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)