유도파를 이용한 시간-주파수 영역 해석을 통한 록볼트 건전도 실험의 경암지반 현장 적용성 평가 = Rock Bolt Integrity Assessment in Time-Frequency Domain : In-situ Application at Hard Rock Site

다국어 초록 (Multilingual 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.

참고문헌 (Reference)

1 Beard, M. D., "Ultrasonic guided waves for inspection of grouted tendon and bolts" ASCE 15 (15): 212-218, 2003

2 Zhang, C. S., "Numerical simulation of wave propagation in grouted rock bolts and the effects of mesh density and wave frequency" 43 (43): 634-639, 2006

3 Beard, M. D., "Non-destructive testing of rock bolts using guided ultrasonic guided waves" 40 : 527-536, 2003

4 Han, S. I., "Non-destructive evaluation for rock bolt integrity using time-frequency analysis of guided ultrasonic dispersive waves" 439-448, 2007

5 Sato, M., "Mathematical foundation of wavelets" 47 (47): 405-423, 1991

6 Han, S. I., "Integrity evaluation of rockbolts encapsulated by cement-mortar grouting using ultrasonic guided waves" 177-178, 2006

7 Jeong, H. J., "Fracture source location in thin plates using the wavelet transform of dispersive waves" 47 (47): 612-619, 2000

8 Inoue, H., "Experimental wavelet analysis for flexural waves in beams" 36 (36): 212-217, 1996

9 Wang, L., "Elastic wave propagation in composites and least-square damage location technique" North Carolina State University 2004

10 Thurner, H. F., "Boltometer-instrument for non-destructive testing of grouted rock bolts" 135-143, 1988