Techniques
Ground Penetrating Radar (GPR)
The Operating Principles of Ground Penetrating Radar
GPR works on almost the same principles as sonar sounding, but instead of sonar signals, the GPR antenna (T) sends electromagnetic pulses to the ground, road or water on UHF and VHF frequencies, which travel through the medium with a velocity which is dependent on the dielectric properties of the material.
Parts of the wave energy are reflected from the interfaces between layers containing different electric properties and are registered by the receiving antenna (R) as voltage amplitude in relation to time.
The pulse radar transmits 50 000 - 400 000 pulses per second, from which a special sampler in hardware in the receiver generates a required number of scans. As the process is repeated from by moving radar, a longitudinal profile image based on up to 200 scans per second is obtained from the material in question.
The radar pulse travels from the transmitting antenna to the receiving antenna, first as an air-borne signal and then as reflections from medium interfaces.
Applications
GPR techniques have proved to be particularly effective in the following road research applications:
Subgrade soil research
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layer thickness of subgrade soils
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depth of bedrock surface and the type of bedrock
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frost susceptibility of subgrade soils
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subgrade soil moisture
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subgrade soil stability
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location of caves, cables, pipelines etc.
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erosion surveys around bridge piers
Pavement structure surveys
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thickness of the base course
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quality of the base course
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other layers in pavement structure, thickness measurements
Pavement research
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pavement thickness
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pavement damages
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void content
Bridge surveys
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condition of protective concrete and water sealing
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condition of the bridge deck
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location of reinforcements
The most demanding aspect of GPR surveys is the interpretation of the results.
Although semiautomatic interpretation software is becoming common in pavement structure research, the value and usability of the measurement results still depends on the skill and competence of the interpreter. Sufficient training of personnel conducting GPR measurements and utilising the results is a prerequisite for assured effectiveness and quality of any GPR project.
Information about GPR training courses provided by Roadscanners can be found on the page entitled Training
