Abstract
Rock bolts, as a type of reinforcing element, are widely adopted in underground excavations and civil engineering structures. Given the importance of rock bolts, the research outlined in this paper attempts to develop a portable non-destructive evaluation method for assessing the length of installed rock bolts for inspection purposes. Traditionally, piezoelectric elements or hammer impacts were used to perform non-destructive evaluation of rock bolts. However, such methods suffered from many major issues, such as the weak energy generated and the requirement for permanent installation for piezoelectric elements, and the inconsistency of wave generation for hammer impact. In this paper, we proposed a portable device for the non-destructive evaluation of rock bolt conditions based on a giant magnetostrictive (GMS) actuator. The GMS actuator generates enough energy to ensure multiple reflections of the stress waves along the rock bolt and a lead zirconate titantate (PZT) sensor is used to detect the reflected waves. A new integrated procedure that involves correlation analysis, wavelet denoising, and Hilbert transform was proposed to process the multiple reflection signals to determine the length of an installed rock bolt. The experimental results from a lab test and field tests showed that, by analyzing the instant phase of the periodic reflections of the stress wave generated by the GMS transducer, the length of an embedded rock bolt can be accurately determined.
Highlights
Rock bolts are widely used as the primary reinforcing members in stabilizing engineering structures, such as underground excavations, slopes, retaining walls, tunnels, and dam foundations.Rock bolts are steel studs that are bolted into the rock mass to prevent the movement and expansion of rock strata and, improving the stability of the structure
The effectiveness of the proposed method was validated through both lab studies and field measurements, which showed that the proposed method was able to measure the rock bolt length accurately
The boosted pulse was fed into the giant magnetostrictive (GMS) transducer to generate a stress wave
Summary
Rock bolts are widely used as the primary reinforcing members in stabilizing engineering structures, such as underground excavations, slopes, retaining walls, tunnels, and dam foundations. If the installed rock bolt length does not meet the design requirements, failures of the reinforced structure could happen and lead to economic and environmental catastrophic losses It is, necessary to measure the length of installed rock bolts in order to ensure the safe operation. The stress wave reflection method, which is a type of quick and effective non-destructive evaluation method for rock bolt condition assessment, relies on the basis of the one-dimensional wave propagation theory. A new integrated signal processing method, including correlation analysis, wavelet denoising, and Hilbert transform, was developed to analyze the reflected stress waves. This new method is simple but effective. The effectiveness of the proposed method was validated through both lab studies and field measurements, which showed that the proposed method was able to measure the rock bolt length accurately
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