TRC1504: Alternative Uses of Ground Penetrating Radar in Highway in Construction and

MaintenanceElisha Wright-Kehner, P.E.

Why GPR?• Practicality• Non-invasive (Non-destructive Testing - NDT)• Real-time results• Continuous data collection• Very fast data collection • Ease of use• Accuracy & Precision• Various levels of resolution and depth• Works with almost every earth material• Progressive advances

Ground-Penetrating RadarGPR is a non-destructive imaging tool that employs electromagnetic (EM) waves.

• Antenna • Console• DMI

• Cables• GPS• Power Source

AHTD EquipmentAir-launched Ground-coupled

• 2010• SIR-30 (4 Ch.)• Upgraded Antennas (2 GHz)• GPS• Highway Speeds• Project & Network Level

• May 2016 - TRC 1504• SIR-4000 (1 Ch.)• 200, 400 MHz • 1.6 GHz• GPS• Walking speeds• Project level

Uses• Pavement thickness• Voids (Air or water-filled)• Concrete cover - Bridge deck thickness*• Rebars, Dowel bars*• Utilities and USTs* (UXOs)• Drains and sewer lines*• Forensics/Cemetery/Burial sites• Concrete/Rebar deterioration/Spalling/Delamination• Changes in pavement density• Bedrock depth/Geotechnical studies• Subsurface/Ground-water contamination• Seepage pathways and sinkholes in levees• Variation in mineral concentrations

In-house ProjectsMay 2016 – Feb 2017

• Utility locating o Broadway Bridge – ROW-Utilities

• Bridge deck thickness & Rebar mat depth (**)o Springdale - BRI

• Dowel bar misalignmento Texarkana – D3

• Pile locating*o LR - SUR

• UST locatingo Hot Springs - ROWo Solgohachia - ENVo Desha - ENV

• Locating septic lineso Hampton – ROW

• Asphalt & Subgrade thicknesso Rogers - SIR

Texarkana• First project with Ground• Faulting slabs on I-30• Dowel bar alignment• 1.6 GHz antenna

Location 1

Location 2

• 6 locations• 1.5 – 2 hours• Satisfactory results

Hot Springs• UST detection• 400 MHz

Broadway Bridge• Utilities• 400 MHz• 350 HS*• 300/800 DF*• 3 months

Broadway Bridge• 7 utilities – 6 not on the plans

Hampton• Sewer Lines• 400 MHz• Calhoun Co Water Lines

Solgohachia

• Historic well• UST/Fuel Iines• Water lines

Desha• USTs• 400 MHz

Springdale• Bridge Deck & Concrete Cover Thickness• First Project using dual systems

o Ground - 1.6 GHzo Air - 2 GHz

Springdale

• 0.38 inches accuracy concrete cover• ~1 inch underestimated deck thickness on average

Rogers• Asphalt and subbase thickness• First Project using ground antenna with air-launched system

o Ground – 400 MHzo Air - 2 GHz

Rogers

Limitations• Water content

o High moisture contento Shallow water table

• Clay• Concrete utilities• Rough terrain (ground-coupled)

o Obstacles• Radio frequencies interference• GPS connection• Resolution and depth of penetration• Metal bridges and elements• Depth is dielectric constant dependent

• TDEMI - SHRP2 Implementation R01B??

Dry Weather – Clean/even Surface – Workable Space

Wikipedia.org

Questions?

A typical GPR survey• Antenna selection – Depth and Resolution

o 200 MHz 15-20 fto 400 MHz 8-10 fto 1.6 GHz 1-2 fto 2 GHz 1-2 ft

• Pre-existing planso Location and extent of utilities/USTs

• Planningo 2Do 3Do Super-3D

• Survey area is always larger than requested!• Assembly 20-30 mins

o 1-2 persons

• Calibrationo Metal plateso Dielectric measurements

• Cores/Ground-truth data• Data processing & Interpretation

Dep

th

Distance

Tim

e

Discontinuities

Dep

th

Distance

Tim

e

Utility Lines

Distance

Tim

e

Dep

th

Utility Lines…

Ground-Penetrating Radar (GPR)

0

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11 11 21 31 41 51 61 71 81

Rel

. Vel

ocity

(m/n

s)Dielectric Constant

Velocity(m/ns)0

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11 11 21 31 41 51 61 71 81

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ocity

Dielectric Constant

Ground-Penetrating Radar (GPR)

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Dielectric Constant

Velocity of EM wave relative to Speed of Light

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11 11 21 31 41 51 61 71 81

Velo

city

Dielectric constant

Velocity(ft/ns)

GPR Theory

EM properties of materials 1. Dielectric Constant, ε2. Electrical Conductivity, σ3. Magnetic Permeability, µ

𝐴𝐴 = 𝐴𝐴0𝑒𝑒−𝛼𝛼𝛼𝛼

R = 𝜀𝜀2− 𝜀𝜀1𝜀𝜀2+ 𝜀𝜀1

υ =𝑐𝑐𝜀𝜀𝑟𝑟

c = 983,571,056 (ft/sec)

GPR Theory

Water content ε σ

Frequency Resolution Frequency Depth

Material Dielectric ConstantSand (dry) 3 - 6Sand (saturated) 20 - 30Silts 5 - 30Shales 5 - 15Clays 5 - 40Humid soil 30Cultivated soil 15Rocky soil 7Sandy soil (dry) 3Sandy soil (saturated) 19Clayey soil (dry) 2Clayey soil (saturated) 15Sandstone (saturated) 6Limestone (dry) 7Limestone (saturated) 4 - 8Basalt (saturated) 8Granite (dry) 5Granite (saturated) 7

Dep

th

Distance

Tim

e

Layered Medium

Dep

th

Distance

Tim

e

Discontinuities

Dep

th

Distance

Tim

e

Utility Lines

Distance

Tim

e

Dep

th

Utility Lines…

Data Collection Practices2D 3D

3D Super-3D

ε1

ε2

ε1

ε2 ε2ε1

ε2

ε1

ε2 ε2

ε1

ε2ε1

ε2 ε2

ε3

ε1

ε2

ε1

ε2

ε1

ε2

Distance

Tim

e

Dep

th

Utility Lines…

Transmitter Receiver

ε1 σ1 µ1

ε2 σ2 µ2

Tim

e

Amplitude

Transmitted Wave

Reflected Wave

GPR Theory

0

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1

1.5

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2.5

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1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81

Wav

elen

gth

(ft)

Dielectric Constant

Wavelength vs Dielectric Constant

200 MHz

400 MHz

1.6 GHz

2 GHz

GPR Theory

0

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Wav

elen

gth

(ft)

Dielectric Constant

900 MHz

1000 MHz

1.6 GHz

2 GHz

0

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Velo

city

(ft/n

s)

Dielectric constantAir Water

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Wav

elen

gth

(ft)

Dielectric Constant

100 MHz

200 MHz

400 MHz

Water Content ε σ

Frequency Resolution

Frequency Depth

GPR Theory

Water Content ε σ

Frequency Resolution

Frequency Depth

Material Dielectric ConstantSand (dry) 3 - 6Sand (saturated) 20 - 30Silts 5 - 30Shales 5 - 15Clays 5 - 40Humid soil 30Cultivated soil 15Rocky soil 7Sandy soil (dry) 3Sandy soil (saturated) 19Clayey soil (dry) 2Clayey soil (saturated) 15Sandstone (saturated) 6Limestone (dry) 7Limestone (saturated) 4 - 8Basalt (saturated) 8Granite (dry) 5Granite (saturated) 7

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 11 21 31 41 51 61 71 81

Wav

elen

gth

(ft)

Dielectric Constant

200 MHz

400 MHz

1.6 GHz

2 GHz

00.10.20.30.40.50.60.70.80.9

1

1 11 21 31 41 51 61 71 81

Velo

city

(ft/n

s)

Dielectric constant

Velocity(ft/ns)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81

Wav

elen

gth

(ft)

Dielectric Constant

200 MHz

400 MHz

1.6 GHz

2 GHz

Air Water

GPR Theory

Water Content ε σ

Frequency Resolution

Frequency Depth

Material Dielectric ConstantSand (dry) 3 - 6Sand (saturated) 20 - 30Silts 5 - 30Shales 5 - 15Clays 5 - 40Humid soil 30Cultivated soil 15Rocky soil 7Sandy soil (dry) 3Sandy soil (saturated) 19Clayey soil (dry) 2Clayey soil (saturated) 15Sandstone (saturated) 6Limestone (dry) 7Limestone (saturated) 4 - 8Basalt (saturated) 8Granite (dry) 5Granite (saturated) 7

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 11 21 31 41 51 61 71 81

Wav

elen

gth

(ft)

Dielectric Constant

200 MHz

400 MHz

1.6 GHz

2 GHz

00.10.20.30.40.50.60.70.80.9

1

1 11 21 31 41 51 61 71 81

Velo

city

(ft/n

s)

Dielectric constant

Velocity(ft/ns)