A new method of 3D direct current resistivity modelling using a long electrode source for forward probing in tunnels

The resistivity method has been widely used to predict the water-bearing structure of tunnels. The traditional resistivity uses the point electrode (PE) source in the tunnel to excite the electric field. Because the tunnel face is inaccessible, its exploration depth is limited and small. In order to overcome this problem, the horizontal pilot hole is used as the long electrode (LE) source in the tunnel. We use the finite element method (FEM) to establish a three-dimensional modeling algorithm for tunnel detection using a long electrode source. The accuracy of the algorithm is verified by using the long electrode source model. By a lot of numerical simulations, a prediction model of a long electrode source for tunnel detection is firstly proposed. The predicted results show that it has good applicability in detecting long-distance anomaly. The comparison of the long electrode source and point electrode source models shows that the detection depth of the long electrode prediction model is farther than that of the point electrode source. This long electrode source method can improve the construction efficiency and effectively prevent water inrush in the tunnel.

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“…For tunnel prediction, the computational formulas under the pole-pole configuration of the LE source have been given [36].…”

Section: Apparent Resistivity Of Le Sourcementioning

confidence: 99%

A Prediction Model Based on the Long Electrode Source for Fault Anomaly in Tunnel

Liu

Yang

et al. 2023

Geofluids

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Vector resistivity monitoring technology assembled on a TBM

Gao,

Jiang,

et al. 2024

Journal of Geophysics and Engineering

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The traditional geophysical advanced detection methods which necessitates the placement of transmitting and receiving devices on the tunnel face and the sidewall, encounters significant limitations when confronted with the challenges of water and mud inrush disasters in TBM tunnels. Given the constraints of efficiency and limited construction space, a vector resistivity monitoring technology is proposed, which involves arranging the current electrodes on the surface and measuring electrodes on TBM. Based on finite element method with unstructured tetrahedral grids, a three-dimensional geophysical model including the tunnel is constructed and forward modelling of low resistivity anomalous bodies with different shapes and positions are carried out. The apparent resistivity in different directions is calculated, and the distance between the anomalous body and TBM is inferred according to the low value anomaly of the vector resistivity curve of both sides. The spatial position of the anomalous body is inferred according to the shape and relative relationship of the vector resistivity curves near the low value anomaly. Finally, the position of the sphere low resistivity anomalous body is predicted through the gated recurrent unit. These results preliminarily verify the feasibility of the vector resistivity monitoring technique assembled on a TBM.

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Analytical formulas for geometrical factor and sensitivity for long electrodes

Butler

2024

Geophysical Prospecting

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In the electrical resistivity method, electrodes are usually modelled as point current sources and point voltage measurements. If the burial depth of the electrode is significant compared with the spacing between electrodes, this point approximation may not be accurate. Common situations employing long electrodes include the use of metal‐cased boreholes as electrodes and small‐scale, high‐resolution environmental, engineering and archaeological surveys where electrode spacings may be very small. In this contribution, I present analytical expressions for the mutual resistance between long electrodes modelled as line current sources. Mutual resistances are then used to calculate geometrical factors. Additionally, I present an expression for the current density and use it to derive an analytical expression for the sensitivity of electrode arrays with long electrodes. The sensitivity is, in turn, used to calculate the mean depth and position which can be used as estimates of depth and position of investigation and as pseudosection plot points. Example calculations using the geometrical factor, sensitivity and mean depth are shown, and comparisons are made with simulations and lab‐scale experiments.

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A new method of 3D direct current resistivity modelling using a long electrode source for forward probing in tunnels

Abstract: 3D direct current long electrode modelling 591 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.

Cited by 3 publications

References 47 publications

A Prediction Model Based on the Long Electrode Source for Fault Anomaly in Tunnel

A Prediction Model Based on the Long Electrode Source for Fault Anomaly in Tunnel

Vector resistivity monitoring technology assembled on a TBM

Analytical formulas for geometrical factor and sensitivity for long electrodes

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