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Gpr survey of utica bridges 0412
1. Findings from
Ground Penetrating Radar Survey
of Bridge Network
in Utica, NY
ARMA International, LLC.
3 Computer Drive West
Ste. 102
Albany, NY 12205
P & F: (518) 813-9269
www.ARMATech.net
2. Outline
Overview of Ground Penetrating Radar (GPR) Methodology
Brief background
Equipment
Steps to results
ASTM Standard
Surveyed Bridges in Utica, NY
GPR Survey Findings
3. GPR: Brief Background
GPR occupies this range of frequencies in
the electromagnetic spectrum
The radiation emitted from a GPR antenna consists of
a broad band of frequencies with a central frequency
that designates what application it is intended for
Frequency determines the range of penetration and
level of resolution
The results generated are based on the dielectric
properties of the material along with other factors
4. GPR: Brief Background (Cont’d)
Pulse Wave Form
Wide range of frequencies
Central frequency has highest amplitude
Amplitude
Frequency
6. GPR System Components
• Transmitter generates
EM wave
• Energy reflected is
captured by a receiving
antenna
• Transmitter and receiver
operate as one unit
• Data captured is processed into images and output is displayed
on color monitor
7. GPR in Layered Systems
The reflection of electromagnetic waves forms a stratigraphy of layers due to
the change in material as the antenna passes along the surface
Position and depth information is found by reading distance traveled along the
line of scan, the travel time of transmission and reflection, and the strength of
the reflected signal
8. GPR for Subsurface Targets
χ1 χ2 χ3 χ4 χ5
χ1 χ2 χ3 χ4 χ5
How Targets Are “Seen”
Concave down parabola
Shaped formed due to travel time
9. Dielectric Value and Its Role
Affects Depth of Penetration and Intensity
Used to determine depth
Material Dielectric
Air 1
Concrete 6-8
c v = wave propagation speed
Asphalt 3-5
v c = speed of light
PVC 3
K K = relative dielectric permittivity
“Average soil" 16
s = interface depth Sand (dry) 3-6
s vt v = wave propagation speed Sand (wet) 25 - 30
2 t = two-way travel time Silt (wet) 10
Clay (wet) 8 - 15
Clay soil (dry) 3
Water (fresh) 81
Water (sea) 81
Pure ice 3.2
10. GPR Equipment
GPR Antenna Types: Air-Coupled and Ground-Coupled
Air-Coupled
Mounted above ground
Fast surveys, about 55 mph
Penetration about 1 meter or less
Low resolution
Ground-Coupled
Maintain ground contact
Slower survey speeds, <10 mph
Penetration ranges from 0.5 m to 25 m
High resolution
11. GPR Equipment (Cont’d)
High Speed Surveys
Performed at posted speeds
Utilize air-horn antennas
Typical data collection rates: 6 scans/ft., 3 ft. spacing between survey
passes
Depth of penetration: approximately 3 ft.
12’
1.5’ 3’ 3’ 3’ 1.5’1.5’
12. GPR Equipment (Cont’d)
Support and Safety
Position and distance measurement
Wheel mounted distance measuring instrument (DMI)
Camera on extending pole provides lane positioning
Safety lights
Strobe and rotating beacons
Arrow board
13. Steps to Results
GPR Data Processing and Interpretation
Calibration
Filtering
Processing
Interpretation
14. ASTM Standard
ASTM D6807-07 entitled “Standard Test Method for Evaluating
Asphalt-Covered Concrete Bridge Decks Using Ground
Penetrating Radar.”
Provides guidance on what type of survey to be used for different
applications
Equipment configuration
Guidance on establishment of threshold to be used as the point
between suspected deterioration and “good” subsurface condition
Provides methods to bring GPR results from a statistical result to real-
world condition through the use of supplemental methods (e.g. cores,
hammer sounding, etc.)
15. Surveyed Bridges in Utica, NY
Small Network
All bridges have bare concrete deck
BIN: 1002281, Carries Rt. 5 Southbound crossing Rt. 5S, 19
spans, 31,702 sq. ft. surveyed
BIN: 1002282, Carries Rt. 5 Northbound crossing Rt. 5S, 18
spans, 31,856 sq. ft. surveyed
BIN: 100228A, On-ramp for Rt. 5 Southbound from Rt. 5S
Westbound, 4 spans, 3,917 sq. ft. surveyed
BIN: 100228B, Off-ramp from Rt. 5 Northbound to Rt. 5S
Westbound, 3 spans, 3,005 sq. ft. surveyed
N
17. GPR Survey Findings (Cont’d)
Wide Variation in Condition
Spans with both localized and large areas or deterioration
Low, medium, and high degrees of deterioration
Small, medium, and large percent areas of deterioration on spans for
each bridge
Overall bridge condition does not really represent the condition
present on spans
Results Focus on Trouble Areas
The maps can guide rehabilitation and repair strategies
Other findings
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