Time-Lapse Electrical Resistivity Tomography for Seepage Failure Monitoring in Earth-Rock Dams

Seepage failure is a primary cause of reservoir dam breaches. Conventional monitoring cannot reveal leakage paths across the dam, and static surveys miss weak-zone evolution. To address these challenges, this study constructs a typical geoelectric numerical model of low-resistivity expansion at a dam abutment. It systematically analyzes the response characteristics of apparent resistivity, independently inverted resistivity, and time-lapse resistivity imaging to the seepage failure process and validates the method through physical model tests and field observations. Inverted resistivity delineates hazards better than apparent resistivity, especially for small targets. Using the initial non-leakage model as a baseline, the resistivity-change profile obtained by ratio processing reveals the development trend of the hazard. Time-lapse inversion suppresses spurious artifacts from independent inversions and images the gradual expansion of the seepage weak zone. The L1-norm-constrained differential inversion further improves the convergence of the low-resistivity region and the accuracy of the anomaly center. Physical tests show rising water level reduces resistivity, especially in leakage-prone areas. Field tests show that after grouting, deep resistivity increases while shallow resistivity decreases. The results demonstrate that the time-lapse differential inversion algorithm based on the L1 norm accurately captures the spatiotemporal evolution of leakage hazards in earth-rock dams, providing reliable technical support for reservoir safety monitoring and evaluation.