Journal of Korean Tunnelling and Underground Space Association (한국터널지하공간학회 논문집)

Korean Tunnelling and Underground Space Association (한국터널지하공간학회)
권호 표지
DOI QR코드

DOI QR Code

Theoretical and experimental studies on influence of electrode variations in electrical resistivity survey for tunnel ahead prediction

터널 굴착면 전방조사를 위한 전기비저항 탐사에서 전극의 변화가 미치는 영향에 대한 이론 및 실험연구

  • Hong, Chang-Ho (Dept. of Civil and Environmental Engineering, KAIST) ;
  • Chong, Song-Hun (Dept. of Civil and Environmental Engineering, Sunchon National University) ;
  • Hong, Eun-Soo (Dept. of Civil and Environmental Engineering, KAIST) ;
  • Cho, Gye-Chun (Dept. of Civil and Environmental Engineering, KAIST) ;
  • Kwon, Tae-Hyuk (Dept. of Civil and Environmental Engineering, KAIST)
  • 홍창호 (한국과학기술원 건설환경공학과) ;
  • 정성훈 (국립순천대학교 건설환경공학과) ;
  • 홍은수 (한국과학기술원 건설환경공학과) ;
  • 조계춘 (한국과학기술원 건설환경공학과) ;
  • 권태혁 (한국과학기술원 건설환경공학과)
  • Received : 2019.01.17
  • Accepted : 2019.02.22
  • Published : 2019.03.31
Download PDF
⟨ Previous Next ⟩

Abstract

Variety of tunnel ahead prediction methods have been performed for safe tunnel construction during tunnel excavation. Pole-pole array among the electrical resistivity survey, which is one of the tunnel ahead prediction method, has been utilized to predict water-bearing sediments or weak zone located within 5 times of tunnel diameter. One of the most important processes is the estimation of virgin ground resistivity and it can be obtained from the following process: 1) calculation of contact area between the electrodes and the medium, and 2) assumption of the electrodes as equivalent spherical electrodes which have a same surface area with the electrodes. This assumption is valid in a small contact area and sufficient distance between the electrodes. Since the measured resistance, in general, varies with the electrode size, shape, and distance between the electrodes, it is necessary to evaluate the influence of these factors. In this study, theoretical equations were derived and experimental tests were conducted considering the electrode size, shape, and distance of cylindrical electrodes which is the most commonly utilized electrode shape. Through this theoretical and experimental study, it is known that one should be careful to use the assumption of the equivalent half-spherical electrode with large ratio between the penetrated depth and radius of the cylindrical electrode, as the error may get larger.

터널의 안정적인 시공을 위해 터널 굴진 도중 터널 전방의 이상영역을 확인할 수 있는 다양한 방법의 터널전방예측 기법들이 사용되고 있다. 터널전방예측 방법 중 하나인 2전극 전기비저항 탐사(Pole-Pole array)는 터널직경 5배 이내의 함수대, 연약대 등을 확인하기 위해 자주 사용되고 있다. 2전극 전기비저항 탐사 시 가장 중요한 것 중 하나는 원지반의 전기비저항값을 유추하는 것이며, 원지반의 전기비저항은 1) 지반과 전극의 접촉면적을 계산하고, 2) 그와 동일한 표면적을 가지는 반구형으로 가정하는 과정을 거쳐 얻어진다. 이러한 가정은 지반과 전극이 접촉하는 면적이 적고 충분한 거리가 떨어져야 한다. 하지만 전극의 크기, 형태 및 전극사이의 거리에 따라 실제 측정되는 저항이 달라지므로 이에 대한 정확한 평가가 필요하다. 따라서 본 연구에서는 전기비저항 탐사에서 주로 사용되는 원기둥형 전극의 크기와 전극사이의 거리에 따른 영향에 관한 이론식을 유도하고, 실험 연구를 통해 검증하였다. 이를 바탕으로 원기둥형 전극의 관입깊이가 반지름에 비해 큰 경우, 등가 반구형 전극의 가정을 사용하면 에러가 증가하므로 적용 시 주의해야 함을 확인하였다.

Keywords

TNTNB3_2019_v21n2_267_f0001.png 이미지

Fig. 1. Equipotential surface shape between two cylindrical electrodes

TNTNB3_2019_v21n2_267_f0002.png 이미지

Fig. 2. Test setup

TNTNB3_2019_v21n2_267_f0003.png 이미지

Fig. 3. Theoretical & experimental resistance and boundary effects (ρ = 52.16 Ωm)

TNTNB3_2019_v21n2_267_f0004.png 이미지

Fig. 4. Theoretical & experimental resistance and boundary effects (ρ = 29.97 Ωm)

TNTNB3_2019_v21n2_267_f0005.png 이미지

Fig. 5. Equipotential surface shape of spherical electrode

TNTNB3_2019_v21n2_267_f0006.png 이미지

Fig. 6. Effect of electrode geometry on the theoretical resistance

TNTNB3_2019_v21n2_267_f0007.png 이미지

Fig. 7. Electrical resistance of cylindrical and its equivalent spherical electrodes (ρ = 52.16 Ωm)

TNTNB3_2019_v21n2_267_f0008.png 이미지

Fig. 8. Electrical resistance of cylindrical and its equivalent spherical electrodes (ρ = 29.97 Ωm)

TNTNB3_2019_v21n2_267_f0009.png 이미지

Fig. 9. Error of the electrical resistance value from the cylindrical electrodes and its equivalent half-spherical electrodes

References

  1. Baishiki, R.S., Osterberg, C.K., Dawalibi, F. (1987), "Earth resistivity measurements using cylindrical electrodes at short spacing", IEEE Transactions on Power Delivery, Vol. 2, No. 1, pp. 64-71. https://doi.org/10.1109/TPWRD.1987.4308074
  2. Blythe, A.R. (1984), "Electrical resistivity measurements of polymer materials", Polymer Testing, Vol. 4, No. 2, pp. 195-209. https://doi.org/10.1016/0142-9418(84)90012-6
  3. Choi, J.S., Cho, G.C., Lee, G.H., Yoon, J.N. (2004), "Prediction of ground-condition ahead of tunnel face using electromagnetic wave - analytical study", Journal of Korean Tunnelling and Underground Space Association, Vol. 6, No. 4, pp. 327-343.
  4. Glover, P.W.J., Hole, M.J., Pous, J. (2000), "A modified Archie's law for two conducting phases", Earth and Planetary Science Letters, Vol. 180, No. 3-4, pp. 369-383. https://doi.org/10.1016/S0012-821X(00)00168-0
  5. Jaschinsky, P., Wensorra, J., Lepsa, M.I., Myslivecek, J., Voigtlander, B. (2008), "Nanoscale charge transport measurements using a double-tip scanning tunneling microscope", Journal of Applied Physics, Vol. 104, No. 9, 094307. https://doi.org/10.1063/1.3006891
  6. Kim, K.S., Kim, J.H., Jeong, L.C., Lee, I.M., Cho, G.C. (2015), "Development for prediction system of TBM tunnel face ahead using probe drilling equipment and drilled hole imaging equipment", Journal of Korean Tunnelling and Underground Space Association, Vol. 17, No. 3, pp. 393-401. https://doi.org/10.9711/KTAJ.2015.17.3.393
  7. Li, S., Liu, B., Xu, X., Nie, L., Liu, Z., Song, J., Sun, H., Chen, L., Fan, K. (2017), "An overview of ahead geological prospecting in tunneling", Tunnelling and Underground Space Technology, Vol. 63, Supplement C, pp. 69-94. https://doi.org/10.1016/j.tust.2016.12.011
  8. Ryu, H.H. (2010), "Development of tunnel electrical resistivity prospecting system and its application", Ph.D. Dissertation, Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST), pp. 269.
  9. Yoo, J.H., You, J.O., Kim, K.C., Ko, K.S. (2009), "The influence of blasting vibration on the concrete lining", Proceedings of the 2009 Korean Society of Civil Engineering Symposium, pp. 3692-3695.