Use of Ground Penetrating Radar to Review MN Roads

Marc LokenMarc Loken

Office of Materials and Road Office of Materials and Road ResearchResearch

Tel: 651-779-5526Tel: 651-779-5526

Marc.loken@dot.state.mn.usMarc.loken@dot.state.mn.us

Minnesota Department of Minnesota Department of TransportationTransportation

Mn/DOTOffice of Materials and Road Research

Outline

Applications of GPRApplications of GPR Basic Principles of GPRBasic Principles of GPR MnDOT GPR EquipmentMnDOT GPR Equipment Current ProjectsCurrent Projects Future ProjectsFuture Projects ConclusionsConclusions

• Determine pavement thickness

• Calculate material properties

• Detect subsurface anomalies

• Determine depth to bedrock

• Detect stripping and/or layer separation

• Analyze rutting mechanisms

• Detect subsurface moisture and/or freezing

Applications of GPR

Basic Principles of GPR

Typical Data Scan

Material Characterization Dielectric Constant

The dielectric constant of a material is its ability to store electrical energy

Dielectric Constants of Some Common Materials

MaterialMaterial εεii

AirAir 1.01.0

AsphaltAsphalt 3-53-5

ConcreteConcrete 4-114-11

GraniteGranite 4-74-7

ShaleShale 5-155-15

WaterWater 8181

MetalMetal InfinityInfinity

Dielectric Constant Calculation

1= [(1+ρ1)/(1- ρ1)]2

 where: 1= dielectric constant of surface layer

1 = A1 / Am

 A1 = amplitude of the surface

reflection from the surface layer  Am = amplitude of the surface

reflection from metal sheet

Calculation of Layer Thickness2*h1 = c t1 / 1

 

where: h1 = thickness of 1st layer

  c = speed of radar in air

= 11.8 in/ns 

t1 = time required to transmit signal

through 1st layer

MnDOT GPR Equipment Data Collection SystemsData Collection Systems

SIR 2000SIR 2000 SIR 020SIR 020

AntennaAntenna 100 MHz (5 to 20 ft depth)100 MHz (5 to 20 ft depth) 400 MHz (2 to 10 ft depth)400 MHz (2 to 10 ft depth) 1 GHz (Air-Coupled) (0 to 4 ft depth)1 GHz (Air-Coupled) (0 to 4 ft depth) 1.5 GHz (0 to 3 ft depth)1.5 GHz (0 to 3 ft depth)

Post-Processing SoftwarePost-Processing Software RADAN NTRADAN NT RoadDoctor (tenatative)RoadDoctor (tenatative)

Equipment – SIR 020

Equipment – Van & Antenna

Current Projects

MnROAD – Calibration, Rutting, Layer Thickness, MnROAD – Calibration, Rutting, Layer Thickness, Material IdentificationMaterial Identification

Olmsted CR 117 – Ground Truth Measurements, Layer Olmsted CR 117 – Ground Truth Measurements, Layer ThicknessThickness

TH 212 – Subsurface Cracks, Pavement Layer TH 212 – Subsurface Cracks, Pavement Layer IdentificationIdentification

TH 22 – Evaluate Pavement Thickness, Road StructureTH 22 – Evaluate Pavement Thickness, Road Structure TH 7 – Stripping Layers and Interface SeparationTH 7 – Stripping Layers and Interface Separation

MnROAD

ObjectivesObjectives CalibrationCalibration Layer ThicknessLayer Thickness Material IdentificationMaterial Identification

Pavement StructurePavement Structure Cells 33-35Cells 33-35

4” Asphalt4” Asphalt 12” Class 612” Class 6

Cell 36Cell 36 6 1/4” Concrete6 1/4” Concrete 5” Class 55” Class 5

MnROAD -- Calibration

MnROAD -- Calibration

Cell 33

MnROAD – Layer Thickness

Cell 34

MnROAD – Material ID

Cell 36

Olmsted CR 117

ObjectivesObjectives Ground Truth MeasurementsGround Truth Measurements Layer ThicknessLayer Thickness

Pavement StructurePavement Structure 6” Asphalt6” Asphalt 12” Class 512” Class 5

Olmsted CR 117

Olmsted CR 117 – Ground Truth Measurements

Olmsted CR 117 – Layer Thickness

Station 130+00

TH 212

ObjectivesObjectives Subsurface CracksSubsurface Cracks Pavement Layer IdentificationPavement Layer Identification

Pavement StructurePavement Structure 9-10” Asphalt9-10” Asphalt 13-14” Gravel Base13-14” Gravel Base Concrete or Clay Loam SubgradeConcrete or Clay Loam Subgrade

TH 212 – Subsurface Cracks

Mile 118.4

TH 212 – Clay Loam

Mile 118.0

TH 212 – Concrete

Mile 118.4

TH 22

ObjectivesObjectives Pavement ThicknessPavement Thickness Road StructureRoad Structure

Pavement Structure Pavement Structure 3-6” Asphalt3-6” Asphalt Concrete or Gravel BaseConcrete or Gravel Base

TH 22 – Pavement Thickness

Greeley Ave

TH 22 – Material Identification

Ford Ave

TH 7

ObjectivesObjectives Stripping LayersStripping Layers Interface SeparationInterface Separation

Pavement StructurePavement Structure 10-12” Asphalt10-12” Asphalt 12-36” Gravel12-36” Gravel

TH 7 – Interface Separation

Mile 152.6

Future Projects

MnROAD (Rutting Mechanisms)MnROAD (Rutting Mechanisms) Pine Co. (Stripping and Overlay History)Pine Co. (Stripping and Overlay History) St. Louis County (Depth to Bedrock)St. Louis County (Depth to Bedrock) TH 55 (Fault Plane Survey)TH 55 (Fault Plane Survey) Interstate Park (Potholes in Bedrock)Interstate Park (Potholes in Bedrock)

Conclusions

GPR is nondestructive field test used to GPR is nondestructive field test used to determine road structuredetermine road structure

GPR utilizes high-speed data collection at GPR utilizes high-speed data collection at speeds up to 50 mph speeds up to 50 mph

Gives a continuous subsurface Gives a continuous subsurface descriptiondescription

GPR can be used to identify subsurface GPR can be used to identify subsurface structures up to 20 ft in depthstructures up to 20 ft in depth