Characterization of the concentrated seepage in a sandbox by self-potential monitoring and modeling

In this study, concentrated seepage tests were conducted in a sandbox. The self-potential responses under different seepage conditions were monitored. The characteristics of self-potential responses to the concentrated seepage were analyzed, and the relevant mechanisms were further explored. The results indicated that there were two distinct phenomena during the concentrated seepage. The first phenomenon was the transient shift of self-potential to the sudden change of flow rates. There was a slight upward jump in the self-potential signal when the water seepage began or the flow rate increased. Conversely, there was a slight downward jump when the water seepage ceased. The variation pattern of transient jump in the self-potential could be explained by the electrokinetic coupling effect. The second phenomenon was that the self-potential decreased in a step-like pattern during the concentrated seepage. When the flow rate of water drainage stabilized, the self-potential decreased gradually to a steady state. There was a significant negative correlation between the self-potential and the flow rate during the stable phase of water seepage. The greater the flow rate of water drainage, the smaller the self-potential value. We attributed the phenomenon to the difference between cations and anions at the outlet interface. A source current directed outward was generated at the outlet interface due to the concentrated seepage. Numerical simulations were employed to model the seepage and self-potential field within the sandbox. The numerical simulation results were compared with measured data to validate mechanisms governing the generation of self-potential signals.