EG46: 3D DC resistivity inversion with and for metallic infrastructures using face and edge conductivity

Highly conductive infrastructures made of metallic materials can be either the interference or the targets of DC resistivity surveys for engineering purposes. Conventional approaches often have difficulties in handling metallic infrastructure because those objects, like steel pipes, fences, are typically thin but with a strong electric effect. A novel forward and inverse modeling method is proposed by simulating the thin metallic objects using faces and edges of a 3D mesh. In addition to the conductivity values defined at cell centers, the new method is able to host a thickness-integrated conductivity model, called face conductivity, on mesh faces, and a cross-sectional area-integrated conductivity model, called edge conductivity, on mesh edges. The utilization of face and edge conductivity model avoids excessively fine discretization while still preserving the equivalent electric effect. Two synthetic examples are presented to demonstrate the capability of our new algorithm. The first example detects a leaky iron pipeline. The leakage plume can be reasonably recovered when the pipeline is modeled using the edge conductivity, whereas the inversion can fail to converge to a meaningful model if the pipeline is not considered. The second example shows how buried steel sheet piles, a type of thin objects difficult for volumetric cells to describe, can be successfully imaged by using face conductivity.