Underground Void Detection

Shallow voiding can be caused by several reasons including:

• Sinkholes (the causes of which can be geological or man-made such as broken water pipes, old sewers, buried basements, and disused mine shafts which have been compromised).
• Material washout due to underground water movement which carries some material with it (typical in coastal promenades and car parks, masonry arch structures and docks & retaining walls).
• Natural subsidence in which the ground itself is moving and settling over time.

Subsidence will be visible from the surface in the form of dipping ground in soft layers and cracks in harder materials. However, in cases when the surface is firm and supports its own weight the material beneath can subside until a significant void has developed underneath the surface layer with no visible warning signs. The surface may then break when heavy loads are applied or, if the void reaches a size in which it can no longer support its own weight, it will collapse on its own.

Voiding can usually be remedied by first exposing and fixing the source (if that is possible), and then pumping material into the void until it is filled. A GPR void detection survey is be the ideal method to determine the extents of the problem.

GPR is a fully non-destructive and non-intrusive technology (NDT), it is relatively light weight equipment which can be used to scan areas of any size and it does not cause any damage to the surface being surveyed. A void detection survey using GPR is a cost-effective way to scan large areas safely.

Ground Penetrating Radar works by transmitting an electromagnetic signal into the ground and recording reflections. In GPR, reflections are caused by any change in the below surface environment. GPR is therefor able to detect most types of underground features including sinkholes, voids and subsidence (provided the voids are large enough to be detected within the resolution and penetration capabilities of the GPR being used).