Lessons Learned to Minimize Signal Coupling between Utilities When Utilizing Electromagnetic Locator

As a newly developing industry, subsurface utility engineering (SUE) is increasingly applied in municipal projects. Economic benefits when performing SUE are primarily derived from reducing unnecessary utility relocations and delay claims. Utility investigation is a critical part of SUE before determining utility relocations. Successful utility investigations include reviewing and documenting existing utility records, applying geophysical devices to detect underground utilities, or physically exposing unobservable utilities. The electromagnetic utility locator is a geophysical device universally applied to detect unseen underground metallic pipelines or cables. However, in congested utility areas, such as intersections, if the clearances between multiple metallic utilities are limited, it is possible that the locator cannot detect the correct utility line. This is because when two cables are too close, the target cable signal can cross over to a more conductive one, which may indicate that an inductive current flows in the non-target cable. This phenomenon is called signal coupling. In this article, the mechanism of this signal coupling will be discussed. Lab research in 2019 indicated that transmitter frequency and the clearance between utilities were related to signal coupling. However, two cases in the Dallas area showed that varying frequencies, power output, or ground wire location did not mitigate the coupling situation. Designators’ working experience can help identify the occurrence of signal coupling.