Multicomponent electromagnetic response analysis of seepage channels in earth‒rock dams via coupled current–seepage excitation

Effective identification of seepage channels in earth‒rock dams is critical for ensuring structural safety. This study proposes a current–seepage coupled excitation method to overcome the challenges of weak electromagnetic responses and poor spatial localization. $B_y$ incorporated the seepage channel into the excitation circuit, and the method simultaneously captured steady-state and transient magnetic signals, facilitating three-dimensional localization. The electromagnetic principle is elaborated, and a three-dimensional finite element model is used to analyze magnetic field distributions and responses under varying burial depths and channel scales. The results indicate that the steady-state magnetic field shows a distinct spindle-shaped pattern, with the magnetic intensity decreasing as the burial depth increases but the lateral influence expanding. At the channel position, the magnetic magnitude $\mathit{B}$ and lateral component $B_y$ reach peaks, whereas the vertical component $B_z$ crosses zero. During transient excitation, magnetic responses exhibit a three-phase structure: a plateau, an inflection point, and rapid decay. Decay rates slow with increasing depth and accelerate with increasing channel scale. A reversed $B_y=0$ curve observed in transient isosurfaces is sensitive to channel depth and scale, offering a new localization criterion. This study demonstrates the feasibility of the method, providing theoretical support for detecting and characterizing internal seepage channels.