high-speed nondestructive testing methods for mapping ... · •detection and characterization of...

High-Speed Nondestructive Testing

Methods for Mapping Voids, Debonding,

Delaminations, Moisture, and Other

Defects Behind or Within Tunnel Linings

SHRP2 R06(G)

IBTTA Facilities Management and Maintenance Workshop

Nashville, Tennessee

Texas A&M/TTI - Andrew Wimsatt, Tom Scullion, Stefan

Hurlebaus, Dan Zollinger

University of Texas at Austin - Fulvio Tonon

German Federal Institute for Materials Research and

Testing (BAM) -Parisa Shokouhi, Herbert Wiggenhauser

University of Texas at El Paso – Soheil Nazarian

Roadscanners - Timo Saarenketo

IBTTA Facilities Management and Maintenance Workshop

Nashville, Tennessee

• Tunnels service high traffic volumes and operate in

aggressive environments

• Timely detection and remediation of problems requires

periodic inspection to assess structural condition over time

• Condition and deterioration rate is key to determining the

appropriate schedule of maintenance and/or rehabilitation

• Keeping tunnels open during inspection is an issue

• Minimize tunnel closures and user delays

• Must balance need to conduct detailed inspections to

ensure user safety

• Objective of investigation - the identification and review of

NDT methods for conditions assessment of tunnel linings

• Applicability, advantages and limitations of the

investigated methods

Introduction

Content

• Laser Scanning: SPACETEC Tunnel Scanner

• Thermal Camera (IR Camera) Systems

• Ultrasonic Linear Array (MIRA)

• Digital Photogrammetry

• Ground Penetrating Radar (GPR)

• Impulse Response (IR) and Impact Echo (IE)

• Ultrasonic Surface Waves (USW)

• Percometer Dielectric Probe Technique

• Concrete Surface Resistivity Testing

• Ultrasound

• Structural Health Monitoring

Applications • Document condition at delivery of new construction

• Survey tunnel prior to reconstruction or renovation measures

• Check tunnel clearance before electrification, the use of new vehicles,

or before the transport of excessive loads

• Conduct regular inspections for the early identification of damage and

for planning repairs

• Allow for detailed data analyses with thermographic recordings or crack

charting

Laser Scanning:

SPACETEC Tunnel Scanner

[http://www.spacetec.de]

Advantages

• High-speed collection

• Analysis of data from three different, simultaneous

measurements

• Delivers high resolution images

• 360° coverage

Limitations

• Cost

• Size

Laser Scanning:

SPACETEC Tunnel Scanner

Imaging Systems (Spacetec)

Spacetec

• Profile recordings - Critical points are

displayed on the screen, where they can

be localized and the areas and volumes

can be computed.

• Visual recordings are needed mainly for

routine checks and for documenting the

tunnel surface. The scaled data allows

lengths, areas, and volumes to be

determined accurately

Spacetec

• Thermographic recordings give indications

of structural damage that is not visible to

the naked eye, for instance water, cavities,

or fluctuations in density in the tunnel

lining.

• SPACETEC also carries out special and

customized data analyses, for instance

crack charting or detailed interpretation of

thermographic recordings.

Examples of Costs

• Germany – Scanning 2 tunnel sections

(each 1 km long), including thermography

measurements, data pre-processing and

analysis costs about €30,000. Cost per

tunnel-km is then €15,000.

• Testing 100 tunnels in Europe, together

about 100 km long, requiring 3 weeks of

measurement, including data pre-

processing and analysis costs €250,000.

Cost per tunnel-km is then only €2,500.

Speed

• As high as about 100 km/hr for coarse

measurement needs

• As low as 2 km/hr for very detailed

investigations.

• The typical measurement speed is usually

in between these two extremes (~5 km/h).

• Chesapeake Bay Tunnel ~ 2 km/h

Resolution Examples

Low Speed High Speed

Data collected in Chesapeake Tunnel, VA, USA, April 11, 2011

Inspection vehicle

Data collected in Chesapeake Tunnel, VA, USA, 11.4.2011

Visual Image


IR Image


Visual and IR Image


Detail

Ceiling

Niche for Fire Extinguisher

Railing Area of Concern

Vent in Ceiling

Area of Concern

Construction Joint

Applications

• Locate voids under roadway surfaces

• Detect distress in concrete and asphalt pavements

• Detect moisture inside or under AC pavements

• Aid in quality control/assurance of asphalt pavements

• Monitor areas affected by freeze-thaw weakening

Thermal Camera (IR Camera) Systems

Advantages

• Best used along with air-coupled GPR on fast moving vehicle

• Quickly covers wide areas

• Easy to interpret results and quickly make maps

• System can be used in other road and bridge surveys

• Associated cost is relatively low.

Limitations

• Dust may interfere with readings

Thermal Camera (IR Camera) Systems

Digital Photogrammetry

Applications

• Monitor deformations along tunnel linings

• Determine fracture trace lengths

• Condition assessment and inspection

• Aggregate characterization

Capture

Images

Determine

Camera

Orientations

Generate

DTMs

Analyze data:

calculate volumes,

digitize vector data,

etc.

Advantages

• Measurement speed

• Low cost

• Easy to transport equipment; small and lightweight cameras

• 3D modeling

• Offers 100% coverage

• No need for specially trained personnel

Digital Photogrammetry

Limitations

• Collects data for objects within a straight line-of-sight,

meaning pictures must be taken from multiple vantage points

to avoid possible obstacles

• Measurements can be influenced by air temperature and

pressure, requiring corrections for atmospheric effects

Applications

• Detection and characterization of cavities, flaws, cracks,

honeycombing, and grouting defects in or behind tunnel lining

• Locate tendon ducts and reinforcement bars within concrete

• Measure concrete member thickness

• Assess the quality of crack repairs

Ultrasonic Linear Array (MIRA)

U

Advantages

• Dry-point contact

• Real-time 2D imaging

• Applicability on rough surfaces

• See beyond reinforcement

• Fast data collection

• Capable for automatic areal coverage

Limitations

• Testing requires physical contact with surface

• Limits collection speed (even when mounted on scanner)

• Test object cannot be less than 50mm thick

• Shallow defects at depths less than 50 mm cannot not be

detected

Ultrasonic Linear Array (MIRA)

23 mm from surface

64 mm from surface

78 mm from surface

80 mm from surface

103 mm from surface

127 mm from surface

131 mm from surface

148 mm from surface

150 mm from surface

167 mm from surface

Ground Penetrating Radar (GPR) –

Ground-Coupled Systems

Applications

• Measure concrete wall thickness

• Detect voids between concrete and test grouting

• Identify water leakage and movement behind linings and

pavements

• Detect cables and pipes

Advantages

• Good penetration depth

• Ability to map areas with high moisture content

• Calculate area of risk for corrosion

Limitations

• Low measurement speed

• Lengthy data processing

• Not for use when tunnel is made of steel reinforced shotcrete


Ground-Coupled Systems

Ground Penetrating Radar

Applications

• Pavement evaluation and forensic investigations

• Could be possibly used for routine monitoring of tunnel walls

and roofs to find changes in electrical properties that indicate

potential problems


Air-Coupled Systems

GPR Horn Antenna Systems for TunnelSurveys

Advantages

• Surveys can be done from a relatively fast moving vehicle

• Measurements are accurate and repeatable

• Analysis works wells along with thermal cameras

• System is well suited for routine monitoring of tunnel walls

and roofs

Limitations

• Sensitive to variation in antenna-to-wall distance

• Sensitive to external radiation (such as cell phone stations)

• Less penetration depth than ground coupled GPR

• Not for use when tunnel is made of steel reinforced shotcrete


Air-Coupled Systems

Air Coupled Ground Penetrating

Radar

Air Coupled GPR Antenna Data

Ultrasound

Applications

• Correlate material strength to standard strength

• Determine thickness of tunnel lining

• Locate cracks, voids, deteriorations

[Taffe and Gehlen, 2008]

Ultrasound

Advantages

• Conventional ultrasonic equipment is readily available

• Fairly inexpensive

• Offers 100% coverage

• Allows for continuous monitoring

Limitations

• Conventional equipment must be in contact with object

• Some issues in the past with poor repeatability and/or

consistency

• Long waits between scan locations due to reinstallation of

transducers

Impulse Response (IR) and

Impact Echo (IE)

Applications

• Detect delamination of linings

• Detect voids behind linings

• Determine thickness of tunnel linings

Advantages

• Results obtained onsite

• Results determined quickly (≤1 minute)

Impulse Response (IR) and

Impact Echo (IE)

Limitations

• Testing is discrete (pointwise)

• Not feasible for rapid, 100% coverage testing

• Cannot provide properties of deeper layers if cosmetic layer

is not fully bonded

Applications

• Measure modulus and strength concrete

• Estimate condition of concrete

• Detect delamination, debonding and loss of strength due to

internal cracking of concrete

Ultrasonic Surface Waves (USW or SASW)

[Nazarian et al., 2006]

Ultrasonic Surface Waves (USW)

Advantages

• Reduces number of destructive tests required

• Results determined quickly (≤1 minute)

• Provides qualitative variation of modulus with depth

• Moisture has small impact on results (ideal for tunnels)

Limitations

• Testing is discrete (pointwise)

• Not feasible for rapid, 100% coverage testing

• Cannot provide properties of layers beyond debonded layers

Applications

• Detect free moisture in concrete walls (directly or through tiles)

• Determine dielectric permittivity of asphalt surfaces

Percometer Dielectric Probe Technique

[Scullion and Saarenketo, 1997]

Percometer Dielectric Probe Technique

Advantages

• Surface, concave and tube probes for multiple applications

• Easy to use

• Fast results

Limitations

• Point measurement

• Surface probes require relatively flat surfaces for reliable

results

• May not work on shotcrete concrete

Dielectric Probe

Dielectric Mapping

Concrete Surface Resistivity Testing

Applications

• Resistivity measurements may give indication of corrosion

• Estimate rate of corrosion

• Assess permeability

Advantages

• Generally good correlation between surface resistivity and

corrosion potential

Limitations

• May not be able to measure resistivity accurately on

concrete surfaces due to affect of carbonation on surface

resistance

• Slow and point specific

• 60+ seconds per test location

Concrete Surface Resistivity Testing

Scanning Systems

Applications

• Allows autonomous damage detection

• Monitor strain of tunnel lining, changes in tilt angles

• Monitor environmental parameters (temperature and humidity)

Structural Health Monitoring

Alternative branches

Used tree branches

Base

Level 1

Level 2

Structural Health Monitoring

Advantages

• Continuous inspection, as opposed to scheduled inspection

• Autonomous

• No lane closures required

• Fairly inexpensive equipment allows for permanent

installation

Limitations

• Sensors require power

Note – this technology will not be field tested under

SHRP2R06G

Conclusions

• Reviewed and evaluated different nondestructive

testing methods for tunnel inspection

• To minimize traffic disruption, it is necessary to use

NDT techniques for high-speed testing of tunnel linings

• Good, high-speed options

• SPACETEC scanner

• combined use of thermal cameras with air-coupled

GPR

• With consistent advancement of NDT, current methods

will continue to improve and new methods will continue

to be developed to aid in tunnel inspections

high-speed nondestructive testing methods for mapping ... · •detection and characterization of...

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