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Research Paper

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

Chang-Ho Hong1
,
Song-Hun Chong2
,
Eun-Soo Hong3
,
Gye-Chun Cho4*
,
Tae-Hyuk Kwon5
홍 창호1
,
정 성훈2
,
홍 은수3
,
조 계춘4*
,
권 태혁5
1Post Doctoral Researcher, Dept. of Civil and Environmental Engineering, KAIST
2Assistant Professor, Dept. of Civil and Environmental Engineering, Sunchon National University
3Associate Research Professor, Dept. of Civil and Environmental Engineering, KAIST
4Professor, Dept. of Civil and Environmental Engineering, KAIST
5Associate Professor, Dept. of Civil and Environmental Engineering, KAIST
1정회원, 한국과학기술원 건설환경공학과 박사후연구원
2정회원, 국립순천대학교 건설환경공학과 조교수
3정회원, 한국과학기술원 건설환경공학과 연구부교수
4정회원, 한국과학기술원 건설환경공학과 교수
5정회원, 한국과학기술원 건설환경공학과 부교수
* Corresponding Author
31 March 2019. pp. 267-278
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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.

Keywords
Tunnel face
Electrical resistivity
Electrode size
Electrode shape
Distance between electrodes

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.

키워드
굴착면
전기비저항
전극 크기
전극 형태
전극 사이 거리
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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 : 21
  • No :2
  • Pages :267-278
  • Received Date : 2019-01-17
  • Revised Date : 2019-02-11
  • Accepted Date : 2019-02-11
  • DOI :https://doi.org/10.9711/KTAJ.2019.21.2.267
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