Gpr survey of utica bridges 0412
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Transcript of Gpr survey of utica bridges 0412
Findings from Ground Penetrating Radar Survey
of Bridge Networkin Utica, NY
ARMA International, LLC.3 Computer Drive West
Ste. 102Albany, NY 12205
P & F: (518) 813-9269www.ARMATech.net
Overview of Ground Penetrating Radar (GPR) Methodology Brief background Equipment Steps to results
ASTM Standard
Surveyed Bridges in Utica, NY
GPR Survey Findings
Outline
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
GPR: Brief Background
GPR: Brief Background (Cont’d)
Pulse Wave Form Wide range of frequencies Central frequency has highest amplitude
Frequency
Amplitude
Radiating Energy Squashed cone
GPR: Brief Background (Cont’d)
GPR System Components
• Data captured is processed into images and output is displayed on color monitor
• Transmitter generates EM wave
• Energy reflected is captured by a receiving antenna
• Transmitter and receiver operate as one unit
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
GPR in Layered Systems
How Targets Are “Seen” Concave down parabola Shaped formed due to travel time
GPR for Subsurface Targetsχ1 χ2 χ3 χ4 χ5
χ1 χ2 χ3 χ4 χ5
Material DielectricAir 1
Concrete 6 - 8Asphalt 3 - 5
PVC 3“Average soil" 16
Sand (dry) 3 - 6Sand (wet) 25 - 30Silt (wet) 10Clay (wet) 8 - 15
Clay soil (dry) 3Water (fresh) 81Water (sea) 81
Pure ice 3.2
Dielectric Value and Its Role
Affects Depth of Penetration and Intensity Used to determine depth
K
cv
v = wave propagation speed c = speed of lightK = relative dielectric permittivity
2vts
s = interface depthv = wave propagation speedt = two-way travel time
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
GPR Equipment
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.
1.5’ 3’
12’
1.5’3’ 3’ 1.5’
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
GPR Equipment (Cont’d)
GPR Data Processing and Interpretation Calibration Filtering Processing Interpretation
Steps to Results
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.)
ASTM Standard
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
Surveyed Bridges in Utica, NY
N
Tables Listing Percent Area of Deterioration for Each Span
Deterioration Maps Visualize Location and Extent of Deterioration
GPR Survey Findings
Approach 28%Span 1 36%Span 2 21%Span 3 16%Span 4 14%Overall 21%
Bridge Only 20%
BIN: 100228APercent Area of Deterioration
Span 1 15%Span 2 31%Span 3 28%
Approach 15%Overall 24%
Bridge Only 26%
BIN: 100228BPercent Area of Deterioration
Approach 22%Span 1 24%Span 2 10%Span 3 17%Span 4 24%Span 5 15%Span 6 6%Span 7 36%Span 8 30%Span 9 3%Span 10 16%Span 11 37%Span 12 18%Span 13 22%Span 14 32%Span 15 38%Span 16 35%Span 17 21%Span 18 8%Span 19 13%
Approach 20%Overall 20%
Bridge Only 20%
Percent Area of DeteriorationBIN: 1002281
Approach 22%Span 1 9%Span 2 15%Span 3 11%Span 4 18%Span 5 18%Span 6 24%Span 7 36%Span 8 27%Span 9 43%Span 10 37%Span 11 43%Span 12 38%Span 13 7%Span 14 16%Span 15 9%Span 16 10%Span 17 9%Span 18 26%
Approach 27%Overall 21%
Bridge Only 21%
BIN: 1002282Percent Area of Deterioration
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 Hmm Hmm
GPR Survey Findings (Cont’d)