Ground Penetrating Radar (GPR) is a high resolution geophysical method for investigating underground structure. One of the most useful nonintrusive site investigation application to accurately locate hidden voids. Clear information is provided about the presence of subsurface voids, often at a fraction of the cost of traditional intrusive methods.

What is a Hidden Void Underground?

A hidden void is an undetected, usually air-filled, space within the foundation of structures such as roadways and buildings. These voids can compromise the structural integrity of the areas where they are located and result in physical damage to the road or building as the void is given the opportunity to expand over time.

Voids can be caused by a variety of occurrences, such as the shifting of earth or flow of water underneath a structure that appears sturdy from the exterior. Voids may occur under any established structure and go undetected for years until finally resulting in collapse. Once a foundation has been compromised, the effects can lead to extensive damage to the existing structure, possible loss of life and high costs in repairs.

There are many subsurface voids that might represent critical safety issues and other concerns – washouts or settlement gaps beneath roadways or floor slabs, ungrouted masonry cells, bubbles in concrete pours, tunnels, mine workings, vaults, and incipient sinkholes or soil pipes. All of these can be detected using nonintrusive geophysical techniques.

While the structure itself may have no reason to fail, it can often be what surrounds the structure that makes the difference. Where there is a void, the material may move and settle, undermining the structure over time.

Wood Inspection Services can provide valuable information about target location or asset evaluation with effective survey results.

Recent Void Detection Projects by Wood

View full screen map

Where Can GPR Detect Underground Voids?

Some common areas where void detection is beneficial are under roadways, bridge supports and dwelling foundation stability following heavy rains and flooding. Detecting these unseen hazards provides the opportunity to protect the property from ultimately irreversible damage. In areas of concern, it is best to be proactive and determine the risk of the existence of hidden voids.

Void detection can best be achieved using ground penetrating radar technology and infrared thermography. These methods offer a noninvasive and nondestructive way to investigate subsurface conditions while increasing the safety of the public and protecting both public and private property.

Using non-intrusive techniques to detect voids can aid in reducing further damage to the foundation that would normally result from an invasive method of testing for stability under an established structure. Scanning underground structures in high resolution is much more likely to be preferred to removing multiple sections of foundation to try and locate a possible void.

What Causes Hidden Voids?

Common causes of hidden underground voids usually result from heavy rains and flooding or damaged, leaking water pipes. This unexpected influx of water can lead to subsurface areas being washed out or eroded away, leaving the surface structures weakened. These voids can lead to a snowball effect of expanding damage if there is shifting of the earth in the area of the void. While obvious structural issues may not be immediately apparent, significant damage may have occurred deeper down. The longer hidden voids remain undetected, the greater their potential for catastrophic damage and structure failure.

How Voids Are Detected With GPR Technology and Infrared Thermography

The science behind using ground penetrating radar technology is a “non-destructive geophysical device used for subsurface exploration and operated by transmitting an electromagnetic pulse from an antenna into the ground and then capturing the partial reflections from subsurface layers,” according to the Texas Department of Transportation. Potential sinkholes and roadway collapses have been avoided using this method of detection, and that saves money for all involved. Infrared thermography is performed by using high definition thermal imaging cameras. Voids are visible due to having a different heat capacity than the surrounding material. Detecting voids in concrete can be done using infrared thermography and assessing the heat conduction that occurs over the course of a determined amount of time. The lack of intrusive operations and the detailed results make infrared thermography a highly desirable means of hidden void detection.