Ground-penetrating radar is nothing new. The technology has existed for many decades but it has only started to be used regularly in other applications such as roads in the last 15 to 20 years after the technology has improved dramatically.
GPR for roads allows engineers to assess the layer thicknesses and the material conditions of trunk roads and pavement structures. It can be costly and time-consuming to get working, and it does have some limitations because GPR collects data at discrete points, rather than across the whole surface. In urban sites, this is not always perfect because conditions can be so variable and urban pavements have a lot of reconstruction work done on them, with maintenance causing significant changes. With that said, GPR for roads is useful because it can flag up many problems, and it is possible to optimize the data that is collected.
Researchers have put a lot of effort into finding ways to improve the data collected through GPR. With the most recent optimizations GPR offers one of the best non-invasive ways of surveying roads to allow for maintenance and repair. GPR can provide information about structural anomalies, moisture content, and other factors that might affect the stability and safety of a road surface.
Why Use GPR
GPR can provide information about the parts of the road that you cannot see, and it does it in a way that is non-invasive. Traditional ways of assessing a surface such as trial pits or core samples can offer some useful information but they are costly and invasive. In addition, when you take a core or a trial pit sample, the only information you get is for that specific sample. GPR is able to get information about a wider area.
GPR uses a radar pulse to pass through the ground, and the system records the length of time it takes the pulse to be bounced back to the antenna. The speed with which the radar waves pass through a material depends on the type of the material, the condition of it and how much water is in the ground. When there are two layers with contrasting properties, the radar energy (or part of it) will be reflected back from the material. This gives an image which is, to those who know how to interpret it, similar to having x-ray vision for the ground.
Innovations in Urban GPR
GPR is not perfect, and it struggles in environments where there are a lot of wet materials because the liquid attenuates the signals. GPR can be used on urban roads along with falling weight deflectometer data to give engineers an idea of the stiffness of pavement layers and to also highlight construction changes, wet patches, and voids which could indicate poor support on the roads. In theory, this allows for proactive maintenance, but in practice, too many companies still use standard GPR methodologies, which are suitable for trunk roads but not urban sites, and they do not get a complete view of the road. It pays to use FWD methods to get a clearer picture.