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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

  • 이인모 (고려대학교 건축.사회환경공학부) ;
  • 한신인 ((주)서영엔지니어링 지반터널설계실) ;
  • 민복기 ((주)현대건설 터널환경사업본부 설계부분) ;
  • 이종섭 (고려대학교 건축.사회환경공학부)
  • 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.)
  • 투고 : 2009.03.11
  • 심사 : 2009.12.10
  • 발행 : 2009.12.31

초록

록볼트는 터널과 지하공간 구조물의 시공에 있어서 주요 지보재 중 하나이며, 이러한 록볼트의 건전도가 전체 구조물의 안정성에 큰 영향을 미치게 되었다. 본 연구의 목적은 실제 현장에서 투과법을 적용하여 록볼트를 따라 전파되는 유도파를 통해 록볼트의 건전도를 평가하는 것이다. 비파괴 실험의 각기 다른 결함비율을 가진 록볼트 시험체를 제작하여 콘크리트 블록 및 실제현장에 매설한 후, 피에조 디스크 엘리먼트로 유도파를 발생시키고 AE(acoustic emission) 센서를 이용하여 신호를 측정하였다. 수집된 신호는 가버 웨이브렛을 사용한 웨이브렛 변환을 이용하여 시간-주파수 영역에서 분석하였다. 시간-주파수 영역에서의 각 파군별 최대 에너지가 나타나는 지점의 시간차는 각 반사파군 간의 이동 시간차를 나타내며, 이를 통해 계산된 유도파의 에너지 속도는 록볼트의 결함비율이 증가함에 따라 증가하는 것으로 나타났다. 실험에 적합한 양생기간을 제안하였으며 그에 따른 두 번의 현장 실험을 통해 록볼트 건전도 실험의 현장 적용성을 검토하였고, 제안된 실험방법이 록볼트의 건전도 평가에 있어서 유용한 평가방안임을 확인하였다.

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.

키워드

참고문헌

  1. Beard, M. D. and Lowe, M. J. S. (2003), "Non-destructive testing of rock bolts using guided ultrasonic guided waves", International Journal of Rock Mechanics and Mining Sciences, Vol.40, pp. 527-536 https://doi.org/10.1016/S1365-1609(03)00027-3
  2. Beard, M. D., Lowe, M. J. S., and Cawley, P. (2003), "Ultrasonic guided waves for inspection of grouted tendon and bolts", Journal of Materials in Civil Engineering, ASCE, Vol.15, No.3, pp.212-218 https://doi.org/10.1061/(ASCE)0899-1561(2003)15:3(212)
  3. Han, S. I., Lee, I. M., Lee, Y. J., and Lee, J. S. (2006), "Integrity evaluation of rockbolts encapsulated by cement-mortar grouting using ultrasonic guided waves", Proc., 27th Symposium on Ultrasonic Electronic, 27, Nagoya, 177-178
  4. Han, S. I., Lee, J. S., Min, B. K., Yu, J.D., Lee, Y.J., and Lee, I. M. (2007), "Non-destructive evaluation for rock bolt integrity using time-frequency analysis of guided ultrasonic dispersive waves", Proc., International symposium on tunnelling for urban development, Pattaya, Thailand, 439-448
  5. Inoue, H., Kishimoto, K., and Shibuya, T. (1996), "Experimental wavelet analysis for flexural waves in beams", Experimental Mechanics, Vol.36, No.3, pp.212-217 https://doi.org/10.1007/BF02318009
  6. Jeong, H. J. and Jang, Y. S. (2000), "Fracture source location in thin plates using the wavelet transform of dispersive waves", IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol.47, No.3, pp.612-619 https://doi.org/10.1109/58.842048
  7. Sato, M. (1991), "Mathematical foundation of wavelets", Journal of Acoustical Society of Japan, Vol.47, No.6, pp.405-423 (in Japanese)
  8. Thurner, H. F. (1988), "Boltometer-instrument for non-destructive testing of grouted rock bolts", Proc., 2nd International Symposium on Field Measurements in Geomechanics, Sakurai(ed.), Rotterdam, pp. 135-143
  9. Wang, L. (2004), "Elastic wave propagation in composites and least-square damage location technique", MSc Thesis, North Carolina State University, NC
  10. Zhang, C. S., Zou, D. H., and Madenga, V. (2006), "Numerical simulation of wave propagation in grouted rock bolts and the effects of mesh density and wave frequency", International Journal of Rock Mechanics and Mining Sciences, Vol.43, No.4, pp.634-639 https://doi.org/10.1016/j.ijrmms.2005.09.006