GPR is a non-destructive technology with almost endless locating capabilities. From safely scanning concrete to detecting non-metallic utilities to uncovering the condition of buried assets, GPR has become a staple for engineering, environmental and construction projects, large and small.
Ground Penetrating Radar (GPR) is an effective technology for locating non-conductive utilities and underground anomalies. GPR should be leveraged when non-metallic utilities are believed to reside in the project area such as plastic, fiber optic, cable TV lines, water and concrete sewer lines, in addition to foundations, ducts and chambers. GPR data can yield a cross section of subsurface utilities and can also be depicted three dimensionally, providing data on the actual depth of utilities. This data can then be integrated with information generated from Electromagnetic (EM) Induction techniques to provide a complete picture of subsurface utilities and highlight conflicting information.
A non-destructive approach to revealing subsurface features
GPR is a non-destructive technology that works by transmitting high frequency radio waves into the ground or structure and analyzing the reflected energy to create a profile of the subsurface features. The reflections are caused by a contrast in the electrical properties of subsurface materials which can be indicative of changes in lithology, water content, void spaces in the ground, rebar or post tension cable corrosion, asphalt deterioration or manmade features such as foundations, pipes and cables, storage tanks, graves, etc. The radio wave is transmitted at regular intervals as the GPR unit travels along a survey line. For each transmitted pulse, the resulting reflected energy from the subsurface is recorded and manifested as a single radar trace. These individual traces are stacked side by side as the data is collected to build up a cross-sectional image or profile of the subsurface.
High frequency GPR
High frequency GPR antennas (1000 MHz or greater) are most commonly used for scanning concrete structures to detect the location of embedded structural elements (rebar, post-tensioned cables, beams) and embedded utilities (primarily electrical lines, telecom/security cabling). Maximum penetration depth in concrete is generally in the 12-16” range (30-40 cm) for the 1000 MHz system. If slabs are greater than 16”, scanning from both sides may be necessary or a lower frequency can be utilized.
Applications for High Frequency GPR include:
Cutting and coring applications (safety, object avoidance)
Detecting defects in concrete structures (delamination, cracks, voids, spalling)
Indoor utility detection and mapping
Detecting voids below concrete floors
Medium frequency GPR
Medium frequency GPR antennas (500-250 MHz) generally reach a penetration depth of 40cm-3m. Units within this range are commonly used for subsurface mapping and utility locating. These systems provide the optimal balance between depth of penetration and resolution. Resolution refers to how close interfaces can be to one another and can still be identified as separate interfaces.
Applications for Medium Frequency GPR include:
Subsurface Utility Mapping (SUM)
Low frequency GPR
Low frequency GPR antennas (250 MHz or lower) are generally used for geologic investigations and for finding large structures buried at depths greater than 3m. The targets are either laterally extensive, flat-lying to sub-horizontal reflectors such as bedrock interfaces, stratigraphic horizons or large structures such as industrial process pipes and sewers. The equipment for these types of surveys is modular in nature and can be moved manually in rough terrain or mounted on a cart in smoother terrain.
Applications for Low Frequency GPR include:
Geotechnical applications (underground storage tank (UST) detection)
Deep Subsurface Utility Mapping (SUM)
To learn more about Ground Penetrating Radar (GPR), check out this video from our valued equipment supplier, Sensors & Software:
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