Simulation Analysis of Void Defect Detection in Sandwich-Structured Immersed Tunnel Using Elastic Wave

Abstract

Void defects can be easily generated between a steel plate and concrete joint due to the complicated internal structure of a sandwich-structured immersed tunnel (SSIT), which affect the overall bearing capacity of the main structure of the immersed tube tunnel. A prototype experiment was conducted to study the application of impact imaging method in the nondestructive detection of void defects in SSITs. The detection criterion for the impact imaging method was established based on the features of the waveform data. Nevertheless, the influence of steel plate thickness, material properties, void location, and structure on the detection accuracy of the impact imaging method is unclear. Therefore, numerical simulation was applied to study the influencing factors by establishing a different condition model. Good agreement between the experimental and numerical results was observed for the response waveform collected from the inspection area. Using the calculation model and identified material parameters validated in the active prototype experiment, numerical simulations of several sets, which considered all influencing factors, were performed. The application scope and sensitivity of the impact image method were recommended to reduce misjudgement in practical applications and improve detection accuracy.

Nondestructive millimeter-scale void detection for thick steel-shell–concrete interface of immersed tube tunnel: case study

“…In addition, the calibration of h i can also be calculated by numerical simulation. We have studied its applicability, 8 but found that although this method can distinguish the degree of void and dense, it is difficult to reach the millimeter-scale, which can be improved in the future.…”

“…The concrete serves as the ballast and bears the pressure. 8 The overall structure has several advantages, such as a high carrying capacity, small section size, good waterproof performance, no temperature control crack prevention problems, and construction convenience. 9 Table 1 shows the major built and under-construction SSITs in the world, 10 the largest being the under-construction Shenzhen-Zhongshan bridge in China.…”

“…It can detect the area and estimate void depth. 27,28 However, from the viewpoint of void-defect detection in steel-shell-concrete immersed tube tunnels, Liu et al 8 reported that when the thickness of steel shell was greater than 10 mm, the structural signal characteristics of the void area were very similar, and the greater the thickness, the less obvious the characteristic frequency, making it difficult to distinguish the extent of voids through spectral analysis.…”

“…shows a comparison of detection results of a typical compartment calculated based on Equation(8) with the results of uncapping on the site, the numbers at the uncapping area in the figure being the calculated equivalent void depth of the measurement points.Again, using holes #1, #3, and #6 as examples: no voids are detected for hole #1, the uncapping result verifying that there are no voids. For hole #3, no voids are detected, and the uncapping result shows slight voids in the lower left corner.…”