Sensitivity Analysis of Geoelectric Parameters in Transient Electromagnetic Method for Tunnels

In order to investigate the characteristics of a transient electromagnetic field in tunnels using the transient electromagnetic method for advanced detection,the propagation characteristics of transient electromagnetic fields in an underground whole-space and in a layered half-space were respectively simulated using the ANSYS software.The sensitivity characteristics of transient electromagnetic fields were investigated by changing the depth,radius,resistivity of an anomalous body and the resistivity of surrounding rock,and the eigenfunctions of response curves for the field were obtained by fitting the data of time response spectrum.The numerical simulation results show that the propagation of the transient eddy current field in surrounding rock indicates a "water wave effect" in the whole-space other than a "smoking ring effect" in the half-space.The time-domain characteristics of the secondary field are greatly changed due to changing the geoelectric parameters of a conductive body,so the transient electromagnetic field in tunnels is sensitive to the geoelectric parameters of the conductive body.The time-domain characteristics of the secondary field are slightly changed duo to changing the geoelectric parameters of surrounding rock,so the transient electromagnetic field are lowly sensitive to the geoelectric parameters of surrounding rock.