A void detection survey using Ground Penetrating Radar (GPR) is a low risk method to scan an area of ground and determine the location and extents of underground voids, sinkholes and subsidence. This can form part of a risk reduction process to check the integrity of the ground before moving or using heavy equipment and cranes, or to determine the extents of potential underground voids and subsidence to aid in remediation planning.
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A GPR survey to detect underground voids is usually performed using handheld equipment which is mounted on a small trolley. Parallel lines of GPR data are collected in two axis to form an orthogonal grid. Each line represents a vertical cross section through the ground at that specific location, these lines of data are saved for office-based processing and interpretation.
In the office the data is loaded into our advanced GPR post processing and imaging software, by compiling the vertical cross sections together a 3D picture is formed. Using this 3D image underground features such as voids, sinkholes and subsidence can be detected and tracked from scan to scan to produce a CAD drawing.
Some examples of void detection surveys include:
This GPR survey to detect underground sinkholes in Manchester. In this case large voids and areas of subsidence were present beneath a surface layer of reinforced concrete, they were caused by a sinkhole 4m deep. 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 and sinkholes 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 two examples, retaining walls were surveyed to detect potential voids caused by material washout. In one case voids were detected – in the other, the retaining wall was confirmed to be sound.
Sinkhole, underground void detection and subsidence survey deliverables
The results from a GPR survey of underground voids and subsidence will usually take the form of CAD drawings and/or a report. The final output may vary depending on the best way to represent the information.
If you require a void detection survey or a survey to detect sink holes and subsidence, please contact KB GPR Surveys for a quotation at firstname.lastname@example.org