1. Basic Ground Penetrating Radar Theory

2. GPR LIMITATIONS
Penetration depth and ability to resolve targets at depth is strongly dependent upon the local soil properties. Highly conductive soils can render the GPR method ineffective.
There must be a sufficient electrical contrast between the target and the host materials
Interpretation of GPR data can be subjective The experience of the interpreter is very important.

3. Penetration depths 25 25 40 Antenna (MHz) In soil (m) In rock (m)
Average penetration depths of radar signals in high resistivity geological environment absent of low resistive layers.

4. D E P T H 1 2 3 4 5 6
Deep utilities must have larger diameters than shallow utilities in order to be detected with GPR
Deep utilities must have larger diameters than shallow utilities in order to be detected with GPR

5. The GPR technique
GPR is an electromagnetic method that detects interfaces between subsurface materials with differing dielectric constants. Your Easy Locator GPR system basically consists of:
An antenna, which houses a transmitter and receiver.
A monitor, which processes the received signal and produces a graphic display of the data.
The transmitter radiates repetitive short-duration electromagnetic signals into the earth from the antenna moving across the ground surface. Electromagnetic waves are reflected back to the receiver by interfaces between materials with differing dielectric constants.
GPR wave propagation from transmitter (Tx) and reflection to the receiver (Rx).

6. How GPR works GPR is, in principal, similar to sonar
equipment (fish finders) found in boats
The transmitter emits a “train” of
electromagnetic impulses which
propagate through the media
Reflection (i.e. scattering) occurs where
the electrical properties of subsurface
materials change
The receiver picks up the “back-scattered”
signal and displays it on a monitor

7. ? GPR signatures Time [ns] Depth [m] Length [m]
The basic principle of reflection measurements. While the GPR unit is moved along the surface, reflections are achieved from underground structures, in theis case a geological boundary and a pipe. The reflections from the pipe form a hyperbolic signature in the diagram.
The GPR method detecs metallic as well as non-metallic objects.

8. Data Examples & Interpretation

9. GPR APPLICATIONS CIVIL/STRUCTURAL ENGINEERING
Utilities (pipes, cables), rebar and voids. Pre-studies for Horizontal Directional Drilling (HDD)
Transportation: Roadways and railroad tracks, ice thickness,
bridge deck and bridge fundation studies.
ENVIRONMENTAL
Hazardous waste mapping, underground storage tanks (UST),
Sedimentology studies, Bathymetry.
GEOTECHNICAL
Stratigraphic mapping, cavities and sinkholes, groundwater, mining hazards, fracture detection, Earth dam studies, foundation studies, tunnel investigations.
MILITARY
Ordinance detection, runway integrity, clearing of trenching routes
ARCHAEOLOGY
site mapping, grave detection, artifacts

10. The most important markets for radar…
Utility detection
Pipe and culvert inspections
Concrete and NDT
Road and bridge deck investigations
Geological mapping
Ice, snow and glacier
Borehole radar

11. The difference in radargram between good and bad soil conditions
The GPR performance
GPR is primarily affected by the conductivity and dielectric permittivity of the mediums.
GPR works best in resistive, sandy or gravely soil types. Difficult, conductive types are typically composed of silts and clays or contains salt water.
Depth of investigation is limited by signal attenuation of conductive soil but also dependent on the antenna selected.
The difference in radargram between good and bad soil conditions

12. Comparison between the SHALLOW and MID antenna.
Electrical Conduits
Shallow antenna
Unknown
Comparison between the SHALLOW and MID antenna.
Water Main
Force Main
Electrical Conduits
Unknown
Mid antenna
Water Main
Force Main

13. Interpretation:
Metallic water pipes shows sharper
Sewer line is large enough to show both top/bottom reflection
Note radiuses of the signatures
Trench shows

14. Thank you!