Experimental study of small fixed-loop transient electromagnetic method for characterizing water-bearing structures in tunnels

Understanding the response of the transient electromagnetic method (TEM) to bad geological bodies is essential to improve the accuracy of tunnel forward geological prediction. Based on considering the similarity criterion, four groups of model tests were established to study the response law of small fixed-loop and central-loop TEM to water-bearing structures in tunnels. In the model tests, the non-central point field correction method was used to correct observation data of small fixed-loop TEM. Subsequently, the response and imaging results of central-loop and small fixed-loop TEM were compared and analyzed. The results show that the response of small fixed-loop TEM is more sensitive to water-bearing structures compared with central-loop TEM. Moreover, the three-dimensional imaging results obtained from the small fixed-loop TEM more accurately depict the spatial location and morphological characteristics of water-bearing structures. Finally, the engineering application demonstrates that the small fixed-loop TEM is effective and successful in detecting water-bearing structures, which can provide practical guidance for tunnel construction and disaster management.