ground penetrating radar gonzolo gallo

8/3/2019 Ground Penetrating Radar Gonzolo Gallo

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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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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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Antennas

Air-coupled

Ground-coupled

Penetradar Corporation



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Vehicular GPRs Single antenna

Multiple antennas

Custom configurations

Penetradar Corporation

GSSI(GeographicalSurvey

Systems, Inc.)$48.000 (includesvehicle, antenna,software and training)



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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.

ground penetrating radar gonzolo gallo

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