Project: Reservoir Void Survey

Xradar were recently hired by a large engineering firm to conduct a void survey at a reservoir. Previous cores undertaken at the site revealed a void in the reservoir was present, and a thorough survey was required to determine the presence and exact location of any voids or anomalies within the site.


With previous cores at the reservoir site revealing voids, it was essential to perform a full scan of the area to analyze the extent of the situation. The reservoir was drained prior to the attendance of Xradar, allowing our technicians to scan the entire site, except a couple of areas which had standing water.

The approximate area of the slab was 70m², excluding areas where obstructions such as pipes were present.


An Xradar technician attended the site and conducted a thorough void survey utilizing Xradar’s™ Enhanced Concrete Scanning methods. The area was scanned with a regular orthogonal grid pattern with collection lines spaced at 0.5m.

A depth calibration was taken on site where a pilot hole had previously been drilled. The hole was physically measured by Xradar personnel, with the slab thickness found to be 285mm. The relative permittivity was adjusted on our equipment until the correct reading was achieved, allowing us to accurately calculate the depths in the report.

The scan highlighted reflections indicative of voids beneath the slab in multiple locations across the site, including a number of weak reflections along with some stronger signals, suggesting more severe/larger voids.

Based on the results of the survey, further destructive investigations should be undertaken to verify the severity and depth of the voids, utilizing verification cores. This will allow the client to determine the extent of the repair work required on the slab.