• Geomechanics and Engineering
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• v.30 no.4
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• pp.337-343
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• 2022

The electrical resistivity method is a well-known geophysical method for observing underground conditions, (such as anomalies) and the properties of soil and rock (such as porosity, saturation, and pore fluid characteristics). The shape of electrodes used in an electrical resistivity survey depends on the purpose of the survey and installation conditions. Most electrodes for field applications are cylindrical for sufficient contact with the ground, while some are conically sharpened at their tips for convenient penetration. Previous study only derived theoretical equations for rod-shaped electrodes with spherical tips. In this study, the theoretical resistance for two cylindrical electrodes with conical tips is derived and verified experimentally. The influence of the penetration depth and tip on the measurement is also discussed.

• Geomechanics and Engineering
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• v.39 no.1
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• pp.105-113
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• 2024

Recently, electrical resistivity surveys have been used to obtain information related to underground structures including burial structure type and depth. However, various field conditions hinder understanding measured electrical resistance, and thus there is a need to understand how various geometries affect electrical resistance. This study explores the effect of geometric parameters of a structure and electrodes on electrical resistance in the framework of the finite element method. First, an electrical resistance module is developed using the generalized mesh modeling technique, and the accuracy of the module is verified by comparing the results with the analytical solution for a cylindrical electrode with conical tip. Then, 387 cases of numerical analysis including geometric parameters of a buried structure and electrodes are conducted to quantitatively estimate the detection depth under a steady-state current condition. The results show that electrical resistance is increased as (1) shallower burial depth of structure, (2) closer distance between ground electrode and structure, (3) longer horizontal electrode distance. In addition, the maximum detection depth corresponding to converged electrical resistance is deeper as (4) closer distance between ground electrode and structure, (5) shorter horizontal electrode distance. The distribution of the electric potential around the electrodes and underground structure is analyzed to provide a better understanding of the measured electrical resistance. As engineering purpose, the empirical equation is proposed to calculate maximum detection depth as first approximation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.2
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• pp.101-120
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• 2023

Electrical resistivity survey have been widely conducted at diverse scales, from a few centimeters for laboratory tests to kilometers for field tests. It measures electrical resistance through relationship of electric potential difference and current between two electrodes penetrated on the surface of medium, and eventually quantifies electrical resistivity known as inherent properties of the medium. In field or full-scale test, it assumes the electrodes as equivalent half-sphere electrodes that have a same surface area with different electrodes for ease of calculation because the contact area between electrode and medium is small and sufficient distance between two electrodes. However, small-scale laboratory test is significantly affected by the electrode geometries (penetrated depth, height, radius of electrode and distance between electrodes), which change the equipotential surface and electric current flow. Indeed, the electrode geometries may eventually cause a difference of electrical resistivity value. This study reviews the theoretical electrical resistance derived with various electrode geometries (half-sphere, cylinder, cylindrical with half-spherical tip, cylindrical with conical tip) and verifies the developed numerical module by comparing results with the theoretical electrical resistance. The distributions of electrical resistance around electrodes and among electrodes are analyzed. In addition, it is discussed how the electrical characteristic of cylindrical electrode with conical tip widely used in field test has effect on the electric current flow.