Evaluation of bonding state of tunnel shotcrete using impact-echo method - numerical analysis

Ki-Il Song; Gye-Chun* Cho; Seok-Bue Chang

doi:None

All Issue

2008 Vol.10, Issue 2 Next Page

Evaluation of bonding state of tunnel shotcrete using impact-echo method - numerical analysis 충격 반향 기법을 이용한 숏크리트 배면 접착 상태 평가에 관한 수치해석적 연구

30 June 2008. pp. 105-118

PDF XML

Abstract

Shotcrete is one of the main support materials in tunnelling. Its bonding state on excavated rock surfaces controls the safety of the tunnel: De-bonding of shotcrete from an excavated surface decreases the safety of the tunnel. Meanwhile, the bonding state of shotcrete is affected by blasting during excavation at tunnel face as well as bench cut. Generally, the bonding state of shotcrete can be classified as void, de-bonded, or fully bonded. In this study, the state of the back-surface of shotcrete is investigated using impact-echo (IE) techniques. Numerical simulation of IE technique is performed with ABAQUS. Signals obtained from the IE simulations were analyzed at time, frequency, and time-frequency domains, respectively. Using an integrated active signal processing technique coupled with a Short-Time Fourier Transform (STFT) analysis, the bonding state of the shotcrete can be evaluated accurately. As the bonding state worsens, the amplitude of the first peak past the maximum amplitude in the time domain waveform and the maximum energy of the autospectral density are increasing. The resonance frequency becomes detectable and calculable and the contour in time-frequency domain has a long tail parallel to the time axis. Signal characteristics with respect to ground condition were obtained in case of fully bonded condition. As the ground condition worsens, the length of a long tail parallel to the time axis is lengthened and the contour is located in low frequency range under 10 kHz.

Keywords

Shotcrete

bonding condition

IE method

time-frequency analysis

numerical analysis

숏크리트는 터널에서 사용되는 중요한 지보재이다. 숏크리트와 암반의 접착상태는 터널의 안정성 및 사용성에 큰 영향을 끼치는 중요한 평가 요소이다. NATM공법을 이용한 터널 굴착시 굴착면 및 벤치부에서 발파에 의해 숏크리트가 부착력을 잃고 암반으로부터 탈락되거나 공동이 형성되는 경우 숏크리트 자체의 파괴뿐만 아니라 터널의 전체적인 안정에도 악영향을 미친다. 숏크리트의 접착상태는 완전 접착, 접착력 상실, 그리고 공동으로 분류할 수 있다. 본 연구에서는 비파괴 시험인 충격반향기법(Impact-Echo)을 이용하여 숏크리트와 암반의 접착상태를 평가하고자 하였다. 범용 유한요소 해석 프로그램인 ABAQUS를 이용하여 충격반향시험에 대한 수치해석을 수행하였다. 수치해석으로부터 획득된 신호를 시간영역, 주파수 영역 및 시간-주파수 영역에서 각각 해석하여 숏크리트와 암반의 접착상태에 따른 신호특성을 분석하였다. 분석결과 능동적 신호 처리 기법인 Short-Time Fourier Transform(STFT)을 이용하여 숏크리트 배면의 접착상태를 효과적으로 예측할 수 있었다. 숏크리트 배면의 접착상태가 불량할수록 시간영역 신호의 최대 진폭 이후 첫 진폭이 커지며, 주파수 영역에서 최대 에너지가 커진다. 또한 뚜렷한 공진 주파수가 나타나므로 숏크리트의 두께의 역산이 가능해진다. 시간-주파수 영역에서 윤곽선은 시간축에 평행한 형상을 나타낸다. 또한 완전 접착조건에서 지반 종류에 따른 신호특성도 분석하였다. 지반조건이 불량할수록 시간-주파수 영역에서 시간축과 평행한 윤곽선의 길이가 길어지며 그 주파수 대역은 10 kHz 이하의 저주파수 영역에서 나타난다.

키워드

숏크리트

접착 상태 평가

충격 반향 기법

시간-주파수 해석

수치해석

References

1.ABAQUS/Standard Ver. 6.5 User Manual, Finite element software package. Hibbitt, Karlsson and Sorenson, Inc.

2.Carino, N.J. and Sansalone, M. (1992), “Detection of voids in grouted ducts using the impact-echo method”, ACI Materials Journal, Vol. 89, No. 3, pp. 296-303.

3.Davis, Allen G. (2003), “The nondestructive impulse response test in North America: 1985-2001”, NDT & E International, Vol. 36, pp. 185-193.

4.Davis, Allen G., Malcolm, K. Lim and Petersen, C.G. (2005), “Rapid and economical evaluation of concrete tunnel linings with impulse response and impulse radar non-destructive methods”, NDT & E International, Vol. 38, pp. 181-186.

5.Gabor, D. (1946), “Theory of Communication”, J.IEE (London), Vol. 93, pp. 429-457.

6.Hassani, F.P., Sadri, A. and Momayez, M. (1997), “A Miniature seismic reflection system for evaluation of concrete linings”, Pure appl. Geophys. Vol. 150, pp. 677-691.

7.Hassani, F.P. and Momayez, M. (2000), “Using NDT for thickness measurement of shotcrete rock support systems in underground mines”, Review of Progress in Quantitative Nondestructive Evaluation: Vol. 19, AIP Conference Proceedings, Vol. 509, pp. 1701-1707.

8.Jaeger, Barbara J., Mary J. Sansalone and Randall W. Poston (1996), “Detecting Voids in Grouted Tendon Ducts of Post-Tensioned Concrete Structures Using the Impact-Echo Method”, ACI structural journal, Vol. 93, No. 4, pp. 462-473.

9.Kim, D.S., Seo, W.S. and Lee, K.M. (2006), “IE-SASW method for nondestructive evaluation of concrete structure”, NDT&E International, Vol. 39, pp. 143-154.

10.Maierhofer, Ch., Krause, M. and Wiggenhauser, H. (1998), “Non-destrucrive investigation of sluices using radar and ultrasonic impulse echo”, NDT & E International, Vol. 31, No. 6, pp. 421-427.

11.Ohtsu, M. and Watanabe, T. (2002), “Stack imaging of spectral amplitudes based on impact-echo for flaw detection”, NDT & E International, Vol. 35, pp. 189-196.

12.Saenger, E.H., Gold, N. and Shapiro, S.A. (2000), “Modeling the propagation of elastic waves using a modified finite- difference grid”, Wave Motion, Vol. 31, No. 1, pp. 77-92.

13.Sansalone, M. and Carino, N.J. (1986), “Impact-Echo: A Method for Flaw Detection in Concrete Using Transient Stress Waves”, NBSIR 86:3452, National Bureau of Standards.

14.Sansalone, M. and Streett, W.B. (1997), “Impact-Echo: Nondestructive Evaluation of Concrete and Masonry”, New York: Bullbrier Press.

15.Santamarina, J.C. and Fratta, D. (1998), “Introduction to Discrete Signals and Inverse Problems in Civil Engineering”, ASCE Press, 1801 Alexander Bell Drive Reston, Virginia.

16.Villiappan, S. and Murti, V. (1984), “Finite element constraints in the analysis of wave propagation problem”, UNICV report NO. R-218, the University of New South Wales, The school of civil engineering.

17.Zerwer, A., Cascante, G. and Hutchinson, J. (2002), “Parameter Estimation in Finite Element Simulations of Rayleigh Waves”, Journal of Geotechnical and Geoenviromental Engineering, Vol. 128, No. 3, pp. 250-261.

Information

Publisher :Korean Tunneling and Underground Space Association
Publisher(Ko) :한국터널지하공간학회
Journal Title :Journal of Korean Tunnelling and Underground Space Association
Journal Title(Ko) :한국터널지하공간학회 논문집
Volume : 10
No :2
Pages :105-118

Journal of Korean Tunnelling and Underground Space Association ISSN:2233-8292(Print) 2287-4747(Online) 한국터널지하공간학회 논문집

All Issue