A new method of 3D direct current resistivity modelling using a long electrode source for forward probing in tunnels. Issue 6 (19th July 2022)

• Record Type: Journal Article
• Authors: Hu, Daiming; Tezkan, Bülent; Yue, Mingxin; Yang, Xiaodong; Wu, Xiaoping
• Other Names: Zhdanov Michael S. guestEditor.; Apostolopoulos George guestEditor.; DiFrancesco Dan guestEditor.
• Is Part Of: Near surface geophysics. Volume 20:Issue 6(2022)
• Page Start: 590
• Page End: 606
• Publication Date: 2022-07-19
• Subjects: Conductivity -- Finite element -- Long electrode source -- Resistivity modelling -- Tunnel; Earth (Planet) -- Surface -- Periodicals; Geophysics -- Technique -- Periodicals; Engineering geology -- Periodicals; Geophysics -- Periodicals; Planets -- Surfaces; Engineering geology; Geophysics -- Technique; Geophysics; Earth (Planet); Periodicals; 550
• DOI: 10.1002/nsg.12224
• Languages: English
• ISSNs: 1569-4445

Abstract

ABSTRACT: The direct current resistivity method has been widely used for the prediction of water‐bearing structures in subway tunnels and mine tunnels. The traditional direct current resistivity uses point electrode sources in tunnels to excite the electric field; potential electrodes are arranged on the back of the tunnel face to measure the position of the anomaly using the apparent resistivity sounding curve. Due to the dimension limitations of the tunnel cavity, the maximum distance of potential electrodes is often restricted. Thus, the exploration depth often cannot cover the target appropriately. Additionally, owing to the inaccessibility of point electrode sources on the tunnel face, point electrode sources can only be set near the tunnel face, so the electric signal excited by point electrode sources cannot be coupled with the water‐bearing anomaly at a large depth. As such the traditional point electrode method for forward probing in tunnels has a shortcoming of small detection depth. To overcome this problem by increasing the detection depth, a horizontal drilling copper casing is first used as a new long electrode source array, which (as far as the authors are aware) has never been reported in forward probing in tunnels. We developed a new method of 3D direct current resistivity modelling with a long electrode source for forward probing in tunnels using the finite‐element method. The long electrode current source was used to replace the conventional point electrode current source, and the observed potential electrodes were respectively arranged in the tunnel floor, tunnel face and horizontal drilling. Theoretical formulas for the long electrode source for the whole‐space direct current method are first applied in forward probing in tunnels. An analytical test for a whole‐space model with the long electrode source has been used to validate the accuracy of the 3D algorithm. Three synthetic geological models for the long electrode source were used to examine the applicability by investigating the detection capability to predict the anomaly. The observed signal of apparent resistivity excited by the long electrode source is stronger than that of the point electrode source because the long electrode source is closer to the anomaly. This new method using the long electrode source greatly improves the resolution of the anomaly, which is of great significance for the safety of the tunnel construction.