GPR: Advantages, Methods and Applications
Ground Penetrating Radar (GPR) technology is used throughout many industries to see through man-made and natural materials. GPR can be used to locate metallic and non-metallic pipes, power lines, conduit, water lines, re-bar and post-tension cables inside concrete - Russell NDE System’s primary use of the technology. Often this service is performed prior to construction or renovations within buildings or concrete structures.
Using GPR over other methods has many advantages including:
- Self-contained, quiet operation
- Can detect non-metallic materials
- No health hazards
- Instant results
- Provides depth estimates
- Can see through up to 2-feet of concrete
- Can see pipes below the floor
- Colour map visuals available in varying depth slices
- Provides a permanent record
GPR services are often used by airports, the automotive industry, commercial construction, government, manufacturing industries, military, municipal infrastructure, ports, power plants, refineries, and water treatment plants.
Pulses of radio waves are sent from a transmitter into a material. These radio waves are usually employed at a frequency between 1 and 1000 MHz. Reflections (or echoes) of this energy are deflected from objects within the material and are sent back into a receiving device (antenna). This device measures the strength of the returning signal, and the travel time. When the transmitted pulse contacts a material differing in electrical conductivity or dielectric permittivity a signal reflection is observed. The contrast of the two differing materials determines the strength (or amplitude) of the returning signal. A map is then be created of the features – such as buried utilities and structures beneath the ground or reinforcing bars and conduits within concrete.
The GPR image below is an image taken at a depth of 5 to 6 inches. The top of the re-bar can be seen in the (Side View Scan) portion or depth area, as the top of the white Hyperbolas. The depth is measured in inches up and down the side of the Hyperbola (up to 24 inches). The distance is shown along the top of the hyperbolas (up to 96 inches).
The distance the signal will travel into a scanned material depends on the device and the material the signal is transmitting through. For example, highly dielectric materials (such as glass and plastics) will slow the signal, and highly conductive materials will attenuate the signal quickly. Metals will not allow the signal to pass through, completely reflecting it back to the receiving antenna. In the case of a scan into a soil or concrete profile where a sheet of metal is located a distance beneath the surface, the signal will only penetrate to the depth of where the metal is located. If anything is present beneath the metal sheet, it will not be visible to the device. For example if the bottom of a floor was constructed with a metal Q-deck, the GPR signal would not penetrate through the metal Q-deck material. The features above the Q-deck can be seen but any pipes or features hanging below the floor would have to be examined visually from below.
Russell NDE Systems’ focus is primarily utility locating applications within concrete. There is an electromagnetic detector feature added to the GPR units Russell utilizes, and the combination of the two technologies allows operators to determine if power is surging through conduit lines. This addition can assist in differentiating features from one another.
In the image above, there is an electrical cable at the bottom of the top left quadrant. It appears as a bright yellow colour (picked up with electromagnetic detectors) whereas the reinforcing bars are orange.
GPR can be used in numerous other applications. Assessing concrete structures for reinforcing bars, post-tension cables, and embedded conduits before cutting for repair or renovations is a popular use of the technology. As mentioned previously, GPR is also widely used to locate buried utilities such as cables, pipelines, concrete structures, and plastic objects beneath the ground or within concrete.
GPR can also be used for:
- Detecting voids and concrete homogeneity, slab-on-grade assessment
- Assessing road and bridge structures
- Detecting environmental and natural structures such as sinkholes, soil structures, water tables, salt water infiltration, ground water channels among others
- Measuring ice thickness which is important in areas where ice roads exist for part of the year and arctic oil exploration
- Detecting underground storage tanks, septic systems, contaminant delineation and assisting remediation efforts
Get in touch with us if you would like to know more about the GPR services Russell NDE Systems Inc. offers.