Underground voids and sinkholes can be created by a number of factors from environmental conditions to damaged pipes leaking underground.  Voids are most commonly found under concrete or asphalt where (because of the rigidity of the surface material) it is quite easy for a small ½” void or larger to begin forming just underneath the surface.  A small ½” void may not seem that bad but in situations where you have a finished floor that is exposed, bad cracking can begin quickly and it can turn a beautiful floor into an ugly floor.  If you suspect a void forming below the surface, it is important to have the void scanned early to identify the exact locations of the voids and get them repaired before more damage is done. We’ll show you an overview of how to detect voids using a highly effective piece of equipment called: Ground Penetrating Radar.

What Causes a Void?

Expansive Soils like clays expand when they come in contact with water and shrink when they dry out.  This movement can cause possibly heaving or voids depending on when the soil was compacted and the floor or foundation that was built on top. If the expansive soil was somewhat wet when it was compacted and then a layer of concrete is poured over the top, large voids can be created as the soil begins to dry out.  The other side of that phenomenon being where dry expansive soil is compacted below the concrete and then that soil gets wet later.


how to detect voids


As the soil gets wet, it expands and can easily move the concrete around to varying degrees. During wetter periods, expansive soils can change in volume by more than ten percent in some cases.  This change in soil volume can put an enormous amount of force and strain leading to cracked concrete flooring and other foundation issues. During drier periods, the soil can shrink and produce voids and fissures that allow for deeper water penetration during wet conditions.  Over time this cycle of shrinking and expanding will continue to increase the size of the underground void.

Poor Soil Compaction

Created where the soil under the concrete is not compacted properly during the construction process. Ideally soil needs to be compacted in 8″-12″ lifts.  During the compaction process it is advised to use proper wetting of the soil, failure to do so can lead to voids appearing later after settling occurs.



Underground Pipe Leakage

Caused by damage to high or low pressure pipes. Damages to underground piping can occur from invasive root damage into the pipe, damages to underground pipes during construction digging activities, or simply the pipe deteriorating over time. It is also possible that a pipe was not installed properly and perhaps a connection joint is leaking or was kinked during the initial installation.


how to detect voids


Underground piping can leak under the concrete slab or asphalt paving, causing the dirt or sub-grade to settle or wash away and create a void.  Underground leaks can also lift heavily compacted soils up (expansive soil) resulting in voids in other areas.

Water Issues and Soil Settling

Occurs naturally over time as any excess water will follow the path of least resistance.  Given enough time and if left untreated, water issues can result in soil settling under concrete slabs and roadways.  Long term problems such as erosion and sinkholes can also develop.

How to Detect Voids with Equipment

Encompass Inspections locates underground voids by combining ground penetrating radar equipment with our highly-trained technicians.  Our inspection technicians survey for underground voids using a GSSI’s SIR-3000 ground penetrating radar unit.  The SIR-3000 is the industry’s number one choice for data accuracy and versatility.  Coupled with the SIR-3000 unit, we can deploy the 400MHz antenna, used in underground utility locating, finding underground storage tanks (UST’s) and void scanning applications.  The 400 MHz antenna allows us to see voids over a larger area and at depths of up to 8 feet deep.


how to detect voids


When Encompass Inspections locates voids in concrete or asphalt, our inspection team relies on the 1600 MHz antenna for its high resolution accuracy and condition assessment capabilities when looking for near-surface voids.  

Void Scanning with Ground Penetrating Radar can help determine:



Detect Voids using Ground Penetrating Radar Sample Image:



how to detect voids


Void Locating Company:

Hiring Encompass Inspections as your void locating company should be the first call you make if you suspect you have an underground void issue.  Delaying dealing with a potential void will only continue to make the problems worse over time, along with increasing the costs of any potential repairs needed.  Repairing the damage from underground voids and sinkholes can range from $10,000 for a simple repair not involving any structural damage, to possibly several hundred thousand dollars or more depending on the size and severity of damage.

Our Survey Process

We have a multiple step survey process to ensure that voids are located accurately.

  1. Select the proper antenna frequency and survey parameters.
  2. We calibrate our equipment to the jobsite.
  3. Create proper file headers for data collection.
  4. Map the project to determine survey bounds and areas of interest.
  5. Create control points by scanning known void areas or known non-void areas and using them as a variable numbering system for void severity.  
  6. Begin collecting the data and taking notes on scanning locations/findings.
  7. Save void cross-sectional scans.
  8. Mark out void severities on the slab or asphalt if able.
  9. Extract the information into our computers for analysis.
  10. Create a report with our findings and conclusions.


Locating Underground Voids Sample Images

Void Scanning Ground Penetrating Radar
Sinkhole Void Damage
Void Detection
Searching for underground voids
Underground void inspection
Detecting voids with GPR scanning
Locating voids under roadways (yellow areas). Orange areas show the areas scanned with GPR
Discovering underground voids


Experienced Underground Inspection

At Encompass Inspections we combine cutting edge equipment, a nationwide coverage area, and a vast amount of underground inspection experience.  Whether you are in need of an underground void survey, a private utility locate, concrete scanning using ground penetrating radar, camera pipe inspections, GPS mapping, or leak detection services, our team of experts has you covered for any issues you may encounter, both underground and in concrete on any commercial or residential project. Our multi-technology approach separates us from smaller companies that may not always have the right tool for the job.  

To review a complete list of the services we provide visit www.encompassinspections.net