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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)
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
Data collected in Chesapeake Tunnel, VA, USA, 11.4.2011
IR Image
Data collected in Chesapeake Tunnel, VA, USA, 11.4.2011
Visual and IR Image
Data collected in Chesapeake Tunnel, VA, USA, 11.4.2011
Detail
Data collected in Chesapeake Tunnel, VA, USA, 11.4.2011
Detail
Data collected in Chesapeake Tunnel, VA, USA, 11.4.2011
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 Penetrating Radar (GPR) –
Ground-Coupled Systems
Ground Penetrating Radar
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
Ground Penetrating Radar (GPR) –
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
Ground Penetrating Radar (GPR) –
Air-Coupled Systems
Air Coupled Ground Penetrating
Radar
Air Coupled GPR Antenna Data
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
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
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