Concrete Slab Scan and Thickness Survey

Xradar™ were hired to conduct a condition assessment on a Dam face in Western Canada. The objective of the project was to measure slab thickness and locate voids beneath the face of the dam. In addition the data would be processed and interpreted for corrosion mapping and concrete cover measurement.


The Dam is an approximately 60 years old, 90m long embankment dam in Western Canada. Located at 1060m above sea level, it holds water for the a Pulp and Paper operation and is only accessible with special 4x4 side-by-sides.

The dam goes through a general maintenance period every September-October and has had several leaks over the past decades, with the most recent ones being repaired in 2017-18. The nominal slab thickness is 12.5cm and the slab contains one layer of welded 6”x6” wire mesh.

The client wanted to carry out an overall condition assessment that included slab thickness measurement and a void identification survey to create a better estimate of the remaining lifespan of the dam.


The client requested an entire scan of the face of the dam in order to assess the slab conditions. Our technicians provided a survey utilizing Ground Penetrating Radar (GPR) and Xradar™.

As the dam was not walkable, our technicians performed the scan using a slide system that would allow us to collect dam using a single rope and a helper at the bottom of the dam. The slide-system is a semi autonomous GPR survey methodology where the control unit and the antenna pull together while the data is being collected along the way. The collection was triggered by a large survey wheel attached to the slide system. The system interaction only occurs at the beginning and at the end of the actual GPR line (to start and to stop the data collection).  

Once collected, the data was processed and interpreted with four maps created. These survey maps outlined slab thickness, concrete cover, corrosion-induced defects and an interpreted void map.

The slab thickness results showed general thickening around the existing joints and several anomalies with less than 9 cm remaining slab thickness.  

The void detection results showed several smaller size voids and potential voids almost evenly distributed on the dam face, with various sizes and minimum depth.

The corrosion distribution showed trends around the joints while rebar cover had a very good correlation with the slab thickness measurement.