A lab study of coupling effects of electromagnetic induction on underground utilities

Electromagnetic induction is the most common technique used for geophysical survey of underground utilities, in planning stage, prior to construction/excavation and maintenance stage of underground's construction projects. Despite its popularity and usefulness, its reliability and accuracy are nevertheless always questionable due to coupling effects amongst the very congested underground utilities. This work studies the disturbed electromagnetic field patterns caused by the coupling effect of neighbouring cables and metallic pipes via a series of validation experiments in PolyU's indoor underground utility laboratory. The ‘fingerprints’ of electromagnetic fields are established corresponding to different below ground conditions. 11 setups with 260 tests were designed to study the coupling effect between a cable and a pipe. The results show that the coupling effect is significant in the active detection of the cable. The experiment also compares the accuracies of cable and pipe detection at different induction frequencies with reference to the accuracy levels in the HK EMSD requirement of competent person for power cable detection and PAS128:2014 British standard. This paper demonstrates the importance of coupling effects in the detection of underground utilities, which should be considered in future revision of standards.