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http://dx.doi.org/10.7843/kgs.2009.25.12.5

Rock Bolt Integrity Assessment in Time-Frequency Domain : In-situ Application at Hard Rock Site  

Lee, In-Mo (School of Civil. Environmental and Architectural Engrg., Korea Univ.)
Han, Shin-In (Geotechnical & Tunneling Division, Seoyoung Engrg. Co. Ltd.)
Min, Bok-Ki (Hyundai Engrg. and Construction Co. Ltd.)
Lee, Jong-Sub (School of Civil. Environmental and Architectural Engrg., Korea Univ.)
Publication Information
Journal of the Korean Geotechnical Society / v.25, no.12, 2009 , pp. 5-12 More about this Journal
Abstract
As rock bolts become one of the main support systems in tunnels and underground structures, the integrity of the rock bolts affects the safety of these structures. The purpose of this study is the evaluation of rock bolt integrity using wavelet transforms of the guided ultrasonic waves by using transmission test in the field. After several rock bolts with various defect ratios are embedded into a large scale concrete block and rock mass, guided waves are generated by a piezo disk element and measured by an acoustic emission (AE) sensor. The captured signals are analyzed in the time-frequency domain using the wavelet transform based on a Gabor wavelet. Peak values in the time-frequency domain represent the interval of travel time of each echo. The energy velocities of the guided waves increase with an increase in the defect ratio. The suitable curing time for the evergy velocity analysis is proposed by the laboratory test, and in-situ tests are performed in two tunnelling sites to verify the applicability of rock bolt integrity tests performed after proposed curing time. This study proves that time-frequency domain analysis is an effective tool for the evaluation of the rock bolt integrity.
Keywords
Curing time; Defect ratio; Energy velocity; Time-frequency domain; Wavelet transform;
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