Ground Penetrating Radar (GPR) can be used to detect the presence and extents of sinkholes, underground voids and subsidence.
Why use GPR to detect underground voids and subsidence
GPR is a fully non-destructive and non-intrusive technology (NDT), it is ideal to survey larger areas for sinkholes, underground voids and subsidence and focus attention for remedial works or trial holes in the right places. Because it is non-invasive and doesn’t require the use of heavy equipment, GPR is a low risk technology to detect underground voids.
How GPR detects underground voids and subsidence
Ground Penetrating Radar works by transmitting an electromagnetic signal into the ground, reflections are caused by changes in the electrical properties of the material the signal is travelling through and those reflections are recorded by the GPR. In GPR, reflections are caused by any change in the below surface environment, GPR is therefor able to detect most types of underground features including sinkholes, voids and subsidence (as long as the voids are large to be detected within the resolution of the GPR being used).
What types of underground voids can be detected
The minimum size of the void which can be detected will vary depending on the frequency of the GPR being used, the depth, and the survey requirement.
KB GPR Surveys have had success detecting sink holes as shown in this example, in this case large voids and areas of subsidence were present beneath a surface layer of reinforced concrete. We were able to successfully detect and map them in our post processed GPR survey even though they were not clearly visible in the data on site.
We also have experience detecting shallow voids in concrete and road structures. As well as badger tunnels and chambers, and man-made voids such as underground tanks, basements, culverts, mine shafts, and gas pipes etc.
In this example, KB GPR Surveys was asked to survey the floor in a church and detect the location, depth and extents of an underground void which was identified as a disused crypt.
In these examples, KB GPR performed surveys of retaining walls to detect potential voids caused by washout. In one case voids were detected – in the other, the retaining wall was confirmed to be sound
How a GPR survey to detect underground voids is performed
Although voids can be detected using several different methods, a typical survey would involve attending site and surveying the surface (ground or wall depending on the survey in question) in an orthogonal grid of regularly spaced scans, allowing us to collect data for all of the site with no gaps in the coverage. It is possible that an underground void or area of subsidence might be detected on site, however it is more likely that the data will be saved and results won’t be available until after office processing and interpretation using our advanced GPR imaging software.
This allows us to subject the saved GPR data to different processes and visualise the underground voids and subsidence in different ways to achieve the best results, we also subject all of our results to an internal quality control before issue.
Underground void and subsidence survey deliverables
The results from a GPR survey of underground voids and subsidence will usually take the form of CAD drawings and a report. The final output may vary depending on the best way to resent the information.
If you require a GPR survey to detect underground voids or subsidence, contact KB GPR Surveys for a quotation at firstname.lastname@example.org