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1This report documents the work conducted under Phase 2 of Strategic Highway Research Pro- gram (SHRP 2) Renewal Project R06G. Renewal Project R06G seeks dependable nondestructive testing (NDT) techniques that minimize disruption to traffic. The objectives of the proposed research are as follows: ⢠Identify NDT technologies for evaluating the condition (e.g., moisture, voids, and corrosion) of various types of tunnel linings (e.g., unreinforced concrete, reinforced concrete, shotcrete, and steel) and tunnel lining finishes such as tile. The techniques must be capable of analyzing conditions within the tunnel lining and the surrounding substrate. ⢠Evaluate the applicability, accuracy, precision, repeatability, ease of use, capacity to minimize disruption to vehicular traffic, and implementation and production costs of the identified technologies. ⢠Within the time limitations of this project, develop the hardware or software for those tech- niques that show potential for technological improvement. ⢠Prove the validity of the selected technologies/techniques to detect flaws within or verify con- ditions of the targeted tunnel components. ⢠Recommend test procedures and protocols to successfully implement those techniques. Chapter 2 reports the advisory expert panelâs findings on performance criteria. According to the results reported in Chapter 3, the following techniques meet the necessary criteria to be candidate solutions: ⢠Air-coupled ground-penetrating radar (GPR); ⢠Thermography (handheld thermal camera); ⢠SPACETEC scanner; ⢠Ground-coupled GPR; ⢠Ultrasonic tomography (UST); ⢠Ultrasonic echo; and ⢠Portable seismic property analyzer (PSPA) ultrasonic surface waves (USW) and impact echo (IE). Each technique should be considered useful for implementation. Table ES.1 summarizes aspects of these technologies. All of these devices will require a combination of classroom and hands-on training for collecting and analyzing data. But each technology also has limitations that need to be assessed. Limitations are outlined in individual appendices. Chapter 4 presents conclusions and recommendations. Executive Summary
2Table ES.1. Summary of Nondestructive Testing (NDT) Devices Device Accuracy Detection Depth Deterioration Mechanisms Detected Tunnel Lining Type Other Information Air-coupled GPR Locates defect within 1 ft of its actual location Does not measure depth, but indicates areas of high mois- ture or low density (high air voids). Such areas may represent problems within or behind the tunnel lining. Tile debonding, delaminations, air-filled voids, water-filled voids, moisture intrusion Concrete, tile- lined concrete, and shotcrete This is a scanning tool that can indicate where to conduct testing with in-depth devices. Thermography (handheld thermal camera) Locates defect within 1 ft of its actual location Does not measure depth, but can indi- cate tile debonding, delaminations up to 1 in., and voids up to 3 in. Tile debonding, delaminations, air-filled voids, water-filled voids, moisture intrusion Concrete, tile- lined concrete, and shotcrete This is a scanning tool that can indicate where to conduct testing with in-depth devices. SPACETEC scanner Locates defect within 1 ft of its actual location Does not measure depth, but can indi- cate tile debonding, possibly delamina- tions up to 1 in., and possibly voids up to 3 in. Tile debonding, delaminations, air-filled voids, water-filled voids, moisture intrusion Concrete, tile- lined concrete, and shotcrete This is a scanning tool that can indicate where to conduct testing with in-depth devices. Testing can only be conducted through a service contract. Ground-coupled GPR Can determine defect depth within 10% of the actual depth with- out reference coresâ 5% if cores are available Can possibly detect defects at any depth within or immediately behind tunnel linings. However, specimen testing indicates it cannot locate 1-sq-ft voids in steel plates behind tunnel linings. Delaminations, air-filled voids, water-filled voids, moisture intrusion Concrete, tile- lined concrete, and shotcrete Experienced personnel are needed to interpret defect locations and depths from the GPR scans. Specimen testing indicates it cannot locate 1-sq-ft voids in steel plates behind tunnel linings. Ultrasonic tomography In concrete, can detect voids within 0.5 in., shallow delaminations within 0.75 in. In shotcrete, can detect air-filled voids within 0.7 in., water-filled voids within 1.21 in., shallow delaminations within 1.88 in. Can detect defects up to 8 in. deep accord- ing to specimen tests. Tunnel tests indicate it can detect possible defects up to 20 in. deep. Delaminations and voids Concrete, tile- lined concrete, and shotcrete This device may not be effective for measuring defects that are 2 in. or less from the lining surface. It may not be accurate enough for measuring defect depths in shotcrete. Ultrasonic echo Comparable to the ultra- sonic tomography system according to tunnel testing with both devices. Can measure tunnel lin- ing thickness within 3% of the actual thickness Comparable to the ultrasonic tomogra- phy system accord- ing to tunnel testing with both devices Delaminations and voids Concrete and shotcrete This device may not be effective for measuring defects that are 2 in. or less from the lining surface. It may not be accurate enough for measuring defect depths in shotcrete. Tunnel tests indicate problems with using this device on tiles. Portable seismic property ana- lyzer (PSPA) ultrasonic sur- face waves and impact echo Ultrasonic surface waves: about 15% of the actual depth for defects up to 6 in. deep Impact echo: 10% for deep delaminations greater than 6 in. deep Ultrasonic surface waves: up to 6 in. deep Impact echo: up to 18 in. deep Delaminations and voids Concrete, tile- lined concrete, and shotcrete Quantifying the depth of defects that are shallow or extensive may be diffi- cult with this device. It may not get good results when testing on very rough concrete surfaces, oily surfaces, and severely curved surfaces.
