steel in concrete slabs
- Debonding of joint sealant
Surveys:
All our surveys are carried out to a "Survey Plan" which ensures that the following information is provided
- Client brief
- Location reference information (using GPS, section and chainage plus written description)
- Calibration of the system
- Quality control procedures for both survey and analysis
- Work programme
- Survey procedure
- Risk assessment
- Presentation of results
Analysis and Reporting of results:
At the outset we discuss the requirements of the client, so we can analyse and provide the results in a format that can be readily understood and which can be easily linked with any other pavement condition data for the project.
The raw data is processed using standard software, which can average the layer thicknesses over varying lengths from 0.25m upwards.
- Tabulation - to be used on all types of management systems (excel, access, HMDIF, ASCII)
- Graphical display
- Written report - summarising the results, assumptions used, measurement accuracy etc.
One of the main advantages of using GPR, apart from it being non-destructive, is that it can be carried out at traffic speed. This not only eliminates the need for traffic management it also considerably reduces disruption to the travelling public and ultimately reduces cost.
All the machines that we use have undergone and paseed an annual correlation trial conducted by TRL, and our survey and analysis procedured conform to HD29/94, this, hopefully guarantees the quality and accuracy of our work
