Ground Penetrating Radar
Ground Penetrating Radar (GPR) is a non-destructive, non-intrusive, subsurface imaging tool. It has a range of applications in transportation infrastructure, energy facilities, and the environment. Some key features of GPR are:
- • Rapid data collection
- • Extensive data collection
- • Options for depth of penetration and resolution
- • Ability to detect both metallic and plastic materials
ARMA offers a broad range of GPR capabilities that are summarized below by application area.
GPR has been used for many years on pavement systems to address a full range of applications. The results from a GPR survey can provide the following:
- • Layer thicknesses
- • Location and extent of voids
- • Create as-builts
- • QC/QA of new or rehabilitated roadways
- • Characterize pavement segments in a roadway network
Data collection for pavement systems can be performed at high speeds with very little interruption to normal traffic patterns. This is typically for applications where a depth of penetration of up to 1 meter is needed. To address applications where greater depths of penetration are needed, lane closures will be needed.
Reinforced Concrete Structures
From top to bottom: a contour plot showing location and extent of corrosion in a bridge deck; and a GPR image showing the location of reinforcement members in concrete.
The ability of GPR to gather data within a structure is a key attribute with regard to reinforced concrete structures. The results from a GPR survey can provide the following:
- • Subsurface condition
- • Location of reinforcement members
- • Open space between embedded structures
- • Concrete cover thickness
- • QC/QA of new or rehabilitated structures
- • Characterize bridge decks in a network of bridges
With this application, the needed depth of penetration is very shallow. High resolution antennas are used either mounted to a vehicle or dragged by hand. Due to the needed data collection rates, a moving lane closure will be needed. A hand drag survey will need a lane closure. Vertical structures are performed by hand.
Many have commented that GPR is an enhanced metal detector. This is because of the strong response metal provides. Because of the way electromagnetic waves behave in materials, plastic structures can also be seen. The results from a GPR survey can provide the following:
- • Location and depth of targets
- • Identify if the structure is metallic or plastic
- • Determine if one object is larger than another
Deep penetrating systems need to be used, which comes at a cost to resolution. Therefore small targets buried deeply cannot be found so easily or at all. In order to determine if one feature is larger than another, the difference is sizes must be great. In addition to providing the horizontal location of a feature, a very good approximation of depth can be determined.