Mapping Voids, Debonding, Delaminations, Moisture, and Other Defects Behind or Within Tunnel Linings (2013) / Chapter Skim
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Pages 109-145
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109 a p p e N D I x M Introduction Field evaluations of four public tunnels and a series of test specimens were conducted for this research. Because the ultrasonic tomography (UST)
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110 The D-scan is like the B-scan in that it images a plane perpendicular to the testing surface, but it is oriented parallel to the scanning direction. On each of the scans, the various intensities reported by the returned waves are color coded, from light blue to deep red, representing low reflectivity (typically sound concrete)
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111 The simulated delaminations in these slabs were constructed from three types of material. Delaminations were imitated by using 0.05-mm (0.002-in.)
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112 For most concrete structures, a backwall reflection is the first discontinuity that is expected to be readily visible because backwall surfaces are usually exposed to air, causing almost complete reflection of the sound waves. This is not the case when a layer is fully bonded to a sublayer.
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113 Figure M.5. Typical C-scans of simulated defects in concrete slabs: Specimens Theta (top left)
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114 Figure M.6. Typical C-scans for simulated defects in shotcrete slabs: Specimens D (top left)
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115 Table M.1. Summary of Concrete and Shotcrete Slab Specimens with Simulated Defects Specimen Name Specimen Depth (mm)
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116 centroid of high reflectivity regions, which denote any sort of discontinuity, represent the depth of these anomalies. Keys are provided alongside each ultrasonic image, as in Figures M.8 and M.9, detailing the intended location of the lumps.
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117 (2.5 in.) below the surface, and below two layers of reinforcing steel at 152 mm (6 in.)
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118 Table M.2. Summary of Simulated Defects in Concrete Bridge Deck Simulated Defect Defect Material Key Legend Actual Dimension (mm)
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119 respectively.
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120 Figure M.14. B-scan showing CK1: construction key (top)
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121 The UST results of the first area tested (Figure M.22, top left) are shown in Figure M.23.
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122 Figure M.23. Typical UST results for I-20 scanning.
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123 Table M.3. Section A, I-20 Evaluations Overlay Tomograph Depth to delamination Varies: 107–127 mm Depth to reinforcement Varies: 117–127 mm Core 1 Tomograph Core Results Depth to asphalt sub-layer 264 mm 259 mm Depth to delamination None None Depth to reinforcement 127 mm 127 mm Core 2 Tomograph Core Results Depth to asphalt sub-layer 254 mm 259 mm Depth to delamination None None Depth to reinforcement None None Table M.4.
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124 first layer interface (Figure M.26, C-scan at bottom right, volume-scan at top right)
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125 Figure M.28. R2 for various defect detection parameters in concrete and shotcrete slabs.
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126 The coefficient of determination shows strong agreement between actual discontinuity measurements and measurements taken by ultrasonic tomography. Defect width and length are characteristics that should be determined after scanning the region in more than one scanning direction because the phased-array tomograph is polarized; shear waves are emitted and received in one direction, the x-scanning direction, or direction normal to the D-scans.
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127 Figure M.30. Eisenhower Memorial Tunnel plenum view indicating interior precast divider wall, structural steel ribs, roadway, and concrete tunnel lining.
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128 and crazing near a joint in the tunnel lining (Figure M.31b) , and areas near severe vertical cracks with stalactite formations (Figure M.31c)
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129 the longitudinal and hoop reinforcement. Interestingly, this supposed debonding also occurs directly below the lining joint.
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130 Figure M.36. Hanging Lake Tunnel: exterior view ( left)
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131 The sound concrete region (Figure M.38c, as well as Figures N.11 and N.12 of test site HLT 10.5-5, 6, 7 in Appendix N) shows that the backwall reflection varies from 752 mm to 823 mm (29.6 in.
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132 did not show any sign of delamination; the surface crack appeared only to follow a single hoop reinforcing rebar. The backwall, however, was clearly distinguished at approximately 752 mm (29.6 in.)
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133 The last area tested at the Hanging Lake Tunnel was a section of tile inside the eastbound bore along the outer wall (see Figure M.39, as well as Figures N.17 and N.18 of test site HLT 10.5-13 in Appendix N)
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134 As testing for this SHRP 2 Renewal project began, a cart with an attached ground-penetrating radar (GPR) antenna was wheeled throughout the entire length of the 1.6-km (1-mi)
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136 reinforcement is 305 mm (12 in.) on center, with the longitudinal reinforcement directly underneath.
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137 (see Figure M.45e, as well as Figures N.29 and N.30 of test site CBBT 10.11-10 in Appendix N)
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138 Channel Tunnel revealed an area detected by the infrared scan, indicating possible debonding. When debonding occurs beneath tile, hammer sounding by ear or by microphone can readily differentiate bonded from debonded tile.
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139 Figure M.53. Region II UST images.
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140 The longitudinal reinforcement is seen, but differentiating between the actual longitudinal rebars and the 51-mm (2-in.) diameter electrical ducts that are present can be difficult.
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141 A specific area of interest in this tunnel was tile debonding. As noted earlier, in tile-lined tunnels such as these, acoustic sounding with hammer tapping can quickly reveal debonded tiles.
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142 Figure M.58. Tile linings via UST ( left)
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143 Figure M.59. Areas tested surrounding debonded tiles: B-scans ( left)
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144 Conclusions of Tunnel Testing The conclusions of the tunnel testing are as follows: • The UST system is exceptional at locating horizontal delaminations ranging in thickness from 0.05 mm to 2.0 mm (0.002 in.
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145 offset with the device's manufacturer. Reproducibility using separate devices with the same testing procedures and an individual calculation of wave speed (with all other parameters equal)
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