Abstract
Electrical resistivity tomography (ERT) is one of the most widely used geophysical methods in geological, hydrogeological, and geo-environmental investigations. Although 3D ERT is now available, 2D ERT remains state-of-the-practice due to its simplicity in fieldwork and lower space requirements. 2D ERT assumes that the ground condition is perpendicular to the survey line and outside the survey line is homogeneous. This assumption can often be violated in conditions such as geologic strikes not perpendicular to the survey line and topographic changes or buried objects near the survey line. Possible errors or artifacts in the 2D resistivity tomogram arising from violating the 2D assumption are often overlooked. This study aimed to numerically investigate the boundary effects on 2D ERT under various simplified conditions. Potential factors including resistivity contrast, depth and size of buried objects, and electrode spacing were considered for the parametric studies. The results revealed that offline geologic features may project onto the 2D tomogram to some extent, depending on the aforementioned factors. The mechanism and implications of boundary effects can be drawn from these parametric studies.
Highlights
Electrical resistivity tomography (ERT) applied to geotechnical investigation has developed rapidly in recent years with the beginning of 1D exploration that is mainly used in groundwater and mining exploration
When the geological formation does not meet the condition where they homogenize in the vertical line direction, since the electric current is flowing in 3D, the 2D ERT result may be in error, so the distortion that this hypothesis may cause is often ignored in the interpretation of the test results
This study explored the effects of the 3D effect and boundary effect on 2D ERT through the parameters of the resistivity ratio, pipeline size, embedding depth, influence distance, and electrode spacing under different conditions and summarized these changes as conclusions and discussed them in detail
Summary
Electrical resistivity tomography (ERT) applied to geotechnical investigation has developed rapidly in recent years with the beginning of 1D exploration that is mainly used in groundwater and mining exploration. Linearity 2D ERT assumes that the geological formation resistivity property is homogeneous in the vertical line direction. When the geological formation does not meet the condition where they homogenize in the vertical line direction, since the electric current is flowing in 3D, the 2D ERT result may be in error, so the distortion that this hypothesis may cause is often ignored in the interpretation of the test results. The 3D effect means that the geological structure outside the 2D resistivity profile will map to the 2D resistivity profile and cause such errors.
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