ground penetrating radar gonzolo gallo
TRANSCRIPT
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Ground Penetrating Radar
Gonzalo Gallo
CEE 498KM
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Outline
Introduction
Principle
Instrumentation Data Analysis
Advantages and Limitations
Manufacturers and costs
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Introduction
RADAR Radio Detection and Ranging
Detect target in free space
Determine the range
Civil engineering applications
Probing into soil to detect pipelines and tanks
Cavities
Thickness determination Locating reinforcement
Identifying deterioration
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Principle
An EM pulse is sentthrough an antenna,penetrating into the
surveyed material A portion of the energy isreflected back to theantenna when aninterface between
materials of dissimilardielectric constants isencountered
http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf
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Principle
The reflected signal hasinformation on: how quickly the signal
traveled
how much was attenuated
These quantities dependon spatial configurationand materials
The thickness of a layeris given by:
where di is the thicknessof layeri, ti the total
travel time through thatlayer, C is the speed oflight and r,i the dielectricconstant of the layer
ir
i
i
Ct
d,
2 I!
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Principle
The amount ofreflected energy at aninterface is governed
by:
where 1,2 is the
reflection coefficientand r1 and r2 are thedielectric constants
21
21
2,1
rr
rr
II
IIV
!
Material Dielectric
Constant
Air 1
Water 81
Concrete 6-12
HMA 4-7Ice 1.5
Metals
Typical Dielectric Constants
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Instrumentation
The typical instrumentation for GPRincludes the following:
Antenna Air-couple Ground-coupled
Control Unit
Display device Storage device
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http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf
Instrumentation
http://georadar.ids-spa.it/images/new/gpr_products/antennas.gif
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Instrumentation
Another configurationis a portablearrangement
Small, hand-helddipole antenna
Used for locatingrebar, embedments,voids, and otherabnormalities
2.4lbs 10penetration
http://www.ndtjames.com/catalog/rebarLocators/datascanMKII.html
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Data Analysis
Before using calibrate
Copper plate Complete reflection
Air Complete transmission
Establish dielectric constant of test surfacewith reflected energy equation
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Advantages and Limitations
Advantages Fast speed scanning with
non-contact antennas
Very sensitive to presence
of embedded metal objects Sensitive to the presence
of moisture
In general, fast scanningand saves money
Limitations Rebar reflects as arch
patterns if dense,individual bars are no
longer discerned Limitations if dielectricproperties are similar
Dielectric propertiesunknown
Material loss
Difficult in thin layers Extensive data
Operator dependant
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Manufacturers and costs
Hand-held
Datascan MKII James Instruments ND
$12.000 IRIS systems
Penetradar
GSSI handy-scan
$6.500 b&w $10.000 color
http://ndtdirect.com/shop/products.asp?viewall=1&stritem=CN-JA-RB1,CN-JA-RB2,CN-JA-RB3&keyword=Concrete&id1=44&id2=136
http://www.penetradar.com/GPR_Vehicles.htm
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Manufacturers and costs
Antennas
Air-coupled
Ground-coupled
Penetradar Corporation
http://www.penetradar.com/GPR_Vehicles.htm
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Manufacturers and costs
Vehicular GPRs Single antenna
Multiple antennas
Custom configurations
Penetradar Corporation
GSSI(GeographicalSurvey
Systems, Inc.)$48.000 (includesvehicle, antenna,software and training)
http://www.penetradar.com/GPR_Vehicles.htm
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Links and References
http://www.geophysical.com/
http://www.penetradar.com/
http://ndtdirect.com/
http://www.ndtjames.com/ http://www.cait.rutgers.edu/finalreports/GPR-RU4474.pdf Al-Qadi, I.L. and Lahouar (2005). Measuring layer
thickness with GPR Theory to practice. Constructionand Building Materials, 19, 763-772
ACI Committee 228, (2003). In-place methods toestimate concrete strength (ACI228.1R-03).Farmington Hills: American Concrete Institute.